Author Topic: Landing gear bow repair  (Read 5485 times)

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Offline atfloyd

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Landing gear bow repair
« on: August 17, 2008, 09:45:58 PM »
Long story, left wheel sheared off about 6" above axle attach point.  Does anyone have any experience or insite in repair of the main landing gear bow.  Would prefer to fix as apposed to replace..Thanks in advance.

Offline Bill James

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Re: Landing gear bow repair
« Reply #1 on: August 18, 2008, 09:24:06 PM »

Grind (and/or saw) a taper on the bad strut up the inside and outside, about 15 to 18 inches. “Scarf” on glass UNI layers on the sides of the strut. If you need to, take a quick look at how they scarf wood joints. It simply allows a long joint.
Details:
Make a mold. Suspend and level the plane with a few inches of space under the main tire locations. The areas under the main wheels should be level relative to each other for accurate axle installation later. Duct tape the inside of the strut for release. Make a simple, quick 24 inch tall mold of the inside of the strut using two layers of BID. This mold will provide a basic shape and include a general location for the axle and the end of the strut.
Yes the shape of the mold is reversed if you have to use the good strut. Use the actual broken strut in place on the bad leg to make the mold if you can. Just do the best you can and move on. Once the basic strut core is reconstructed it can be shaped more precisely. Extend the mold to the floor, using any hard scrap material for the extension.
More detail on tapering the bad strut- Mark the longitudinal center on the bottom of the broken strut with a magic marker. That center line mark should remain indicating the center of your new layup. Grind a 15 to 18 inch taper up on each side. You want a rough surface.
Use LongEZ spar UNI glass tape, from AC Spruce. Start the layups on the inside of the strut with long lengths. Extend below the bottom mark.  Additional lengths get slightly shorter from the top, extending below where the bottom of the strut will be. The layup should be on the wet side per EZ practice. Add flox initially to the epoxy for the rough tapered area, and a moderate amount of flox thereafter so it will still penetrate the UNI adequately.
Us a hair dryer every few layers. Periodically lay on peel ply and trial fit the 2 ply BID mold. In this process you can remove the mold and peel ply and add layers to shape to your satisfaction and try the mold again. Avoid air pockets of course. A squeegee is a good tool with the hair dryer, gently stroking up.
If you are artistic you can do this free hand using the peel ply and tape to mold the shape. Good luck. The mold is highly recommended.
With the inside layers on good and peel ply-ed, the mold can be bondo-ed to the floor. This provides a relatively accurate shape and secure support. After cure the outside layers can be added. Or with the mold secure they can be added now if you want. In my experience the epoxy was hardening enough that the UNI stayed in place. But the glob of glass strands could all slide down and plop to the floor if you aren’t holding your tongue right.
After cure remove the exterior glass wraps around the upper strut as high as practical and blend and finish the strut shape. Replace the exterior wraps per plans. Install the axle and all else per plans.
Read this multiple times and get all of the other advice you can. Focus on getting the axle area correct during the layup. Have a helper or two. The strut is tough. Plan your work so you all stay clean and cool and uncontaminated by the grinding dust, even after an hour or two when you are exhausted and your back and knees are out of sorts and just want to be done. A fan will often times actually pull the dust back around onto you. Eye protection! I insist on using a vacuum to capture the dust. This is a quick note, improve on it.
I have performed this on three canards, thankfully for others. Nothin to it.
Bill James, Fort Worth VariEze N95BJ
Downdraft Plenums, QuickCowls
There was supposed to be anhedral?
ATP, Society of Flight Test Engineers

Offline kwiatkma

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Re: Landing gear bow repair
« Reply #2 on: September 25, 2008, 08:36:13 PM »
Another Long Story short  :-\, gear leg overheated (melted at the point the aluminum heat shield was RTVed on.)  The brake disk was almost touching the aluminum shield (about 1/16" clearance).  The space used to be about 1/2"+ gear leg is definitely distorted.

I've attached pictures after all has been removed(axel and such)

OK how about a bow gear leg that got over heated?  What would be the recommended procedure for the fix?  Heat, reshape, rewrap with bi direction glass wrap, done?  Or cut off the distorted part and repair as described above by Sonset?



« Last Edit: September 25, 2008, 08:47:51 PM by kwiatkma »

Offline flyingwaldo

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Re: Landing gear bow repair
« Reply #3 on: September 25, 2008, 11:30:31 PM »
After two "Long story short" posts asking for help, I think it's only fitting we get some details on what caused these issues!  I'm putting brake cooling vents in my wheel pants, contrary to some expert advice, because I think I'm not good enough to never make these same mistakes and feel some drag and/or efficiency loss is preferrable to the results of these pictures.
So WHAT HAPPENED?  How do we rookies avoid this?

Offline kwiatkma

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Re: Landing gear bow repair
« Reply #4 on: September 26, 2008, 07:20:15 AM »
Well I'm doing the repair, but it's not my plane.  The Longer version is an Engine came back from overhaul, put back on the airframe and the pilot wanted to do a couple short taxi test with the wheel pants on(non-vented).  Don't do that!  We were also trouble shooting brake leaks and rudder travel issues(which prevented the brakes from being fully actuated), so during the taxi test the rudders were disconnected.  This aggravated the braking required to keep the aircraft centered on the runway (instead of using the rudder force) so a couple factors added into a problem, no single point of failure.  The builders out there build such tight wheel pants they act like ovens.  Read the Canard pushers, specifically CP57,CP70.  Don't do taxi test with wheel pants on (and if you're a new pilot to the Canard type aircraft, think twice about putting them on during getting "comfortable" with the plane).  If you do put on wheel pants, wrap the gear leg with fiberfax and aluminum tape, put on the heat shield and vent the pants so the hot air has somewhere to go.

That should keep your gear leg from melting.

Offline Radioflyer

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Re: Landing gear bow repair
« Reply #5 on: September 28, 2008, 11:05:08 AM »
Kwiatkma's advice is right on the mark. I would add that if you concentrate on landing at the correct speeds, not fast, then you can usually delay braking until the end of the runway. That way, you bleed off some speed before having to apply the brakes. Within reason, use all the runway you have, instead of trying to stop before the first turnoff.