(a) For the side load condition, the airplane is assumed to be in the level attitude with only the main wheels contacting the ground, in accordance with figure 5 of Appendix A.

(b) Side loads of 0.8 of the vertical reaction (on one side) acting inward and 0.6 of the vertical reaction (on the other side) acting outward must be combined with one-half of the maximum vertical ground reactions obtained in the level landing conditions. These loads are assumed to be applied at the ground contact point and to be resisted by the inertia of the airplane. The drag loads may be assumed to be zero.

§ 25.487 Rebound landing condition.

(a) The landing gear and its supporting structure must be investigated for the loads occurring during rebound of the airplane from the landing surface.

(b) With the landing gear fully extended and not in contact with the ground, a load factor of 20.0 must act on the unsprung weights of the landing gear. This load factor must act in the direction of motion of the unsprung weights as they reach their limiting positions in extending with relation to the sprung parts of the landing gear. § 25.489 Ground handling conditions.

Unless otherwise prescribed, the landing gear and airplane structure must be investigated for the conditions in §§ 25.491 through 25.509 with the airplane at the design takeoff weight. No wing lift may be considered. The shock absorbers and tires may be assumed to be in their static position.

§ 25.491 Takeoff run.

The landing gear and the airplane structure are assumed to be subjected to loads not less than those obtained under conditions described in § 25.235. § 25.493 Braked roll conditions.

(a) An airplane with a tail wheel is assumed to be in the level attitude with the load on the main wheels, in accordance with figure 6 of Appendix A. The limit vertical load factor is 1.2 at the design landing weight, and 1.0 at the design takeoff weight. A drag reaction equal to the vertical reaction multiplied by a coefficient of friction of 0.8, must be combined with the vertical ground reaction and applied at the ground contact point.

(b) For an airplane with a nose wh the limit vertical load factor is 1.2 at design landing weight, and 1.0 at design takeoff weight. A drag react equal to the vertical reaction, multip by a coefficient of friction of 0.8, must combined with the vertical reaction applied at the ground contact point each wheel with brakes. The follow two attitudes, in accordance with fig 6 of Appendix A, must be considered:

(1) The level attitude with the whe contacting the ground and the loads tributed between the main and nose ge Zero pitching acceleration is assumed

(2) The level attitude with only main gear contacting the ground with the pitching moment resisted angular acceleration.

(c) A drag reaction lower than t prescribed in paragraphs (a) and of this section may be used if it is s stantiated that an effective drag force 0.8 times the vertical reaction cannot attained under any likely loading con tion.

(a) A vertical ground reaction eq to the static load on the tail wheel combination with a side component equal magnitude, is assumed.

(b) If there is a swivel, the tail wh is assumed to be swiveled 90° to the plane longitudinal axis with the res ant load passing through the axle.

(c) If there is a lock, steering dev or shimmy damper the tail wheel is assumed to be in the trailing posit with the side load acting at the gro contact point.

§ 25.499 Nose-wheel yaw.

(a) A vertical load factor of 1.0 the airplane center of gravity, and a component at the nose wheel grot contact equal to 0.8 of the vertical grot reaction at that point are assumed.

(b) With the airplane assumed to in static equilibrium with the loads

Iting from the use of brakes on one side the main landing gear, the nose gear, attaching structure, and the fuselage ructure must be designed for the folwing loads:

(1) A vertical load factor at the center gravity of 1.0.

(2) A forward acting load at the airane center of gravity of 0.8 times the rtical load on one main gear.

(3) Side and vertical loads at the ound contact point on the nose gear at are required for static equilibrium. (4) A side load factor at the airplane nter of gravity of zero.

(c) If the loads prescribed in paraaph (a) of this section result in a nose ar side load higher than 0.8 times the rtical nose gear load, the design nose ar side load may be limited to 0.8 times e vertical load, with unbalanced yawmoments assumed to be resisted by rplane inertia forces.

(d) For the landing gear and airplane ucture, the loading conditions are Ose prescribed in paragraph (b) of this ction, except that—

(1) A lower drag reaction may be used an effective drag force of 0.8 times the rtical reaction cannot be reached unrany likely loading condition; and (2) The forward acting load at the ater of gravity need not exceed the aximum drag reaction on one main ar, determined in accordance with 25.493 (b).

25.503 Pivoting.

(a) The airplane is assumed to pivot out one side of the main gear with the akes on that side locked. The limit rtical load factor must be 1.0 and the efficient of friction 0.8.

(b) The airplane is assumed to be in tic equilibrium, with the loads being plied at the ground contact points, in cordance with figure 8 of Appendix A. $5.507 Reversed braking.

(a) The airplane must be in a three int static ground attitude. Horizontal actions parallel to the ground and dicted forward must be applied at the ound contact point of each wheel with akes. The limit loads must be equal 0.55 times the vertical load at each heel or to the load developed by 1.2 nes the nominal maximum static brake rque, whichever is less.

(b) For airplanes with nose wheels, le pitching moment must be balanced rotational inertia.

