arising from all likely combinations of tab setting, primary control position, and airplane speed, obtainable without exceeding the flight load conditions prescribed for the airplane as a whole, when the effect of the tab is being opposed by pilot effort loads up to those specified in § 4b.220 (a).

(b) Balancing tabs. Balancing tabs shall be designed for deflections consistent with the primary control surface loading conditions.

(c) Servo tabs. Servo tabs shall be designed for all deflections consistent with the primary control surface loading conditions achievable within the pilot maneuvering effort (see § 4b.220 (a)) with due regard to possible opposition from the trim tabs.

[Amdt. 4b-6, 17 F. R. 1090, Feb. 5, 1952] § 4b.223 Special devices.

The loading for special devices employing aerodynamic surfaces, such as slots and spoilers, shall be based on test data.

§ 4b.224 Primary flight control systems.

Elevator, aileron, and rudder control systems and their supporting structures shall be designed for loads corresponding with 125 percent of the computed hinge moments of the movable control surface in the conditions prescribed in § 4b.220, subject to the following provisions:

(a) The system limit loads, except the ground loads resulting from gusts (§ 4b.226), need not exceed those which can be produced by the pilot or pilots and by automatic devices operating the controls. Acceptable maximum and minimum pilot loads for elevator, aileron, and rudder controls are shown in figure 4b-5. These pilot loads shall be assumed to act at the appropriate control grips or pads in a manner simulating flight conditions and to be reacted at the attachment of the control system to the control surface horn.

(b) The loads shall in any case be sufficient to provide a rugged system for service use, including considerations of jamming, ground gusts, taxiing tail to wind, control inertia, and friction.

§ 4b.225 Dual primary flight control systems.

(a) When dual controls are provided, the system shall be designed for the

pilots operating in opposition, using individual pilot loads equal to 75 percent of those obtained in accordance with § 4b.224, except that the individual pilot loads shall not be less than the minimum loads specified in figure 4b-5.

(b) The control system shall be designed for the pilots acting in conjunction, using individual pilot loads equal to 75 percent of those obtained in accordance with § 4b.224.

§ 4b.226

Ground gust conditions.

The following conditions intended to simulate the loadings on control surfaces due to ground gusts and when taxying downwind shall be investigated:

(a) The control system between the stops nearest the surfaces and the cockpit controls shall be designed for loads corresponding with the limit hinge moments H of paragraph (b) of this section, except that these loads need not exceed those corresponding with the maxima or figure 4b-5 for each pilot alone, or with 75 percent of these maxima for each pilot when the pilots act in conjunction.

(b) The control system stops nearest the surfaces, the control system locks, and the portions of the systems, if any, between such stops and locks and the control surface horns shall be designed for limit hinge moments H obtained from the following formula:

H=KcSq,

where:

H=limit hinge moment (ft. lbs.),

c=mean chord of the control surface aft

of the hinge line (ft.),

S area of the control surface aft of the hinge line (sq. ft.),

8

than

q=dynamic pressure (p. s. f.) based on less design speed not 10VW/S+10 (m. p. h.), except that

the design speed need not exceed 60 m. p. h.,

K=factor as specified in figure 4b-4.

[15 F. R. 3543, June 8, 1950; 15 F. R. 4171, June 29, 1950, as amended by Amdt. 4b-2, 20 F. R. 5305, July 26, 1955]

§ 4b.227 Secondary control systems.

Secondary controls, such as wheel brake, spoiler, and tab controls, shall be designed for the loads based on the maximum which a pilot is likely to apply to the control in question. The values of figure 4b-6 are considered acceptable.

visions of paragraph (a) of this section shall be complied with. In addition, for the landing conditions of §§ 4b.231 through 4b.234 the airplane shall be assumed to be subjected to forces and descent velocities prescribed in paragraph (b) of this section. (The basic landing gear dimensional data are given in figure 4b-7.)

(a) Center of gravity positions. The critical center of gravity positions within the certification limits shall be selected so that the maximum design loads in each of the landing gear elements are obtained in the landing and the ground handling conditions.

(b) Load factors, descent velocities, and design weights for landing conditions. (1) In the landing conditions the limit vertical inertia load factors at the center of gravity of the airplane shall be chosen by the applicant, except that they shall not be less than the values which would be obtained in the attitude and subject to the drag loads associated with the particular landing condition, and with the following limit descent velocities and weights:

(i) 10 f. p. s. at the design landing weight, and

(ii) 6 f. p. s. at the design take-off weight.

(2) It shall be acceptable to assume a wing lift not exceeding the airplane weight to exist throughout the landing impact and to act through the center of gravity of the airplane.

