Technical bulletin no. 46. Development of military aircraft material for United States Army Air Service under supervision of Engineering Division

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B)''_f)lRE_CTfON OF Cf::IIEF )JF ~m:-SEIWICE
VOLUME Y~
AIR SERVICE INFORMATION CIRCULAR
VOLUME V
(AVIATION AND AEROSTATION)
BY DIRECTION OF CHIEF OF AIR SERVICE
FIRST QUARTER - 1926
TECHNICAL BUL.LETIN
No. 46
DEVELOPMENT OF MILITARY AIRCRAFT
FOR THE UNITED STATES ARMY AIR SERVICE
UNDER SUPERVISION OF THE ENGINEERING DIVISION.
Prepared and Published
By D irection of the Chief of Air Service
and under the supervision of
JOHN F. CURRY, Major, A. S.,
Chief of Engineering Division.
McCook Field 7-1 - 26-lM
NUMBER 488
CONFIDENTIAL
The information contained herein is confidential and therefor·e
must not be republished, either as a whole or in part, without
express permission of the Chief of Air Service, U. S. Army .
•
•
CONTENTS
AIRCRAFT DEVELOPMENT
AIRPLANES
Curtiss Pursuit Airplanes, P-1 and P-2 ______________________________________________ _ -- ---- ---- ----- --- 7
Thomas-Morse All Metal Purnuit ----------------··--- --------------------------·---- -·---------· ------- ---- --- ---·· 7
LB-1 Received for Test------------------- ------- -- ---- ··----·-- ---------------________ ______ ----- ---- -- -------- 8
New Light Bomber XLB-2 Planned ·-·---- -·· ----------- -··-- ··--- ----- ·-------- ---- ------ --------_________ ____________ ___ \l
Wing Panel for XHB-1 Passes Static Tests -----·· ·-· --------·-------- __ --·--- ---- --- -·-- ------·--- --·-------- -- -- -· - 9
Heavy Bombardment Airplan2 (Monoplane Type) ----- ------- ------ ·-----·--- -· ---·-- ---- -- ---· ------·----·-- -·-­First
Curtiss 0-1 Received ··-·--····- --- --·-··-- ---- ----···· -- -··-·· -- -- -·- ----··--- ---- ------------ -- --- -- ·-----------­Additional
0-2's Ordered ·-·---·--·--------------- -------·------·---··-··--------- --- --- ·----- ·--·--- -- ·-- ---·---------·-------- -·- 10
10
9
Conversion of 0-2 for Ground Attack._·------·----··---·----- ------- ------ ------ --- ------ ---------------- -- ----------·-·- 10
Original Night Observation Design Abandoned --··-----------·--- ·---- -- -------- ------- ------------ -- ---- ---- ____ 10
Douglas Car,go Airplanes ------------- --- ---- -------------- --- --- -·--- ---- ---- ----- -- ---- ----- -·------ ---------- --- ----·-------- - 11
Atlantic to Build Cargo Airplanes, Model C-2 -------- --------·------ --------- --- -- --- -- ----- ------ ·-- ______ 11
Huff-Daland Advanced Training Airplane, Model AT-1 -·-- -------· -- ----- ·-- --- ·---- ----·-- --- ·-------·----· 11
Driggs "Dart" Airplane ------- ------ ---- ------------ --- ---- ---- ---- --···---- ------------·------- --·--------------- 15
Metal Wings for Boeing Pursuit ------------------------- --- -- ---- -- -- ---- ---- ----- -- --- --------------- ---- ------ --·------- 15
Propeller Development ------····----------·- ·--- -·--·· ··--·· --··------ -- ------ ·--------- ---- --------------------·-·-------------- 15
AIRSHIPS AND BALLOONS
The RS-1 Airship -- ---- -- ------------------------------------------ --- --- ----- -- --- ---- --- ----- --- - ________ __ __ --- ----- -- -·----------- 16
ARMAMENT
Gun Sight C-1 --------------- ----- -------- -- ---- -- -------------- ------ ----- --- --- -- ---- -- -----·------------- ---- - ------- --· ----------- ---- 22
Gun Sight C-2 ---------- -- ----------------------------------------- --- ---------- ----------------- ----- -- --- -------- ---- -- -- 22
Machine Gun Synchronizer, Type C-11 ----- -- ------- -- ----------- ------- ----------- -----·------ --- 23
Wing Mounted Guns ------ -- -----------------·---- _________ -- -------------- ------- ------- ------- ---· __ 23
Aut omatic Bomb Release Handle, Type A-1 ______ __ _________ -------· ---------------- --------- ----- --· -------- 23
Bomb Service Dolly ----··-- --- ---- ··----··--- -··---- -- ---- -- -------- -- -----·- --- ·----· .... . _________ -- ------------- ------------- 24
EQUIPMENT
Universal Aircraft Camera Mount, Type C-1 ______ ___ --- --- --··-------- ---·------ --- ------------- ·-- ·-- ·--·----- 24
K-3A Automatic Camera (formerly K-8) ------ ------ ----··----------------·- 25
New Instrument Projects------ ---- --- --------- ----------- ------ ----- ----- ------- -- --- -·-- -- ---·------------· ------- 25
Flight Indicator Improved ---- ------ -------------------------- ---- ----- ---- -------- --- -------- -- --· -- -- -· ----------- 26
Experiments to Increase Life of Aircraft Storage Batteries_____ _ _____ -- -------- ---·- ----- -- 28
Air Starters for Aircraft Engines ------ ---------- ---- ----------------------------- -- --·· ·--·-- ---·---· - ___ _________ _______ 28
Radio Broadcasts ---- ··---- --·--- -------··-- ------ ---·- --- ------ ----- --- ·-- --- ---- --------- -· ·--- --- ---------- ·--··-·---------- --- --- --- - 28
Model Radio Beacon System _____ ____________ ----- -------------- ·----- ·---· ______ .: __ ----------· ·--·--·-----------· 28
Short vVave Tests ------- -····· ···---- -- -- ··-----·--·--·-- -- ---- -----·--------·----------- -·--·--·-- ---- -------- ----- ------ ---- 28
POWER PLANTS
Changes in Curtiss V-1400 Engine __ ____ _______ ---·----- -- -------- -- --------- ----
Inverted Air-Cooled Liberty Engines ---- -- -------------·---- -- -------·----- ---·- ----- ____ ___ _
29
30
The Cam Engine ------ ------ -------- ---------- -- -------- ---- ------ -- -------- -- ----·--- --· __ ________________ ---- --- ·--------- 31
Packard 2A Engines ---- --- -------------- -------,--------------- -- ---------------·-- ----- -·------- -- ---- -- ---- ------- - ··----- 31
Heinrich Radiators ________ ---··- ------- --- -------· -------- ----- ---- -----------------·------ -- __ ___ -- ---- ------·- -- ·----- 32
C 0 N T E N T S - (Cont'd)
RESEARCH AND EXPERIMENT.
RESUME' OF ENGINEERING DIVISION SERIAL REPORTS
Test of Kerber-Boulton Second Experimental Spar ---- --- ------------ -- --------- -- --- ----- --------- ------ ----- 34
Test of Thomas-Morse Extruded Duralumin Spar ------------ ------------ ------------------ -- ------ --- --------- 34
Thomas-Morse DH-4MB Metal Wings --------- ---- -- ----- ---- ---------- -- -- -------------- ----- ------- ---------- -------- -- 34
Test of Roche Adjustable Seat No. L __ ______ ______________ ____ _________ ______________ __________ _______ ________ : ___ ________ 35
Visual Study of Flow Discontinuity of Cylindrical Camber Airfoils --- ----------- ------ -------- -- 35
Test of Model of Huff-Daland XHB-1 Bombardment Airplane --- ------------- ---- ------ ------- ------- -- 35
Re-Calibration of McCook Field 5-Foot Wind Tunnel ---- ---- ----------------- -·-- -------- --------- ----- ----- 35
Test of Mark II Wing Tip Flares -------- --- ------ --- ---- ------ --- ------------------------------- ---------- -- --- -- --------- -- 37
Procedure for Installing Airplane Radio ---- ---------------------------------------------- -- -- -------------- -- ---------- -- 37
Aircraft Sextant Observations -------- -- --- --- -- -- ---- --- -- ---- -- ---- ------- --- --- --- ---- -- ---- ---- --- -- -------------- ---- ------ 37
A Method of Reducing Sextant Obser vations -- -- --------- -- --- ---- --- --- ---------- ----- ---- -- ---- ------------- --- --- -- 37
Performance Tests ------ --- -- ----------------- --- -------- ---- -- -------------- ---- --- -- ------ -- -- --- ---- --- --- --------- --- --- ---- ----- --- --38
Pyroxylin Finishes for Aircraft -- ------- -------------------------- ----- ---------- -------------------- ---- -- -- ---- ------ --- -- --- 38
Study of Training Type Engines of 150 H. P. -------------- --- --- --- ---- --- ---- --- --- -- --- --------------- ---------- 38
Calibration of Morehouse Eighty Cubic Inch Engine __ _____ __ _______ -- -------- ---- ---- -- ---------- ------ --- ---- 38
Test of First Ex perimental Cam Engine --------- ------ ------------- ---- ------- --- ------------- ------------------------- 39
Bearing Loads of Model X-4520 Engine for Rating of 1200 B. H. P. a t 1500 R. P. M. ____ 40
Square Cell Ribbon Type Radiator Core vs. Standard A. S. Honeycomb Type Core ___ ___ 40
Moments of Inert ia of Generator Armatures and Magneto Rotors ______ ____ ___ ___ __________ _________ 40
Bearing Loads and Weight Determination for 16-CyEnder "X" Type Engine Rated
at 1000 B. H. P . at 2000 R. P. M. ---------------------------- --- --- ---------- ------- ----- ------ ------------ ---- -- -- -- -- 40
INVESTIGATION OF MATERIALS
Duco vs. Pigmented Varnish Dope for Airfoils -- ---- ------ ----------- -- ------------- ---- ---- -------- ------ --- ----- -- 40
Protective Coatings for Steel ------------------- -------- -------- ------- -- ---------------------------·----------------------------- 41
M:etallon ----------- ------------ --- ---- -- --------------------- -- ------- --- ---- ------- -- ----- -------- ---- ---------- -- ---- ---- ----- ----- -- ---- ---- - 41
Impact Tests for Hickory Used in Tail Skids --- -- ---------- ---- ----- --- -----·- ------------- ------- --- --- ------ -· ---- -- 41
NEW BOOKS AND DOCUMENTS
Additions to Engineering Division Technical Files During First Quar t er , 1926 __________ 42
J
LIST OF ILLUSTRATIONS
'!'he U. S. Army Semi-Rigid Airship, RS-1 ·---------- ------- ---- ------ -- -- ------- -------- ------ ------ ------- ------- - 6
Thomas-Morse All-Metal Pursuit Airplane, TM-23 ------ -- --- --- -- -------- ------ ---- ------ -------- ------ --- -- - 8
Huff-Daland Advanced Training Airplane, Model AT-1 -- ------ ---- --- -- ---- --- ---------- ------- ---- ----- 12
Comparative Performance Curves of Huff-Daland AT-1 and 9urtiss JN-6HG-1E
Airplanes --- --- -- ---- ----- ------- ------ ------- ----- -------- ---- -------- -------- ------ --- --- -- -------- ------ -- --- --- ------ -------- -- -- -- 14
Close-Up Views of RS-1 Airship --- ------- ------ ------ ---- -------- -- ------ --------------- --------- --- ----- ------ --------- ----- 17
General Arrangement of RS-1 Airship ----- ----- -- -- ----- ----- ---- --- ---- --- ---- --------------- ----------- ---- ----- --- -- 20
Characteristics of RS-1 Airship (table) --- -------- --- --- ------- ------ -------- -- ------- ----- -- ---------- ----------- --- 21
Gun Sight, Type C-2, with Sighting Accessories ----- ------ ------ ------- -------- -- ---------- ------- -------------- - 22
Generato1~ Cam Adjustment on Machine Gun Synchronizer, Type C-lL____ __ ___ ____ ___ ____ ____ 23
"Cniversal Camera Mount, Type C-1 --- ------- ------ -------- ----- -- -- -------- --- ------ ---- ----- -- ------------------ ----- -- 24
Improved Flight Indicator, A. S. Type A-4, Showing Modifications____ ___ __ ______ _____ __ ________ ____ 27
Inverted Air-Cooled Epicyclic Geared Liberty Engine ---- --- --- ----- -------- --- -------- ----- --- ----- ---- -- - 30
Crankcase at Main Bearing in Packard 2A-1500 Engine ------------- ------- -- ------ ---,--- ------ ------ --- 32
Heinrich Radiator ln:stallation on Boeing PW-9 Airplane_ _______ __ ________ ____ _______ _____ _________ ____ ___ 33
Ail'plane Adjustable Seat ---- ----- --- -- -- ---- -- -- -- --- ---- -- -- --- -- -- -- --- ------ --- --- ---- --- --- - --- ---- ---- -- ---- ----- ------ --- 35
New Duplex Straightener at McCook Field 5-Foot Wind Tunnel______ __ _______ _______ ___ __ __ __ ___ __ 36
Morehouse Eighty Cubic Inch Engine --- --- ---- ----- ----- -- --------- ---- ----- ---- ------ -- ------------------------- --- ---- 39
'
6 T E C H N I C A L B U L L E T I N N o. 4 6
THE U. S. ARMY SEMI-RIGID AIRSHIP, RS-1.
AIRCRAFT DEVELOPMENT
ON ENGINEERING DIVISION PROGRAM
AIRPLANES
Curtiss Pursuit Airplanes, P-1 and P-2.
Deliveries on Air Service Order 25422 for ten P-1 and five P-2 pursuit type airplanes were
consummated in January, 1926. The only essential difference between these models is in the
power plants, the P-1 using a standard Curti ss D-12 engine, rated 435 h. p. at 2300 r. p. m. , and the
l:'-2 the new Curtiss V-1400 engine, rated 500 h. p. at 2100 r.p.m. The latter in stallation also in­volves
the use of a different propeller and larger radiator to accommodate the increased power of
the engine.
All of the above airplanes were assigned to Selfridge Field for service test with the exception
of two, one of each model, which were flown to the Division for tests. Shortly after bei11g placed in
service it became necessary to have the radiators repaired and reinforced and new mounting brack­ets
in stalled. Performance tests of the . P -2 assigned to McCook Field were delayed by timing gea ~
spring coupling failures in the V-1400 engine. These couplings have since been replaced by new
ones of Curtiss design in all V-1400 engines in service.
