Adam,
Chris Z has often mentioned that the mis-position of the shuttle valve can
lead to high pressure on both up and down sides of the system. However,
you point out the use of the dump valve to alter the pressure and then get a
successful pump down of the system. It is important to note why this works
for extension and not for retraction, and why this is an important item
on anyone's gear-down problem check-list.
The gear down and locked case is a rigidly static system - with the down
locks in place, nothing can be changed by maneuvers, dump valve, etc.
Since only hydraulic pressure keeps the gear up, gravity, door actuator
springs and the correct pressure in the nose gear gas spring has a
significant effect on changing the system pressures when the dump valve is
opened.
Scott Krueger
In a message dated 4/16/2012 7:14:50 A.M. Central Daylight Time,
adam@validationpartners.com writes:
On my fourth test flight I tested the normal and emergency gear
extension/retraction and everything worked fine. My first landing attempt
resulted in a go-around due to gusty winds. When I extended the gear again on
downwind nothing happened. After a few seconds of head-scratching I
momentarily cracked the dump valve. That fixed the problem and the landing was
uneventful (if a bit firm). http://www.youtube.com/watch?v=fo1qnhBuqS8
The attached JPG file shows the up and down hydraulic pressure readings
throughout the flight. The x-axis is time, with the flight beginning at 20:32Z
and ending at 21:12Z. You can see the gear retraction tests beginning around
20:43 and 3500' altitude. Notice that after the last test the down pressure
remains around 500psi for about 90 seconds even though the gear is retracted.
The up pressure fluctuates a bit then the down pressure drops to near
zero.
The bottom graph is a closer view of the landing sequence. The go-around
occurs at 21:05Z. When I retracted the gear the up pressure went to 950psi as
expected, but the down pressure fluctuated around 500psi. This kept the down
pressure switch open, preventing gear extension.
Does anyone have an idea as to what's causing the pressure buildup on the
down side?
Thanks,
Adam Molny
N181AM 6.1hrs hobbs time
--
For archives and unsub
http://mail.lancaironline.net:81/lists/lml/List.html