REFLECTOR: wheel shimmy

[Rene Dugas]

I do not get shimmy with air pressure below 25 pounds but will with 45
pounds and less than adequate tension on the BIG nut.  The down side to low
pressure is if one loads the plane the weight compresses the nose tire and
it can be VERY difficult to get the nose up.  Short story for emphasis:
Scheduled two hours of aerobatic training in a Super Decathlon at and
airport with 3000 ft runway.  Flew up there in the Velo and completed my
hour no problems.  Went back to my home airport and completed some work on
another plane.  I filled the tanks and flew back to the small runway.  After
the Aerobatic training the instructor said he wanted to fly the Velo.  NO
PROBLEM.  Preflight no problem.  Instructor was about 230 or more pounds
(I'm 160).  I did not look at the tire after we loaded (with full fuel).
Taxi and run up was normal.  Accelerated down runway and no nose lift off.
I pushed the throttle to be sure it  was all the way forward.  Good.
Accelerated thru 95 knots no rotation.  I leaned back and jerked the stick
with both hands and started planning what trees I would come to rest
against.  It lifted and missed the tree tops by maybe 5 ft.  My instructor
asked if I always take off that close to the trees and I said, "Just for
him" as calmly as possible.  Plane flew fine and he enjoyed it.  After
landing, I jumped out and looked at the tire before he got out and it was
half way depressed so it would be worse with me in the seat.  I now fly with
45 pounds in the nose and tight BIG nut.  Leave the trees alone.  Instructor
was Greg Koontz if any of you have seen him at Oshkosh or Sun and Fun in his
red plane.  My brakes would not have stopped me before the runway end but I
had a run off of grass then trees.

Apply as desired to your flying.
Rene'
> 450 hrs Velo XL RG


-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of aminetech at bluefrog.com
Sent: Monday, February 16, 2009 4:29 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: wheel shimmy

I don't know why, but my nose wheel tension is low at about 3-4 lbs and I
don't get shimmy with a normal landing.  If the nose hits hard I get a
"buzz" type of shimmy which isn't that bad and it goes away in a few
seconds.  Several years ago I experienced that bad, bone-rattling shimmy
when my tension was low, so I know what that feels like.  The only
difference I'm aware of is that I replaced my wide slick type tire with a
narrower, tread tire and I replaced the phenolic washer with one I made from
a plastic drum.

John

--- bill.stockman at daytonaero.com wrote:

From: "Stockman, Bill" <bill.stockman at daytonaero.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Subject: Re: REFLECTOR: wheel shimmy
Date: Mon, 16 Feb 2009 16:53:55 -0500

I wouldn't quite say 100%.   I had his system and it failed on my
173FGE.    The problem with Kens system is what happens when you fail to
pull the pin and turn your airplane--such as leaving the runway quickly
when someone is landing behind you.    Normally the tire just scoots and
everything is fine.   But if the tire actually grabs the runway, then
something has to give--either the pin or the rest of the mechanism.   In
my case it pulled the mechanism up and stripped out the mounting
hardware.   After pulling the pin while taxing, the mechanism set back
down into place and looked totally normal--no evidence of failure (no, I
didn't attempt to tighten the screws which might have indicated a
problem).  Guess what happens next time you "lock" the wheel, fly around
and try to land?   Now the mechanism is not screwed down and if there is
any perturbation at all, it kicks the wheel sideways (shimmy) and now
the mechanism lifts up and moves, screws and all and will actually lock
the wheel sideways or at an angle and you get a real Disneyland ride.   

My wife was not impressed with the ride, but my friends on the side who
witnessed it thought it was rather impressive.

I think Ken has a good idea, but it biggest fault is that the pin is
stronger than the rest of the mechanism and will not shear off before
damaging the rest of the wheel and holding mechanism.   I realize others
have used this system successfully with no apparent problems.  However,
if you ever forget to pull the pin and turn the plane--especially at
speed--you need to fully inspect the system--which is really tough to do
after you cover it with your wheel pant--which was the whole purpose of
installing the system.   MTCW.   

Bill Stockman, Senior Associate
Dayton Aerospace
 
(937) 369-4799 cell
(937) 426-4300 work
bill.stockman at daytonaero.com

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