” ENGIN. LIB.
gr l‘ a ‘ “ ANC 2
r ' R ‘i B 802,420 I October 1952
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Ground
Loads “

MUNITIONS‘ BOARD
AIRCRAFT COMMITTEE
i‘
NMVERSW 0F
hEa-LN Lk
ANC-2 BULLETIN
Ground Loads
DEPARTMENT OF THE AIR FORCE
AIR RESEARCH AND DEVELOPMENT COMMAND
DEPARTMENT OF THE NAVY
BUREAU OF AERONAUTICS
DEPARTMENT OF COMMERCE
CIVIL AERONAUTICS ADMINISTRATION

- For sale by the Superintendent of Documents, U. 3. Government Printing Ofﬁce, Washington 25, D. C.
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ISSUED BY THE SUBCOMMITTEE ON “AIR FORCE-NAVY~CIVIL AIRCRAFT DESIGN CRITERIA .
OF THE MUNITIONS BOARD AIRCRAFT COMMITTEE
The contents of this Document shall not be reproduced in whole or in part without speciﬁc authorization of the
Munitions Board Aircraft Committee
Price 15 cents
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NOTICE
The reader is hereby notiﬁed that this document is subject to revision when and where
such revision or amendment is necessary to effect agreement with the latest approved infor-
mation on aircraft design criteria. When using this document the reader should therefore
make certain that it is the latest edition and that all issued amendments, if any, are
included herein. When ordering this document from the Superintendent of Documents,
United States Government Printing Ofﬁce, a request for all revisions and amendments
thereto should be made to insure receipt of a complete document.
Copies of this document and amendments thereto may be obtained from the Superin-
tendent of Documents, United States Government Printing Office, Washington 25, D. G.
This edition supersedes all previous editions of ANG-2 and ANC—2a.
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CONTENTS
CHAPTER 1 . GENERAL
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1. 1. Introduction __________________________________________________ _ _
1.2. Factor of Safety ______________________________________________ __
1.3. Load Application ______________________________________________ _ -
1.4. Dynamic Loads _______________________________________________ _ _
1.41. Landing Impact _______________________________________________ __
1.42. Other Dynamic Conditions _____________________________________ _ -
1.5. Alternate Conditions ___________________________________________ _ _
1.6. Design Parameters ____________________________________________ _ -
1.61. Weights ______________________________________________________ __
1.62. ‘Center of Gravity Positions _____________________________________ __
1.7. Symbols ______________________________________________________ _ _
I—lI—II—II—ll—II—ll—li—ll—lI—lH
CHAPTER 2. LANDING CONDITIONS
2.1. General- _____________________________________________________ __
\ 2.11. Landing Parameters ____________ __~ _____________________________ _ _
2.12. Deﬂections of Landing Gear Elements ___________________________ __
2.2. Ground Reactions _____________________________________________ __
2.21. Maximum Spin-Up ____________________________________________ _ _
2.22. Dynamic Spring-Back __________________________________________ __
2.23. Maximum Vertical Reaction ____________________________________ __
2.3. Landing Conditions ____________________________________________ __
2.31. Nose Wheel Type _____________________________________________ __
2.32._ Tail Wheel Type ______________________________________________ _ _
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CHAPTER 3. TAXIING CONDITIONS
3.1. General ______________________________________________________ __
3.2. Braking Conditions ____________________________________________ _ _
3.21. Nose Wheel Type ____________________ __' _______________________ __
3.22. Tail Wheel Type ______________________________________________ __
3.3. Turning ______________________________________________________ __
3.31. Outside Gear __________________________________________________ __
3.32. Inside Gear ___________________________________________________ __
3.33. Auxiliary Gear ________________________________________________ __
3.4. Pivoting ______________________________________________________ _ _
3.5. Minimum Load Factor For Take-Off _____________________________ __
3.6. Special Tail Wheel Conditions ___________________________________ __
OQODQODGIOEOTUICHCHUI
CHAPTER 4. HANDLING CONDITIONS
4.1 . General ______________________________________________________ _ _
4.2. Towing _______________________________________________________ - _
4.3. lacking ______________________________________________________ _ _
4.4. Hoisting ______________________________________________________ _ _
4.41. Navy Planes and Air Force Water Planes _______________ __i ________ __
4.42. Air Force Land Planes _________________________________________ __
4.5. Mooring ______________________________________________________ _ _
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CHAPTER 5. MISCELLANEOUS CONDITIONS
Page
5.1. Rebound- ____________________________________________________ -_ ‘10
5.2. Extension and Retraction ______________________________________ __ 10
5.21. Flight Loads ___________________________________________________ __ 10
5.22. Friction, Inertia, and Air Loads _________________________________ __ 10
5.23. Gyroscopic Moments ___________________________________________ __ 10
5.24. Braking Loads ________________________________________________ __ 10
5.3. Load Distribution on Multiple Wheels ___________________________ __ 10
5.31. Dual or Twin Wheels (Side by Side) _____________________________ __ 10
5.32. Multiple Wheels Other Than Dual or Twin _______________________ _ _ 10
5.4. Tail Bumper Criteria- _________________________________________ __ 11
5.5. Turn-Over ___________________________________________________ __‘_ 11
CHAPTER 6. UNCONVENTIONAL GEAR CONFIGURATIONS AND HELICOPTERS
6.1. General ______________________________________________________ __ 12
6.2. Design Conditions _____________________________________________ _.. 12
6.21. Bicycle _______________________________________________________ __ 12
6.22. Quadricycle ___________________________________________________ __ 12
6.23. Cross-Wind ___________________________________________________ __ 12
6.24. Track ________________________________________________________ __ 12
6.25. Ski__ ___________________________________________________ 12
6.26. Skid _______ "7 _______________________________________________ __ 12
6.27. Helicopter ____________________________________________________ __ 13
6.28. Special _______________________________________________________ __ 13
CHAPTER 7. METHODS OF ANALYSIS
7.1. General ______________________________________________________ __ 14
7.2. Dynamic Landing Loads_ ______________________________________ __ 14
7.3. Spin-Up and Spring-Back Loads _________________________________ __ 14
7.31. Maximum Spin-Up- ___________________________________________ __ 14
7.32. Dynamic Spring-Back __________________________________________ __ 14
7.33. Dynamic Response__ __________________________________________ __ 15
7.4. Turning ______________________________________________________ __ 15
7.41. Outside Gear _____________________________________________ __*_ _ ___ 15
7.42. Inside Gear ___________________________________________________ __ 15
7.43. Auxiliary Gear ________________________________________________ __ 15
7.5. Braking Torque _______________________________________________ __ 15
7.51. Experimental Method _________________________________________ -_ 15
7.52. Alternate Method_ ____________________________________________ _- 16
7.53. Hydraulic Brakes ______________________________________________ __ 16
CHAPTER 1
GENERAL

1 .1 Introduction -
The ground loads and loading conditions speci-
ﬁed in the following requirements are those that
shall be considered as the minimum acceptable
structural requirements for design. The require-
ments of this bulletin (except Chapter 6) shall
apply to the design of airplanes equipped with
conventional main and nose or tail wheel gear
conﬁgurations. They shall also apply to air-
planes with unconventional gear conﬁgurations,
except where replaced by pertinent criteria in
Chapter 6 of this bulletin, or by requirements ap-
proved by the procuring service or certiﬁcating
agency.
1.2 Factor of \Safety
The loads speciﬁed in this bulletin are limit
loads and shall be multiplied by a minimum factor
of safety of 1.5 to obtain design ultimate loads.
1 .3 Load Application
The loads speciﬁed in this bulletin shall be con-
sidered as external forces applied to the airplane
structure, and shall be placed in equilibrium by
means of translational and/or rotational inertia
forces applied in accordance with rational or
conservative methods.
1 .4 Dynamic Loads
An investigation shall be made to determine the
dynamic loads in the airplane structure and the
landing gear when such loads may be signiﬁcant.
1.41. LANDING IMPACT. The requirements and
acceptable methods for determining the dynamic
landing loads are given in Chapter 7 of this
bulletin.
1.42. OTHER DYNAMIC CoNDITIoNs. When dy-
namic loads resulting from conditions other than
the landing impact may be signiﬁcant, they shall
be investigated using methods acceptable to the
procuring service or certiﬁcating agency.
1.5 Alternate Conditions
Deviations from the requirements set forth in
this bulletin, or the substitution of alternate con-
ditions or methods of analysis, shall be subject to
the prior approval of the procuring service or
certiﬁcating agency.
1 .6 Design Parameters
1.61. WEIGHTS. The design take-off weights
and the design landing weights shall be speciﬁed
by the procuring service or certiﬁcating agency.
1.62. CENTER or GRAVITY POSITIONS. The loads
specified in this bulletin shall be determined for
each of the design weight conditions and the cor-
responding center of gravity positions, which pro-
duce the maximum design loads.
1.7 Symbols
The following symbols are used throughout this
bulletin:
d, Total deﬂection (feet) at time 25,,
taken equal to x,+0.5 so, where
a:,=tire deﬂection and wo=total
oleo stroke.
FDSU Maximum spin-up drag load, par-
allel to ground line, before cor-
rection for dynamic magniﬁ-
cation, lbs.
F0 Static ground reaction; the verti-
cal component of the load on
any gear corresponding to a
resultant load factor of lg ver-
tical acting through the c. g.
F0, Static reaction on a jacking or
hoisting point.
FS Side load, lbs.
FTOW Towing load, lbs.
FV Vertical load, lbs.
FVMAX Maximum vertical load, lbs.
VSU Vertical load at tsu.
g Gravitational constant, ft/sec.2
1,, Polar mass moment of inertia of
rotating wheel assembly, slug
ftg.
KSB
Ksv
1»
1st!
Dynamic response (magniﬁcation)
factor for spring-back load.
Dynamic response (magniﬁcation)
factor for spin-up load.
Airplane pitching radius of gyra-
tion, ft.
Distance from most critical 0. g.
position to airplane tail bumper,
measured normal to the line of
action of the resultant force at
the tail bumper, ft.
Wing lift, lbs.
Effective mass, slugs.
Side load factor at the cg.
Ground reaction factor; the ratio
of the vertical component of the
total ground reaction on any
gear to the vertical component
of the static reaction on that
gear.
Tire rolling radius, ft.
Natural period of landing gear in
fore and aft vibration, sec.
Time required for wheel circumfer-
ential velocity to reach ground
velocity, sec.
Time required to develop maxi-
mum vertical reaction after ini-
tial instant of contact, sec.
Landing speed for condition under
investigation, ft/sec.
Power-off stalling speed in the
landing conﬁguration for stand-
ard sea level conditions, ft/sec.
Power-on stalling speed in the
take-off conﬁguration for stand-
ard sea level conditions, ft/sec.
Airplane vertical velocity (sinking
speed), ft/sec.
Sinking speed for tail bumper de-
sign, ft/sec.
Design landing Weight, lbs.
Design maximum take—off Weight,
lbs.
Angle between oleo center line and
the vertical, deg. (Positive for
oleo inclined forward from wing
or fuselage.)
CHAPTER 2
LANDING CONDITIONS

