(e) Landing gear shock absorption tests (see § 7.332). (f) Such additional tests as may be found necessary by the Administrator to substantiate new and unusual features of the design. [21 F.R. 3744, June 2, 1956, as amended by Amdt. 7-4, Sept. 1, 1959] § 7.204 Design limitations. The following values shall be established by the applicant for purposes of showing compliance with the structural requirements specified in this subpart: (a) Maximum and minimum design weights, (b) Power-on and power-off main rotor rpm ranges (see §§ 7.103 and 7.713 through 7.714 (b)), (c) Maximum forward speeds for the power-on and power-off main rotor rpm ranges established in accordance with paragraph (b) of this section (see § 7.713), (d) Maximum rearward and sideward flight speeds, (e) Extreme positions of rotorcraft center of gravity to be used in conjunction with the limitations of paragraphs (b), (c), and (d) of this section, (f) Rotational speed ratios between the powerplant and all connected rotating components, and (g) Positive and negative limit maneuvering load factors. neuvering limit load factor of 1.0, except that lesser values shall be allowed if the applicant shows by analytical study and flight demonstrations that the probability of exceeding the values selected is extremely remote. Where such lesser values of maneuvering load factor are selected, the values selected shall be appropriate to each design weight condition between design minimum and design maximum values. In no case shall the limit load factors be less than 2.0 positive and 0.5 negative. Air loads shall be assumed to be applied at the center(s) of the rotor hub (s) and at any auxiliary lifting surface(s) and to act in such directions with distributions of load among the rotor(s) and auxiliary lifting surface(s) as necessary to represent all critical maneuvering motions of the rotorcraft applicable to the particular type, including flight at the maximum design rotor tip speed ratio under poweron and power-off conditions. § 7.213 Gust conditions. The rotorcraft structure shall be designed to withstand the loading due to vertical and horizontal gusts of 30 fps in velocity in conjunction with the critical rotorcraft air speeds, including hovering. The rotorcraft shall be designed for loads resulting from conditions specified in this section. Unbalanced aerodynamic moments about the center of gravity shall be reacted in a rational or a conservative manner considering the principal masses furnishing the reacting inertia forces. With the maximum main rotor speed and at a forward speed up to VNE Or VH, whichever is less, the following maneuvers shall be considered: (a) With the rotorcraft in unaccelerated flight at zero yaw, it shall be assumed that the cockpit directional control is suddenly displaced to the maximum deflection as limited by the control stops or by maximum pilot effort. (b) With the directional control deflected as in paragraph (a) of this section, it shall be assumed that the rotorcraft yaws to a resulting sideslip angle. (c) With the rotorcraft yawed to the static sideslip angle corresponding with the directional control deflection specified in paragraph (a) of this section, it shall be assumed that the directional control is suddenly returned to neutral. When a tail rotor is provided on a rotorcraft, it shall not be possible for the tail rotor to contact the landing medium during a normal landing. If a tail rotor guard is provided which will contact the landing medium during landings and thus prevent tail rotor contact, suitable design loads for the guard shall be established, and the guard and its supporting structure shall be designed to withstand the established loads. § 7.224 Stabilizing and control surfaces. Stabilizing and control surfaces shall be designed to withstand the critical loading from maneuvers or from combined maneuver and gust. In no case shall the limit load be less than 15 pounds per square foot or a load due to CN=0.55 at the maximum design speed. The load distribution shall simulate closely the actual pressure distribution conditions. § 7.225 Primary control systems; general. Longitudinal, lateral, vertical (collective pitch), and directional control systems shall be designed to the minimum requirements set forth in paragraphs (a) and (b) of this section: (a) Manually operated control systems, including their supporting structure, shall be designed to withstand the loads resulting from the limit pilot-applied forces as set forth in subparagraphs (1) through (3) of this paragraph, or the maximum loads which can be obtained in normal operation of the rotorcraft, including any single power