Static test of the Curtiss PW-8 single-seater pursuit airplane (Airplane Section report)

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€0NFIDEN I IAL
File D 52.1/Curtiss PW-8/ I
AIR SERVICE INFORMATION CIRCULAR
Vol. V
<AVIATION )
PUBLISHED BY THE CHIEF OF AIR SERVICE, WASHINGTON, D. C.
December 1, 1924 No. 492
STATIC TEST OF THE CURTISS PW-. 8
SINGLE-SEATER PURSUIT AIRPLANE
r AIRPLANE SECTION REPORT)
P repared by E. R. Weaver
Engineering Division, Air Service
McCook Field, Dayton, Ohio
July 29, 1924
WASHINGTON
GOVERNMENT PRINTING OFFICE
1925
Ralph Brown Draughon
LIBRARY
MAY 17 2013
Non·Depoitory
Auburn University
CERTIFICATE: By direction of the Secretary of War the matter contained
herein is published as administrative information and is required for the proper
transaction of the public business.
(II)
. \
INDEX
Page
Fig. 1. Plan view of airplane_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6
Fig. 2. Front and side elevation ____ __ __ ____ ______ _______ ___ _____ ·-- - - ----- - ----- - -"--- - -- ---- - - 6
Fig. 3. Assembly drawing, upper wing, spar sections and typical rib ___ _____ ________ ________ _:- ______ 7
Fig. 4. Assembly drawing, lower wing, spar sections and typical rib ___ ____ ___ _______ _______ _______ 7
Fig. 5. Drawing of typical spar fittings and struts __ ______ ___ __ ___ ______ __ _________ c _ _ _ _ · _ ______ _ _ 8
Fig. 6. Loading schedule (reversed flight) __ ____ _____ ______ _____ ___ ____ ____ ____ ___ ______ ________ 8
Fig. 7. Chart of the wing spar deflections (reversed flight) ____ ____ _____ ________________ ______ _____ 9
Fig. 8. Wing spar deflection curves (reversed flight)__ __ __ _____________ ______ __________ __ _______ 9
Fig. 9. Loading sch edule (low incidence)_ _____ __ ________ ____ ___ _______ _________ ________ ________ 10
Fig. 10. Chart of wing spar deflections (low inciden ce) ___ _______ ___ _______ _____________ ___ ________ 10
Fig. 11. Wing spar deflection curves (low incidence) _____ ·---- - - --- - ----- --- - - - -- - ---.-- - --- ----- - -- 11
Fig. 12. Loading schedule (high incidence) __ ________ _______ ___ ___ ___ _______ _______ ~ _____ ~ __ _ __ _ _ 11
Fig. 13. Wing spar deflection chart (high incidence) __ ___ _____________ _______ _____ __ ____ __ ____ c _ _ _ 12
Fig. 14. Wing spar deflection curves (high incidence) ________ ____ ____ _____ ____ _______ ___________ __ 12
Fig. 15. Torsiona l wing d eflection curves for low incidence_____ _________ _________ ___ __ ___ _________ 13
Fig. 16. Torsional wing d eflection curves for high incidence _____ _______ ____ ___________ ____ _______ __ 13
Fig. 17. Drawing of the structure of the aileron ___ ______ ______ ______
0
__ _ _ _ _ _ _ ___ _ _ _ __ _ ____ __ _ ___ _ 14
Fig. 18. Loading schedule and results of aileron test_ _______ ___ ____ ______ ___ _____ ___________ ______ 14
Fig. 19. Drawing of elevator and stabilizer structure ______ ____________ ____ ___ _____ _______ _______ _ 15
r
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(
Fig. 20. Loading schedule deflections and results of elevator and stabilizer t est s ___ _____ ___ ___________ 15
Fig. 21. Drawing of the rudder and fin structure ______ _______ _________ ____ _____ ____ ___ ________ __ 16
Fig. 22. Loading schedule and results of rudder and fin test___ ________ ___ __ ____ ___________ _____ __ _ 16
Fig. 23. Assembly drawing, plan and side view of fuselage __ __ ________ ______ ___ _______ ____ _________ 17
Fig. 24. Loading schedule and deflections of fuselage test_ __ ___ __ __ _______ ______________ ___ _______ 17
Fig. 25. Set-up for tail skid test giving results______ ______ _______ ____ __ ______ ___________ _______ __ 18
Fig. 26. Set-up for landing chassis, dynamic test_ _______ ________________ __________ ___ __ _________ _ 18
Fig. 27. Results and deflections of landing chassis test_____ ____________ ___ ____ __________ ____ ___ ___ 19
Fig. 28. Photograph of failure of rear spar of lower left wing (low incidence)_ _____ ____________ _____ __ 19
Fig. 29. Photograph of failure of rear spar of lower right wing (low incidence) _ ___________ ____ ___ ____ 20
Fig. 30. Photograph of failure of front and rear spars upper right wing panel_ __ ______ ______ _________ 20
Fig. 31. Photograph of failure of front and rear spars upper right wing pane!_ ____________ ___________ 21
Fig. 32. Photograph of failure of lower longerons in fuselage -- - - ------ --- ---------------- ---~------ 21
Fig. 33. Photograph of failure of rear part of fuselage in tail skid test ______ __________ _______ ___ ____ _ 22
Fig. 34. Photograph of failure of wheels during landing chassis tesn_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 23
Fig. 35. Photograph of failure of wheels during landing chassis t est _______ ___ __________ ______ o______ 24
(III)
STATIC TEST OF THE CURTISS PW-8 SINGLE~SEATER
PURSUIT AIRPLANE
SUMMARY OF RESULTS
Airplane : Curtiss PW- 8.
Type: Pursuit.
Total weight: 2,768 pounds.
Wing cellule weight : 508."5 pounds.
Wing area: 268 square feet.
Engine: Curtiss D-12, 375 horsepower.
Description: Single-seater biplane; airfoil, Curtiss
No. 27; tubular steel fuselage with welded joints; em­pennage
structure, a combination of steel and dura­lumin;
axleless landing chassis; Curtiss wing radiators.
