Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Mon, 30 Jun 2003 00:45:08 -0400
Message-ID: <redirect-2449270@logan.com>
From: "Larry Henney" <LHenney@dellepro.com>
Subject: RE: [LML] Legacy sequenced gear doors
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Importance: Normal
In-Reply-To: <list-2448803@logan.com>


Adam,

Very elegant.  Cool and I want it.  But....... Do I need it?

>Key Assumption:
During the initial retract phase, the doors are moving down at the same
time the gear is moving up. Since the door cylinders are smaller
diameter, the doors will move faster than the gear. Additionally, the
doors are moving with gravity, while the gear is moving against it.
Hydraulic fluid will take the path of least resistance, feeding the
doors first, and only moving the gear when the door cylinders hit their
stops and pressure builds up. 

I buy all this.  Reasonable. Confirm with testing; then add a restrictor
to the retract side of the main gear if you percieve any timing
interference threats.

>Disadvantage:
Since the down switches are wired in series, a separate pair of switches
must be used for the gear indicator lights. 

When carefully installed these microswitches are very reliable.  Not a
big drawback.

The tough part for me would be to weigh the possible ground failure
against the benefits.  That is; if the pressure is released off the
hyd's on the ground it's fathomable (albeit improbable) to find your
plane sitting partially gear collapsed.  

The benefits sound like, less drag during gear down operation and less
noise (with of course beauty being ancillary).  One plus to having more
drag during the landing phase is sitting on a higher power setting on
final.  This engine spool up provides a nice power band in the LNC2 at
least.  Additionally, when one pulls power to idle there is a nice
deceleration (from the aero drag).  Of course overheating would be the
opposing argument.  I'd imagine this is all irrelevant on a Legacy (not
much drag or overheating from the doors).

If I were building again, I'd just do it for elegance (it's very cool!);
however, from an aviator and failure analysis view, I'd argue it's not
such a good idea.  I like a little pressure on my gear sitting on the
ground (or by contrast; I'd rather not fly waiting for the solenoid to
fail and open the inner gear doors at cruise speed).

Ok, Ok, just thinking out loud here;  Go with the loss of pressure upon
shut down circuit.  Then, add a manual valve which locks the pressure to
the system (affectively overriding the loss of solenoid power issue).
You could then close this valve just prior to killing the master.  That
way inflight solenoid failure would be a non issue and you'd have the
super cool look while shut down on the ground.

Or better yet.... Do more research on the solenoid valve.  I'd imagine
you could buy one that is not spring failing either way.  That is, power
it both ways.  Then it would sit there in either position with no
tendency to reverse upon depowering.  Also, when the solenoid fails,
normal freefall is still available.

Good Luck and Let us Know,

Larry Henney
LNC2 IO-360
Ft Worth, TX 
Moving to Pecan :)