Technical bulletin no. 42. Development of military aircraft material for United States Army Air Service under supervision of Engineering Division

              AIR SERVICE INFORMATION CIRCULAR
VOLUME V
(AVIATION AND AEROSTATION)
BY DIRECTION OF CHIEF OF AIR SERVICE
FIRST QUARTER - 1925
TECHNICAL BULLETIN
No. 42
NUMBER 484
DEVELOPMENT OF MILITARY AIRCRAFT MATERIAL FOR UNITED STATES
ARMY AIR SERVICE UNDER SUPERVISION OF ENGINEERING DIVISION.
Prepared and Published
By Direction of the Chief of Air Service
and under the supervision of
JOHN F. CURRY, Major, A. S.,
Chief of Engineering Division.
McCook Fie ld 3- 23 -25 -1 M
CONFIDENTIAL
The information contained herein is confidential and therefore
must not be republished, either as a whole or in part, without
express permision of the Chief of Air Service, U. S. Army.
'
I
CONTENTS
AIRCRAFT DEVELOPMENT
AIRPLANES
"XO" Observation Airplane Competition ........ ...... .......... ......................... ........... .. ........... ... · 7
New Curtiss Observation X0-1 (description) ............ . .... .............................. ...................... 10
Boeing and Curtiss Pursuits in Combat ------ ------ -.-··· ---- ---- --··--·· ··· ·······---······ ····· ..................... 14
Production Amphibian on Performance Test-Polar Flight ···- --- -- ---- -----··-- ------ -----·--····· ··· · 14
Bids Received for Heavy Bomber .. ......... ....... ..... ............ .... ···· ····--------- -----······-- ---------····- -- 15
Curtiss XNBS-4 Makes Favorable Showing (description of first article) ...................... 15
First Ambulance Airplane Received (XA-1) ... .......... ...... ................... .... ..... ... ..................... 19
New Training Types Received, Models AT-1 and PT-1..... ........ ............. .... .................... 19
Water Spray Tests on Propeller Tipping ... ... ....... .......... ................................ -------- --· ·····..... 19
Effects of Gunfire on Dural Propeller... ........ .. ............. ............... ................. . ........... ..... . 21
Fnselage Effect on Propeller Efficiency (T-3 Transport) ...................... .......................... 21
AIRSHIPS AND BALLOONS
Highly Mobile Balloon Winch (including history of balloon Winches ) ... ................ ......... 21
Firection of RS-1 Airship Delayed ····· ········--·--···········------------------------ - ............... ............. 27
ARMAMENT
Tests on Tracer Ammunition for Aircraft Use..... ........ ..... ............................................. 28
Aircraft Gunnery Target .... ......... .............................. ............. . __ ___ ............................. .. 29
Gliding Bom.bs ........ ........................ ------· ·········· ····----···- ------ _ ......... ....... ···-············ ----- ----·-··--- ---- 29
EQUIPMENT
Accelerometers for Impact Tests ......................... ....... .. .................................. ................. .... 29
New Aircraft Storage Batteries under Development... ............... ... ....................... ........ 31
Luminosity of Instrument Dials Improved....... ..... ................ ........... .............. ....... ........... ... 32
Developing Time for T-1 Film Shortened ···· ············-- ----- ----------·-- --- ----·--···· · ··-----~-- --··· · · · · --- --- 32
Flash Powder for Night Aerial Photography --····-··-- --------·--·· ······-- ········--------- -- ----·-·---·--- . 32
New Single-Lens Cameras, Models K-7 and K-8............. ........... ... ................... .. 33
Five-Lens Camera Proposed for Aerial Mapping.......... ............... ......................... ....... ... . 33
Night Triangulation with Searchlight Beams........... ... ......... .......... ............... ........ 33
POWER PLANTS
Almen "Barrel" Engine, Model A-4...... ....... ... ...... .... ..... .. .. ...... .. ....... ... ........... .. .............. .. 38
The Experimental "Cam" Engine ____ ___________ ---- -·---·-··-- ·----· .............. --------··········-···· 38
New Curtiss V-1400 Engine Passes Endurance Test .. --- -----···--·-·· -----· ----------······ ... 40
More Packard Engines Ordered --- ---- ------·---- ----- -----· ·····----··-- ····· ···· ··· ....... ........ ----·------·---- 41
RESEARCH AND EXPERIMENT.
RESUME' OF ENGINEERING DIVISION SERIAL REPORTS.
Structural Members Under Combined Axial and Transverse Loads......... .. ... ................... . 42
Study of Fr~nch S. T. Ae' Formula for Load Factors.... ............. ..... .................................... 42
l\Iethod of Computing Horsepower Available for Performance Prediction..................... 42
Loadings for Experimental Wing Spars ..... ......... ....... ....... .............. 43
Flow of Air Around Rotating Cylinder (Flettner's "Buckau" .................... -----·-·-·----- ··· 43
C 0 NT ENT S - (Cont'd)
Predicting Cruising Range of Proposed Airplane .. .. .... ............... ...... ... :............................. 43
Large Capacity Skis ....... ........ .......... ................. .. .... ................................. .... .......... ...... .... ......... 43
Tor sional Test of Curtiss XNBS-4 Fuselage......... .... ... ............. .. ............ ............................... 43
Torsional Test of Curtiss (Martin) NBS-1 Bomber. ...... ... ........... ............ ............. ..... ......... 43
Static Tes ts Conducted at the Engineering Division..... ..... ........................... .......... .... ....... 44
vVind Tunnel Tests ..... ........ .. .. .... ...... . .. . ........ ......... ... ... ... ......... . ..................... ... . . .... 44
Experimentation on Bombardment Canrnon for Airplanes... ... ........ ....... ... .... .... .................. 44
Remedies for Machine Gun Malfunctioning ..... ....... .... .... .. ..... ........ ....... .............................. 44
Porosity of Parachute Fabrics ....... ..... ........ ....... ............................. ..... ....... ......... .... ....... ...... .. 44
"Tasco" Distant-Reading Gasoline Gage ............................ .... ........... ..... .............. ......... .. ..... 45
Take-Off and Landing Characteristics of an Airplane....... ...................................... ........... 45
Control Stick Force Indicator ................ ............ ........ .......... ..... .. ............ ........................... .... 45
Carbon-Coated Paper fo11 Recording Instruments .. .. ..... ..... ... .... ... .... ...... ............. ............... 46
Performance Tests ... ...... .. ................. .... ......... .......... ..... ............ ............. .. ........ .... ....... 46
Heat Treatment of Al-Cu-Fe-Mg (Piston) Alloy. .. ......... ......... ....... ...... ............................. 46
Airplane Wheel and Tire, Size 64xl4.. .......... .............. .. ..... .......... ........ ................ ............ ....... 46
Comparison of Reheated Piston Alloys at Room Temperature.... ... ...... .......... ................... 46
Al -Cu-Si Alloy as Sand-Cast and as Heat-Treated .. .. .. .. .. ... ........ ....... ............ ....... ............ 46
Power Plant Laboratory Standard Test Methods and Computations........... ..................... 47
The Airplane and the Future .. ........... .......... ..... ... .... .... ............ ........ ........ .... .......... ................. 47
P erformance and Carburetor Data on P ackard lA-1500 Engine ........ ... ........................... 47
F ifty-Hour Endurance Test of Inverted Liberty ········· ·;;·· ···· ·· ········ ··· ·········· ····················· ·· 47
Lonerg an; Radiator ............ ................... .. ........ ......... ........ ..... ........ ... .............. ............................ 4"'7
Test of Stromberg Carburetors on Curt'ss D-12 Engine..................... ........ ......................... 48
Carburetion of Wright T-3 Engine with NA-U6T Carburetors..... ..................... .............. 48
Magnesium Alloys as Bearing Materials ········ · ········ ······ · ··· ·· ·· · ················· ···········-~ -- -·· ·· ······· 48
Bearing Loads for Proposed 1200-h. p. Aircraft Engine ........ :.. ... ........ ................... .. ........ 49
l n;:tructions for Reenforcing Liberty Cylinders................................ .... ............... ............... 49
Preliminary P erformance of Packard lA-1500 Engine.............. ..... ....... ... ..... ............... 49
Wright "E" Eng:ne P erformance with NA-U5 and NA-D4 Carburetors... ............... 49
INVESTIGATION OF MATERIALS
Balanced Balloon Fabric .............. ... ............ .. ....... .. .. ... ............ .. ......... ............ .................... .... .
Processed Castor Oil ........................... ... ........ ......... ............ ... ... ... __ ....................... ..... ........ ..... .
Piston · Alloys .................. .... ...... ........... ......... ... .... ....... ..... ....... .... ......... ..... .. ...... ..... .... ......... .... .
Reverse Bending Machine ............. ... ........... .................... ........ .................................... ............ .
Straight-Side Airplan€ Tire and Wheel Development .. .......... ..... ... .. ........ ........ ..... ......... .. .
NEW BOOKS AND DOCUMENTS
49
50
50
50
51
Documents Added to Technical Files during First Quarter, 1925..... ..... .......... ...... ......... 53
Accessions to Engill€ering Division Technical Library during 1924 .. .............. ...... :....... HO
LIST OF ILLUSTRATIONS
Page
Entries in the "XO" Observation Airplane Competition _______ _____ ___ -- --···--·-········----- -- ---- --- -- 6
GeP.eral Arrangement of Wright X0-3 ·· ·- --·--·--- ------------------------- --· --- ·-- -··---·-- ····- --··------- -- ---- --- 9
New Curtiss Observation X0-1 with Packard Engine -··-··--------·-- --- --- --- -------·--··· ·-- ----- -·-· -- --- 11
Side View of Curtiss X0-1. .. ·----- -- ----------- ----------·- ·------------ ---- --··----·· ·--·-------- -- -------·--------- ---- ---·-- -
General Arrangement of Curt!ss X0->1 with Packard lA-1500 Engine ________ ________ __ ______ _
Curtiss Night Bomber XNBS-4--- ------ ----- --·· ····· ·-·------ ---- -···---·--··· ·--------- --- --- -- --····· ·--·----- --­General
Arrangement of Curtiss XNBS-4-------- -- --- --- ---- ---- ------------- -- --- -- ------ ------····-- -- -· -­Effects
of Water: and Ice on Propeller Tipping __ ··-----·-· ··--· ······· --·--·-- --------------·---- ---------
The Highly Mobile Balloon Wiruches, Types A-1 and A-2-- ---------- -·---------···-------------·------ ---·
Curtiss-Reed Duralumin Propeller _. ______. _ .... ______. _____. __ . _______ . _____ . ___. _________________ . . ··-
Early Types of Balloon Winches --· ········-·· -- __ -- ---- ···-···· ···-······-------·--···-······ ···· ·· ·--·- --- -----
Features of the Highly Mobile Balloon Winch __ ___ -------·--··· ····- -------- -----·---·--····---- ---
Erection Views of RS-1 Airship --------- --- --·---------- --- . --· ----------·-------- ·--·--·- --- -- -------·----- ·--·-----·-- -
Armor Plate Pierced by Tracer Ammunit:on
New Combination Tracer and Armor-Piercing Bullet ____ __________ _
Aircraft Gunnery Target ·---· ·--- --- ----- ----- --·------------ -- --- -- --------------------·------ ------ ---·--··----·-·- --
Accelerometer s, First and Second Models ------ -- -- --- --- ---------------- -- ------ ----- '--- -----··------- -·
Diagram showing Spindle Element of Accelerometer ___ _________ ___ _
Proposed Cell Arrangement for A. S. No. 3 Storage Battery _
New Luminous Dials for Am- and Voltmet er s ___ ___ --------------·-·· ··------ ---- -- --
Night Flashlight Photograph of McCook Field
Searchlight Beam Used a s Target in Night Tr ia ngula tion _______ ___ ____ ______________________ ____ _____
60-inch Open Type Searchlight and Cadillac Tr.uck-Iru Operation ___ ______ _·· ····· ·
Alidade and Plane-Table as Used in Night Tri a ngulation ..... ·----------·- -·--··--·-··----·------ ---
Map Showing Location of Searchlights in Night Triangulation Experiments _________ ____ _
Almen "Barrel" Engine, Model A-4 ----- --- --·------------ ------ ------ ------- ·-··--- ·-·------·------···--·-···-- ----------
The Experimental "Cam" Engine --·-- ----- ----- ·------- -·--- -·-----·----- ·-··-·-·---- -- -- ---- ·-· ·----··· ·-- ·-- ------- ---­New
Curtiss Aircraft Engine, Model V-1400__ ___ ---·-· ·· ·····--- -- --- ·-- ---- --·-···· -· ·------ --- -- -----·
Control Stick Forces on DH-4B Under Full Power (chart) ----·- -- ----- ---·--· ··--·---· ·-----
Sectional Drawing Illustrating Airplane Wheel and Tire Development__ ___________ _
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41
45
52
6 T E C H N I C J\ L B U L L E T T ~ N o. 4 2
ENTRIES IN THE .. XO" OBSERVATION AIRPLANE COMPETITION.
(Left) Doug las X0-2 with Packard lA-1500.
(Right) Wright X0-3 w ith Wright T-3.
(Center) Curtiss X0-1 with Packard lA-1500.
(Winner of t he contest)
AIRCRAFT DEVELOPMENT
ON ENGINEERING DIVISION PROGRAM
AIRPLANES
"XO" Observation Airplane Competition.
T he "XO" observation airplane competition was held at McCook F ield from December 20,
1924, to J anuary 23, 1925, for the purpose of selecting a new type of experimental two-seater
observation airplane designed around the Wright T -3, Curtiss D-1 2, L~berty or new Packard
1 A-1500 engine, the new type to be designated model "XO" in accordance with the new Air Service
classification for observation airplanes.
T his contest was won by the Curtiss X0-1 with P ackard engine in competition with two
other airplanes, the Douglas X0-2 (Packard engine) and the -w right X0-3 (Wright engine).
and should not be confused with a previous competi tion. wor: by the Douglas X0-2, for a new
service type of observation airplane to supersede the obsolescent DH-4B in which the Curtiss X0-1.
Douglas X0-2 and several other a irplanes all mount ing Liberty engines participated. (A com­plete
account of the earlier competi tion was publi shed in T echnical Bulletin No. 41) .
T he competing airplanes in the "XO" competition were built in accordance with designs ac­cepted
under Air Service Circular Proposal No. 2453 issued February 5, 1924, to which twelve air­craft
manufacturers responded ( see Page 12, Tec hn ical Bnlletin N o. 39) . Altho four of these de­signs
were accepted under this proposal as being the most desirable, only three sample airplanes
were subsequently built owing to the fact that one manufacturer, the Glenn L. Martin Company,
was then engaged in _production work and for that and other reasons withdrew from fhe compe­tition.