RESULTS OF TEST
D ate Part t ested Load required
Pounds per
square foot
or factor
supported
F ailed
at- Weight
Jan. 28, 1924_ __ ITorizontal stabi- 35 pounds per 55 pounds per ______ __ 1.96 pounds per
lize r. sq . ft. sq. ft. sq. ft.
Do __ ______ Elevator_ ___ __ ____ _____ do __ __ _____ ____ do __ ______ - -- ----- 1.01 pounds per
sq. ft.
Do _____ ___ Elevator controL ___ ___ do ________ _____ do ____ ____ ___ ___ __ - - - ---- ---- - ---- - -
Do ___ _____ Verti.cal fin ___ _____ 30 pounds per 50 pounds per - - - -- - --1 1.56 pounds per
sq . ft. sq. ft. sq. ft.
Do_ -------1 Rudder _- - ---- -- - - _____ do __ ____ __ _____ do __ ___ ___ ___ _____ l.~~pg~nds per
Jan.~K- i 924:::\ ~il~r~~;s~~~1_1~·~::: ::1-35~~~y~1Cis-rc;.- -45~~~ytn'1s-rcr- ::::::::1-i: ~~~~i'.''1-cis-rer -
no ________ ~~jt::,'go~efl:ij~~o!___ ____ __ do _______ _ ___ __ do ____ __ _____ __ ___ -- - - - -- - -- ----- -- -
F eh .11, 1924-__ j llighincidence __ 12 _____ __ ___ ___ 7.5_ --- - -- - - - - - 8 1.9 pounds per
sq . ft.
Feb. 7, 1924_ __ Low incidence __ 6.5 . _____ ____ __ 4_ ___ ____ ___ ___ 4. 5 - -- ---- -- -- -- - - -- -
Jan. 31, 1924___ Re.verse load ____ 4 ______ ___ _____ 3.5_ __ ___ ___ ___ 4 - -- ----- - - --- - - ---
Six-foot length of - - ------- --- - - -- - - - -- -- - - --- ---- ________ - ------ ---- - - -- - --
F ailure
Withstood 57 per cent overload, no failure.
Do.
Do.
Withstood U7 per cent overload, no failure.
Do.
Do.
Wit hstood 28 per cent overl oad, uo failure.
Do.
Upper front and rear spars of ri ght wiug panel
failed in cmnpression.
Rear spars at right and left lower pauels failed in
compression.
Rear spar, lower left wing failed in compression.
leading edge.
:Feb. 14, 1924- . :Fuselage _____ __ ___ 7 _____ _______ __ 6.5 ___ ________ 191 pounds ____ __ Lower longerons in third bay failed in compres-sion
after supporting load for 7 minutes.
:F eb. 15, 1924 __ T ail skid _____ ___ __ 30-inch drop___ 30-inch drop___ _____ _ _ _ _ _ _ ___ _ _ _ Rear bay at fuselage fa iled. Tail skid is satisfac-
Chassis:
F cb .1 8, 1924_ .. _ Struts-- ---- - - - - -'}48-in ch drop, } ...
tory.
Chassis structure satisfactory.
wheels failed during test .
Axle ________ ___J half load I Wheels failnrc onl y. Three sets of
Shock absorber. .! ·
-"- -"--
DISCUSSION
The wings of this a irplane were below the strength
requirement due to the fact that the plywood wing
cover was not strong enough to transmit the stresses
from the intermediate spars to the spars to which the
fittings were bolted. The original wheels were also
below the strength requirement.
OBJECT
This static test was conducted for the purpose of
determining the structural strength of the Curtiss
P\V- 8 airplane submitted in accordance with contract
No. 640, dated April 27, 1923.
DATE AND PLACE
The various tests on this airplane were performed at
McCook Field, Dayt on, Ohio, on dates as follows:
Jan. 28, 1924 ____ __ _ Elevator and stabilizer.
Jan . 28, 1924 __ __ __ Rudder and fin.
Jan. 30, 1924 ______ Ailerons.
Jan. 21, 1924 ____ __ _ Wing cellule (reversed flight).
Feb. 7, 1924 _____ __ Wing cellule (low incidence).
Feb. 11, 1924 __ ____ Wing cellule (high incidence).
Feb. 14, 1924 _ _ _ _ _ _ Fuselage.
Feb. 15, 1924 ______ Tail skid.
Feb. 18, 1924- _ _ _ _ _ Chassis.
WITNESSES
Lieut. C. W. P yle _____ _____ _____ __ ___ ___ __ All tests
W. E. Savage ______ ___ ___ ____ _____ ___ __ __ All tests
D. B. Weaver_ _____ ______ ____ ____ __ - - - ____ All tests
C. A. Lewis ______ ___ ______ ___ _____ ________ All tests
E. R. Weaver_ _____ ___ __ ____ ___ ______ ~ ____ All tests
(1)
DESCRIPTION
The Curtiss PW-8 pursuit airplane is a single­seater
with biplane wings and powered by a Curtiss
D- 12, 375 horsepower engine.
The desired performance of this airplane is a climb
at ground of 1,830 feet per minute and a speed of 168
miles per hour, with a service propeller.
The total weight of the airplane as in flight is 2, 768
pounds, with a useful load of 960 pounds.
The total wing area is 268 square feet.
The weight of wings plus struts and wires is 508.5
pounds.
The weight per square foot of wing surface is 1.96
pounds.
The rated horsepower of Curtiss D- 12 engine is 375
(low compression).
The weight per horsepower is 7.4 pounds.
The airfoil used is the Curtiss No. 27.
2
The armament and equipment carried is accon;:ling
to specifications in Paragraphs·v and VI, contract No.
640.
Figure 1 is a plan view of the airplane, while Figure
2 shows a front and side elevation.
WING CELLULE
The wing panels are of wood construction C'overed
with two-ply spruce plywood between the forward
spar and the rear spar. This plywood is used on both
top and bottom surfaces. That part of the wings to
the rear of the rear spar is covered with fabric and the
ribs are channel section sheet duralumin which are
attached to the rear spar with screws.
