Yep, springs too loose, tightening the nut will only work for a short time. This sort of things also doesn't happen very often on grass, so you'll think you've fixed it.
One suggestion if you haven’t done it already, use a slightly heavier spring on one side than the other. Each one will have a different resonance frequency and the tail wheel will be less likely to shimmy.
You may also discover that with the tyre contact area centre wearing down so that the profile is flat to the edges, incrementally a small added amount of air pressure in the tyre may be required to raise the centre slightly to prevent the tyre edges becoming the primary load bearing areas of the profile and getting into a "your turn - my turn - your turn" shimmy reaction. After that bit of violence, it may be prudent to check the fuselage attachment of the leaf spring for ovaling of fastener holes.
You said it yourself on short approach “wow we are hauling ass” meaning you were not a stabilized approach. You then let your tail down early in the rollout. Keeping the tail up would have reduced the chance of a shimmy at higher speeds. Also your tailwheel springs are entirely too loose. The springs should have just a tad of compression when you are sitting in it.
Had the same thing with Pawnees in the early 70,s after many landings on bush strips. Periodically the entire tail wheel assembly would disintegrate scattering washers and other bits along the strip. We would gather them all together then clean them in avgas ,oil them and reattach to the tail wheel stem ,then carry on the with the job until the next time. (ps. I witnessed a catalina in 2008 land on a runway and suffer a nose wheel shimmy. The shimmy effect had an alarming reaction on the tailplane which twisted and flexed in sympathy with the nose wheel.)
get marine quality stainless steel springs and take out the play no woggling .......p.s. soloed my mothers umbrella 1954..my shoe came off. they were loose like your springs...thanks for your work on you tube..
Nice plane.... I have about 800 hours in a KF2 and a couple hundred in other versions of KF. My guess is too loose springs and way to fast to touch pavement which I avoid as much as I can.... I have flown mine to OSH a few times ...listen to the old TW guys... good luck
If the nut is a bit loose, it throws off the caster which will cause the shimmy. Sometimes extra weight or too much speed can also cause it. Nice looking Kitfox!
I'd be wondering why that bolt was loose while having the cotter pin still in place. Like you say the caster angle may have become negative causing the shimmy. It takes like 3 minutes to measure for positive caster with a bench square. That rudder also took a good beating.
I read somewhere not too long ago that if the forward edge of the wheel falls too far behind the vertical axis of the pivot point, that can lead to wheel shimmy.
Kitfox is geometricly totally shitt desing. Wing root pins are vertical not horizontal to allove hinge phenomeon when spars are flexing. Only a smart aircraft designers realise that.
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No tension on the tailwheel steering control springs.
Agree
Yep, springs too loose, tightening the nut will only work for a short time. This sort of things also doesn't happen very often on grass, so you'll think you've fixed it.
My thoughts also. Those chains need to be tensioned to stopped the shuttering.
One suggestion if you haven’t done it already, use a slightly heavier spring on one side than the other. Each one will have a different resonance frequency and the tail wheel will be less likely to shimmy.
You may also discover that with the tyre contact area centre wearing down so that the profile is flat to the edges, incrementally a small added amount of air pressure in the tyre may be required to raise the centre slightly to prevent the tyre edges becoming the primary load bearing areas of the profile and getting into a "your turn - my turn - your turn" shimmy reaction. After that bit of violence, it may be prudent to check the fuselage attachment of the leaf spring for ovaling of fastener holes.
You said it yourself on short approach “wow we are hauling ass” meaning you were not a stabilized approach. You then let your tail down early in the rollout. Keeping the tail up would have reduced the chance of a shimmy at higher speeds. Also your tailwheel springs are entirely too loose. The springs should have just a tad of compression when you are sitting in it.
Seems like you need to move the chains up a link to take some of the slack out so the compression springs can do their job. 🤷♂️
Dude, 17k views!!? Nice work!
Had the same thing with Pawnees in the early 70,s after many landings on bush strips. Periodically the entire tail wheel assembly would disintegrate scattering washers and other bits along the strip. We would gather them all together then clean them in avgas ,oil them and reattach to the tail wheel stem ,then carry on the with the job until the next time. (ps. I witnessed a catalina in 2008 land on a runway and suffer a nose wheel shimmy. The shimmy effect had an alarming reaction on the tailplane which twisted and flexed in sympathy with the nose wheel.)
I’ve always like a little tension on my springs.
alittle more tension on the springs will fix it
Good to see ya again.👍 it's been awhile! I had the same thing happen last year.
Thanks Man
Apparently if the pivot isn't vertical it can cause this. Especially if the pivot leans forward. Perhaps check the angle with weight on the wheel.
I'm happy to see that it was a simple fix for you. 😊👍
Spent time diagnosing a Citabria wheel shimmy. Preload on the bearings was the issue
get marine quality stainless steel springs and take out the play no woggling .......p.s. soloed my mothers umbrella 1954..my shoe came off. they were loose like your springs...thanks for your work on you tube..
Nice plane.... I have about 800 hours in a KF2 and a couple hundred in other versions of KF. My guess is too loose springs and way to fast to touch pavement which I avoid as much as I can.... I have flown mine to OSH a few times ...listen to the old TW guys... good luck
I believe a wide (tundra) tailwheel is prone to shimmy on pavement
If the nut is a bit loose, it throws off the caster which will cause the shimmy. Sometimes extra weight or too much speed can also cause it. Nice looking Kitfox!
I'd be wondering why that bolt was loose while having the cotter pin still in place. Like you say the caster angle may have become negative causing the shimmy. It takes like 3 minutes to measure for positive caster with a bench square. That rudder also took a good beating.
I read somewhere not too long ago that if the forward edge of the wheel falls too far behind the vertical axis of the pivot point, that can lead to wheel shimmy.
Trent Palmer claims to have no springs/free spinning tail wheel. What is that all about?
Springs and chains are not needed. you just steer with your brakes and not your rudder. Its all what you want. Thanks for watching
You said you were super fast on short final. Did you touch down fast?
no normal speeds when touchdown. its all fixed and works great again
Tail wheel shimmy.
Do you wheel land all the time? If so why?
On pavement I usually do. And that’s so I can see where I’m going. On grass I do both.
It’s the caster that’s in error.
Kitfox is geometricly totally shitt desing. Wing root pins are vertical not horizontal to allove hinge phenomeon when spars are flexing. Only a smart aircraft designers realise that.
And yet there has never been a failure! hope you feel better🙂
YUP... Consider that time has shown the Kitfox to be hold'n her own...:)
IT is a Kit Airplane. Use a little Testors Glue. LOL.YIKES !!!!!
Dad ground looped his biplane because one of the tailwheel springs broke. It destroyed the air frame and a wing tip . So take this stuff seriously.
So what Sonex are you building?
that is the A model and its for sale if you know of anybody
What that was, is a very bad landing, looks like he did a three point landing and then bounced it into a wheel landing.
ya really think so