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