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jb92563
Joined: 23 Mar 2007
Posts: 314
Location: Southern California
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 Posted: Thu Feb 28, 2008 7:29 am Post subject: Rear Spar Attachment questions |
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I was wondering about the rear spar attachment on the UltraStar.
The wing rear spar fitting has a flattened steel tube that is maybe 1/4" thick and the fuselage attach "U" bracket is maybe 1" wide, leaving a big gap between the two.
I know that Spar Bolts are typically designed to work in shear but by just having all that space between the two parts the bolt will likely bend a lot easier.
Does this work as designed or should I be using washers/spacers to fill the void and make for a fit that I can torque down more?
Not sure is this was designed to allow some flexibility and assembly freedom or not, or maybe I am just missing some assembly parts?
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Ray
Kolb UltraStar (Cuyuna UL-202)
Moni MotorGlider
Schreder HP-11 Glider
Grob 109 Motorglider
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worrybear(at)verizon.net
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| Posted: Thu Feb 28, 2008 6:00 pm Post subject: Rear Spar Attachment questions |
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JetPilot
Joined: 10 Jan 2006
Posts: 1246
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| Posted: Thu Feb 28, 2008 8:57 pm Post subject: Re: Rear Spar Attachment questions |
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There is very little stress on the rear spar attachment on a Kolb. The forces involved insignificant compared to what you would find on attach points of the main spar and the struts. You are correct that the bolt is not as strong in bending as in shear, but given the little amount of force on a rear spar of a Kolb, I would not think it would ever make a bolt fail.
You should post some pictures of the place you are talking about, but be aware and be very careful, some parts of a Kolb are designed to have play in them, and that tightening them againste each other rather than allowing them to " Float " freely can cuase fatigue from bending and vibration that will cause something to fail.
Mike
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"NO FEAR" - If you have no fear you did not go as fast as you could have !!!
Kolb MK-III Xtra, 912-S |
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Fri Feb 29, 2008 10:27 am Post subject: Rear Spar Attachment questions |
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> You should post some pictures of the place you are talking about, but be
aware and be very careful, some parts of a Kolb are designed to have play in
them, and that tightening them againste each other rather than allowing them
to " Float " freely can cuase fatigue from bending and vibration that will
cause something to fail.
Mike B:
I don't know where you got the above info.
My understanding is "play and float" are not designed but rigged into the
Kolbs because of the folding wing capability. They have to be a little
loose and making some hardware which connects less than precise helps in
unfolding and folding the Kolb.
All three of my Kolbs were rigged to fly without folding. That means I
tighten everything down nice and snug. Inititially, because I did put a lot
of time on all my Kolbs in a short period of time, we drilled and welded
bushings in the lift strut fittings so we could snug them up tight. This
prevented elongating the holes and wearing out bolts from vibration. My
mkIII has well over 2,700 hours with no indicated problems with stress
failure because I have a nice tight airplane. In addition, the rear wing
attachments, universals, are snugged up nice and tight. I have to loosen
them up if I intend to fold a wing or remove a wing.
Take care,
john h - Disagreeing with someone's post on the Kolb List does not
necessarily indicate the individual is personally attacking that individual.
Referring to members of the Kolb List, at large, as idiots, stupid, and
dumb, is enough to get the hair up on the back of my neck.
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John Hauck
MKIII/912ULS
hauck's holler
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JetPilot
Joined: 10 Jan 2006
Posts: 1246
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| Posted: Fri Feb 29, 2008 4:03 pm Post subject: Re: Rear Spar Attachment questions |
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John,
I am not trying to tell him not to tighten the rear wing attachment on the ultrastar, I am just telling him in general to be very careful and have an understanding before doing that type of thing. One example is that some people have wanted to tighten up the front attachment of the horizontal stab, which will cause failure of the tab over time due to flexing when it cant float free on its attachment bolt.
Bottom line is that if someone is not sure, then they should not do it until finding out from someone here on the list or from Kolb.
Mike
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"NO FEAR" - If you have no fear you did not go as fast as you could have !!!
Kolb MK-III Xtra, 912-S |
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