T he three sample airplanes eventually submitted fo r competitive tests were as follows:
*Curtiss X0-1 ( P ackard engine) - Curtiss Aeroplane & Motor Co.
*Douglas X0-2 ( P ackard engine)-The Douglas Company.
\Vright X0-3 (\Vright engine)-Wright Aeronautical Corporation.
The competition was based upon a system of ratings in which a definite number of points was
ao,signed to various characteri stics of the type of airplane desired in order to give manufacturers an
idea of the relati ve importance placed upon these characteristics by the Air Service. T he total num­ber
of points was placed at 145 to avoid fractional distinctions. this maximum number of points
being given to the airplane showing the best qualities by which the others could be rated accordingly.
T his system of ratings was intended to assist manufacturers in developing a type of airplane that
would be satisfactory to the Air Service and at the same time reAect credit upon themselves. To
thi s encl the entire facilities of the Air Service, particularly those of the E ngineering Divi sion, were
placed at the service of all participants.
A Board of fi ve officers having expert knowledge of the requirements was appointed by the
Chief of Air Ser vice to decide upon the relative merits of the three sample airpl anes submjttecl.
After the customary in spection and per £ormance tests by the E ngineering Division, members of the
Board Aight tested each airplane and rated it in accordance with the provisions of the circular
and the Air Ser vice specification for the type.
The findings of the Board which are given in detail on the foll owing page resulted in the
selection of the Curti ss X0-1 as the winner of the competition. This airplane received the high­est
rating, the total number of points being three higher than the required 145, and was conse­quently
purchased by the Government for $70,000 in accordance with the terms of the contest.
T he Douglas X0-2 ranked second . . It received the required total of 145 points and was pur­chased
for $60,000. The third contestant, the VI right X0-3, with a low score of only 79 points
fa iled to meet the performance requirements and was consequent ly eliminated from the competition.
*These smne airplanes equipped with L1:berty engines participated ·i11 the A ir S ervice Competi­tion
/or Observa tion Airpla11es mounting the Liberty engine-see T echuical Bulletin No. 41.
8 T E C H N I C A L B U L L E T I N N 0. 4 ~
FINDINGS IN "XO" COMPETITION.
BASIS OF RA TING. · RELATIVE STANDING.
Clw.racteristfrs . Points
P erformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
High speed at ground--150 m. p. h. . . . . . . . . . . 10
( 1 point for each m. p. h. )
Service ceiling-21,000 feet . . . . . . . . . . . . . . . . 10
( 1 point for each 200 feet)
Climbing Time to 15,000 ft.-20 min.. . . . . . . . J
( 1 point for each minute )
Crui sing Range-450 miles . . . . . . . . . . . . . . . . . 5
( 1 point for each 25 miles over)
( 1 point for each 10 miles under)
Flying Qualities . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Maneuverability and Controllability . . . . . . . . . 10
Landing and Taxi-ing. . . . . . . . . . . . . . . . . . . . . 10
Take off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Power Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Airplane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Ease of Reproduction . . . . . . . . . . . . . . . . . . . . . . . 10
Miscellaneous Features . . . . . . . . . . . . . . . . . . . . . . 50
Safety of crew........... .. .... .. .. . . ..... 10
Vulnerability of cooling system .. .. .. ..... ... 10
Vision . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . 5
Armament in stallation . . . . . . . . . . . . . . . . . . . . . 5
Equipment installation . . . . . . . . . . . . . . . . . . . . . 5
Extra fuel and oil capacity . . . . . . . . . . . . . . . . . 4
Engine starter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Cockpit arrangement . . . . . . . . . . . . . . . . . . . . . . 2
Control mechani sm . . . . . . . . . . . . . . . . . . . . . . . . 2
Stabilizer adjustment . . . . . . . . . . . . . . . . . . . . . . 2
Provision for supercharger . . . . . . . . . . . . . . . . . 2
Grand Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
X0-1
53
14
22
12
5
32
7
10
10
5
18
9
9
6
39
8
10
5
3
3
0
3
1
2
2
2
148
X0-2
32
10
11
6
34
10
9
10
5
20
10
10
10
49
10
10
5
5
5
3
3
2
2
2
2
145
X0-3
9
6
- 3
1
9
6
6
4
13
7
6
6
26
7
0
4
4
3
0
1
2
2
1
2
79
As a result of the observation airplane competitions discussed in both this and the previous issue
of Technical Bulletin, the Army Air Service has placed orders for the following airplanes:
The Douglas Company-75 ai rplanes from X0-2 design
70-Douglas 0-2 airplanes (Liberty engine.)
3-Douglas 0 -7 airplanes (Packard '1.A-1500 engine.)
I-Douglas 0-8 airplane (Inverted Packard l A-15.00 engine.)
I-Douglas 0-9 ai rplane (Geared Packard JA-1500 engine.)
The Curtiss Aeroplane & Motor Company-from X0-1 design
10-Curti ss 0-1 airplanes (Liberty engine. )
Brief desc riptions of the cornpe.ting ai rplanes in the "XO" competition follow on page 10.
~
--- 15'-4'---~..J
4 c1•
~::-- -------
s':....6 '
Airplane
Type
GENERAL DESCRIPTION.
.... Wrig ht X0-3
... Observation Biplane
Status ........ . ....... Experimental
Man.J.iactun~r ____ Wrig ht Aeronautical
Power Plant ...... ... ... .. Wrig ht T-3 Eng ine
Supporting Surface . .450.23 oq. f t.
Gross Wcight ....... ... .. 5,997 lb.
Useful Load ... ........... 1.804 lb.
Wing Loading ..... .... .. 13.31 lb./sq. ft.
Power Loading .... ...... 9.3 lb. / h . p.
Corp.
r--------------4J~ o·--------------.l I'--------- J/'-o"-------.J
.·'
6 :... 4•
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GENERAL ARRANGEMENT OF WRIGHT X 0 -3 WITH WRIGHT T -3 ENGINE.
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10 T E C H N I C A L B lT L L E T I N N o. 4 2
Curtiss X 0-1. This design is a single bay, wire-braced biplane of wood, steel and duralumin
construction. The wings are of unequal span with the outer panels of the larger upper wing
sweeping back from the center section. Interplane bracing is furnished by N-struts. The fu selage
is of riveted duralumin construction supporting a detachable steel tube engine mount, a feature that
permits the in stallation of either the Liberty, new Packard or new Curtiss engine without ap­preciably
changing the balance. The airplane has an overall span of 38 feet and weighs 3857 pounds
with Packard lA-1500 engine installation. (A more detai led description is given in the article be­ginning
at the bottom of this page.)
Do1t.r;las X 0-2. This is the same airplane that won the Air Service competition for Liberty­engined
observation airplanes except that wings of sma ller area ( 370 sq. ft .) and new Packard
1 A-1500 engine are substituted for the original wings ( 4 11 sq. ft.) and Liberty engine used in the
earlier competition. T he wings are of wood, arranged with a single bay squared truss. The
fuselage is of chrome-molybdenum welded steel tubing, with a detachable engine mount-a fea ture
that permits the airplane to be powered with eith er the Liberty or Packard l A-1500 engin e. T he
airplane has been flown for comparati ve tests with both engines and sets of wings.
The fuselage is very roomy, allowing a vari ety of installations in equipment, baggage. etc ..
without change of balance. The fuel supply installation affords unus11al safety in that the main sup­ply
is contained in two droppable tanks. each of 60-gallons capacity, in the lower wing panels on
each side of the fu selage. A small gravity tank of 10 gallons capacity in the upper wing and a 40-
gallon auxiliary tank in the fuselage bring the total tankage up to 170 gall ons. (A detailed de­~
cripti o n of this airplane is given in T echnical Bulleti'll No. 41.)
W ri.r;ht X0-3. The \ i\Tright X0-3 airplane, submitted by the \ iV right Aeronautical Corpora­tion,
is of the double hav. wire-braced biplane type. A Clark "Y" section is used for the wings
which are of conventional wood and fa bric construction thrnout utili zing symmetri cal panels of
equal span and chord with ailerons on both wings. There is no stagger or sweephack. The
fuselage is built of welded steel tube, wire-trussed , with the engine mount removable at the firewall.
A rugged type axleless chassis equipped with 32" x6" wheels is attached to the lower fu selage
longerons giving a tread of 6 ft. 4 in. The tail skid is of the telescoping tube type, an excellent
design. F uel and oil tanks are of aluminum, the former being rubber-covered or crash-proofed
and carried in the fu selage. The power plant incorporates a \ i\T right "T-3" 12-cylinder water­cooled
· engine of 645 h. p. at 2000 r. p. m .. fitted with a three-bladed duralumii1 propeller wi th de­tachable
blades. Cooling is affected by means of wing surface radiators similar to the type used
on the Curti ss racers.
The airplane has an overall span of 45 ft. and a chord of 5 ft. 6 in. and giving a wing a rea of
450.23 sq. ft. The overall length and height are 31 ft. and 19 ft . 7 in .. respectively. \Vith a useful
load of 1804 pounds, the gross weight totals 5,997 pounds. The performance, using a three-hlaclecl
propell er and wing radiator s, is as follows :
High speed at ground . . .. . .. .. . .. .... . . . .. ..... . . . . . .. .
Ini tial rate of climb . ..... . . . .............. .. .. .. . . . .. .
Service cei ling .. ........... .. .... . .... . .. . . . . ....... .
Absolute ceiling . .. . . . . . .... . ... ..... . ..... ... .. .... .. .
146 m. p. h.
11 25 ft. per
18.450 feet
20,200 feet
111111.
After the competition , check tests were run on the X0-3 at the contractor's request to deter­mine
its per formance with two and three-bladed propellers as well as with and without the wing
surface radiator s (the Lamblin strut type radia tors being substituted in the latter case). T hese
tests have been concluded and the airplane return ed to the manu facturer.
New Curtiss Observation X0-1.
The Curtiss X0-1 with Packard engme. the w111ner of the recent Anny .A ir Service "XO"'
competition for a new and advanced type of obser vation airplane. is an experimental two-seater
sample observation airplane designed and built by the Curtiss Aeroplane & fotor Company. Inc ..
Garden City, N. Y. Altho primarily built for this particular competition . this same airplane with
Liberty engine installed participated in an earlier competition for a service type observation air­plane
mounting the Liberty engine, in which it tobk second place ; its eligibility in each competi­tion
being effected thru interchangeability of engine mounts.
The X0-1 airplane is of the single bay, externally braced biplane type. characteri zed hy the
unusual arrangement of the upper wing panels which sweep back quite sharply from the center
A I R C R A FT D E VE 1. 0 P M E N T 11
NEW CURTISS OBSERVATION X0-1 WITH PACKARD lA-15()0 ENGINE.
section producing a very pronounced variable positi ve stagger. the detachable engine section and
tunnel type radiator under the nose, and the location of the cockpits rather close to the tail. Dura­lumin
is employed thruout the entire structure with the exception of the wings which a re of con­\'
entional wood construction. Steel is used only for such high I y stressed parts as brace wires,
control cables. and certain important fittings ancl tubes including the chassis and engine mounting.
Very little pl ywood is used since practically all surfaces are covered with eloped cotton fab ric or
aluminum cowling.
Tn the building of this airplane, the Curti ss Company has introclucecl·a type of construction quite
new in this country, known as ri veted duralumin tube. whose merits are as yet unproven. This
type of construction resulted in reduced structural weight as shown in the fu selage skeleton of this
airplane which weighs only 106 pounds without the engine mount. Such weight-saving permits a
noteworthy increase in climb ancl ceiling. It may be cited i'n this connection that the X0-1
weighed about 300 pounds less than any of its competitors in either competition.
SIDE VIEW OF CURTISS X0-1 .
12 T E C H N I C A L B U L L E T I N N o. 4 2
The wing cellule is a wire braced biplane structure supported by four cabane struts above the
fuselage and single N struts near the tips. The lower wing is built straight across with left and
right panels pin-hinged to the lower fu selage longerons, whereas the larger upper wing has three
panels, the outer sweeping back at a 9° angle from the center producing a variable stagger with the
lower wing which reaches its maximum at the center and its minimum at the tips. E ach panel is
built around two spruce box spars with 8-inch rih spacing in the slipstream and 10-inch spacing
outside. Internal drag bracing is furni shed by cluralumin tube compression struts ar.d diagonai
piano wires. Two extra heavy ribs in the lower wing provide an anchorage for the aileron control
pulleys.
The four ail erons, two of which are inserted in the outer trailing edges of each wing with the
larger set above, are duralumin structures, fabric covered, with angular ribbing resembling a \Var­ren
truss. The control system is actuated by a set of flexible steel cables running from the control
stick over ball-bearing guide pulleys and thru aluminum tubing in the lower wing panels to an out­board
sheave fr om which a short tubular member connects with the lower aileron control mast
thru the covering. Attached to this mast is an upright control strut which actuates the upper aileron.
Continuous pin type hinges with reduced diameter between the bearings attach the ailerons to the
rear wing spqrs, the upper aileron having six bearings and the lower five.
Both vertical and horizontal tail surfaces are of duralwnin construction , fabric covered, with
external streamline wire bracing above and below the stabilizer. The fin mast extends the full
depth of the fuselage affording a rigid support for the balanced rudder which swings from it on four
hinges. The stabilizer is hinged to the fuselage at the rear spar in such a manner that the incidence
may be adjusted from the cockpit by means of chain-driven adjusting screws threading swivel nuts
fastened in the front spar. The brace wires from top of fin and lower longerons are attached to
the rear stabilizer spar in order to be least affected by a change in setting. The elevator, a single
assembly, is fastened to the rear stabilizer spar by seven hinges. The center hinge has a short pin,
but the three outer hinges on each side have continuous pins relieved between the bearing points.
Control is effected by means of flexible steel cal.des actuating the elevator masts on each side of the
centerline.
The fu selage is quite short and narrow, bringing the cockpits in close proximity to each other
and to the tail. This necessitates a stretching out of the equipment in stallation longitudinally
which makes the airplane susceptible to slight changes in balance. The fuel supply is concentrated in
one droppable tank of 119 gallons capacity inside the fuselage. The tank is supported at four cor­ners
in such a manner that the two front supports may be released by the pilot at will thru a
tripping device which severs the connections and allows the tank to fall clear of the 'plane. The
fuselage structure proper is built almost exclusively of riveted duralumin tube incorporating a
system uf tubular longerons rigidly trussed by tubular cross and diagonal members, the whole held
together by wrapped fittings and duralumin rivets. The only steel used is in the two cross rnc~m­bers
between the lower longerons, carrying tension loads of the fl ying wires, the rear member
being a plain tube and the front member a channel section which serves as part of the landing gear.
