CS 27.497 Ground loading conditions: landing gear with tail wheels

• ED Decision 2003/15/RM found in: CS-27 Amdt 9 - Small Rotorcraft (Dec 2021)

CS 27.497 Ground loading conditions: landing gear with tail wheels ED Decision 2003/15/RM (a) *General*. Rotorcraft with landing gear with two wheels forward, and one wheel aft, of the centre of gravity must be designed for loading conditions as prescribed in this paragraph. (b) *Level landing attitude with only the forward wheels contacting the ground.* In this attitude: (1) The vertical loads must be applied under [CS 27.471](#_DxCrossRefBm472493289) to [27.475](#_DxCrossRefBm472493292); (2) The vertical load at each axle must be combined with a drag load at that axle of not less than 25% of that vertical load; and (3) Unbalanced pitching moments are assumed to be resisted by angular inertia forces. (c) *Level landing attitude with all wheels contacting the ground simultaneously*. In this attitude, the rotorcraft must be designed for landing loading conditions as prescribed in sub-paragraph (b). (d) *Maximum nose-up attitude with only the rear wheel contacting the ground*. The attitude for this condition must be the maximum nose-up attitude expected in normal operation, including autorotative landings. In this attitude: (1) The appropriate ground loads specified in sub-paragraphs (b)(1) and (2) must be determined and applied, using a rational method to account for the moment arm between the rear wheel ground reaction and the rotorcraft centre of gravity; or (2) The probability of landing with initial contact on the rear wheel must be shown to be extremely remote. (e) *Level landing attitude with only one forward wheel contacting the ground*. In this attitude, the rotorcraft must be designed for ground loads as specified in sub-paragraphs (b) (1) and (3). (f) *Side loads in the level landing attitude*. In the attitudes specified in sub-paragraphs (b) and (c) the following apply: (1) The side loads must be combined at each wheel with one-half of the maximum vertical ground reactions obtained for that wheel under sub-paragraphs (b) and (c). In this condition the side loads must be: (i) For the forward wheels, 0.8 times the vertical reaction (on one side) acting inward, and 0.6 times the vertical reaction (on the other side) acting outward; and (ii) For the rear wheel, 0.8 times the vertical reaction. (2) The loads specified in sub-paragraph (f)(1) must be applied: (i) At the ground contact point with the wheel in the trailing position (for non-full swivelling landing gear or for full-swivelling landing gear with a lock, steering device, or shimmy damper to keep the wheel in the trailing position); or (ii) At the centre of the axle (for full swivelling landing gear without a lock, steering device, or shimmy damper). (g) *Braked roll conditions in the level landing attitude*. In the attitudes specified in sub-paragraphs (b) and (c), and with shock absorbers in their static positions, the rotorcraft must be designed for braked roll loads as follows: (1) The limit vertical load must be based on a limit vertical load factor of not less than: (i) 1.0 for the attitude specified in sub-paragraph (b); and (ii) 1.33, for the attitude specified in sub-paragraph (c). (2) For each wheel with brakes, a drag load must be applied, at the ground contact point, of not less than the lesser of: (i) 0.8 times the vertical load; and (ii) The maximum based on limiting brake torque. (h) *Rear wheel turning loads in the static ground attitude*. In the static ground attitude, and with the shock absorbers and tyres in their static positions, the rotorcraft must be designed for rear wheel turning loads as follows: (1) A vertical ground reaction equal to the static load on the rear wheel must be combined with an equal sideload. (2) The load specified in sub-paragraph (h)(1) must be applied to the rear landing gear: (i) Through the axle, if there is a swivel (the rear wheel being assumed to be swivelled 90° to the longitudinal axis of the rotorcraft); or (ii) At the ground contact point, if there is a lock, steering device or shimmy damper (the rear wheel being assumed to be in the trailing position). (i) *Taxying condition*. The rotorcraft and its landing gear must be designed for loads that would occur when the rotorcraft is taxied over the roughest ground that may reasonably be expected in normal operation. CS 27.497 Ground loading conditions: landing gear with tail wheels ED Decision 2003/15/RM (a) *General*. Rotorcraft with landing gear with two wheels forward, and one wheel aft, of the centre of gravity must be designed for loading conditions as prescribed in this paragraph. (b) *Level landing attitude with only the forward wheels contacting the ground.