The wing span is 32 feet, the upper wing chord is
60Yz inches and the lower wing chord is 48Yz inches.
The lower wing is composed of two panels, while
the upper wing consists of two panels and a center sec­tion.
The upper right and left panels carry the wing
radiators. These radiators take the shape of the air­foil.
Figure 3 is an assembly drawing of the upper wing
showing spar sections and typical rib.
Figure 4 is an assembly drawing of the lower wing
showing spar sections and typical rib.
Figure 5 is a drawing showing typical spar fitting
and strut.
Figures 30 and 31 are photographs showing wing
radiators.
PROCEDURE FOR TEST--REVERSED ~'LIGHT
The airplane was assembled, rerigged and placed on
the proper supports in a right side up position. The
angle of inclination or angle between the wing chord
and the horizontal was 14° trailing edge down. This
angle of inclination is a standard setting for all air­planes
when tested for reversed flight.
The center of gravity of the load is located at 25 per
cent of the wing chord from the leading edge, which
corresponds to the center of pressure of the airfoil in
reversed flight.
. The wing structure was loaded as indicated in the
loading schedule in Figure 6.
The requi~ed load factor for reversed flight for this
airplane is 4, the structure to be strong enough to
support this load without signs of failure.
RESULTS
The wing structure supported loads equivalent to the
respective factors 2, 3, and 3.5 without failure. The
next half factors of the load was applied and while the
supporting jacks were being let down the rear spar of
the left lower wing panel failed in compression.
Figure 7 is a chart of the wing spar deflections.
Figure 8 gives the spar deflection curves.
DISCUSSION
In the lower panel the four wing spars were joined
top and bottom with 2-ply spruce, grain at 45° to the
spars. This plywood wing cover is designed to carry
the stresses from the two inner spars to the two outer
spars, to which the fittings are attached. This con­struction
is not adequate to transfer the stresses in the
intermediate spars to the outer spars.
RECOMMENDATION
Redesign wing to support load factor of 4.
PROCEDURE FOR TEST--LOW I NCIDENCE TEST
After the wings had been repaired, the airplane was
assembled and sr.t for the low incidence test.
The angle of inclination of the wings was determined
as follows:
a = - 1° 6'
/3=cot-1 11.5=4° 58'
-y=f'l-a=4° 58'-( - 1° 6') =6° 4'
-y=6° '4'
The wings were set with the wing chord making an
angle of 6° 4' to the horizontal, trailing edge down.
The center of gravity of the load was located at 60
per cent of the wing chord from the leading edge which
corresponds to the center of pressure of the airfoil for
the high-~peed angle.
The wing structure was loaded according to the
loading schedule in figure 9.
Required load factor for low incidences=6.5.
RESULTS
The wing structure supported a load factor of 4
without failure, but when another factor of the load
was added the rear spars of the lower wing failed in
compression at a point about 12 inches from the center
of the spar-fitting hinge pins:
Figure 28 is a photograph of the right rear spar
failure, lower wing.
Figure 29 is a photograph of the left rear spar failure,
lower wing.
Figure 10 is a chart of the wing spar deflections.
Figure 11 shows the spar deflection curves.
Figure 15 shows the torsional wing deflection curves.
DISCUSSION
The wing spars are 27 per cent lower in strength than
the factor for which the wings were designed, which
was 5.5. However, this was the standard specification
for a pursuit type airplane wing at the time the con­tract
was let.
In view of the fact that the new Engineering Division
specifications call for a factor of 6.5, the wings are
really 38.5 per cent lower in strength than is required.
CONCLUSION
The wings are 38.5 per cent below the requirement
for strength.
RECOMMENDATIONS
Redesign wings to meet new specifications which is a
load factor of 6.5 for the low incidence test.
PROCEDURE FOR TEST--HIGH INCIDENCE
After repairing the lower wing panels and reassem­bling
the wings, the airplane was reset for the high in­cidence
test.
The angle of inclination or the angle between the
wing chord and the horizontal was 3° 27' ·' The center
of pressure at most forward. position (at 10° angle of
attack).
This angle was determined as follows:
a=l0°
,B=L/D=cot-1 8.7=6° 33'
')'=a-,8=10°-6° 33'=3° 27,.
')'=3° 27'
The wings were set at this angle with leading edge
down. The center of gravity of the load was located
at 31 per cent of the wing chord from the leading· edge;
this corresponds to the center of pressure of the wings
when a=l0°.
The wings were loaded in accordance with the load­ing
schedule in figure 12.
Load factor required for high. incidence= 12.
RESULTS
The wing structure supported without fai lure all
loads varying in magnitudes from 3 to 7.5 factors.
When the next half factor of the load was added the
upper front and rear spars of the right wing panel
failed in compression. Figures 30 and 31 are photo­graphs
of the failures.
The wing spar deflection .chart may be seen in figure
13, while figure 14 shows the wing spar deflection
curves. Figure 16 shows the torsional wing deflection
curves.
DISCUSSION
This wing failure was caused by the same weakness
as was manifested during all the other wing tests,
namely, the plywood wing skin was inadequate to carry
the stresses . from the intermediate spars to the front
and rear spars to which the fittings were attached.
CONCLUSION
In view of the fact that the PW- 8 wings were
designed to meet the strength requirement of the old
specifications which was a factor of 8.5 for the high
incidence test and actual test revealed these wings to
satisfactorily support a load equivalent to 7.5, the
wings are about 12 per cent below the strength for
which they were designed.
3
The new specifications call for a load factor of 12
for a pursuit airplane, so that the wings are 3772 per
cent below present specifications in strength.
RECOMMENDATIONS
Redesign wings to meet the new specifications for
strength.
AILERON
DESCRIPTION
The aileron is a metal structure covered with fabric,
built on one steel tube spar to which the hinges are
attached. The trailing edge is a flattened steel tube
formed to shape and riveted to each rib. The ribs are
channel section duralumin formed from sheet stock.
The leading edge or balanced portion is covered with
sheet duralumin. All joints in the structure are riveted·.