2.1 General
The landing gear and the airplane structure
shall be investigated for the landing conditions at
both landing and take—off weights.
2.11. LANDING PARAMETERS. The ground reac-
tion factors, ﬂy, for the landing attitudes, the sink-
ing speeds, Vv, for both landing and take-off design
weight conditions, and the amounts of wing lift,
L, acting shall be speciﬁed by the procuring service
or certiﬁcating agency.
2.12. DEFLECTIONS or LANDING GEAR ELEMENTs.
2.121. H ydraulie Shock Struts. The vertical
component of the ground reaction shall be assumed
to develop with time in the manner speciﬁed in
paragraph 7.31 unless otherwise substantiated.
2.122. Rubber or Spring Shock Struts. The
load factor shall be assumed to be proportional to
strut deﬂection with the maximum occurring with
100 percent deﬂection.
2.123. Tires. Either the actual tire deﬂection
developed in the particular condition, or the static
deﬂection of the tire obtained from the Tire and
Rim Association Yearbook shall be used.
2.2 Ground Reactions
Three combinations of vertical and drag forces
acting at the center line of the axle shall be investi—
gated in each of the landing conditions. (Refer to
ch. 7 for acceptable methods of analysis.)
2.21. MAXIMUM SPIN—UP. A drag component
(spin-up load) equal to the maximum force re-
quired to accelerate the wheel assembly up to speed
during the landing impact shall be combined with
the vertical ground reaction existing at the time
of the maximum spin-up load. This condition
shall be investigated for the landing gear and the
airplane structure. The load shall be distributed
to the airplane structure in a rational or conserva-
tive manner.
2.22. DYNAMIC SPRING-BACK. The loads in this
condition shall simulate the forward acting dy-
namic response of the landing gear subsequent to
the initial impact. The maximum forward acting
load shall be combined with the vertical ground
reaction existing at the time of the maximum for-
ward acting load. If the characteristics of the
gear are such that the maximum vertical load has
not developed at the time of maximum spring-
back load, additional cycles of peak forward act-
ing drag load shall be investigated to determine
the combinations of peak forward acting drag load
and vertical load that are critical for design. This
condition shall be investigated for the landing
gear and the airplane structure. The load shall
be distributed to the airplane structure in a
rational or conservative manner.
2.23. MAXIMUM VERTICAL REACTION. The max-
imum vertical ground reaction shall be combined
with a drag load equal to one-quarter of the
maximum vertical ground reaction. This condi-
tion shall be investigated for the landing gear and
the complete airplane structure as a rationally or
conservatively balanced condition.
2.3 Landing Conditions
2.31. NosE WHEEL TYPE.
2.311. Le’veZ Landing, Three Point. The
main and auxiliary wheels shall contact the
ground simultaneously. A range of forward ve-
locities of from 1.0 VSL to 1.2 VSL shall be con-
sidered. (Usually the main gear need not be
investigated for this condition.) The vertical
components of the ground reactions shall be those
which would result from contacts with the speci-
ﬁed sinking speeds, wing lift, and energy distribu-
tion to the landing gear units. For the spin-up
and spring-back investigations, the rate of descent
energy at contact shall be apportioned to the land-
ing gear units in accordance with the static ground
reactions, F 0. For the maximum vertical reaction
investigation, the rate of descent energy at contact
shall be apportioned to the landing gear units in
accordance with one load factor vertical and one_
quarter load factor horizontal acting through
the cg.
2.312. Le’vel Landing, Two Point. The main
wheels shall contact the ground with the nose
wheel just clear of the ground. A range of for-
ward velocities of from 1.0 V SL to 1.2 VSL shall be
considered. The vertical components of the
ground reactions shall be those which would result
from contacts with the speciﬁed sinking speeds
and wing lifts.
2.313. Tail Down Landing. The airplane
shall contact the ground in the attitude of maxi-
mum lift, or in the maximum angle permitting
ground clearance by all parts of the airplane,
whichever is the lesser. The forward velocity at
contact shall be VSU The vertical components of
the ground reactions shall be those which would
result from contacts with the speciﬁed sinking
speeds and wing lifts.
2.314. One-Wheel Landing. The airplane
shall land on one wheel with the same landing gear
loads, attitude, and loading conditions as of para-
graph 2.312. The wing and fuselage structure
shall be analyzed for this condition. The unbal-
anced rolling and yawing moments shall be ra-
tionally or conservatively reacted by airplane
inertia. The unbalanced pitching moments may
be neglected.
2.315. Drift Landing. The airplane shall be
in the level attitude with only the main wheels
contacting the ground. The vertical reaction on
each main gear shall be equal to one-half of the
maximum vertical ground reaction obtained in the
two point level landing condition, paragraph
2.312. The side loads shall consist of an inward
acting load equal to 0.8 of the speciﬁed vertical
reaction and an outward acting load equal to 0.6
of the speciﬁed vertical reaction. These loads,
acting simultaneously, are applied at the ground
contact points, and may be assumed resisted by
airplane inertia. Drag loads may be assumed
zero.
2.32. TAIL WHEEL TYPE.
2.321. Level Landing. The airplane refer-
ence axis shall be assumed to be horizontal at
ground contact. A range of forward velocities of
from 1.0 VSL to 1.2 VSL shall be considered. The
vertical components of the ground reactions shall
be those which would result from contact with the
speciﬁed sinking speeds and wing lift.
2.322. Tail Down Landing. The main and
auxiliary gears shall contact the ground simul-
taneously, with a forward velocity of VSL, The
vertical components of the ground reactions shall
be those which would result from contact with the
speciﬁed sinking speeds and wing lift. The rate
of descent energy at contact shall be apportioned
to the landing gear units in accordance with the
static ground reactions, F0.
2.323. One Wheel Landing. The airplane
shall land on one wheel with the same landing gear
loads, attitude, and loading conditions as of para-
graph 2.321. The wing and fuselage structure
shall be analyzed for this condition. The un-
balanced rolling and yawing moments shall be
rationally or conservatively reacted by airplane
inertia. The unbalanced pitching moment may
be neglected.
2.324. Drift Landing. The airplane shall be
in the level attitude with only the main wheels
contacting the ground. The vertical reaction on
each main gear shall be equal to one half of the
maximum vertical ground reaction obtained in
the level landing condition, paragraph 2.321. The
side loads shall consist of an inward acting load
equal to 0.8 of the speciﬁed vertical reaction, and
an outward acting load equal to 0.6 of the speciﬁed
vertical reaction. These loads, acting simultane-
ously, are applied at the ground contact point and
may be assumed to be resisted by airplane inertia.
Drag loads may be assumed to be zero.
CHAPTER 3
TAXIING CONDITIONS

3.] General
Unless otherwise speciﬁed herein, the landing
gear and airplane structure shall be investigated
for the taxiing conditions at landing and take-off
gross weights, with zero wing lift acting, and
with the shock struts and tires in static positions.
3.2 Braking Conditions
3.21. N OSE WHEEL TYPE.
3.211. Brall'recl Roll, T’wlO Point. The air-
plane shall be in the three point attitude, with
the nose wheel just clear of the ground. The
vertical load factor acting at the cg shall be 1.2
at landing weight or 1.0 at take-off weight, which-
ever is the more critical. A drag reaction, at each
wheel in contact equipped with brakes, shall be
assumed acting at the ground equal to 0.8 of the
vertical reaction, and shall be combined with the
vertical reaction. The pitching moment shall be
balanced by airplane rotational inertia.
3.212. Braised Roll, Three Point. The air-
plane shall be in the three point attitude. The
vertical load factor acting at the cg shall be 1.2
at landing weight or 1.0 at take-off weight, which-
ever is the more critical. A drag reaction, at each
wheel in contact equipped with brakes, shall be
assumed acting at the ground equal to 0.8 of the
vertical reaction and shall be combined with the
vertical reaction. The pitching moment shall be
balanced by airplane wheel reactions.
3.213. Unsg/mmetrlcal Braking. The auxil-
iary gear and fuselage structure shall be investi-
gated for the loads developed in this condition.
The airplane shall be in the three point attitude.
The vertical load factor shall be 1.0 at the cg. One
main gear shall be assumed braked and developing
a drag load at the ground equal to 0.8 of the verti-
cal reaction of that gear. The airplane shall be
placed in static equilibrium, with side loads at the
main and nose gears reacting the yawing moment,
and vertical loads at the main and nose gears
reacting the pitching moment. The forward act-
ing load at the cg shall be 0.8 of the vertical reac-
224~486——-62-—-—2
tion on that main gear which is braked. The side
load at the cg shall be assumed zero. The side
load at the nose wheel shall be assumed acting at
the ground, and need not exceed the vertical reac-
tion multiplied by a coeﬂicient of friction of 0.8.
The nose wheel shall lie in a fore and aft plane.
3.214. Reverse Braking. The airplane shall
be in the three point attitude with the nose wheel
just clear of the ground. The vertical load factor
at the cg shall be 1.0. A forward acting drag
reaction, acting at the ground, equal to 0.8 of the
vertical reaction, shall be combined with the verti-
cal reaction, for each wheel in contact equipped
with brakes. The pitching moment shall be
balanced by rotational inertia.
3.22. TAIL WHEEL TYPE.
3.221. Braised Roll, Two Point. The air-
plane reference axis shall be horizontal. The ver-
tical load factor acting at the cg shall be 1.2 at
landing weight, or 1.0 at take-off weight, which-
ever is the more critical. A drag reaction at the
ground, at each wheel in contact equipped with
brakes, equal to 0.8 of the vertical reaction shall be
combined with the vertical reaction. The pitching
moment shall be balanced by airplane rotational
inertia.
3.222. Reverse Brakthtg. The airplane shall
be in the three point attitude. The vertical load
factor at the cg‘ shall be 1.0. A forward acting
drag reaction, acting at the ground, equal to 0.8 of
the vertical reaction shall be combined with the
vertical reaction, for each wheel in contact
equipped with brakes. The pitching moment shall
be balanced by wheel reactions.
3.3 Turning
The airplane in the static position shall execute
steady turns by means of differential power or
nose gear steering. The vertical load factor shall
be 1.0 at the cg. The ratio of side to vertical load
components shall be equal on all wheels. (See par.
7.4 for analysis.)
3.31. OUTSIDE GEAR. For that gear which is on
the outside of a turn, the side load factor developed
at the. cg shall be that value which is limited by
overturning, except that it need not exceed 0.5.
3.32. INSIDE GEAR. For that gear which is on
the inside of a turn, the side load factor developed
at the cg shall be that value which results in the
maximum outward load on the gear, except that
it need not exceed 0.5.
3.33. AUXILIARY GEAR. For the auxiliary gear,
the side load factor developed at the cg shall be
that developed in the turn speciﬁed in paragraph
3.31.
3.4 Pivoting
With brakes assumed locked on the wheels of
the gear unit about which the airplane is rotating,
the airplane shall pivot about one wheel, or in the
case of multiple wheels, about the centroid of con-
tact area of all wheels in the gear unit. The verti-
cal load factor at the cg shall be 1.0, and the tire
coefficient of friction shall be 0.8.
3.5 Minimum Load Factor for Take-Off
The minimum limit load factor at the gear for
the design of the airplane for taxiing at the max-
imum take-off weight condition shall be 2.0. The
airplane shall be in the three point attitude. This
factor shall apply to the vertical reaction only,
with zero drag and zero side loads acting. No
wing lift may be considered acting. (This condi-
tion is not required by the CAA.
3.6 Special Tail Wheel Conditions
The airplane shall be in the three point attitude
with the tail wheel swiveled 90° from the trailing
position, or the maximum angle obtainable, which-
ever is the lesser. A side load, acting at the
ground, equal to the maximum static vertical reac-
tion shall be combined with the maximum static
vertical reaction. If the tail wheel is equipped
with a shimmy damper, lock, or steering mech-
anism, the gear shall be investigated for this side
load with the wheel also in the trailing position
and with the side load acting at the ground.
CHAPTER 4
HANDLING CONDITIONS‘

