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Strut Attachment Lugs - Loose Bushes

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Strut Attachment Lugs - Loose Bushes

Postby sunlot2001 » Sun Nov 18, 2018 7:34 am

Yesterday, I was carrying out a routine bolt replacement on our 1600 hour Jabiru UL450 and noticed a small amount of radial movement between the bush and strut attachment lugs (at both ends of the strut). The bush is also free to rotate in the lug, but I didn't feel it wanted to unscrew.
Our aircraft is quite an early model, we got the kit in 2001. I would ideally like to remove the bushes, clean the holes and re-bond in position. Does anyone know how the bushes come out - should they unscrew or should I knock them out?

Any advice would be much appreciated.
Thanks,
Pete
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Re: Strut Attachment Lugs - Loose Bushes

Postby PKnight » Mon Nov 19, 2018 9:41 am

This is not an unusual problem with the early Jabirus, particularly at the lower bush where the strut is attached to the fuselage. The bushes are epoxied into the fuselage and not easy to shift even when they are slightly loose. I attach at the bottom of this reply a quote from an old discussion on the builders forum. Although it is about the wing fold kit the issue is the same so it gives you an idea of the work that needs to be done. I seem to recall an instruction in the SP470 build instructions that when installing the strut for the first time you ensured alignment by attaching it to the lug and applying heat to the lug bolt to soften the fitting just enough to ensure that the strut was perpendicular to the airframe. One way of warming the bush sufficiently was to place a soldering iron inside for a few seconds. Only on the basis of a distant memory I would probably try the second option first. needless to say this is a critical part of the aircraft and the utmost care needs to be taken to ensure that the final alignment is correct of strain free.

Best of luck

Peter


Folding wings
My folding wing kit required replacement of the 1/4" bore bushes in the wing roots with larger tapered bore bushes. Be aware they are screwed and epoxied in, so cannot be heated & pressed out. To remove, a screwdriver slot was ground across one face with a dremmel 3/4 dia. abrasive disc. The bush was heated with a 100Watt tapered bit soldering iron & srewed out The replacement bushes were reluctant to screw in due to the epoxy re-hardening. Not having a suitable tap, I modified an original bush to make an improvised tap I turned back a couple of thread pitches to form an alignment guide then filed two deep grooves across the remaining threads like a proper tap. After a couple of passes the new bushes could be fitted The new bushes were clamped between two 1/4" nuts on a piece of studding, floxed & screwed in with a spanner.
An alternative method to the above is to insert a bolt with a nut on it thro. the old bush and put a nut on the other side. Heat up the bolt with a hot air gun and unscrew the bush. Imediately screw the new bush in with 24hr resin/flock while the threaded hole in the wing root is still warm. Try to ensure that the bush is set inline with the bush in the other spar on the same wing.
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Re: Strut Attachment Lugs - Loose Bushes

Postby Matt » Tue Nov 20, 2018 5:59 pm

I had to replace all the ring root bushings on my SK. It really wasn't that hard in the end. The hardest part was removing the wings. It should be easier doing the strut bushes. Just need to support the wing. I think I used a heat gun to warm the bushes up before removal. Think the manual gives a good write up on it.
I found that the new bushes screwed in ok and I had no problems with the holes lining up. I would suggest if there is any wear in your old bushes, just replace them. Also your going to have to get all the old adhesive off the bushes and lugs. Other wise the joint will not have the required cross sectional area for the bonded joint to have the correct amount of strength. I remember running a tap through the wing root stubs.
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Re: Strut Attachment Lugs - Loose Bushes

Postby sunlot2001 » Tue Nov 20, 2018 7:16 pm

Thanks Peter and Matt for your advice on the strut attachment bushes. I think I have a much clearer idea of what to do now.

Best regards,
Pete
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Re: Strut Attachment Lugs - Loose Bushes

Postby diablo » Wed Nov 21, 2018 8:21 am

Just in case you need something bespoke made up, I have machining facilities (lathe, mill and anything else) and can work to very tight tolerances.
Sent from my "Electronic Numerical Integrator And Calculator" E-N-I-A-C
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