A comparison of the performances of the P-1 and P -2 airplanes with the same di sposable lead
of 788 pounds and without the auxiliary underslung fuel tank is as follows:
P-1 'C~·ith 28" x4" tires
High speed at ground ......... 163.0 m. p. h.@2340 r.p.m.
Initial Rate of Climb ......... 1810 ft. / min.
Climb to 10,000 feet . . ...... .. 7.2 min.
Service ceiling .............. 22,500 ft.
P-2 with 32"x6" tires
172.0 m. p. h.@2075 r. p. Ill.
2170 ft. / min.
6.0 min.
22,950 ft.
On each of the above models, the addition of an unclerslung auxiliary fuel tank which doubles fuel
capacity reduces the high speed at ground from 2 to 3 miles an hour.
A production order (A. S. 2644) for twenty-five additional pursuit type airplanes has been
placed with the Curtiss Aeroplane and Motor Company. Twenty-three .of these articles, except for
comparatively minor changes, will be identical with the P-1 's now in service and will be desig­nated,
model P-lA. One of the airplanes on this order will be fitted with the new Curtiss R-1454
radial engine, rated 400 h. p. at 1650 r. p. m. This article will be designated XP-3 and used to de­termine
the adaptability of this air-cooled engine for pursuit purposes. It was originally planned
to in stall the R-1454 engine in one of the airplan es on A. S. O rder 25422 as stated on page 7, T ech­nical
Rullrti:11 No. 43, but there was no engine available at that time. The remaining airplane on A . .
S. Order 2644 will be equipped as a training pursuit airplane with a Wright engine (rated 200 h. p.
at 1800 r. p. m.), according to Change Order W-392. This airplane will be clesignatecl, l\foclel A T-4.
Thomas-Morse All Metal Pursuit.
An all metal pursuit airplane, developed by theThornas-Morse Aircraft Corporation, Ithaca, New
York, about a governmi:,nt-ownecl Curtiss D-12 engine loaned under a bailment contract in 1923, has
been received at the Division for inspection and tests. The particular feature of interest in this
experimental design which is known as the TM-23 is the exclusive use of metal throughout the
structure. This incorporates thin section wings, cl uralumin and fabric covered tail surfaces, split­ax
le vee type chassis, steerable tail skid, and short monocoque fuselage of duralumin and steel
8 T E C H N I C A L B U L L E T I N N o. 4 6
THC MAS-MORSE ALL-MET AL PURSUIT AIRPLANE, TM-23
(Curtiss D -12 Engine)
similar to that used' in the 1922 Thomas-Morse ra cer. Departures from conventional practice are
seen in the shape of the fu selage cross section, in the position of the radiator and in the use of an
anxiliary trimming plane above the stabili zer.
In preliminary fli ghts, a high speed of 167.0 miles an hour at ground was obtained with the
radiator shntters practica!ly closed. Stability, both directionally and laterally, appeared to be sati s­factory,
but the airplane did not handle well on the ground. It has a very high landing speep and
a tendency to ground loop, and the cockpit is small and uncomfo rtabl e. Concensus o f~10n of
variou s pilots who have flown it is that the present design is not suited for pursuit purposes.
The characteri stics of this airplane are as fol lows:
Model designation .. . . .. .. ... ... . . . .. . . . . . .. .. . TM-23
T ype . ... .. .. . . .... .. . . . . ....... .. .... . . ..... pursuit biplane
Manufacturer .. ... .. .. . .. ...... ... .... . ..... . Thomas-Morse Aircraft Corp.
Power plant . . .. .. . ... . . ... .. . ...... . .. ... . .. . Curtiss D-12
Overall span ... ..... . .. .. .. . .. . . . . ... .. . .. . . . 25 ft. 0 in.
Overall length .. .. ... .. ... . . . . . . .. . . . .. ..... . . 18 ft . 8 in.
Overall height . .... .. ... . . .......... .... ... . . . 7 ft. 5 in.
Supporting area . .. ... . ... . ... . . . .... ...... ... 199.72 sq. ft.
Gross weight . .. ... . ... .. .. .. ..... .. .. .. ..... . 2,655 lb.
Military load ... ... .. ... ... .. . .... ....... . .. .. 773.5 lb.
LB-1 Received for Test.
The fir st LTI-1 to be completed by H uff, Daland and Co. on Air Service Order 2686 fo r ten
service test articles has been received at the Divis ion for inspection and tests. T hi s airplane incor­porates
several improvements over. the original experimental model XLB-1 , the most important of
which are the rearranged fu selage to accomrnoda te a crew of four instead of three as formerly
carried . a rebuilt engine section with tunnel type radiator, an enlarged bomb bay to provide in­creased
bomb capacity. and the mounting of two fi xed machine guns in side the lower outboard
wings T n thi !3 parti cul ar article a tentative dua I rnntroi in stallation has been placed in the pilots'
cockpit for experimental purposes. T his in stalla tion is not standard , however. Per formance tests
will be made as soon as the airplane is released for flight.
In connection with the development of t his type of airplane, the Division is preparing specifi­cations
covering a new light bombardment airp lane of similar design, powered with two air­cooled
Liberty engines, to be designated model XLB-3.
AIRCRAFT DEVELOPMENT 9
New Light Bomber XLB-2 Planned.
Negotiations are underway with the Atlantic Aircraft Corporation for the procurement of a
new light bombardment airplane to be designated XLB-2. The proposed airplane will be of mono­plane
construction similar to the Fokker F-VII, utilizing two inverted air-cooled Liberty engines
for propulsion. It will be designed to carry a normal military load of 6107 pounds, which includes
a crew of five persons, 295 gallons of fuel, five machine guns, radio apparatus and bombing equip­ment.
\!\Tith this load a high speed of 129.5 miles an hour at sea-level and a service ceiling of
10,500 feet are anticipated. In addition the airplane with one-half normal fuel load but without
bomb load should be capable of attaining a mini mum service ceiling of 900 feet with one engine
operating.
In the proposed design the crew will be allocated in a manner similar to that used in conven­tional
twin-engined biplane bombers, that is, gunner in nose, pilot and bomber in main cockpit for­ward
of the wmg, floor gunner at rear of bomb compartment, and gunner in rear. The main cock­pit
will be so arranged tnat the bomber may also act as assistant pilot. For this purpose there will
De installed eithec dual controls or some form of single control which is transferable to either
side of the cockpit to permit the machine to be flown by either pilot in emergency. The floor gunner
will have access to the rear cockpit to permit him to serve in dual capacity as radio operator when he
is not engaged in manipulating the floor gun.
For carrying the bombs a new internal rack, type G-6, will be used. This rack accommo­dates
any of the four following combinations: twenty 100, six 300, four 600 or two 1100-lb. bombs.
By attaching external racks to the above rack four 600 and one 2000-lb. bombs may be carried as
an alternative load. ·with normal military load the gross weight of the airplane is estimated at
11,807 pounds, requiring a supporting surface of 739 square feet.
Wing Panel for XHB-1 Passes Static Tests.
An upper wing panel, constructed by Huff, Daland and Company under a preliminary con­tract
in connection with the development of an experimental heavy bombardment airplane, model
XHB-L has been received, inspected and subjected to static tests at the Division with satisfactory
results. In low incidence condition the loading was carried to the required factor of 3.0 without
failure and in high incidence condition, to a factor of 5.0 without failure or 0.5 factor overload. The
factors were based upon an estimated gross weight of 16,142 lb. for the complete airplane.
Upon completion of the above tests six intermediate tubular drag trusses were removed from
the panel, and a second test was made for high incidence condition, in which a load factor of 5.0
was sustained without failure as before. The pan el was then reset for test in low incidence condi­tion.
In this position, the rear spar failed under a load equivalent to a factor of 3.75. As soon as
repairs are made, retest in high incidence condition will be carried to failure. Inasmuch as all
static test requirements have already been fulfilled in these tests, the intermediate drag trusses will
be omitted fro!Jl the final wing structure.
Construction is proceeding on a complete airplane for flight test as authorized under a subse­quent
contract. This airplane will be of the single bay biplane type of construction utilizing metal
throughout with the exception of the covering which will be fabric. The design is built about one
800-h. p. Packard geared engine and incorporates symmetrical wings, welded tube fuselage, split­axle
chassis and conventional tail surfaces. The wings will have a span of'approximately 85 feet
and an area of 1550 square feet. Performance requirements stipulate a minimum high speed
of 100 miles on 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 of which are to be attained without the use of a
supercharger.
Heavy Bombardment Airplane (Monoplane Type).
Revision of the heavy bombardment monoplane design submitted by Huff, Daland and Com­pany
in the competition last October is proceeding under contract. The revised design contem­plates
the use of two 800-h. p. Packard geared engines, with contingen1' changes in the landing gear,
in place of one 1200 h. p. "X" type engine in the original design. The contract also provides for
the submission of a wind tunnel model incorporating the above changes and three skeleton wing
10 T E C H N I C A L B U L L E T I N N o. 4 6
structures, for static test. The latter, made to a scale of 1 to 2.4. will incorporate three diffe rent
types of construction, employing two. three and multiple spars, to determine their relativ.e rigidity
for monoplane use. Option to purchase a full sea le wing is re served.
In connection with the study of large monoplane wings, the Gallauclet DB-lB clay bomber, a
large thick wing monoplane built in 1923, has been reconditioned by the Division and flown to or:,­tain
additional performance data on this type of construction.
First Curtiss 0-1 Received.
The first of the new type observation airplanes, Model 0-1, ten of which have been ordered
from the Curtiss Aeroplane and Motor Compa ny for service test, has been received at the
Division. T his airplane, which is provided with an interchangeable engine mount, is now powered
with a Curtiss D-12 engine instead of a Liberty "12" engine as originally proposed. The change in
engines together with other refinements has res ulted in a considerable saving in structural weight.
lt has been decided to service test the 0 -1 as a two seater pursuit airplane in view of the high per­formance
and maneuverability di spl a~d by the experimental article in the competition. These tests
will be fo llowed with unusual interest in view of the extensive use of cluralumin in its construction
as it is sought to determine the desirability of this material from the standpoints of weight-saving
and maintenance in comparison with steel used to the same extent.
For use in connection with the service tests, a manual has been prepared giving all present
available infor mation on this airplane. Comments of the service are requested thereon as it is
proposed to incorporate the same in a revised manual to be issued later in event t his airplane is
adopted as standard.
Additional 0-2's Ordered.
Thirty-seven additional 0-2 airplanes are being procured from the Douglas Company, Santa
Monica, Cali fornia, under Air Service Order 26364 recently authorized by the Chief of Air Service.
These ai rplanes will carry model designations 0 -2C and 0-2D, the latter designation applying to
two articles equipped with dual control in stallati on. Deliveries are scheduled for completion on
or before September 30, 1926.
In general design and equipment the new articles will be essentially the same as the night flying
articles 0 -2A and 0-2B, described in the last T ee fin ical Bulletin. Among the new features to be
incorporated are oleo landing gears with 36 by 8- inch wheels, air-cooled aluminum exhaust stacks,
and detachable blade metal propellers. The normal military load of the 0-2C model compri ses prac­tically
the same items as carried on the standard 0 -2 model ; namely, crew of two, one forward
svnchronizecl and two rear flexible machine guns, radio and interphone apparatus and provision for
i~1 stall ati on of both single and multiple lens came ras. Special armament and combustible loads are
also provided for in addition to the normal load. On the dual control articles, however, all arma­ment
with the exception of the airways flare ra cks will be omitted.
Conversion of 0-2 for Ground Attack.
A contract has been negotiated with the Douglas Company, Santa Monica, Cali fo rnia, for the
conversion of one standard 0"2 observation airplane on Air Service Order 25421 into a ground
attack airplane to be designated XA-2. The modifications involve the substitution of an inverted
ai r-cooled Liberty engine in place of the standard Liberty engine and the in stallation of wing
mounted guns and bomb racks. A special sight will be provided for use with the wing guns which
are capable of being depressed thru an angle of 15 degrees from the direction of flight line of fire.
Another feature to be in stalled is an automatic bomb release handl e and power release unit. The
gross weight of the modified airplane is estimated at 4745 pounds.
Original Night Observation Design Abandoned.
Failure of the wind tunnel test model to come up to required performance has led to the
tentative abandonment of the single-engined pusher type night observation XN0-1 design under
development by the Douglas Company. Considerable di sappointment in the arrangement of the
mock-up which necessitated a compromise in some essential characteri stics also contributed to this
decision. As a result a study is being made of a new design of experimental night observation
airplane powered with two \ i\T right 200-h. p. rad ial engines, including the possibility of flight with
only one engine.
AIRCRAFT DEVELOPMENT 11
A description of the original design was published in Trchnical Bulletin No. 43 under project
entitled "Design Competition for Night Observation Airplane."
Douglas Cargo Airplanes.
Nine Douglas cargo airplanes, Model C-1, were constructed and delivered to the service last year
by the Douglas Company, completing their con tract. Of these articles, all of which were placed
on service test, two were equipped with epicyclic geared Liberty engines and the remainder with
standard Liberty engines. To distinguish these models, the designation "C-lA Douglas Cargo"
has been recent! y assignee! to the articles using epicyclic geared engines. Seven aclclitional air­planes,
model C-lA, have been ordered.
There was some delay in terminating the service test contract because of a stipulation therein
that each of the nine airplanes should be flight tested with specified load for high speed and ceiling.
Inasmuch as these airplanes have been allocated to various activities for service tests. it was neces­sary
to have each activity involved conduct the required performanec tests to satisfy the require­ments
of the contract. In all cases the requirem ents were amply exceeded.
Atlantic to Build Cargo Airplanes, Model C-2.
A contract has been awarded to the Atlantic Aircraft Corporation, Hasbrouck Heights, New
Jersey, for the construction of three cargo airplanes to he designated, Model C-2. These air­planes,
each mounting three \i\T right "\Vhirlwin cl" J-5 air-cooled radial engines, will be similar to
the Fokker transport F -VII which participated in the Ford Reliability Tour last year and which
was afterwards submitted to the Engineering Division for examination. The principal changes to
be incorporated in the C-2's involve a rearrangement of the pilot's cockpit to a position farther
forward, not hemmed in by the wing, and of the ca bin to make it adaptable for both transport and
ambulance use. The later modification necessitates the installation of suitable fittings for carrying
~ ix litters and other ambulance equipment and a re arrangement of the doors to facilitate the handling
of patients. The fuselage will also be provided with a hoist capable of lifting a Liberty engine
into the cabin.