(c) For airplanes with tail wheels, the resultant of the ground reactions must pass through the center of gravity of the airplane.

§ 25.509 Towing loads.

(a) The towing loads specified in paragraph (d) of this section must be considered separately. These loads must be applied at the towing fittings and must act parallel to the ground. In addition

(1) A vertical load factor equal to 1.0 must be considered acting at the center of gravity;

(2) The shock struts and tires must be in their static positions; and

(3) With WT as the design maximum takeoff weight, the towing load, Frow, is(1) 0.3 W for W, less than 30,000 pounds;

(ii)

T

6W+450,000 70

T

for WT between 30,000 and 100,000 pounds; and (iii) 0.15 Wr for Wr over 100,000 pounds.

T

(b) For towing points not on the landing gear but near the plane of symmetry of the airplane, the drag and side tow load components specified for the auxiliary gear apply. For towing points located outboard of the main gear, the drag and side tow load components specified for the main gear apply. Where the specified angle of swivel cannot be reached, the maximum obtainable angle must be used.

(c) The towing loads specified in paragraph (d) of this section must be reacted as follows:

(1) The side component of the towing load at the main gear must be reacted by a side force at the static ground line of the wheel to which the load is applied.

(2) The towing loads at the auxiliary gear and the drag components of the towing loads at the main gear must be reacted as follows:

(1) A reaction with a maximum value equal to the vertical reaction must be applied at the axle of the wheel to which the load is applied. Enough airplane inertia to achieve equilibrium must be applied.

(ii) The loads must be reacted by airplane inertia.

§ 25.511

Ground load: unsymmetrical loads on multiple-wheel units.

(a) General. Multiple-wheel landing gear units are assumed to be subjected to the limit ground loads prescribed in this subpart under paragraphs (b) through (f) of this section. In addition

(1) A tandem strut gear arrangement is a multiple-wheel unit; and

(2) In determining the total load on a gear unit with respect to the provisions of paragraphs (b) through (f) of this section, the transverse shift in the load centroid, due to unsymmetrical load distribution on the wheels, may be neglected.

(b) Distribution of limit loads to wheels; tires inflated. The distribution of the limit loads among the wheels of the landing gear must be established for each landing, taxiing, and ground handling condition, taking into account the effects of the following factors:

(1) The number of wheels and their physical arrangements. For truck type landing gear units, the effects of any seesaw motion of the truck during the landing impact must be considered in determining the maximum design loads for the fore and aft wheel pairs.

(2) Any differentials in tire diameters resulting from a combination of manufacturing tolerances, tire growth, and tire wear. A maximum tire-diameter differential equal to 2/3 of the most unfavorable combination of diameter variations that is obtained when taking into account manufacturing tolerances, tire growth, and tire wear, may be assumed.

(3) Any unequal tire inflation pressure, assuming the maximum variation to be 5 percent of the nominal tire inflation pressure.

Forward, in plane of wheel. Aft, in plane of wheel.

Forward, in plane of wheel. Aft, in plane of wheel.

(4) A runway crown of zero and runway crown having a convex upwa shape that may be approximated by slope of 12 percent with the horizont Runway crown effects must be consider with the nose gear unit on either slo of the crown.

(5) The airplane attitude.

(6) Any structural deflections.

(c) Deflated tires. The effect of d flated tires on the structure must be co sidered with respect to the loadi conditions specified in paragraphs ( through (f) of this section, taking in account the physical arrangement of th gear components. In addition—

(1) The deflation of any one tire f each multiple wheel landing gear un and the deflation of any two critic tires for each landing gear unit usi four or more wheels per unit, must considered; and

(2) The ground reactions must be a plied to the wheels with inflated ti except that, for multiple-wheel ge units with more than one shock strut rational distribution of the ground rea tions between the deflated and inflat tires, accounting for the differences shock strut extensions resulting from deflated tire, may be used.

(d) Landing conditions. For one a for two deflated tires, the applied lo to each gear unit is assumed to be percent and 50 percent, respectively, the limit load applied to each gear f each of the prescribed landing cond tions. However, for the drift landi condition of § 25.485, 100 percent of t vertical load must be applied.

(e) Taxiing and ground handling contions. For one and for two deflated

es

(1) The applied side or drag load ctor, or both factors, at the center of avity must be the most critical value to 50 percent and 40 percent, respecvely, of the limit side or drag load ctors, or both factors, corresponding to e most severe condition resulting from nsideration of the prescribed taxiing id ground handling conditions;

(2) For the braked roll conditions of 25.493 (a) and (b) (2), the drag loads teach inflated tire may not be less than ose at each tire for the symmetrical ad distribution with no deflated tires; (3) The vertical load factor at the nter of gravity must be 60 percent and percent, respectively, of the factor th no deflated tires, except that it may it be less than 1g; and

(4) Pivoting need not be considered. (f) Towing conditions. For one and two deflated tires, the towing load, ow, must be 60 percent and 50 percent, spectively, of the load prescribed.