(3) The provisions of subparagraphs (1) and (2) of this paragraph shall be predicated on conventional arrangements of main and nose gears, or main and tail gears, and on normal operating techniques. It shall be acceptable to modify the prescribed descent velocities if it is shown that the airplane embodies features of design which make it impossible to develop these velocities. (See § 4b.332 (a) for requirements on energy absorption tests which determine the minimum limit inertia load factors corresponding with the required limit descent velocities.)

[15 F. R. 3543, June 8, 1950, as amended by Amdt. 4b-3, 21 F. R. 991, Feb. 11, 1956]

FIGURE 4b-7-Basic landing gear dimension data.

§ 4b.231

Level loading conditions.

(a) General. In the level attitude the airplane shall be assumed to contact the ground at forward velocity components parallel to the ground ranging from VL1 to 1.25 Vi2 and shall be assumed to be subjected to the load factors prescribed in § 4b.230 (b) (1) where VL, is equal to Vso (TAS) at the appropriate landing weight and in standard sea level conditions and where VL2 is equal to Vs。 (TAS) at the appropriate landing weight and altitudes in a hot day temperature of 41° F. above standard. When approval of landings downwind exceeding 10 mph is sought, the effect of increased contact speeds shall be investigated. The following three combinations of vertical and drag components shall be considered acting at the axle center line:

(1) Condition of maximum wheel spinup load. Drag components simulating the forces required to accelerate the wheel rolling assembly up to the specified ground speed shall be combined with the vertical ground reactions existing at the instant of peak drag loads. It shall be acceptable to establish the coefficient of friction between the tires and the ground by considering the effects of skidding velocity and tire pressure, except that it need not be greater than 0.8. It shall be acceptable to apply this condition only to the landing gear, directly affected attaching structure, and large mass items (i.e. external fuel tanks, nacelles, etc.).

(2) Condition of maximum wheel vertical load. An aft acting drag component not less than 25 percent of the maximum vertical ground reaction shall be combined with the maximum ground reaction of § 4b.230 (b).

(3) Condition of maximum springback load. Forward-acting horizontal loads resulting from a rapid reduction of the spin-up drag loads shall be combined with the vertical ground reactions at the instant of the peak forward load. It shall be acceptable to apply this condition only to the landing gear, directly affected attaching structure, and large mass items (i. e. external fuel tanks, nacelles, etc.).

(b) Level landing; tail-wheel type. The airplane horizontal reference line shall be assumed to be horizontal. The conditions specified in paragraph (a) of this section shall be investigated (See fig. 4b-8.)

(c) Level landing; nose-wheel type. The following airplane attitudes shall be considered: (See fig. 4b-8.)

(1) Main wheels shall be assumed to contact the ground with the nose wheel just clear of the ground. The conditions specified in paragraph (a) of this section shall be investigated.

(2) Nose and main wheels shall be assumed to contact the ground simultaneously. Conditions in this attitude need not be investigated if this attitude cannot reasonably be attained at the specified descent and forward velocities. The conditions specified in paragraph (a) of this section shall be investigated, except that in conditions (a) (1) and (a) (3) it shall be acceptable to investigate the nose and main gear separately neglecting the pitching moments due to wheel spin-up and spring-back loads, while in condition (a) (2) the pitching moment shall be assumed to be resisted by the nose gear.

[15 F. R. 3543, June 8, 1950, as amended by Amdt. 4b-8, 18 F. R. 2214, Apr. 18, 1953; Amdt. 4b-2, 20 F. R. 5306, July 26, 1955; Amdt. 4b-3, 21 F.R. 991, Feb. 11, 1956; Amdt. 4b-11, 24 F.R. 7069, Sept. 1, 1959]

§ 4b.232 Tail-down landing conditions.

In the conditions of paragraphs (a) and (b) of this section the airplane shall be assumed to contact the ground at forward velocity components parallel to the ground, ranging from Vы, to VL2, where VL, and VL2 are as indicated in § 4b.231 (a). The load factors prescribed in § 4b.230 (b) (1) shall apply. The combination of vertical and drag components specified in § 4b.231 (a) (1) and (3) shall be considered acting at the main wheel axle centerline.

(a) Tail-wheel type. The main and tail wheels shall be assumed to contact the ground simultaneously. (See fig. 4b-9). Two conditions of ground reaction on the tail wheel shall be assumed to act in the following directions: (1) Vertical,

(2) Up and aft through the axle at 45° to the ground line.

(b) Nose-wheel type. The airplane shall be assumed to be at an attitude corresponding with either the stalling angle or the maximum angle permitting clearance with the ground by all parts of the airplane other than the main wheels, whichever is the lesser. (See fig. 4b-9.) [15 F. R. 3543, June 8, 1950, as amended by Amdt. 4b-3, 21 F. R. 991, Feb. 11, 1956]