Technical bulletin no. 44. Development of military aircraft material for United States Army Air Service under supervision of Engineering Division

              AIR SERVICE INFORMATION CIRCULAR
VOLUME V
(AVIATION AND AEROSTATION)
BY DIRECTION OF CHIEF OF AIR SERVICE
THIRD QUARTER - 1925
TECHNICAL BULLETIN
No. 44
NUMBER 486
DEVELOPMENT OF MILITARY AIRCRAFT MATERIAL FOR UNITED STATES
ARMY AIR SERVICE UNDER SUPERVISION OF ENGINEERING DIVISIOK.
Prepared and Published
By Direction of the Chief of Air Service
and under the supervision of
JOHN F . CURRY, Major, A. S.,
Chie f of Engineering Division.
McCook Fie ld 1 2 -1 5 -25-lM
CONFIDENTIAL
The information contained herein is confidential and therefore
must not be republished, either as a whole or in part, without
express permission of the Chief of Air Service, U. S. Army.
-J
CONTENTS
AIRCRAFT DEVELOPMENT
AIRPLANES
Loening Amphibian COA-1 (Production Model) ____________ -·--· _ -- ---·------ --- --- _ 7
Cox-Klemin Ambulance Airplane, Model XA-1 -- --- -- -- -------- --- -- --- ·-------- _____ -- ---·-- 13
P erformance Tests on Curtiss P-1 -------------····-· ·-- ------- ······ ··-·---- --- -·---------- 18
Performance of Douglas Transport with Different Propellers______ _______ _ _________ ____ 13
P erformance Increase with Geared Engine and Large Propeller (L-Vl -F Transport) 18
Huff-Daland Advanced Training Airplane ("Dog Ship")_ ___ __ _ _____ --- --------- 19
Bids Asked on Heavy Bombardment Monoplane _ ___ _____________ ________ __________ 19
Complete XHB-1 Heavy Bomber to be Built __ __ --------------·----- -- --- ---- ---- ---- - 19
D-12 Eng ines for Curtiss 0-l's _____ _____ __ ___ _ __________ ___ _ --- ---------- ·-- - 20
Design Studies __ -- -------· ···· ·-··· ---- -····· ·--·-- --- -- __ ------- ------- --- -· -- -- ----- ·-----·· 20
Disposition of the World Cruisers ··· ·---- _____ ___________ -- -- ---- ·· -·-- _ -- ·--·- ·-·---- 20
lHetal Wings (Thomas-Morse Design) __ ------------- ------ -------- ---- ----- -------·------- __ ______ 20
·woven Plywood Wing (Forest Products Laboratory) ------ -- -·-- -- ------------ ---- ------ ------ ---- -- --·- -- -- 21
Crop Census by Airplane ---- ----- ---- ------- -- --- --- -----·- ------ ---- --- ----------- --- --- --- ------- -- 2J
Collecting Rust Spores in the Upper Atmosphere ___ __ ___________ __ _____ ____ ___ ___ 21
AIRSHIPS AND BALLOONS
All-Metal Car for TE-1 Airship __ ____ --- --- --·------------------------------- _
RS-1 Airship ---- ---- ----- --- -- ------ -- _____________ _____ ------ ----·-------- ___ __________ __ _
Balloon Development ----·---- --- ----- ------·· ---
ARMAMENT
22
22
22
Aircraft Bomb Truck, Type A-1 22
Nelson Synchronizer Adapted to Late Model Engines ___ ___ _ _____ ·---- -- -·--- 27
Tests on Wing Tip Flares ______ __ ___ ---· --------- -- ____ ____ ·· ···---- _______ __ ________ -27
"\Vind Det ection Signals ____ --- -------------- --- --- --------- ----- -- ---- --·- __ ______________ 28
Machine Guns to be Mounted Inside Wing ___ ___ ___ -- ------·- --·-- -- -- ---------- --·----------------- 28
New Machine Gun Synchronizer, Type E-4___________ ----- -------- --------- ----- 28
EQUIPMENT
Aerial Photographs Transmitted over Telephone Wires __ _ __ ---· ··---- __ -- --- -----·
Transmitting Tests on Radio Set SCR-134 _______ __ __________ _
Ground Lighting E quipment ______ ______ ______ --- --- ---- ---- -- --------------- -------- --- ---
Landing Light Mounting on DH-4B Standardized
Airship Instruments __________ __ __ ___ ______ ______ --------- ------ -- --- ---- ------- - ___ ------- --------- ___ ______ ___ -·-- -- --
E xperimental Engine Starters -·· ··- ·-·---- ------ --------- ·- -·- ----- ----·-- ·--·
Ignition Shielding for Liberty Engine __ --- ·--- --·-------- -- --- --- ------ ----
POWER PLANTS
Curtiss R-1.454 Engine with Type "M" Cylinders
Development of Almen "Barrel" Engine _________ ___ _
Tests on Packard Engines ____ ------------------------------
Shrunk-On Propeller Hub Flange ____ ___ ____ _______ _
.Jump-Gap Distributor Heads ____ ----- ---·-- -----··· ___ ..
Combination Generator and Magneto Mounting Flange ·--- --- -·- ----·------ -- ------··-·--· ---- -·----- ··
Investigation of Bearing Loads -·-··--- -------------- --- -- ------- -- ____ . __ ·-- -- ------- --- ·--·-- -- ·-- -----·-- -----------
28
2D
29
29
29
29
30
30
30
30
31
31
31
31
C 0 N T E N T S - (Cont'd)
RESEARCH AND EXPERIMENT.
RESUME' OF ENGINEERING DIVISION SERIAL REPORTS.
Long itudinal Stability of Airplanes ___ _____ ---- --- -- --- ------- ------------- -- -- -------- ---- --- --- - 32
Correlation of Flight Test and Wind Tunnel Data ---- -- ----- ----- -- -- --- ------ ----- ---- -- --·---- -·--- ----- -- ·-- 32
Compa rative Tests on Experimental Met a l Ribs and Spars ___ ___ ___ _____ ___ --- --- -- -·----- --· ··- 33
Test of Valves f or RS-1 Airship -- ---- ----·-- -·· -----· ·-·--- --· ·-·---------··- -- -- --·-- --- ---· ·---- -- 33
Static Tests Conducted at the Engineering Division____ _______ ________ _____ ___ 33
Y./ind Tunnel Tests -·-···--·- -- ··--·-- -- ·-- --·-- -- --- ------ -- -- -·---- -- -- -- ---- -- -· ------ -- --- ------ ------ --------·--- -··--- 34
Test of F okker Synchronizer -- --· ------- -····---- --- --·-··-- --- -- ·--· ···---·-·- -······ ·-··· ·- 34
Inst r uctions for Mounting Type III Airways Flares -- --- ·· ---- --··---- -··---- -- --- -· -- --·---- ··--·-- 34
Hacks for Mounting Type III Airwa ys Flares ------------------ -- ---·---- --- --- ·------·-·---------- -·---- ----·----- 3-1
Test of Cannier Gun Sight -··------- --- ----- --·-·--- ---- -··-·· -- -··· --- ___ ---·- ·-- --- -·--··-·--·-- ···- - 34
Ignition Interfer ence in Airplane Radio Reception --·--- ---- ------- --------- ------- -- --- ·---- -- -- ·-- ----··--- 35
Altimeter Calibration Standard --· ·--- --· ________ ----·-·· --- --- --- ---- ·--··--- -- ---·-- -- ----·· ----·--- ----·····- 35
Barometr ic Altimetry and Altimet er Calibration Standards ---- -·- ·------- -- ··---- ·----··---- -·----·-- - 36
Prerminary Repor t of Crash Tests --- --- -···--- -----·--- --- --- -·----- -- ------- -- ---·--- ---- -- -- --·-- -- -- --- ·-·--- --····-· 36
Location of Vent Opening in Fuel Tank __ ___ -- ---- ---- --- ----- --- ---·- ···-- --- -·-- ·--------- ··------·- ··-- -- 37
Insta llation of LeNiv ex Hydrostatic Fuel Level Gage _____ _______ ---··--· ---·- -··-- ---·-· ·-·--- 37
Service Radio Equipment -· ····- -- --- --·-- --- --- -···- · ---- -·-·--- ____ .·- ----- ··-- ---· --· --- --- ----- --- -- ---·-- -·-·· -·--· ·-- 37
Navigation Methods ----- -- --- ··· ·------ --·-·-- -- ·- --- --···--- --- -------- -- ------- -----·· --- --· ----·- ·-- -·----··--- 37
Tests on Purox Liquid Oxygen Storag e and Shipping Container ---- -- --·- -··-- -·-- -···------ -· ··· -- 3~
Practical Field Service Use of Oxygen ·---·--- ----·-·· -- -- ---·· ·-·-----·-- _ -- ·····--------·-------- -- ·-·-·· 39
Performance of Airspeed Tubes in Rain and F r eezing Rain ____ __ ____ ___ ____ _______ ___ _________ 39
French Leakproof Tanks (S. E. M. A. P . E. ) -- ----- -------- ----- --------- ---- -·--- ---- -···--- -----··--- ---- ----··-- 40
Dopes and Their Application ·---------- -- --- ----- --- ------- ---- -----·---- --- ---- --· ---· ·--· - -··-·- ·-·--·--···--·------·---- 41
Performa nce Tests --····--·---· ·-··- --------- ---- ---·---- ------ ···------ --···---- -- -··-·- ---- -- -····-·--- -·· -· --- 42
Test of Honeywell Automa tic Shutter Control -----·--·--- --· -·-··- -- ·-----···-··- -·- _____ -- ---·----- 42
Piston Side Thrust in Model R-1 Radial E ngine ·-·-·---- 42
Bearing Loads and Stress Analysis of Model X-4520 Eng ine ___ ---· -·---- ---· ----- ---- ------- - 43
Development of Slipper Type Piston for Packard l A-1500 Engine.-----····---- -- -·-·---- -- -- ·-- --- 43
Cooling Test of "Zero-Foe" Radiator Anti-Freeze ....... .... -· -·· ·--·· -- --··- ·--- -- --- -- ··- 43
Standard Test of Curtiss D-12 Low and High Compression E ngines __ __ ·-- -- ·--··-·- 43
INVESTIGATION OF MATERIALS
Army-Navy Conference on Standa rds and Specifications ···­One
Type of Dope for All Airfoil Surfaces ---- --- ---- ---- -·- ··--- ---- ·· ···
Tru-Lay Cable ··-···------- --- ---- -·-------- ----- ---- ---- -·--- ----·-·-- -- -----------·-- -- -----
NEW BOOKS AND DOCUMENTS
44
44
44
Additions to Eng ineering Division Technical Files during Third Quar t er, 1925. ___ _____ 45
LIST OF ILLUSTRATIONS
Loening Amphibian Airplane, Model COA-1 ------ ------- _________ __ _______ ------ --- --- ---- --- ------------ ---- -- 6
Integral Fuselage and Hull Construction on COA-1 ------ ---------- -- --- ------- -- ---- ---------- -------------- 8
\>\'heel Retracted in Hull of COA-1 ----------------------------------------------- --- -- -- -- -- ------- ----- -- ---- --- -- ----- -- 9
Operating Principle of Retractable Landing Gear on Amphibian ------------------ ---------- -- -- --- --- 9
Inverted Engine Installation on Loening Amphibian ________ __ ____ ___ ---- ---- -- ---- ---- -- -- ------- -- ---- ---- 10
Pilot's Cockpit in COA-1 ------------------- --- -- ----- ------------ -- - ___________________ ------- -- -- -------- -------- -- ------- 11
Single Tank Fuel System in Loening Amphib'ian ------------------------------------ -- ----- --- ---- ------ -------- 11 ·
Cox-Klemin Ambulance Airplane, Model XA-1 --- ---- ----- -----·------------------------------------------------ 14
Arrangement of Patients in Ambulance Airplane ------ -- -- -- --- ---- -- ---- ---- -- ----- ---------- -- ----------- -- --- 15
General Arrangement of Cox-Klemin Ambulance Airplane XA-1 -------- ----- --- ------ -- -·- --- ------ 17
Aircraft Bomb Truck, Type A-1, Handling 4000-lb. Bomb ----------------- --- ---- -- -- ----- --- -- -- -- ---- 23
Body Elevation Details on Aircraft Bomb Truck -------------- -- -- --------------------- ----- -------- --·--·----- 21
Combination Sk'id and Body Side Member on Aircraft Bomb Truck. _____________ __ ___ _____________ 25
Skid Used as Body Side Member-Bomb Clearances on Skid_____ __ ____ ___ _______________ 26
Wing Tip Flares on Comparative Test ------ -- -------- -- ------ ----- ---- --- ---------------------- -------- --- -- -----·----- 27
Wind Detection Signal -- ---- ----- --- ---------- ---------- ---------- ---·-- -- ------- -- ----- ------ -- --- ----------------- -- --- --------- -- 28
Pressure--Altitude Char·t ------ ------ -- ---- ---- --- -- ----- --- -------- -- -- ---- --- --- ---- -- ------ -- ------ --- -- -------------- ------ -- 35
Early Crash Test Showing Fire Resulting From Fuel Entering Hot Manifold__ __ ___ _______ 36
Purox Liquid Oxygen Container -- --- --------- --------- --- -------------- --- ---------- -- --- -------------- -- -------- ---------- 38
Airspeed Tubes Used in Freezing Rain Tests __ ____ __ ___ ----- .------ ---- ---- -- ----- ------ ----------- -- -- -- --- ---- 39
Ice Formation on Airspeed Tubes -------- -------- -- --- --- -------- - --- --- ---- --- ---- -- ---- ----- ------ --- --- ------ 40
Pi tot-Static Head Proposed to Obviate Interference from Rain or Ice .... ___________ _ 40
Equipment Used for Applying Dope _____ __ -- -- ----- -------- ----- ----- ------ ----- ------ --------·- ---- ---------- 41
6 T E C H N I C A L B U L L E T I N N o. 4 4
LOENING AMPHIBIAN AIRPLANE, MODEL COA-1
(Inverted Liberty "12" Engine)
AIRCRAFT DEVELOPMENT
ON ENGINEERING DIVISION PROGRAM
AIRPLANES
Loening Amphibian COA-1 (Production Model)
The first amphibian airplane to be built for the Army Air Service was designed and built by
the Loening Aeronautical Engineering Corporation, New York City, on experimental contract.
This article, designated l\fodel XCOA-1, was completed in June, 1924, and flown on acceptance
tests in New York harbor by Engineering Division personnel during which it became accidentally
damaged in landing upon the water. The damaged 'plane was later salvaged and shipped to Mc­Cook
Field for static test. In view of the excellent qualities displayed by this airplane in the ac­ceptance
tests, the Government ordered ten production articles.
The first production article, Model COA-1. which is described in the following, was flown to
McCook Field in February, 1925, for performance tests. Many refinements and other minor
changes have been incorporated in this article to improve flying qualities and maintenance.