4.1 General
Handling conditions are not required by the
CAA.
4.2 Towing
Towing loads shall be those speciﬁed in table
4.1, considering each condition separately. These
loads shall be applied at the towing ﬁttings and
shall act parallel to the ground. A vertical load
factor of one shall be considered acting at the cg.
The shock struts and tires shall be in their static
positions. The towing load, FTOW, is deﬁned by
ﬁgure 4.1, and shall be based on the maximum
take-off weight. For towing points not on the
landing gear but located near the plane of sym-
metry of the airplane, the drag and side tow load
components speciﬁed for the auxiliary gear shall
apply. For tow points located outboard of the
main gear the drag and side tow load components
speciﬁed for the main gear shall apply. When
the speciﬁed angle of swivel cannot be obtained,
the maximum obtainable angle shall be used.
Note: Attention is called to the possibility of attempt
to steer the airplane with the tow bar, resulting in a
moment at the tow bar attachment.
4.3 Jacking
J acking loads shall be those speciﬁed in table
4.2. The load components shall besconsidered in
all combinations which include the vertical com-
ponent. The horizontal loads at the jack points
shall be assumed to be reacted by inertia forces
in such a manner as to cause no change in the verti-
cal loads at the jack points.
4.4 Hoisting
4.41. NAVY PLANES AND AIR FORCE WATER
PLANEs. The airplane shall be in the level atti-
tude. The vertical component shall be 2.67 F01,
where F o is the maximum reaction at a hoisting
point based on a vertical load factor of one acting
through the center of gravity and on a suitable
gross weight approved by the procuring service
(usually the maximum take-off gross weight).
Horizontal loads shall be assumed zero.
4.42. AIR FORCE LAND PLANEs. The airplane
shall be in both the level and the three point atti-
tudes. The vertical component shall be 2.0 F 01,
where F oj is deﬁned in paragraph 4.41. Horizon-
tal loads shall be assumed zero.
4.5 Mooring
Mooring ﬁttings and the structure to which
they are attached shall be analyzed for loads re-
sulting from a 7 5 m. p. h. wind parallel to the
ground at any direction to the airplane. (Air
Force requirement only. For Navy requirements
see Bureau of Aeronautics Speciﬁcation SS—l.)
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Table 4.1. Towing loads


Load
Tow point Position
Magnitude No. Direction
1 Forward, parallel to drag axis.
. . . 2 Forward, at 30° to drag axis.
Main gear. 0.75 F'Tow per-‘main gear unit. 3 Ari; parallel to drag axis.
- 4 Aft, at 30° to drag axis.
I 5 Forward.
Swiveled forward. 6 Aft.
1-0 FTow.
. 7 Forward.
Swiveled aft. 8 Aft‘
Auxiliary gear.
. 9 Forward in plane of wheel.
0 7
Swiveled :15 from forward. 10 Afe, in plane of wheel.
0-5 Frow.
. 11 Forward in plane of wheel.
0 I
Swlveled 45 from aft’ 12 Aft, in plane of wheel.

BALANCING FORCES


The side component of the towing load at the main gear is reacted by a side force at the static ground line at the
wheel to which load is applied.
The towing loads at the auxiliary gear and the drag components of the towing loads at the main gear should be
reacted in each of the following ways:
a. Reaction shall be applied at the axle of the wheel to which load is applied, this reaction having a maximum
value equal to the vertical reaction. Airplane inertia may be applied as required for equilibrium.
1). The loads shall be reacted by airplane inertia.
Table 4.2. J aching Loads
Landing gear Primary ﬂight
Component jacking points; structure jacking
three-point attitude points; level attitude
Vertical ________________________________ -_ 1.35 F0; 2.0 F0,-
Fore or aft _____________________________ __ 0.4 F0,- 0.5 F0,-
Lateral ________________________________ __ 0.4 F0; 0.5 F0,-
F0,- shall be based on a suitable gross weight approved by the procuring
service


