§ 4b.234a Rebound landing condition.

The landing gear and its supporting structure shall be investigated for the loads occurring during rebound of the airplane from the landing surface. With the landing gear fully extended and not in contact with the ground, a load factor of 20.0 shall act on the unsprung weights of the landing gear. This load factor shall act in the direction of motion of the unsprung weights as they reach their limiting positions in extending with relation to the sprung portions of the landing gear.

[Amdt. 4b-3, 21 F. R. 991, Feb. 11, 1956] § 4b.235 Ground handling conditions.

The landing gear and airplane structure shall be investigated for the conditions of this section with the airplane at the design take-off weight, unless otherwise prescribed. No wing lift shall be considered. It shall be acceptable to assume the shock absorbers and tires to be deflected to their static position. In the conditions of paragraph (b)(1) and (2), it shall be acceptable to use a drag reaction lower than prescribed therein if it is substantiated that an effective drag force of 0.8 times the vertical reaction cannot be attained under any likely loading condition.

(a) Take-off run. The landing gear and the airplane structure shall be assumed to be subjected to loads not less than those encountered under conditions described in § 4b.172.

(b) Braked roll—(1) Tail-wheel type. The airplane shall be assumed to be in the level attitude with all load on the main wheels. The limit vertical load factor shall be 1.2 for the airplane at the design landing weight, and 1.0 for the airplane at the design take-off weight. A drag reaction equal to the vertical reaction multiplied by a coefficient of friction of 0.8 shall be combined with the vertical ground reaction and applied at the ground contact point. (See fig. 4b-12.)

(2) Nose-wheel type. The limit vertical load factor shall be 1.2 for the airplane at the design landing weight, and 1.0 for the airplane at the design take-off weight. A drag reaction equal to the vertical reaction multiplied by a coefficient of friction of 0.8 shall be combined with the vertical reaction and applied at the ground contact point of each wheel having brakes. The following

two airplane attitudes shall be considered: (See fig. 4b-12.)

(1) The airplane shall be assumed to be in the level attitude with all wheels contacting the ground and the loads distributed between the main and nose gear. Zero pitching acceleration shall be assumed.

(ii) The airplane shall be assumed to be in the level attitude with only the main gear contacting the ground and the pitching moment resisted by angular acceleration.

(c) Turning. The airplane in the static position shall be assumed to execute a steady turn by nose gear steering or by application of differential power such that the limit load factors applied at the center of gravity are 1.0 vertically and 0.5 laterally. (See fig. 4b-13.) The side ground reaction of each wheel shall be 0.5 of the vertical reaction.

(d) Pivoting. The airplane shall be assumed to pivot about one side of the main gear, the brakes on that side being locked. The limit vertical load factor shall be 1.0 and the coefficient of friction 0.8. The airplane shall be assumed to be in static equilibrium, the loads being applied at the ground contact points. (See fig. 4b-14.)

(e) Nose-wheel yawing. (1) A vertical load factor of 1.0 at the airplane center of gravity and a side component at the nose wheel ground contact equal to 0.8 of the vertical ground reaction at that point shall be assumed.

(2) The airplane shall be assumed to be in static equilibrium with the loads resulting from the application of the brakes on one side of the main gear. The vertical load factor at the center of gravity shall be 1.0. The forward acting load at the airplane center of gravity shall be 0.8 times the vertical load on one main gear. The side and vertical loads at the ground contact point on the nose gear shall be those required for static equilibrium. The side load factor at the airplane center of gravity shall be assumed to be zero. Where this condition results in a nose gear side load in excess of 0.8 times the vertical nose gear load, it shall be acceptable to limit the design nose gear side load to 0.8 times the vertical load with the unbalanced yawing moments assumed to be resisted by aircraft inertia forces.

(f) Tail-wheel yawing. (1) A vertical ground reaction equal to the static

load on the tail wheel in combination with a side component of equal magnitude shall be assumed.

(2) When a swivel is provided, the tail wheel shall be assumed to be swiveled 90° to the airplane longitudinal axis with the resultant load passing through the axle. When a lock, steering device, or shimmy damper is provided, the tail wheel shall also be assumed to be in the trailing position with the side load acting at the ground contact point.

(g) Reversed braking. The airplane shall be in a three point static ground

attitude. Horizontal reactions parallel to the ground and directed forward shall be applied at the ground contact point of each wheel equipped with brakes. The limit loads shall be equal either to 0.55 times the vertical load at each wheel or to the load developed by 1.2 times the nominal maximum static brake torque, whichever is the lesser. For nosewheel types, the pitching moment shall be balanced by rotational inertia. For tailwheel types, the resultant of the ground reactions shall pass through the center of gravity of the airplane.