CS 27.723 Shock absorption tests
ED Decision 2003/15/RM
The landing inertia load factor and the reserve energy absorption capacity of the landing gear must be substantiated by the tests prescribed in CS 27.725 and 27.727, respectively. These tests must be conducted on the complete rotorcraft or on units consisting of wheel, tyre, and shock absorber in their proper relation.
ED Decision 2003/15/RM
The limit drop test must be conducted as follows:
(a) The drop height must be –
(1) 0.33 m (13 inches) from the lowest point of the landing gear to the ground; or
(2) Any lesser height, not less than 0.20 m (8 in), resulting in a drop contact velocity equal to the greatest probable sinking speed likely to occur at ground contact in normal power-off landings.
(b) If considered, the rotor lift specified in CS 27.473(a) must be introduced into the drop test by appropriate energy absorbing devices or by the use of an effective mass.
(c) Each landing gear unit must be tested in the attitude simulating the landing condition that is most critical from the standpoint of the energy to be absorbed by it.
(d) When an effective mass is used in showing compliance with sub-paragraph (b) the following formula may be used instead of more rational computations:
where:
We = the effective weight to be used in the drop test.
W = WM for main gear units, equal to the static reaction on the particular unit with the rotorcraft in the most critical attitude. A rational method may be used in computing a main gear static reaction, taking into consideration the moment arm between the main wheel reaction and the rotorcraft centre of gravity.
W = WN for nose gear units, equal to the vertical component of the static reaction that would exist at the nose wheel, assuming that the mass of the rotorcraft acts at the centre of gravity and exerts a force of 1.0 g downward and 0.25 g forward.
W = WT for tailwheel units equal to whichever of the following is critical:
(1) The static weight on the tailwheel with the rotorcraft resting on all wheels; or
(2) The vertical component of the ground reaction that would occur at the tailwheel, assuming that the mass of the rotorcraft acts at the centre of gravity and exerts a force of 1 g downward with the rotorcraft in the maximum nose-up attitude considered in the nose-up landing conditions.
h = specified free drop height.
L = ratio of assumed rotor lift to the rotorcraft weight.
d = deflection under impact of the tyre (at the proper inflation pressure) plus the vertical component of the axle travel relative to the drop mass.
n = limit inertia load factor.
nj = the load factor developed, during impact, on the mass used in the drop test (i.e., the acceleration dv/dt in g recorded in the drop test plus 1.0).
CS 27.727 Reserve energy absorption drop test
ED Decision 2003/15/RM
The reserve energy absorption drop test must be conducted as follows:
(a) The drop height must be 1.5 times that specified in CS 27.725(a).
(b) Rotor lift, where considered in a manner similar to that prescribed in CS 27.725(b), may not exceed 1.5 times the lift allowed under that paragraph.
(c) The landing gear must withstand this test without collapsing. Collapse of the landing gear occurs when a member of the nose, tail, or main gear will not support the rotorcraft in the proper attitude or allows the rotorcraft structure, other than the landing gear and external accessories, to impact the landing surface.
CS 27.729 Retracting mechanism
ED Decision 2003/15/RM
For rotorcraft with retractable landing gear, the following apply:
(a) Loads. The landing gear, retracting mechanism, wheel-well doors, and supporting structure must be designed for –
(1) The loads occurring in any manoeuvring condition with the gear retracted;
(2) The combined friction, inertia, and air loads occurring during retraction and extension at any airspeed up to the design maximum landing gear operating speed; and
(3) The flight loads, including those in yawed flight, occurring with the gear extended at any airspeed up to the design maximum landing gear extended speed.
(b) Landing gear lock. A positive means must be provided to keep the gear extended.
(c) Emergency operation. When other than manual power is used to operate the gear, emergency means must be provided for extending the gear in the event of –
(1) Any reasonably probable failure in the normal retraction system; or
(2) The failure of any single source of hydraulic, electric, or equivalent energy.
(d) Operation tests. The proper functioning of the retracting mechanism must be shown by operation tests.
(e) Position indicator. There must be a means to indicate to the pilot when the gear is secured in the extreme positions.
(f) Control. The location and the operation of the retraction control must meet the requirements of CS 27.777 and 27.779.
(g) Landing gear warning. An aural or equally effective landing gear warning device must be provided that functions continuously when the rotorcraft is in a normal landing mode and the landing gear is not fully extended and locked. A manual shut-off capability must be provided for the warning device and the warning system must automatically reset when the rotorcraft is no longer in the landing mode.
ED Decision 2003/15/RM
(a) Each landing gear wheel must be approved.
(b) The maximum static load rating of each wheel may not be less than the corresponding static ground reaction with:
(1) Maximum weight; and
(2) Critical centre of gravity.
(c) The maximum limit load rating of each wheel must equal or exceed the maximum radial limit load determined under the applicable ground load requirements of this CS-27.
ED Decision 2003/15/RM
(a) Each landing gear wheel must have a tyre:
(1) That is a proper fit on the rim of the wheel; and
(2) Of the proper rating.
(b) The maximum static load rating of each tyre must equal or exceed the static ground reaction obtained at its wheel, assuming:
(1) The design maximum weight; and
(2) The most unfavourable centre of gravity.
(c) Each tyre installed on a retractable landing gear system must, at the maximum size of the tyre type expected in service, have a clearance to surrounding structure and systems that is adequate to prevent contact between the tyre and any part of the structure or systems.
ED Decision 2003/15/RM
For rotorcraft with wheel-type landing gear, a braking device must be installed that is:
(a) Controllable by the pilot;
(b) Usable during power-off landings; and
(c) Adequate to:
(1) Counteract any normal unbalanced torque when starting or stopping the rotor; and
(2) Hold the rotorcraft parked on a 10° slope on a dry, smooth pavement.
ED Decision 2003/15/RM
The maximum limit load rating of each ski must equal or exceed the maximum limit load determined under the applicable ground load requirements of this CS-27.