CHAPTER 5
MISCELLANEOUS CONDITIONS

5.l Rebound
A rebound load factor of —- 20.0 shall be assumed
to act on the unsprung weight along the line of
motion of the strut as it approaches the fully
extended position.
5.2. Extension and Retraction
The landing gear, retracting mechanism, and
supporting structure shall be designed for the fol-
lowing loads:
5.21. FLIGHT LoADs. The loads occurring in
the airplane ﬂight conditions shall be considered in
the design of the landing gear in the retracted
position.
5.22. FRIoTIoN, INERTIA, AND AIR LoADs. The
design shall consider the friction, inertia, and air
loads occurring during retraction and extension at
any airspeed up to the maximum landing gear
operating speed, except not less than 1.75 VSL and
any load factors up to those speciﬁed for the ﬂaps
extended conﬁguration.
5.23. GYRosooPIo MOMENTS. The design shall
consider the gyroscopic moments due to motions
of the wheels about axes other than parallel to the
axle centerline during extension and retraction.
5.24. BRAKING LoADs. All landing gear parts
shall possess sufﬁcient strength to withstand the
loads imposed by the application of brakes, in-
cluding spring-back effects, immediately after
take-off. (See par. 7.5 for acceptable methods of
determination.) The take-off speed shall be as-
sumed as 1.3 VST at the take-oﬁ weight. The gear
shall be in the fully extended position and in any
position between fully extended and fully re-
tracted. The following loads shall be considered
acting simultaneously:
a. Air loads resulting at an equivalent air-
speed up to the take-off speed.
5. Dead weight loads at a vertical load factor
of 1.0.
0. Brake torque as necessary to stop the rota-
tion of the wheels from an initial peripheral veloc—
ity equal to the take-off speed.
5.3 Load Distribution on Multiple Wheels
5.31. DUAL oR TWIN VVIIEELs (SIDE BY SIDE).
When dual or twin wheels are used for the auxil-
iary landing gear and/ or for each half of the main
gear, the following load distributions between the
wheels shall be investigated for each condition (ex-
cept pars. 3.213, 3.214, 3.222 and 3.4), and the
most severe loads resulting from these distribu-
tions shall be used in the design of the structure:
5.311. Symmetrical Distribution. Fifty per-'
cent on each wheel.
5.312. Unsymmetrioal Distribution.
5.3121. Unequal tire inﬂation. Sixty percent
on one wheel (forty percent on the other) of the
total vertical, drag and side loads for the landing
gear unit. (In the Drift Landing Conditions,
pars. 2.315 and 2.324, and the Turning Condition,
par. 3.3, the sixty percent need not be applied to
the inboard wheel of the outside gear with an in-
ward acting side load, nor to the outboard wheel
of the inside gear with an outward acting side
load.)
5.3122. Flat tire. For the condition of one
ﬂat tire, the entire load speciﬁed for a particular
gear unit in the following subparagraphs shall be
applied to the other wheel.
5.31221. Landing conditions. Sixty percent
of those loads speciﬁed for each condition with no
tire ﬂat. (The airplane need not be rebalanced
for these conditions.)
5.31222. Taaiiing and handling conditions. A
vertical load factor of one shall be considered
acting at the cg. The side and/ or drag load factor
at the cg shall be the most critical value up to ﬁfty
percent of that resulting from the most severe
condition speciﬁed for no tires ﬂat, except that the
towing load, FTOW, shall be that deﬁned by ﬁgure
4.1.
5.32. MULTIPLE WHmLs OTHER THAN DUAL oR
TWIN. When multiple and/or tandem wheels are
used for the auxiliary gear and/or for each half
of the main gear, proposed criteria for load distri-
10
-..
bution shall be submitted for approval to the pro-
curing service or certiﬁcating agency.
5.4 Tail Bumper Criteria
The tail bumper must be able to absorb the
kinetic energy of the airplane in its most unfavor-
able cg position in a tail down attitude. A tail
bumper ﬁrst landing shall be assumed. The
kinetic energy should be determined as follows:
KE=-2- Vvb
__ L [6112
Where Me—"g—
A side load equal to 0.5 times the vertical load shall
be combined with the vertical load. Vvb shall be
‘speciﬁed by the procuring service or certiﬁcating
agency.
5.5 Turn-Over
When turn-over structure is required, the fol—
lowing load conditions shall be considered. The
airplane shall be assumed to rest on the ground in
at least one of the attitudes through which it
passes or rests after turning over, whichever ap-
pears most critical for the safety of the occupants,
either as to immediate injury or damage to the
means of exit. The turn-over structure and fuse-
lage shall be designed for all possible combinations
of the following loads acting at the cg, and con-
taining a component normal to the thrust line
of 3.0 WL:
a. A forward acting component parallel to the
thrust line equal to 1.33 WL.
b. A component normal to the plane of sym-
metry equal to 1.0 WL.
11
CHAPTER 6
UNCONVENTIONAL GEAR CONFIGURATIONS AND HELICOPTERS
k
6.1 General
The ground load criteria for the design of air-
planes equipped with unconventional type landing
gears, and for helicopters, shall be, where appli-
cable, in accordance with the requirements es-
tablished in this bulletin for the design of air-
planes equipped with conventional type landing
gears, except as modiﬁed by this chapter. If the
requirements of this bulletin are inapplicable or
inadequate, proposed substitute criteria shall be
submitted for approval to the procuring service or
certiﬁcating agency.
6.2 Design Conditions
6.21. BIoYoLE. Criteria will be inserted here
when available.
6.22. QUADRIOYGLE. Criteria will be inserted
here when available.
6.23. CRoss-WINn.
here when available.
6.24. TRAoK. Criteria will be inserted here
when available.
6.25. SKI.
6.251. General. Compliance with the follow-
ing recommendations may be established by cal-
culations, when the shock absorbing characteristics
are known (for example, from tests on land plane
landing gear).
6.252. Landing C'onditions. No types of
ground reactions analogous to the Maximum
Spin—up or Dynamic Spring-back conditions need
be investigated, but in lieu thereof, a Vertical Re-
action condition should be investigated. In this
condition, a vertical reaction equal to the maxi-
mum vertical ground reaction should be applied
through the center line of pedestal bearing and
through the center line of the ski. In all of the
Maximum Strut Reaction conditions and in the
One-Ski Landing conditions, a drag load equal to
25 percent of the vertical load should be applied at
the center line of the pedestal bearing at a position
above the center line of the ski. In the Drift
Criteria will be inserted
Landing Condition, the side load should be applied
at the ski bottom directly under the pedestal
bearing.
6.253. Tawiing and Handling Conditions.
6.2531. Turning. The attitude and the
loads should be those established for a wheel type
landing gear (par. 3.3). The side load should
be applied at the ski bottom directly under the
pedestal bearing. The vertical load should be ap-
plied at the center line of the pedestal bearing.
6.2532. Tovgne. To provide strength for
normal landing, taxiing, and ground handling
conditions, a torque equal to 0.67 WT lb-ft should
be applied about the vertical axis through the cen-
ter line of each main ski pedestal bearing. For a
steerable nose ski the torque should be equal to
that applied to the main pedestal bearing multi-
plied by the ratio of the nose ski static load to the
main ski static load except that the torque on the
nose ski need not exceed that which can be reacted
by the maximum pilot effort speciﬁed for the de-
sign of the steering control. A vertical reaction
equal to the static reaction on the ski shall be ap-
plied in each case through the center line of the
pedestal bearing.
6.26 SKID.
6.261. Level Landing. The resultant ground
reaction shall pass through the center of the skid’s
contact area, and shall be obtained by combining
the vertical component with a rearward acting
horizontal component equal to one-half of the
vertical component. Any unbalanced moments
shall be balanced by a rational or conservative
method.
6.262. Level Landing With Side Load. A
side load equal to one-half of the vertical com-
ponent of this paragraph shall be combined with
one-half of the loads speciﬁed in the Level Land-
ing condition, paragraph 6.261. These loads shall
be applied at the center of the contact area of the
skid. Unbalanced moments shall be balanced by
a rational or conservative method. If more than
12
one skid is provided, each skid shall be capable of
resisting this load.
6.263. Nose Down Landing. The airplane
shall be considered to land in a 15° nose down
attitude.~ The ground reactions shall be those of
condition 6.261 with the resultant reaction passing
through the most forward point suitable for the
application of oblique loads. For aircraft with
wheels and skid, the aircraft shall contact the
ground on the nose skid and wheel(s) . The
minimum resultant inertia force shall act at the
center of gravity of the aircraft forward and
downward at an angle of 14° to the vertical.
6.264. Note. Although only two points on
the skid need be investigated, the skid and its sup-
port should be of approximately uniform struc-
ture throughout. ‘
6.27. HELICOPTER. Criteria will be inserted
here when available.
6.28. SPECIAL. Criteria will be inserted here
when pertinent and available.
13
CHAPTER 7
METHODS OF ANALYSIS