In the Loening Amphibian are combined the essential characteristics o,f two widely divergent
types of aircraft, the landplane and the seaplane. This combination is effected by an ingenious
merging of fuselage and hull into a single unified structure, thereby dispensing with the hanging
floats of the hydroplane and the elevated power plant of the seaplane. Such unity in body in con­junction
with inverted engine and retra.ctable chassis makes possible a type of aircraft whose sphere
of action is practically unlimited.
The design is centered about the inverted Liberty engine. It incorporates a double bay wire
braced biplane construction in wood and metal , with float-tipped wings and close-coupled fuselage
surmounting a seaplane hull. One of the principal features is the retractable landing gear, the wheels
of which fold into the hull when not in use.
The wing cellule resembles that of a DH with "N" struts and appencbnt floats but is of lighter
weight and larger area. It is composed of four symmetrical panels and a narrow center section, ex­ternally
braced with streamline wires and steel struts. Each panel is built about two spruce spars
of rectangular section supporting duralumin ribs and fabric covering. DTag is taken by steel struts
and swagecl wires placed between the spars. All attachment fittings are of the conventional "U"
type, the same as on the DH, but the external brace wire fittings and clevises in the bays are of
better design affording universal action.
Symmetry of the wing tips is preserved by the ailerons which are inserted in the outer tra>iling
edges. All are of the same size and design, making them interchangeable by simply changing the
fittings. Actuation is effected by means of wheel and stick type controls and linkage connected in
seri es. 1 on-flexible steel cables are used in the straight sections, chains at the bends, and control
struts to upper aileron s. For safety, the chain on the pilot's control column is completely encased.
\,Yater-tight floats are suspended beneath the lower wing near the tips. These aid greatly in
maneuvering on the water when forced down by the ailerons.
Tail surfaces are practically all-wood structures, spruce being used for spars and ribs. balsa for
fairing and linen fabric for covering. Some mahogany plywood is used to stiffen the leading edges
of the elevators and rudder. Except for the hinges, the only metal used is the sheet duralumin
forming the trailing edges. Stabilizers and elevators are built in halves and hinged together. The
stabilizer half is a wooden framework of two spar construction with intermediate ribs and balsa
faired leading edge and tip, whereas the elevator half is built about a single box spar with solid
ribs, spruce-backed balsa tip , mahogany covered leading edge and metal trailing edge. The latter
type of construction is also used for the rudder which is pin-hinged to fin and fuselage. No adjust­ment
of the fin is possible as it is built integral with the fuselage. On each side, the stabilizers are
rigidly supported from the fin by single streamline wires and from the fuselage by pairs of
streamline metal struts.
8 T E C H N I C A L B U L L E T I N N o. 4 4
The movable surfaces are actuated by means of flexible steel cables attached to the control
masts. Both elevator and rudder control cables are provided with elastic cord compensation. Ad­justment
of the stabilizer is possible only on the ground.
Fuselage and hull present a massive appearance, yet the entire structure weights only 832
pounds without equipment. These units are built integrally, the combined structure measuring 31
feet 11 ;Yti inches from bow to fin post and 90 inches from keel to top longeron. The hull proper
..
"+'
1--------------J/'- /J.75 ' - -------- - --- - - ---i
~ - - - - - - ,: - - - - -~- - - - - - - - -- ·-- --
-<': i::" "~-,,,_ \
INTEGRAL FUSELAGE AND HULL CONSTRUCTION ON COA-1.
has a beam of 60 inches whereas the maximum width of the fuselage is only 29}~ 'inches. The
structure is composed chiefly of replacable spru ce members, duralumin covered, but there are
several steel tubes and wires in the bracing. Both fuselage and hull are entirely covered with sheet
cluralumin secured to the wood structure by screws, making the entire exterior water-tight.
The hull follows seaplane lines with sloping sides and stepped keel. It is divided into two
water-tight compartments, one forward and one aft, separated by a recess in the hull for receiving
the retractable landing wheels. The bow proj ects for a considerable distance beyond the fuse­lage.
On the hull the covering is of heavier gage than on the fu selage because it is subjected to
greaiter shocks in water landings. That on the bottom from bow to step is the heaviest, being 1/ 16
Of an inch in thickness, whereas the deck. sides and rear bottom are covered with 1/ 32-inch sheet.
T he covering on the fuselage is only twenty-five thousandts of an inch thick.
About six feet from the bow the fuselage rises abruptly to a hight of 63 inches. In view of
the high thrust axis possible with the inverted engine, this height is sufficient to give one inch clear­ance
with an 8-foot 4-inch propeller. From nose to fin post the top longerons form a horizontal line,
the cowling being raised over the forward portion to accommodate the engine and fixed gun mount­ing.
The engine section is so designed that the engine together with the bearers, oil tank and other
accessories can be easily removed as a unit. Accessibility to the power plant is obtained by re­moving
the cowling which is secured to the structure by simple spring clip fasteners. The cockpits
are placed close together directly above the step and behind the raised cowling which shields them
from the slipstream. This location with reference to the wings and the inyerted power plant in­stallation
affords good visibility in all directions. particularly to the rear where the high setting of
the stabilizer allows an unobstructed view. The fuel supply is carried in one large main tank
placed below the floor of the pilot's cockpit, with two-thirds of its bulk resting in the hull.
AIRCRAFT DEVELOPMENT 9
A feature of unusual interest is the landing
gear upon which depends the abil ity of the amphi­bian
to maneuver on land. It consists of two re­tractable
units pivoted on opposite sides of the hull
in such a manner that they may be raised or low­ered
simultaneousl;y at the will of the pilot. Each
chassis is fitted with a 32"x6" wheel incorporat­ing
a shock absorbing unit within the hub. In the
1etarded position a portion of the wheel projects
above the hull. \Vhen the landing gear is fu lly
extended or in the clow11 position, it gives a tread
of eight feet between the wheels and holds the
hull clear of the ground.
Raising or lowering the chassis requires only
about ten seconds. The wheels are mainipulated
by means of a retracting mechanism operated by
a Bijur electric starting motor or by a hand crank
WHEEL RETRACTED IN HULL OF COA-1. in emergency. The motor drives two long offset
screws thru bevel gearing, the screws being secure­ly
anchored to the hull at their extremities. A projecting arm connects each driving screw with
its respective chassis. As this arm is caused to travel along the screw it raises or lowers the chassis
depending upon which direction the screw is rotating. The amount of travel 1n either direction
is safeguarded by means of a pair of solenoid switches which automatically cut out the motor when
the arm reaches the extreme position. The travel of the chassis is illustrated in the accompanying
sketch.
175 0 D X.065 W/lLL
2-Tt/B£S I ODX.062 IYALL
2 T{IB£S /. 0 D ,/'.083 MILL
I~
OPERATING PRINCIPLE OF RETRACTABLE LANDING GEAR ON AMPHIBIAN.
For ground landing, a swivel type tail skid is provided. This unit is of steel tubing weighing
about six pounds and is wrapped with 5/ 8-inch elastic cord. It protrudes from the bottom of the
fuselage at rear of hull, offering little resistance to air or water .
Only thru the use of the inverted engine are compactness of design and unity of body possible
in this airplane. The inverted arrangement provides the necessary height for the propeller thrust
axis above the hull. Otherwise the power plant would have to be placed above the wing as in the
usual seapbne construction. Improved visibi lity and accessibility are attendant features of the in­verted
in stallation.
The power plant consists of a water-cooled Liberty " 12" engine modified for inverted opera­tion.
The engine has a rated output of 420 horsepower at l 700 revolutions per n~inute , which
power is exerted upon a fo ur-bladed wooden propeller, 8 feet 2 inches in diameter, with tip clear­ance
of two inches over the deck. In flying position, the axis of the propeller is 7 feet 10 inches
CJ.boye the ground. Both engine and propeller are of Engineering Division design. A performance
10 T E C H N I C A L B U L L ET I N N o. 4 4
has also been run with a three-bladed metal propeller with adjustable blades. \ i\Tith this propeller
which measures 8 feet 4 inches in diameter, the tip clearance over the hull is only one inch.
The engine is equipped with standard Zenith carburetors and 12-volt generator-battery igni­tion.
Short exhaust stacks are used, but clue to the im·erted position of the engine the exhaust
gases are carried clear of the cockpits. Fuel is supplied to the carburetors from one 140-gallon
capacity tank in the hull by means of a Type C-5 gear pump dri ven by the engine, and by means
of a wabhle type kmcl pump for starting and emergencies. The tank is made of aluminum, of
118-inch wall thickness. There are no baffles required because of its peculiar shape. J\ ltho only
a single tank system, a reserve supply of 30 gallons is retained by placing the fu el intakes at dif­ferent
levels as shown in the fuel system layout on the opposite page.
Oil is carried above the engine in an irregularly shaped tank holding 14.5 gallons.
The radiator is mounted fo rward nnclerneath the engine. It has a 9-inch U. S. cartridge type
core giving a frontal area of 3.14 square feet and a total cooling surface of 279 square feet­all
direct. Temperature of the water i ~ regulated by means of an eight-vaned shutter which allows
the air to pass thru the core and escape from the open space below the cylinders where it is de­flected
by a firewall. An aluminum expansion tank mounted aboYe the engine initiates the nose
streamline.
Engine controis are of the standard push-and-pull rod and lever type actuated by new engme
control units.
INVERTED ENGINE INSTALLATION IN LOENING AMPHIBIAN.
A IRCR AFT DEVELOPMENT 11
Exceptional roominess in the cockpits affords ample accommodations for armament and equip­ment
at no sacrifice to comfort or visibility. All instruments are placed in the front cockpit, leav-ing
tlw rear free for the installation of a camera
and other accesso ries. The camera, a Type K-3
automatic, is ideally located in the lower part of
the cockpit which virtually forms a cabin entirely
protected from the wind. Exposures are made
thru port holes in the bottom of the hull, the open­ings
being sealed with water-tight covers when not
in use. Besides the motor for retracting the chassis,
the electri cal equipment includes a combination en­g
·ine starter with hand attachment and the neces­sary
wi;-ing for operating camera motors and elec­tric
running and landing lights when in stalled.
Current is supplied by a Type lL generator and a
Type AS-3 storage battery.
PILOT'S COCKPIT ON COA-1. Defensive armament consists of one Browning
aircraft synchronized machine gun , either .30 or
.SO caliber, mounted under the fo rward cowling and two .30 caliber Lewis machine guns fl exibly
mounted on the ring. Provision is also made for attaching Type A-3 external bomb racks under
the lower wings.
All performance requirements 111 the contract were exceeded.
In general , the flying qualities of the COA-1 are excellent. Performance 1s comparable to a
landplane of similar size. Take-off or landing is easi ly effected from either cockpit . T he airplane
rolls only a short distance after contact with the ground and responds well to controls in taxiing
on either land or water. In the latter case maneuverability is facilitated by ai leron action in fo rcing
wing tips into the water and by slipstream action in the pocket formed by the large rudder area
below the elevators. Maneuyering on water is also aided bv lowering the landing wheels which
-- {,;'ff ON CONNECTION --- HOSE COh'JYEr.rroN
SINGLE TANK FUEL SYSTEM
IN LOENING AMPHIBIAN.
I
4
PRESSURE f?AOE
BULKHEAD
12 T E C H N I C A L B U L L E T I N N o. 4 4
LOE ' ING AMPHIBIAN, MODEL COA-1.
Dimensions :
Overall span . ... .. ..... ....... ... .... ........... . . .... . ..... . . .
Overall length .. ... ...... ... ...... .. . .. ............ ... ... . ..... .
Overall height . ... . . ....................... ... ....... . .... .... . .
Span (upper ancl lower wing same) . . . ......... . .................. .
Chord of wings ............. ... . . . . .. .... .... . . ... . .. .. .... ... . .
A.irfoil . . .. .................................... . .. . . ........ . . .
Gap . . ........... ... .. ... ........... . . ... ............ . . . .. .. .. .
Stagger ........... .. ... . ... .. ... . ..... . . . ... ................ .. .
Dihedral ...... .. ... .. .............. . . .. . ... ...... .... . . .... .. . .
Incidence . . .. . ... . ... .. ... ... . .. .. ... . .... .. ........ . .. ... . . . . .
Sweep back . ... .... ........ ... .. ... ... ... . . .. . ... . ... . ......... .
Height of propeller axis in flying position .. .... . . ..... ..... . .... .... .
Areas (square feet) :
Total supporting surface ....... .......... .... .. . ........ . ........ .
Upp er wing (including center section) ......... ... ..... . .......... .
Lower wing .... . ................... . .. . .... ... ........ .. ... . .. . .
Center section .. .......... .. ........... . . . . . ..... . ......... . ... .
Ailerons ....... . .. . .. . . .. ... .... .. ............. . ........ ... ... .
Elevator ...... .. .................... .. .. ........ ............. . .
*Fin .......... .. ....... .. .. . ... .. .... .. .. . ....... . .... . ... .. .. .
*Rudder .... ....... .... ..... .. . .. . ... . .... .. .. . .... . ..... . ..... .
Stabilizer .. ...... .... ....... .. ..... .. : .. .. ... . .... . .. . .... . ... .
Weights (pounds):
Fully loaded ... .. ... . .......... .... ... . ..... .. ..... . ..... ... ... .
Empty, with water .. . ...... . .. ................... . .. ... ... ..... .
~1 ilitary load . . . ... . .. ....... ....... ........................ ... .
Axn1ament ..... . .. . ............... . .... . . .. .... . . ...... .... .. . .
Equipment . ............ . .................. .. ............... . .. .
Crew ( t~ro) . ... .. ............... .. ... . ...... .... .. . .... ...... . .
Fuel (91.5 gal. @ 5.9 lbs.) .. ......... .... ... ......... . ...... . .... .
Oil (9.6 gal. @ 7.5 lbs.) ... . ......... .. ... . .. .............. . . .... .
\ i\T ing loading (pounds per square foot) ....... . .. .. ... ... . ...... . .. .
Power loading (pounds per horsepower ) . . .. . . .... . . ...... . ..... .. . .
Performances :
45' 0"
34' 7"
12' 1"
45' 0"
6' 0"
Loening lOA
5' 10"
l' 0"
2° 45'
30
None
7' 10"
495.1
255.6
239.5
12.08
68.4
27.3
10.75
16.27
44.5
5010**
3440
1570
203
395
360
540
72
10.12
11.7
Speed in level flight at sea level . .. . . .. . ... .
4-blade wood prop .
118.8 m.p.h.
107.2 m.p.h.
27.6 min.
630 ft ./min.
11 ,825 °feet
14,000 feet
3-blade metal prop.
124.1 m.p.h.
Speed at 10,000 feet .. . . ............. . .. .
Climb, time to 10,000 feet ................ .
Rate of climb at ground . . . . . .. . ... . . . ... .
Service cei ling .. .... . ...... . ..... ... ... .
Absolute ceiling .......... . ......... ... .
Landing speed (airspeed recorder) .. .. .... .
Endurance at 10,000 feet incl. climb ........ .
