KR> RE: KR nose wheel shimmy

[Chris Hird]

I saw Ross inspecting and repairing this. So it would seem it was a fault not a 
design or implementation problem.
cheers

KR> RE: KR nose wheel shimmy

[mbz...@comcast.net]

Like you, I have my experience with cars. I would like to know how negative the 
caster angle was on the plane. 
Yes, unlike in cars where the caster angle is positive, and the more positive 
it is, the better stability, and wheel return. 
But its harder to turn the wheel. 
In the nose wheel of a plane, the caster angle is negative, very much like in a 
shoping cart. But similar principles apply. 
Stability should improve with a more negative angle, and wheel return to center 
should be better 
but it should be harder to turn. 
In a shopping cart, when the wheel doesn't have a full load, it will also 
shimmy. Im also curious 
if the weight of the plane in motion is evenly distributed to all wheels, or is 
the weight on the nose wheel light. 
and if the air pressure in the tire was adjusted to compensate for a lighter 
load. 
IMHO most common causes for a shimmy like that would be an over inflated tire, 
a tire out of round, or an unbalanced tire. 
Also there is a posibility that the wheel was modded in a way that the caster 
angle was decreased, (moved closer to 0) 
If everything checks out, Im betting on an over-inflated tire same can be 
observed in a car when the tires are over-inflated 
going over a bump, the tire will bounce, and steering wheel will oscilate. 
I do agree that the wheel pants could amplify the oscilation. In the past open 
wheel race cars suffered from catastrophic 
crashes due to aerodynamics on the open wheel. 
I really dont know anything about airplane landing gear, but am comparing the 
sympthoms to automotive tech. I do admit, 
no where on a car or a bike is the wheel caster negative so its hard to compare 
the two. 



"Maybe I should have emphasized caster angle a little more... caster angle 
(the angle from the vertical pivot point to the contact patch of the tire on 
the pavement, similar to the trail on a motorcycle) can improve the 
stability and natural tendency of the tire to track true. I agree with all 
of the points that Mark L has made, but the video I saw showed the shimmy 
continuing all the way down the runway... if the caster angle and balance 
had been properly done, the shimmy would tend to cancel out as the plane 
went down the runway. Granted, I know more about motorcycles and cars than I 
do about planes, but once the bird is on the ground, I would think similar 
rules would apply. Yes damping is important, but if the geometry of the 
set-up is off, it won't help the shimmy unless the gear is "locked in" (too 
stiff) which kind of defeats the purpose of a castering nose wheel doesn't 
it?"

KR> RE: KR nose wheel shimmy

[Randy Smith]

I had Les Palmers do that on first flight and the wheel pants just 
dicetagrated. He added a couple of washers and used a tighter spring, never 
happened again and I have had that plane at 100 mph on the runway, Down wind 
engine out.

--- On Sat, 4/25/09, Mark Langford <n5...@hiwaay.net> wrote:

From: Mark Langford <n5...@hiwaay.net>
Subject: Re: KR> RE: KR nose wheel shimmy
To: "KRnet" <kr...@mylist.net>
List-Post: krnet@list.krnet.org
Date: Saturday, April 25, 2009, 5:52 AM

Mark W wrote:

> If the caster angle and wheel & tire balance are right, you
shouldn't have
> this problem... think GM/Ford/Chrysler front end alignment... not shopping
> cart. I've yet to see a Corvette experience 'shimmy' at speeds
exceeding
> anything a KR would land at.

I would have to disagree with that.  You can have a perfectly balanced 
wheel/tire, but external forces such as which way the wheel is pointed at 
touchdown, or even which way the wind is blowing, can get the shimmy 
started.  That's a side to side phenomenon, not a "perpendicular to
the 
axis" thing.  But it's really a matter of insufficient damping, which
is the 
real cure for a shimmy like that, regardless of what got it started.

