Federal Aviation Administration, DOT

Section 27.729

at ground contact in normal power-off
landings.
(b) If considered, the rotor lift specified in Section 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 paragraph (b)
of this section, the following formula
may be used instead of more rational
computations:

We = W 
n = nj

h + (1  -  L )d
; and
h+d

We
+L
W

where:
We = the effective weight to be used in the
drop test (lbs.);
W = WM for main gear units (lbs.), 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 center of gravity.
W = WN for nose gear units (lbs.), 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 center of gravity
and exerts a force of 1.0g downward and
0.25g forward.
W = WT for tailwheel units (lbs.), equal to
whichever of the following is critical:

h = specified free drop height (inches).
L = ration of assumed rotor lift to the rotorcraft weight.
d = deflection under impact of the tire (at
the proper inflation pressure) plus the
vertical component of the axle travels
(inches) 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.,

Section 27.727 Reserve energy absorption
drop test.
The reserve energy absorption drop
test must be conducted as follows:
(a) The drop height must be 1.5 times
that specified in Section 27.725(a).
(b) Rotor lift, where considered in a
manner similar to that prescribed in
Section 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.
[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27-26, 55 FR 8001, Mar. 6,
1990]

Section 27.729 Retracting mechanism.
For rotorcraft with retractable landing gear, the following apply:
(a) Loads. The landing gear, retracting mechansim, wheel-well doors, and
supporting structure must be designed
for - 
(1) The loads occurring in any maneuvering 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.

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(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 center of gravity and exerts a
force of lg downward with the rotorcraft in
the maximum nose-up attitude considered in
the nose-up landing conditions.

the acceleration dv/dt in g-s recorded in
the drop test plus 1.0).