Excerpts
from the P-51A, P-51B-5, and P-51C-1 Erection and Maintenance Manual
Relating to the position of inner gear doors and flaps after
shutdown
There
has been so much discussion about gear doors and flaps on
Mustangs, so I spent much of the afternoon studying the Erection
and Maintenance manual I have which is a WW II document.
It covers the P-51A, P-51B-5 and P-51C-1 Mustangs. The
long and short is that all these airplanes had identical landing
gear and flap systems. The was a mechanical uplock on the
inner gear doors, but it was mechanically linked to the main
strut actuator and only engaged when the main gear strut was in
the retracted position. It was held in the unlocked
position when the gear was down. The main gear strut down
lock was the only part of the system that remained locked in
position when hydraulic power was lost. It had an internal
spring which held it to the locked position, and it required
hydraulic pressure to cause it to disengage and allow the strut
to retract. The inner gear doors and the flaps had no
other means of staying up than the remaining hydraulic pressure
after shutdown. There was an accumulator in the system but
it would not hold pressure indefinitely. The bleed down
rate would depend on the internal leakage of the system, which
is usually better on new components than old ones. I once
flew an L-17 in the FT Eustis military flying club that had so
much internal leakage that if you tried to raise the flaps
before the gear was fully retracted everything just came to a
stop until the gear was dropped to the down position again,
reducing demand on hydraulic pressure and flow rate.
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