The area of the aileron is 8.42 square feet, its weight
is 8.5 pounds, and the weight per square foot is 1.01
pounds.
Figure 17 is a drawing of the aileron structure.
PROCEDURE FOR TEST
The aileron controls were adjusted and put in order
and the aileron surface of the right wing panel was
loaded in accordance with the loading schedule in
Figure 18.
A spring balance was CQupled to the control stick to
register the pull on the stick. This is done to measure
the force necessary to operate the ailerons when
under load.
The required load for the aileron of a pursuit type
airplane is 35 pounds per square foot. Location of
center of gravity of load equals f.z of chord from hinge
center.
RESULTS
The aileron supported the required load without
signs of failure, no serious deflections at any time were
noticed.
The load was then increased until 45 pounds per
square foot was on the surface. Very little stretch
was noticed in the control cables, after all load was
removed the surfaces showed no perceptible distortion.
Figure 18 gives results of the test. ·
CONCLUSION
The aileron and controls are structurally satisfactory,
having supported a 28.6 per cent overload.
ELEVATOR AND STABILIZER
DESCRIPTION
The stabilizer and elevator are both metal struc­tures,
a combination of duralumin and steel, riveted at
all joints. The stabilizer has two steel tube spars and
the elevator has one steel tube spar. Sheet steel fit­tings
are riveted and soldered to the alloy steel tubular
spars and to these the channel section form.ed sheet
duralumin ribs are riveted. The leading edge of the
stabilizer and the trailing edge of the elevator are both
flattened steel tubes which are secured by rivets to
each rib. Fabric is used for coverings on both hori­zoptal
tail surfaces. The elevator is of the balanced
type.
Figure 19 is a drawing of the elevator and stabilizer
structures.
Weight Area
Weight
per square
foot
4
Elevator _____ __ ____ __ ______ __ ___ _ _
Stabilizer __ ___ ___ ___ ___ __ __ ____ _ _
Poimds
12
24
Square feet
11. 9
12. 22
Pounds
1.01
I. 96 .
PROCEDURE FOR TEST
The elevator and stabilizer were assembled on the
uselage which was supported so that the stabilizer
vas approximately level.
A spring balance was coupled to the control stick
to indicate the pounds pull necessary to move the ele­vator
while supporting the various loads. A uniform
load was applied to the stabilizer. The load on the
elevator trailing edge was one-third that at the hinge
center.
The surfaces were loaded according to the loading
schedule in Figure 20.
The required load per square foot for the horizontal
tail surfaces is 35 pounds.
RESULTS
The horizontal tail surfaces supported all increments
of the required load without failure and only very
slight deflection was noticed. When the load was
equivalent in magnitude to 25 pounds per square foot
the stabilizer adjustment wheel required the force of
both hands to move it, but this device could be oper­ated
when the surfaces were supporting a load of 55
pounds per square foot. This was the equivalent of
an overload of 57 per cent with no failure. However,
the elevator sagged badly.
Figure 20 gives the loading schedule, clefle<;tions, and
results of test.
CONCLUSION
The horizontal tail surfaces are structurally satis­factory.
·
RUDDER AND FIN
DESCRIPTION
The rudder and fin are of all steel construction,
fabric covered. The rudder being of the balanced
type, built on one main tube to which the hinges are
fastened. A %-inch steel tube or stiffener parallels the
main tube midway between the trailin·g edge tube and
main tube. At the points where this small tube passes
through the ribs, solder is used to make the joint secure.
The ribs are channel section formed from sheet steel
and lightened in weight by lightening holes. The trail­ing
edge is a flattened tube riveted to the ribs. This
same construction is used throughout the fin.
Figu.re 21 is· a drawing of the rudder and fin structure.
Rudder __ , _____ _____ __ ____ _____ , __
Fin-- ---- ---- -- ----- -- ------------
Weight
Pounds
9. 5
5. 0
Area
Sq11a.re feet
8. 7
3. 2
Weight
per square
foot
Pounds
1. 09
I. 56
PROCEDURE FOR TEST
The rudder and fin were assembled on the fuselage
which was turned on its side and supported so the fin
was horizontal. The surfaces were loaded in accord­ance
with the loading schedule in Figure 22. The fin
was uniformly loaclecl, while the load on the rudder
tapered off to one-third the magnitude of the hinge
load at the trailing edge. A spring balance was
coupled to the rudder bar to measure the force neces­sary
to move the rudder under the various loads-.
The required load for the rudder and fin _is 30
pounds per square foot.
RESULTS
The rudder and fin supported a static load of 50
pounds per square foot without signs of failure.
The deflections were not excessive at any time during
the test.
Figure 22 gives the deflections.
CONCLUSION
The rudder and fin are structurally satisfactory,
having supported a 67 per cent overload.
NoTE.-After these surfaces were uncovered and
their structures carefully examined, considerable rust
was noticed. This condition was caused by the use
of acid in the process of soldering the joints. There
seemed to be little evidence of a~y attempt at neutraliz­ing
the acid on the structures after the soldering opera­tion.
The main rib in the fin was found to have been broken
and repaired. This was clone previous to the static
test.
FUSELAGE
DESCRIPTION
The Curtiss PW-8 fuselage is a tubular steel struc­ture,
torch welded at all joints. Streamline wires,
clevised at each end, serve the structure for all diagonal
and cross bracing. No turnbuckles are used due to the
fact that one brace wi~e end is threaded right hand and
the other encl threaded left hand. The gussets to
which the wires are fastened are welded to the tubes at
the intersections.
Figure 23 is an assembly drawing-showing plan and
side view.
This fuselage is rectangular in section and 19.5 feet
Icing.
The weight of the fuselage structure is 191 pounds.
PROCEDURE FOR TEST
The fuselage structure was supported on a special
jig in such a way that the struts and wires to the upper
wing supported the fuselage weight plus the first three
load factors. Then supporting blocks were fitted under
the lower longerons at the lower wing fittings and the
test continued.
All the various weights of pilot, engine, fuel tanks,
equipment, armament, etc., are represented in the four
loads, A, B, C, and D, as shown in Figure 24, which
shows the loading schedule.
