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Gear Leg Shimmy

 
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lbmathias(at)verizon.net
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PostPosted: Sat Feb 16, 2008 3:34 pm    Post subject: Gear Leg Shimmy Reply with quote

Well folks, we changed the tires on the main wheels today to Goodyear Flight Custom IIIs; one of the original tires definitely was out of round and quite obvious while spinning it on the axle during removal. The new tires improved the shimmy a bit but it hasn't gone away. However, we have a new theory: during the tire changing, we noticed that the axle is quite loose on both main gear. The next idea is to put some shim stock around the axle to tighten its fit in the socket. Has anyone else noticed that the axle doesn't fit tightly?

I'll post the results when we get the axle tightened.

Linda Mathias

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catalpaaviation(at)wideba
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PostPosted: Sat Feb 16, 2008 10:24 pm    Post subject: Gear Leg Shimmy Reply with quote

Hullo from Australia, I have kit 32 and my axles were very loose.  I had 2 half inch washers made up for the outboard side with a taper and holes for the nuts.  On the inboard side leave the axle full length and cut a thread on the axle and a tapered (very small taper) washer and nut to hold the axle centre and tight, all you then have to do is drill the ¼ hole and AN 4 bolt and nut according to the plans.  As it was I had cut the axle to length so I had a tap put in the axle and bolted it in with a tapered washer and bolt with locking nut and safety wire to stop axle rotating.

I do have a question relating to the flaps, when I fitted the port flap I could almost get my fingers between the flap and wing in the retracted position.  As you cannot unbolt the flap brackets and you cannot bend, cut or weld them I had larger bronze bushes made and I drilled them out of centre with the flaps in place.  I still have a fair gap as I was running out of meat on the flap brackets, what do I do now to make the gap neat and just big enough to clear?  The starboard wing and flaps are just fine.

Anthony Morrison
Lighting 19-5301


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N1BZRich(at)aol.com
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PostPosted: Sun Feb 17, 2008 6:40 pm    Post subject: Gear Leg Shimmy Reply with quote

In a message dated 2/16/2008 6:36:20 P.M. Eastern Standard Time, lbmathias(at)verizon.net writes:
Quote:
one of the original tires definitely was out of round and quite obvious while spinning it on the axle during removal.


Hi Linda,
Two thoughts: First, I would not be concerned about a tire out of round in the winter if your airplane has set for a day or so. That is going to happen with the bias constructed tires that aviation uses (at least on the relatively low end of the dollar spectrum). Heavies and jets probably do have radial constructied tires available but cost closer to a grand each. The out of round condition goes away as the tire heats up taxing to the runway.
As to the loose axle in the lower gear leg fitting, I found that on my airplane as well. I spot welded the axle to the fitting on the back side of the fitting (toward the center of the airplane). The way the fitting is built, that area where the axle comes through the fitting is far enough away from the rest of the fitting that I will be able to grind the four spot welds off if I ever need to replace the axle. It had no effect on shimmy, but hopefully "your mileage will vary".
Glad to hear the new Custom IIIs did help some. I assume you took off the aluminum V angle that we had clamped on.
Blue Skies,
Buz

Delicious ideas to please the pickiest eaters. Watch the video on AOL Living.
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landonp(at)bigpond.com
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PostPosted: Mon Feb 18, 2008 8:58 pm    Post subject: Gear Leg Shimmy Reply with quote

Hi Anthony
Had the same problem on both wings.(Kit #31) The flap brackets were out (not lined up). Requested replacement brackets (sent undrilled at pivot). Had to cut a hole (round) either side of bracket (in flap for access). Unbolted hinges ,and replaced..Clamped flap in place on wing brackets to suit (even gap about1/8th in). Then marked pivot holes, drilled, bolted up, perfect. (repaired holes).

Cheers
BK
Australia
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lbmathias(at)verizon.net
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PostPosted: Sat Feb 23, 2008 4:03 pm    Post subject: Gear Leg Shimmy Reply with quote

Report on experiment # 2:

Today we removed the wheels and axles from the Lightning; wrapped some shim material (beer can aluminum fits almost perfectly) around the axle and reinstalled the wheels. I then performed taxi tests; taxiing up to 33 kts ground speed, there was little to no shimmy. Ceiling never raised above pattern altitude all day so taxi was the only possibility. The slight roughness I felt at the highest speeds was probably the runway surface. I want to fly it a couple of times before I remove the aluminum angle Buz put on the gear then see if that makes any difference. However, between the upgraded tires and the axle shimming, we have greatly improved the situation. Assuming this continues to offer improvement, we will probably remove the shim material when it wears down and weld the axle into the socket to avoid having to periodically replace the shim material.

Regards, Linda

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155LT



Joined: 14 Sep 2006
Posts: 24
Location: Crossville TN

PostPosted: Sun Feb 24, 2008 5:09 am    Post subject: Gear Leg Shimmy Reply with quote

Linda
Did you have that much slop between the axle and the wheel? Welding Steel to aluminum is tricky Good Look.

John


From: owner-lightning-list-server(at)matronics.com [mailto:owner-lightning-list-server(at)matronics.com] On Behalf Of JOSEPH MATHIAS LINDA MATHIAS
Sent: Saturday, February 23, 2008 6:00 PM
To: lightning-list(at)matronics.com
Subject: Re: Gear Leg Shimmy


Report on experiment # 2:



Today we removed the wheels and axles from the Lightning; wrapped some shim material (beer can aluminum fits almost perfectly) around the axle and reinstalled the wheels. I then performed taxi tests; taxiing up to 33 kts ground speed, there was little to no shimmy. Ceiling never raised above pattern altitude all day so taxi was the only possibility. The slight roughness I felt at the highest speeds was probably the runway surface. I want to fly it a couple of times before I remove the aluminum angle Buz put on the gear then see if that makes any difference. However, between the upgraded tires and the axle shimming, we have greatly improved the situation. Assuming this continues to offer improvement, we will probably remove the shim material when it wears down and weld the axle into the socket to avoid having to periodically replace the shim material.



Regards, Linda



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N1BZRich(at)aol.com
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PostPosted: Sun Feb 24, 2008 8:51 am    Post subject: Gear Leg Shimmy Reply with quote

In a message dated 2/24/2008 8:11:23 A.M. Eastern Standard Time, johnsdtn40(at)charter.net writes:
Quote:
Welding Steel to aluminum is tricky


John,
Linda is not talking about welding steel to aluminum. She is talking about welding the "steel" axle which fits inside the "steel" lower gear leg assembly, which then bolts onto the aluminum gear leg. On the original set up the axle bolts to the lower gear leg assembly (on the inside or toward the aircraft centerline) and may eventually ends up with a slightly loose fit. I put three small spot welds on the inside (toward the aircraft centerline) where the axle comes through the lower gear leg assembly. I noticed that the axle was slightly loose inside the lower gear leg assemble at about the 350 hour point and the spot welds took care of that. If I ever need to replace an axle for any reason the spot welds can be ground off to remove the old axle. 
Blue Skies,
Buz

Delicious ideas to please the pickiest eaters. Watch the video on AOL Living.
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