Effective horsepower at sea level .... ... . .. .
3-1 / 4 hours
428 @ 1745
111.8 m.p.h.
26.2 min.
607 ft. / min.
13,100 feet
15,650 feet
58.5 m.p.h.
3-1 / 4 hours
434@ 1780
*With balanced type rudder, area of rudder is increased to 18.27 sq. ft. and t hf! area of fin reduced to 5.75 s q. ft.
**Weig ht of airplane increased to 5080 pounds by three bladed, adjustable pitch metal propeller weighing 60 pounds
more than original propeller and by new bulkhead and tail skid weighing 10 pounds additional.
cause extra drag and keel effect. In flight, the airplane is very stable and exhibits excellent aileron
control in banks. This is attributed to the coincidence of the center of fin area with the center of
gravity. Directional stability is not so good, requiring constant pressure on rudder to hold straight
course. However, an arrangement using shock absorber cord is installed to relieve this, and with a
redesign of the vertical tail surfaces the fault may be obviated.
AIR C R A FT DEVELOPMENT 13
The versa;tility of the COA-1 in being capable of operating from either land or water with
equal facility makes it an ideal military type for use along coastlines or in insular possessions. For
commercial ayiation it is particularly adaptable for operating inland airways over lake regions and
for exploration. In the latter in stance, three of the amphibians have been used by the Navy De­partment
in the MacMillan polar expedition.
At this writing, the article allocated to McCook F ield has just returned from an aerial photo­graphic
survey of the Rainy Lake watershed in the vicinity of Duluth, Minnesota. This pro ject in­volved
the photographing with a T-1 ( tri-lens) ca_rnera at a scale of 1/ 20000 approximately 1500
square miles of territor y along the Canadian border and at a larger scale in the vicinity of fi f teen
tentative clam sites. Topography of the country in this region is such as to make the use of an air­pla11e
of this type imperative.
Cox-Klemin Ambulance Airplane, Model XA-1
Earl y attempts to c01wert mulitary aircraft into aerial ambul ances for transportation of sick and
wounded have demonstrated the inapplicability of the typical military airplane for this work. Hence,
in 1923, the Engineering Division decided to design an airplane built expressly for ambulance pur­poses.
This design as finally approved by the Army Medical Ccrps led to the construction of the
fir st strictly ambulance 'plane to be built in this country.
The fi rst XA-1 , as this airplane was designated, was built and delivered to McCook F ield in
February, 1925, by the Cox-Klemin Aircraft Corporation, Baldwin, L. I., N. Y., under a contract
awarded the preceding June for two experimental articles. T he second article followed in August
of the present year.
The design incorporates a biplane construction about the Liberty engine, with provision for
carrying a pilot, medical offi cer, and two patients in litters. It is characterized by the following
features: single bay, square-tipped wings ; hump-backed fuselage with exposed cockpit behind en­gine
for pilot, and an enclosed compartment or cabin for a physician and his patients ; diagonally
braced lower wing stubs housing the fuel supply; split-axle chassis ; and absence of vertical fin .
The most interesting featm'e is the ambulance compartment. Virtually it consti tutes an emerg­ency
hospital where patients may receive fir st aid treatment while in flight. It is so arranged and
has such ample proportions as to accommodate two patients on stretchers with the attending ph v­sician
or nurse alongside. By removing the stretchers, four sitting cases can be substituted. In
stretcher cases the patients a re placed in litters, one above the other , on the right side of the compart­ment
in such a position that the physician, seated on the left, has access to all parts of the patients'
bodies. Ordinarily the physician is a medical offi cer or flight surgeon who is in charge of the flight.
In this case he can communicate with the pilot thru a speaking tube. A clock and altimeter are also
provided for his convenience. Medical supplies are stored in a metal cabinet built into the cabin
in front of the officer. Several thermos bottles, splints 'and other accessories including water for
medicinal use are provided.
The compartment measures 80 inches long. 48 inches wide and 65 inches high, enabling the
average person to stand almost erect. There are no structural members in this section to interfere
with the handling of the litters which are loaded or removed thru a large double-hinged door in the
right side of the fu selage. T he physician gains access thru a small door on the left. Plenty of light
and ventilation are provided.
The pati ents are strapped in the litter s. These are made of steel tubing cov,ered with wire
mesh. confo rming to a design adopted by the air services for transporting sick or woumlecl. Shi fting
in flight is prevented by clamps which hold the litters on their supports in the airplane.
To preserve balance, the pilot is placed high on the left side of the fu selage in front of the
cabin. This position affords excellent vision for cross-country flying and for landing. T he cock­pit
is equipped with single controls consisting of conventional wheel and rubber bar. No vibration is
noticeable even with engine at full throttle, which acids greatly to comfort.
The wings are of wood construction, Gottingen 387 section, being of constant chord and thick­ness
except for the taper at the tips. All four panels are of the same size and design, due to the use
of lower wing butts and large upper center section. The spars are of rectangular box section
with spruce flanges and two-ply spruce webs, whereas the ribs are built np of spruce, balsa and
mahogany. Ailerons of the unbalanced type are inserted in the outer trailing edges.
14 T E C H N I C A L B U L L E T I N N o. 4 4
COX-KLEMIN AMBULANCE AIRPLANE, MODEL XA-1.
(Liberty "12" Engine)
AIRCRAFT DEVELOPME NT 15
Absence of fin and square shape of rudder mai(e the tail surfaces conspicuous. The stabilizer is
supported on a level with the top of the fu selage by struts ancl wires from longerons. It is hinged at
the leading edge, making it adj ustable in flight. Above the stern post the rudder ri ses quite a di stance
fi nding support by strut and brace wire from each side of the stabili zer.
\ Velcled steel tube with rod tru ssing is used thruout the fu selage structure, the members of
which arc replaceable by welding. T he engine bearers are faced with wood. Special tru ssing is em­ployed
in the ambulance section to give free access for the removal of the litters.
T he landing gear is of the divided type, an excellent design for tax iing in long g ra ss or stubh!e.
The two main supporting struts form a vee on each side of the fuselage with its open ends pivot­ed
at the center of the fuselage and its apex conn ected with the vertical leg from the wing stub in
such a manner that the landing shock is taken by a rubber cord abso;·ber in the plane of the wing
stub fron t spar. Long stroke shock absorbers on both landing gear and steerable tail skid, to­gether
with the 32" x6" wheels, do much to ease shocks in landing.
Propul sion is effected by a standard Liberty engine swinging a two-bladed propeller, 10' 4"
in diameter. The engine is equipped with two Zenith US-52 ca rburetors and ·standard 12-volt
ignition with T ype lL generator. To eliminate noise of the exhaust from the cabin , the exhaust
stacks are fitted with silencers of Engineering Division design. F uel is carried in two 54-gallon
tanks enclosed in the lower wing butts, from which it is forced to the carburetors by means of a
Type C-5 engine-driven gear pump connected in series with a T ype D-1 wabble hand pump for
sta rting and emergency.
For cooling, a nose type radiator of Cox-Klemin design is mounted above the propeller hub. It
is fitted with standard 5x7 inch core giving a total cooling sur face of 312 square feet. Tempera­ture_
is controlled by means of manually operated shutters.
ARRANGEMENT OF PATIENTS IN AMBULANCE AIRPLANE.
16 T E C H N I C A L B U L L E T I N N o. 4 4
All engine and naviga ting in struments including a flight indicator are mounted in the pilot's
cockpit, the only exception being the clock and altimeter in the cabin. The in strument board is il­luminated
for night flying, and wing and fu selage are wired for both running and landing lights
although none are in stalled. The cabin is lighted by two ceiling lights in addition to the triplex
glass windows. N-0 armament, radi o or photograp hic equipment is carried .
·w recking tools are provided as special equipment for use in extricating the injured in crashes.
The flying qualities of J-he XA-1 as determined in the per fo rmance tests at McCook Field show
that this type of airplane is admirably adapted for crash rescue in isolated or otherwise inconveni ent
localities.
One of these airplanes has been shipped to the Panama Canal Zone for service test.
COX-lZLEMIN AMBULANCE AIRPLANE, MODEL XA-1.
Dimensions :
Overall span .. .. . . . . . .. . . ... .. . .. . .. . . . . . . . . .. .. . .. . . .. . .. . .. . .
Overall length . .. . .. . . . . .. ... .. .. . . ... .. . .. . . . ..... .. ... . ... . .. .
Qyerall height . . . . . . . . . . . . ..... ... . . . . . .. . . . ..... . . ... . . . . .. . . . .
Span of wings (upper and lower same) .... . .. . .. . . ... ... ... . .. . .. . .
Chord of wings ( upper an cl lower same ) .... . .... .. .... . . . . .... .. .. . .
Airfoil . .. .... ... .. . .. .... ... . . . .. . .. . . ... . ..... .. . . . . . .. .. ... .
Gan . ... .. .. . . . .. . . . . . .. .. ...... . ... . . . . . .. .... . . .. ... . . .. . . . . .
St;gger . . . . .. .. ... .. . . . . . . . .. .. .. . . .. . . ... . .. .... . . .. . . . . . . . .. .
Dihedral . ..... . .. . . . . .. . . . . .. . . . .. . . .... ... .. . . . . . .. . . .. .. . . . . .
Incidence . . .. . .. . .. . . . ... . . .. ... ..... .. . ... . . . . . . . . . . . .. . . . . .. .
Sweep back .. .. ... . .. . . . .. . . . . ..... . . . . .. . .. . ... ... .. . . . .. ... .. .
Height of propeller axis in flying position . . . .. .. . . . . .. . .. .. ..... .. . . .
Tread . . . ... . ..... . . . . ... . ... . .. .. . . . . . .. .. .. . . ...... . .. . ..... .
Areas ( square feet) :
Total supporting surface . . .. . .. .. .... .. . . .. . . . ... . ... . ... .. . . ... .
Upper wing, including center section .. . . . . . .. . . . .. . . . . .. . . . . . .. . .. .
Lower vving, including wing butts .. . . . . . . . .... ... . . . . . ... . . . . . . . .. .
Center section . .. . . ... . . . . . ... ... . . . . . . ........ . . .. . . .. . .. .. .. . .
Ailerons . . .. . . . .. . ... . . . . .. .. . . . . . . . . . . . .. . . . . . . . ... . . . . .. . . . . .
E levator ...... . . . . .. ... .. . . .. . . .. .. . ..... . . . . . .. . . . . ... .. . . ... .
Rudder .. . . . .. .. .. . . . . . .. . . . ... .. . . .. . .... . . .. . . . .. ..... . ... . . .
Stabilizer . . ..... .. .... . . . . .. . .. . .. .. .. . . .. . .. . . .. . . .. . .. . . . ... .
Weights (pounds) :
Gross . . . . ... ........ . . . ... . . . . .. .. . . . . . .. . .... . . ... . .. .. ... . . .
Empty with water ... . .. . ... . .. .. . . . . ... . . . . . .. . . . . . . ..... . .. . .. .
Use ful load . . ..... .. . . ... .. . .. . ....... . . . ... .. . . . .... . . . . . .. . . .
Equipment . .. ... . . ... . . . . . . . . ..... . . . .. . . . . .... .. . .. ... . . .. . . . .
Crew of four ,- pilot, medical officer and two patients . . . .. . . . . . . . . .. .
F uel ( 108 gal. @ 5.9 lb. each ) .. . . . . . . .. . .. . . ... . . .. .... . ... . . . ... .
Oil ( 11 gal. @ 7.5 lb. each ) . . . ... . . . .. . . .. . . . . .... . . .. . . . . . .. . . . . .
\Ving loading ( pounds per square feet) .. . . . . . . . . . . . . . . . . . . . . . .. . . . .
Power loading (pounds per hor sepower ) .. . · . .. . .... . . .. . . . .. .. . . .. . .
Performance:
44' 9"
30' 8"
11' 2"
44' 9"
6' 0"
Gottingen 387
6' 7-1 / 4"
None
1° 30' oo
None
5' 10"
8' 9"
510.00
266.75
243.25
49.0
34.2
26.22
13.77
35 .45
4797.00
3013.15
1783.85
344.25
720.0
37.0
82.60
9.41
11.32
High speed at ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.2 m.p.h.
High speed at 10,000 feet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.8 m.p.h.
Climb, time to 10,000 feet. . .. ... . . . ...... . ... . . .. . . . . . .. .. . .. . . . .. 15.67 min.
Rate .of cli~b at ground. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 948 ft ./ min.
Service ce1lmg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15,500 feet
Absolute ceiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17,300 feet
Landing speed (approx .) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 m.p.h.
E ndurance full throttle at 5,000 feet, including one-half hour at sea level .. 3 hr. 10 min.
•
i-----15 :..;;-z1 . =--------i
-- ,J 4~{f
r--------.d4'--'"- ------1
'.3'!.
COX-KLEMIN AMBULANCE AIRPLANE, MODEL XA-1.
Type
Status
Manufacture l'
Power plan t
Gross weig ht
Useful load
Wing loading
Power loading
biplane
---- ·-·· .. . ·- ··· ·· -·-.Experimen ta l
Cox -Klemin Aircraf t Corp.
"12"
4797 lb.
... 1783.85 lb.
9 .41 lb ./sq . ft.
11.32 lb./h . p_
Jo'-d" ----
GENERAL ARRANGEMENT OF COX-KLEMIN AMBULANCE AIRPLANE XA-1 WITH LIBERTY ENGINE.
>-
;-; ,,,__
n
~
>
'Ti
~
0
M
<
M
l'
0
'tj
';?
H
M z
~
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'1
JS T E C J-J N l C f\ L B 0 L L E T I N N o. 4 4
Performance Tests on Curtiss P-1.
Performance tests on the new Curtiss pursuit. Model P-1, are in progress at the Division.
\ i\Tith low compression Curtiss D-12 engine ( 449.5 effective horsepower at 2340 r. p. 111.) and a
Curti ss-Reed duralurnin propeller (X-32973-84), the fo llowing re~ ult s were obtained:
High speed at ground (:?340 r. p. rn.) . . . . . .. .. . . .. .. ......... ... 163 111. p. h.
H igh speed at 10.000 feet (2240 r. p. 111.) . ... ...... .. . .......... . 153.5 m. p. h.
Ciimb to 10.000 feet ........ . .. . .. . ..... .. . . ... ... . . ...... . . . . 7.2 min.
Rate of climb at ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1810 ft./mit~.
Service ceiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22,500 feet
Absolute ceiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23,800 feet
Landing speed (approximate) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 rn. p. h.
F light tests will be continued with different types of wood and metal propellers to determine
which give maximum performance in speed and climb. It is also planned to conduct tests on night··
fl ying equipment, including central electric power plant and airways parachute flares , which will
be in stalled in the P -1 airplane in conjunction with the in stallation of radio apparatus and ignition
shielding.
In the cooling tests. this airplane showed an increase in cooling efficiency of six per cent over
reqnirements with an air scoop fitted to the radiator. A three-mile decrease in high speed was
noted with the addition of an underslung auxiliary fuel tank which doubles the fuel capacity.
