REFLECTOR: Damper

Craig and Denise Woolston cdwoolston at sbcglobal.net
Tue Aug 30 07:01:23 CDT 2011


By the way, I should also add a VERY HEARTY THANK YOU to Andy for continuing
to pursue this rather than devote more time to finishing his airplane and to
Scott & the factory for following through.

 

Craig

 

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From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Craig and Denise Woolston
Sent: Monday, August 29, 2011 8:37 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Damper

 

I agree with Andy, everything in aircraft design is a compromise.  But, one
small disagreement though, some of which is antidotal, some hard
engineering.  I’ve had three “shimmy events” on my XL-FG in 4 years
(650hours).  The first I wasn’t smart enough to measure nut tension after to
“prove” that is was fine and I was a beginner Velocity pilot so you might be
able to contribute that to “pilot technique” but I would argue that last two
were not pilot technique errors.  The next two the tension was accurate, the
problem is each of our planes is built slightly different based on
measurement guidelines from the factory but the shimmy equations of motion
and whether the system is stable our unstable is highly dependent on small
differences in geometry, which is why people have had difference results.
There is also a difference in a limit cycle oscillation shimmy event which
is what most people experience with a “loose” nose gear nut and I believe is
more prevalent on the RGs because of the geometry difference (go read the
papers if you don’t believe us) and is stable and a divergent oscillation
shimmy event which is what I’ve had on the last two which result in the nose
wheel completing 360 degrees of rotation, obviously unstable.  Andy’s right,
I never want to do that again.  I’ve shed nose gear pant parts during these
events and got lucky they didn’t take out that expense rotating composite
part on the back of the aircraft, not to mention I believe it could lead to
nose gear failure.  Which is what is in video footage of this phenomena on
youTube in believe or not a canard type aircraft and nose gear fails.  So, I
politely disagree with Andy’s statement that the current system works, the
current design is not robust enough to variations in aircraft build,
aircraft load configurations and real world flight test.

 

Craig

 

 

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From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Andy Millin
Sent: Monday, August 29, 2011 8:28 AM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Damper

 

The damper is like everything on an airplane; a compromise.

 

My motivation comes in large part from talking with those that have had a
shimmy.  Those that have had a shimmy, don’t EVER WANT TO DO THAT AGAIN.

 

Those that haven’t are not as concerned, or may even see this as frivolous
and unnecessary.  To each his own.

 

A bad shimmy doesn’t just shake the confidence, it can damage the plane and
possibly leave one stranded.

 

Scott Swing was sure that proper landing technique can eliminate most of the
shimmy problem.  One must gain the experience first though.  :)

 

Mark Riley suffered a bad shimmy incident with his XL/RG just before coming
to Oshkosh.  The difference between shimmy and no shimmy was ¼ turn of the
nut.

 

Let me be clear.  I believe the current setup works.  One must check the nut
tension as part of the pre-flight.  Forgetting once can be unforgiving.

 

The new damper costs more, weighs more, and adds complexity.  Like most
stuff in aviation.  It also provides positive damping and improved ground
handling. 

 

Andy

 

 

 

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Douglas Holub
Sent: Monday, August 29, 2011 10:06 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Damper

 

Before I started flying I installed a locking pin a la Mishler on my Cozy
nose wheel just in case there were any shimmy problems. My design wouldn't
let the nose wheel rotate 360 degrees, and it was a nuisance moving the
plane. It sounds like this damper is a good idea, but I'm sure you'll want
to make a tow bar and find a place for it in the plane for traveling.

 

I never got around to making a tow bar, and then after I started flying I've
never had a hint of a shimmy.  My pre-flight does include checking the nose
wheel for tightness. (If it is not hard to move with my foot it is too
loose), but maybe the more flexible fiberglass strut has something to do
with it, too. 

 

I removed the locking pin this year, and I love having a full castering nose
wheel again. I hope I'm not putting a damper on this promising damper idea.

 

Doug Holub

Standard FG with electric nose lift.

----- Original Message ----- 

From: Andy Millin <mailto:amillin at sbcglobal.net>  

To: 'Velocity Aircraft <mailto:reflector at tvbf.org>  Owners and Builders
list' 

Sent: Monday, August 29, 2011 9:34 AM

Subject: Re: REFLECTOR: Damper

 

Not shown in the picture was the steering limiter.  If you look at the
Damper 3 picture, you’ll see the studs sticking out of the top of the gear
fork.  They are AN-4 bolts that have the heads cut off.  There is a pawl
mounted on the king pin.  The pawl hits the stops before it hits the limits
on the damper.

 

So, yes, we will need to have some type of steering/tow bar.  This is the
same arrangement that you have on just about all production aircraft.

 

I would ask John to comment on what it was like to push the plane around
with the damper on it.

 

I know this solution is not for everyone.  I feel what I am gaining is worth
more than what I am giving up.

 

You may feel differently.

 

Andy

 

 

 

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of John Dibble
Sent: Monday, August 29, 2011 8:58 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Damper

 

  

Andy Millin wrote: 

  

Items of Note: 

                The damper is hydraulic.  It is an arm that sweeps inside of
a pie shaped chamber.  There is enough range to do a single wheel locked
turn.  It will not spin 360 degrees. 

  

So, pushing the plane backwards won't be easy?

John


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