* In this attitude: (1) The vertical loads must be applied under [CS 27.471](#_DxCrossRefBm8893858) to [27.475](#_DxCrossRefBm8893861); (2) The vertical load at each axle must be combined with a drag load at that axle of not less than 25% of that vertical load; and (3) Unbalanced pitching moments are assumed to be resisted by angular inertia forces. (c) *Level landing attitude with all wheels contacting the ground simultaneously*. In this attitude, the rotorcraft must be designed for landing loading conditions as prescribed in sub-paragraph (b). (d) *Maximum nose-up attitude with only the rear wheel contacting the ground*. The attitude for this condition must be the maximum nose-up attitude expected in normal operation, including autorotative landings. In this attitude: (1) The appropriate ground loads specified in sub-paragraphs (b)(1) and (2) must be determined and applied, using a rational method to account for the moment arm between the rear wheel ground reaction and the rotorcraft centre of gravity; or (2) The probability of landing with initial contact on the rear wheel must be shown to be extremely remote. (e) *Level landing attitude with only one forward wheel contacting the ground*. In this attitude, the rotorcraft must be designed for ground loads as specified in sub-paragraphs (b) (1) and (3). (f) *Side loads in the level landing attitude*. In the attitudes specified in sub-paragraphs (b) and (c) the following apply: (1) The side loads must be combined at each wheel with one-half of the maximum vertical ground reactions obtained for that wheel under sub-paragraphs (b) and (c). In this condition the side loads must be: (i) For the forward wheels, 0.8 times the vertical reaction (on one side) acting inward, and 0.6 times the vertical reaction (on the other side) acting outward; and (ii) For the rear wheel, 0.8 times the vertical reaction. (2) The loads specified in sub-paragraph (f)(1) must be applied: (i) At the ground contact point with the wheel in the trailing position (for non-full swivelling landing gear or for full-swivelling landing gear with a lock, steering device, or shimmy damper to keep the wheel in the trailing position); or (ii) At the centre of the axle (for full swivelling landing gear without a lock, steering device, or shimmy damper). (g) *Braked roll conditions in the level landing attitude*. In the attitudes specified in sub-paragraphs (b) and (c), and with shock absorbers in their static positions, the rotorcraft must be designed for braked roll loads as follows: (1) The limit vertical load must be based on a limit vertical load factor of not less than: (i) 1.0 for the attitude specified in sub-paragraph (b); and (ii) 1.33, for the attitude specified in sub-paragraph (c). (2) For each wheel with brakes, a drag load must be applied, at the ground contact point, of not less than the lesser of: (i) 0.8 times the vertical load; and (ii) The maximum based on limiting brake torque. (h) *Rear wheel turning loads in the static ground attitude*. In the static ground attitude, and with the shock absorbers and tyres in their static positions, the rotorcraft must be designed for rear wheel turning loads as follows: (1) A vertical ground reaction equal to the static load on the rear wheel must be combined with an equal sideload. (2) The load specified in sub-paragraph (h)(1) must be applied to the rear landing gear: (i) Through the axle, if there is a swivel (the rear wheel being assumed to be swivelled 90° to the longitudinal axis of the rotorcraft); or (ii) At the ground contact point, if there is a lock, steering device or shimmy damper (the rear wheel being assumed to be in the trailing position). (i) *Taxying condition*. The rotorcraft and its landing gear must be designed for loads that would occur when the rotorcraft is taxied over the roughest ground that may reasonably be expected in normal operation.