REFLECTOR: sequence valve

[Al Gietzen]

Dave;

 

I think you are talking about the "old" standard installation. You might
want to check the "current" standard installation. It is the idea I came up
with some years ago (like 5 or 6 - yeah I've been building that long) using
the gusset at the gear pivot to actuate the sequence valve.  My nose gear
comes up and the doors fully close before the main gear come up.

 

Although I find it curious that it is not always consistent.  Every once in
a while the doors don't fully close until the main gear reach the end of the
stroke and then snap shut.  I guess it depends on what mood it's in.

 

Al

 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Dave Black
Sent: Monday, March 21, 2005 6:20 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: NOSE WHEEL GOT SIDEWAYS

 

John,

 

> I think the reason for the 95% closing is because the gas spring reqires 

> extra force to retract the nose gear the last inch and the hydraulic 

> pressure isn't high enough until the mains fully retract.  The nose doors 

> are held open a bit because the nose wheel isn't all the way up. 

 

The gas spring is a reasonable explanation. But isn't it strange that the
last

5% of gas spring travel should offer so much more resistance than the first

95%? And that it should be so repeatable (always 95%) from one kit to
another?

 

In my experimentation with the standard install, I found the gear ALWAYS

retracted EXACTLY to the point where it made contact with the sequence
valve.

This is the famous 95% point. The inertia of the gear hitting the sequence

valve momentarily opens the valve, causing the nose doors to close or jiggle

slightly. If you manually assist the gear at this point, the doors close

completely, without slamming. 

 

Since your sequence valve is closer to a pivot point, you get not only more

torque on the pushbutton, but more inertia from the moving gear. Hence the

valve stays open longer before it forces the gear back down to the 95%
point. 

 

Your installation is VERY CLOSE to working the way it was intended! 

 

In fact, it's so close that the manually assisted retraction test I
suggested

for the standard installation may not convince you it's the sequence valve

causing your gear to hang out. The following test will be more difficult,
but

should convince you: Temporarily move your sequence valve aside so it is no

longer activated by the retracting gear. Then watch the gear retract. I'll
bet

you big bucks the nose gear will go up 100% without so much as a pause at
the

95% point. 

 

Of course, the nose doors won't close at all, unless you push the sequence

valve button manually. Once the nose gear is up, try giving your sequence

valve a push. If you are able to push it at all, the doors will close 100%.

This portion of the test will also demonstrate just how hard it is to push

that button when it's pressurized, and why more leverage is needed. 

 

I understand that you are happy with your current installation, so suggest
the

above only as an educational exercise. 

 

Dave Black

Shortwing RG

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