Performance of Douglas Transport with Different Propell~rs.
Up to October L 1925, six of the nine transport airplanes, Model C-1, under construction by
the Douglas Company. Santa Monica. California, had been completed and deli vered. One of these
is equipped with an epicyclic geared Liberty engine.
The C-1 transport, which is a single-engined biplane designed about the standard Liberty en­gine
for carrying passengers and freight. has made a commendable showing in the performance
tests 'conducted at the Division. Different types of propellers were used in these tests, resulting
in considerable variations in performance as may be noted in the fo llowing comparison :
High Speed at Servirr Absolute Rate o.f Climb at
Propc!frr
Wood-10'6" c!ia. (068891)
Grou nd m. p. h. Ceiling .ft. Cfiling .ft. Ground .ft. / min.
115.8 14,850 17,500 645
Dural-10' 6" dia . n603) .. .. .. . . .
Dural-JO' 0" dia. (X-47409) .. ... .
119.7 15,900 18,700 657
121.0 13,800 16,600 595
Dural-10' 6" clia. (X-49699) . .. .. . 123.2 15.175 18,000 640
The above tests were made with standard Liberty " 12" engme installation and with a load
equi valent to six passengers, 1080 pounds, and crew of two. 360 pounds. The various propel­ler
instal lations caused a variation of 40 pounds in the total weight of the airplane. making it vary
from 6443 to 6483 pounds.
A quantity of spares for C-1 tran sports has been ordered under a separate contract recentlv
awarded by the Government.
Performance Increase with Geared Engine and Large Propeller (L-W-F Transport).
In consummation of a series of tests conducted by the Engineering Division on the L-\iV-F
transport airplane. Model T-3. the fo llowing summary of per fo rmances is offered to show the in­crease
in performance resnlting from use of gear ed engines and large propell ers. The engines usfcl
in these tests were all Liberties of the fo llowing types: standard engine, Navy epicyclic geared ·
engine and Allison geared engine (Engineering Div ision design reduction gear ).
ENGINE AND PROPELLER GROUPS USED ON L-W-F TRANSPORT.
Engines ( h. p. / r. p. 111.) ..... . ...... .... . .
Propellers ( clia.) ....... .. .. .. . .... .... .
Reduction ratio ......... ... .... . . . . . . . . .
Weight empty (lb. ) . . ... . . . .. ....... . .. .
Weight loaded ( lb. )_ ... . . .. . .. . . ... . . ... .
Useful load ( lb. ) .... .. . . .. .. . . .. .... ... .
Power loading ( lb. / h. p.) .. . ... .. ....... . .
Sta ndard
426/ 1795
10' 6"
Direct
4656
7016
2360
16.45
E pic31clic
443/1855
14' 0"
5 : 3
5022
7240
2218
16.33
A llison
447/ 1900
15' 0"
2 : 1
4936
7240
2304
16.18
A IR C R AF T D EVELO P M EN T 19
PERFO RMAN CE OF L- W- F TR AN SPORT WJTH STANDARD A N D GEARED E N GI NES.
Standard E picyclic A llison
High speed at ground. . . . . . . . . . . . . . . . . . . . 98.7 m. p. h. 102.7 m. p. h. 108.3 m. p. h.
High speed at 6,500 feet. . ... . .. .. . .. . ... . 89.0 m. p. h. 93.5 m. p. h. 98.4 m. p. h.
Time to 6.500 feet. . . . . . . . . . . . . . . . . . . . . . . 36.2 min. 16.5 min. 15.5 min.
Rate of climb at ground . . . . . . . . . . . . . . . . . . 280 ft ./ min. 550 ft ./ mii1. 618 f t./min.
Service ceiling . . . . . . . . . . . . . . . . . . . . . . . . . . 6 .650 feet 10.400 feet 9.600 feet
Absolute cei ling . . . . . . . . . . . . . . . . . . . . . . . . 10,300 feet 12,650 feet 11 ,400 feet
F rom the above table it is evident that a decided improvement results from the use of the
geared engine with large propeller.
In connection with experiments on t his airplane. the effect of fu selage ;interference on pro­peller
efficiency has been previously demonstrated and the account publi shed in T echnical Bulletin
.!Vo. 42.
Huff-Daland Advanced Training Airplane ("Dog Ship")
A combination ad vanced trainin g and gunnery type airplane, built by H uff, Daland & Company,
Inc., Bri stol, Pa. , was submitted to the Division for examination. This airplane (designated by
its builder as the "Dog Ship") was built hy the ccntractor at hi s own expense under a bailment con­tract
entered into with the Army Air Service P rocurement Section at \Vashington, D. C., covering
the loan of government equipment. It represents a combination of the fu selage of the T A-6 air­plane
with the wings of 'the TW-5 airplane, two experimental t raining type airplanes formerl y pro­duced
by this firm.
At McCook F ield, the airplane was inspected and flown by members of a special training board
appointed by the Chief of Air Service, which concluded that the airplane did not have sufficiently
advanced characteri stics to justify its adoption for either advanced training or advanced gunnery
purposes.
Bids Asked on Heavy Bombardment Monoplane.
On July 25, 1925 , a circular proposal was forwarded by the Army Air Ser vice to the fo llowing
aircraft designers and manufacturers asking· for bids on a heavy bombardment monoplane to be
built about the new 1200-h. p. Type "X" air-cooled engine now under development. Other de­signers
whom the E ngineering Division thought might be interested were also notified of the issuance
and general nature of the proposal.
Atlanti c Aircraft Corporation
Cox-Klemin Aircraf t Corporation
Curt iss Aeroplane & Motor Company, Inc.
The Douglas Company
Eberhart Steel P roducts Company
G. E lias & Bro. , Incorporated
Charles Ward Hall
Huff, Daland & Company, Inc.
Kirkham P roducts Company
Lawson Aircraft Corporation
Thomas-l\ Iorse Aircraft Corporation.
This competition has been held. and negotiations entered into with two of the above firms for
some preliminary engineerin g and development work.
Complete XHB-1 Heavy Bomber to be Built.
By virtue of its option in a preliminary contract with H uff , Daland & Company, Inc., Bristol,
Pa., ( formerly of Ogdensburg, N. Y ~) for the development of certain parts of an experimental
heavy bombardment type airplane designated as Model XHB-1, the E ngineering Division has
ordered the construction of one complete airpl2ne.
This airplane will he designed about the 800-h. p. P ackard l A-2500 engine with 2 :1 reduction
gear, with provision in the design for installation of a side type supercharger. It is to be built of
all metal construction with the possible exception of th~ co v~ri11 g which may be of fabric, incor-.
20 AIRCRAYT DEVELOPME~T
porating the complete set of wings called for in the original contract. Per formance requirements
stipulate a minimum high speed of 100 miles an hour at sea level, a minimum rate of climb of 500
feet a minute at ground, and a service ceiling of not less than 10,000 feet- all requirements to be
met without supercharger installation.
A brief description of the design is .publi shed under "Design Competition for Heav_v Bombard­ment
Airplane" on page 10, Terl111ical Bulletin No. 43.
D-12 Engines for Curtiss 0-l's.
Change in power plant has been made in the ten 0-1 obser vation airplanes under con ~ tructi o n
for service test b_v the Curtiss Aeroplane & Motor Company, lnc .. New York. All of these air­planes
will be equipped with Curtiss D-12 engines in stead of Liberty engines as specified in the
original contract. It is estimated that thi s change of engines together with other contingent modi­fi
ca tions will effect a saving of 256 pounds in the gross weight of the airplane.
A description of the experimental Curtiss X0-1 obser vation airplane with P ackard l A-1500
and Liberty " 12" engines was publi shed in T echnical B ulletin No. 42.
Design Studies.
The fo ll owing design studies were made b_v the E ngineering Di vision within the past year. Tht>
data compri sing these studies are at present incorporated as part of the project records, but at a
later elate it is planned to make them available in the form of serial reports for publication in the
Bulletin.
Design Stud·y N (I . Z--Long Distance Reconnaissance Airplane ( \Ving on Fuselage) .
Design Study .l\' o. 2-- Long Distance Reconnaissance Airplane ( \ \Ting above F uselage ) .
Design Study No. 3-Heavy Bombardment Monoplane About Single 1200 h. p. Air-cooled
Type "X" E ngine.
Design Study N o. 1- Heavy Bombardment Monoplane About Two 1200 h. p. Air-cooled T ype
"X" Engin es.
Desi.r;n Stud·y :\' o. 5-Heavy Bombardment Monoplane About Two Geared P ackard l A-2500
Engines.
Design Study [\To. 5-Heavy Bombardment Monoplan e About Two Geared Curtiss V-1400
E ngin es- Carrying Useful Load Called for in Specification No. 1751.
Design Study No. 7- Heavy Bombardment Monoplane About Two Geared Curtiss V-1400
E ngines-Carrying Useful Load Specified by Bombardment Conference at Kelly F ield.
Design S tud')' N o. 8-NBS-4 Airplane with Two Geared Curti ss V-1400 Engines- Carrying
Useful Load Specified by Bombardment Confe rence at Kelly Field.
Design Study IVo. 9-NBS-4 Airplane with Two Curti ss R-1454 Air-cooled E ngines-Carry­ing
Useful Load Specified by Bombardment Confe rence at Kell v F ield .
Desiq11 S tud)I No . I O- Curtiss P -1 Airplane with Curtiss D-12 Engine Replaced by Curtiss
l~- 1 4 54 Engine. ·
Disposition of the World Cruisers.
The famous Douglas \ Vorld Cruise airplanes which made the fir st round-the-world flight last
vear have been allocated as fo l!ows :
The "Chicago," piloted by Lieutenant Lowell Smith. has been di smantled at the Di vision
for shipment to the Smithsonian Institute. \ J\/ashington, D. C.
T he "New Orleans," piloted by Lieutenant Eric Nelson, has been retained at the Di vision
and pbced in the McCook Field museum.
The "Boston II." pil oted by Lieutenant Leigh \1\Tade, has been reconditioned for long dis­tance
navigation test at McCook F ield.
Metal Wings (Thomas-Morse Design)
In an endeavor to quickly develop metal wmgs sui table for observation and pursuit type air­planes,
the Army Air Service has ordered from the Thomas-Morse Aircra ft Corporation . Ithaca.
N. Y., some experimental metal wings for DH -4M-2 and P\tV-9 airplanes. Two set s of wings
were ordered for each type of airplane, one for static test and the other for flight test. The wings
for the DH have been received.
AIRCRAFT DEVELOPM EN T 21
The DH cellule consists of four straight panels and center section with steel "N" struts and
streamline wire interplane bracing. Each panel incorporates a two spar construction with metal
ribs and fabric covering. The spars ~re formed of extruded durafomin of "I" beam section,
whereas the ribs are built up from oval section duralumin tube. Steel wires are used for drag brac­ing.
The cellule weighs 711 pounds, complete.
Jn static tests, the wings held the required load factor of 5.5 in low incidence position. In high
incidence position, the wing spar fl ying wire fittings fai led at a load factor of 7.5. New fittings
were installed, and the test continued to a factor of 10.5 without failure. Failure fin ally occurred
at a factor of 11.0 when the right inner struts buckled. A load factor of 8. 5 is required.
Following static test, a half cellule composed of these same wings was used as a counter­weight
in testing a set of experiniental plywood wings. The load in this test was so arranged that
for each load factor imposed on the plywood wings there resulted a load equivalent to a factor of
2.0 at the outer strut points of the metal wings, including ·the .30 per cent increase in moment speci­fied
in the design. The plywood wings failed at a factor of 7.0, but the metal wings remained in­tact.
This showed that the metal wings supported a load equivalent to a factor of 14.0 at the tips
without fai lure.
On a subsequent contract, the Thomas-Morse Company is to furnish two sets of metal tapered
wings for use on the Boeing pursuit, Model P \V-9, together with one test spar and six test ribs.
These wings will be designed to carry loads equivalent to factors of 12, 6.5 and 4 in high and low
incidence and in inverted flight positions, respectively.
Woven Plywood Wing (Forest Products Laboratory)
A sample wing panel built of woven plywood was submitted by the Forest Products Labora­tory
for static test. The wing was of RAF-15 section, designed as an upper right panel for a DH
airplane. It was built entirely of wood, held together with glue, no screws or nails being used. The
spars. front and rear, were of multiple construction, each being composed of five plywood " I"
beams joined at the strut points by spruce blocks, glued and pinned. T he covering, supported on
plywood ri bs, was formed hy two thin layers of interwoven plywood separated by corrugations of
the same material. The panel had a supporting area of 106.6 square feet and weighed 111 pound s.
In the static test, the panel sustained a load factor of 4.5 in low incidence position when thP
front spar fittings showed signs of fai lure. The fittings were rein fo rced, and t!1e load carried to a
factor of 6.5 in high incidence position without failur e. At a load factor of 7.0, however. the
wing collapsed. The required load factor for wings on new standard observation airplanes is 8.5 in
this position. The panel fa iled to meet requirements.
Crop Census by Airplane.
A new method of taking crop census was initiated by representati ves from the Department of
Agriculture in collaboration with the E ngin eering Division. This method consists in taking aeri:t!
photographs fl f agricultural districts from an altitude givi ng maximum acreage without loss of crop
identifi cation, and in estimating acreages from the photographs.
In the past the customary methods employed by the Department of Agri culture to obtain in ­formation
on crops involved direct interviewing of farmers as to the amount of acreage planted
in wheat, corn , oats, etc. , or driving about the country making actual measurements of the field s. The
method of photographing these areas from an airplane sayes an incalculable amount of time am!
expense and makes possible the issuing of crop predictions at a much ea rlier elate.
Collecting Rust Spores in the Upper Atmosphere.
1n an effort to t race the source and propagation of a destructive grain di sease known as "stem
rust," a series of flights were conducted by E ngineering Division personnel in cooperation with the
Bureau of P lant Industry, Department of Agriculture. The fl oating rust spores or germs were col­lecting
by exposing gelatin-coated glass slides to the prevailing ai r currents at various altitudes.
In this way it was sought to determine the prevalence of rust spores from clay to clay and ascertain
what relation the air currents bore to the propagation of the disease. E leven slides were made and
fo rwarded to the Department of Agriculture.
It is planned to conduct similar tests at other flying fi elds in order to determine the abundance
of rn st spores in the atmosphere in that part of the country.
22 T E C H N I C A L B U LL E T I N N o. 4 4
AIRSHIPS AND . BALLOONS
All-Metal Car for TE-1 Airship.
An all-metal car for the one-man training airship, Model TE-1 , built by the Aircraft Develop­ment
Corporation. Detroit, Michigan, under a sub-contract from Air ships, Incorporated, H am­mondsport,
New York, which is building the envelope, has been received at McCook Field for ac­ceptance
test. T he car which is made of duralumin was fir st weighed to determine the center of
gravity and then suspended from a specially. constructed framework by means of pulleys and counter­weighted
cables in such a manner as to simulate its suspension and balance when attached to th e air­ship.