A wye level was used to check the deflections.
RESULTS
The required load factor for a fuselage of this type
is 7.
The fuselage structure supported all loads up to and
including a load factor of 6.5 without failure or
excessive deflections.
After the next half factor of the load was added and
the jacks were released allowing the structure to sup­port
the full load, the lower longerons failed in com­pression
in the third bay from fire wall, after having
supported the required load for seven minutes, the
required time being five minutes. See Figure 24.
Figure 32 is a photograph of the failure of the
lower longerons.
CONCLUSION
The fuselage supported the required load in a satis­factory
manner under static test condition.
TAIL SKID
PROCEDURE FOR TEST
This dynamic test was performed in the following
manner: The wheels on the landing chassis were
allowed to rest on a level platform, while the platform
on which the tail skid rested made an angle of 9° 27'
with the floor or horizontal. By inclining this plat­form
to one side the worst landing condition is simu­lated.
The reaction at the tail skid in the tail low
position was found to be 412 pounds. This load was
lashed to the fuselage and the rear portion of the
fuselage and tail skid was hoisted and dropped in the
succession of 6, 9, 12, 15 inches, etc.
The required height from which tail skid must drop
without failure is 30 inches.
RESULTS
The structure showed no signs of failure on being
dropped a distance of 27 inches, but when the struc­ture
was dropped 30 inches the rear bay of the fuselage
structure collapi;ed, the primary failure being the
failure of the clevises.
No damage was done to the tail skid during the test.
Figure 33 is a photograph of the rear portion of fusel­age
after test. Figure 25 shows the set up for test as
well as the loads and results.
CONCLUSION
. The tail skid' is satisfactory, but the rear portion of
the fuselage is too weak to withstand the dynamic test
designed for tail skid.
22222-25t-- 2
5
RECOMMENDATIONS
Redesign rear portion of fuselage so as to eliminate
failure during tail skid test.
LANDING CHASSIS-DYNAMIC TEST
PROCEDURE FOR TEST
The landing chassis was assembled on the fuselage
with the wheels resting on a platform inclined to one
side and making an angle of 9° 27' with the horizontal.
This method of testing combines direct load and side
thrust.
The fuselage was elevated at the rear end so that the
angle the thrust line made with the horizontal was
13.5°, this setting brought the center of gravity of the
load, or of the airplane vertically over the center of the
axle. Each tire contained 73 pounds per square inch
air pressure. Size of original tires 26 by 4.
The distance this landing chassis was required to
drop with full load was 24 inches or 48 inches with
half load.
Figure 26 shows the set-up for landing chassis test.
RESULTS
Full load was applied at the start of the test, but
when the wheels collapsed after being dropped 13,Y:;
inches, it was considered advisable to remove half the
load and very necessary to install heavier wheels and
tires-28 by 4 tires and wheels were fitted. This
change having been made, the test was continued.
The second set of wheels withstood the 18, 21, 24, and
27 inch drops satisfactorily, but on being dropped
30 inches the wheels again failed.
A third set of wheels, size 750 by 125 millimeters,
was assembled on the chassis and test was resumed.
The chassis withstood all shoc)l:s inflicted by 30 to 48
inch drops, inclusive; although after the 48-inch drop
an inspection of the wheels revealed the fact that the
wheels had been stressed to the limit and to continue
the test would only mean failure of the wheels. The
chassis structure showed no signs of failure.
Figure 27 is a chart of the deflections and results.
Figures 34 and 35 are photographs showing the
wheel failures.
CONCLUSIONS
The landing chassis structure is structurally satis­factory.
The wheels with which the chassis was fitted (the
original wheels as fitted at Curtiss factory) are 45 per
cent under the strength requirement for a pursuit
type airplane, such as the PW- 8.
I
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6
FIG. 1
FIG . 2
cu.tlTISS PUltSUIT ~w a
" iv
CllmlSS PUR!SU/T P. W. -8
FRONT AND 51DE YIEWS
7
ltllJ ARIWGE/fCNf
RAOIATOA
FIG . 3
CURnss flJR.SIJIT
Clf'PE/t W/Nla
----- - -------111-:..14 '.. <J" ~
NOTE.; - FOHWlfRD JI . C0'1"£RED WITH J" 2 PLY SPRUCE
HEAR 17"DURllL RIBS. FlllJRIC COVER . ONL.Y
TYPICAL SECTION
OF QyRAL RIB
FIG . 4
CURTIS PCIRSJIT
LOWER WING
8
------.zeT'!---~-~
fl
~ .. !?.''
l !
r1
L
~!
t
I
I
I
J. PIN ·
.16.I
,!la ...
t ~3.1_
Load
fac-tor
--
2
3
3.5
4
11(T£R,.1...11NE · smur
FIG. 5
Vl'PE.R WING
l'NONT
.!:!!2m.I..
!!!e..
~
q...,,.,,... POSITION OF .Ji'MR
'1' \
: 1\\
I I \ \
\J'. . \\ \ \ \
\ \
----.......
__./
I\
i ....
~ l
J6.I ~ .1 J,.I 41.6-6. •
LOWU WING
f.l!MI -.............
/flDDU I\
£M. ~
~ ___.,/
J.1.6 J.JG JJ.6 .ns-6.-
LOADING SCHEDULE
Upper Lower
Front Middle Rear Total Front Middle Rear Total
------- - - - - - -----
l, 150 580 570 2,300 850 430 440 1, 720
1,800 910 890 3,600 1, 340 670 680 2,690
2, 130 1,070 1, 050 4, 2.10 1,580 790 800 3, 170
2,460 1,230 1, 210 4,900 1, 820 910 920 3,650
Fig. &-Curtiss Pursuit PW-8. Reverse load
HOLE.
9
---+G. - - -- --¥'-- - - -¥---~ --~----tK---- - -tr..
Load
factor
2
3
3. 5
4
---- -~--- -rn=--
--+---- 66/- --..+---- --~---- 6'f 6/li =+ cZ;4
DEFLECTIONS. Horizontal deflections.