It is expected that the first article will be ready for service test early in the next fiscal year.
Huff-Daland Advanced Training Airplane, Model AT-1.
Early in 1925, two" new types of training 'planes were submitted to the Engineering Division
for inspection and test, preparatory to their release to the service. These models, the first to be
built under the new classification for training type aircraft, were the Consolidated PT-1 for pri­mary
training and the Ffnff-Daland AT-1 for advanced training. The model AT-1, ten of which
were built for service test, was produced by Hu ff, Daland and Co., Inc., then of Ogdensburg.
New York, after several years of cooperative development with the Army air service.
The design of the present model had its inception in 1922 in the original T A-2 tandem seater
biplane mounting the Lawrance 140-h. p. air-cooled radial engine. In the following year, the TA-2
was superseded by the T A-6. an improved model having larger wings and engine, a Lawrance 200-
11. p. radial. From this design was developed the model TW-5, an airplane of almost identical ap­pearance
and construction as its predecessor wi th the exception of the power plant which in this
article was a water-cooled engine, the vVright Model E of 180 h. p. The latest type, the AT-1.
is a refinement of the T\V-5. its design having been selected for production in service test quantity
in the competitions held by the Army air service at Brooks Field, Texas, as a stop-gap advanced
training type.
The Huff-Dalancl AT-1 is a tandem seater of single bay internally braced biplane construc­tion.
Its characterizing features are the semi-thick tapered wings with large overhanging upper
panel, the square-nosed fuselage with close coupled cockpits, and the split-axle landing gear with
oleo type shock absorber units forming the out er legs of the tripods.
Conventional wood and metal.construction with fabrie covering prevails thruout the structure,
wood being used for the wings and surfaces and steel tubing for the fuselage, chassis and inter­plane
bracing. · The wings are one-piece panels of USA-35 section, tapering along both chord and
12 T E CH N I CA L B U LL ET I N N o. 4 6
HUFF-DALAND ADV NCED TRAINING AIRPLANE, MODEL AT-I
(Wright "E" 180-H. P . Engine)
AIRCRAFT DEVELOPMENT 13
span. The upper panel with its pronounced over hang is nearly double the area of the lower de­spite
the large cutout section in the trailing edge above the cockpits. Due to the absence of ex­ternal
bracing all stresses are taken by the spars which find support in the wing tripods and vee
struts at the fuselage and in the elliptical section N struts at the tips. These tripods together with
the fin skeleton form an integral part of the fuselage structure which comprises a rigid truss of
HUFF-Dc\LAND ADVANCED TRAINING, MODEL AT-1
Dimensions:
Overall span ... . .................... . ......................... .
Overall length . ................................ . ............... .
Overall height .. ..................... . .... . ......... . .... . ..... .
Span of upper wing, proper ......... ...... ......... ... ... ... ..... .
Span of lower wing ................................ . ............ .
Chord, upper wing (root ....... ........... ... ........... ...... .. .
(tip . .. .......... ... ............... . ..... ..... .
Chord, lower wing (root ................................. . ....... .
(tip .... . .......... . ....... . .. .. ........ . .. .. .
\!\Ting curve ... ... .... ......... . . .. .. .............. ... ..... .... .
Gap (mean) ...... .. .. . ... ........ . . .............. . ..... ... .. . .
Stagger .... .. . . ..... . ... . ..... . .............................. .
Dihedral .. . ................ . ...... . ........................... .
Sweep back ....... .. ....... .. ...................... ..... . ..... .
Incidence. upper wing ................ . . .... .. .... ..... ... . .. . .. .
Incidence, lower wing (right ............... ............. .... ..... .
( left .......... . . ................. . . · · · · · · ·
Height of propeller axis in flying position .. .. .. .............. .... ... .
Tread . ... .............. ... ............ .. .................... .
Areas: (sq1wrc .feet) :
Total supporting surface ......................... .. ............ . .
Upper wing ... . ............................................... .
Lower wing ........... . ........... ...... ..... ... ....... ...... .
Ailerons (upper wing only) ......................... , . .. .... .... .
Elevators ......... ............ .............. .. .. . .. ... ... ... .. .
Fin ...... . ... . .................................... . .......... .
Rudder ...................................................... .
Stabilizer . ... . .. ........ . .. ... .. ...... .................. .. . ... .
W ciqhts (pounds):
Total weight loaded . . . . . ............ .. ... .. .. . ... ........... ... .
Empty, with water .................. .... . .. ..... .. ..... . .... ... .
Militarv load (without armament) ... ....... ...... .. ... . ..... ..... .
Equipment .. . . ..... ......... .. . . ........... ... . ..... ...... .. . . .
Crew .. . ..... . ................... .. .. ..... .... . . ... . . .. ..... . .
Fuel ( 43 gal.(@6.0 lb. per gal.) ............ .. . .. .................. .
Oil ( 4.25 g·al.@7.5 lb. per gal.) ... ...... .. .. ..... ..... ... ... . .... .
\Ving loading (pounds per square foot) .... . . ... ........ ...... ... .. .
Power loading (pounds per rated horsepower-179 h. p.) . ... . ....... .
Perfonnances:
Speed in level flight at sea level ................................... .
Speed at 10,000 feet altitude . .................................... .
Time to climb to 10,000 feet. ... .... ......................... ..... .
Rate of climb at ground ......................... ........ ........ . .
Service ceiling ......................... .. ................. . .... .
Absolute ceiling .. . .... .. .... .. ...... ... .... .......... . .... .... .
Landing speed (approx.) ........................................ .
Endurance at 10,000 feet including climb .... .. ... . ................. .
31' 1"
24' 8"
9' 3"
29' 4"
5' 6"
23' 10"
3' 6"
4' 5"
3' 0"
USA-35
4' 11"
2' 0"
None
Tapered wings
30
0° 22' 30"
1 ° 45' 0"
5' 2Yz"
6' 101'
214.0
129.5
72.5
12.0
15.0
3.5
11.S
17.8
2358
1607
751
101
360
258
32
11.01
13.17
112.4 111. p. h.
98.3 m. p. h.
26.1 min.
660 ft. / min.
12,075 feet
14,200 feet
58 m. p. h.
3 hr. 20 min.
14 T E C H N I C A L B U L L E T I N N o. 4 6
PERFOR)..'£4/YCE TE.ST or
HUFF- ...LJALAND ATI./
WlrH
W.R/GHT :£' "' S JY6Vl):X
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COMPARATIVE PERFORMANCE CURVES OF HUFF-DALAND AT-1 AND CURTISS JN-6HG-1E AIRPLANES.
torch-welded steel tube with tubular diagonals, a t ype of construction similar to that used in the En­gineering
Division TP-1. \Velded tubing is also used for the engine section, access to which is
gained thru quickly detachable sections of aluminum cowling . All tail surfaces are of wood and
fabric construction as previously mentioned, with the exception of the fin and the forming edge of
the rudder which are of steel tubing. The stabili z er, a unit structure extending thru the fuselage, is
mounted with the hinge at the front and the adju stment at the rear in the same manner as on the
SE-5, a method that somewhat hinders removal for replacement or repair. External bracing is
provided on each side by two rigid braces from the lower longeron and one wire · brace from the fin.
The setting of the stabili zer with its appendant elevators is effected from the cockpit.
Landing gear compri ses welded tube individual chasses of the divided axle type and a steer­able
tail skid. The chasses are hinged at the centerline of the fu selage forward of the lower lead­ing
edge and equipped with oleo shock absorbers and 28 by 4-inch straight side wheels. T he oleo
units are optional and may be replaced with conventional rubber cord absorbers by a minor substi­tu
tion of parts.
Propulsion is furni shed by a 180-h. p. ·wright "E" engine, driving a two-bladed tractor pro­peller,
8 ft. 8 in. in diameter, which gives a ground clearance of 10 ;.~ inches in flying position. The
engine is equipped with two Dixie magnetos and one Stromberg NA-D4 twin type carburetor hav­ing
a hand operated mix ture cont rol. Fuel is supplied ent irely by gravity feed from two 21.5-gal.
terne plate tanks in the upper wing. No pump is required as there is a two-foot fuel head in level
fl ight. Lubrication is provided by a dry sump pressure system operated by a sliding vane eccen­tric
type pump geared to the engine. The oil is carried in an irregularly shaped tank of eight gal­lons
capacity mounted beneath the engine with its bottom surface exposed to the slipstream for cool­ing.
E ngine cooling is effected by a closed water system utili zing two nose type radiators of iden­tical
size, joined at the top by an expansion tank. T he core units are of the cartridge tube type,
four inches in depth, so disposed on each side of the propeller hub as to provide 116 sq. ft . of
cooling surface, all direct. Temperature is regulated by means of vertical shutters.
AIRCRAFT DEVELOPMENT 15
Ordinarily the normal military load carried by the AT-1 is 751 pounds, that is, without arma­ment.
This comprises a crew of two persons; a combustible load sufficient for full throttle flight
of three hours and twenty minutes at 10,000 feet altitude; and other incidental equipment. Since
there are no central instrument boards, the various in struments are installed about the sides of the
cockpit and cowling. Dual controls are provided; these are of a conventional type, including stick
and rudder bar units, engine ·lever controls and the like. For gunnery training, provision is made
for mounting one .30 caliber synchronized machine gun under the forward cowling for the pilot
and two .30 caliber flexible machine guns on the rear ring mount for the observer. No radio or
photographic apparatus is carried.
At present, the DH-4M2 airplane is being used for transformation from primary training to
service types with the ultimate intention of using the standard observation type airplane for this
purpose. Several airplanes, one of which is a refinement of the A T-1, are being developed for use
in pursuit training until enough standard pursuit airplanes become available for this purpose.
Driggs "Dart" Airplane.
A small airplane for use in obtaining flight data on slotted wings, aileron flaps, and other aero­dynamic
problems is being procured from I van H. Driggs, an aeronautical engineer doing busi­ness
at Dayton, Ohio, under the trade name of Driggs Airplanes. This article, known as the Driggs
"Dart" model, will be of a special type, designed to carry a disposable load of 229.5 pounds, includ­ing
pilot, parachute, safety belt, and combustible load of 29 pounds. It will be powered with a two­cylinder,
air-cooled \ i\Tright-Morehouse engine of ~O cubic inches displacement. The engine weighs
89.5 lb. and develops 29.1 h. p. at 2500 r. p. m. at a specific fuel consumption of 0.513 lb./ h. p. hr.
Other equipment includes an altimeter, airspeed indicator, oil pressure gage, oil thermometer, and
tachometer.
The airplane will be of monoplane construction incorporating wood wings with plywood cover­ing,
welded steel tube fuselage, split-axle landing gear , and steerable tail skid. The total weight
ready for flight is not to exceed 550 pounds.
Metal Wings for Boeing Pursuit.
Static tests have been completed on the first set of tapered metal wings constructed by the
Thomas-1\forse Aircraft Corporation for use on the Boeing pursuit airplane, P \N-9A. The wings
were found to comply with the present air service load factors for pursuit aircraft as required in the
contract. The second set of metal wings, now being fabricated, will be flight tested on an airplane
of the above type. These wings are of Clark Y section with metal ribs and spars and conform in
size and shape with the wood wings now used on this airplane. The top surfaces are covered with
corrugated sheet duralumin and the bottom with fabric.
Propeller Development.
Experimentation with wide tip detachable aluminum a lloy blades 1s 111 progress in an effort to
improve the static thrust of metal propellers. In a whirling- test conducted on an experimental pro­peller,
10 feet in diameter, the blades fluttered badly and finally failed. A study of the failure dis­closed
that wide tip blades must be materially strengthened before a satisfactory design is obtained.
Tests will be continued with a set of blades for a propeller, 10 ft. 6 in. in diameter.
To determine the effectiveness of rubber as a protective against water spray two sets of rub­ber-
covered metal propeller blades were submitted bv the Goodrich Rubber Company for whirling
and water spray tests. Both sets passed the whirling tests satisfactorily. but in the water spray tests
the rubber loosened from the blades. The covering had been applied with a special cement and then
cured on the blade for thirty minutes under pressure until cool. The blades were returned to the
manufacturer for further development.
Destructive whirling tests have been started on two experimental propellers, a Heath variable
pitch propeller and a Leitner-\Vatts metal propeller. The Heath propeller has had ten hours'
testing on a Liberty engine and is awaiting whirling test as soon as opportunity permits.
16 T E C H N I C A L B U L L E T I N N o. 4 6
AIRSHIPS AND BALLOONS
The RS-1 Airship.
The initial flight of the RS-1 at Scott Field, early this year, marks the culmination of approxi­mately
four years' cooperative effort by the Goodyear Tire and Rubber Company of Akron, Ohio,
and the Army Air Service in developing the first semi-rigid airship ever built in America.
Altho the project was initiated in 1922, it was not until three years later that the design and
fabrication were completed and the parts shipped to Scott Field for erection. That so much time
should be spent in developing this airship is clue to the highly experimental nature of the pro­ject
and the complete absence of engineering data on this type of construction in this country. At
the time the project was conceived Italy was the only country having success with semi-rigid con­struction,
but the government of that country was reluctant to release any detailed information there­on.
Consequently, it remained for the Army Air Service to conduct, with the aid of various gov­ernment
agencies and other research in stitutions, the fundamental research and experimentation
necessary to in sure success of the project. As a re sult a great amount of data has been accumulated
that could not all be applied in this particular development but whicr will be of inestimable value in
future design.
The RS-1 is an airshi'p of the semi-rigid type, designed primarily for long distance recon­naissance.
It has a designed volume of 719,SOO cubic feet with helium and measures 282 ft. 3 in.
in length, 74 ft. 6 in. in greatest width, and 80 ft. in height as measured from landing pontoon to
fop of envelope. Upon the basis of an envelope volume of 7SS ,SOO cubic feet, which includes five
per cent stretch, its gross lift with helium at SS ponnds per thonsancl cubic feet of capacity is
41 ,SSO pounds. Of this total 29,412 pounds is fixed weight, leaving 12.138 pounds available for
crew, ballast and combustible load. Propulsion is furnished by two 170 -foot propellers, driven by
four Liberty engines thru reduction gearing. For airship use, the engines have been choked to give
only 300 horsepower each at lSSO r. p. m. , but the aggregate output is sufficient to drive the airship
at a high speed of 80 m. p. h. (estimated). \Vi th a crew of nine and full load of fuel , the endur­ance
at thi s speed is 11.2 hours, which gives a range of 900 miles. At cruising speed, 64 m. p. h.,
the above estimated endurance is doubled.
