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Fred,
This is one reason we have the hydraulic accumulator on the IV-P. It SHOULD absorb the slight volume change with temperature that causes the 2-seater hydraulic systems, without any buffer, to spike. Any chance your accumulator is “flat?”
The test is operating your flaps (speed brakes?) with the hydraulic system power off. My flaps will do about 1 ½ cycles before the pressure goes to zero. If the accumulator has lost
it’s pre-loaded pressure on the air side, the flaps won’t even operate through one cycle; probably won’t even extend fully?
Bob
From:
Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Frederick Moreno
Sent: Monday, September 03, 2012 2:54 PM
To: lml@lancaironline.net
Subject: [LML] Re: Thermal influence on Hydraulic Pressure
I have an MPV-50 engine monitor that includes continuous reading of the hydraulic system pressure on my Lancair IV/ I have seen the same
thing, particularly on a flight that started on a cool morning departure from my home drome and took us to the desert for a 110+F day. On descent, pressure rose from its customary 1250 to 1500 psi at which point Bitching Betty started to complain so I bumped
my speed brakes which are hydraulic, and lowered pressure back down to my customary range. Same thing sometimes happens in reverse, a hot soak on the ground, then a climb to 10-11,000 feet for a cool soak, and at some point the hydraulic pump kicks on to
restore pressure to the desired level. My TR-182 used to the the same thing routinely when departing Phoenix in the summertime.
It is a real effect, and makes one wonder about very high pressure events arising from FL 270 (say) cold soak terminating in Phoenix on a July
afternoon. Hmmmm....
-------Original Message-------
-took this photo after a descent from 16.5k to 1,500 ft.
OAT went from 42 to 94 degrees.
High Pressure gauge is pegged at 2,000+ psi
-Didn't get a photo, but the opposite happened on the ramp in Spokane. After
sitting for an hour, the low pressure gauge was pegged at 1,200 psi+. Spokane might not be the warmest spot in the country, but at 85 deg F, it was 55 degrees warmer than the cold soak on the previous leg.
Temperature changes have a big impact on system pressure.
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