boost system failure (see § 7.328), whichever is greater. Where it can be shown that the system design or the normal operating loads are such that a portion of the system cannot react the specified pilot-applied forces of subparagraphs (1) through (3) of this paragraph, that portion of the system shall be designed to withstand the maximum loads which can be obtained in normal operation of the rotorcraft. The minimum design loads shall in any case be sufficient to provide a rugged system for service use, including consideration of fatigue, jamming, ground gusts, control inertia, and friction loads. In the absence of a rational analysis, the design loads resulting from 0.60 of the specified pilot-applied forces shall be considered as acceptable minimum design loads. (1) Foot-type controls-130 pounds. (2) Stick-type controls-100 pounds fore and aft-67 pounds laterally. (3) Wheel-type controls-100 pounds fore and aft-53D inch-pounds couple at the rim of the control wheel (where D is wheel diameter, inches). (b) The reaction to the applied loads shall be provided as follows: (1) By the control stops only, (3) By the irreversible mechanism only (with the irreversible mechanism locked and with the control surface in all critical positions for the affected portions of the system within its limit of motion), (4) By the attachment of the control system to the rotor blade pitch control horn only (with the control in all critical positions for the affected portions of the system within the limits of its motion), and (5) By the attachment of the control system to the control surface horn (with the control in all critical positions for the affected portions of the system within the limits of its motion). [21 F.R. 3744, June 2, 1956, as amended by Amdt. 7-4, 24 F.R. 7075, Sept. 1, 1959] § 7.226 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 § 7.225. (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 § 7.225. (a) Loads and equilibrium. The limit loads obtained in the landing conditions shall be considered as external loads which would occur in a rotorcraft structure if it were acting as a rigid body. In each of the conditions the external loads shall be placed in equilibrium with the linear and angular inertia loads in a rational or conservative manner. In applying the specified conditions the provisions of paragraphs (b) through (e) of this section shall be complied with. (b) 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. (c) Design weight. The design weight used in the landing conditions shall not be less than the maximum weight of the rotorcraft. It shall be acceptable to assume a rotor lift, equal to two-thirds the design maximum weight, to exist throughout the landing impact and to act through the center of gravity of the rotorcraft. Higher values of rotor lift shall be acceptable if substantiated by tests and/or data which are applicable to the particular rotorcraft. (d) Load factor. The structure shall be designed for a limit load factor selected by the applicant, of not less than the value of the limit inertia load factor substantiated in accordance with the provisions of § 7.332, except in conditions in which other values of load factors are prescribed. (e) Landing gear position. The tires shall be assumed to be in their static position, and the shock absorbers shall be assumed to be in the most critical position, unless otherwise prescribed. (f) Landing gear arrangement. The provisions of §§ 7.231 through 7.236 shall be applicable to landing gear arrangements where two wheels are located aft and one or more wheels are located forward of the center of gravity. § 7.231 Level landing conditions. (a) Under loading conditions prescribed in paragraphs (b) and (c) of this section, the rotorcraft shall be assumed to be in the following two level landing attitudes: (1) All wheels contacting the ground simultaneously, and (2) The aft wheels contacting the ground with the forward wheel(s) being just clear of the ground. (b) The following two level landing loading conditions shall be considered. Where the forward portion of the landing gear has two wheels, the total load applied to the forward wheels shall be divided between the two wheels in a 40 60 proportion. (1) Vertical loads shall be applied in accordance with the provisions of § 7.230. (2) The vertical loads specified in subparagraph (1) of this paragraph shall be combined with a drag load at each wheel. The drag loads shall not be less than 25 percent of the respective vertical loads. For the attitude prescribed in paragraph (a) (1) of this section the resulting pitching moment shall be assumed resisted by the forward