The two engines, Lawrance L-4 radials mounted on outriggers, were run to test the strength
of the structure, but the vibration was so excessive that failures resulted at several points, necessi­tating
a redesign of the mounting before the tests could be completed.
T he airship proper including envelope, suspension rigging, control surfaces, etc., is nearing com­pletion
at the plant of Air ships, I ncorporated. The all-metal car was substituted in the original
design to effect a saving in weight as well as to initiate experimental development of the all-metal
car for non-rigid airships.
T he T E-1 ai rship is an experimental type designed for one-man tra111111g purposes. It has a
capacity for 80,000 cubic feet of helium and is propelled by two Lawrance 60 hor sepower engmes
mounted upon out riggers. On! y one model is being built.
RS-1 Airship.
T he R S-1 airship has been re-erected at Scott Field where hangar test s are in progress prepara­tory
to flight. Many al te rations have been made in the power plant, including the oil system, cool­ing
system and exhaust piping. Gas diffusion is reported to produce an average drop in purity of
.06 per cent a day. The airship will be ready for trial flights as soon as the elevator control system
is fini shed, which is expected to be in December , 1925.
Balloon Development.
The high al titude observation balloon is being redesigned to incorporate changes recommended
as a result of service tests. These include redesign of lobes and suspensions, relocation of gas
valve and improvement in method of inflation and defl ation.
An improved type barrage balloon, smaller than the first model, is contemplated. This work.
however, will not be started immediately owing to priority o f. other projects.
Drawings for spherical balloons of 19,000, 3S.OOO and 80,000 cubic feet capacities are being re­drawn
to E ngineering Division standards. P roduction drawings are also being made for a 12,000-
cubic foot spherical balloon to replace the present 9.000 cubic foot size for solo flight training.
ARMAMENT
Aircraft Bomb Truck, Type A-1.
Coincident with post war development of fragmentation, chemical and demolition bombs, vary­ing
in weight from 100 to 4000 pounds, came the increasing difficulty of handling the larger sizes.
It was therefore imperative that the Army Air Service provide some means of transporting and
handling these bombs. To meet this specific demand the E ngineering Division at McCook Field
undertook the development of a vehicle known as the "Aircraft Bomb Truck."
After considerable study of trucks, tractors and artillery vehicles, constituting the transporta­tion
equipment at present used by the various branches of the Service, definite requin:ments for an
aircraft bomb truck were formulated. T he principal 1features embodied in these requirement s,
especially those of paramount importance. were as fo llows:
a. Mobility-to negotiate paved roads or rough terrain.
b. Durability-to withstand severe continuous service conditions.
c. Interchangeability- to permit replacements and r epair of parts at a minimum expendi­ture
of time and effort.
AIRCRAFT DEVELOPMENT 23
AIRCRAFT BOMB TRUCK, TYPE A-1, HANDLING 4000-LB. BOMB.
General specifications, as out lined for this development, indicated that the vehicle selected
should be capable of transporting bombs. varying in weight from 100 to 4000 pounds. from the rail­head
or ammunition dump. across improved roads or unimproved terrain, to the flying field . Also.
that this ,-ehicle should be pro,·ided with bomb handling equipment capable of handling the bombs
to and from the body platform as well as m.oving them into position on the ground under the
fuselage of the airplane. T he bomb handling equipment was designed to accommodate. under ser­\'
ice conditions, any one of the following loads.
1-4000 lb. Mark I demolition horniJ and stabili ze r.
2-2000 lb. Mark I demolition bombs and stabi li zers.
4-1100 lb. J\f ark I demolition bombs and stabili zers.
4- 600 lb. Mark I demolition bombs and stabilizers.
12- 300 lb. Mark I demolition bombs and stabi li zer s.
20 or more 100 lb. Mark I demolition bombs and stabilizers not exceeding 4400 lbs.
In all cases the stabilizer s, which are detachable from all bombs except the 100-lb. size. were
to be carried with the bombs.
In formulating these specifications and requirements. no reference could be made to any par­ticular
Yehicle clue to the fact that during the !ate war motor vehicle equipment was not especiallv
designed for the tran sportation of bombs. Further studv and investigation indicated that the
1-1 /2 to 2 ton Qu:utermaster "TTL,'' four-wheel drive pneumatic tired, cargo truck would be
most suitable as the standard _,·ehicle for development. Accordingly a chassis was procured from
the Engineering Section, ).[otor Transport Division Quartermaster Corps, located at Camp Bola-
T E C H N I C A L B U L L E T I N N o. 4 4
bird, Maryland, and subjected to extensive road tests to indicate what chassis changes would be
necessary to meet the requirements for an aircra ft bornh truck Thf: cha nges effected , and here­inafter
referred to, incl uded the in sta llation of dual wheels on the rear and mod ification of the front
and center cliffen·n ti als.
The bomb handl ing equipment which was designed, constructed and applied to th is chassis hy
the Engineering Division. includes a platform body. a power take-off unit. a hori zontal hyd raulic
hoist uni t, detachable skids and a davit unit provided with suitable hoisting cable and sheaves.
The platform body whi ch is pivoted at the rear end of th e chassis can be elevated. by power,
to a maximum angle of 20 degrees from the horizontal. The body side members. referred to as
detachable skids. consist of two duralumin units , designed to sen ·e as side members, ·when placed
vertically on the body plat form . and as a means of loading or unloading the bombs. when detacheci
BODY ELEVATION DETAILS ON AIRCRAFT BOMB TRUCK .
Upper-Body elevated to m aximum position.
Lower Left-Under Body Construct ion Showing Horizonta l Hydraulic Ho is t.
Lower Ri ght-Adjustable Davit with Overrunning Cable Safety Release.
A IRCR AF T DEV E LOPM E~T 25
and hinged to the rear of the truck. Removable head and tail gates of suitably reinforced steel are
provided for cargo purposes. A power-take-off unit transmits power from the engine through the
cen ter transfer case to the hor izonta l hyd raulic hoist unit . T hese un it·s. together with the hydraul ic
pump yalve mav be selectively operated fr om the driver's seat. !\ 11 adj ustable davit unit, com­prising
sheaYe. cable and hook, and a locking arrangement is mounted on the forwar d encl of the
platform body. T his unit is so designed and located that elevation or depression of the body does
not appreciably alter the position of the hook with respect to the body. T o guard again st over ­runni
ng. hevond norma l. when loading a bomb. a safety feature is provided which autornaticalh·
di;ocontinues operation of the winch control, with cable at tached .
T he Type A-1 vehicle is powered by a single 50-h. p. Model 500. 4-1/ 4" x5- l / 2" , fo ur -cylinder
1-l inkle.v motor. which propels both the chassis and the bomb handl ing equipment . independently or
simultaneously. as desired. T he transmission is of the Covert type. T his unit in connection with
a special Quartermaster transfer-case enables a selection of gear ratios which provides ample power
to meet all requirements of a 1·ehicle of this type. There are fo ur speeds forward and one reverse.
To improve the mobili ty of t hi s vehi cle in nego1-iating unimproYecl te rrain with fu ll load, dual
pneumatic rear wheels Were in stalled. T hat the resul tant r eduction in unit ground pressure justi­fi
ecl thi s change was evidenced by improved mobility in soft ground. Continuous operation of this
Yehicle during experimental road tests resulted in the su b~ti tuti on of a stanclci.rd bevel gear type dif­fe
rential in place of the rol ler type in the front axle.-and the repbcemcnt of the center differen tial
·Nith a solid sha ft.
At the rear of the chassis a standard Quar termaster winch unit is mounted in a position having
adequate cleannce for the rear axle differential and the road. T his unit is selectively power­operated
by a propeller shaft from the transfer case and pro1,ides a means of operating the hoist
cable through sheaYes on the elevati ng body and davit assembly.
T he front and rear axle ratios are the same. namely : 7.11 to l . T his reduction, with the
chassis transmission and special Quartermaster trans fer case. provides a selection of engine to wheel
ratios. in the forward direction . from 7.11 :1 to 74.0: l ; and in reverse fr om 51.8 :1 to 103.6 :1.
Hence the vehicle is enabled to obtain a maximum speed of thirty miles per hour on good roads
as well as to negotiate steep incl ines or sof t terrain.
'When equipped with 38" x7" penumatic ti res ancl rarrving one loaded Mark I demolition bomb
weighing 4200 pounds. the bomb truck weighs approximately seven and one-half tons. The road
clea rance is 16 inches. Complete turn s. r ight and left . can he accompli shed by t his vehicle in
approximately 25 feet and 45 feet, respecti vely. T he difference in turning to right or left is due to the
Ir.cation of the steering as::;embl _v on the left front side of the vehicle.
COMBINATION SKID AND BODY SIDE MEMBER FOR AIR CRAFT BOMB TRUCK.
26 T E C H N I C A L B U L L E T I N N o. 4 4
Among the interesting features are the detachable skids. These form t he sides of the body dur­ing
transportation of the cargo and serve as skids during loading or unloading of the truck, as
shown in the accompanying sketches. In the latter usage the skids are inclined, and with the body
elevated, form a continuously sloping surface. Each skid is designed with specially shaped slides and
rollers which facilitate the loading or unloading of cylindrical objects. The rollers are arranaed
at intervals along opposite sides of the skid and are inclined toward the center. The slides which
ru~ lengthwise of th ~ skid are so spaced between the rollers as to permit the moving of cylindrical
obiects of smaller diameter than those accommodated by the rollers. The relative position and
height of the rollers with respect to the slides are such that the large 1100-lb. , 2000-Ib. and 4000-lh.
bombs ride on the rollers clearing the slides and the smaller bombs skid 011 the slides clearing the
rollers.
---, ----,----,-
SKID USED AS BODY SIDE MEMBER
. ON AIRCRAFT BOMB TRUCK. (On left)
BOMB CLEARANCES ON SKID.
The skid complete ·weighs only 175 pounds. making it ligh enough for two men to handle.
This desirable feature was secured thru the use of duralumin, 3/ 16-inch gage. The rollers and at­tachment
fittings are of steel. The sur~ace of the skid is treated with a special protective to inhibit
corrosion by salt air or water.
Recent development of the Coleman 5-ton vehicle by the Quartermaster Corps, and its possible
standardization in the near future to replace the present "TTH" and "Militor" trucks, has made ad­visable
the consideration of the conversion of the Coleman truck into a second model aircraft bomb
truck.
Exten sive roadibility tests conducted on April 1 to 5, 1925, at Aberdeen Proving Ground.
Maryland. provided sufficient evidence for judging the comparati ve performances of the Coleman
vehicle, the "Militor" and the Class "C" six-wheel cargo . trucks.
The Coleman truck is a four-wheel drive vehicl e, equipped with a 4- l / 2"x6" Buda or Hinklev
motor, a F uller transmission, Spicer driveshafts. a transfer case having a selective reduction of
either 1 to 1 or 3 to 1, and \Visconsin double reduction front and rear axles. In this vehicle
weight is evenly distributed on the wheels which are equipped with 42"x9" penumatic tires. T he
axle ratio of 7.72 to 1 provides a selection of engine-to-wheel ratios in the forward direction from
7.75 :l to 139 :1 and in reverse, from 50.4 :1 to 188.8 :1. The pay load is five tons, which is of suf­ficient
capacity for transporting two 4200-lb. demolition bombs without difficulty.
In recent service tests conducted by various Air Service tactical units at P hillips Field, Aber­deen
Proving Ground, Maryland, the performance of fir st Type A-1 aircraft bomb truck elicited
much commendation. A vehicle of this character included as part of the transportation equipment
of tactical or service squadrons, provides, when not actually employed in the handling of bombs . an
efficient and useful adjunct for lifting heavy loads by its own power. It is also useful as a cargo
vehicle for handling crated engines and supplies. The Type A-1 Aircraft Bomb Truck is now lo­cated
at Langley Field, Virginia, where extensive tests are in progress.
AIRCRAFT DEVELOPMENT 27
Nelson Synchronizer Adapted to Late Model Engines.
The Nelson synchronizer has been adapted to all late model Cnrtiss, Packard and Wright en­gines.
In service tests on the Curtiss D-12 engine in pursuit aircraft, however, both the coupling
flange and the engine drive unit showed excessive wear due to the higher speed of operation. Change
in material and more frequent lubrication have been recommended as a remedy for this condition
until the new gear is forthcoming. The Nel son gear has given sati sfactory service on the Libertv
and \!\/right 180-h. p. and 300-h. p. engines.
Tests on Wing Tip Flares.
Qualitative tests were made at the Division on the new H olt guarded type wing tip flares and
brackets, used by the British Air Service. in comparison with the Air Service standard Mark I flare
and the new experimental Type E-2 bracket now under con sideration. The E ngli sh brackets are of
an improved type, designed by Colonel Holt. who is al so the designer of the present standard Air
Sen ice Mark I wing tip flare bracket. The English Holt flare brackets are designated Mark VII
( double guarded type ) and Mark IX ( single guarded type ) which represent the standard types
adopted by the British Air Service for observation and pursuit purposes, respectively. For the
tests all of the respective brackets were fitted with the late5t type high candlepower flares.
All tests were conducted during night flights hy different pilots under varying weather condi­tions.
The improved type English flares proved of higher candlepower and longer burning than
the Air Service flares, the burning time approximating two minutes or about twice as long as that
of the standard Mark I flare . One type of Engli sh flare candle gave off a yellowi sh light while
the other burned with a reddish hue. These colored lights were supposed to be fog-piercing, but
that feature could not be substantiated since no flights were made in what might be termed den se
fog although in several instances a heavy ground mist was present. The white light of the standard
Mark I flare pierced this ground mist equally as well as the colored illumination given off by the
Engli sh flare s. The results showed that the special guard on the E ngli sh brackets and the illumi­nating
efficiency of the flares used therein were no improvement over the standard Mark I flare
candle in the new T ype E-2 flare bracket now on service test.
The various types of wing tip flares used in these tests are shown below. A descriptinn of the
Air Service experimental Type E-2 shielclecl bracket was publi shed in T cd1J1 ical Bulletin N o. 34 .
WING TIP FLARES ON COMPARATIVE TEST.
Left to Right-Electric Land1):ig Light; Experimental Type E-2 Flare Bracket; English Mark VII Holt Flare, double guarded
type ; Air Service Standard Mark I Flare Bracket; and English Mark IX Holt Fla·re Bracket, Single Guarded Type.
28 T E C I-I N I C A L B U L L E T I N 1 o. 4 4
Wind Detection Signals.
Wind detection signal s. Type PX 58.84-2, submitted bv the Ordnance Department, were tested
and found sritisfactory both in functioning and for landing and navigating purposes insofar as these
characteristics could be determined by experi ­mental
test. The wind detection signal , shown
herewith. consists of a 42 mm. caliber cartridge
filled with approximately one pound of powder
which burns for about two minutes, emitting a
th ick, yellow smoke. It is discharged fr om 'the
aircraft by means of a pyrotechnic projector. In
the tests the signals were observed against back­g
rounds of various colors under different at­mospheric
conditions at altitudes up to 9000 feet
over land and up to 1500 feet above water.