7.1 General
The methods of analysis presented in this chap-
ter shall be considered acceptable by the procuring
service or certiﬁcating agency. However, other
rational methods, based on theory or experimental
data will be acceptable, subject to approval by the
procuring service or certiﬁcating agency.
7.2 Dynamic Landing Loads
The dynamic loads imposed by landing impacts
may result in more critical loads than those assum-
ing the aircraft structure to be rigid. The meth-
ods outlined in A. F. T. R. No. 5815, “Prediction
of Dynamic Landing Loads”, may be employed
in the computation of these dynamic loads. In
cases where the natural frequency of the landing
gear in a fore and aft direction approaches the
natural frequency of a major structural compo-
nent, the analysis shall be extended to investigate
this condition.
7.3 Spin-Up and Spring-Back Loads
7.31. MAXIMUM SPIN-Ur. Assuming that the
vertical load on the wheel develops sinusoidally
with time and that an average coefficient of sliding
friction equal to 0.55 exists during the spin-up pe-
riod, the basic maximum spin-up loads may be
considered as:
- 7l'
FVSU=FVMAX s1ntSU>
for tSU<tV
FDSU== 0.55 FVMAX sin av)
or FVSUZFVMAX
for tSU>tV
FDSUZO'55FVMAX
The basic loads (VSU, DSU) should be resolved
parallel to, and normal to the oleo axis. After
modifying the component normal to the oleo axis
to account for dynamic magniﬁcation, the result-
ant design loads will then be determined as com-
prising the following componnets (see ﬁg. 7.1) :
Normal to oleo (aft)
: KS U (FI
DSU cos G—FVSU sin 6),
Parallel to oleo
=‘FVSU cos H—l—FDSU sin 6,
(See ﬁg. 7 .3 for the determination of the dynamic
response factor, KSU.) In lieu of applicable test
data, the values of tv and tSU may be obtained from
the following formulae:
t ___VV_ [VVZ—29.8 dV ng11/2
V'- - 14.9%,

2tv _ [ 'I/TL IW'II'
t =— cos 1 1 —- ———-———————— fort t
S” w 1.1tVr2FVMAX SU< V
VLIW
T'ZFVMAX