gear, while for the attitude prescribed in paragraph (a) (2) of this section the resulting pitching moment shall be assumed resisted by angular inertia forces. (c) Drag components simulating the forces required to accelerate the wheel rolling assembly up to the specified ground speed shall be combined with the vertical reactions existing at the instant of peak drag loads. The ground speed for determination of the spin-up loads shall be assumed equal to 75 percent of the optimum forward flight speed for minimum rate of descent in autorotative flight. The vertical loads under this loading condition shall be in accordance with the provisions of § 7.230 (d). It shall be acceptable to apply this condition only to the landing gear and the attaching structure. § 7.232 Nose-up landing condition. The rotorcraft shall be assumed in the maximum nose-up attitude permitting clearance of the ground by all parts of the rotorcraft. The ground loads shall be applied perpendicularly to the ground. § 7.233 One-wheel landing condition. The rotorcraft shall be assumed in the level attitude to contact the ground on one of the wheels located aft of the center of gravity. The vertical load shall be the same as that obtained on the one side in the condition specified in § 7.231 (b) (1). The unbalanced external loads shall be reacted by the inertia of the rotorcraft. § 7.234 Lateral-drift landing condition. (a) The rotorcraft shall be assumed in the level landing attitude. Side loads shall be combined with one-half the maximum ground reactions obtained in the level landing conditions of § 7.231 (b) (1). These loads shall be applied at the ground contact point, unless the landing gear is of the full-swiveling type in which case the loads shall be applied at the center of the axle. The conditions set forth in paragraphs (b) and (c) of this section shall be considered. (b) Only the wheels aft of the center of gravity shall be assumed to contact the ground. Side loads equal to 0.8 of the vertical reaction acting inward (on one side) and 0.6 of the vertical reaction acting outward (on the other side) shall be combined with the vertical loads specified in paragraph (a) of this section. (c) The forward and aft wheels shall be assumed to contact the ground simultaneously. Side loads on the wheels aft of the center of gravity shall be applied in accordance with paragraph (b) of this section. A side load at the forward gear equal to 0.8 of the vertical reaction shall be combined with the vertical load specified in paragraph (a) of this section. § 7.235 Brake roll conditions. The rotorcraft attitudes shall be assumed to be the same as those prescribed for the level landing conditions in § 7.231(a), with the shock absorbers deflected to their static position. The limit vertical load shall be based upon a load factor of 1.33 when the rotorcraft attitude is as specified in § 7.231(a) (1); the limit vertical load factor may be reduced to 1.0 when the attitude is as specified in § 7.231(a) (2). A drag load equal to the vertical load multiplied by a coefficient of friction of 0.8 shall be applied at the ground contact point of each wheel equipped with brakes, except that the drag load need not exceed the maximum value based on limiting brake torque. [21 F.R. 3744, June 2, 1956, as amended by Amdt. 7-4, 24 F.R. 7075, Sept. 1, 1959] § 7.236 Taxiing condition. The rotorcraft and its landing gear shall be designed for loads which occur when the rotorcraft is taxied over the roughest ground which it is reasonable to expect in normal operation. § 7.240 Ski landing conditions. The structure of a rotorcraft equipped with skis shall be designed in compliance with the loading conditions set forth in paragraphs (a) through (c) of this section: (a) Up load conditions. (1) A vertical load of Pn and a horizontal load of Pn/4 shall be applied simultaneously at the pedestal bearings, P being the maximum static weight on each ski when the rotorcraft is loaded to the maximum design weight. The limit load factor n shall be determined in accordance with § 7.230 (d). (2) A vertical load equal to 1.33 P shall be applied at the pedestal bearings. (For P see subparagraph (1) of this paragraph.) (b) Side-load condition. A side load of 0.35 Pn shall be applied in a horizontal plane perpendicular to the center line of the rotorcraft at the pedestal bearing. (For P and n see paragraph (a) (1) of this section.) (c) Torque-load condition. A torque load equal to 1.33 P (ft.