(a) Seaplanes must be designed for the ater loads developed during takeoff and nding, with the seaplane in any attide likely to occur in normal operation, d at the appropriate forward and sinkg velocities under the most severe sea nditions likely to be encountered. (b) Unless a more rational analysis of e water loads is made, or the standards ANC-3 are used, §§ 25.523 through 537 apply.

(c) The requirements of this section d§§ 25.523 through 25.537 apply also amphibians.

25.523 Design weights and center of gravity positions.

(a) Design weights. The water load quirements must be met at each opering weight up to the design landing ight except that, for the takeoff contion prescribed in § 25.531, the design keoff weight must be used.

(b) Center of gravity positions. The itical centers of gravity within the nits for which certification is requested ust be considered to reach maximum esign loads for each part of the seaplane ructure.

25.525 Application of loads.

(a) Unless otherwise prescribed, the aplane as a whole is assumed to be sub

jected to the loads corresponding to the load factors specified in § 25.527.

(b) In applying the loads resulting from the load factors prescribed in § 25.527, the loads may be distributed over the hull or main float bottom (in order to avoid excessive local shear loads and bending moments at the location of water load application) using pressures not less than those prescribed in § 25.533 (b).

(c) For twin float seaplanes, each float must be treated as an equivalent hull on a fictitious seaplane with a weight equal to one-half the weight of the twin float seaplane.

(d) Except in the takeoff condition of § 25.531, the aerodynamic lift on the seaplane during the impact is assumed to be 23 of the weight of the seaplane.

§ 25.527 Hull and main float load fac

tors.

(b) The following values are used: (1) n=water reaction load factor (that is, the water reaction divided by seaplane weight).

(2) C1=empirical seaplane operations factor equal to 0.012 (except that this factor may not be less than that necessary to obtain the minimum value of step load factor of 2.33).

(3) Vs=seaplane stalling speed with flaps extended in the appropriate landing position and with no slipstream effect.

(4) Bangle of dead rise at the longitudinal station at which the load factor is being determined, in accordance with figure 1 of Appendix B.

(5) W=seaplane design landing weight in pounds.

center of gravity of the seaplane to the hull longitudinal station at which the load factor is being computed to the radius of gyration in pitch of the seaplane, the hull reference axis being a straight line, in the plane of symmetry, tangential to the keel at the main step.

1

(c) For a twin float seaplane, because of the effect of flexibility of the attachment of the floats to the seaplane, the factor K1 may be reduced at the bow and stern to 0.8 of the value shown in figure 2 of Appendix B. This reduction applies only to the design of the carrythrough and seaplane structure.

§ 25.529 Hull and main float landing conditions.

(a) Symmetrical step, bow, and stern landing. For symmetrical step, bow, and stern landings, the limit water reaction load factors are those computed under § 25.527. In addition

(1) For symmetrical step landings, the resultant water load must be applied at the keel, through the center of gravity, and must be directed perpendicularly to the keel line;

(2) For symmetrical bow landings, the resultant water load must be applied at the keel, one-fifth of the longitudinal distance from the bow to the step, and must be directed perpendicularly to the keel line; and

(3) For symmetrical stern landings, the resultant water load must be applied at the keel, at a point 85 percent of the longitudinal distance from the step to the stern post, and must be directed perpendicularly to the keel line.

(b) Unsymmetrical landing for hull and single float seaplanes. Unsymmetrical step, bow, and stern landing conditions must be investigated. In addition

(1) The loading for each condition consists of an upward component and a side component equal, respectively, to 0.75 and 0.25 tan ẞ times the resultant load in the corresponding symmetrical landing condition; and

(2) The point of application and direction of the upward component of the load is the same as that in the symmetrical condition, and the point of application of the side component is at the same longitudinal station as the upward component but is directed inward perpendicularly to the plane of symmetry at a point midway between the keel and chine lines.

(c) Unsymmetrical landing; twin float

seaplanes. The unsymmetrical loadi consists of an upward load at the step each float of 0.75 and a side load of 0. tan ẞ at one float times the step landi load reached under § 25.527. The si load is directed inboard, perpendicular to the plane of symmetry midway b tween the keel and chine lines of t float, at the same longitudinal stati as the upward load.

§ 25.531 Hull and main float take condition.

For the wing and its attachment to t hull or main float

(a) The aerodynamic wing lift is a sumed to be zero; and

(b) A downward inertia load, corr sponding to a load factor computed fro the following formula, must be applie CTOVS ̧2

where

2

n= tan 2/38W1/3

(a) General. The hull and main flo structure, including frames and bul heads, stringers, and bottom platin must be designed under this section.

(b) Local pressures. For the desi of the bottom plating and stringers a their attachments to the supporti structure, the following pressure dist butions must be applied:

(1) For an unflared bottom, the pr sure at the chine is 0.75 times the pr sure at the keel, and the pressures tween the keel and chine vary linear in accordance with figure 3 of Appen B. The pressure at the keel (psi) computed as follows: