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MIL-P-26366A
(2) A feathering system operable
3.28.3 Speed synchronization. Synchroni-
zation of propellers for multi-engine aircraft
under all flight conditions in-
shall be provided as a secondary speed control
cluding windmilling dives. An
and shall be specified in the model specification,
emergency means of initiating
The control shall act to maintain the rotational
feathering shall be incorporated
speed of the slave propeller(s) to that of the
which is independent of the
master propeller within 2 rpm in the pro-
normal means for such opera-
peller normal governing range.
tions.
3.28.4 Governing. Normal and reverse gov-
(3) A control linkage which when
erning shall be specified in the model specifica-
connected with the engine NTS
tion. Selective constant speed governing at
output mechanism shall pro-
vide protection against cata-
any selected speed within the range necessary
for. optimum performance of the applicable
strophic drag.
(4) An adequate mechanical pitch
engine shall be incorporated in the propeller,
look that shall engage in the
3.28.4.1 Governors. Where the propeller is
event of overspending or loss of
controlled by a governor which is not an inte-
hydraulic pressure or similar
gral part of the propeller assembly, the gov-
ernor shall be constructed to conform to the
failure. The pitch lock shall
act, when engaged, to prevent
mounting specified by the applicable engine
motion of the blades toward
model specification.  The governor shall regu-
low pitch in the normal govern-
late the propeller speed between the limits spec-
i n g range but shall permit
ified in the model specification.
motion of the blades toward
3.28.5 Input mechanism at the propeller.
high pitch. Pitch lock settings
A single input (pitch actuating) mechanism
shall be specified in the mode?
shall be provided for the propeller to modulate
blade pitch throughout the operating range.
specification.
( d ) Phase synchronization that shall
3.28.5.1 Input mechanism travel. The total
maintain the blade phase angle rela-
travel and position of this mechanism shall be
tionship of all propellers to one another
compatible with the aircraft system. In the
within + 15 degrees under all normal
governing and beta regimes, the relationship be-
steady-state flight conditions in smooth
tween the motion of the propeller input mech-
air.
anism and resulting changes in governor setting
and propeller pitch shall be essentially linear.
(e) Reverse operation to a fixed negative
blade angle compatible with the en-
3.28.5.2 Reversing input mechanism. If re-
versing features are provided as part of the
gine. Overspeed during propeller re-
versal shall be compatible with engine
propeller system, a reverse thrust condition
overspeed limits.  Maximum time to
shall be reached by movement of an appropri-
reverse from the low pitch stop shall be
ate input. mechanism.  The total travel and po-
as specified in the model specification.
sition shall be compatible with the aircraft
system.
(f) The propeller response shall be suf-
ficiently rapid that it will not permit
3 . 2 8 . 5 . 3 Input mechanism torque. T h e
overspeeds in excess of those specified
torque required to operate the input mechanism
in the engine model specification.
through its range of travel shall not exceed 25
Transient limitations may be a func-
pound-inches and torque variation shall not ex-
tion of the engine overspeed mecha-
ceed 10 pound-inches.  With the propeller op-
nism on installations where applicable.
erating, the absence of external torque shall
The system exclusive of the synchro-
not result in input mechanism creep within the
operating range.  The estimated input mecha-
nizer shall prevent speed oscillations
nism torque shall be specified in the model
in excess of 0.5 percent under stabi-
specification.
lizer flight conditions.
11

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