Last question: On the pic you see
the small red pressure cylinder that is mounted in connection with the
hydraulic oil system. Can anybody tell me when you need the function of that
little pressure tank. As I understood it the high pressure in the small
should be enough to lower and lock the gears if main pump fails. But then you
have your manual handle to pump down the gears with. So what is the use for
this pressure tank? It should be filled with high pressure nitrogen but there
is no info in kit instruction how high. Anybody knows that?
Christer,
The
hydraulic oil tank and pump assembly for the Lancair IV/IV-P is designed so the
input for the electric pump is higher in the tank than the input for the hand
pump. This allows it to have about one quart of oil in the tank that is
available to the hand pump but not to the electric pump. At least in theory,
you should have oil available to the hand pump after the electric pump “runs
dry.” I have looked at and measured these items in the tank, but have not
actually tested this operation. I have added a procedure in my checklist,
however that says basically, if you sense a hydraulic problem—specifically
if the electric pump starts running for any unknown reason, you should
immediately slow and lower the gear—while you can do it with the electric
system. My rationale for this is that some leaks, including failures within the
actuator, can make it difficult or impossible to hand pump the gear all the way
to the locked position. Better to let the electric pump give it the first try
if you can. This doesn’t preclude trying the hand pump as an alternative,
but the electric pump is much stronger and has a better chance of success as
long as it has oil A long time ago I flew fighters that had a compressed
nitrogen bottle that could be applied to “blow down” the landing
gear. It works, but is a heavy and complex solution to a very infrequent
problem.
The
red cylinder you ask about is a hydraulic accumulator. In the IV-P it serves
mostly as a “shock absorber” for the hydraulic system. You’ve
already noted that it is of insufficient volume to lower the gear even one
time, although I can usually get 3-4 flap cycles out of it. A larger one would
ideally give you one gear down cycle, but this thing needs to hold fluid and
nitrogen at more than 1000 PSI, and the weight goes up exponentially as you
increase the size. Don’t know why the designer didn’t use a larger
accumulator, given that he used one at all, but I suspect it was a weight/cost
issue. I’ve read in the LML about servicing this accumulator, but as this
would be at least third-hand information, I’ll leave it for the experts
to respond to this.
Hope this helps,
Bob
Pastusek