In this airship the entire structure evolves a bout the keel. To it are attached the envelope, the
nose cap and mooring outrigger, the lower vertical surfaces, and the cars; while within it are
suspended the fuel, 9il and ballast and the handling equipment. The keel is a continuous structure
of triangular cross section, extending with its apex upward along the lower contour of the hull in­side
the envelope to within 23.38 feet of the tail. giving a proj ected length of 2S8.87 feet along the
ship's axis. It is built of Phoenix type aluminum alloy columns. hinged together at twenty-seven
points. At each station, the transverse members terminate in forged aluminum alloy housings to
form rigid triangular uprights which are joined at the corners by three lon1:6tudinal members se­cured
in a ball and socket arrangement. The keel structure weighs approximately 5231 pounds
and is about 10 by 12 feet at its maximum cross section.
The keel is suspended by means of three catenary curtains running lengthwise of the envelope,
one extending full length along the top and the other two attaching the keel terminals along the
lower sides of the envelope. From the upper catenary. suspension cables of varying lengths drop to
the keel where they are atta ched to the upper terminals of the triangular uprights at each of the
twenty-eight stations. In this method of suspension, the load carried by the upper catenary causeo
the envelope to assume a heart-shape cross section.
The envelope is divided into four gas compartments by means of three transverse partitions to
prevent surging of the gas ; two 18-inch diameter holes are provided in each partition to equalize
pressures in the compartments. There are four ballonets, one for each compartment, evenly dis­tributed
along the lower part of the envelope, the two front and two rear being interconnected with
surge holes in the same manner as the gas compartments above. The ballonets, by means of an air
scoop and emergency air blower and a system of va lves releasing to the atmosphere, serve to main­tain
the necessary fl ying pressures in the envelope and preserve its shape during fluctuations in gas
volume with altitude and temperature. Gas and air volumes in the envelope are controlled by
several 18 and 28-inch automatic valves. Valving with air valves only allows a rise of 7SO feet
per minute, but in extreme cases when gas must be valved a rise of 16SO feet per minutes is possible.
For emergency use, four rip panels are provided.
A IR C R AF T D E V E L O P MENT 17
CLOSE-UP VIEWS OF RS-1 AIRSHIP
1. Side View of Control Car 4. Front View of Power Cars.
2. Interior of Control Car looking forward. 5. Interior of Power Ca·r looking forward.
3 . Rear Compartment in Control Car. 6. Rear View of Power Cars.
7 . Arrangement of Control and Power Cars.
18 T E C H N I C A L B U L L E T I N N o. 4 6
The envelope fabric has a specified machine strength of 90 pounds per inch. The circumferential
tension is 14 pounds per inch at one-half -inch water pressure. This gives a factor of safety of 6.4.
The material used is of two kinds, air-tight and gas-tight, the latter forming all surfaces in con­tact
with the helium. Gas-tightness around the catenary suspension cables where they enter the
gas compartments is secured by the use of telescopic sleeves.
At the nose, the envelope is stiffened by the nose cap and mooring outrigger, the latter receiv­ing
its support directly from the keel. The nose cap structure, concealed under a cover, consists of
19 duralumin battens of channel and lattice construction, radiating from a circular flange on the out­rigger
over the surface of the envelope. Besid es being secured to the envelope by eyelet patches
and finger terminal patches, the battens are stiffened circumferentially by means of two telescopic
rings and laterally by means of crossed brace wires. By this arrangement mooring strains are
evenly distributed over the entire hull when the airship is attached to a mast.
The cruciform arrangement used for the tail surfaces includes four fixed and three movable
panels. The fixed or stabilizing surfaces, which are of equal area with the exception of the larger
lower vertical fin carrying the rudder, are brae ed externally by numerous wires, attached to
finger patches on the envelope. The movable or controlling surfaces, elevators and rudder, are
equipped with balance vanes to facilitate actuation.
The combustible load and water ballast are distributed along the keel, with the main fuel supply
disposed in seven aluminum tanks, suspended from the keel terminals at stations 5, 7, 10, 11, 19,
20 and 23 (see page 20.) A SO-gallon gravity fuel tank, mounted between the power cars, provides the
fuel head for the carburetors. All of the main tanks are equipped with clump valves by which the
entire fuel supply can be released in approximate! y three minutes. A large reserve supply of oil is
carried in a tank suspended at station 14, and the water for ballast in four collapsible fabric bags
between stations 4 and 5, 8 and 9, 21 and 22, a.ncl 25 and 26. The bags have a total capacity of
4000 lb., which can he discharged thru controls in the control car. The rate of discharge for the
two main bags is 40 pounds per second under a 3- foot head, whereas discharge from the smaller
emergency bags is instantaneous.
The control car which is attached to the keel between stations 6 and 9 is a composite structure
of duralumin and fabric, 36 feet long by 8 feet wide. Its well-lighted interior has a clear height of
78 inches above the corrugated metal floor and is divided into two compartments. The front com­partment
or control room contains two capstans, navigating in struments, navigator's table and en­gine
telegraph. The capstans, one for directional control and the other for altitude control. oper­ate
thrn a non-locking worm gear and drum mechanism the control cables comjng clown from the
keel alongside the partition separating the compartments. The rear compartment accommodates the
crew and military equipment. It contains, in acldi ti on to the radio apparatus and blower unit, four
bunks, a wall seat, stools, provision cabinets and a lavatory. Provision is also made for the installa­tion
of suitable photographic, bombing ... ancl machine gun equipment, the latter to be installed in
the open cockpit at rear of car. 111e blower unit, designed by Goodyear. is driven by a Harley­Da
viclson motorcycle engine and supplies air to the ballonets at a capacity rate of 5000 cubic feet
μer minute against one-inch water pressure. For alternate use, a blower of double capacity, driven
by a Morehou~e engine, has been developed by the Division. To the bottom of the car i5 attached
an air-inflated pontoon, 78 inches long by 34 inches in diameter , to absorb shocks in landing.
The power plant is carried in two metal frame cars suspended from the keel as a unit between
stations 15 and 17. The cars, which measure 18 Yi feet long by 6 feet wide by 70 feet high over­all.
are held apart by spreaders and suspended by struts from the outer keel terminals at a suf­ficient
distance from each other and from the envelope to provide a proneller-tip-to-tip clearance of
12 inches and a propeller-to-bag clearance of appro x:imately 36 inches. Each car is provided with
two doors and four circular windows, one door opening on the outside and the other on the walk
connecting the cars.
In each power car the ' two engines, arranged in tandem, are connected by means of disengag­ing
disk clutches to a Fawick dual engine transmission which drives the propeller thru a speed re­duction
of 12 to 5. The transmission unit weighs about 750 pounds and permits forward opera­tion
of the propeller by either or both engines and reverse operation of the propeller by one engine
only thru an idler gear. The engines are equipped with electric starters and whirl chamber exhaust
. silencers.
AIRCRAFT DEVELOPMENT 19
The 170 -foot propellers originally constructed for use with these transmissions were made of
balsa wood. These propellers, however, failed in the whirling tests conducted at the Division some
six months after their completion due to shrinkage of the balsa core from the surface plies. As a
consequence new propellers of laminated mahogany were constructed for use in flight.
For landing purposes two 325-foot drag ropes are attached fore and aft to the keel structure
and six handling lines to the sides of the envelope by finger patches, two forward, two amidships
and two aft. The forward handling lines are 86 feet long. Mooring to a mast is effected by use
of a mooring cable threaded thru the outrigger and reeled in by a winch installed in the keel section
forward of the control car.
Access to all parts of the airship, the fore and aft drag ropes, the mooring winch, as well as the
fu el, oil and ballast containers, is provided for by a corrugated metal keel walk, one foot wide, ex­tending
full length of the keel. Ascent or desc ent to the control and power cars is facilitated by
ladders connecting with the keel walk.
The design and construction of the RS-1 air ship involved the solution of many difficult prob­lems,
among the more important of which are the following: complete wind tunnel data 'on pres­sure
distribution over the hull and surfaces by the Bureau of Standards, determination of inertia
factors of ellipsoids for use in airship design by the National Advisory Commjttee for Aeronautics,
study of statical longitudinal stability with refer ence to the RS-1 and water model tests to deter­mine
keel and envelope deflections by Professor Hovgaard of the Massachusetts Institute of Tech­nology,
formulation of materi al specifications, analysis and test of materials, development of large
duralumin columr.s of 100,000 pounds strength, tests of gas valves and engine transmissions, pro­cess
inspection and development of what are probably the largest aircraft propellers every con­structed,
by the Engineering Division. In additio n, the services of the Italian engineer, Umberto
Nobile, designer of the Italian N-1 airship, now the "Norge," were employed in an advisory ca­pacity.
The erection of the RS-1 at Scott Field, consummated by Goodyear personnel under super­vision
of the Division, necessitated a new experi rnent in airship assembly. Its accomplishment in­volved
the construction of special cribbing upon which the keel sections were erected and joined to­gether.
When this was completed, the envelope was partially inflated, floated over the keel and
secured thereto. Upon complete inflation, the control and power cars were moved into position on
the floor of the hangar and attached. Shortly after inflation of the envelope, however, an excessive
drop in purity of the helium was observed, which necessitated complete deflation and repurification
of the gas. This unfortunate circumstance which was caused by an untoward accident during the
erection process de1ayed considerably the initial flight of the airship.
Upon re-erection and subsequent inflation, a series of hangar tests were conducted to verify
the water model tests and to determine the functi oning of various controls and mechanical devices,
preparatory to flight. fo repeating the water model tes 1 full scale with the assembled airship,
the observed keel deflections at both half and fu 11 load ere found to be less, practically without
exception, than those calculated by Professor Hovgaard at \ iVright Field.
The RS-1 took the air for the fir st time on J anuary 8, 1926. Jn the trial flights which fol­lowed,
measurements of the fl ying stresses were taken by means of electric strain gages before
performance tests at full power were permitted. The prescribed fli ght tests, now in progress, in­clude
the measurement of lift, altitude and high speed, and the determination of turning radius and
the rates of ascent and descent as limited by en gine power and controls. Upon completion, the
airship will be released for service test.
Since the conception of the design of the RS-1 many improvements have been made in aircraft
power plants and water recovery apparatus which, if applied to this airship, would greatly increase
its performance and efficiency. The present power plant in stallation of four Liberty engines with
their output restricted to only 1200 horsepower obviously imposes a burden of 400 horsepower which
cannot be utilized. \Vith the advent of the new Packard 500-h. p. engine weighing considerably less
than two Liberty engines, this handicap has been removed, and as a result the Engineering Division
has prepared an alternative design of power car utilizing a single Packard engine in place of the
dual Liberty engines now installed. The proposed Packard engine in stallation will effect a saving
of approximately 2500 pounds which may be utili zed in carrying a fifty per cent greater fuel load,
giving a proportionate increase in range and endu ranee.
I I i I I . I
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GENERAL ARRANGEMENT OF
U. S. ARMY SEMI-RIGID AIRSHIP,
MODEL RS 1.
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CHARACTERISTICS OF U. S. ARMY RS-1 AIRSHIP
.•
A-HULL B-CONTROL CAR. E-USEFUL LOAD.
1.
2.
3.
4 .
Envelope
Volume, (designed) ____ ___ ·--- ·· ... 719,500 cu. ft.
Volume, with 5% stretch .......... 755,500 cu. ft.
Length of envelope ... .. ........ ... ..... ... 276 ft. 6 in.
Length, overall, incl. nose cone ...... 282 ft . 3 in.
Maximum height ···-- ·-····-···· --- ··-·- .. .. 66 ft. 3 in.
Maximum width ··· ·-·· ·-· ·· ·· ·- ---- ··- .. .. 74 ft. 6 in.
Profile fineness ratio ··· · -·- ---···--- ---· _____ .4.25 : 1
Surface area
Ballonets
Volume -----·- --- -------- ······ ·-- ________ 215,000 cu. ft;
Percent of envelope volume _ ............. .... ... ... . 30
Tot al surface --·-··· ··-- __ --- --··· __________ 2342 sq. yd.
Ceiling based upon ballonet capacity 13,500 ft.
Co~trol and Stabilizing Surface.s.
Keel.
sq. ft.
sq. ft .
591 sq. f~.
524 sq. ft.
480 sq. ft.
960 sq. ft.
180 sq. ft.
60 sq . ft.
271sq.ft.
80 sq. ft .
Projected length -····--- ----···········--- _____ 258.87 ft.
Width at maximum cross
section 1 ft . 11 3/4 in.
Height at maximum cross
section ft. 4-1 /2 in.
1.
2.
Dimensions.
Length
Width
Height
Air Blower Unit.
ft .
ft.
ft.
Capacity at l" pressure ...... 5000 cu . ft. / n1in.
Weight ·· -· ...... ... __________ ---- ·- --- __________ 110 lb.
Engine ____ ·--- -·· ------ -.. 7.5 h . P. at 1350 r.p.m.
C-POWER CARS
1. Dimensions (each car)
Length __ ___ ___ -------- ···· ·- -··· ----···----18 ft. 3 in.
Width ___ ·--- -·-·· ·- ····-·· _____________ --- -6 ft. 0 in.
Height ·-· _______ -- -- -------- --- -··· ·----·-·-- ____ __ 7 ft. 6 in.
2. Power Plant.
Engines (Liberty dirigible) ____ ..... ·-- ··- ... .. .. .4
Total output (restricted) --------1200 h. p.
Speed of rotation __ -- --·----- .. 154 6 r . p. m.
Speed of propellers __ ··-· ·· ····- ----------640 r. p. m.
Transmission reduction __ _ ___ .......... 12 to 5
Diameter of propeller ---···-···----· ···----17 ft. 6 in.
Radiator capacity (per engine) -· ·· --··-- 18. 6 gal.
D-WEIGHTS (estimated)
1. Structure
Hull _ ·--··-·· ··-···---- --·-------- -- -···-·-- 9,469 lb.
Keel .... ····-···· ------------· ··-· ···· -···· ····- .. ... 5,231 lb.
