In a message dated 2/26/2007 5:56:40 P.M. Central Standard Time,
kneadedpleasures@sbcglobal.net writes:
Don't think I caused this problem but I certainly have to deal with it -
gear door closed before gear retracted in flight - no accident but could
have been if the gear had strongly jammed into retract such that low pressure
on extension might not have been sufficient to permit extension; possible prop
strike.
Didn't know of this condition until I was safely on the ground - didn't
use the emergency gear extension - nor did I flip the gear-pressure-release
valve - don't think I changed anything from the careful routines that I have
used in dozens of previous flights. So what might have caused this
scenario? What must be done to prevent it in the future (besides "not
flying")? Thanks for your comments.
Greg,
You have not provided enough information. Main or Nose? Ow, the
nose gear door would be messy while the mains would probably remain not up
tight.
Here is one possibility:
1. Gear retraction is initiated. It is usual to see mains start up
until there is enough pressure the start the nose over center link (held in
place by the 100# gas spring).
2. At this pulse of high pressure, enough to start the over
center link to move, one of the sequence valves fail and high pressure is
supplied to a door.
3. Since the door spring is weak, it closes while the system is overcoming
the strong nose gear gas spring.
4. The retract sequence is completed - I.E. the pressure builds high enough
to turn off the pump.
Note that the sequence valve is only a check valve that is defeated when
the plunger is depressed. Oh, that leads to a second scenario just as
possible. To wit:
1. On extension, the sequences valve is stuck in the "plunger pushed in"
condition (maybe the plunger is dirty or bent).
2. Extension only pressurizes the down side, making the check valve against
up pressure irrelevant.
3. With the sequence valve "stuck", retract causes the door to close
early as in the first possibility.
Let us know what your analysis.
Scott Krueger
AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL
(KARR)
Darwinian culling phrase: Watch
This!