'\. B C D I E • F I G H I I J I K / L Unpgphetr Lr?igwhetr Ulpepfte r Lolewfte r --- - --1-----1-- ---- 1. 2 . 7 0. 4 . 1 I o. 4 o. 5 o. 9 o. 6 o. 4 I o. 3 o. 3 I o. 4 o. 2 · o o. 9 o
1.8 1.1 .6 .5 .8 I. I 1.5 1.1 .6 . 5 .7 1.0 - . 5 -. 1 - 1 0
2. 2 1.3 .8 .5 1.0 1. 5 1.8 1.3 .8 .5 .8 1. 3 -. 6 -.2 -1 0
Left lower wing, rear spar failed in compression while jacks were being let down.
22222- 25t- 3
FIG. 7- Curtiss Pursuit PW- 8. Reverse flight test.
---,..""'°---,,-------..,.._-----"ll_EFCEt~<'ENCE LINE
L(HO F!K.TO!f
z .
.I
J.S
!i'EFE. '£NCC l/N£
LOAD FACTO!f
---'--z
CPlf'TIJS .Pv1r''"T
P.H( -8
.REYE-¥.SE rU~
'Vll'C1'1QN~
FIG. 8
.J
3 .S
10
I I/. p f:u. 'ff!Nfl.
i NO l.ll'ID
I\
i ~ '
BU6. J I
i NO !ONJ ~:=J6~ ~36./ 3 6.I J6.I 3 6./
.~.
r .-
1 t-i
i-
1'
L
I
LO't<Ull 'f{/N6
~
" ' ~
fi!M l/
./
NO L 1i.n __.,-
~JJ'.6__j__-J.J.6-,......_ .J.J.6 -f----J.l'.6 .1 . J7.S- ' ..
LOADING SCHEDULE
Upper Lower
Load
factor
Middle Rear Total Middle Rear 'rota!
--------------- ------
3 1,990 1, 990 3,980 1, 150 1, 140 2, 290
4 2, 710 2, 710 5,420 1, 560 1, 550 3, 110
5 3, 430 3, 430 6, 860 1, 970 1, 960 3, 930
5. 5 3, 790 3, 790 7, 580 2, 170 2, 170 4,340
6 4, 150 4, 150 8,300 2, 370 2, 380 4, 750
6. 5 4, 510 4, 510 9,020 2, 570 2, 590 5, 160
-
Fm. 9.-Curtiss Pursuit PW-8. Low incidence loads.
l.Cll0/1'G E06t!.
A---+.B--tc----tn-+- ~g-- -1T---- +c---
'
~1----Ejv----+ir--+z:---+-·-+n-----+n----+o- --~
t7J 4==4,, -~--so-__... .1. . ...- -47--;, .1.~-s6---,.--46------49J -••'1"1• ----
DEFLECTIONS. Plumb bob deflections.
I
Load A B c D E F G H I J K L M N 0 p Upper Lower Upper Lower
factor right right left left
------ - - -- -- - - -- ---------- ------- - --- --- ------
3 0. 6 0. 3 0. 3 0. 2 0.1 0. 4 0.5 0. 7 0. 9 0. 7 0. 5 0. 3 0. 2 0. 5 0. 7 1. 3 +.4 +o. 9 +0.2 +Ll
4 .8 . 3 . 4 .2 .2 .5 . 7 .9 1.4 1. 0 . 7 . 3 . 3 . 7 1. 3 1. 7 +.4 +1.6 +.2 +1.6
5 Lower rear spars failed at points about 6" from inner fittings.
FIG. 10.- Curtiss Pursuit PW- 8. Low incidence test
Fli'ONT 5PA_1
/fORIZONTll/.. REFERENCE UllE
L(W) FlfCT'Olf
J ...
I I
I I I I
~
l
"'
I
....,
...., 1 I I REllR Jft'IR
'
I I
I I I -...........i.. --+-J
!i I I I --+-+
~'ti
ivi, l ~,P~,fl/-. - -8 -
")/ /...ow /N&ID.ENU
'EFLEC'TT()ll'I CuirVE$
-.Sc"' e.,.-fr."= I~
FIG. 11
_,_--.,,i.-
r r
t­~
t- "'llb
~
L
I
I
I
I
I
I
f-~.J6.I
lill
~I
"1 l.~ I+-
i + ' '-P I .L
i ~ f-.--..rJ.6
Ul'Pf,, WING
FIONT
\
' ~
~
I)
J 6.t .1. .J6.I m---1-- .:::J, LOWU W/116
FRONT
I\
HIOOL£ '
NO LOllO l!