Tail surfaces ············-····-····· ·····- .. ...... 1,630 lb .
Nose structure ·············- ····- -- ----·· 857 lb.
Mooring equipment . ..... ......... .. ----- -- -- 447 lb .
Control car ---·-··· ··· --- ·· ·- ------------· 1,895 lb.
Power cars (two) ---- .. ······-· -- ·-··· ....... 8.240 lh.
Power car suspen sion ... ____ -----·-·-- 5~5 lb.
Fuel system -- --······--·-- ------ -- ·- ----· ------· 817 lb.
Electric system in keel --- ---- ----· ..... .. 87 ~b.
Water ballast system ..... .. ... .. 126 lb.
Controls for fuel and ballast _ ------··· 32 lb.
Control lines in keel ·--------······---- ·· · 4 6 lb.
Total weig ht without bomb racks __ _ 29,412 i!J .
1. Fuel, Oil and Ballast Capacities.
Fuel (1762 gal. at 6 lb. per gal.) .... 10,5 72 lb.
6-keel tanks-270 gal. each.
1-keel tank-142 gal.
l-gravity tank-50 g-a].
Oil (1G2 gal. at 7.5 lb. per gal.) _______ l,215 lb.
J-keel tank-1.42 gal.
2-engine tanks-20 gal.
Water ballast --- ------·· ··· ·-···-- -- ·- .4,000 lb.
1-service bag-1750 lb.
1-service bag-1250 lb.
2-emergency bags-] 000 lb.
~. Normal Disposition of Load.
Crew (nine persons) ----------· ·- -----· -·-- .1,800 lb.
Fuel (1236.3 gal.) ···· ·-··· ·---- .. ···-···· ... 7,418 lb.
Oil (123 gal.) ............... .. .. ...... ... ......... 920 lb.
Water ballast ·····-- ··-·····-··--·· ·· ·· ··· ·· ··- .. 2,000 lb.
Total disposable load _______ --- --- .. -.. -1 2,1 38 lb.
3. Lift (with helium)
Gross lift ( 755,500 at 55 lb. /per
1000 cu. ft.) ------·-··--· ··· ·­Structural
weight ·--- ·· ---- ---· ··
Useful load at sea-level ····­Per
cent of total
F-PERFORMANCE (estimated)•
41,550 lb.
..29,412 lb.
.12,138 lb .
____ 29.2
High speed __ -------·- ··-- -····-· ...... ___ ,, ____ go m. p. h.
Cruising speed ___ -- -·-- __ __ _______ __ 64 m. p. h.
Rate of ascent or descent .......... ... 750 ft. / min.
Ceiling (ballonet capacity) _ _ _______ 13,50,0 ft.
Enduranc.1 at full speed________ ----· ---- .. 11.2 hr.
Endurance at cruising speed ........ 22.4 hr.
Range at cruising speed .. .. ..... .. ...... 1435 miles
Range at full speed ... ·-- -·-··-· ______ _____ __ 900 miles
Normal flying pressure ___ ....... 1/~" water
*Based on fuel consumption of 55 lb. per h. p . hr. and normal disposable load under Item E-2.
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22 T E C H N I C A L B U L L E T I N N o. 4 6
To take advantage of this increased fuel capacity, however, will necessitate the in stallation of
water recovery apparatus to compensate for the in crease in lightness on long flights clue to loss of
fuel thru combustion in order to preserve static equilibrium. Such in stallation will permit the air­ship
to be flown at all times at or very close to the point of static equilibrium by recovering from the
exhaust gases suffi cient water to compensate for the ·weight of fuel consumed. In this manner it
will be possible to obtain maximum flight economy and obviate the necessity of valving helium in
order to effect a landing after a long flight.
ARMAMENT
Gun Sight C-1.
Favorable reports of the type C-1 gun sight on service test at Selfridge Field has warranted
the in stallation of this type of sight on the new pr oduction P\tV-9 airplanes under construction at
the Boeing Airplane Company, Seattle, \ i\Tashington. Accordingly a sample sight together with
in struct ions for its in stallation and operation has been forwarded to this manufacturer in order that
provision can be made for its eventual in stallation in the service.
Gun Sight C- 1 is designed especially for use as a sighting medium for fixed guns on pursuit
aircraft. It is intended to eliminate the effects of vibration by providing a longer sighting base for
roughly aligning the target. It consists of a tu bu Jar bar about three feet in length carrying a bead
at the front end and a notched ring or peep sight at the rear . The sight is supported on adjustable
bases as an integral part of the gun mount. In so me in stallations adapters are used to elevate the
sight to the proper height for the pilot.
Gun Sight C-2.
A new gun sight. known as type C-2, has be en constructed for service test. This sight is
similar to the type C-1 just mentioned but differs from the latter in that it is adjustable in flight.
The adjustment is effected by mean s of two knobs at the rear of the sight, which enable the pilot
to elevate and traverse the barrel while fl ying. A va ri ety of beads and apertures has been provided
fo r use with this sight for the purpose of obtaining the opinion of the service as to which combi-nations
are preferabl e. ·
TTTT
GUN SIGHT, TYPE C-2, WITH SIGHTING ACCESSORIES.
AIRCRAFT DEVELOPME NT 23
Two models of the type C-2 gun sight have been built and sent out for test , one to Kelly Field
and the other to Selfridge Field. It is anticipa tee! that the new sight will re11lace the present
standard ring and bead sights for directing fire of fixed machine gun s on ground attack airplanes.
Machine Gun Synchronizer, Type C-11.
Machine gun synchronizer, type C-11, is a modification of the Nelson synchronizer for use on
high speed engines such as the new Curtiss and P ackarcl models. This synchronizer incorporates
two important features; namely, a simplified means of adjusting the generator cam on the cam
shaft and a flexible di sk coupling which compensates for any misalignment between the synchro­ni
zer generator cam shaft and the engine drive shaft. The flexible coupling replaces the standard
vernier flange of the Nelson gear, which develop ed excessive wear in high speed operation. The
new cam shaft adjustment provides an easy and accessible means of locating the cam by the aid
of two special wrenches, after removal of the generator cap. As a result of favorable reports on
an experimental model sent to Selfridge Field f or test, twenty synchronize rs of this type are being
constructed for service test. ·
GENERATOR CAM ADJUSTMENT ON MACHINE GUN SYNCHRONIZER, TYPE C-11.
Wing Mounted Guns.
Preparatory to converting a standard Dougla s 0-2 observation airplane for ground attack pur­poses,
a mock-up section of the wing with a Browning .30 caliber machine gun mounted therein was
subj ected to firing tests . These test s showed that there was no apparent clanger of fire resulting
from an over-heated gun mounted in this manner. The converted airplane for which a contract
has been let as previously stated in this Bulletin will be known as the XA-2.
In case of a similar in stallation in the new H uff-Dalancl LB-1 recently received at the Division
(see page 8), the ammunition box and curved fe eel chute for the wing mounted fixed gun were
removed from the wing for functioning tests. Five hundred rounds were fired under conditions
pres11111ecl to be more severe than those likely to be encountered in service. The tests were suc­cessful.
Automatic Bomb Release Handle, Type A-1.
In order to eliminate personal time lag or ti me lost by the bomber in operating the regular re­lease
handle at the desired instant of release, a new automatic release handle has been developed for
use with external bomb racks, types B-3 and C-3. This handle is a compact unit, weighing about
eight pounds. It consists of an electric solenoid which trips the release mechanism, and several
compression springs which supply the force necessary to release the bombs from the rack. The
bomb release cable attached to the unit may be con nectecl directly to the bomb rack or to the regular
bomb release cable from the standard manually operated release handle. The solenoid is ener­gized
by current from the ordinary 12-volt ignition system now standard on most aircraft. vVhen
the automatic unit is used in connection with a bomb sight making electrical contact at the desired
time of release, the bomb is released instantly. In other in stallations a push button or switch may
be used.
24 T E C H N I C A L B U L L E T I N N o. 4 6
Bomb Service Dolly.
The DiYision is conducting a study of a born b ser vice dollv for transporting la rge bombs from
the rai l head to the fl ying field and for airdrome nse. Initial prog ress has resulted in a tentative
layout of a two-wheeled vehi cle equipped with a hand-operated hoist for rai sing bombs into posi ­tion
on the airplane. This design has been desig nated type A-1.
EQUIPMENT
Universal Aircraft Camera Mount, Type C-1 (Automatic Oscillating).
A new uni versal camera mount, known as the Air Sen·ice T ype C-1, is under development at
the Division. This mount, a view of which is sh own herewith, is designed to oscillate any Air Ser­Yice
standard aircraft single-lens automatic cam era at various speeds to take overlapping vertical
and oblique photographs. \\' ith it may be obtained on a single flight one or more series of oblique
views in addition to the usual series of vertical views. T he oblique views are made to overlap
the verti cal view, and in case more than one obliq ue is taken on each side of the line of flight it is
also possible to make each oblique overlap the pre ceding one, thereby greatly increasing the angular
scope of the area photographed . With this mount, it is possible to photograph from hori zon to
horizon, that is, 180 degrees. but it has been fou ncl practical to limit the angul ar scope to 130 de­grees
in cases where the obliques are to be trans formed to equi val ent verticals for use in recon­naissance
maps.
UNIVERSAL CAMERA MOUNT, TYPE C-1 (Automatic Os cillating)
AIRCRAFT DEVELOPMENT 25
The mount is so designed that it may be either rigidly attached to the airplane or hand-leveled
to compensate for rolling and pitching during flight. Its use as an automatic oscillating mount effec­ti
vely increases the area that may be photograp heel with a single-lens camera in one flight, and
by using a long focus camera in this manner it is possible to combine the advantages of large scale
with large area in the resulting photographs.
In order to utili ze the obliques taken with this mount, it is necessary to transform them. For
this purpose a special printer, A. S. Type B-5, has been constructed and adjusted for making trans­formed
prints from the oblique negatives taken with a camera fitted with a 10-inch lens and os­cillating
40 degrees from the vertical. The trans formed prints are approximately 15 by 18 inches
in size, and when combined with the vertical make a composite photograph about 15 by 42 inches.
The scale of the photograph taken with a 10-inch camera at an altitude of 8,300 feet is 1 to
10,000. Therefore, the composite photograph made from this altitude covers a strip of ground
more than six and one-half miles wide. By fl ying at a speed of 100 miles an hour at an altitude
of 30,000 feet, it is possible to include an area of 2300 square miles in an hour's time.
K-3A Automatic Camera (Formerly K-8).
One of the latest developments in aerial photographic equipment is the new single-lens auto­matic
camera recently developed by the Fairchild Aerial Camera Corporation in cooperation with
the Division. This camera, now knokn as the K-3A, has all of the advantages of the present stand­ard
air service K-3 model and in addition is much simpler in operation and requires less work in
making exposures. Operation is entirely automatic; the exposures follow one another automatic­ally
at set intervals upon starting the intervolometer. Warning of each succeeding exposure is
given six seconds in advance by means of small electric signal lamps mounted on the pilot's and
photographer's in strument boards. These lamps remain lighted until the exposure is completed, in­dicating
that the camera should be held level during that operation.
The camera is of the daylight-loading type, with a film capacity for one hundred twenty ex­posures.
The film is carried in a new light-tight. waterproof magazine which may be changed in
about three seconds by substituting an extra magazine previously loaded for the purpose. Three
lenses of short, long and medium foci, respectively, are provided for use with this camera. These
are mounted in separate interchangeable cones for use in three different kinds of photographic work
---large areas (short focus), high altitude (long focus) , an average conditions (medium focus).
Each lens is fitted with a between-lens shutter and uses an interchangeable filter.
The labor-saving feature in this camera is the data recording mechanism. This machine dur­ing
exposure automatically numbers the negatives in series and at the same time records on each
negative the altitude at which the exposure is made, the tilt of the camera and the clay and time of
exposure. Obviously, thi s eliminates the necess ity of compiling such data in flight for subsequent
identification in the laboratory. Thus all data are presented in a permanent and uni form manner
with the possibility of personal error precluded.
New Instrument Projects.
An altimeter of the vertical scale type has b een receiYecl from the Pioneer Instrument Com­pany
for calibration and test. This in strument, A. S. type B-7, has the same range (0-30,000 feet)
as the standard altimeter. Calibration tests were sati sfactory.
T en conventional dial altimeters, range 0-50,000 feet. are on order with the Tavlor Instrument
Company, for sen·ice tests. This firm is also working on four compensated altimeters and two air­plane
meteorographs, the latter to be used in flight performance work.
Preliminary sketches and specifications have been prepared for an improved magnetic type
compass to supersede the present B-3 and B-4 compasses iti service use. The new compass, five of
which will be procured from the Star Compass Co., Dorchester, Massachusetts, will be designated
type B-5. For experimentation there have been received two Campbell-Bennett aperiodic com­passes
from E ngland and one sample magnetic card type compass from the Pioneer Instrument
Company. The latter in strument is of special form for mounting on under surface of wing center
section. The foreign compasses are being service tested on lighter-than-air craft at Scott Field.
26 T E C H N I C A L B U L L E T I N N o. 4 6
Two manufacturers, the General Electric Company and the Pioneer Instrument Company, are
making deliveries on orders for fifteen induction compasses, A. S. Type A-8. Two of these com­passes,
one of each make, were installed in the Douglas world cruiser, the Boston II, for naviga­tion
tests at the Division. In twenty-eight hours of flying already completed, both instruments have
given equally satisfactory performances, and as soon as the tests are completed they will be sent out
for service test.
An investigation is being made in regard to the elimination of rubber tubing between the air­speed
indicator and its head. Experimental installations will be made using 1/ 4 and 3/ 16-inch
tubing.
Flight Indicator Improved.
Few pilots are capable of relying solely upon their sense of balance and direction for main­taining
a course through clouds or fog even though aided by a compass and a lateral inclinometer in­asmuch
as these instruments are fallible under conditions of accelerated flight. Under such concli­tions
the flight indicator becomes of great assistance in that it indicates any deviation of the air­craft
from straight and level flight, undisturbed by accelerations. Hence it serves as an easily ob­served
point of reference independent of the horizon and other landmarks.
Essentially the flight indicator contains three distinct elements which indicate banking, turning.
and pitching. These elements are grouped compactly in a rectangular metal case of the vertical dial
type.
