In a message dated 11/4/2005 12:25:00 P.M. Central Standard Time,
dryan@gt.rr.com writes:
I think
the main breaker only pulls power off of the relays through to the motor? I
better check.
I'm not sure that your pump tests emulate the sequence I
probably experienced.
Probably not, we just don't have the failed parts to try to figure out
exactly what happened. Did you wire the airplane? Is there a circuit
diagram or was it wired per the Lancair scheme and you have 2 breakers, one for
the motor (50 A) and one for the relays (5 A)? Did you pull only the 50A
breaker for some time during flight and not the 5A, that would have caused
the intermittent UP relay to remain powered for a long time?
First the down press switch would have opened, the gear down
long enough for the press to build to open the switch. I would think that this
is the more common state, unless there is a leak somewhere?
If there was a bad enough leak, the pump would have continued to run.
If it was not bad, the pump would be running frequently to re-build the
pressure.
Second the HP switch is activated, (the down circuit is not
powered) and the up circuit is powered.
What happens then when the down
switch tries to reverse direction?
The state of the up pressure switch is irrelevant. If the panel switch
was in the gear down position, power could only be directed to the down relay
coil thru the down pressure switch. After all, the down pressure switch
has no problem when the gear up function is selected after takeoff. If the
relays are undamaged, the only way to actually select the wrong relay is thru
the panel switch itself or by a short between the wires leading back to the
relays (highly improbable).
Did your tests follow such a sequence?
Not quite, all I demonstrated is that the motor can run unpredictably if
both motor circuits are made sequentially and the power remains on.
Note that both relays can be closed (conducting electricity to the
motor) without regard to the state of the pressure switches if a relay has
been damaged. The only other way to actually select the wrong relay is
thru the panel switch itself or by a short between the wires leading back to the
relays (highly improbable).
If the pump was weakly trying to raise the gear, the nose could have
remained down and locked because of the 100 lb gas strut. Did that occur
(only the mains collapsed)?