The engine mount is a separate structure built entirely of welded steel -tube and is detachable
as a unit from the fu selage proper at the firewall by simply removing four taper pins. The mounts
are adaptable for the Liberty, new P ackard lA-1500 or new Curtiss V-1400 engine without ap­preciably
affecting the halance of the airplane. The Liberty engine unit weighs about 39 pounds.
Beneath the fuselage proper is mounted a spl it type axle landing gear similar to that used on
the Curtiss pursuit. It is built of welded steel tu be with the shock absorbing units located in side
the fuselage behind the firewall. These units a re formed of several rubber discs, about one-half
inch thick and four inches in diameter. connected together in such a manner that the impact
energy of landing· is dissipated by compression. The axles are fitted with straight-side wheels
and tires. size 32"x6" . A tubular tail skid of r eenfo rced alloy steel with built-up runner bolted
to ground encl completes the landing equipment.
In thi s a rti cle, propulsion is furni shed by a new Packard Model 1 A-1500 aircraft engine rated
510 h. p. _at 2080 r. p. m. and equipped with a two-bladed drop-forged dural propeller, 9 ft. 8 in.
diameter. The engine is fitted with Stromberg carburetors, type C-3 fuel pump and Splitdorf dual
magneto. Cooling is provided by a tunnel type radiator having 300 sq. ft. of cooling surface,
shuttered with streamline shaped vanes.
The equipment includes one· synchronized gun forward and two fl exible Lewis guns on the
rear ring mount. Provision is made for the installation of camera and radio apparatus.
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Airplane
Type
GENERAL DESCRIPTION.
.. .. ... ... ..... .. Curtiss X0-1
.Observation Biplane
Status ..... .............. .. Experimental
Manufacturer .. .. ...... Curtiss Aeropla ne & M. Corp.
Power Plant .......... .... Packard lA-1 500 Engine
Supporting Surface .. 349.6 sQ. ft.
Gros ~ Weig ht ..... ....... 3,857 lb.
Useful Load .... . . ..... .. 1,580 lb.
Win ~ Loading .......... 11.01 lb. /sq. ft.
Pow'" Loading .. ........ 7 .5G lb. / h. p.
i--~~~~~~~~~20~4··~~~~~~~~---i
GENERAL ARRANGEMENT OF CURTISS X0-1 WITH PACKARD lA-1500 ENGINE.
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14 T E C H N I C A L B U L L E T I N N o. 4 2
In the performance tests, the X0-1 displayed excellent fl ying qualities and remarkably high
performance comparable .in maneuverability to a pursuit type. Due to the fact that the type of
construction used in this airplane was new and untried from a military standpoint, only ten air­planes
were ordered-a quantity sufficient for service test.
CHARACTERISTICS AND PERFORMANCE
(CURTISS X0-1)
Overall span . .......... ... ....... .
Overall length ........... ... .. . .. . .
Overall height . .. .. . ...... ... . ..... .
Gap ...... ... . ... . . ...... ... . .. .. .
Stagger at center (variable) .... .... . .
Stagger at N strut (variable) . .. . . .. . .
Sweepback .......... .. . .. . .... . . . . .
Dihedral ......... . ...... . ...... . . .
Airfoil ........ ... ... ...... ... . .. . .
Total supporting surface .. . .. .. .. ... .
Gross weight . ..... . . .. . . .. . . ...... .
Disposable load .. .... ......... . . .. .
Wing loading per square foot ... .... . .
Power loading per horsepower .... . . . .
H igh speed at ground . ...... .. .... . . .
Initial rate of climb . . ... . . . .. , .. . .. . .
Service ceiling .... . ........ .. ...... .
Absolute cei ling ... . ..... . ...... .. . .
Landing speed (approximate) . .... ... .
Boeing and Curtiss Pursuits in Combat.
Packard
38'
28' 4"
10' 1"
5' 4-:0"
3' 11 %''
2' 3)-4"
90 oo
Clark "Y"
349.6 sq. ft.
3,857 lb.
1,580 lb.
11.01 lb.
7.56 lb.
154.1 111. p. h.
1725 ft. / min.
23 ,400 feet
24.800 feet
62 m. p. h.
Liberty
Same
"
4,075 lh.
] .615 lh.
11.64 lb.
9.45 lb.
152 111. p. h.
J 235 ft. / min.
18,700 feet
20.300 feet
Sarne
In recent combat maneuvers conducted at the Division by pilots of the F irst Pursuit Group.
Selfridge F ield, Michigan, the new improved Curtiss · pursuit. Model XPW-8B, proved quite
superior to either the experimental Boeing pursuit, Model XPvV-9, or the standard Curtiss pursuit,
Model PW-8, in both offensive and defensive combat. This superiority was attri buted to slightly
better performance in climb, speed in climb, and speed in level flight at altitude as well as in the
dive. In individual maneuverability, however, the Boeing proved the best o{ the three.
These maneuvers were prematurely terminated on March 20, 1925, by an accident in which the
XPvV-8B became unmanageable and crashed. The pi lot saved his life with a parachute by cata­pulting
from the 'plane. Subsequent inspection of the wrecked airplane revealed that the accid ent
was caused by failure of right stabili zer adjusting bolt which rendered the horizontal surfaces in­operative.
As a resul t, the design of these parts has been changed on all Curti ss pursuits in the
ser vice to preclude possible accident from this so urce.
Prior to the above maneuvers, the E ngineering Division conducted tests on these airplanes to
determine the effects of firing synchroni zed guns during dives at 30° or more below the hori zontal.
Each airplane was fitted with accelerometers for measuring the accelerations and decelerations clue
to firing.
The Curtiss XP\ i\f-8B, originally flown with the old type straight wings in the 1924 P ulitzer
Race under the designation "XPW -~:\," is a refi nement of the standard Cui"tiss P\ i\f -8 pursuit
airplane utili zing tapered wings and tunnel radiator similar to those used on the Boeing pursuit. It
has been placed in production under the new Air Ser vice type designation for pursuit airplanes,
namely ; the "P-1" and "P-2." according to the kind of engine used, that is, the Curtiss D-12 or
Curti ss V -1400, respectively.
The Boeing pursuit has gone into production with an order of thirty 'planes from the Boein&;
Ai rcraft Company, Seattle, \ i\fashington, some of which will he equipped with supercharger s.
Production Amphibian on Performance Test.-Polar Flight.
A production model Loening amphibian airp lane, Model COA-1, flown to the Engineering
Division in February. is undergoing performance tests. This was the fir st of ten airplanes to he
built by the Loening Aeronautical E ng ineering Company. Three others have been completed :lml
loaned to the ~avy Ai r Service for use in connection with the l\.facM illan polar Right.
A IR CR A F T DE V E L 0 P :;\[ EN T 15
Bids Received for Heavy Bomber.
During January (1925) the Army Air Service solicited bids under Circular Proposal E -2321
for a new type of heavy bombardment airplane to be built in accordance with specifications laid
down by the Engineering Division and suggestions by the Training and \Var Plans Division. Ten
aircraft manufacturers responded, the bids being opened on March 11, 1925, as follows :
Atlantic Aircraft Corporation Kirkham Products Company
C. Ward Hall, Incorporated. Eberhart Steel Products Company
Cox-Klemin Aircraft Company Lawson Aircraft Company
*Huff, Daland & Company, Inc. G. Elias & Bro., Incorporated
The Douglas Company Thomas-Morse Aircraft Company.
Curtiss XNBS-4 Makes Favorable Showing-Description of First Article.
In the tests recently concluded at the E ngineering Di vision, the new Curti ss XN'BS-4 experi­mental
night bomber di splayed a high per forma nce for a twin-engined airplane, the results di s­closing
a marked improvement over the standard NBS-1 night bomber now in service. The only
criticism on the flying qualities cited was the ineffectiveness of the aileron control. which was par­ticularly
evident in rough air near the ground. The tail flexure observed in the initial tri als had
practi cally di sappeared due to reenfo rcement of th is part of the fuselage as discussed on page 10,
Tech11 iral Bulletin l\T o. 40.
The tests were fl own with and without the bomb bay covered, the airplane weighing 13,975
lb. gross, of which 5,93 1 lb. consti tuted useful load. A considerable improvement was observed
with the bomb bay covered as is shown by the following performance compari son :
Open Closed
H igh speed at ground ( m. p. h. ) . .... . . . . ..... ... . ·. . . . . 100.2 103.6
Initial rate of climb (feet per minute) .... . ....... .. .... 529 557
Service ceiling (feet ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.750 11.100
Absolute ceiling (feet ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13,000 13,500
Curti ss-Reed duralumin propellers, diameter 11 ft. 2 in. , were used in both in stances.
The XNBS-4 is a large two Liberty-engined airplane incorporating an externally braced bi­plane
cellule with two-bay outer sections, a long deep fuselage with biplane tail structure, and a
wide spreading landing gear supporting two neatly cowled engine nacelles on the lower inboard
wing sections. The distingui shing feature of the design is the nose of the fu selage which is offset
and glazed to give unobstructed vision for landing. A good idea of the principal characteristics
of the XNBS-4 may be obtained from the following comparison with the Curtiss NBS-1 , the latter
being essentiall y the same in all fundamental characteri stics as its predecessor, the lVfartin Bomber
!\113-2 :
CHAIV\ CTERI STICS /\ ND PEH.FORi\T AN CE.
Overall span .. . . .... ... . . ........ ..... .
Overall length . . . . . . . . ... . . .... . . ... .
Overall height . . . . . . . . . . ... .. .. ... . .. . .
Gap .. . .. . . . . .. . . . ... . ... ... . .. .. .. . . .
Dihedral ( lower wing only) ............. .
Chord ( both wings same) . .. .. . .. . . . . . .. .
Total supporting surface .. .. . .. . . ... . ... .
Landing gear tread ...... . . ... .... . .. .. . .
Total weight .. . . ... . ... ..... .. .. ... . .. .
Useful load ........ ... .. . . . .... . . ... .. .
Wing loading ..... ... . . ... . . ..... . ... . .
High speed at ground .. . . .. . .. . . . .. .. . . .
Initial rate of climb . . . . . ... . .. . .. . . ... . ..
Service ceiling . . . .. . . .. . . .. .. ......... .
Absolute ceiling .. . . . . . . . . ... .... . ... .. .
XNBS-4 NBS-1
90' 2" 7 4' 2"
46' 5" 42' 7)'.'.i"
15' 9" 14' 8"
10' 8' 6"
30
9'
1524.4 sq. ft.
18'
13.795 lb.
5.931 lb.
9.05 lb./sq. ft.
103.6 111. p. h.
557 f t. / min.
11,100 . f t.
13,500 f t.
20
7' 10-15/16"
11 21 sq. ft.
16' 8"
12.064 lb.
4.797.5 lb.
10.76 lb./sq. ft.
98.7 m. p. h.
391 f t./min.
8.500 ft.
10,000 ft.
*,·'/ccord i11.1J to rrcr 11t aww1111 rr111r11 t , the design a'ward and ro 11tract 1c•rrr gi11r11 to this firm.
lG T E C H N I C A L B U L L E T I N N o. 4 2
CURTISS NIGHT BOMBER XNBS-4.
(Two Liberty Engines )
AIRCRAFT DEVELOP MEN T 17
In general construction. the XNBS-4 follows conventional lines, using wood and fabric for the
wings, wire trussed steel tubing for the fuselage, welded steel tube for the nacelle structure, and
metal and fabric for the tail surfaces. The wings are sectionalized as in all large airplanes to facili­tate
folding and replacement, and the lower inboard panels which carry the nacelles are metal
covered top and bottom. The elliptical tips are fitted with Handley-Page balanced type ailerons
occupying about one-third of the wing chord, each aileron being pin-hinged to the rear spar of the
outer panel. The wing curvature conforms to the U SA-27 airfoil section.
l\faximum visibility is the keynote of the fuselage design. This is accomplished by the peculiar
shape of the semi-circular nose, narrower than the fuselage proper, which affords unusual sight­ing
angles for the bomber and greater vision for the pilot thru the glazed offsets than is ordinarily
possible with the straight-side fuselage. In other respects the fuselage follow's the customary ar­rangement
for twin-engined types, namely; front and rear cockpits surmounted with gun rings, a
wide pilot's cockpit directly behind the bomber and a long deep bomb compartment extending full
length of the wing chord. The nose cockpit is of sufficient depth to permit both gunner and bomber
to operate without interference. Its proximity to the pilot provides close liaison. an essential pre­requi
site in present day bombing. There is a wheel control for the pilot.
The engine controls are of the familiar hell crank and push rod type similar to that used in the
NBS-I. The bomb compartment is equipped with an internal rack fitted with adaptors for hang­ing
extra external racks. Removable decking over the top permits the installation of bomb hoi sts
for loading the racks.
The entire empennage is supported as a unit above the fu selage by means of an inverted wire­trussed.
vee strut arrangement in such a manner that the whole structure may be raised or
lowered from the pilot's cockpit. The tail cellule is a thin section biplane structure of 1 to 6
aspect ratio incorporating a vertical twin fin and balanced rudder arrangement mounted between
upper and lower horizontal stabilizers carrying ltn balanced elevators. The lower set of horizontal
surfaces. elevator and stabili zer. has the larger area and projects beyond the fin and rudder on each
side of the fuselage. The control cables are attached to the lower elevator only, actuation of the
upper surface being effected thru an interconnecting strut. The fins are not adj ustahle since they
are attached and externally braced to the lower stabilizer. The vertical surfaces have an effective
area of 62.82 square feet and the horizontal surfaces, 145.07 square feet.
A non-continuous type landing gear spreads out from each lower fu selage longeron to points of
attachment directly under the nacelles, giving a tread of 18 feet between the wheels. Each chassis
is of all steel construction and is equipped with a 44"xl0" wheel and tire and a 5/ 8-inch elastic
cord shock absorber. A short steel skid swivels beneath the tail of the fu selage at which point a
substructure <has been added to prevent injury in case of skid failure. (This latter feature was in­stalled
at the Division and is not shown in the photographs.)