01' list]: IOI' tsU>tV
7.32. DYNAMIC SPRING—BACK. Subsequent to
the instant of maximum spin-up load and the cor-
responding rearward deformation, the wheel rota-
tional speed is considered to have reached the air-
plane’s rolling speed and the magnitude of the slid-
ing friction load at the ground reduces rapidly to
zero. The strain energy stored in the rearward
deformation of the gear is considered to result in a
springing forward of the axle and its associated
masses so that, at the instant of reaching the maxi-
mum forward deformation, a dynamic spring—back
load may be considered to consist of the inertia of
the effective mass at the axle acting forward nor-
mal to the oleo. At this instant the vertical
ground reaction is considered to have reached its
maximum value. Taking into account dynamic
14
magniﬁcations resulting from the rapid reduction
in spin-up load and the elasticity of the structure,
the resulting design load will be determined as
comprising the following components‘ (see ﬁg.
7.2) :
Normal to oleo (fwd)
=KSB(FDSU cos B—FVSU sin 0H—
F
FVSU (aw-lg) sin 0,
Vsv
Along oleo
=FVMAX cos 0,
(See ﬁg. 7.3 for the determination of the dynamic
response factor, K83.)
7.33. DYNAMIC REsroNsE.
7.331. Dynamic Response Factors. The dy-
namic response factors, KSU and K513 shall be cal-
culated by the use of ﬁgure 7.3. However, to
eliminate the necessity for calculating the param-
eter tn, required to determine the dynamic response
factors, KSU may be taken equal to 1.4 and KSB
may be taken equal to 1.25.
7.332. Landing Gear Natural Period. The
landing gear natural period, in, is best determined
from vibration tests of the gear as actually in-
stalled in the airplane. It ‘may be computed from
landing gears having oleo struts whose longitudi-
nal center lines are within 20° of the vertical with
the airplane thrust line horizontal, by the follow-
ing formula:
in=0.32‘/5
where w is the structural deﬂection (inches) of
the axle, with the oleo fully extended, caused by
an aft load which is normal to the oleo and equal
to. the total Weight of the wheel assembly and the
part of the strut extending from the center line
of the wheel to a distance equal to the tire radius.
The reactions for this force shall be assumed to
be applied at the airplane fuselage.
7.333. Special Dynamic Analysis. Special
dynamic analysis should be made for landing gears
having oleostruts whose longitudinal center lines
are at an angle greater than 20° with the vertical
with the airplane thrust line horizontal, since for
these cases the method used to compute ﬁgure 7.3
may not be applicable.
7.4 Turning
The following formulae may be used to estab-
lish the loads in connection with paragraph 3.3:
(see ﬁg. 7 .4)
7.41. OUTsIDE GEAR.
FVM1=+7LS
where ns=0.5 bt/de (which is the overturning
value) although ns need not be greater than 0.5.
FSM1=ns FVM1
FVA= W a/d
FSA =ns FVA
7.42. INsIDE GEAR.
FVM2= 0.5 Wb/d—ns We/t
where ns=0.25 bt/de (which is the value giving
maximum vertical and side load on the wheel on
the inside of the turn), although ns need not be
greater than 0.5.
FSM2=nS FVM2
7.43. AUXILIARY GEAR. The values of para-
graph 7.41 shall be used.
7.5 Braking Torque
The following methods may be used for obtain-
ing the braking torque for use with paragraph
5.24:
7.51. EXPERIMENTAL METHOD. Support the air-
plane with the wheels clear of the ground. Turn
the wheels up to take-off speed. Impose rapid
application of the brakes. Use strain gages or
other suitable instrimientation to measure the
brake torque. Correction should be made for dy-
namic magniﬁcation of the structure.
*When the oleo is inclined aft from the wing or fuselage, i. e., where sin 0 is negative, the factor 0.9 shall be taken as equal to zero.
15
7 .52. ALTERNATE METHon. It may be assumed
that the torque is equal to the nominal maximum
static brake torque. The spring-back torque may
be assumed equal to 2/3 of the ‘stopping torque.
7 .53. HYDRAULIC BRAKES. When hydraulic
brakes are used a rational analysis for determining
braking torque may be made by making the fol-
lowing assumptions:
a. Brake pressure increases linearly from zero
toﬁa maximum in 0.2 seconds.
I). Sliding coefficient of friction exists be—
tween the wheel and the brake lining of 0.2 with
an increase of 0.1 at the instant of stopping (un-
less other values can be established by test data).
0. The dynamic response factors of ﬁgure 7.3
apply.
16
.aseﬁeeoa asésam .2. 23mg


m 2633 + 3 e835


226.. “5-2:; 22mg A
wc<o.._ n5 lz_n_m 064m

3 2533 .. o woe if
Dw> “-
= am
@ Em we“. +¢ moo >h_ ll/

8 263?. i w 3039.32
<_._.mu2_ 4wmI>>


l7


* _
0.9 FVSUSIN e -
ALLOWANCE FOR NASNIFICATION
RESULTING FROM SUDDEN REDUC-
TION TO ZERO OF SPIN-UP LOAD
AT SROU


AS EOUAL TO ZERO
WHEN O IS NEGATIVE.


KSBIFDSUOOS e- Fvs sm e)=
U
ALLOWANCE FOR ELASTIC SPRING-
BACK FROM DEFLECTION DURING
SPIN-UP, INCLUDING DYNAMIC
RESPONSE NASNIFICATION FACTOR.

BASIC SPRING-BACK LOADS
I‘
+ F (0.9 +
Vsu
(4») runs FACTOR ls TAKEN
K$B(FDSUCO$ 9 - FVSUSIN 6)
F
v
F—"ilidsme
Vsu


F 00$ 9
VMAx
) DESIGN SPRING-BACK LOADS

Figure 7.2. Spring-back
reactions.
8|.
0.5
0.5
L0
Figure 7.3. Dynamic response factors for land/mg gea/r drag loads.

//\\
\
l \\\
/ \\
/ \\\~~
/
1' SU
I O O 33$) {*0 t n
// /
///
//
,/
///
/
\ /
\ /
l9


F
sMl
F WHEELS 0N
VIM OUTSIDE
OF TURN
"SW '
w
F
s
M2
Fv WHEELS on
M2 INSIDE
OF TURN
<1 ——-i
d


PLAN VIEW


§—> nsw
W
e
i [1 FSA. FSM|
i VA VM|
'‘ i
END VIEW
Figure 7.4. Tmwmg.
U. 5. GOVERNMENT PRINTING OFFICE: 1952

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