-
-==..-.l----.Ju--t-- J'i';j 6 .1. .JJ.6 • j • ~
LOADING SCHEDULE
Upper Lower
Load
factor IM. Front Middle Total F ront I iddle Total
- - ------- ---
~1~
---
3 1, 860 2, 120 3, 980 2, 290
4 2, 540 2, 880 5, 420 I, 460 I, 650 3, llO
5 3, 220 3, 640 6, 860 I, 840 2, 090 3, 930
6 3, 900 4, 400 8, 300 2, 220 2, 530 4, 750
6. 5 4, 240 4, 780 9, 020 2, 410 I 2, 150 5, 180
7 4, 580 5, 160 9, 740 2, 600 2, 970 5, 570
7. 5 4, 920 5, 540 10, 460 2, 790 3, 190 5, 980
8 5, 260 5, 920 ll, 180 2, 980 3, 410 6, 390
8. 5 5, 600 6, 300 ll, 900 3, 170 3, 630 6,800
9 5, 940 6, 680 12, 620 3, 360 3,850 7, 210
9. 5 6, 280 7,060 13, 340 3, 550 4, 070 7, 620
JO 6, 620 7, 440 14, 060 3, 740 4, 290 8, 030
10. 5 6, 960 7, 820 14, 780 3, 930 4, 510 8, 440
11 7, 300 8, 200 15, 500 4, 120 4, 730 8, 850
II. 5 7, 640 8, 580 10, 220 4, 310 4, 950 9, 260
12 7, 980 8, 960 16, 940 4, 500 5, 110 I 9, 610
FIG. 12.-Curtiss Pursuit PW-8. High incidence
' (-
12
LElflJ/lfG EDtiE
'A - --~---t--- -+n-·t-·~--~- --+a----H
'
rl7------.~-- +K --~-+- - -+rr--+,r--- +o----
14J C::.so;.-....... - - .s1 ---t•-+l. -... - -...s- -+--- -s6--l..- .. 7- --•'"li... .~ -sot - ....j.. ... - -s2
DEFLECTIONS Plumb bob deflections
Load
lac-tor
--
3
4
5
6
6. 5
7
7. 5
8
A B c D E F G H I J K L M N 0
- - --- - - - --- - ---- - - - - - - --- - ----
2 0.8 0.4 0. 1 0.1 0.6 1 1. 2 0. 7 o. 4 0. 3 0. 2 0.2 0. 5 o. 9
2.3 .9 .'1 .2 .2 . 7 1 1. 7 1. 0 . 6 . 5 .3 . 3 . 7 1. 1
2.65 1. 2 . 7 . 3 .3 1.0 1.6 2.1 1. 2 .8 . 6 . ~ .3 .8 1. 3
2. 8 1. 4 . 7 .3 .3 1. 1 2 2. 6 1. 5 1. 0 .6 .3 . 3 .9 1. 6
3.1 1. 5 . 7 . 3 .4 1. 2 2.15 2. 9 1. 6 1. 1 . 7 .4 .4 LO 1. 75
3. 3 1. 5 .9 . 4 . 5 1.3 2. 3 3.1 1.7 1. 2 .8 .4 .4 1. 1 1.9
3. 5 1.9 .9 . 4 . 5 1.4 2. 5 3.4 1. 9 1.2 .8 .4 .5 1.3 2.1
Upper right rear failed n ext to fuselage.
FIG. 13.-Curt iss P ursuit PW-8. High incidence t est
REllR SPAR
C111f'TrSll',,'fS11n­P.
w,-e
Hr' N l..VC/llENC~
IJIFJ.E&TN:JNUJAWS
Fm. 14
J .
5.
6.
6.5
7.5
3.
4 .
.5.
6
6.S
7
7 S
p Upper Lower Upper Lower
right right left left
- - --- --- --- - --
1 + 0.2 - 0.l + o.s 0
1. 5 +.2 -.2 +.6 +.l
1. 7 +.3 -.3 +. 7 + 1.s
2. 2 +.3 -. 3 + 1 .3
2.4 +.3 -.3 + 1 + .4
2. 6 +.35 -. 4 +1.2 +.4
2.8 +.35 -.4 +t.3 +.4
R£FEREf'ICE I.IN£
11£FERENC£ LINE
TO/lf.SJONl'fL.
ff£1'EIJENCE LIIV£
REFERENCE LINE
13
WINI; OEFL.£Crl0N
I
~
'· I
FIG. 15
F IG. 16
LEllOJNG EO<;E -·
--~
Tli'lllLING EDGE
CU!i'Tl.SS Pl/RSUIT P. W. - 8
LOW' INCIDENCE
LE.llDING EDGE·
THNLIN6 EDGE
....-b!:.:L
/~
l.. .F. " 5
L.F. • "
-~
L.F. • 7
-L.F.=7.5
CLl6TISS AIHSVI r fr W. ·8
Hl6H INC/OENCE.
14
---------~----------eif~---------------------11+-i
_ s-+-+---e ~sJ. --t-~i e-.---.. B 8 e sa 1
:: ::· II II ·::
I 11 II II 11 II
~-;-- =: :!'-:- ----....n.=.=..:-_-=-=-:ic _-~:: -t- - - - _ - -1
BOLT.S
~ OF A/LEHON TORWE. TIJBE
/
0 0 .D . )( . 049WALL
:' :...n.... --:: --_- L
AILERON HINGf
CU~TIS PURSUIT
AILERON
FIG. 17
AILERON TEST AND LOADING SCHEDULE AREA OF
AILERON=8.42 SQUARE FEET
Pounds Added
per load Total Pull
square for on Remarks feet each load stick factor
- --- - - ---
Pounds Pounds
5 42 42 10 The control stick showed ouly a
slight defiection even with the
maximum load on the surfaces.
10 42 84 15
15 42 126 20. Very little stretch was noticed in
the control cables.
20 42 108 25
22.5 21 189 27. 5
25 21 210 30
27. 5 21 231 35
30 21 252 40
32. 5 21 273 45·
35 21 294 50 Required load .
37. 5 21 315 55 Left aileron sagged down 2" when
control stick was in neutral
40 21 336
position.
57. 5
42. 5 21 357 60 After load was removed the sur-faces
showed no perceptible dis·
tortion.
I 45 21 378 62. 5
Fm. 18.-Curtiss Pursuit PW-8
15
NOTt - JTU.4, RIB.S
:SWEATED TO .SP'4RS
i----- Z3-J ------<~
1-+~~~~~~~~~~~~~~~~~~~~~~11~
CVRTISS PVRSVIT
E [YATOR 8.. S111BILIZER
FrG.19
G B
LOADING SCHEDULE AND R E SULTS OF ELEVATOR AND STABILIZER TEST
Pounds
. per
square
foot
5
JO
15
20
22. 5
25
27. 5
30
32. 5
35
37. 5
40
42. 5
45
47. 5
50
55
!'17. 5
A
Deflections in inches at-
- ------~-~- -- _____ ,
13 c D E F G H
P ull
on
stick
Pou11ds
Stab.
adj.