Machine Guns to be Mounted Inside Wing.
T he mounting of Browning .30 caliber aircraft
machine guns on the lower wing of an airp lane
for ground a ttack purposes having proved success­ful
(see page 19, Technical Bulletin N o. 40) . it
WIND DETECTION SIGNAL. is now proposed to mount these guns. ent irely in-side
the wing, thereby eliminating parasite resist ­ance.
Howe1·er, to completely house the standard aircraft machine gun in this manner is danger­ous
m that during even a very short burst of fire the gun generates enough heat to set fi re to the
internal st ructure of the wing. It is therefore imperative that the gun be cooled or some means
be taken to prevent fi re. A method has been proposed for obviating this hazard. T his is to surround
the gun with an air duct about 4 inches in diameter. packed with asbestos. open in front and vented
in the rear in such a manner as to allow a flow of air completely around the gun.
It has been found practical to house the ammunition box
the box is made oblong in shape to conform to the section.
guns are remotely controlled from the cockpit.
New Machine Gun Synchronizer, Type E-4.
within the wing also. Jn this case
\Vhen mounted in this manner the
An experimental machine gun synchronizer. designated as the Type E-4, is under development
by the Division for application to aircraft engines. It is designed to be in stalled within the en­gine
and synchronized along with the original timing of the valve mechanism. T he following ad­va
ntages a re alleged for this type of installation :
a. J t permits a more simplified mechanism using a lesser number of parts. which results in
decreased weight and greater ease in maintenance.
b. Lubrication of the synchronizer could be accompl ished hy the same fo rce-feed oiling system
as used on the engine.
c. Synchronization would be simplified as th is would be taken care of in timing the valves
upon assembly of the engin e. thereby practically eli n1i nating synchroni zing troubles in the
fie ld.
cl. In new engines. the in stallation of the svnchroni zer would he taken ca re of by the manu­facturer.
EQUIPMENT
Aerial Photographs Transmitted Over Telephone Wires.
On September 25 . 1025, the American Telephone and Telegraph Company, assisted by a rep­resentative
from the Engineering Division, transmitted the first aeri al photographs over telephone
wires. The transmission was made fr om New York to Chicago and return , the operation req uiring
only seven minutes, and was considered highly suc\essful. It is belie1·ed that this method of tran s­mitting
aerial photographs has g reat military possibilities.
AIRCRAFT DEVELOPMENT 29
Later aerial photographs were t ransmitted simultaneously to New Yark, Chicago and San
Francisco at the military photographic demonstra tion held at Fort Lea\·enworth, Kansas.
Transmitting Tests on Radio Set SCR-134.
Both telephone and continuous wave signals transmitted from an SCR-134 radio transm1tt111g
and receiving set in flight have been received by airway radio stations over two hundred miles dis­tant
from McCook Field. T he flights were made as a test of the transmitting range of this set
equipped with special receivers.
In a subsequent test, the set was in stalled in an NBS-1 airplane and flown to Detroit, Mid1i­gan.
1t was possible to receive telephone communication from the airplane until it reached its
destination. reception at McCook Field being obtained by means of a four-tube Type BC-137 re­ceiver
from the SCR-132 radio set. At Detroit, radio demonstrations with two-way communica­tion
were gi \·en as part of the Aeronautical Show held at that place.
Ground Lighting Equipment.
A new type of 375 111111. Interflash gas- A.ashing beacon under night observation at McCook Field
appears to have greater visibi lity than previous beacons of this type. T he A.asher in this light is set
to consume one fi lling of gas is about one and one-half months.
Photomet ric tests ha\·e been made on a new special Fresnel lens flood light submitted by the
General Electric Curnpan y. Fairly satisfactory results were obtained by both 30-volt, 30-ampere and
1000-watt 110-volt stereopticon lamps.
Landing Light Mounting on DH-4B Standardized.
It is planned to standardize the location of landing lights on DH-4B airplanes by mounting them
on the bottom of the lower wing as near the tips as possible. Recent flight tests indicate that
the slight loss in speed (about two mil es per hour with lights mounted in this position will be
more than compensated for by decreased cost of in stallation.
New mounting brackets ha\·e been built to accommodate the in sta llation of Type A-2 landing
lights in this position.
Airship Instruments.
Two new in struments . a rate-o f-climb indicator and a valve opening recorder. have been cle­\
·clopecl for lighter-than-air use and placed on service test at Scott F ield. The fi rst is a modifi ca­tion
of the standard rate-of -climb indicator . used on heavier-than-ai r craft, to obtain a more sensi­tive
in strument for determining rate of ascent or descent of an ai rship in flight. particularly for
weighing off preparatory to landing. T he standard indicator which gives the ri se and fall in hun­dreds
of feet per minute over a range of 3000 feet in ascent and 2000 feet in descent has been
modifi ed to giYe the same rate of indication over a range of only 1000 feet in either direction.
The reworked in strument has larger volume. longer capillary leak. and a new dial , but the operating
mechani sm remains the same as in the standard indicator. Upon installation, the pointer of the in­strument
may be set at zero by means of a small adjusting screw.
The second instrument for lighter-than-air use was built by the Foxboro Instrument Company
fo r timing and recording the opening of the gas valve on the airship. This in strument has passed
acceptance test at the Division.
Experimental Engine Starters.
A combination hand and electric operated inertia starter, built by the E clipse JVfachine Com­pany,
has been submitted to the Engineering Divi sion for test and criticism. The electric motor
which is removable weighs only seven pounds, whereas the inertia portion alone weighs about thirty
pounds. In preliminary te sts without load. suffi cient friction developed to retard the flywheel a1)­preciably.
This nndue fr iction has since been largely eliminated.
An air sta rter. manufactured by the Detroit Air Appliance Company, has been procured for
in vestigation . T his starter which is operated by compressed air has passed torque stand tests sati s­factor
ily and is now ready for installation in an airplane.
30 T E C H N I C A L B U L L E T I N N o. 4 4
Ignition Shielding for Liberty Engine.
Satisfactory ignition shielding has been developed for the Liberty engine. This shielding, desig­nated
as the Type A-4, is intended for use on NBS-1 and DH-4 airplanes carrying radio equip­ment.
The installation does not interfere with any existing equipment. Production drawings have
been made, and the wiring harnesses ordered.
POWER PLANTS
Curtiss R-1454 Engine with Type "M" Cylinders.
Following preliminary endurance tests at the Division, the first experimental Model R-1454
radial engine built by the Curtiss Aeroplane & Motor Company, Inc., New York, was returned to
the manufacturer for incorporation of Type "M" cylinders and other improvements in place of the
Type "J" cylinders with which this engine was originally equipped. The revised engine has been
recently received at McCook Field for an endurance test which is now in progress.
The original engine with Type "J" cylinders developed 405 h. p. at full throttle ( 1650 r. p. m.).
Improved performance is anticipated with the new Type "M" cylinders clue to their increased ef­ficiency
although these cylinders are of the same size as those on the original engine, namely ; bore
5-5 / 8", stroke 6-1 / 2".
Six engin.es are now on order, but construction of the last three will be held in abeyance pend­ing
results of the endurance test on the revised engine.
Development of Almen "Barrel" Engine.
Bringing the Almen "Barrel" engine to the production stage has been a somewhat slow process
for the reason that such a radical departure in aircraft engine design involved the solution of many
new and difficult problems not incident to conventional design. The fourth experimental engine.
the Model A-4, has successfully passed acceptance tests at the Engineering Division and has since
been undergoing improvement to meet production requirements. The nature and extent of these
improvements which have consumed much time in assembling and disassembling the engine are as
follows:
a. Test and installation of a new Kingsburv type thrust bearing on the drive shaft to replace
the double row ball hearing previously installed;
b. Changes in oiling system for the purpose of lubricating the new Kingsbury bearing;
c. Change from magneto to battery-generator ignition clue to failure of former.
d. Installation of new circular oil-sealing sylphons of steel to replace those of cast iron which
failed to hold up. ·
e. Installation of new wabbler plate of heavier construction than the original design.
During a 45-minute full throttle run at two-thirds power. the Model A-4 engine developed 254.5
h. p. at 1400 r. p. m. with remarkable smoothness in operation. The output of this engine is rated
425 h. p. at 2000 r.p.m. A view of the Model A-4engine was published in Technical Bulletin No. 42.
Tests on Packard Engines.
A standard SO-hour endurance test will be conducted at the Di vision on a Packard Model
lA-1500 geared engine incorporating the following modifications : new type crankcase. new pro­peller
shaft and thrust bearing, steel-backed main bearings with modified oil grooves, steel-backed
connecting rod bearings without babbitt on ends, new light weight full skirt pistons with light weight
pins, new salt-cooled exhaust valves, Stromberg NA Y-6 carbnretor and special ignition.
A similar test will be conducted on the larger Packard geared engine, Model l A-2500. which
develops 800 h. p. This engine will be modified as follows: new type thrust bearing, steel-backed
main bearings, light weight full skirt pistons with light weight pins, ·new salt-cooled exhaust val­ves,
and redesigned valve housing.
Both engines are fitted with Allison 2: 1 reduction gearing.
AIRCRAFT DEVELOPMENT 31
Shrunk-On Propeller Hub Flange.
\Vith a view to reducing engine weight and simplifying manufacture, a stu<ly has been made at
the Division on the integral flange propeller shaft with shrunk-on hub to replace the detachable pro­peller
hub in present use. In this investigation several experimental hub flanges and shafts were
made and subjected to torsional tests to determine the strength of various shrink fit allowances.
As a result of these studies propeller hubs with integral flanges have been ordered for the Packard
lA-lSOO engines.
This research has led into a study of thrust bearings which can he assembled on integral flange
crankshafts. A thrust bearing of the Michel type has therefore been designed for the Curtiss
D-12 engine for test purposes.
Jump-Gap Distributor Heads.
Results of service tests, both at the Division and at various flying fields in the service, indi­cate
that the jump-gap type of distributor head will eventually be adopted as standard equipment on
Liberty engines. This type of head gives longer service and less operating trouble than the rubbing
contact type head used in present standard distributors.
Combination Generator and Magneto Mounting Flange.
A combination generator mounting flange has been adopted as standard equipment on all future
Curtiss V-1400 and Packard lA-lSOO and 1A-2SOO engines. This mounting permits interchange­abi
lity of generator and magneto ignition units. The engines equipped with the new standard gener­ator
mounting flange will also be provided with a special coupling designed by the Division for use
until the feasibility of the rigid drive has beeri thoroughly investigated.
Investigation of Bearing Loads.
An investigation is in progress on higher bearing loads and effects of oil temperature on bear­ing
capacity. At the end of SO hours endurance testing at 1700 r. p. m. , an experimental bearing·
with babbitt, 1-7/ 8 inches in width, in the connecting rod of the single cylinder Liberty engine was
found in excellent condition. At the encl of a second SO hours run at 2100 r. p. m., the bearing wa~
found slightly cracked but with very little sign of wear. Another experimental babbitt bearing of
greater width, 2-1/8 inches, is now on test.
RESEARCH AND EXPERIMENT
I
RESUME OF ENGINEERING DIYISION
SERIAL REPORTS.
S erial l?cports marA'Cd with au astcris!? (*) will
{;c issncd by the Chief of Air Service as
"Air Service l11forniation Circulars."
AlRPJ,ANE SECTION
Longitudinal Stability of Airplanes. ':'Serial No. 2531
In t his treatise is presented a practical definition of longitudinal or apparent stability of an air­plane
in flight and its relation to static or basic stability (stability at constant speed and at various
angles of attack ) which can be either calculated or measured in the wind tunnel.
After several years' study of numberless experiments and flight tests made at the Engineering
Division, it is now considered possible to predict with suffi cient accuracy the longitudinal stability
of an airplane by a simple graphi cal method, the only accurate data required being the wind tunnel
test results of the airfoil used and the design characteri stics of the airplane. The results obtained
by this method. even though not mathematically correct. fulfill a purely practical purpose in designing
a good fl ying airplane and in correcting defects of poor design in existing types.
Thirty-nine charts are appended to the report.
Correlation of Flight Test and Wind Tunnel Data. Serial No. 2570
This study proposes to show the magnitude and nature of the difference between data obtained
in flight performance tests and those which are computed from model characteristics as determined
in the McCook Field fi ve-foot wind tunnel. and, if possible, to determine what correction should be
appli ed to make the computed performance agree with the actual. Agreement in this case means
that the computed performance shall be neither consistently optimistic nor consistently pessimistic in
order that in selecting new designs it \vill be possible to know which will meet the specified perform­ance.
In other words it is desirable to have a method of pre-determining performance that will giw
results as close to flight test results as possible. ·
T he method of per formance prediction outlined in the 1925 Edition of the "Handbook of In­structions
for Airplane Designers" and more fully described in Chapter V of "Airplane Design"
( Serials 2496 and 2497), a new handbook now in pnblication . was developed to check flight test re­sults
from model characteristics obtained in the four-foot '"'ind tunnel of the Massachusetts Insti­tute
of Technology. Jn this method no corrections are made for model characteristi cs. the diffe r­ence
between flight test and wind tunnel results being absorbed in the propeller characteri stics. Con­sequentl
y. when model character istics obtained in the McCook Field five-foot wind tunnel were
used in the above method. it was found that the computed performances were consistently pessi­misti
c.
An opportunity to determine what difference existed between performance as computed in the
l\fcCook Field wind tunnel and that obtained in flight test was taken adYantage of in the recent ob­servation
airplane competitions held at McCook Field. In these contests complete wind tunnel and
Right test data were obtained on the Curtiss X0-1 . the Douglas X0-2 and the E ngineering Division
XC0-5 and XC0-6 airplanes. Data of similar nature were also obtained on the Boeing and Curtiss
pursuits.
RESEARCH AN D EXPER IM ENT 33
As a result of this study. it was found that a correction for model characteristics was necessary
in computing performances from McCook Field wind tunnel data by the method given in the De­signers'
Handbook, but that the rule given therein would still apply to model results from all wind
tunnels other than that at McCook F ield until suffic ient data on other wind tunnels are available to
demonstrate that a correction is justifiable.
This in vestigation also establ ished a curve of efficiency fo r metal propellers which will be used
until a curve giving better results has been evaluated.
Comparative Tests on Experimental Metal Ribs and Spars. *Serial No. 2575
Early in 1923 contracts were awarded to several aircraft designers and manufacturers for the
design and construction of fi ve experimental types of metal wing spars and seven types of metal
wing ribs. Both spars and ribs were designed for a specified load system so arranged as to develop
stresses of the magnitude of those extant in an airplane weighing 16,000 pounds. U nder this speci ­fication
the resulting structures would, when tested, furni sh data leading to the development of a
sati sfactory type of all-metal wing for use on large airplanes.