The bank element indicates departures from the apparent vertical about the longitudinal axis
of the aircraft or in other words lateral inclination. It is an inclinometer of the rolling ball type,
in which a steel ball is sealed in a curved glass tu be filled with liquid to clamp its movements. In
level flight or during properly banked turns, the ball remains in the center of the tube, but in
straight flight when one wing tip clips lower than the other it rolls toward the lower side, indicating
that the pilot must move the control column in the opposite direction to correct the condition. Like
other unstabilizecl inclinometers, the ball inclinometer is subject to errors, hut in conjunction with a
turn indicator it aids greatly in maintaining level flight. The reason for this is that when no turn
is taking place as shown by the turn indicator, the ball inclinometer is free from disturbing accelera­tions
and hence gives correct indication.
The turn element indicates the component of turning about a vertical axis; that is to say, devia­tion
to left or right of normal flight. This element is actuated by the precession of an air-driven
gyroscope acting against the tension of a centralizing spring when a turn about a vertical axis oc­curs.
The direction of the turn and the relative rate of turning are indicated by a pointer which
moves to left or right as the aircraft changes its course, the distance the pointer travels being pro­portional
to the rate of ttirning. \i\Then no turn is occurring the/ pointer remains at .the center or
neutral point.
Pitch or longitudinal inclination is indicated hy the pitch element. This comprises a simple
pendulum linked with an air-driven gyroscope. In view of the fact that any simple pendulum in­dicates
the true vertical only under conditions of uni form flight, its indications are unreliable when
affected bv accelerations arising from the pitching and variations in speed of the airplane. Con­sequently
·a gyroscope is employed to overcome the accelerational effect on the pendulum. Pitching
of the aircraft causes the gyroscope to precess. The precessional force thus generated being
greater than the accelerational force acting simultaneously on the pendulum nullifies the latter and
permits the pendulum to give a correct indication of the pitch. As soon as uniform level flight
is resumed along the new path the precessional force ceases, and the pendulum again returns to
the true vertical. thus indicating the angle of glide or climb. The whole system is damped to elimi­nate
disturbing vibrations.
The gyroscopes used in the turn and pitch indicating elements are spun by means of air impinged
upon slots in their peripheries. The air is directed against the gyroscopes thru air jets in the walls
of the case which is partially evacuated during flight by suction produced from a Venturi tube con­nected
with the instrument and mounted in the slipstream.
In order to determine the utility of the flight indicator under actual service conditions several
model 1923 instruments (A. S. Type A-3) were placed on service test. Concensus of opinion as
A IR C R AF T D E V E L O P M E N T 27
expressed in the reports of these tests favored the use of the in strument, particularly in emergencies.
T here were also advanced at that time several well directed criti cisms which may be summarized as
fo llows :
a. The ball .inclinometer was too sensitive and of in sul'ficient range. It was also subj ect to
serious errors under excessive vibration.
b. The pitch indicator was too sensitive and difficult of adjustment.
c. The pitch scale had too many divisions to be ready easily.
d. The valve handles had sharp edges which constituted a menace in event of a crash.
After considerable experimentation the obj ec tionable features were practicall y eliminated. A
study of the ball inclinometer led to the adoption of a ball of greater effi ciency, a tube of better
curvature, ci.ncl a liquid mix ture which provided the necessary clamping effect without becoming too
viscous at low temperatures. T he range of the scale was also increased five degrees on each side
of the zero in order to provide for greater oscillation of the ball in rough weather.
IMPROVED FLIGHT INDICATOR, A. S. TYPE A-4, SHOWING MODIFICATIONS
A. Pitch gyroscope with centrifugal brake. B. Pitch indicator with slotted gyroscope.
Modification "B" was adopted because of its simpler c.onstruction.
The pi tch indicator presented a more difficult problem. The chief trouble with this element
was its supersensitiveness, a condition found to ha ve been caused by the variation in speed 11f the
gyroscope, hence its precessional force, with the changes in speed of the aircraft. Various plans to
hold the speed of the gyro scope constant result ed in the adoption of a centrifugal brake as shown
in modifi cation "A" in the accompanying photograph . This feature not only limited the speed of the
gyroscope sati sfactorily but al so di spensed with th e valve control handl es. An order was then placed
with the Pioneer Instrument Company for two ex perimental in struments incorporating the proposed
changes. T his firm offered an alternative form of constant speed control or slotted gyroscope
which was later incorporated in one of the in struments as shown in modification " B."
In the flight tests conducted by the Division both in struments per formed with equal sati sfac­tion.
The one with the slotted gyroscope, howeve r, was adopted as a tentati ve standard because of
its simpler construction, the in strument using this modification being designated as the A. S. Type
A-4. Ninety-four flight indicators are being reworked by the Pioneer Instrument Company to in­corporate
the above modification.
28 T E C H N I C A L B U L L E T I N N o. 4 6
Experiments to Increase Life of Aircraft Storage Batteries.
Six experimental aircraft storage batteries a re being procured for the purpose of determining
what increase in the life of the battery results fr om the use of heavier separators. The new bat­teries,
which are being manufactured by the Cin cinnati. \Villard and E x ide companies, ;:re of
smaller capacity than the present service type aircraft storage battery. The Cincinnati batteries, the
first to be received, have passed acceptance tests and are now undergoing life test. The other
batteries have not yet been received.
Air Starters for Aircraft Engines.
Two types of air starters are being tested at the Division to determine their adaptability to
aircraft engines. One of these, the Heywood sta rter, manufactured by the Detroit Air Appliance
Company, gave fairly satisfactory operation in ground tests and is now awaiting routine flying tests
tn determine what changes are necessary in service installations. The other model, a Herzmark air
starter, developed several minor troubles in preli min;:ry trials on account of a leaky air p~mp .
Preparations are being made for conducting official performance tests on this sta rter before rep­resentatives
of tlie Navy and Ordnance <lepartments.
Radio Broadcasts.
ln connection with the development of aircraft radio apparatus, the Division has conducted a
series of weekly broadcast tests in collaboration with Station WL \V at Cincinnati. In these tests
the messages were picked up directly from the air plane transmitting set and rebroadcast by the
Cincinnati station.
Model Radio Beacon System.
The radio beacon system now in operation at \ \! right Field was clevelopecl in its present form
by the Signai Corps aircraft radio laboratory stationed at the Division, for use primarily as an ::tic!
to aerial navigation in fog or inclement weather It consists of two crossed loop antennas for trans­mitting
N and A signals in Morse code. In practice a transmitting goniometer permits the shift­ing
of the bisector of the projected angle to any desired position. The N and A signals combine
into a single dash or T along the bisector of the proj ected angle which is the line of flight.
In flying by means of the radio beacon the pilot so directs his course as to hear the T signal
which is received at regular intervals on a stancla rd airplane radio receiving set. This automatically
compensates for errors clue to cross winds which must be corrected by the pilot when navigating by
other known methods.
The model for demonstrating the radio beacon system to student officers consists of a large
map of that section of the United States between Chicago and the Atlantic coast. The transmitting
station is assume9 to be at Chicago, and the cross eel loops for transmitting are represented by two
transparent lines placed at an angle of 120 clegr ees to each other. The course is assumed to be
from Chicago to Philadelphia, and the equi -signal zone corresponding to this course is outlined by
two thin white lines diverging from the transmitting station at Chicago at an angle of one degree
and reaching to the Atlantic coast. At a distance of 250 miles from the beacon, the T zone, which
is represented by white lamps similar to those used on telephone switchboards, is 4-3.18 miles wide.
The N and A zones which in this instance correspond to the areas north and south of the course
-are represented by green and red lamps, respecti ;_,ely.
Inside the map case is located the automatic key with its electric driving motor, together with
a small step-down transformer for reducing the 110-volt lighting current to a suitable voltage for
operating the small telephone switchboard lamps that are used. When the switch in the main line
is closed the motor starts and the automatic key causes the various .colored lamps to be lighted on
the surface of the map. The lamps flash the letters "N" and "A" in Morse code, representing the
area north and south of the course respectively. The white lights along the course represent the
interlocking of the N and A signals and remain Ii ghted during the interval that the red and green
lights are showing.
Short Wave Tests.
Routine flight tests have been made, using sh ort wave receiving and transmitting sets. The re­ceiving
set used in the airplane consisted of a detector and two stages of audio amplification while
AIRCRAFT DEVELOPME NT 29
the ·ground transmitter was of the master oscillator, power amplifier type using a 250-watt tube in
each case. These tests were conducted at a frequency of 8000 KC.
Good signal strength was obtained at a radius of 70 miles, which
it is believed that the signals could be heard at twice that distance.
was noticed when using the standard system of shielding.
POWER PLANTS
Changes in Curtiss V-1400 Engine.
was the limit of the flights, but
Very little ignition disturbance
Development of the V-1400 engine began in 1924 when the Curtiss Aeroplane and Motor
Company was given an order for four experimen ta! engines. Though similar to the Curtiss D-12
model in general design, the new engine has greater displacement and power at less weight clue to
an increase in bore and stroke and to the use of new materials and advanced methods of design.
Upon proving satisfactory for flight the first engines were installed in the 1925 Army and Navy
Curtiss P ulitzer racers. Later four additional engines were constructed for service test in the new
P -2 pursuit airplanes recently delivered to the service by the same manufacturer.
The standard V-1400 engine has a piston dis placement of 1420 cubic inches and a normal rat­ing
of 500 h. p. at 2100 r. p. m., with a compression ratio of 5.5 to 1. Following acceptance tests,
the first engine on the original contract was fitted with high compression pistons, raising the com­pression
ratio to 6.25, to determine its power output and operating characteristics at speeds up to
2600 r. p. m. In these tests which were conduct eel at the Curtiss factory in accordance with the
Division's in structions, the engine developed 620 h. p. at 2500 r. p. m. and operated satisfactorily
at this speed on domestic aviation gasoline without detonation. It is now proposed to conduct a
50-honr endurance test at the Division on a similar engine operating at 2500 r. p. m.
Recent investigation by the Division into the carburetion of the standard V-1400 engine has re­sulted
in improved acceleration. This has been effected by venting the carburetors directly into the
air intake scoop instead of into the air intake chamber of each carburetor as formerly. It was
found that the fuel economy was not improved by using a double air intake in place of the single
air intake used in th~ present standard installation. Experimentation with other proposed modifi­cations
will be continued.
At the beg-inning of the present v<.>ar four en gines of the geared type were ordered. These
engines were designated as model VG-1400. Shortly after placing the order, however, it was de­cided
to increa:ce the bore of the engine 1/4 in ch, thereby raising the piston displacement from
1400 to 1550 cubic inches (actual displacement, 1569 cu. in .) to obtain greater power. This in­crease
in displacement did not necessitate any major changes in design or any appreciable increase
in weight inasmuch as the same cylinder block castings, crankcase, crankshaft, connecting rod bear­ings
;me\ other parts could be used. The designation of the enginr:, however, was changed to model
VG-1550, by which it will hereinafter be referred to.
A comparison of the Curtiss D-12, V-1400 and VG-1550 engmes may be obtained from the
following data:
D-12
Bore .... · ... . ........... ..... ..... . ... . 4.5 in.
Stro.ke ... . .... ...... . .............. . .. o.O in .
Displacement .. .... .... . .. . . .. . ..... .... J 145 cu. in.
Rated horsepower .... ...... .. ..... .. .... 400@2000
Compression ratio .... . ........ ... ....... 5 ~ : 1
Weight, dry .......... .. . ... ..... .. . .. .. 693 lb.
vVeight, per rated horsepower .. .... . . . .... 1.84 lb.
V-1400
4.875 in.
6.25 in.
1420 cu. in.
500@2100
5.5 : 1
r.70 lb.
1.34 lb.
VG-1550
5.125 in.
6.25 in.
1550 cu. in.
525@2100
5.5 : 1
*800 lb.
*l.52
*Estimated, incJuding reduction gear. In the direct drive model, the g uaranteed weight of 700 lb. will g ive a ratio of
1. z 3 lb. per horsepower
According to the revised specifications, the new model VG-1550 engine is required to de­velop
at lea5t 525 h. p. at 2100 r. p. m. , at a weight not exceeding 800 pounds ·as equipped with
propeller reduction gear having ratio of 2 to 1. The first engine will be subjected to a SO-hour
endurance test at the manufacturer's plant, prior to its delivery in July, 1926. At this writing,
another contract has been placed with the same manufacturer for three direct drive engines of
30 T E C H N I C A L B U L L E T I N N o. 4 6
this same design, to be designated model V-1550, for deli very in August, 1926. The advent of the
larger engine of 1550 cubic inches di splacement obviously makes the original V-1400 model more or
less obsolescent.
Inverted Air-Cooled Liberty Engines.
Three in verted air-cooled Liberty engines have been received from the Allison E ngineer­ing
Company, completing a production order awarded last year. The first engine, a direct drive
INVERTED AIR-COOLED EPICYCLIC GEARED LIBERTY ENGINE.
type, received its initial flight trials in the Engineering Division XC0-6 airplane during the Inter­national
Air Races at Mitchel Field last October, and is now undergoing flight tests at the Division.
The second and third engines, received later, we re equipped with Allison type epicyclic propeller
reduction gears, incorporating flexible spring coup lings and Hoffman roller planet bearings. One of
the latter engines has been placed on the dynamometer for calibration and for investigation into the
cooling efficiency with the slower moving propeller required with the reduction gear.
The inverted type air-cooled Liberty engine is designed along the same lines as the fir st ex­perimental
air-cooled upright model developed at the Division. The principal difference is in the
design of the lubrication system to permit inverted operation. This is effected by so arranging
the system that the oil from the crankcase drain s into the camshaft housings from which it is re­turned
to the tank by double scavenging pumps on each housing. A pressure oil pump in stalled in
the crankcase maintains pressure to the bearings. The engines on this order are provided with ro­tary
induction systems.
As this issue goes to press negotiations have been completed with the Alli son Engineering
Company for the construction · of twelve air-cool eel Libertv engines, eight to be of the inverted
A IRCR A FT DEVELOPME N T 31
direct drive type and four of the inverted geared type, to be known as models V-1410 and VG-
1410, respectively. The engines to be applied on this contract have been withdrawn from stores
and shipped to the manufacturer, together with some cylinder pattern equipment, for conversion into
air-cooled types.
The same manufacturer is also engaged in re conditioning and remodeling ten standard water­cooled
Liberty engines for inverted operation, the fir st of which has been tested. T he contract for
this work was awarded under circular proposal, di stributed last October.