-lb.) shall be applied to the ski about the vertical axis through the center line of the pedestal bearings. (For P see paragraph (a) (1) of this section.) § 7.245 Float landing conditions. The structure of a rotorcraft equipped with floats shall be designed in compliance with the loading conditions set forth in paragraphs (a) and (b) of this section: (a) Up load conditions. (1) With the rotorcraft assumed in the static level attitude a load shall be applied so that the resultant water reaction passes vertically through the center of gravity of the rotorcraft. The limit load factor shall be determined in accordance with § 7.230 (d) or shall be assumed to be the same as the load factor determined for the ground type landing gear. (2) The vertical load prescribed in subparagraph (1) of this paragraph shall be applied together with an aft component equal to 0.25 the vertical component. (b) Side load condition. The vertical load in this condition equal to 0.75 the vertical load prescribed in paragraph (a) (1) of this section, divided equally between the floats, shall be applied together with a side component. The total side component shall be equal to 0.25 the total vertical load in this condition and shall be applied to one float only. § 7.246 Tail-wheel type landing gear ground loading conditions. The structure of a rotorcraft equipped with landing gears arranged such that two wheels are located forward and one wheel is located aft of the center of gravity shall be assumed to be subjected to the loading conditions in accordance with paragraphs (a) through (h) of this section: (a) Level landing on forward gear only. The rotorcraft shall be assumed to be in the level landing attitude with only the forward wheels contacting the ground. (1) Vertical loads shall be applied in accordance with provisions of § 7.230. (2) The vertical loads specified in subparagraph (1) of this paragraph shall be combined with a drag load at each wheel axle of not less than 25 percent of the respective vertical load. (3) In the conditions of subparagraphs (1) and (2) of this paragraph, unbalanced pitching moments shall be assumed resisted by angular inertia forces. (b) Level landings; all wheels contacting simultaneously. The rotorcraft shall be assumed to be in the level landing attitude with all wheels contacting the ground simultaneously. (1) Vertical loads shall be applied in accordance with the provisions of § 7.230. (2) The vertical loads specified in subparagraph (1) of this paragraph shall be combined with a drag load at each wheel axle of not less than 25 percent of the respective vertical load. Unbalanced pitching moments shall be assumed resisted by angular inertia forces. (c) Nose-up landing condition. The rotorcraft shall be assumed to contact the ground on the rear wheel only at the maximum nose-up attitude to be expected under all operational landing conditions including landings in autorotation. The conditions of this paragraph need not be applied if it can be demonstrated that the probability of landing with initial contact on the rear wheel is extremely remote. In determining the applicable ground loads, it shall be acceptable to use a rational method to account for the distance between the direction of the rear wheel ground reactions and the rotorcraft c.g. (1) Vertical loads shall be applied in accordance with the provisions of § 7.230. (2) The vertical loads specified in subparagraph (1) of this paragraph shall be combined with a drag load at the wheel axle of not less than 25 percent of the vertical load. (d) One-wheel landing condition. The rotorcraft shall be assumed in the level attitude to contact the ground on one of the wheels located forward of the c.g. The vertical load shall be the same as that obtained on the one side in the condition specified in paragraph (a) (1) of this section. Unbalanced moments shall be assumed resisted by angular inertia forces. (e) Side load landing condition. The rotorcraft shall be assumed in the landing attitudes of paragraphs (a) and (b) of this section. Side loads in combination with one-half the maximum vertical ground reactions obtained in the landing conditions of paragraphs (a)(1) and (b) (1) of this section shall be applied at each wheel. The magnitude of the side loads on the forward wheels in each case shall be 0.8 of the vertical reaction (on one side) acting inward and 0.6 of the vertical reaction (on the other side) acting outward. The magnitude of the side load on the rear wheel shall be equal to 0.8 of the vertical reaction. These loads shall be applied at the ground contact point, unless the landing gear is of the full-swiveling type in which case the loads shall be applied at the center of the axle. When a lock, steering device, or shimmy damper is provided, the swiveled wheel shall also be assumed to |