Each type of spar and rib was tested at the Division under identical conditions which afforded
a positive means of comparing its merits. The spars were rated on a basis of strength-to-weight
and strength-to-weight-and-deflection ratios in comparison with a model 15-inch spruce box spar
designed and built by the E ngineering Di vision fo1 use as a criterion for the metal types. The ribs
were compared on the basis of strength-to-weight ratio with some consideration for ease of produc-tion
and maintenance. ·
The data collected during the tests are presented to show the comparative desirability of the
,·arious types for use in airplane wings, the int ricate problen:is of design, and a tentative metbud of
structural analysis. The report is divided into two parts, profusely illustrated, the first deaiing with
wing spars and the second with wing ribs. Each part is complete in itself and gives the methods
used in testing and rating, and the conclusions reached, with comments on the behavior of the parts
during the tests.
Test of Valves for RS-1 Airship. Serial No. 2583
Due to the fact that the helium valves for the new RS-1 semi-rigid airship recent! y completed
for the Army Air Service were too large for test with ordinary facilities, it was necessary to erect
a special test rig in order to determine the discharge rate of these valves under various conditions
uf valve setting, internal pressure, air velocit ies, etc. The test was made by suspending a 5000-cubic
foot supply balloon in such a ma nner that it could be raised . lowered, ti lted, skewed or rolled in
;rny desired position, the valves being placed in the side of the bag about midway frum the ends.
The valves under test were the Gammeter 20" and Goodyear 18" and 28" valves.
No defin ite conclusions are drawn from these tests, but the data obtained are presented in suf­ficient
detail to enable those interested to make their own deductions. The tests give a good idea of
the mechanical action of the valves and permit a fair comparison of their relative merits, provided
due allowance is made for the difference between test conditions and those in flight.
These tests were made in conjunction with the Lighter-than-Air Section.
Static Tests Conducted at the Engineering Division.
The fo llowing reports contain accounts of static tests conducted by the E ngineering Division at
McCook Field on various airplanes and airplane parts to determine their structural strength. Each
report gives a summary of results, a description of the structure and a discussion of the test and is
illustrated with drawings and photographs.
Serial No. 2536-Loening Amphibian Airplane, Model XCOA-1.
Serial No. 2540-Fuselage of H uff-Daland XLB-1 (Light Bomber ) .
Serial No. 2578-Consoliclatecl P T-1 (Primary Training) Airplane.
*Serial No. 2581 - Douglas Observation, Model 0-2, including static proof test of horizontal tail
surfaces.
Serial N'o. 2592'--Static Proof Test of Ailerons and Horizontal Tail Surfaces on \ i\T right X0-3
Observation Airplane.
Serial No. 2596- Static Proof Test of Hori zontal Tail Surfaces of Huff-Daland "Dog" Ship (Ad­vanced
Training), Model A T-2.
34 T E C H N I C A L B U L L E T I N N o. 4 4
Wind Tunnel Tests.
The following reports contain aerodynamical data on various airplane models and surfaces as
determined in the wind tunnel.
Serial No. 2564--Moclel of Proposed Air-Cooled Pursuit Airplane. Type X-PA (Test made at
lVIassachusetts Institute of Technology).
*Serial No. 2565-Model of Loening Observation Airplane.
Seri;i l No_ 2566---Model of Curtiss Observation Airplane, X0-1.
*Serial No. 2568----Model of Douglas Transport Airplane, C-1.
*Serial No. 2571-Model of Douglas Observation Airplan e, X0-2.
Serial No. 2589-Model of Proposed 1925 Pulitzer "A" Racer with Inverted Packard l A-1 500
Engine.
Serial No. 2590-Model of Proposed 1925 Pulitzer Racer with standard Packard l A-2500 Engine.
Serial No. 2591-Model of Proposed Air-cooled Pursuit, Type X-PA (Test made at McCook
Field).
ARMAMENT SECTION
Test of Fokker Synchronizer. Serial No. 2492
A Fokker synchronizer was installed on a Liberty engine in a DH-4B airplane and connected
with a Vickers machine gun for test in the conventional manner. The gun was bore-sighted so that
dispersion of shots would pass between the blades of a test club propeller to which a steel disk had
been attached to show position of the shots. Twenty-five rounds were fired at 500, 1000 and 1650
revolutions per minute, respectively. The results averaged a dispersion of 16 to 18 degrees, 44 to
60 degrees, and 67 to 81 degrees, at these respective speeds. A number of wild shots ranging up
to 140 degrees in dispersion were encountered. The results were regarded as unsatisfactory in com­parison
with those obtained with the Nelson synchronizer which gives under similar conditions an
average dispersion of about 50 degrees with no wild shots.
The development of the Fokker synchronizer was not recommended.
Instructions for Mounting Type III Airways Flares. Serial No. 2493
This report contains instructions and drawings for mounting Type III airways parachute
flares on the DH-4B and NBS-1 airplanes. This flare is carried in a vertical position inside the
fuselage and is used for night landing purposes in reconnaissance and observation. The illumination
of the flare has an intensity of approximately 200,000 candlepower. It burns for about four
minutes and descends at the rate of about 400 fret per minute. This combination allows the flare
to be used with reasonable safety to illuminate the ground from an altitude as low as 1200 feet.
Racks for Mounting Type III Airways Flares. Serial No. 2533
Type ITI airways flares , provided by the Ordnance Department, are designed for vertical in­stallations
within the fuselage of the airplane. For this reason the racks used to mount them vary
with the design of the airplane, and should therefore be provided by the manufacturer. In order
to establish a uniform design for future aircraft and provide a means of mounting these flares on
present aircraft, experimental racks were built and installed on the DH-4B and NBS-1 airplanes
for test. The results of these tests and the recommendations drawn therefrom are given in this re­port.
This report also gives an account of night flights conducted by different pilots of McCook F ield
to determine the efficiency of the flares for night landings. Jn this respect it differs from the informa­tion
given in the foregoing Serial No. 2493 which merely describes the equipment and its installation.
Test of Carmier Gun Sight. Serial No. 2586
The Carmier gun sight is of French design and functions much the same as the Air Service
standard wind vane sight. It is fitted with automatic compensation for speed of the gun platform.
which is based upon the principle that a current of air striking a surface imposes upon that sur­face
a pressure proportionate to the square of the airspeed. The surface in this sight is a cone which
y~rks the position of the bead in proportion to the air pressure upon it.
RESEARCH AND EXPERIMENT 35
In the tests, both in flight and in the wind tunnel, the sight was found to be theoretically accu­rate
within certain limitations. Its range of directional compensation, however, proved to be seriottsly
below that of present standard wind vane sights. There was also considerable blind area due to the
size and position of the wind cone. The extent of these limitation s, however, can only be deter­mined
by extensive service tests.
EQUIPMENT SECTION
Ignition Interference in Airplane Radio Reception. Serial No. 2451
Ignition interference with radio reception on aircraft is similar to that found on small motor
boats, submarine chasers, and submarines. It is clue to the noise of the ignition which prevents in­telligible
reception. The report gives an account of the experiments conducted at McCook Field
for the purpose of finding a means of satisfactorily eliminating such interference in aircraft re­ceiving
sets.
Altimeter Calibration Standard. Serial No. 2468
For convenience and accuracy in converting pressure to altitude, the following chart has beer.
prepared. Ordinarily, if the data contained therein were expressed with the same accuracy in the
form of tables, it would require several pages to accommodate them, with no convenient means of in­terpolating
the figures.
The chart is based upon the formulas which were adopted at the special conference on alti­meter
calibration standards held on December 6, 1924, by the sub-committee on aerodynamics of
the National Advisory Committee for Aeronautics. The lower scale gives the pressures in milli­meters
of mercury whereas the upper one gives the corresponding altitudes in thousands of feet
from 1,000 feet below to 50,000 feet above sea level. It will be noted that the pressure scale is uni­form
throughout whereas the altitude scale becomes cramped at the higher altitudes. There is no
objection to this, since the percentage of accuracy with which altitudes can be read is practically
constant. Upon observing the chart it is apparent that to find the altitude corresponding to a
certain pressure is just as easy as to find the pressure corresponding to a certain altitude.
The altimeter calibration standard upon which the chart is based approximates the yearly aver­age
for the United States. Therefore the temperature corrections which must be applied for devia­tion
from the assumed mean temperatures are less than those in the heretofore used standard in
which a constant mean temperature of plus 10 degrees Centigrade at all altitudes is assumed.
The data for this chart were computed at the Engineering Division.
PRE55U RE - ALTITU OE CHA.RT so.i' "'·!'°~ I ,."Yi! t "j·~ I .. r>O.) I I "~-~ I '1
e1• j !~ I 90 ~ 94 ,.. ~ .,_
1
);!.
1
500 J.1:,000 .J•,SOO )0,!.00 !>O,OC:O -''.C.00 l"-'""° '"-"i""'°
=r'- +-t~-1_ .,....·~1".''"'"•-'r~~....,...,_,~~__.,....,,,..,,,.,..,,_,.,..!,,_'"'•""',T!."'', ..,,. .,.......,..._.~......,_,_~~1~~t~~~ro I 1.. 1)0 I ~~ ~i'"°° I l"i"~ i i.I~ '1 '-j~ I "":'i~I
( ~ (I .. ~.4 .i.- it... l.40 (~
:r >= '·j ·~
'
I
(O~ ' I
<;,171. ~!...
36 T E C H N I CA. L B U L L E T I N N o. 4 4
Barometric Altimetry and Altimeter Calibration Standards. Serial No. 2440
T he barometric method of measuring height of aircraft above the earth is used by the Army
Air Service almost exclusively. T he aneroid barometer is used to measure the decreased pressure
of the upper atmosphere. T his in strument when graduated in units of height is c~ll ed an "alti­meter."
T he aneroid a ltimeter is calibrated in isothermal altitudes or heights corresponding to cer­tain
pressures when the mean temperature of the air column beneath the aircraft is plus 10 degrees
Centigrade. Since distribution of temperature in this column of air is seldom such that the mean
is plus 10 degrees, the actual altitudes can be obtained only by applying temperature corrections to
the indicated altitudes. Furthermore, since the actual mean temperature clecrea es with altitude and
becomes less than plus 10 degrees Centigrade at low altitude, these temperature correct ions become
excessive. These corrections can be reduced considerably or disregarded only when approximate
altitudes are desired. provided certain temperatures decreasing with a ltitude to approximate the
yearly average are incorporated in the pressure-temperature-altitude formula.
T his report descr ibes the present standard method and charts the errors clue to its use. It then
gives a description of a newly proposed standard method with its attendant errors, as based upon
the assumption of a certain temperature decrease. T he repor t also describes several types of ane­roid
altimeters. together with views of the same, some of which represent attempts to co rrect alti­meter
indication for air temperature.
Several valuable conver sion charts are appended.
Preliminary Report of Crash Tests. Serial No. 2522
This report contains an account of the p rel iminary crash tests conducted by the Engineering
Division from August. 1924, to May, 1925, for the purpose of determining the causes of fire in air­plane
accident5. The results cover twenty-six crashes of seven different types of ai rplanes. In four
out of the six cases in which fi res occurred, the cause of the fire was attributed to gasoline entering
the exhaust manifolds. Steps are being taken to eliminate thi s.
The tests vvere conducted on obsolete aircraft, minus wings, by running them clown a 500-foot
incline against a concrete buttment. F ires from ignition sources were precluded by removing the
EARLY CRASH TEST SHOWING FIRE RESULTING FROM FUEL ENTERING HOT MANIFOLD.
RESEARCH AND EXPERIME N T 37
generator from the engine and placing the battery on the landing gear axle where it was knocked
off by a stop before the airplane crashed against the buttment.. Motion pictures of the crashes
were taken from behind heavy screens, in order that the causes of the fire could be traced.
Location of Vent Opening in Fuel Tank. Serial No. 2530
Up to the present time location of the vent in aircraf t fuel tanks was considered inconsequential
except when the operation of the fuel system was effected. In most installations the vent opens in
the direction of flight, the opening being situated immediately above the upper leading edge of the
renter section ( in biplanes) . Al tho this position has been used for some time, it has one unde­sirable
feature in that it allows moisture and rain to be drawn into the vent opening and mix with
the gasoline.
\Nith the advent of the hydrostatic type fuel gage, adopted by the Army Air Service, the
method of venting becomes a serious factor sinre any variation in pressure above the liquid in
the tank effects the indication of the gage. This is due to the fact that the vent tube leading to
the top of the tank transmits the varying pressures in the area surrounding the vent opening to
the air space above the gasoline. If the pressure is below atmospheric the gage which measures the
head of liquid in the tank will read low and vice versa.
Such conditions are encountered in service where the vent opens above the wing in the region
of varying pressures. The tests indicated that it is undesirable to locate the vent opening at any
point along the leading edge. and in view of this fact the trailing edge of the w1ng shows the best
possibilities.
Installation of LeNivex Hydrostatic Fuel Level Gage. Serial No. 2535
The information given in this report is relative to the in stallation of the LeNivex hydrostatic
fuel level gage in con junction with various types of fu el systems used on aircraft. T his gage
which is known as Air Service Type D-3 consists of three units. a pressure indicator. a hand air
pump. and a check valve- all connected by primer tubing. 1/8-inch in outside diameter. The gage is
not continuous indicating but registers the fuel content of the tank only when the pump is operated.
Detailed in structions are given for in stalling the LeNivex gage on aircraft using typical fu ei
systems adopted by the Army Air Service with the exception of the old pressure system in which
case the gage is not recommended.
Several views of the in strument and an in stallation diagram are appended.
Service Radio Equipment. Serial No. 2543
A description of aircraft radio equipment in present use by the f\ rmy Air Service is given in
this report. Each set is described in detail, and the general characteristics of the various types are
set forth in tabular form. Views of the sets and the method of shielding the ignition are shown._ , ,
;1,
Navigation Methods. Serial No. 2559
During the past two year s, the Engineering Divis'.on has conducted a series of long distance non­stop
flights from 600 to 700 miles in length for the primary purpose of testing newly developed
aircraft instruments. Incident to these flights there evolved certain methods of preparing for a11d
conducting them, which methods are set forth in this report. Particular emphasis is placed upon the
proper laying out of the course, the obtaining of meteorological information prior to take-off, crnd
the measuring of drift during flight. .,
All navigation flights we re made over territory having few known landmarks, or above clouds
where possibl e, by pilots who had never before flown over that particular region, in order to demon­state
the practicability of using in struments and methods of navigation in lieu of landmark flying
O\·er long distances.
The in struments commonly used in these flights included the distant-reading induction com­pass,
the flight indicator, the aerial sextant and the drift sight. Two standard f\. S. T ype B-3
magnetic needle compasses were carried on each flight as a precaution in event of mechanical
failure of the induction compass which was still in the experimental stage. Thus the flights al so
served to demonstate the efficacy of in struments over different types of terrain.