The Carn Engine.
In order to investigate further the feasibility of the cam principle as applied to aircraft power
plants, a four-cylinder, air-cooled engine of this type is being procured from the Fairchild-Cami­nez
E ngine Corporation of New York. T his dev elopment is a continuation of the experimentation
initiated at the Division on an experimental engine described in T ech11ical Bulletin No. 42. T his
engine which had a rating of 200 h. p. at 1350 r. p. m. was designed by Mr. Caminez while in the
employ of the Division.
In this type of engine reciprocating motion of the piston is converted into rotary motion of the
drive shaft by means of a cam and roller mechanism which replaces the connecting rod and crank­shaft
in the conventional type of combustion engine. T he cam engine utilizes four cylinder s, or
multiples of four, disposed radially at 90--degree intervals about a double lobed cam on the drive
shaft. The pistons are linked together and actu ate the cam, hence the shaft, by means of rollers
attached to their lower ends. The contour of the cam is such as to cause each piston to make four
strokes every revolution of the drive shaft as against two in the conventional engine. Obviously
this application of the four stroke cycle necessitates high speed operation of the valve mechanism,
which corresponds to double valve operating speed at conventional engine speed.
Requirements for the second experimental engine now under construction on the above men­tioned
order, have been somewhat reduced in or er to determine the feasibility of the cam principle
under high speed operation. Consequently the weight requirements have been modified and the
power rating of the engine reduced to 100 h. p. at 1200 r. p. m.
Packard 2A Engines.
Twenty-five new series 2A engines have been ordered from the Packard Motor Car Com­pany.
Eighteen of these engines, model 2A-2500, which are of the 800-h. p. geared type, will be used
in the new H uff-Daland LB-1 bombardment airplanes now under construction for service test, with
the exception of two engines allotted to the Divis ion fo r dynamometer calibration. Of the seven
smaller size engines, model 2A-1500, ordered under experimental contract, fi ve will be of the geared
type and two of the direct drive type. T hree of the geared engines on thi s order will be equipped
the same as similar engines now being built by this firm for the Navy Department, whereas the
remainder will incorporate several improvements desired by the Division. The new 2A-1500 en­gines
have a power rating of 600 h. p. at 2500 r . p. m., which is considerably higher than the fi rst
experimental engines, series lA.
Development of the 2A engines was in stigated as a result of weaknesses disclosed in endur­ance
tests of the experimental model l A engines at the Division. In one of these tests on a
model l A-1 500 engine, to obtain increased power output at higher than normal operating speed.
crankcase fa ilure occurred at the center main bearing- web. Investigation into the causes of this
failure, together with a consideration of other desirable modifications for higher speed operation,
led the Packard company to redesign the engine, incorporating therein a new crankcase and other
contemplated imp rovements. The modified engines a re now designated as model 2A.
The most important change that di stinguishes the 2A from the lA engine is in the crankcase
design and main bearing construction. T his involves the use of angularly disposed thru-bolts to
unite the cylinder hold-down flanges with the ma in bearing caps as shown on page 32. By this
arrangement explosion loads are taken directly by the thru-bolts, thereby removing all tensile
stresses from the crankcase webs. The slight increase in weight incident to this construction is
32 T E C H N I C A L B U L L E T I N N o. 4 6
offset by the decrease in weight of the new desig n connecting rods which are scaled clown repro­ductions
of the rods developed fo r the larger model l A-2500 engine. T he other changes characteri z­ing
the 2A engine are the improved valve and po rt arrangement whi ch provides more clearance
between the valves and the cylinder bore, and the increase in depth of the water space over the tops
of the cylinders which stiffens the heads and recluces·valve seat deflections. Valve seat conditions have
CRANKCASE AT MAIN BEARtNG IN PACKARD 2A-1500 ENGINE.
(ShowEng Thru -bolt construction)
also been improved by giving new contours to the exhaust cams on the closing side. This retards
acceleration of the cam follower during the clos in g of the exhaust valve, thereby reducing the
pounding of the va lve on the seat. Carburetion of the new 2A-1500 and 2A-2500 engines will be
improved by built-in manifold jackets for exhau st or water heating. The Division is also investi­gating
the possibility of improving the carbureti on of the 2A-2500 engines by the use of a double
carburetor and divided mani fold.
Two Packard l A-1500 engines have been overhauled at the Division for installation in the
Curtiss XNBS-4 night bombardment airplane for performance tests. These engines are equipped
v.,-ith steel-backed bearings, full skirt pi stons and salt-cooled valves. Imp roved per formance of
this airplane is anticipated in view of more favorabl e power-weight ratio of the Packard engine in ­stallation
over the original Liberty engine installation.
Heinrich Radiators.
Following cooling test s on the standard core type radiator on the Boeing PW-9 pursuit air­plane
at the Division, a set of Heinrich plate ty pe radiato rs were procured from the H einrich E n­ginee
ring Corporation, F reeport, New York, for experimental purposes and in stalled on this air­plane
fo r comparative tests. In these tests the H einrich radiator s, without shutter s or other tern-
AIRCRAFT DEVELOPlVIEN T 33
perature controlling device as shown in the illustration, cooled more efficiently, surface for sur­face,
than the standard radiator and in additi on facilitated a gain in speed of approximately five miles
an hour. Although several leaks developed clur ing the test, clue to Yibration of the cooling ele­ments,
it w'as found that these radiators could be repaired as easily as standard radiators and that
the cause of the leaks could be eliminated to a certain extent in future production. It is planned to
install shutters on these radiators and change the cowling to obtain temperature control without
impairing the high speed of the airplane. In view of the encouraging results so far obtained, the
manufacturer has been in structed to prepare desi gns adapting this type of radiator to the 0 -1, 0 -2,
P-1, and P-2 airplanes for further experimentation.
HEINRICH RADIATOR INSTALLATION ON BOEING PW-9 AIRPLANE.
RESEARCH AND EXPERIMENT
RESUME OF ENGINEERING DIYISION
SERIAL REPORTS.
Serial R eports 11wrked 'Wi th all asterisk (*) will
be issued lry the Chief of Air Service as
"A :r Serv ice I11 fo rmatio11 Circulars."
AIRPI,ANE SECTION
Test of Kerber-Boulton Second Experimental Spar. *Serial No. 2620
This report gives the results of static tests on a Kerber-Boulton experimental metal test spar,
second design. This spar was of the \ l\Tarren tru ss type, built up of cluralumin and steel. The
fh:.nges were of duralumin tubes and the web members of steel tubes, having maximum diameters of
20 and 1 inches respectively in the heavier section. The web or diagonal members were joined
at their extremeties to a semi-circular saddle fitting bolted thru the flanges. The encl and strut
point fittings were made of sheet cluralumin, rein forced and riveted together, and bolted to the
flanges in the same manner as the diagonals. The test spar, a 20-foot section, weighed 46.5 pounds.
In the fir st test the spar failed at 15 per cent below the required strength, whereupon it was
rebuilt at a slight increase in weight and again tes tecl. In the second test it proved structurally
· satisfactory, having sustained the designed load at failure.
Test of Thomas-Morse Extruded Duralumin Spar. Serial No. 2623
An extruded duralnmin test spar submitted by the Thomas-Morse Aircraft Corporation
proved structurally satisfactory in static tests conducted at the Division, in which it sustained a load
10 per cent over designed load before failure. The spar was of special design, the test section
measuring 108 inches long and weighing 19.12 pounds. The cross section resembled an "I" beam
with c'irved flanges and had a web thickness of 7 /64 inches. Circular fittings of steel, flanged and
ribbed, were provided at the encl and strut pain ts for attachment purposes.
Views of the spar are appended.
Thomas-Morse DH-4MB Metal Wings. Serial No. 2626
This is a complete report of the static test of a special DH-4BM biplane wing cellule of metal
construction, submitted several months ago by the Thomas-Morse Aircraft Corporation as stated on
page 20, T ech11ical BuJleti11 No. 44. The cellnle consists of four straigN.t panels and an upper center
section, having an overall span of 38.75 feet and chord of 73 inches. The wing structure which
utili zes a T. M. 22 airfoil contour is composed of two ex truded duralumin I -section straight flange
~pa rs with oval section duralumin ribs and steel wire drag bracing. The panels are covered with
fabr ic and braced interplane by steel tube "N" ·struts and i!itreamline wires. The complete cellule
weighs 711 pounds as against 685 pounds for the standard DH-4B cellule.
The cellule proved to be structurually satisfactory, having withstood an overload of 23.5 per
cent in high incidence condition.
Several photographs of the test are appended.
RESEARCH AND EXPERil\fE NT 35
Test of Roche Adjustable Seat No. 1. Serial No. 2624
This report gives an account of the static test of an adjustable seat developed at the Division
fo r use in observation airplanes. The seat, a bucket type, is constructed of sheet duralumin, riveted
together and attached to two parallel upright tubes
which form the main supporting structure. Ad­justment
is provided for by means of a series of
holes in the right support tube, which holes are
engaged by a locking pin actuated by lever and rod
on the side of the seat. Upon releasing the pin
the seat is automatically raised to the desired posi­tion
by means of an ela stic cord hooked to the back
oi the seat.
In the test the seat failed under a load of 1180
pounds, which upon a basis of 198 pounds for oik1t
and parachute is equivalent to a factor of 5.95~ At
a load of 1100 pounds, that is, at a factor of 5.5,
the lower supporting cross tube took a permanent
set, indicating in sufilcient strength in this m~mber
in comparison with that required of the this section
of the fuselage. As a result tubing of heavier
gage was recommended.
Visual Study of Flow Discontinuity of
Cylindrical Camber Airfoils. *Serial No. 2635
This test was made as a supplementary study
in connection with the determination of wall in­terference
in the McCook F ield 5-foot wind tunnel.
In previous wind tunnel investigations it has
been observed that the angle at which the airflow
breaks ,about various thick cylindrical camber
AIRPLANE ADJUSTABLE SEAT (First design) airfoils varies somewhat with changes in speed,
size and turbulence, and by this investigation it was
sought to determine the character of flow cm each side of the critical angle which is unconventional
in airfoils of this type.
The tests were made at the Division in the 14-inch high speed wind tunnel , ilsing a model airfoil
intersected by a steel plate at mid-section , parallel to the line of flow. Air foil and plate were then
coated with a mixture of lampblack and kerosene which under the influence of the air blast formed
chan nel s on the surfaces by which the character of the flow was visualized. The surfaces were
photographed for every hai°f-degree of the angle of attack from 6 to 13 degrees. T he conclusions
reached from a study of the photographs given in this report are of a preliminary nature, how­ever,
pending a study of photographs on other m ore conventional airfoils to be tested in the smoke
chamber.
The report contains 39 photographs in addition to the text.
Test of Model of Huff-Daland XHB-1 Bombardment Airplane. Serial No. 2648
This re])ort gives in detail an account of the wind tunnel test of a 1/ 50 scale model of the
Huff-Daland XHB-1 heavv bombardment airplane now under construction, including a description
of the test. aeroclynamical data and photographs. The test was made in the McCook Field 5-foot
wind tunnel.
Re·Calibration of McCook Field 5-Foot Wind Tunnel with
New Straightener and Other Changes. Serial No. 2636
This report discusses the changes made in the l\1cCook Field 5-foot wind tunnel hst year and
the new calibration constant computed in July, 1925. When the tunnel was constructed in 1922, it
36 T E C H N I C A L B U L L E T I N N o. 4 6
was equipped w!th a honeycomb straightener upstream of the N. P . L. balance and a portable
straightener at the bell mouth and calibrated aga inst a single static plate ori lice placed three feet
forward of the balance. As now modifi ed, the hon eycomb has been removed and the tunnel equipped
with a new intake straightener containing a lar ge number of radial and peripheral vanes and a
new eight-unit static orifice placed upstream of the balance. The new calibration constant is
based upon two mean velocities for speeds around 40 and 120 miles an hour, respectively. The
precision of the results for the speeds tested as based upon a study of flunctuations in readings
and velocity di stribution along a 46-inch diameter is as fo llows:
T he velocity fluctuation in time is plus of minus 3/ 8 of 1 per cent. T his compares with plus or
minus 1.3 per cent in the previous arrangement of the tunnel, and about plus or minus 7 per
cent with neither honeycomb nor straightener. ] t was also found that velocity does not vary
from the mean at any point along the 46-inch traverse by more than plu s or minus 7 / 10 of 1
per cent. T his compares with plus or minus 2. 1 per cent in the previous a rrangement of the
tunnel in which large peaks in the traverse curve were caused by eddies from the edges of the
honeycomb. This velocity di ffe rence would be still less, if it were not for the 21-inch core
of the new straightener. The greatest impact pressure losses along the 46-inch traverse were
observed near the center ; and even with the co re removed, some irregularity still remains in
dynamic head readings.
From the above it is eYident that flow conditions in the rearranged tunnel have been consider­ably
improved by the new straightener and that the turbul ence with ensuing loss of energy, caused
by the presence of the honeycomb, has al so been materially reduced. The new arrangement also
decreases the loss in velocity head to 2.2 per cent as again st 12 per cent with the previous honey­comb
installation.
NEW DUPLEX STRAIGHTENER AT McCOOK FIELD 5-FOOT WIND TUNNEL.
RESEARCH AND EXPERIMENT 37
ARMAMENT SECTION
Test of Mark II Wing Tip Flares. Serial No. 2646
Both ground and flight tests of the modified Mark II wing tip flares, manufactured by the
Ordnance Department, have disclosed that these flares are satisfactory for use on airplanes not
equipped with electric landing lights. In compari son with electric landing lights, the flare gives a
more intense illumination, rendering landings more precise, but has the disadvantage of exposed fire
in event of crash. It was therefore recommended that electric landing lights be retained and in­stalled
on all regular night-flying aircraft, and that the Mark II flare, mounted in a Type E-2 flare
bracket, be adopted as standard equipment for auxiliary purposes on all future ai rplanes.
A view of the Mark II flare installation, installation drawing and the comments of several pilots
and engineers conducting the test are appended.
EQUIPMENT SECTION
Procedure for Installation of Airplane Radio. Serial No. 2629
In this report are given general instructions, accompanied by several diagrams, for the proper
installation of airplane radio apparatus. Before full efficiency of operation can be obtained on
present service types of airplane radio sets, the following conditions must be met: complete metalli z­ing
and bonding of the airplane ; complete and effective shielding of the ignition system and all
related electrical circuits to eliminate undesirable disturbances in the receiving apparatus ; and
proper in stallation of radio s.ets.