Each nacelle houses a complete power plant unit consisting of a standard Mode! 1921 Lib­erty
engine equipped with two Zenith carburetors. Type C-5 engine driven fuel pump. Delco ignition
and a two-bladed duralum~n propeller, 11' 2" in diameter. The main fuel supply for each engine
is carried in a 152-gallon tank mounted in the nacelle aft of the terne plate firewall. the auxiliary
supply being carried in 17-gallon gravity tank in the upper wing. The entire nacelle is covered
with aluminum cowling in conveniently detachable sections supported by a bulkhead and the welded
tube engine mounting. A free air radiator of Curtiss design is erected against the front cabane strut
which rises above each nacelle at rear of engine. Each radiator measures 53 inches high by 1 6~,0
inches wide giving a frontal area of 4.97 square feet regulated by shutters. The top part of the
radiator forms the expansion tank.
1\ 11 the oil is carried in two 17-gallon tanks h oused inside the lower inboard wing panels a bout
halfway between the nacelles and fuselage.
In addition to the regular bombing equipme.nt which also provides for carrying two 2.000-
pound bombs or one 4,000-pound bomb on external racks attached below the bomb bay. the air­plane
carries an armament of double Lewis flexible machine guns front and rear and a floor gun
under the tail. The equipment also includes night-flying accessories such as wing tip and para­chute
flares beneath the lower wing and electric wiring ior operating wing tip landing and naviga­tion
lights.
The second article has been completed and clelivered to the service at Mitchel Field. thereby
concluding the experimental contract.
--~~~~~~~~~~~~~~~-.xJ~z ·
19 1
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GENERAL DESCRIPTION.
Airpla ne .. ... ...... .... Curtiss XNBS-4
Type ....... ......... ...... Night Bomber Bipla n.,
Status .... .... .... ... ........ Experimental
Manufacturer ____ __ ____ Curtiss Aeroplane & M. Corp.
Power Plant ......... .... Two Liberty Engines
Supporting Surfoce .. 1.524.4 sq. ft .
Gross Weig ht .. . .. ..... 13,795 lb.
U sef ul Loarl ..... ... ...... 5,931 lb.
Wing Loading ..... ..... 9.05 lb. / s q. f t .
Power Loading .. ........ 15.8 lb. / h . p.
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GENERAL ARRANGEMENT OF CURTISS XNBS-4.
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AIRCRAFT DEVELOPME N T 19
First Ambulance Airplane Received (XA-1)
The XA-1 , the first ~xpe rimental airplane to he designed by the Ai r Service exclusively for
ambulance purposes, was designed at the Engineering Division and built by the Cox-Klemin Air­craft
Corporation. This airplane incorporates an externally braced single bay biplane construction
mounting a standard Liberty engine. It has a "hump-backed" fu selage behind the pilot's cockpit
that is deep enough to accommodate a surgeon and two patients in litter s. In view of the excellent
flying qualities displayed in the flight tests recently concluded, there is no doubt but what this air­plane
will be very useful in getting in and out of small fields.
New Training Types Received, Models AT-1 and PT-1.
Two new model training 'planes have been received at the Di vision for in spection and test s,
namely : the Huff-Daland advanced training model AT-1 and the Consolidated primary trai ning
model PT-1. Both models are tandem seaters of biplane construction mounting \ i\T right Model "E''
or "I" engines, developed as a result of competitive ser vice tests conducted by the A rmy Air
Service at Brooks F ield. Texas. They are the fir st airplanes to be built under the new cla ssifica­tion
for training types.
T he AT-1 is a refin ement of the Huff-Daland T\i\T-5 with \Vright "E" 180-h. p . engine. It was
brought to the Division for the purpose of testing the machine gun in stallation in firi ng tests on
the ground and in the air , preparatory to gunnery manem·ers at Kelly F ield. Texas.
The PT-1 is a conversion of the Consolidated T\i\T-3 airplane with sicle-hy-sicle seating arrange­ment
into a tandem seater mounting either the VVright 1\'[odel "E" or "I" engine. U pon comple­tion
of the inspection and tests by the Di vision. these airplanes. two of which were received. were
flown by members of the T rainin g Airplane Board for their commendations as to changes in suc­ceeding
articles.
Water Spray Tests on Propeller Tipping.
A wooden propeller , one blade tipped with Stainl ess iron and the other with l\fone: metal,
was subjected to whirling test in water sp ray with the fo llowing results : both metals resisted water
spray with equal facility but Stainless iron tipping proved quite superior in resisting ice effects.
From the standpoint of manufacture, however, Stainless iron is impracti cal as it is hard to in stall,
especially in the case of a propeller made frcrn soft wood in which case the spring effect of the iron
is sufficient to loosen the screws.
EFFECTS OF WATER AND ICE ON PROPELLER TIPPING.
Monel metal (left) Stainless Iron (right)
20 T E C H N I C A L B U L L E T I N N o. 4 2
THE HIGHLY MOBILE BALLOON WINCHES, TYPES A-1 (above) AND A-2 (below) .
AIRCRAFT DEVEI.OP1\f EN T 21
Effects of Gunfire on Dural Propeller.
In order to study the effect of gunfire on the strength of duralurnin propeller blades, a Curtiss­Reed
propeller was pierced by .30 caliber bullets and then subj ected to whirling test. T he tests
indicated that one or two bullet holes would not seriously weaken the propeller, since actual fa ilure
did not occur until a large number of shots had been fired thru it. T he continued use of an
aluminum alloy propeller after it has been struck by gunfire is not recommended.
CURTISS-REED DURALUMIN PROPELLER.
The Curti ss-Reed propeller, designed by S. Albert Eeed and manufactured hy the Curti ss Aero-­plane
and Motor Company, con~ist s of a single plate of fo rged cluralumin, 1 inch or less in thick­ness,
tapered toward the tips. rnachined and formed to airfoil section, and then twi sted to the proper
pitch . T he blade is mounted with aluminum fill er bosses fitt ing the central twi sted surfaces on the
same style of hub as that used on the ordinary wooden propeller.
Fuselage Effect on Propeller Efficiency (T-3 Transport.)
The effect of fu selage interference on propel !er efficiency is illu strated in a series of interesting
tests conducted at the Division on the L-vV-F T ransport, 1\foc!el T-3. the la st airplane bui lt by the
L-Vl-F E ngineering Company. Inc .. New York, before di scontinuing business.
T he fuselage of this airplane widens out from the pointed nose, partly exposing the engine, to
form a spacious cabin of rectangular shape, 80 in ches by 56 inches at maximum cross section, ac­commodating
six passengers (see views and description on Page 20, T Pcl111ical Bu/frtin No. 39.)
The initial performance as equipped with standard Liberty engine and a 10-1 / 2-foot propeller h<tv­ing
a pitch of 4.34 feet showed a high speed of 94 m. p. h .. a climbing rate of 315 feet per minute.
a ser vice ceiling of 6,150 feet and an absolute ceiling of 9 .000 feet. Another propeller of the same
diameter but designed for turning at a higher speed resulted in :m improvement of 4.7 m. p. h. in
high speed, 500 feet in service ceiling and 1.300 feet in absol11te ceiling but a drop 0f 35 feet per
minute in rate o climb. The general ineffectiveness of these propellers on the transport airplane
was then demonstrated by a comparative test of the same in stal lation on the standard DH-4B.
F rom the in formation thus obtained, the Division designed a propeller of larger diameter for use
wi th a geared engine.
T his special propeller measured 14 feet in diameter and had a pitch of 7.34 feet. In combi­nation
with an epicyclic geared Liberty engine ( 5 : 3 reduction) which had been obtained from the
Navy Air Service, a decided im.p rovernent in performance was obser ved . The results showed in­creases
in speed, ceiling and rate of clirnb as follows: high speed at sea level- 102.7 m. p. h.;
initial rate of climh--550 feet per rninute; service ceiling-10.400 feet; and absolute ceiline·-
12,650 feet. The useful load thruout these tests was the same in each case, namely; 2360 pom~ds.
The landing speed with geared engine and large propeller was observed to be approxi1m1tel _y 45
miles per hour.
F urther te st s on the T-3 tran sport have been made, us111g the E ngineering DiYi sion geared
Liberty with 2 : l reduction gear.
AIRSHIPS AND BALLOONS
Highly Mobile Balloon Winch including History of Balloon Winches.
To meet the exigencies of modern warfare which demand the use of larger and more rapidly
maneuverable observation balloons than heretofore conceived, the Army Air Service has developed
the highly mobile balloon winch upon which the fulfillment of this purpose wholly depends. Two
types of this winch have been designed and built. The fir st model, the Type A-1 , is under o-oing
service tests at Scott F ield , Illinois, whereas the second model, of improved design known a~ the
Type A-2. is still in the experimental stage under preliminary trial and refi nement at the En­gin
eering Division's Lighter-than-Air flight station at \Vilbur \Vright Field.
22 T E C H N I C A L B U L L E T I N N o. 4 2
Before discussing the highly mobile winch, it is thought that a clearer conception and keener
appreciation of its development might be obtained by a brief history of balloon winches from the
early mule-drawn vehicle of 1909 to the highly efficient product of the present clay citing a few im­portant
features and shortcomings of the earlier types and the problems attending their develop­ment.
For convenience in following this development the various types are discussed in chrono­ogical
order.
M ule-Drawn Ba!loo11 W£11ch. The first attempt of the U nited States :Military Establi shment
to design a machine for the purpose of operating observation balloons was the mule-drawn balloon
winch. This project began in 1909 with the purchase of an observation balloon from the German
government for use by the U. S. Army Signal Corps in maneuvers at its school at Fort Omaha,
Nebraska. Since no winch was then available for operating the balloon, the Signal Corps im­mediately
proceeded to design and construct one, and in view of the meager knowledge available at
that :time, the · results achieved in this first experiment a re worthy of note.
This fir st winch was mounted on a frame att:tched to the wheels and axles of a gun caisson.
and was drawn from place to place by mules or horses. The winch proper embodied all the es­sential
elements such as surge drums. storage drum, cable, laying gear, etc. , the power to operate
them being furnished by a four-cylinder air-cooled Franklin engine. At that time. the mule-drawn
winch was considered satisfactory, and as a result it served for several years in maneuvers at Fort
Omaha and also in the East. In 1917 it was di smantled as it had then become incapabl e of oper­ating
modern observation balloons sati sfactorily.
I'-1 Packard Balloon Winch. The Packard balloon winch. Type P-1, was the first design at­tempted
by the Aviation Engineering Department, U. S . . t\rmy Signal Corps, Fort Omaha . Ne­braska.
This design was entirely original , the winch being mounted on a three-ton Packard truck
chassis and ch·iyen by the truck engine thru a power take-off from the transmi ssion. The chief
faults which developed in this winch were insufficie.vt power in high winds, inadequate hauling-in
speed and poor mobility over bad roads.
P-2 Paclmrd Balloon Winch. The second Packard winch. T ype P-2, was substantially the
same as the first model except for some improved mechanical features. 'vVhile this winch was
undergoing tests at Fort Omaha, it came under th e observation of French army officers who had
seen service with balloon squadrons in the World \ Var and who were then serving as in structors
at the U. S. Army Balloon School. These officers recommended the procurement of a French
Delehaye winch for instruction purposes at the school. and in clue time the French winch was re­ceived
and placed under observation of the balloon school official s.
French Delrhaye Winch. This winch, a typi cally French design, was mounted upon a Dele­haye
type 78 chassis, equipped with pneumatic tires, dual on the rear , chain-driven. A maximum
:-peed of 45 m. p. h. was possible over good roaJs. The winch mechanism consisted of two com­plete
windlasses mounted side by side, under the same hou sing. on the rear of the chassis and was
driven by the truck engine. This arrangement was considered the most economical and sati sfac­tory
means of having a balloon winch constantly available for operation. The accessories were
very complete, even to the extent of including electric lights in the winch compartment to facilitate
operation and repair at night. This winch was used to some extent by the French during the \ i\T oriel
War, but it never proved entirely sati sfactory due principa liy to its complicated mechanism. its lia­bility
to breakage and its failure to operate in emergencies. It was later superseded by the Caquot
winch which was used thruout the \ i\Torld War by both American and French forces.
I'rench Caquot U7 inch. The Caquot winch d eri ves its name from Captain Caquot who de­signed
it and is a tribute to his ingenuity in that it far surpassed in adaptability and reliability any
winch heretofore designed. It is still the standard balloon winch in the U. S. Army Air Service.
The American Caquot winch is an exact duplicate of the French model with the exception of the
power phnt which is an American Cunningham engine of 82 horsepower at 2400 r. p. m. whereas
the French winch uses the De Dion Bouton engine of 72 horsepower. The Caquot winch marks
the fir st attempt to design a winch unit operating indepenclentl v of the chassis power plant, a fea­ture
that makes simultaneous operation of the chassis and balloon possible.
The American Caquot winch is mounted on an F. W. D. (four-wheel-drive) three-ton truck
chassis, model 1917. The winch unit is quite satisfactory with the exception of a few undesirable
features of a minor nature. One of its great est limitations is that no chassis of sufficient
mobility has ever been developed for carrying this winch. With the development of larger balloons
now underway, this type will soon become obsolete.
(Upper left) French Caquot Winch.
(Lower left) Tank Winch.
EARLY TYPES OF BALLOON WINCHES.
(Center) American Caquot Winch-Present U. S . Army Standard.
~-
(npper right) N C L Electric Winch.
(Lower right) F-4 Winch (Burton Type)
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24 T E C H N I C A L B U L L E T I ~'J N o. 4 2
F -3 Balloon W1:nch. This development was begun during the late World \Var, the design
being based on recognized limitations of existing winches. The winch mechanism, commonly known
as the Burton type, was mounted on an F. \V. D. three-ton chassis and independently driven by a
four-cylinder \Visconsin engine. The chassis could be driven by the winch engine thru special
gearing. This winch failed to come up to anticipated performance, principally on account of poor
mobility of the chassis. lack of accessibility and failure of mechanical parts used in the indirect
transmission of power.
F-4- Ballo on W in ch. The F -4 winch practically duplicated the earlier F-3 design except that
the power plant was changed to a 120-h. p. six-cylinder \Visconsin engine to increase mobility of the
F . 'vV. D. chassis. The rear axle vvas removed to accommodate the installation of a Holt cater­pillar
axle and tracks. The speed over good roads with the caterpillar arrangement proyecJ in­sufficient,
which coupled with frequent breakage of the treads, finally resulted in the discontinuance
of the design.
