631 

Federal Aviation Administration, DOT 

§ 29.935 

the remaining transmission torque in-
puts the maximum torque attainable 
under probable operating conditions, 
assuming that torque limiting devices, 
if any, function properly. Each trans-
mission input must be tested at this 
maximum torque for at least fifteen 
minutes. 

(c) 

Lubrication system failure. For lu-

brication systems required for proper 
operation of rotor drive systems, the 
following apply: 

(1) 

Category A. Unless such failures 

are extremely remote, it must be 
shown by test that any failure which 
results in loss of lubricant in any nor-
mal use lubrication system will not 
prevent continued safe operation, al-
though not necessarily without dam-
age, at a torque and rotational speed 
prescribed by the applicant for contin-
ued flight, for at least 30 minutes after 
perception by the flightcrew of the lu-
brication system failure or loss of lu-
bricant. 

(2) 

Category B. The requirements of 

Category A apply except that the rotor 
drive system need only be capable of 
operating under autorotative condi-
tions for at least 15 minutes. 

(d) 

Overspeed test. The rotor drive sys-

tem must be subjected to 50 overspeed 
runs, each 30 

±

3 seconds in duration, at 

not less than either the higher of the 
rotational speed to be expected from an 
engine control device failure or 105 per-
cent of the maximum rotational speed, 
including transients, to be expected in 
service. If speed and torque limiting 
devices are installed, are independent 
of the normal engine control, and are 
shown to be reliable, their rotational 
speed limits need not be exceeded. 
These runs must be conducted as fol-
lows: 

(1) Overspeed runs must be alternated 

with stabilizing runs of from 1 to 5 
minutes duration each at 60 to 80 per-
cent of maximum continuous speed. 

(2) Acceleration and deceleration 

must be accomplished in a period not 
longer than 10 seconds (except where 
maximum engine acceleration rate will 
require more than 10 seconds), and the 
time for changing speeds may not be 
deducted from the specified time for 
the overspeed runs. 

(3) Overspeed runs must be made with 

the rotors in the flattest pitch for 
smooth operation. 

(e) The tests prescribed in paragraphs 

(b) and (d) of this section must be con-
ducted on the rotorcraft and the torque 
must be absorbed by the rotors to be 
installed, except that other ground or 
flight test facilities with other appro-
priate methods of torque absorption 
may be used if the conditions of sup-
port and vibration closely simulate the 
conditions that would exist during a 
test on the rotorcraft. 

(f) Each test prescribed by this sec-

tion must be conducted without inter-
vening disassembly and, except for the 
lubrication system failure test re-
quired by paragraph (c) of this section, 
each part tested must be in a service-
able condition at the conclusion of the 
test. 

(Secs. 313(a), 601, 603, 604, Federal Aviation 
Act of 1958 (49 U.S.C. 1354(a), 1421, 1423 1424), 
sec. 6(c), Dept. of Transportation Act (49 
U.S.C. 1655(c))) 

[Amdt. 29–3, 33 FR 969, Jan. 26, 1968, as 
amended by Amdt. 29–17, 43 FR 50601, Oct. 30, 
1978; Amdt. 29–26, 53 FR 34216, Sept. 2, 1988] 

§ 29.931

Shafting critical speed. 

(a) The critical speeds of any shafting 

must be determined by demonstration 
except that analytical methods may be 
used if reliable methods of analysis are 
available for the particular design. 

(b) If any critical speed lies within, 

or close to, the operating ranges for 
idling, power-on, and autorotative con-
ditions, the stresses occurring at that 
speed must be within safe limits. This 
must be shown by tests. 

(c) If analytical methods are used and 

show that no critical speed lies within 
the permissible operating ranges, the 
margins between the calculated crit-
ical speeds and the limits of the allow-
able operating ranges must be adequate 
to allow for possible variations be-
tween the computed and actual values. 

[Amdt. 29–12, 41 FR 55472, Dec. 20, 1976] 

§ 29.935

Shafting joints. 

Each universal joint, slip joint, and 

other shafting joints whose lubrication 
is necessary for operation must have 
provision for lubrication. 

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