38 T E C H N I C A L B U L L E T I N N o. 4 4
The report gives in detail the preparation necessary for making a navigation flight, including
the reason for selecting the great circle or orthodromic course in preference to the Mercator course,
the method of making a satisfactory strip map of the route, and the actual laying out and mark­ing
of the course. T he interpretation of meteorological data prior to flight and the observance of
drift during flight are also di scussed. Sample calculations for flight s, east and west or north and
sonth, are given.
That a careful interpretation of meteorological conditions preceding the flight is essential to
the success of long distance cross country flights has been demonstrated in several instances. On
March 12, 1924, a non-stop flight from Mitchel Field, Long Island, to McCook Field, Ohio, was
made at 7,000 feet altitude above twD dense cloud layers for a distance of 400 miles without sight
of the ground so that measurement of drift was impossible. The flight started in a SO-mile cross
wind, making a 30-degree crab necessary. From a study of weather maps of the preceding
days, the navigator was able to determine the direction and rate of travel of high and low pressure
areas and construct for himself a weather map for that clay which he afterwards found to check
with the official weather map of that date. Upon this information and previous experience in
the use of instruments, he was able to gradually reduce the amount of crab and to estimate ground­speed
on assumed wind changes until upon descending thru the clouds after 3 hours and 40 minutes
it was found that the airplane was only 15 miles north of the course. Since about 400 miles had
been traversed without any check on landmarks, the error amounted to only 2 degrees.
In other instances, a study of weather conditions in advance of the flight has revealed the
presence of favorable winds at different altitudes, making it possible to fly long di stances in a re­markably
short time.
Tests on Purox Liquid Oxygen Storage and Shipping Container. Serial No. 2572
PVROX LIQUID OXYGEN CONTAINER.
These tests were conducted for two purposes:
first , to determine by evaporation the suitability
of containers manufactured by the Purox Com~
pany, Denver, Colorado, for storage and shipment
of liquid oxygen; and second, to determine what
material is best for use in the "absorbent blister"
or "charcoal pocket" of the container to resi st in­cendiary
rifle fire.
The P urox container is a double walled ves­sel
with the space between walls evacuated. In
this space is an "absorbent blister" or "pocket"
soldered to the bottom of the inner wall. in which
charcoal, silica gel or otI1er air-absorbing material
is placed. This material absorbs the residual air
between the walls which cannot be evacuated by
the ordinary vacuum or the mercury vapor pumps.
This air finds access to the pocket thru four
breathers or screened holes. The vessel is encased
in a protective metal housing to guard against
damage in handling.
In the evaporation tests the Purox container
proved very satisfactory for storing and shipping
liquid oxygen, the rate of evaporation being less
than that of the German container now at the
Division and as low or lower than that specified
for foreign makes. Charcoal in the absorbent
blister showed a lower rate of evaporation than
silica gel, but the latter was considered superior for
use where containers were exposed to rifle fire.
The Purox Company is the only firm in this
country making containers of this type.
RESEARCH AND EXPERIMENT 39
Practical Field Service Use of Oxygen. *Serial No. 24 78
Due to the rarity of the air at high altitudes it is necessary to supply aviators with oxygen above
a certain altitude. This altitude varies somewhat with the individual : some need oxygen at 15 . 000
feet, but all must have it above 20,000 feet. The oxygen is stored and carried in the airplane in
small steel cylinders at a pressure of about 2000 pounds per square inch, and the flow of gas to the
aviator is controlled by means of a regulator.
The report contains a detailed description of the Prouty oxygen apparatus adopted by the Air
Service and the instructions for handling it.
Performance of Airspeed Tubes in Rain and Freezing Rain. *Serial No. 2585
In the past slight attention was paid to the effect of rain drops or ice formation on airspeed
indicator tubes or heads for the reason that very little flying was clone during inclement weather.
With the daily oper:ition of ·the Air Mail in all kinds of weather, however, the failure of the air­speed
indicator from either of these causes at a time when it is most needed made imperative an
investigation into the action of airspeed tubes when exposed to rain drops or freezing rain.
To overcome these difficulties, the Engineering Division conducted laboratory tests on various
types of airspeed tubes in a 6-inch suction type wind tunnel especially constructed and operated to
simulate conditions encountered in actual flight. The effect of freezing rain was reproduced by
operating the tunnel in a refrigeration chamber.
The airspeed tubes used in the tests included the three. principal types in standard use, both in
this country and abroacl,- the Pitot-static, the Pitot-Venturi and the Venturi-static-and some ex­perimental
types purposely designed for this investigation.
c D
0
L
AIRSPEED TUBES USED IN FREEZING RAIN TESTS.
A-British Concentric Pitot-Stat-ic
B-U. S A. S. Standard Pitot-Statk
C-Briti~h Pitot-Static with Slots
D-British Mark IV Pitot-Static
£-Pioneer Concentric Pitot-Static
F-U. S. A. S. Standard Venturl-Pitot
G-French Concentric Static-Venturi
H-French Double Throat Venturi
I-Glass Pitot
J-Brass Pitot
K-Blunt Pitot, Inside Bevel
L-Blunt Pitot, Outside Bevel
M-Electrically Heated .Pi tot
N-Streamlined Deflector Pitot
0-Double Tube Pitot
P-Triple Tube Pltot-Static
40 T E C H N I C A L B U L L E T I N N o. 4 4
In drawing conclusions regarding airspeed tubes, the various types were considered individually
as P itot, static or Venturi, in stead of in combination. It was found that dynamic pressure in the
P itot tube is practically unaffected by formation of ice on the tip, so long as a hole or air passage
remains through the ice and the ice formation is symmetrical to the axis of the tube. The length of
time required for the tube to freeze over depends upon its diameter. Accum,ulation of rain drops
can be obviated either by the use of drain holes or by giving the tube an upward bend not more
ICE FORMATION ON AIRSPEED TUBES.
Early and Advanced Stages of Ice Formation on U. S . A. S. Standard Pitot-Static and Venturi Tubes .
than fi ve diameters from the tip. In the case of the static tube, with openings at the proper dis­tance
from the tip, it was shown that the efficiency of the tube was unimpaired by formation of ice,
but tliat rain drops caused a film to form over the openings, which seriously interfered with the
operation of the tube. With the Venturi tube, whose use is fast becoming obsolete because of its
abnormal sensitivity under service conditions, it was found that a slight amount of ice reduced its
efficiency to such an extent as to r ender the tube useless, whereas rain drops did not seriously affect
its operation.
Several schemes we re advanced to reduce if not entirely eliminate the effect of rain and ice on
the P itot tube which is now becoming recognized a s superior to the Venturi tube as a means of
measnring air speed. P rotection against rain can be effected by bending the P itot tube upward
and providing properly protected drain ho es. Interf erence from ice may be obviated either by elec­trically
heating the tube or by increa sing its diameter sufficiently to prevent it freezing over and
becoming inoperative before the airplane on which it is mounted would be forced down by the
weight of ice on its wings and structure. The static tube may be protected against rain by using
circumferen tial slots in stead of small holes, and again st ice, by placing the static openings at
least fi ve diameters from the tip. Thus it is evident that a combination of P itot and static tubes,
arranged concentrically about each other , affords a minimum frontal resi stance or air drag an cl
the most reliable means fo r measuring airspeed under adverse weather conditions.
A more detailed discussion will be found in the report.
I
PITOT-STATIC HEAD PROPOSED TO OBVIATE
INTERFERENCE FROM RAIN OR ICE.
'="....-,;..,,,;.; 1-o-_o_o--'o---0'------4:~-~~~!:~J_,_ C]C]·g~~~@~1: ~·: ~~~:;:;::a~~=]
\ TUBE. TO CCOMMOO TE ANGLE
OF STRUT IF NEC.E.$SARY.
TINO F"ITTll"IGS roR LU.D~ To 1!'101Cl'\TOROM INSTllUMl'1T 60ARQ.
French Leakproof Tank (S. E. M. A. P. E.) Serial No. 2579
Two leakproof fuel tanks ma111~1factured by the Societe E lectro Mechanique D' Appareillage
P our ]'Essence of France were subjected to firing tests at the Division.
RESEARCH A N D EXPER I MENT 41
These tanks are cubical in shape and hold 61 U . S. gallons each as determined by weighing
their content of water. Each tank is made with an inner tank of sheet copper, encased by a patented
covering deYised hy the manufacturer , and weighs about the same per gallon capacity as the
standard Air Service leakproof fu el tank. In some respects the F rench tank proved superior to
the A. S. design. but it is not adapted to American production methods.
MATERIAL SECTION
Dopes and Their Application. *Serial No. 2550
Any fabr ic COYered surface without the addition of a protective film is very susceptible to
changes in humidity, becoming slack or taut with every increase or decrea se of moisture in the
atmosphere. Therefore, fabr ic that is used for covering on aircraft will not only rapidly lose its
strength but will also fail to protect the in terior structure of the wing. Hence, hy applying dope, the
fa bric is made waterproof and caused to cling to the contour of the wing, adding rigidity to the airfoil.
Dope is essent ially a colloidal solution of cel!ulose acetate or cellulose nitrate. mixed with
properly proportioned softeners to produce when dry a smooth, homogeneous, Aexible film. It
serves two important purposes: fi rst, to render fa bric impervious to moisture and second, to make
fab ric taut ancl stronger.
Clear dope, however, is tran sparent to sunlight. Since sunlight constitutes the greatest factor
in the deteriorntion or weathering of elopes ancl fabrics, it is necessary to apply an opaque coating on
top of the clear elope to preserve the fini sh. This coating is a elope similar to clear elope with an
EQUIPMENT USED FOR APPL YING DOPE
Note me thod of using DeVilbiss spray gun, steam coils for heating airfoil and "Fumexer" in wall for exhausting
dangerous fumes.
42 T E C H N I C A L B U L L E T I N N o. 4 4
inert opaque pigment added to exclude the actinic rays of sunlight. Application of pigmented
dope oyer clear dope is of utmost importance inasmuch as the latter will withstand only a few
months of constant exposure to the weather, whereas the same finish protected by the opaque
coating will last for several years.
The report gives in general the practice and methods recommended for the care, storage
and application of elope, together with views of the spraying equipment and instructions for its use.
FL YING SECTION
Performance Tests.
The following reports contain detailed accounts of performance tests conducted by the Army
Air Service Engineering Division at McCook Field.
*Serial No. 2525-Loening Amphibian, Model XCOA-1, with Inverted Liberty Engine.
*Serial No. 2544-Douglas Transport, Model C-l , with Liberty Engine and Hartzell Propeller.
Serial No. 2554-Boeing Observation, Model XC0-7B, with Inverted Liberty Engine.
Serial No. 2557-Thomas-Morse All-Metal Observation, Model TM-24, with Curtiss D-12 Low
Compression Engine. .
Serial No. 2560-Engineering Division Observation, Model XC0-6, with Standard Liberty Engine.
Serial No. 2561- Curtiss Pursuit, Model PW-SB, with Curtiss D-12 Low Compression Engine.
Serial No. 2562-L. 'vV. F. Transport, Model T-3, with Allison 2 :1 Geared Liberty, and also
summary of performance with Epicyclic Geared Liberty.
Serial No. 2563-L. \A/. F. Transport. Model T-3, with Standard Liberty Engine and Eng. Div.
Propeller No. X-47743.
Serial No. 2569-Huff-Dalancl Advanced Training, l\Iodel AT-1 , with \\!right "E" Engine.
Serial No. 2573-Cox-Klemin Ambulance, Model XA-1, with Liberty Engine and Curtiss Pro­peller
No. 047315.
Serial No. 2574-Douglas Transport, :Model C-1 , with Liberty Engine and Standard Steel Pro­peller
Company's Propeller No. X-47409.
Serial. Io. 2582-Phillips Alouette Light Airplane equipped with Lawrance L-4 Engine and Hart­zell
Propeller No. X-23311.
POWER PLANT SECTION
Test of Honeywell Automatic Shutter Control. Serial No. 2499
The practicability of applying the automatic shutter control manufactured by the Honeywell
Heating Specialties Company, vVabash, Indiana, to aircraft radiators proved satisfactory clue to the
fact that the lag of this apparatus under actual operating conditions proved so great that it inter­fered
with the performance of the airplane. This was especially noticeable with an alcohol-water
mixture, the boiling point of which is close to the desired operating temperature. It was further
concluded that any type of automatic shutter control is undesirable on aircraft radiators because
such apparatus can not anticipate the coming temperatures and operate the shutters in time to
obtain maximum effectiveness from the cooling system.
The Honeywell automatic shut~er control consists of a thermostat, designated as the "Aquastat."
inserted in the water line and electrically connected to a geared type 12-volt direct current motor
which operates the shutters.
Views of the installation of this apparatus in the airplane are given.
Piston Side Thrust in Model R-1 Radial Engine. Serial No. 2504
As a result of a series of tests conducted at the Engineering Division, the overall diameter of
the large 400-h. p. Model R-1 air-cooled radial engine was reduced five inches (from 55-5/ 8 inches
to 50-5/ 8 inches), making a ten per cent reduction in frontal area. This was accomplished by
using short connecting rods and cutting away portions of the piston skirts on the anti-thrust side.
On test, however, piston failure occurred as a result of excessive side pressure. In view of the
fact that these pistons had previously passed an endurance test on the singie cylinder testing engine
using long connecting rods, it was decided to investigate the failure by conducting another test on the
testing engine using the same type of piston with short rod in order to duplicate the side thrust
conditions encountered in the R-1 engine.
RESE A RCH AN D EXP ER JMENT 43
An analysis of the latter test disclosed that the side thrust in the modified R-1 radial engme
is double that of the Liberty " 12," E ngineering Division Model "W-1 ," or single cvlinder testing
engine, which accounts for the piston failure.
Several charts and views of the pistons are appended.
Bearing Loads and Stress Analysis of Model X-4520 Engine. Serial No. 2508
This report contain s a discussion and an anal ysis of the probable bearing loads and stresses
in the new experimental 24-cylinder "X" type air-cooled engine now being built for the Army Air
Sen·ice by the Allison E ngineering Company. The proposed engine will have a rated output of
1200 brake horsepower at 1800 revolutions per minute. A few detai ls of the design were pub­li
shed on page 21, T echnical Bulletin No . 43.
Since this report was prepared while the design was in progress, some of the values given
on estimated weights and bearings loads, together with sketches of the engine, will not be con­sistent
and will therefore require revision in accordance with the final design.
Development of Slipper Type Piston for Packard lA-1500 Engine. Serial No. 2517
The original Packard slipper type piston for the Model l A-1500 engine appeared to be a very
attractive design from the standpoint of light weight, comparing favorably with other types of
pistons used in aircraft engines. It was thought, however, that by intensive development a satis­factory
design of less weight could be obtained. v\'ith this object in view, the Engineering Division
proceeded to design, cast and construct three experimental types of pistons for test in the universal
testing engine.
The slipper type piston developed by the Division differs from the Packard type in t_hat it
has thinner head and wa!l sections and employs internal ribbing for rein fo rcement and cooling. The
pin bosses are also brought closer together, allowing a shorter and lighter piston pin. Assembled
with pin and rings, the E ngineering Division piston weigh