NCL E lectric W in ch. This unit was primarily designed for the use of the Navy Depart­ment,
hut it was later turned over to the Army to d etermine its adaptability for fi eld service. The
winch proper was mounted on an F. \V. D. truck chassis and driven hy an independent power
plant. The characteristic features of the design was the unusual arrangement of the maj or units,
the most original of which was the means of supplying, transmitting and controlling the power.
Initial energy was furni shed by means of an eight-cylinder gasoline engine whose flywheel formed
the rotating field of an electric generator. The current which varied with the speed was used to
drive an electric motor direct ly coupled to the winch mechani sm. Such an arrangement eliminated
all clutches and transmi ssions as the power was transmitted magnetically thru a quadrant type con­troller.
Liability to structural and functional failures in electrical circuits, thereby requiring the
services of an experienced electrician to keep it in commission. rendered the NCL winch unsatis­factory
for field service.
Tank Bal/0011 T!fh11cl1. This design originat~d with the E ngineering Department, U. S. Army
Balloon School at Fort Omaha, fr.om a:1 idea based on the perfection of a caterpillar vehicle cap­able
of negotiating any possible condition of terrain . T~1e winch unit proper was of the Burton
type, similar to the earlier mechani sms used in tbe F-3 and F-4 winches. It was mounted on a
caterpillar tractor of an entirely new design prop elled by two Hall-Scott 150-h. p. aircraft engines.
placed side by side and coupled by fri ction clut ches to a common transmission. By means of
gearing it was possible to operate either the chassis or the winch with either or both engines.
Steering was accomplished thru friction clutches fixed to the driving sprockets. one sprocket be­ing
held stationary by a brake while the other rotated under full power. Failure o[ the steering
mechanism was a common occurrence clue to the extremely large size of the dri ving sprocket
clutches and the inadequacy of the brakes. The principal reason which threw this type of winch
into discard, however, was its enforced low speed over hard roads clue to the fact that no tractor
of this type could long withstand the severe ro::i.d shucks when traveling at high speed.
The results 0f these ~eve ral years' experimen ~a ti o n with the foregoing types of balloon winches
coupled with the more recent knowledge gained in the \Vorlcl \Var formed -the basis of a study which
finally culminated in the adoption of definite requirements for an observation balloon winch. The
two principal factors laid clown in these requirem ents were hauling-in speed and an improved means
of tran smitting power to the winch mechanism.
In formulating these requirements, the French Caquot winch hy virtue of its success and ex­tensive
use by the Allied Forces during the late \Var was used as a basis of comparison. vVith 'this
winch, the hauling-in speed of the DeDion Bouton 8-cylincler, 72-h. p. engine pulling a type k
obser vation balloon was 1200 feet per minute in calm air. The maximum cable tension of 2200
pounds was reached in "high gear" at a hauling rate of 800 feet per minute. The desirable speed
for the proposed winch, that is, a speed sufficient to minimize hazard to the balloon from attack
by enemy aircraft, was fixed at the rate of 1600 feet per minute with a cable tension of 2000
pounds. The winch transmission used in the Caquot winch was of the planetary type, supplying
two speeds for hauling in and one for paying- out. Considering high gear as "one," the oiher
speed ratios were 3 to 1 fo r low and 2 to 1 for reverse. U nder ordinary conditions the cable is
paid out by the ascensional force of the balloon but at times it is necessary to use the reverse gear
to force the balloon to the greatest possible altitude. The low gear ratio of this winch was
satisfactory.
A I R C RA F T D EV E L 0 P Al E N T 25
FEATURES OF THE HIGHLY MOBILE BALLOON WINCH.
26 T E C H N I C A L 13 U L L E T I N N o. 4 2
In hauling clown an observation balloon, it is often necesary to shift gears and so vary the
hauling-in speed to accommioclate the vicissitudes of wind velocities at different altitudes which
cause a variation in cable tension clue to the wind forces on the balloon. For instance, at a certain
elevation a high wind WDulcl cause too much resistance for operating with high gear, and perhaps
after hauling clown a few hundred feet in low gear the tension would be greatly decreased allowing
a return to high gear; or these conditions might be reversed necessitating a quick change from
high to low gear to prevent stalling the engine. To shift the gears, the brakes must be applied,
the balloon stopped, the er~gine declutcherl, the gears changed and the starting operation resumed.
This is due to the fact that the upward pull of the balloon on the cable is practically constant and
the instant the power is released, the cable stops and starts paying out. There is no coasting in­terval
during the cleclutching period as in the case with an automobile. It should he understood
that in service the balloon is elevated to the most suitable altitude for observation and is rarely
moyed except to haul clown fot relief of ob~ervers or in event of an enemy attack. In the latter
case the only protection possible is for the balloo1~ to be hauled clown rapidly without stopping
until within safe range of friendly ground defenses. Here lies the great importance of having
the balloon rapidly maneuverable-for which purpose it is solely dependent upon the winch.
Highly M obilc Winches, Type A-1 and A-2. The highly mobile balloon winch represents an
embodiment of the ideals proposed in the foregoing requirements. It is a development of tbe
Engim·ering DiYision of the Army Air Service altho the design originated in the Engineering De­partment
of the U . S. Army Balloon School, Fort Omaha. Nebra ska, prior to its removal to
and incorporation with the Engineering Division at McCook Field.
As previously stated two designs of this winch were constructed, the Type A-1 and the Type
A-2. Each type has a four-wheel-clriYe chassis designed by the E ngineering Division and equipped
with standard QMC (Quartermaster Corps) TTL axles, front and rear, propeller shaft, steering
gear, towing hook and other minor acce<;sories. Each type is powered by a single four-cylinder
150-h. p. Sterling engine which propels both chassis and windlass, independently or simultaneously
as desired. The windlass mechanism is similar to that used in the tank winch. The outstanding
feature is the winch transmission which has two speeds for hauling clown and one reverse for pay­ing
out, the change in gear ratios being effected without shifting into a neutral position. The ad­vantages
accruing from such an arrangement together with the greater amount of power avail­able
place this type of winch in the foremost class, surpas~ing all other existing types both as a
winch and as a mobile unit.
The chassis transmission is of special design, a product of the E ngineering Division. It has
eight speeds forward and two reverse, giving a selection of engine to wheel ratios from 5 :1 to 75 :L
This enables the winch to attain a maximum speed of approximately 50 m. p. h. on good roads
as well as negotiate steep inclines and marshy terrain. In addition, the transmission permits the
hauling-down of the balloon simultaneously with the maneuvering of the vehicle on the ground.
The highly mobile balloon winch, Type A-1, weighs about six tons and has a road clearance
of 16 inches when equipped with 40"x8" pneum:itic tires, both frnnt and rear. The Type A-2
winch differs only slightly in general design and is equipped with dual 40"x8" penurnatic tires
on the rear wheels. Each hub of the front axle is specially designed to accommodate one 40"x8"
tire and one 36"x6" tire, with the latter on the outside. This feature provides increased mobility
over very soft soil such as is encountered in plowed fields, fine sand, snow and the like.
The operating features of the balloon winch mechanism are so simple that no special training
is required of the operator. Since the engine power is transmitted thru a sha 1 t directly to the
windlass transmission, the friction losses are cut to the minimum. This provides adequate power
to haul clown a Caquot observation balloon at the rate of 1600 feet per minute in a twenty-mile
wind agaihst a cable tension in slight excess of 2000 pounds.
Two road tests, one from Dayton, Ohio, to Scott Field, Illinois, and the other from Cleve­land
to Dayton, demonstrated that this type of winch can withstand a sustained speed of 35 miles
per hour- a record that exceeds the road performance of an automotive vehicle of like weight.
\ i\!ith the contemplated change in power plant to a six-cylinder engine of the same power, a sti!!
better performance and greater fuel economy are anticipated.
From all standpoints such as hauling-in capacity, road speed and fuel consumption, maneuver­ability,
mobility and ease 9f operation, the highly mobile balloon winch is without a doubt the
best of all types heretofore developed.
A IR CRAFT DEVELOPM EN T 27
Erection of RS-1 Airship Delayed.
Accidental tearing of a ballonet partition has delayed the erection of the RS-1 airship at
Scott F ield . Illinois, and necessitated defl ation of the envelope for repair s. As a result the design
of all the ballonet curtains has been changed t o allow a freer movement under varying pressures,
and it is hoped that thi s change will preclncle further failure s. This work will be completed about
July l. but the inflation of the envelope will pr0bahly be clelayecl for a month longer pending the
pmifi cation of the helium used in the fi rst infl ation.
ERECTION VIEWS OF RS-1 AIRSHIP.
I. Nose Battens in Position.
3. Fuel Tank and Ballast Bag.
5 . Keel and Infla·tion Net Layout.
2. Mooring Outrigger.
4. Power Car with Liberty Transm !ssion.
6. Bag Being Lowered over Keel.
28 T E C H N I C A L l3 L L E T I N N o. 4 :?
T he building of this air ship which has been und er construction at the Goodyear T ire & Rub­ber
Company for the past two years has necessitated a g reat amount of research by both this com­pany
ancl the Army Air Service to bring it to a successful conclu sion, the benefits of which are not
all utili zed in th is particular air ship but which will be of great n lue for future use. T hat such
extensive research was necessar y on t his well-kn own Ita lian design of seyeral years' standing is
clue to the fact that there was practically no technical in fo rmation available in th is country .
. \ mong the problems which ha Ye been successf ully solved in the construction of th is air ship
are the deYelopment of large duralumin columns of 100.000 pounds compressive strength . a dual
transmi ssion for Liberty engines. a new type of nose cap. and. what are perhaps the largest ever
built. prnpdlers measuring 17;/z feet in diameter. A more detailed description of the design and
spec ial features of th is air ship will be covered in a future arti cle.
ARMAMENT
Tests on Tracer Ammunition for Aircraft Use.
r\ series of interesting experiments has been conducted by the Army Air Service in collabora­tion
with the Ordnance Department on .30 .. 4S and
.SO ca liber tracer ammunition for the purpose
of adapti ng it to aircraft use. It was found ·~ hat
.SO cal. tracer ammuniti on would penetrate armor
plate up to 1'a inch in thi ckness but not armor
plate %-inch thick. In a test again st a square
leak-proof tank. three-fourths full of ga soline. at
a range of SO yards, the sixth tracer bullet set
fire to the tank. H owever. it was necesarv to re­ject
the ammunition because of in sufficie1;t recoil
energy which caused malfunct ioning of the gun
mechanism af ter each shot altho the gun func­tioned
sati sfactorily with .SO caliber armor pierc­ing
and other kind s of an~muniti on. This condi­tion
is not serious but it is thought advisable "lo
modify the tracer ammunition to elimi nate the dif ­ficu
lty. Accordingly, the O rdnance Department
has been requested to check the results obtained
with a view to impro ving the ammuni tion.
Lots of .4S caliber green and red t racer am­muni
tion received from ·che O rdnance Depart­ment
were tested primarily for visibili ty. ·This
ammunition functioned satisfactorily for signal­ling
purposes at night inasmuch as the Army J\ ir
Service has no other use for it. For clay sig­na
lli ng . however . the tracer could not be fo llowed
except for a ver y short di stance fr om the muzzle.
ARMOR PLATE PIERCED BY TRACER AMMUNITION. Conseqnentl y, the Ordnance Department was re-quested
to reduce the muzzle velocity and increase
the amount of illumination in ord er to make the ammunition sati sfactory fo r a ircraft nse. No
information has yet been recei1·ecl that these changes wi ll he carried out.
Comparative tests are in prog ress on .30 tra cer ammuni tion , models 1920. 1922 and 1923. to
determine whi ch kind is most sui table for stand ardi za tion from the standpoint of visibility, in­cend
iary and armor-piercing qualiti es.
NEW COMBINATION TRACER AND ARMOR-PIERCING BULLET,
A I R c R A F T D E v E L 0 p :vl E :\J r 29
Aircraft Gunnery Target.
Targets for aircraft gunnery practice have been standardized at a saving 111 cost of manu­facture
oYer the old method of stretching cloth targets on wooden frames. T he new target,
shown in the illustration, consists of a heavy Manila paper ten-foot square with a large dead black
hull's-eye, 5 feet in diameter, in the center. The target is laced together along the center in
order that it may be easily disassembled, rolled and stored in a 5-foot cardboard tube.
AIRCRAFT GUNNERY TARGET.
Gliding Bombs.
One of the most recently conceived weapons of aerial warfare is the gl iding bomb which may
find an important military application in the aerial barrage of the future. It is proposed to carry
these bombs beneath the wings of an airplane, releasing them at altitudes fron1 one to three miles.
By using some pre-determined gliding angle, it would be possible to release them at a suffic ient
height to strike objectives five to fifteen miles away. Such a barrage could be. directed against
the enemy from above the attacker's own lin es. From experiments conducted at the Engineering
Divi sion on a 50-lb. bomb, it appears that this idea is by no means fantastic.
T he gliding bomb is a winged bomb fitted with stabili zing surfaces to give just enough lateral
and longitudinal stability to cause it to assume the desired gliding angle fo llowing its release from
the airplane. The bomb actually flies: a surprisingly small wing surface is required to carry a 100-
lb. bomb at 150 to 200 ni.iles per hour. The problem is to design the proper type of wing and bal­ancing
surfaces that will in sure the quite unusual degree of inherent stability required to restore the
bomb to a defini te glidin g angle from the drop before it. has attained a sustaining speed in excess
of that at which it was released. In add ition, the design of these surfaces must also prevent undue
banking or spiralling and loss of init ial direction. The problem of stability has been practically
solved to give a reasonable degree of directional stability, and two methods have been ad vanced
for guiding the bomb, one by radio control and the other by automatic rudder control. The latter
system has been worked out by the Division in the form of a comparatively inexpensive and
simple device, operated by the bomb's own ai rspeed, which is believed to be capable of holding the
bom.b fo r a period of ten minutes with in a degr ee or so of its initi ally imparted direction.
T he experiments have been ca rried to a stage requiring more extensive trial s over te rritory
that will permit the winged bomb to glide from high alti tudes for long di stances in any direction.
The bomb is carried on the ordinary wing rack.
EQUIPMENT
Accelerometers for Impact Tests.
Two types of accelerometers have been designed and built by the E ngineering Divi sion for
the purpose of determining dynamic loads on landing gears under impact test. T he fir st experi-
30 T E C H N I C A L B U L L BT I N N o. 4 2
mental model, a maximum indicating type, did not prove entirely sati sfactory for indicating the
maximum acceleration reached clue to the short period of acceleration and the time required for
the plunger of the instrument to stretch the spring to tlw equivalent tension. In the second de­sign,
the error caused by time lag was practically eliminated. Both in struments, however, are in­teresting
and their descriptions follow.
The fir st accelerometer, illustrated herewith, consists of a slotted brass tube, polished on the
in side, in which a weight is suspended on a heli cal spring. A shoulder attached to the weight ex­tends
thru the slot in the tube, carrying a pawl which engages a rack on the outside of the tube.
ACCELEROMETERS
Firs t Mode l (le ft)-Second Model (right)
The pawl is held in contact with the rack by means of a weak sp ring which offers little resistance
to downward movement but prevents upward movement. T hus the weight is held in the lowest
position reached during an acceleration. In use the accelerometer is swung from the landing gear
under test by means of a wire attached to the screw that extends above the top of the tube. T he
calibration is made by removing the cap at the bottom of the tube and hooking the weights on the
plunger . These weights. three in all, represent accelerations of 5, 10 and 15 times gravity, r e­spectively,
which may be read on the scale on the side of the in strument.
The second 1noclel is a compact or modified form of an accelerometer developed by Dr. Zahm.
l\'ational Advisory Committee for Aeronauti cs, fo r recording accelerations encountered in land­ing
airpl anes. The improved in strument record s accelerations on a paper tl1ru a seri es of per­forati
ons made by a set of ten spindles a rranged concentri cally as shown in the accompanying
photograph and sketch. In detail, the spindle element fits into the reamed holes in the top ancl
bottom plates with an easy sliding fit, the movement of the spindle being restri cted by a knurled
knob and collar at its upper encl. The travel of the spindle is so adj usted that when the spindie
is in the clown position, the needle pricks a small hole in the paper clamped to the base plate. A
heli cal spring fitting loosely around the spin lie is restrained by a olla1· which may be Ic,ckecl in
place with ;:i set screw. Compression of the spring is then adjusted by locking the collar at the
desired position on the spindle, or in other words the spindle can be set to record any accelerati on
within the limits of the spring.
A IR CRA F T DE V ELO P MEN T 31
For in stan ce to record an acceleration reaching ten times g ravity, the spring must be so ad­justed
that it compresses just enough to cause the
needle to prick ~.he paper when t he apparent
weight of the spindle is ten times normal. The
effect of any acceleration can be d uplicated by
simply placing a load on top of the spindle equiva-
HOOi<
TOf' I'll/Tc
Sf'R//16
lent to nine t imes the combined weight of the
spindle and collars plu s one-half the weight of
the spring. \ 'Vhen the sp ring is ad jnsted th is
weight will press the needle sufficiently to perfor­ate
the paper. In a similar manner , the other or
remaining spindles may be set to r ecord values
representing 10 to 19 times gravity; an accelera­t
ion of 14 times gravity. for example, beii:g re­corded
by fi ve holes in the paper.
In the impact tests on airplane structu res
such as landing gear s, tail skids, and other shock
absorbing devices as conducted at the Divisioe,
the accelerometer is rigidly fastened at the center
of g ravity of the fuselage and the accelerations
measured for drops from various heights. In this
manner comparative data on shock absorbing
systems and structural strength can be obtained.
New Aircraft Storage Batteries Under Development.
A new arrangement of cells has been tried for the Air Service type AS-3 storage batte ry.
T hi s arrangement gives a battery of +he s;:i.me height and width as the type AS-2 battery but makes
the length one'.-third longer. T he new experimental ;\ S-3 battery has a capacity double that of the
type AS-2 battery, namely, 68 amperes-hours, and weig hs about two pounds more than the stan-
PROPOSED ARRANGEMENT FOR NEW A. S. 3 STORAGE BATTERY.
(Old a r rangement shown in in s ert . )
32 T E C H N I C A L B U L L E T I N N o. 4 2
dard AS-3 battery with the old cell arrangement. If present tests result sati sfa ctoril y, the nev.r
AS-3 battery will replace the present service rnodel for starting purposes.
A new type AS-1 electric storage battery is under development by the A rmy Air Service.
T his battery will have a capacity of 17 ampere-hours or about one-half the capacity of the present
type AS-2 storage battery, and will be used to suppl y current for ignition. heated clothing and
camera motors in in stallations where no starting motors are provided.
Luminosity of Instrument Dials Improved.
Luminous dials of an improved design recommended by the E ngineering Division for nse on
in strument boards in night-flying
airplanes have proved sati sfa c­tory.
The in struments on test
were the l\'[odel ~ 5 4 ammetPr ,
scale 30-0-30 , and the Model 301
voltmeter, scale 0-20, ma nu fac­tured
for the service by the \i\1 es­ton
E lectri cal In strument Com­pany.
The new method of illumi­na
tion whicl1 is shown in the
photographs is recommended for
all sen ·ice meter s on present
order. F ormerly, the dials on
these in struments were illumi­nated
by means of a 111mi1n us
NEW LUMINOUS DIALS FOR AM-AND VOLTMETERS. band placed un derneath the flat
pointer.
Developing Time for T-1 Film Shortened.
T he time required to develop, fi x . wash and dry the roll film used in the Air Ser vice T-1
( tri -lens) camera will be reduced to less than two hours if the new apparatus for handling this
fi lm proves successful. At present it requires a total elapsed time of about six hours to completely
develop one ro11 of fi lm. The new apparatus sh ould handle this amount of film in two hours in a
more simplified manner. In its present form, t he apparatus consists of a monel metal sheet
fixed in the form of a spiral on a revolving sha ft. The roll of film _is threaded into the spiral
whi ch draws the entire film from the developer thru to the dri er without furth er handling.
Flash Powder for Night Aerial Photography.
T he E ngin eering Di vision is experimenting with spec ial fla sh powders for use in night aerial
photography. In preliminary ground tests to determine the amount o f light and speed required to
obtain satisfactory photographs. a picture of McCook F ield was taken with an aerial camera with
wide open lens, mounted on an elevated platform. A SO-pound charge of special magnesium fla sh
powder was exploded at one encl of the field , a nd the speed of the fla sh as recorded by a high
speed motion picture camera was found to be approximately 1/ 25 of a second. T he photograph
made in this experiment depicts very cl early the vari ous hangars and oth er buildings from a
distance approximating 2500 feet as shown in the accompanying illu stration.
NIGHT FLASHLIGHT PHOTOGRAPH OF McCOOK FIELD
{Taken with SO-lb. charge at 2500 feet distance.)
A IR C R A FT D E V E L OPME N f 33
The method of exploding the flash from the air has not yet been determined but it 1s be­lieved
that a small glider released from the photographic airplane might serve thi s purpose.
New Single-Lens Cameras, Models K-7 and K-8.
Two new types of single-lens cameras, Models K -i and K-8 . are under development at the
Division. Model K-7 for high altitude work as mentioned in T echnical Bulletin No. 41 is design­ed
with a focal length of 36 inches for producing negatives on standard K -1 film , size 9,0" by 23".
This camera will be mounted with its optical axis parallel to the longitudinal ax is of the airplane
in such a manner that either oblique or vertical views may be taken thru a pri sm. T he specifications
for the Model K-8 camera provide fo r a single-lens camera fo r use in making reconnaissance
mosaics that are expected to he far superior to the present standard . Both cameras are in the
experimental stage where fin al detail s of the design are still indeterminant.
In connection with single-lens cameras, a large capacity film magazine is being designed for
use with the service cameras, Models K -3 and K-4. T his magazine will find its greatest usefulness
on automatic cameras in single-seater airplanes when large areas or long strips of terrain are to be
photographed.
Five-Lens Camera Proposed for Aerial Mapping.
A fi ve-lens camera based on the same principle as the Bagley tri-lens carnera (A. S. Model
T-1 ) has been proposed. T his arrangement of lenses give one vertical view and four oblique views,
two of the latter providing the desired wide angle. T he oblique lenses will be matched as re­gards
the length into two sets : two transforming printers will therefore be required. In com­pari
son with the T -1 camera, the new camera will be capable of photographing eight times as
much terrain in the direction of flight. Its great est advantages, .however, lie in increased accur­acy
in aerial mapping by having widely separated control points photographed successively at dif­fe
rent angles from two sicles,-a feature that is believed to be the ultimate solution for obtaining
accurate contours.
Night Triangulation with Searchlight Beams.
In view of the success attending experiments of tbe E ngineering Division in laying out the
courses for the Air Races at Wilbur \ iV right Field , last October, it is believed that a new and
rapid method has been found for establi shing primary control in the application of aerial. photo­graphy
to military map-making . This method involves night triangulation using vertical search­light
beams as targets.
H eretofore in military work, ordinary ground-surveying methods have been employed for this
purpose. T hese methods, however, though highly ·standardized and 6atisfactory in many re­spects,
are too slow for emergencies and habitually involve costly delays in the location and erec­tion
of suitable targets. £yen the running of traverse lines, which may be clone expeditiously dur­ing
day or night, often involves too much computation and time in plotting and adjusting sta­tions
to warrant its use in emergencies. On the other hand . the newer method of employing search­light
beams in night triangul ation offers sufficient accuracy combined with two other distinct ad­vantages
not possible by conventional methods, n amely ; mobility and speed . in accompli shment.
T he method is primarily intended as a quick means of obtaining control in aerial surveys where it
would be necessary to tie the work in with adj acent t r iangulation, if such existed.
The efficacy of the new method may be shown by a compari son of the conventional processes
now employed in map-making. The usual methods involve in sequence the obtainment of primary
control poi nts ( the relative location, horizontally and vertically, of a limited number of points
disposed about the perimeter of an area in such a manner t hat a second series of points in greater
number s. known as secondary control points, can be located therefrom), secondary control
points, planimetric data and contours. All of this work is accomplished in the fi eld, whereas the
completion of the processes such as drafting, tying-in with other maps and final reproduction is
clone in the office.
But since aerial photography has become definitely established as practicabl e and its technique
clevelopecl to a satisfactory stage, it is now possible to make complete maps of extended areas from
aerial photographs, performing all of the steps of map-making in the office with the exception of
obtaining primary control and contours. The obtainment of primary control in a quick and ac­curate
manner is the purpose of this newly developed method described herein, whereas the obtain­ment
of contours, according to some commercial produce rs, has already been successfully ac­complished
for small areas from areial photographs.
T E C H N I C A L B U L L E T I N N o. 4 2
Nig ht triangulation as conducted during the se experiments departs from standard practice in
two respects ; fi rst, the vertical beam of a search light is sighted upon as a target , and second, all
angles are graphically recorded on · a plane-table sheet.
T he equipment used (see illustrations) consi sted of two U. S. Army Cadillac trucks carrying
60-inch open type searchlights demountable from the truck proper, and a comp lete generating
unit ; one U. S. Army Mack searchlight truck with generator, carrying a 36-inch closed type
drum searchlight r igidly mounted on the truck frame; one 25"x36" plane-table mounted on a
John son-head tripod and fitted with a grained alu min urn plate in stead of the usual double mounted
paper ; and one telescopic alidade mounted upon a 35-inch base and rigged with dry cell battery
and in candescent lamp to illuminate the r eticule fo r night observation.
SEARCHLIGHT BEAM USED AS TARGET IN NIGHT TRIANGULATION.
AIRCRAFT DEVELOP:'.\1E. T 35
The fi rst step in the experiments which were conducted in the vicinity of Dayton, Ohio. was to
obtain a base line between two known points surveyed by the U. S. Geological Survey, namely:
Simms station in the Dayton quadrangle and Enon station in the Springfield quadrangle, a distance of
9.13 miles (see map). Upon this base, a net of triangulation was constructed.
For the field work, a plane-table was set up at Simms station, and the searchlights spotted at
Enon. New Carlisle and Sulphur Grove stations where their beams were projected vertically into
the sky. The plane-table was oriented to bring the long dimension in the direction of the longest
sight. The included angles "Sulphur Grove-Simms-Enon," "Carli sle-Simms-Enon" and "Sulphur
Grove-Simms-Carlisle" were then plotted direct! y upon the aluminum sheet of the plane-table by
means of a stylus, at least five observations of each angle being recorded. Similar obserYations
were then repeated at each of the stations until the field work was concluded.
60-INCH OPEN TYPE SEARCHLIGHT AND CADILLAC TRUCK-IN OPERATION.
36 T E C H N I C A L B U L L E T I N N o. 4 2
At the office the work was completed by laying out the base line on another sheet of grained
aluminum, size 36"x60", and then transferring the angles by means of beam compasses from the
field sheet to the final sheet, the stations being located by intersection.
Altha this method of obtaining primary central treats the problem as one in plane surveying,
there are no measurable errors at ordinary scale work clue to this treatment provided the total
area under consideration is not over 600 square miles laid nut roughly in the form of a square. Over
a distance of fifty miles, the displacement of a sight from this source is about 10 seconds of arc.
Certain errors are introduced in setting the searchlights. It is possible to accurately locate the
center of the reflector over the station by simply dropping a plumb-line from the lamp core and moY­ing
the sea rchlight until the plumb-bob is directly over the establi shed station. By assumjng that
the axis of the parabolic reflector is perpendicular to the plane of the reflector's edge, the beam
may be pointed to the vertical by simply rotating the refl ector upon its gimbal mounting until its
circular edge is hori zontal. In case the beam is slightly tilted, say at an angle of 0° 15' from the
verti cal, and is sighted from a distance of ten miles at a point on the heam 1.000 feet above the
ground, a displacement of 4.3 feet results, making an er ror of 1/ 12,300 in this distance.
T he slight inaccuracies in adjusting the pla ne-table to the hori zontal produce onl y a negligible
effect in deranging the observed angles and may therefore be disregarded.
Some difficulty was experienced in sighting the center of the searchlight beam. On sights,
3 to 4 miles in length, more trouble was experi en cecl than on ~ig hts 10 to ] 3 miles in length, due to
the brilliancy of the beam at closer range. To get the verti cal wire of the alida<le on the center of
the beam, the telescope was aimed as nearly as possibl e in the proper direction, and the incan­descent
lamp flicked on and off to illuminate the reticule until the position of the alida<le had been
correctly adjusted. The searchlight beams used in these experiments had a divergence of one and
one-ha! f degrees, so that the greatest errors in the field occurred in sighting upon the beam at high
altitude. These errors could be obviated, however, by so selecting the sites to avoid trees, houses
and other obstructions near the occupied points and thus permit sighting near the bottom of the
beam. Errors from this source in a ten-mile sig ht may run as high as 1/10.000.
