Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Mon, 30 Jun 2003 08:31:34 -0400
Message-ID: <redirect-2449551@logan.com>
From: Adam Molny <Adam@ValidationPartners.com>
Subject: Re: [LML] Legacy sequenced gear doors
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Hi Jeff - 

Disclaimer - I am an idiot, I know nothing, and I have never built a
plane before.

No, you're not smoking anything -- these are legitimate concerns. I
figured someone would catch the leakage thing. The rate you mention is
measured at 5000psi. We operate at 1000psi or less. Does that mean the
leakage rate would be proportionately lower? Did the manufacturer spec a
worst case scenario with worn O-ring seals? I don't know. I will have to
do more research to see if other brands have similar leakage. 

For our systems, you really want the leakage rate to be nil. An internal
leak (either at the valve or in one of the cylinders) causes pressure to
bleed from the high side to the low side. When the pressure drops
enough, the pump kicks in for a few seconds to restore it. This should
happen before the pressure drops enough to let the gear or doors sag
down. People have complained about the pump kicking in every few minutes
for the duration of the flight. This is probably not acceptable.

>From the gear test videos I have seen, the doors open MUCH faster than
the gear. Of course, this is with the plane on jacks. Things may behave
differently in flight when aerodynamic loads are applied. In any case,
this is not a safety-critical issue. If the gear hits the door, it would
cause cosmetic damage only, and the gear should still extend when
needed. I looked at using a sequence valve to block the gear from coming
up, but the parts count, plumbing, and complexity start to skyrocket! In
order to block the gear from coming up, you have to know when the doors
are fully down. This means you must either add another pair of
microswitches, or somehow actuate the sequence valve's plunger when the
door reachs the full open position. If you use microswitches, you will
need an electrically controlled blocking valve. If the valve sticks in
the blocked position, the emergency gear extension won't work. So now,
you need a blocking valve that is fail-safe. I'm sure there is a way to
do it. North American did it on the P51 Mustang 60 years ago!

BTW, I purchased the Mustang maintenance manual on CD-ROM as part of my
research. They also use a single valve to control both gear doors. The
valve's directional control plunger is operated by mechanical linkages
connecting it to the main gear legs. The main gear have spring-loaded
down lock pins. The pins retract when hydraulic pressure rises enough to
overcome the springs. That pressure spike happens when the doors hit
their stops at the fully open position.

During the first phase of gear extension, my system works the same as a
normal Legacy. Therefore, I will be vulnerable to the same rubbing
problem.

Overall, this is a complex problem, and I'm sure there are lots of
subtle gotcha's out there. I'll keep plugging away at it.

-Adam

"Jeffrey W. Skiba" wrote:
> 
> I have been thinking about doing this on my legacy for some time, I have my
> gear working (mains).
> 
> Some things I first noticed that I ran into while trying to do this....
> Your spool valve has 82cc/minute internal leakage (5cu in./minute) Do you
> think that's okay ?? I am no engineer but if it leaks within the valve will
> it not want to start to pressurize the side you do NOT want pressurized??
> Maybe you can stop that with another valve that opens the side that should
> not have pressure to the return line ???
> 
> Next,
> I upgraded my Hydraulic pump to the high capacity pump, which now by the way
> comes standard on the Legacy kit, it takes gear cycle time from 10-12
> seconds to like 6-8 !!! And sometimes even faster, so I would be very
> careful about the door closed gear out and then go to retract. Maybe you
> might want to stop pressure to the gear UP until the inner door is fully
> opened???
> 
> Next side note, The Regular Stock gear system on the Legacy during normal
> powered gear extension has a tendency to rub the inner gear doors by the
> main wheels. ( I have been told this by Mark Manke that it's one of those
> "things")
> 
> I really hope you can tell me the issues I bring up, you already thought
> about and I am smoking something because I would love to have a system like
> this.... Need any help testing ??? I would be happy to help...
> 
> I will pull out my old diagrams from when I was kicking it around and see if
> I can think of anything else....
> 
> Jeff Skiba
> Legacy #191