Inasmuch as the theory of bonding, metallizing and shielding is comparatively new in aircraft
work, a brief explanation of these subj ects is given in order that in structions will be more clearly
comprehended than if only the procedure itself were outlined. The in structions given herein are of
a general nature in order to embrace all types of airplanes. In dealing with any specific type of air­plane,
definite instructions pertaining to various units will be issued in the detail specifications.
Aircraft SextaJ:.lt Observations. Serial No. 2630
In this report has been brought together some pertinent in formation on the accuracy of the
aircraft sextant in general as well as a statement of the work accompli shed at the Engineering
Division. In discussing astronomic navigation with sextants using a natural horizon and those
using an artificial hori zon, the following conclusions are advanced:
\ i\Tith a sea horizon, a sextant should permit a position line to be found with an average error
of less than 5 miles. A haze hori zon may give a fair accuracy of 10 to 20 miles in summer,
but in autumn or winter it is subject to large errors, clue to the irregularity ..of the upper sur­face
of the haze layer . Cloud hori zons are quite unreliable. \Vith artificial horizons, those of
the bubble type cause a mean error of 25 minutes of arc under average conditions, whereas in
bumpy air the error is much greater. Pendulums and gyroscopes have not shown up well in
the tests. •
The effect of accelerations, brief descriptions of several kinds of aircraft sextants, and a con­cise
account of the use of the sextant in several notable flights are given in the appendices.
A Method of Reducing Sextant Observations. Serial No. 2631
In aircraft navigation by astronomical meth ods. it is essential that the time of reducing sex­tant
observations be decreased to the minimum sin ce the determination of the position of fast-mov­ing
aircraft by the usual method employee\ in sea navigation which requires 20 to 30 minutes would
be of little value. Hence a method of reducing sig-hts. applicable to aircraft use . has been evolved
by the Engineering Division and publish~d for the first tim_e in this report. By this method the
position-line can be drawn within half a minute after taking the sight, the operation involving one
simple interpolation and one substraction.
The method involves precomputation of astronomical tables before flight by a properly qualified
person, the use of which will enable any aviator with only an elementary knowledge of astronomy to
perform a minimum of calculation in the air.
38 T E C H N I C A L B U L L E T I N N o. 4 6
FL YING SECTION
Performance Tests.
T he foll owing reports contain detailed accounts of performance tests conducted by the Army
Air Service E ngineering Di vision at McCook Fie ld.
Serial No. 2621- Comparative Per formance of E lias XNBS-3 and Curtiss XNBS-4 Bom­bardment
Airplanes . using Douglas W orld Crui se P ropellers.
Serial No. 2627- I-J igh Speed of Douglas X0-2 with P ackard l A-1500 Engine.
Serial No. 2650-Per formance of Boeing Pursuit PW-9, equipped with low compression
Curtiss D-1 2 engine and Curti ss-Reed propell er EX-32977-88.
MATERIAL SECTION
Pyroxylin Finishes for Aircraft. *Serial No. 2632
T his report di scloses the results of an investi gation 0f pyroxylin fini shes for use as protecti ve
coatings for aircraf t. These fin ishes have the advantage over conventional spar varnishes, aircra ft.
enamels, and other relatively slow air-drying pain ts, in the compa ratively brief time required for ap­plication,
a factor of considerable importance in expediting production. A li st 0f the recommended
fi ni shes for metal parts, that have shown sati sf actory results after atmospheric exposure for a
period of one yea r, is given, together with in struc tions for their application .
POWER PLANTS
Study of Training Type Engines of 150 h. p. Serial No. 2507
Following recommendations of an Army Air Ser vice tra ining board convened in 1924, that a
study of various types of air-cooled engines of 150 h or ~epowe r be made by the E ngineering Division,
four types were subsequently selected as suitable for primary training purposes. T hese included a
six-cylinder-in-line vertical engine, a seven-cylind er radial engine, a fo ur-cylinder cam engine, and
an eight-cylinder vee engine, whose characteri stics ar e presented in t he report in suffic ient detail for
the airplane designer, the manufacturer , or other interested persons to obtain a clear conception of
what is desired.
Jn addi tion to dimensions, weight, and other engineering data, the report also contains several
drawings showing the general arrangements of the engines recommended.
Calibration of Morehouse Eighty Cubic Inch Engine. Serial No. 2547
This report gives a brief description of the 80-ctthic-inch Morehouse light airplane engine.
scrnnd design, and its per formance characteri stics as calibrated at the E ngineering Division. ~Th e
fir$t engine of this type, a smaller model of 42.4 cubic inches displacement. was built at the Division
for use in dri ving an air blower for inflating ballo nets in lighter -than-air cra ft.
T he second model is a two-cylinder, horizontal opposed, fo ur-cycle, air-cooled engine, having a
bor e and stroke of 3~ and 3% inches, respective !y, and a pi ston displacement of 80.10 cubic in­ches.
It weighs 89.5 pounds and has a rated output of 28 h. p. at a normal speed of 2,500 r. p. m.
and a compression ra tio of 5.10. T he crankca se is of cast aluminum with an oil pump bolted to the
bottom. It supports a two-throw integral forged steel crankshaft on two plain type babbitt-lined
bronze bearings which take both radial and thrust loads. The shaf t is drill ed to permit passage of
oil from the main to the crankpin bearings. The cylinders are of cast iron with integral fin s and
valve seats, so mounted on the crankcase that the lower portion of the barrel is cooled by oil in a
compartment formed by the lower pilot fl anges. E ach cylinder is fi tted with a four-ring aluminum
pi ston which is attached to an H -section fo rged duralumin connecting rod by a fl oating pin ca r ­ried
in a bronze bu shing shrunk in the end of the rod. Both intake and exhaust valves are of the
tulip type and intercha1;geable. T he valves are o perated by adjustable push rods and rocker arms
actuated from a steel camshaft placed parall el to and above the crankshaft. · The propeller hub is
.RESEARCH AND EXPERIMENT 39
keved to the front end of the cranks ha ft and the accessory drive gear to the rear. Lubrication is
effected by· means of a single gear type oil pump mounted upon the rear cover, which supplies oil to
the main crankshaft, idler gear and camshaft bearings. The overflow from a relief valve flows
through a compartment around the cylinder skirts.
MOREHOUSE EIGHTY CUBIC INCH ENGINE.
Induction is supplied by a single Stromberg OX-2 carburetor connected with an oil-jacketted elbow
on the rear cover plate, from which the fuel mixture is conducted by manifolds to the cylinders.
A Scintilla magneto driyen from the rear of the camshaft furnishes ignition , and provision is made
at the rear of the crankshaft for driving a tachometer and attaching a hand-starting gear.
In the calibration test the following performance and weight data were obtained at full
throttle (2500 r.p.m.):
Sea-level brake horsepower ...... .. .. ...... .. .. . . .. ...... .
Sea-level brake mean effective pressure ....... . ......... . .. .
Specific fu el consumption . .... .. ................ . . .... . . .
Total weight, dry .... . ............... ... .......... .. ... .
\ iV eight per normal brake horsepower ...................... .
\ iV eight per cubic inch displacement. . . .................... .
Test of First Experimental Cam Engine.
29.10
115 lb ./ sq. in.
0.513 lb. / h. p./ hr.
89.5 lb.
3.08 lb.
1.119 lb.
Serial No. 2612
Jn this report is summarized the work done at the Di vision on the fir st experimental radial
cam type ai r-cooled engine to determine the endurance and performance characteristics · of this un­conventional
type of construction. The cam engine used in the test incorporated a two-lobed drive
cam mounted on the propeller shaft in place of the customary crank and connecting rod arrange­ment
found in conventional engines. The pistons were fitted with rollers which operated directly
upon the drive earn to produce the turning moment on the shaft. Contact with the cam was main­tained
hy a system ot linkage interconnecting the pistons. (For further reference, a description ot
the first experimental earn engine will be found in Technical Bu!Tetin No. 42).
The arrangement of the cam type engine possesses several advantages over that of conventional
type engine for aircraft propulsion. For instance, the "X" arrangement of the four radial cylinders
affords complete inertia balance, and the double-lo bed earn provides four strokes of the pi ston for
every revolution of the drive shaft, that is, producing twice as many impulses as a conventional en­gine
at a given speed. This gives the effect of a 2 to 1 reduction without the added weight and
40 T E C H N I C A L B U L L E T I N N o. 4 6
complications of gear s. The reduced shaft speed also makes it possible to drive the valve gear
thru earns on the propeller shaft without interme diate gearing. All of these features .result in
simplicity of design and reduction in number of parts required, making an engine of this type
!ess expensive to manufacture than a convention al engine of like power.
Bearing Loads of Model X-4520 Engine for Rating of 1200 B. H.P. at
1500 R.P.M. Serial No. 2617
This investigation was made to determine the probable load s on the crankshaft bearings of the
new experimental 24-cylinder, "X" type, air-cooled Model X-4520 engine, now under construction
by the Allison E ngineering Company, at a lower operating speed. T his report is supplementary to
Serial No. 2508 entitled "Bearing Loads and Str ess Analysis of l\fodel X-4520 E ngine Rated 1200
H.P. at 1800 R. P . '.\1." which was reviewed in T echnical Bulletin No. 44 . Because of the high
bearing loads di sclosed in that investigation, it was desired to determine how much these loads
would be reduced by operating the engine at 1500 r. p. m., assuming the same power.
Square Cell Ribbon Type Radiator Core vs. A. S. Standard
Honeycomb Type Core. Serial No. 2618
These tests were made to determine the rela tive cooling efficiency of two types of racli-ator
cores. the Air Service standard honeycomb type co re and the square cell ribbon type core now used
as standard on DH -4B airplanes, in stalled in two radiators of identical size and cooling area. T he
results disclosed equal cooling efficiency, but in view of certain advantages, such as repai rability and
good flow capacity a fter long service, inherent in the honeycomb type core. it was recommended
that all DH-4B radiators in the future be equipped with t his type of core as made in accordance
with A. S. Drawing 048842-7.
Moments of Inertia of Generator Armatures and Magneto Rotors. Serial No. 2622
In view of the ser ious diffic ulties encountered in driving electric generators and magnetos, clue
to variation in angul ar velocity of the cr ankshaft and rapid acceleration when the engine throttle
is opened. the moments of inert ia for all generat or armatnres atx l magneto rotors used on various
aircra ft engines now in service and under development have been determined and presented in this
report to fac ilitate more accurate calcu]aiions of the strength of drive required for the diffe rent
accessories.
Bearing Loads and Weight Determination for 16-Cylinder "X" Type
Engine Rated at 1000 B. H.P. at 2000 R. P. M. Serial No. 2625
This report presents in general a continuation of the 'studies of aircraft engines of 1000 h. p. or
larger for use in heavy bombardment airplanes, a nd in particluar a determination and analysis of
the probable bearing loads and weight of a proposed 16-cylincler, "X" type air-cooled engine rated
1000 b. h. p. at 2000 r. p. m. T he proposed eng ine, with its 16 cylinder s arranged in four banks,
90 degrees apart, foll ows the same general layout as the l\fodel X-4520 engine described on page 21,
T echnical B ul/cti11 No . 43. T he design calls for a di splacement of 3000 cubic inches.
INVESTIGATION OF MATERIALS.
Duco vs. Pigmented Varnish Dope for Airfoils.
T he relative durability of the present air ser vice eloping scheme in compari son with a doping
scheme using an enamel top coat and a eloping sch eme using pyroxylin pigmented varni shes, such as
Duco, Nitro-Valspar and other new fini shes is un der investigation. T his in vestigation has for its
object the improvement of fini shing coatings for fabrics; fir st, by determining whether a pyroxylin
lacquer which is suitable for fi ni shing wood and metal can also be used for fab ric to give a uni form
color fini sh over the airplane structure; . and second, by determining whether a pyroxylin fini sh
with high gloss can be obtained that will elimin ate the necessity of applying varni sh. Pyroxylin
varni shes have the advantage in that they are more easily cleaned than spar varnishes and can be
applied as a repair or refini shing coat directly over pyroxylin lacquer without removing any of the
material as is now the case when spar varnish is used.
RESEARCH AND EXPERIMENT 41
Solicitation of sample finishes from various paint and elope manufacturers as a result of dis­tributing
samples of pigmented doped fabric with and without addition of spar varnish has met with
ready response. As a result several samples are undergoing laboratory and outdoor exposure tests.
Protective Coatings for Steel.
Ejght months' exposure tests of various kinds of recommended protective coatings for steel
have been recently completed. These coatings which contained various corrosion-resistant materials
had been applied to an experimental steel spar as stated in Technical Bulletin No. 43. The results
of the tests are summarized in the following:
Spar varnish, asphalt paints and pyroxylin primers without top coats failed to withstand the ex­posure
tests, whereas pigmented enamels of both aluminum and yellow varieties, together with
cadmium and zinc plating, survived the tests in good condition. Pyroxylin coatings under doped
fabric also failed, and the steel thereunder is badly rusted, but aluminized enamel coating under
doped fabric is still good.
A report of these tests has been prepared by the Division.
Me talion.
Several samples of Metallon plastic paint have been received from the Air Service military
attache' in England for test. It was stated in the communication that this material is a new kind of
protective coating in use in England.
Metallon consists of what is probably a solution of sodium silicate to which metallic powders
are added just before applying. Since the material has no flowing properties and sets rapidly, ap­plication
is difficult and must be done with a brush. The surface when finished is rough and of
the color of the particular metallic powder used as pigment.
Test specimens, made by coating strips of sheet steel and aluminum with the paint, led to the
following conclusions as a result of the tests :
1. That the application of Metallon paints is a very slow process, and that the finished coating
is extremely rough, thick, and heavy.
2. That two coats of the paint weigh from 1 to 1-1/ 2 ounces per square foot.
3. That the paints, when air dried, are soluble in water.
4. That baking at 212° F. or above makes the film insoluble in water and fairly resistant to
corrosion.
5. That paints are not affected by heat up to at least 500° F.
6. That these paints are not recommended for use, as they are not superior to other types of
protective coatings now used by the Air Service.
Impact Tests for Hickory Used in Tail Skids.
Several tests have been made to determine the limiting impact value for hickory used in the
manufacture of tail skids. It has been found