On the field sheets, the vertexes of the ang les as plci;tted did not habitually fall at the center
of the plane-table, but rather toward the edge, ca using a maximum di splacement of approximately
1.8' on the ground. This represented an error of 1/ 29,300 in a ten-mile sight. '
The greatest errors were introduced in the office work in transferring the data from the fi eld
sheets to the final projection sheet: the magnitude of these errors vary inversely as the scale of
the final projection. For in stance, the diameter of a point made by the stylus upon the field sheet
was about 0.15 mm. which represented , at a sca le of 1/ 16,000. a distance of 7.9 feet. The finest
line practical to draw had a width of 0.075 mm. or 3.85 feet at this scale. In transferring angles
from the field sheet to the final sheet with the beam compasses, distances along the base line could
not be laid off closer than about 0.125 mm.
In checking the results of the experiments in establi shing the five stations shown on the ac­companying
map, namely, Brandt P ike, Sulphur Grove, New Carli sle, Anlo and Valley Pike, there
were no measurable triangles of error at any stat ion except the last where the length of the longest
ALIDADE AND PLANE-TABLE AS USED IN NIGHT TRIANGULATION.
L-Reticule Lamp. S-Sighting Devices. SW-Switch. RH-Rheos tat. R-35" Base.
AIRCRAFT DEVELOPMENT 37
side in the triangle of error amounted to 0.5 mm., representing a distance of 26.5 feet. Checks
were applied to test the accuracy of the relativP. locations of certain station s. In one case the distance
between New Carlisle and Anlo, which were 19,770.0 feet apart and joined by a straight and near­ly
level road, was chained twice, and corrections a pp lied for vertical angles. The discrepancy be­tween
the chained distance and that obtained from the office sheet amounted to 4.7 feet, an indi­cated
error well within the limits with which such distances could be scaled from thi s sheet. This
indicated error was only 1/ 4 ,200, and in view of the excellent intersections obtained on the final
sheet for these two stations is probably an error in scaling di stance rci.ther than in locating the sta­tions
ihemselves. A further check was applied by running a traverse from Simms station to the
Brandt Pike station. The position of the latter as plotted by latitude and departure computed
from this traYerse coincided with the point at the center of the triangle of error at thi s station. In
consideration of the data obtained in these experiments it is beli eved that the locations of points by
night triangulation upon searchlight beams are correct to within 1/ 2,000.
In the application of aerial photography to military map-making of the usual area considered,
that is, the 15-minute quadrangle, the disposition of the primary control depends to some extent
upon the type of camera used to obtain the photographs. If a single-lens camera be used it is de­sirable
to have eight points along the north and south borders of the quadrangle under consideration
(assuming that the flights are being made north and south ), and an additional six points at the
corners of the middle tier (east and west ) of 5-minute quadrangles, thus making a total of twenty­four
points necessary to properly control the area. If a multiple-lens camera be used it is desir­able
to have nine points along the significant border and a minimum of eight additional points
equally spaced about the remaining three sides of the quadrangle.
These primary control points must be located by ground methods of surveying. As already
stated, there are two standard methods available, one requiring ordinary triangulation upim:.;targets
over the points whose location is desired and the other by running a primary traverse- a procedure
involving measurement of distances and angles around the desired area. Besides the objections al­ready
advanced . there is the factor of visibility of targets entering into the fir5t method, which is
often un sati sfactory on account of flat or hilly country or of poor atmospheric conditions. In the
MAP SHOWING LOCATION OF SEARCHLIGHTS IN NIGHT TRIANGULATION EXPERIMENTS.
(These positions mark course of 1924 Air Races near Dayton, Ohio.)
38 T E C H N I C A L B U L L E T I N N o. 4 2
second method, inadvertent errors irrespective of personal exactitude often enter into the measure­ments,
which can only be discovered by re-traversing the entire line, a rather slow and tedious
process.
Herein lie the advantages of night triangula tion upon searchlight beams which afford practical
immunity from poor visibility and the difficulties incident to the selection of suitably located points.
lt is believed that this method can be developed to a satisfactory degree of speed and accuracy
where it will be adopted as the standard method of obtaining primary control for aerial maps.
POWER PLANTS
Almen "Barrel" Engine, Model A-4.
Culminating several years experimentation, the Almen Model A-4 "Barrel" engine, the fourth
engme to be designed and built for the Air Ser vice hy the Almen Motors, Incorporated, Seattle,
ALMEN "BARREL" ENGINE, MODEL A-4.
(425 h . p. at 2000 r. p. m . )
\Vashington, has passed the acceptance tests at the Division. This model incorporates many refine­ments
over the previous ones, the efficacy of which will be determined during the coming months.
In the opinion of the Engineering Division, the Almen engine possesses far-reaching possibilities
that warrant its future development, and if the present tests prove the correctness of these as­sumptions,
this engine will be recommended for production.
The latest Almen engine presents an exceptionally neat appearance. It compactness and small
diameter (about twenty inches) are made possible by the hori zontal arrangement of its eighteen
water-cooled cylinders in opposed position parallel to the drive shaft. Rotation of the drive
shaft is effected by means of a wabbler disk or nutator on the perimeter of which the double-ended
pistons exert a reciprocating action. The adoption of this type of engine for the propulsion of
aircraft will tend to revolutionize present clay con ceptions of aircraft design.
The Experimental "Cam" Engine.
A new and unconventional type of engine for aircraft is under development at the Engineering
Division. In this engine the reciprocating motion of the piston is converted into rotary motion
of the drive shaft by means of a cam and roller mechanism instead of by_ means of the conven­tional
crankshait and connecting rod . Hence, it is termed the "Cam" engine.
AIRC R AFT DEVELOPMENT 39
In principle, the cam engine incorporates four cylinders (or multiples of four ) arranged
radially about a central cam mounted on the engine drive shaft. T he piston of each cylinder is
provided with a roller that acts directly upon and follows the central driving cam, the shape of
which is such that it causes the piston to make four complete strokes during every revolution of
the drive shaft. T he motion of the pistons in opposite cylinders is identical with respect to the axis
of the engine, thereby maintaining balanced inertia forces in the plane of motion. This is an ad­vantage
in that no counterweighting or other means of balancing are required as in the conven­tional
radial engine.
The possibilities of the radial cam engine may be illustrated by a comparison with rhe con­ventional
air-cooled radial type of like horsepower. At present, the most advanced design of con­ventional
crank type air-cooled engine capable of developing 400 h. p. at an efficient propeller speed
is a 9-cylinder radial engine weighing about 700 pounds and having an overall diameter of 49 inches.
\Vith sufficient development it appears possible to build an 8-cylinder cam type engine, less than 40
inches in overall diameter, capable of delivering 400 h. p. at 1500 r. p. m. of the drive shaft at a
weight of about 530 pounds. In other words, in comparison with the conventional crank type
radial engine of 400 h. p., a cam type engine of like output would be 25 per cent lighter and have
about one-third less frontal area. From the standpoint of low weight and minimum frontal area .
two criteria of advanced aircraft engine design, the superiority of the cam type engine is apparent.
After an analytical study of the engineering principles in volved in this unusual type of engine.
the Engineering Division constructed at slight expense an experimental model to test the cam
mechanism without paying any particular attenti on to minimum weight or diameter. The experi­mental
engine which is shown herewith weighs about 405 pounds, is 40 inches in diameter, and is
rated 200 h. p. at 1350 r. p. m. and 220 h. p. at 1500 r . p. m. It is a short stroke, four-cylinder
THE EXPERIMENT AL "CAM" ENGINE.
(200 h . p. at 1350 r . p. m.)
40 T E C H N I C A L B U L L E T I N N o. 4 2
air-cooled radial engine with the cylinders set at 90-degree intervals around the drive shaft on
which a double-lobed drive cam is mounted. The pistons are linked about this central cam in such
a manner that the roller in the lower end of the piston is made to ride the cam contour. Since in
the cam engin e each piston ma kes four strokes p er revolution in stead of two as in the conventional
crank engine-and consequently the number of power impulses per revolution is likewise doubled
- a large bore cylinder w:ith comparatively short stroke is used in order to obtain sufficient valve
area to enable the cylinder to function effici ently at 1500 r. p. rn ., the desirable speed for a medium
sized engine of this type, which speed corresponds to 3000 r. p. rn . in the conventional engine.
T he characteristics of the experimental "Cam" engine built by the Division are as follows:
Type . . '. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Air-cooled radial
Cylinders . .. .. .. .. . : . . .. . .. : . . . . . . . . . . . . . . . . . . . . . Four, radially opposed
Bore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYs"
Stroke ... . ...... ....... .. .. _. . . . . . . . . . . . . . . . . . . . . . 4 0 "
Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 cubic inches
Compression ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 :1
Rated horsepower .. ... .............. ·. . . . . . . . . . . . . . 200 at 1350 r. p. rn.
Overall diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 inches
F rontal area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 square feet
Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 pounds
VI/ eight per maximum rated hor sepower . . . . . . . . . . . . . . . 1.84 pounds
Advantages of the earn type engine over the crank type air-cooled radial engine may be sum­mari
zed as fo llows : lighter weight and smaller fr ontal area per hor sepower, full power at lower
propeller speed giving the equivalent of a 2 to 1 propeller reduction gear, lower cost of manufac­ture
and maintenance due to fewer and simpler parts, perfect inertia balance and absence of critical
drive shaft speeds and ability to p rovide adequa te ball or ro ller bearings at all important bearings.
Due to the fact that the val ve mechani sm of the cam type engine must operate at a high speed
equivalent to 3000 r. p. rn. of the conventional crank engine, and that the push-rod type of valve
operating mechani sm employed in present aircra ft radial engines operates sati sfactoril y only up to
approximately 2400 r. p. in. conventional speed, it will be necessary to perfect a suitabl e val ve
mechani sm for thi s engine, a problem that should offer no in surmountable di fficulties.
New Curtiss V-1400 Engine Passes Endurance Test.
T he fir st Curtiss Model V-1400 aircraft eng ine, eight of which are being developed for the
Air Service by the , Curtiss Aeroplane and Motor Company, Inc. , under experimental contracts, has
successfuJly passed the standard SO-hour endurance test at the contractor's plant at Buffalo , N. Y ..
thereby demonstrating its suitability for flight se rvice.
T he new V-1400 which follows the Curtiss Model D-12 in general design is a 12-cylinder, 60°
vee type water-cooled engine having a normal rating of 500 h. p. at 2100 r. p. m. The bore and
stroke, 4-7/8 by 6-1 / 4 inches respecti vely, give a total piston di splacement of 1400 cubic inches.
T he engine is equipped with two Stromberg NA-Y6 ca rburetors and an induction system suitable
for supercharger operation. P rovision is made for t,he in stallation and operation of the latest
approved accessories ~ncluding an electric genera tor , Bijur electric starter with hand-crank attach­ment,
tachometer, and Air Service Type C-5 or Curtiss Triplex fuel pump. Ignition is optional
with either a Delco battery-generator system or a Splitdorf dual magneto in stallation. T he weight
of the fir st engine is well below the 700-pound lini it specifi ed in the contract, clue to the applica­tion
of recent developments in metals and advanced engineering p ractice.
In general construction the new engine di ffe rs from the D-12 model in the following respects:
the cylinder sleeves have open ends in stead of close<;l/ ones as in the D-12 and are screwed into an
aluminum en bloc head which carries the alun'i'inum-bronze valve seats. The carnshatt dri ve has
been changed to fun ction by means of a spur idler gear and shaft carrying bevel drive gear s. The
camshaft bearing studs in the head casting have been extended in order to provide attachment
for the cylinder head cover , giving the engine a cleaner appearance. T his has been furth er en­hanced
by cutting off the exhaust pipe mounting pad near ly Vertical to reduce weight and head
resistance, and by eliminating one mounting lug on each side of the crankcase near the propeller
end. The propeller hub is now made integral, with the flange splined directly on the shaft and
held in place by a nut threaded to the cranksha ft. Two other departures from the D-12 design
involve changes in the ignition and lubricating systerns- one involves the substitution of either a
battery-generator ignition or a dual magneto ignition in place of the two magnetos formerly used,
A I RCRAFT DEVELOPMENT 41
and the other , the connection of the oil scavenging pumps in series in stead of in parallel to eliminate
foam from oil tank and cooler.
All accessories and gear trains of the engine are driven thru an Allison spring coupling built
into the main drive gear on the crankshaft. Two optional drives for the tachometer are provided
thru helical gears on the camshaft drive shaf ts. T he fuel pump . d rive is the .s ame as on the D-1 2
engme.
NEW CURTISS AIRCRAFT ENGINE, MODEL V-1400.
(500 h . p . at 2100 r . p . m.)
T hruout the SO-hour test at the contractor's plant the engine ran smoothly, even more so than
the D-1 2 on similar test, giving good performance wi th very sati sfactory fuel and oil consumption.
\tVhat failures did occur were mostly of the mino r nature such as malfunctioning of the ignition
system and failure of the wa ter pump sha ft whi ch was made of stainless steel. T here were no
valve spring failur es, indicating that the use of ri ght-hand outside and lef t-hand inside coils is
satisfactory. The average consumption of fuel and oil was below the cont ract limit, being 0.490
pounds per brake horsepower hour for fuel and 0.018 pounds per brake horsepower hour fo r oil
as agai nst the specified limits of 0.530 and 0.025 pounds, respectively. T he diffe rence in oil tem­perature
between inlet and outlet varied only 12° to 14° F.
Upon completion of the endurance test, the first experimental engine was retainer! hy the
Curti ss Company for further tests with high compression pistons of 6.25: l ratio to obtain power
curve up to 2600 r. p. rn . in accordance with in structions from the Division.
More Packard Engines Ordered.
E ight improved P ackard Model l A-1 500 air craft engines have been ordered from the Packard
l\Iotor Car Company, Detroit , Michigan, by the A rmy Air Service. Three of these w111 be
standard upright engines, three geared and two in verted. T he Model l A-1 500 engine has been
redesigned to eliminate the undersirable features found in the three experimental engines cle­liver.
ed on t~1e first contract. T he improved design gives promise of developing into a sati sfactory
service engme.
In the larger 800-h. p. size, three Packard Model l A-2500 engi nes have been ordered in addi­tion
to the three already built on experimental contract. T hese engines ar e all of the geared type,
being equipped with Alli son 2 to l reduction gear, and will weigh about 1300 pounds or abou1
200 pounds heavier than the standard engine. T he new engines will inco rporate several improve­men
ts over the exper imental models, chief among which will be the modified valve ho u si 1~gs, the
larger oil lines and an improved crankcase. The geared engine will be the standard in stallation in
the new XLB-1 light bomber recently completed by th e H uff-Da lancl Company.