There's an aerodynamic effect (it has a name but it's been 10 years
since I 
read about it) which describes how this oscillation happens to aero 
controls, or even stop signs in a high wind...similar to flutter.  Damping 
is the key to fixing it, not balance.  Stop signs have no damping, just a 
metal post which acts a spring to help perpetuate it.  Diehl accounts for 
damping through washers or something, and as mentioned, there's an 
adjustment/cure.  If that were my plane I'd have that nose gear off and be 
checking for cracks and wallowed out attachment points though


Mark Langford
N56ML "at" hiwaay.net
website at http://www.N56ML.com



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KR> RE: KR nose wheel shimmy

[John Gotschall]

Here's some super thick damping fluid, almost a gelatin

http://www.turntablebasics.com/silicone.html

jg

KR> RE: KR nose wheel shimmy

[gbmc...@aol.com]

Jeff
Van has been using front wheels? on some of the rvs for some time without any 
problems. My front gear as you know
was designed after the rv, The only time I get hint of shimmy is when the 
breakout is less than the 22 pounds specified
on the plans. The rv guys tell me it is the?same with?the standard rv gear. It 
is a easy?fix using a? fish scale attached at the axle,? the breakout should be 
set to?22 pounds if not tighten the nut. This maybe a good way to?check the 
tail wheel on your plane.
The picture you send is great? looks a lot like my new project.
george
pueblo colorado


-Original Message-
From: jscott.pi...@juno.com
To: kr...@mylist.net
Sent: Sat, 25 Apr 2009 10:13 pm
Subject: Re: KR> RE: KR nose wheel shimmy




On Sat, 25 Apr 2009 16:16:47 -0400 "Dan Heath" <da...@windstream.net>
writes:
> I have to be a "smart A" here and say that there is one sure fire 
> cure for nose wheel shimmy.
> 
> Daniel R. Heath - Lexington, SC

Yep.  Then you get a tail wheel shimmy. :o)

FWIW, caster, tire pressure, and damping all apply whether we're talking
about nosewheel or tailwheel shimmy.  I get an occassional shimmy in the
tailwheel on my KR.  Since I can't adjust the tire pressure in my hard
tire, and can't adjust the caster unless I want to bend the tailwheel
spring, it is always addressed with damping by snugging down the nut on
the tailwheel shaft where it goes vertically through the tailwheel frame.
 I usually need to snug it down every 75 - 100 hours to prevent shimmy.

Jeff Scott
Los Alamos, NM

Click here to find the right business program for you and take your career to 
the next level. 
http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTESUSWFxsIXsZmWRnsNzY0eju5tnCPBlQUFyBlGpdKBAOgSCuHNcc/

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KR> RE: KR nose wheel shimmy

[Glenn Martin]

I never was fond of the shimmy...or the funky chicken either.

-- 
Glenn Martin
KR2 N1333A

KR> RE: KR nose wheel shimmy

[jscott.pi...@juno.com]

On Sat, 25 Apr 2009 16:16:47 -0400 "Dan Heath" 
writes:
> I have to be a "smart A" here and say that there is one sure fire 
> cure for nose wheel shimmy.
> 
> Daniel R. Heath - Lexington, SC

Yep.  Then you get a tail wheel shimmy. :o)

FWIW, caster, tire pressure, and damping all apply whether we're talking
about nosewheel or tailwheel shimmy.  I get an occassional shimmy in the
tailwheel on my KR.  Since I can't adjust the tire pressure in my hard
tire, and can't adjust the caster unless I want to bend the tailwheel
spring, it is always addressed with damping by snugging down the nut on
the tailwheel shaft where it goes vertically through the tailwheel frame.
 I usually need to snug it down every 75 - 100 hours to prevent shimmy.

Jeff Scott
Los Alamos, NM

Click here to find the right business program for you and take your career to 
the next level. 
http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTESUSWFxsIXsZmWRnsNzY0eju5tnCPBlQUFyBlGpdKBAOgSCuHNcc/

KR> RE: KR nose wheel shimmy

[Dan Heath]

I have to be a "smart A" here and say that there is one sure fire cure for
nose wheel shimmy.

See N64KR at http://KRBuilder.org - Then click on the pics 
See you at the 2009 - KR Gathering in Mt. Vernon, Ill
There is a time for building and a time for FLYING and the time for Flying
has begun.
Daniel R. Heath - Lexington, SC

-Original Message-

If that were my plane I'd have that nose gear 

KR> RE: KR nose wheel shimmy

[Mark Wegmet]

Mark L's response to my comment, and my expansion on my earlier remarks.

