Message-ID: <19981106182520.1185.qmail@www01.netaddress.usa.net>
Date: Fri, 06 Nov 1998 18:25:20
From: Dan Schaefer <dfschaefer@usa.net>
To: lancair.list@olsusa.com
Subject: hydro system lo pressure
Mime-Version: 1.0

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To Angier Ames: You asked if Lancairs have a gear down-lock problem 
should the hydro pressure bleed down over time, and the answer is NO.

I'm not surprised that this warning came from the Glasair community
because the Glasair definitely DOES have the problem since they rely
on hydro pressure for their down-lock (at least on the Glasair III). 
Lancairs don't have the problem because, as you know, Lancairs use 
mechanical, over-center down locks, energized by coil or pneumatic 
springs. The equivalent to the Glasair bleed down problem in a Lancair
would be to have the gas spring on the nose gear go flat, i.e., bleed
down, and have the down-lock coil springs on the main gear fail. An
unlikely event just sitting on the ground for a while. As a matter
of fact, when I get ready to leave my hangar, I usually crack the gear 
dump valve momentarily to relieve the pressure in the system. Since 
any hydro system will bleed down sooner or later, and even the best
systems will seep some small amount of fluid while doing so, it makes
sense to just beat it to the punch and relieve the pressure right up 
front. A secondary benefit of this is a definite indication of pump
operation when I power up the next time. If I don't hear the pump run
briefly (about 1 second) while it brings up system pressure when the master is turned on, I will stop and figure out why. Hasn't happened 
yet, but I'll catch it if it does.

The gear down-locks in this case, are the same ones you are
going to rely on if the day ever comes where a electrical or hydro
failure makes you use the emergency gear extension - you will have 
zero hydro pressure then too. In a Lancair, it's a non-event (assuming
of course, you've done an emergency gear drop test in the last month,
IN THE AIR, and all goes as it should - in my airplane, the gear 
actually goes down and locks faster that way than when pumped down!)
In a Glasair, it's probably best described as a disaster because the 
gear will almost certainly fold without pressure.

I'm not speaking from any kind of prejudice here, either - the fellow
in the hangar next to mine has a Glasair III which just last year had
the gear fold up as he turned off the runway because his hydro system 
had failed. When he got it back to the hangar, I went over to see 
what had happened (and look at his redesigned three-blade Hoffman 
prop - shorter is definitely NOT in!) and that's when I found out 
about the way it down-locks (or not, as the case may be). Couldn't 
believe my ears when he told me! Thanks, but no thanks - I'll take 
the Lancair system any day - and if I was a Glasair driver, I'd sure 
figure a way to modify the down-lock to be pressure independent, like 
Lancair's.

Dan Schaefer
N235SP


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