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Dana
Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA
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 Posted: Mon Jul 12, 2010 11:48 pm Post subject: UltraStar tailwheel strut |
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The mention a few days ago of a fiberglass rod for the tailwheel strut got me wondering.
I'm having a problem with the tailwheel strut on my UltraStar. It was bent a bit when I got the plane, looks like it had been bent and straightened a few times. It bent, and the 5/8 tube crinkled a bit, right at the end of the 3/4" tube it slips into. I've straightened it out twice myself, but it keeps bending… the crinkled are weakens it, of course, but I don't know how much it tends to bend when straight. One solution is to cut it and splice a new piece of 5/8", but will it bend again? Was this a common problem with the UltraStar? It tends to get bent not on landing, but when moving the plane around with the wings folded (at least that's where I felt it bend the last time). One problem may be that when I got the plane, the 3/4" tube was cut off straight rather than angled per the plans (I've since corrected this), which makes a much worse stress concentration on the inner tube, contributing to its bending (and weakening) the first time.
I could extend the 3/4" tube farther back which would make it quite a bit stronger, but it would also be less springy, which could lead to damage elsewhere; damage which would be harder to repair. Or go to a fiberglass rod (is that original on later Kolbs or is it an owner mod?). A 5/8" solid fiberglass rod is slightly weaker in simple bending than 5/8OD x .035 steel tube, but it's less prone to local crippling which seems to be my problem. Or perhaps somebody's come up with a better solution?
-Dana
--
Government cannot give you anything it does not first take away from someone. [quote][b]
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williamtsullivan(at)att.n
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| Posted: Tue Jul 13, 2010 2:53 am Post subject: Ultrastar tailwheel strut |
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Dana- Which way is the tube bending? Sideways, or up (from bouncing)? Next, do you know if the factory specified tubing of that particular grade, or having it hardened? Is it original? My Firestar does have a fiberglass rod tail spring. No bends or cracks, but I'm careful to lift it when going sideways around the yard. I worry more about bending the tubing on the "skeg", or doing some kind of damage to the main fuselage tube. I seem to remember that the Ultrastar tail spring was longer, though. Could be wrong.
Bill Sullivan
Windsor locks, Ct.
FS 447
[quote][b]
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Tue Jul 13, 2010 4:39 am Post subject: UltraStar tailwheel strut |
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Dana:
Normalized 4130 steel tubing makes a very poor spring, unless heat treated, of course.
The tail wheel strut should be a spring.
I use .120" wall 4130 heat treated to 48 RC for my tail wheel strut on the mkIII. An US could use something with a thinner wall, like .090".
I have also shortened tail wheel struts dramatically on all three model Kolbs I built, US, FS, mkIII.
john h
mkIII
[quote] A 5/8" solid fiberglass rod is slightly weaker in simple bending than 5/8OD x .035 steel tube, but it's less prone to local crippling which seems to be my problem. Or perhaps somebody's come up with a better solution?
-Dana
[b]
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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WhiskeyVictor36(at)aol.co
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| Posted: Tue Jul 13, 2010 7:37 pm Post subject: UltraStar tailwheel strut |
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In a message dated 7/13/2010 3:48:45 A.M. Eastern Daylight Time, d-m-hague(at)comcast.net writes:
| Quote: | Or go to a fiberglass rod (is that original on later Kolbs or is it an owner mod?)
Dana,
FYI
Fiberglass tail rod was standard on my original FireStar and also on my buddy's KXP. It worked great on turf, but was too springy on pavement. When I taxied on pavement, the spring would start oscillating and the nose and tail would start going up and down. This would get worse and I would have to stop to get it to settle down. Then as soon as I started to taxi it would start doing it again.
Bill Varnes
Original Kolb FireStar
Audubon NJ
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[quote][b]
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Wed Jul 14, 2010 6:02 am Post subject: UltraStar tailwheel strut |
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Shorten the fiberglass rod considerably. This should reduce springiness.
john h
mkIII
[quote] It worked great on turf, but was too springy on pavement. When I taxied on pavement, the spring would start oscillating and the nose and tail would start going up and down. This would get worse and I would have to stop to get it to settle down. Then as soon as I started to taxi it would start doing it again.
[b]
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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