0 - . 2 . l . 3 . 3 . 3 . 2 0 10 OK
=: ~ =: ~ I : ~ : ~ 1: 5 1: 6 : ~ : ~ ~ g~
. 0 - 4 . 7 1.1 1. 3 1. 4 . 6 . 5 50 OK
- - ----- --- - -- ----------- - ----- - - -- - --- ---- - --- - --- --- ---- - ----- - -------- OK
--~~~-- --;~~--!---~~~-- ---~~:-- ---~~:-- ---~~~-- ----~:-- ----~~-- ----:-----~:~---
- .1 -. 2 1.7 2.2 2.6 2.6 1.0 . 7 90 (')
- . 1 -. 2 1. 8 2. 4 2. 9 2. 8 1. 0 . 7 95 (')
:::::::: :::::::: ::::::::i:::::::: :::::::: :::::::: :::::::: :::::::: ::::::::[:::::::: No failures were noticed but elevator sagged badly ___ ___ __ _______ _ ______ __ ____ ___ ----------- ---- ------------------------------ ------ ---- --- ------ ---- ------ -- - --- -- --
1 Stab ilizer adjustment required both hands to operate wheel.
FIG. 20.-Curtiss Pursuit PW-8
Total loads in pounds
Elev.
21
42
63
84
95
105
116
126
137
147
158
168
179
189
200
210
221
232
Elev.
Bal.
. 3
6
9
12
14
15
17
18
20
21
23
24
26
27
29
30
32
33
Stab.
36
72
l08
144
162
180
198
216
234
252
270
288
306
324
342
360
378
396
16
.,,,.
'<>
,/!;==:r--=~:p===*=~ -+
.03+
171
l.J It)
...
11..i
~ t-.: j 1;faa x. o-42 WALL. I ·1
1J.o.o . )( .012 WALL · =--i~====~=====;~
j 0 . D. X .035 ll'ALL . -I+ jj_
f-4...-- - - 29 i ___ __,...,, :i---- 24 .1
/tfOTE. :- HIBS ARE CHANN£L. 5£CTION , .Cle5 .5T~EL, , .. FLANGE.5
FIG. 21-Curtiss Pur•uit-fin and rudder.
DEFLECTIONS AND LOADING SCHEDULE FOR RUDDER
AND FIN TEST
Deflections in inches at­Pounds
per 1---------­square
foot A B C D
5 . ] . 1 . - . 1 -.2
10 .1 .2 - .2 -.4
15 .2 .4 .9 . 5
20 .3 . 5 1. 4 . 9
22. 5 .3 . 6 1. 4 .9
25 . 3 . 7 2. 4 1. 7
27. 5 . 4 .8 2. 4 1. 7
30 .4 .8 2. 6 1. 8
32. 5 . 5 .9 2.9 1.9
35 .4 .9 37. 5 ::~:~J:~:~::
40
42. 5 ------ ----- - -------1------- 45 ------- ------- 47. 5 --- --- ---- ---- 50 ------- ---- ---
I
Pull
on
stick
P ounds
30
45
eo
75
90
100
no
120
135
145
--- -----
Loads in pounds on-
Fin
21
42
63
84
94
105 .
ll5
126
136
147
157
168
178
189
199
210
Rud. Rud.
Bal. Main
6 37
12 75
18 112
24 150
27 ,169
30 187
33 206
36 224
39 243
42 261
45 280
48 298
51 317
54 335
57 354
60 372
Rudder and fin supported average load of 50 pounds per square
foot without failure.
FIG. 22.-Curtiss Pursuit PW-8
17
PUINE OllCY
A
B
c
D
E
!! F
(;
FIG. 23.- Curtiss Pursuit fu selage
B
LOADING SCHEDULE AND DEFLECTIONS IN FUSELAGE
TEST
Deflections Load in pounds, at-
Load at~
factor Remarks
l ~\~ _ A l_B c D
2 .8 .4
!
0 l, 952 I , 603 639 392
3 1.0 . 6 . 5 2, 948 2,417 981 603
4 I. 2 . 6 . 3 3, 944 3, 231 1,323 814
5 I. 2 .7 . 5 4, 940 4,045 1, 665 1,025
5. 5 ]. 3 .7 . 5 5, 438 4,452 1, 836 I, 130
6 I. 3 . 7 . 7 5, 936 4, 859 2,007 1, 235
6. 5 I. 3 -~7l~- 6, 434 5, 266 2, 178 1,340
7 6, 932 5, 673 2, 349 I, 445 Failure of lower
longerons in
third bay.
FIG. 24.-Curtiss Pursuit PW-8
't
TIJllL .511:,U
I. ~o Q,/2: ~2 !\'ALL.
I.ZS " . . 061
I. I ZS .. .0(,,2
1.00 " .052
JJ7S - .0]4
.7f. .. .034
.62S
D
6
9
12
15
18
21
24
27
30
o. K.
0 . K .
0. K.
0.K.
0.K.
0.K.
0. K .
0. K.
18
Last baY o r ruselagefailed.
NOTE.- Thirty inches .r equi. red drop
FIG. 25 .- Cn r t"! SS Pursuit PW' -8 t ai' I ski. d drop t es ts
FIG. 26
r
CllHTISJ l'!JffSUIT p W. ·8
DYNMIC TEST OF CHl'ISSIS
19
DYNAMIC TEST OF LANDING CHASSIS
Full load - 2,528 pounds required distance dropped through=24 inches
Half load - 1,264 pounds required dist ance dropped through =48 inches
I
Deflection, in
Dis- inches, of shock
d~~~~~d absorbers
through ' _____ __ ,
Left Right
Remarks
----------1--- - - -------------1
Inch es
3
6
9
107§
12
137§
18
21
24
27
30
30
33
36
39
42
45
48
51
--------1-------- Original 26X4 'wheels and tires, pressure
in tires 73 pounds, full load of 2,528
pounds was imposed on chassis at begin­ning
of test.
Wheel collapsed.
New wheels and 28X4 tires were fitted ;
test was continued· with half load.
:::::::: ::::::::1 Right wheel collapsed.
lH 2 New wheels and 750Xl25 tires were fi tted ;
2 2%
test was continued with half load .
Right wtieel bending, while chassis struc­ture
showed no signs of failure at 48
inches, the required distance dropped
through. Test discontinued.
FIG . 27.- Curt iss Pursuit PW-8
FIG. 28
21
7
22
23
24
FIG. 35
0
•f