>Mark W wrote:

>> If the caster angle and wheel & tire balance are right, you shouldn't
have
>> this problem... think GM/Ford/Chrysler front end alignment... not
shopping
>> cart. I've yet to see a Corvette experience 'shimmy' at speeds exceeding
>> anything a KR would land at.


>Mark L wrote:
>I would have to disagree with that.  You can have a perfectly balanced 
>wheel/tire, but external forces such as which way the wheel is pointed at 
>touchdown, or even which way the wind is blowing, can get the shimmy 
>started.  That's a side to side phenomenon, ..
>Mark Langford
>

Maybe I should have emphasized caster angle a little more... caster angle
(the angle from the vertical pivot point to the contact patch of the tire on
the pavement, similar to the trail on a motorcycle) can improve the
stability and natural tendency of the tire to track true. I agree with all
of the points that Mark L has made, but the video I saw showed the shimmy
continuing all the way down the runway... if the caster angle and balance
had been properly done, the shimmy would tend to cancel out as the plane
went down the runway. Granted, I know more about motorcycles and cars than I
do about planes, but once the bird is on the ground, I would think similar
rules would apply. Yes damping is important, but if the geometry of the
set-up is off, it won't help the shimmy unless the gear is "locked in" (too
stiff) which kind of defeats the purpose of a castering nose wheel doesn't
it?

JMHO

Mark W
N952MW

KR> RE: KR nose wheel shimmy

[Mark Langford]

Mark W wrote:

> If the caster angle and wheel & tire balance are right, you shouldn't have
> this problem... think GM/Ford/Chrysler front end alignment... not shopping
> cart. I've yet to see a Corvette experience 'shimmy' at speeds exceeding
> anything a KR would land at.

I would have to disagree with that.  You can have a perfectly balanced 
wheel/tire, but external forces such as which way the wheel is pointed at 
touchdown, or even which way the wind is blowing, can get the shimmy 
started.  That's a side to side phenomenon, not a "perpendicular to the 
axis" thing.  But it's really a matter of insufficient damping, which is the 
real cure for a shimmy like that, regardless of what got it started.

There's an aerodynamic effect (it has a name but it's been 10 years since I 
read about it) which describes how this oscillation happens to aero 
controls, or even stop signs in a high wind...similar to flutter.  Damping 
is the key to fixing it, not balance.  Stop signs have no damping, just a 
metal post which acts a spring to help perpetuate it.  Diehl accounts for 
damping through washers or something, and as mentioned, there's an 
adjustment/cure.  If that were my plane I'd have that nose gear off and be 
checking for cracks and wallowed out attachment points though


Mark Langford
N56ML "at" hiwaay.net
website at http://www.N56ML.com

KR> RE: KR nose wheel shimmy

[Mark Wegmet]

If the caster angle and wheel & tire balance are right, you shouldn't have
this problem... think GM/Ford/Chrysler front end alignment... not shopping
cart. I've yet to see a Corvette experience 'shimmy' at speeds exceeding
anything a KR would land at.

Mark W
N952MW

-Original Message-
From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net] On Behalf
Of Joe Beyer
Sent: Friday, April 24, 2009 10:51 AM
To: kr...@mylist.net
Subject: KR> RE: KR nose wheel shimmy

I had that problem with my nose wheel due to the belview washers losing
their spring force. I had to change them out and add some more shims. Now
the nose wheel caster is 

KR> RE: KR nose wheel shimmy

[Joe Beyer]

I had that problem with my nose wheel due to the belview washers losing
their spring force. I had to change them out and add some more shims. Now
the nose wheel caster is stiff but doesn't shimmy at speed. That Diehl nose
wheel in the video needs some attention.

-Joe

Scappoose Ore.

> I have just found a video of Ross Evans' landing at Narromine 
> '09.  The slow motion footage of his nose wheel shimmy is impressive.
> http://www.youtube.com/watch?v=LIPrIurhybE=channel_page
> 
> I have a collection of over 70 KR clips in my You Tube 
> favorites for anyone with a spare couple of hours.
> http://www.youtube.com/profile?user=kr2sdarren=favorites
> 
> 
> Cheers
> --
> Darren Crompton
> AUSTRALIA
> 
> My web site: www.kr-2s.com