REFLECTOR: Nose Gear Almost Up

[steve korney]

That's a great explaination Dave... Thanks



Best... Steve




----Original Message Follows----
From: Dave Black <dvblack at comcast.net>
Reply-To: dvblack at comcast.net,        Velocity Aircraft Owners and Builders 
list <reflector at tvbf.org>
To: Chuck Jensen <cjensen at dts9000.com>,        Velocity Aircraft Owners and 
Builders list <reflector at tvbf.org>
Subject: Re: REFLECTOR: Nose Gear Almost Up
Date: Tue, 12 Jul 2005 18:27:19 -0400

Chuck,

 > Well, mine works a little differently, but I don’t know
 > exactly how/why its different.  Normally, during the retract
 > cycle, my nose gear comes up first (about 95% of a full
 > retraction, then the mains go through their clean-n-jerk, then
 > the nose gear “jumps” up the last few inches of travel, which
 > triggers the sequence valve to close the doors.

No, yours is NOT different!!

That's exactly how they all work, unless the sequence valve has been 
relocated
to make it operate smoothly. The gear stops at the 95% point precisely 
because
that's when it hits the Sequence Valve. The Sequence Valve is VERY hard to
depress, so acts as a stop. The nose gear stops there until the hydraulic
pressure reaches a level high enough to operate the valve. With standard
placement of the Sequence Valve, that does not occur until after the mains 
are
up.

I should mention here that our hydraulic system operates three things in
PARALLEL: The Nose Gear, the Nose Doors, and the Main Gear. Under this
arrangement, the one requiring least force (lowest hydraulic pressure) 
occurs
first. Were it not for the Sequence Valve, the Nose Doors would close first.
But that valve delays the Nose Doors closing until the Nose Gear is up. The
second easiest is raising the Nose Gear. Third is raising the Mains. Hardest
of all (because of poor leverage) is activating the Sequence Valve. If you
were to put a pressure meter on your hydraulic system, you'd see that during
the retract cycle the hydraulic pressure increases in fits and spurts until
the high-pressure cut-off is reached. In your case, the high-pressure limit 
is
often reached before your Sequence Valve gets pushed.

 > Just before leaving on a trip to the Midwest on Sunday (racing
 > ahead of Dennis), I cycled it on the ground.  The nose gear
 > ‘jumped’ all the way up to its final position, then settled
 > back down to about 75%-80% of the up position and never moved
 > again.

When that happened, the Nose Doors will have closed slightly, as the 
Sequence
Valve was instantaneously depressed, then released as the gear bounced off 
it.
Again, COMPLETELY NORMAL with the standard placement of the Sequence Valve.

 > The next time I cycled it, I applied a small amount of force
 > against the nose wheel as it came up, so that it could not
 > bounce.  It went up to its 95% tentative position, then
 > finished the retract cycle with doors closing just fine.  The
 > next 6 cycles went perfect.  To say the least, I was
 > ‘watchful’ with each of 4 retracts during the trip, but
 > everything worked flawlessly.

This "manual assist" test proves that all works as intended IF the gear has
enough force to activate the Sequence Valve. Your lifting past the 95% point
provided the force to activate the Sequence Valve. Maybe once the valve
actuated smoothly it self-lubricated enough to allow it to continue to
function as desired.

It's possible that with a little lubrication on your Sequence Valve, your 
gear
may continue to operate as intended for some time. Or until you leave it sit
for a couple weeks. But I really don't expect it to change much unless you
either relocate the Sequence Valve or increase the upper pressure (cut-off)
limit on your hydraulic pump. 98% of builders opt to increase the upper
pressure limit, and simply put up with the Bounce & Slam of the nose gear 
and
doors.

If you do relocate the Sequence Valve, however, you'll find the Nose Gear
always comes up fully, the doors close smoothly, and then the mains retract.

 > I’m in favor of flawless functioning, but I did NOTHING
 > different for the retract cycles that failed and the ones that
 > worked as designed, hence I’m clueless as to what was wrong,
 > why it was wrong and what to fix to prevent it from happening
 > in the future.  The intermittent, non-repeatable problems are
 > always the worst, but thanks all for a couple ideas.

Don't worry, the problem WILL be back! It's intermittent because of several
variables:
1) The Sequence Valve requires more force to operate one time than the next.
2) Your high-pressure limit switch will trigger slightly differently each 
time.
3) The inertia of the nose gear as it hits the Sequence Valve one time
compared to the next.
4) Sequence Valve may have self-lubricated after one or two successful 
retracts.

In your specific case, the fact that the Nose Gear sometimes does not 
retract
fully can be solved simply by increasing the upper limit on the 
high-pressure
cut-off switch.

The fix for the "Bounce & Slam" problem in ALL Velocities is to relocate the
Sequence valve nearer to a pivot point. Or alternatively, to replace the
Sequence Valve and hydraulic door closure with a mechanical system.

I first became aware of "Bounce & Slam" when I built my retract system 10
years ago. I thought I had built something wrong. I was surprised when I saw
the retraction test in the demo videos do exactly the same thing. That's 
when
I discovered the cause, then relocated my Sequence Valve. Now my Nose Gear
works the way it was intended.


Dave Black
Shortwing RG
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