Panos engineered and installed a damper, and may
have drawings to share.
Another solution is to balance the entire nose
wheel assembly, including any wheel pant, on the
axis of the nose gear.
It took a couple of pounds in the nose of the wheel pant to accomplish this.
One Titan owner did that, and solved his nose
wheel shimmy completely. See below.
Hugh Sontag
>
>Hello all,
>
>A while back there was a thread on nose wheel
>shimmy during takeoff and landing. I can't seem
>to find the thread in the archives.
>
>Can anyone remember the date it was started? I looked through Sept and Oct.
>
>I've balanced my wheel/tire staticly by using
>the "random stop" test, I've checked the tire
>for out of round, and I've spun the tire and
>wheel up with the edge of a 7" buffer. I don't
>think the buffer got the wheel up beyond about
>25 mph unfortunately.
>
>My shaking starts around 45mph and is pretty bad.
>
>I think the old thread has a link to a steering
>damper. I'd really like to try that.
>
>thanks
>Ed B
>
>Comment: DomainKeys? See http://antispam.yahoo.com/domainkeys
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>From: "Ken Korenek" <korenke@voughtaircraft.com>
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>Date: Sun, 29 Jan 2006 22:37:41 -0000
>Subject: [Titanaircraft] Re: Nose Gear Shimmy
>Reply-To: Titanaircraft@yahoogroups.com
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><korenke@voughtaircraft.com> forward (good
>recip) [167/9]
>
>All,
>
>Yesterday, I did all the shimmy testing just like I reported it in
>last night's post. When I left the hangar last night, the nose pant
>was standing on end while the 14 ounce slurry of lead shot and epoxy
>pooled and dried it the front inside tip of the pant.
>
>This morning, I installed the nose pant with the weight dried in place
>and did one more taxi test to verify yesterday's findings.
>
>I got up to the usual 38 MPH and the shimmy hit with a vengence- It
>was so bad and would not stop that it threw me off the runway and down
>the embankment. The onset of shimmy was 36 to 38 MPH and would
>stop when I hit the brakes and kept up until about 10 MPH or so when I
>went off the runway.
>
>I checked to see that the wheel weights are still in place, tire
>pressure is at the usual 10 PSI, I removed the wheel pant, removed the
>spring steering and hooked up direct steering. I run up and down the
>runway twice- too much direct crosswind to go very fast 45 to 50 MPH
>only and no shimmy.
>
>I rechecked the pant balance around the axle- still OK, I checked for
>tightness of all the steering components- all tight, I reinstalled the
>wheel pant and hit the runway again. I ran up and down only once and
>the only hint of shimmy was when a side gust hit hard and at the speed
>I was at, the whole plane started bouncing toward the side of the
>runway. I slowed down and was still at the 35 MPH range and no hint
>of shimmy.
>
>All that I can tell right now is that shimmy is only a problem if you
>have a nose pant. It doesn't seem to appear even with spring
>steering if you run with out the nose pant.
>
>The next thing to try is to rig up a jig that will allow the entire
>fork, wheel, pant and all and balance the whole system about the
>steering centerline, but that won't be anytime soon. If I have to
>fly without a wheel pant and with direct steering, then that's what I
>will do.
>
>I can not figure out what is different between yesterday and today.
>The only obvious thing is the crosswind. Yesterday, it was 9
>straight down the runway to 20 degrees to the west and today it is 12
>and direct cross. Other than that, I looked at the conditions and
>my methods and can not find a difference. All I can think of is that
>I disturbed some Karma somewhere and the shimmy gods are displeased
>with me.
>
>If the wind dies down this evening, I plan to do some more high speed
>taxiing to see if the shimmy will return.
>
>How can it be so different one day to the next? I was sure excited
>about getting rid of my shimmy problem. I don't like this mouthfull
>of crow that I'm having to feast on today...
>
>
>Ken Korenek
>Pig Iron
>GRAND CHAMPION, Light Planes
>Airventure Oshkosh 2005
>215.1 Hrs
>Arlington, Texas
>
>
>
>
>
>
>
>
>
>
>--- In Titanaircraft@yahoogroups.com, "Guy" <guy@t...> wrote:
>>
>> First, I want to thank Ken for testing all this stuff. He did it the
>> way it should have been done- one change at a time, then test. So
>> many times I try to evaluate what happened after several changes were
>> made before testing. That just doesn't work well.
>>
>> Next- caster and trail are two different things.
>>
>> Caster is the angle of the steering axis. 0° caster means the
>> steering axis is 90° from the pavement. 3° caster would mean the
>> steering axis is tilted out at the bottom and back at the top 3°. -3°
>> caster would be the opposite- it would be tilted forward at the top
>> and back at the bottom. Generally, increased positive caster will
>> make steering more sensitive, but shimmy more likely. Negative caster
>> will usually make steering less sensitive (wander) and shimmy less
>> likely.
>>
>> Trail is the distance between the steering axis and the axle. 1" of
>> trail means the axle is one inch behind the steering axis. Lead would
>> be the other direction. 1" of lead would mean the the axle is one
>> inch ahead of the steering axis. With 0° caster or negative caster,
>> trail will keep the wheel going straight. If much positive caster is
>> present, trail will make things worse. A motorcycle is an example of
>> a vehicle with a lot of positive caster. Most motorcycles have a
>> couple of inches of lead.
>>
>> The Tornado caster angle is close to 0°. I think it is actually
>> slightly positive in the later frames. Of course, main gear height
>> and main gear tire diameter will change that angle, so individual
>> aircraft may be different. Because the caster angle is so close to
>> 0°, I wanted to start at 0" trail. I was pretty sure 0" trail
>> wouldn't shimmy, but I didn't think about ALL the feel going away.
>>
>> What really surprised me- the caster angle and trail were okay the
>> way they were and the wheel pant needed to be balanced. That's so
>> good. It's a much simpler fix. And, Barry brings up a good point-
>> lower tire pressure will act as a good dampener.
>>
>> Ken- thanks for being brave enough to try this and for doing it right.
>>
> > -- Guy
>>
>
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