RESEARCH AND EXPERIMENT
I
RESUME OF ENGINEERING DIVISION
SERIAL REPORTS.
Serial Reports marked with an astcris!? (*) will
br issurd by tire Chief of Air S ervice as
"Air Service I 11f ormatiou Circulars."
AIRPLANE SECTION.
Structural Members Under Combined Axial and
Transverse Loads. *Serial No. 2400. Section II
Section I of this report referred to in Teclruical Bulletin No. 40 as covering the theoretical
μhases of the derivation of Air Service formulas used in the computation of stresses in structural
members subjected to combined axial and transverse loads has already been published as an Air
Service Information Circular (No. 493). Section II herein discussed continues with a verifica­tion
of these formulas as demonstrated in a series of tests on small spruce struts loaded axially be­tween
knife-edges with a concentrated load applied at mid-span. Each section of the report is self­contained,
the second being divided as follows:
Part III- Tests of pin-ended axially loaded struts.
Appendix 2-Test of E ul er struts.
Appendix 3- Comparison of practical and ideal columns.
Appendix 4- Graphic methods for moments and deflections.
The results of a second series of tests on airplane trusses, one-half actual size, whose chords
were subjected to a combination of axial and lateral loads exactly simulating those in an airplane
lift truss will be published as Part IV-Section III of this report- as soon as definite conclusions
have been reached.
Study of French S. T. Ae' Formula for Load Factors. *Serial No. 2441
A study to compare the load factors for wing design as obtaineJ from the French S. T. Ae'
fo rmula with those used by the Air Service with a view to adopting the French method or one
based upon a similar theory disclosed that computations by the French method agreed fairly well
in most specific cases with those in use by the AirService. In cases where there was much differ­ence
between the French and American values, the latter were considered more reasonable.
The French formula is partly theoretical and partly empirical, whereas the Air Service rules are
purely empirical. In the French formula, the theoretical and empirical factors are combined in such
a manner that with certain types of design they do not give suitable load factors. In one case
particularly, the load factor obtained by the French formula is less than that actually recorded in
flight.
It appears that the only proper solution of the problem of load factors lies in the study and com­pilation
of full scale acceleration tests, such as those recently instituted by the Air Service, to com­plete
the existing fragmentary data. Such a study might result in the adoption of a fo rmula for
computing the required load factor, but it is believed that the \·ariables and arbitrary constants used
in such a formula would differ materially from those employed in the S. T. Ae' fo rmula.
Method of Computing Horsepower Available for Performance
Prediction. *Serial No. 2443
This report presents a method used by the Engineering Di,,ision for computing the horse­power
available from an engine with a two-bladed wooden propeller fo r use in the prediction of per~
formance. For illustration, the method is applied to both the Liberty and Curtiss D-12 engines for
propel lers of variously designed speeds, giving the available horsepower at sea level, 10,000 feet and
15,000 feet in both tabular and graphic forms.
RESEARCH AN D EXPERIMENT 43
Loadings for Experimental Wing Spars. *Serial No. 2450
This investigation was undertaken to develop a simple and inexpensive system of loadings for
testing and rating experimental wing spars for various types of airplanes. As a result it was found
that a set of standard loadings could be devised and a very simple loading jig built at minimum cost
fo r testing the spars. The proposed testing jig, a schematic arrangement of which is given in the
report, is a development of a similar one used hy the Forest Products Laboratory, as shown on
Page 6 of the N. A. C. A. Report No. 188, "Stresses in Wood Members Subjected to Combined
Column and Beam Action."
Flow of Air -~round Rotating Cylinder. *Serial No. 2462
This report contains a brief account of a demonstration in the wind tunnel to illustrate the
change in flow of air around a rotating cylinder, a principle applied in Flettner's wind-propelled sail­less
ship, Buckau.
The phenomenon is analagous to the "curved ball" in baseball and the "sliced ball" in golf. in
which the viscuous friction between the air and the surface of the ball results in a flow of air
similar to that produced hy an airfoil.
Predicting Cruising Range of Proposed Airplane. Serial No. 2464
The method of predicting the crui sing range of a proposed airplane presented in this report is
based upon the theory underlying cruising performance of airplanes as expounded in Technical
Note No. 133, Navy Department Bureau of Aeronautics. By fo llowing the procedure given in the
report, the theory can be applied to any case in about two hours, which makes the method prac­tical
and available in preparing comparative estimates while the airplane is still in the preliminary
design stage.
Large Capacity Skis. Serial No. 24 7 4
This report contains design analyses for two large capacity skis-one of 4,000 pounds capacity
and the other of 8,000 pounds capacity-for use on airplanes having maximum gross weights of
8,000 and 16,000 pounds respectively. T he smaller ski is designed to replace a 36"x8" wheel using
a 13-gage axle, 2.75 inches in diameter, and the larger to replace a 44"x10" wheel using a 11-gage
axle, 3.25 inches in diameter. T he framework of both skis is constructed of low carbon steel tube
trusses connected to T-shaped cross beams made of low carbon steel plates with the flange on the
lower side and the stem vertical. All connections are welded. The runner is formed of corrugated
duralumin riveted to the flanges of the cross beams with steel rivets. The cross beams are arched to
facilitate taxi-ing.
Torsional Test of Curtiss XNBS-4 Fuselage. *Serial No. 2476
This report contains an account of the torsional deflection tests conducted at the Division on
the fuselage and tail surfaces of the Curtiss XNBS-4 night bomber to determine the cause of tail
flutter observed in flight as mentioned on Page 10, T echnical Bulletin No. 40. The tests were made
by elevating the rear portion of the fuselage until the line of thrust was practically horizontal as
in flight and applying unbalanced loads of five and seven and one-half pounds per square foot, re­spectively,
to only one side of the empennage. Torsional deflections were carefully measured after
each load had been imposed for a period of five minutes.
Torsional Test of Curtiss (Martin) NBS-1 Bomber. *Serial No. 24 79
This test was conducted in a similar manner to that just mentioned in Serial No. 2476 by apply­ing
eccentric loads to the horizontal tail surfaces. By a comparison of results obtained in preced­ing
tests on the fuselages of the Elias XNBS-3 and Curtiss XNBS-4 bombers as shown below, it
is evident that the fuselage of the Cur tiss NBS-1 is the weakest of the three with regard to tor­sional
deflection.
Airpla11e Max. A 11gle of Twist (worst co11ditio 11 )
1st Test XNBS-3 (E lias) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0° 54'
2nd Test XNBS-4 (Curtiss) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1° 22'
3rd Test NBS-1 (Curtiss) . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . 1 ° 47'
44 T E C H N I C A L B U L L E T I N N o. 4 2
Static Tests Conducted at the Engineering Division.
Complete accounts of the static tests conducted by the Engineering Division at McCook Field
on various airplanes and airplane parts to determine their structural fitness for flight are contained
in the fo llowing reports, each of which is r eplete with drawings and photographs of the structure.
a summary of the results obtained and. a di scussion of the test.
*Serial No. 2455-Engineering Division XC0-6 Observation.
Serial No. 2458-Army Curtiss Racer , Model R-6.
Serial No. 2461-vVing Spar for Cox-Klemin Ambulance XA-1.
*Serial No. 2475-Atlantic DH-4M2 Steel Tube Fuselage.
*Serial No. 2477-Proof Test of Aileron, E levator and Stabilizer of Cox-Klernin (Hein­ke!)
Observation .
Serial No. 2i84---U. S. Air Mail Plane No. 509 (Bellanca DH).
Wind Tunnel Tests.
The following serial reports contain aerodynamical data on van ous airplane models and sur­faces
as determined in the wind tunnnel :
Serial No. 2431--Army Racer R -3 (Verville-Sperry- 1922 Model ) .
*Serial No. 2445-Curtiss P ursuit, Nf ode! P \V-8.
*Serial No. 2463-Six Designs of Hori zontal Tai l Surfaces Using USA-47 Airfoil
Section.
Serial No. 2465-Tests of Venturi for Operating Pi lot Director.
ARMAMENT SECTION.
Experimentation on Bombardment Cannon for Airplanes. Serial No. 2329
The scope of this investigation which began in 1919 embraces experimentation on all types of
bombardment cannon available for aircraft including the fo llowing:
Baldwin 37 mm. Automatic Semi-flexible Aircraft Cannon.
Coventrv 37 mm. l\lark III Automatic Airplane Cannon.
37 mm. Semi-automatic Motor Cannon modified for flexible use.
Modified 2.95-inch Mountain Gun.
Davis 3-inch Non-recoil Cannon.
In addition to the tests on the above guns. a large number of reports on foreign developments
were investigated.
Remedies for Machine Gun Malfunctions. *Serial No. 2442
This report is a resume' of various Air Service Technical Orders on the malfunctions of syn­chronized
machine gun s supplemented with explanatory matter wherever it was found advisable.
EQUIPMENT SECTION.
Porosity of Parachute Fabrics. Serial No. 2429
vVhether or not porosity of the silk used in parachutes is a ponderable factor in the rate of
descent forms the basis of this laboratory investigation. The fabrics-Type "A" Habutai ( heav­iest
), Domestic \1Veave, Pongee, A. S. Spec. No. 40,009, and A. E. F . H abutai ( lightest)-were
first tested fo r relative air porosity by means of a Sargent wet test gas meter and then for wind
resistance in the wind tunnel under the assumption that the silk offering the g reatest resistance
would be the slowest in descent. A comparison of the rates of descent from wind tunnel data, by
porosity and by estimation disclosed some valuable in formation on the suitability of parachute
silks. But it was concluded , however, that the only way to definite! y establish the actual relations
between porosity and rate of descent is to supplement the laboratory tests with flight drop-tests of
identical parachutes made of the different material s.
RESEARCH AN D EXPER I 1\1EN T 45
"Tasco" Distant-reading Gasoline Gage. Serial No. 2480
This report deals with the test of the "Tas~o" gage, a di stant-reading gasoline gage manu­factured
by the Akron-Selle Company, Akron, Ohio, to · determine its suitability for aircraft use.
This gage is of the float type utilizing two indicator s, one on the tank and the other on the instru­ment
board, the former being directly actuated by means of a cam fastened to the same shaft, the
cam moving horizontally as the float moves vertically. A trigger connected to the cam mechanism
by means of piano wire protected by a brass tube, in such a manner that the amount of travel
is regulated by the cam, permits the reading of the clash-indicator so long as it is held out. The gage
is well constructed but has several serious defects that preclude reliable operation in aircraft usage.
FLYING SECTION
Take-Off and Landing Characteristics of an Airplane. Serial No. 2375
T he "take-off" and landing characteristics of an airplane a re governing . factors in the selection
of landing fields and in the operation of given types of a irplanes in and out of such fi elds. Both
problems involve the minimum distance of approach into the wind and over obstructions, and for
their solution some simple rules on the estimation of th is minimum di stance have been worked
out upon a mathematical basis and a general formula derived which is applicable to either case, the
onl y differences in its application being in the sign and quantitative value of the terms.
Control Stick Force Indicator. Serial No. 2385
T his report gives a brief description of an in strument for indicating the fo rces exerted on the
control stick of an airplane. It consists of two main parts, a JT\Ovable grip fitted around the control
stick and two standard pressure indicators mouilted on the side of the cockpit. Two sylphons, one
on the grip and the other on a fixed yoke attached to the stick column. transmit the pul l impulses
to the indicators thru tubing fi lled with kerosene, the cleAection of the pointers being proportional
to the force applied to the grip. (Accompanying chart shows control stick fo rces on DH-4B as
measured by this in strument.)
-
CO!YlteOL S7/6K .IOKCES
OF DH-4B U!YiJER
FULL POWER
·.-~ .~..
I)
A ~
A ~ Scab //zer Se t 0?_~ h :- - --· - <: e:.-... ..... ---..,
Sta '/hzer - Set~ l>rsp~ o' o/' best 1,., -/ /---z_ - - r-- --r--..
A \ -s-,."'6 :>.-__
---.::::: /~~~ r-- p-__ -- I\) --~ -~ - :o>"" ..-::::
A ~ ~ ';>Q"_,...-r-..- ...............
::::.
-..... r-- I
-..........
~~ •? ~ . t-:---.. K I ............ "
·- r---r--....
~~
f'....... , __
--t--
~ N ' ~·
!~
I r-....
· - - -·- ---
W./. H.
?0 ,;.n .9) /( 0 11'0 /' 0 J-- 0
46 T E C H N I C A L B U L L E T I N N o. 4 2
From results obtained in actual flight tests in a DH-4 airplane, it was concluded that this in­strument
when fully developed would prove less complicated and of greater preci sion than the con­trol
force recorder developed by the National Advisory Committee for Aeronautics.
Two views of the instrument are appended.
Carbon-coated Paper for Recording Instruments. Serial No. 2409
A simple method has been de~ i sed for coating and fixing the surface of .paper drums used
on recording instruments such as barographs. It consists in spraying the paper strips with a mix­ture
of fine lampblack and gasoline-a decided improvement over the present method of smoking in
the rapidity and ease of application as well as in the quality of the recording sur face.
Performance Tests.
The following serial reports contain complete accounts of the performance tests recentl y con­ducted
by the Engineering Division.
*Serial No. 2436-·Curtiss P \V-8A with low compression engine.
Serial No. 2437- Atlantic A0-1 with Liberty engine,
*Serial No. 2438-Fokker C0-4 ( Service test model. )
*Serial No. 2449-Boeing PW-9 with low compression engine.
Serial No. 2453-Curtiss P\V-8 with low compression engine.
Serial No. 2454--Curtiss XNBS-4 Night Bomber.
*Serial No. 2459- Douglas X0-2 with Liberty engine.
MATERIAL SECTION
Heat Treatment of Al-Cu-Fe-Mg (Piston) Alloy. Serial No. 2439
T his investigation forms part of the work undertaken 111 companng two piston material s or
alloys of aluminum, one containing iron (Al-Cu-Fe-Mg) and the other nickel (Al-Cu- Ti-Mg) .
T his particular report deals with the heat treatment of the fir st alloy as covered by A. S. Speci­fi
cation No. 11 ,024 and compares the properties imparted by boiling water and air as quenching
mediums.
The results show that the tensile strength and ha rdness of the sand cast alloy may be greatlv
increased by proper heat treatment which can be controlled by a close study of the meta llography of
the alloy.
Airplane Wheel and Tire, Size 64x14. Serial No. 2444
This report contains a more detail ed account of the development and test of the new 64"x 14"
straight-side wheel and tire, believed to be the l