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cv93436(at)windstream.net
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 Posted: Wed Dec 12, 2012 12:55 pm Post subject: Main gear vibration |
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Lew, I think it is easier to oblong the thin walled mounting bracket tube than drill out the bracket and leg. This is some hard steel and I would be afraid of weakening the landing leg by drilling it's hole bigger. The gear fixation bolt is 3/8 inch. A 3/8 inch washer has the right inside curvature. You will have grind the eliptical moon shape on the out side of the washer. It will be small, perhapes only 1/32 to 1/16 inch thick by 3/8 inch. None-the-less, You need to take up the space in the oblong hole so the gear leg can not rotate in the mounting bracket tube. The gear leg is 2 inches thick and will not oblong as easily as the thin wall of the tube while turning the 7.9mm bit in the bracket and leg while twisting the leg.
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Gordon Anderson
Joined: 16 Apr 2012
Posts: 41
Location: Switzerland
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| Posted: Wed Dec 12, 2012 1:23 pm Post subject: Main gear vibration |
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Hope this isn't a late night dumb question, but here goes. Since most of my landings are somewhat unstraight anyway, I am wondering why an unequal toe-in on left and right gears would matter? Presumeably the aircraft will just track in the direction giving equal side forces from the wheels (plus or minus crosswinds) which would be a degree or two off fuselage centerline. Is the critical issue causing vibration perhaps the total toe-in, rather than the inequality?
Having been instructed by the plans to drum up a peculiarly (under)sized drill-bit to ensure there is minimal bolt clearance, it seems questionable to enlarge the holes in any way which might introduce (more) slop in the system (which already exists with the 7.9mm hole).
Just my 2 centimes.
Gordon Anderson
41014 Switzerland
On Dec 12, 2012, at 9:55 PM, Carroll L. Verhage wrote:
| Quote: | Lew, I think it is easier to oblong the thin walled mounting bracket tube than drill out the bracket and leg. This is some hard steel and I would be afraid of weakening the landing leg by drilling it's hole bigger. The gear fixation bolt is 3/8 inch. A 3/8 inch washer has the right inside curvature. You will have grind the eliptical moon shape on the out side of the washer. It will be small, perhapes only 1/32 to 1/16 inch thick by 3/8 inch. None-the-less, You need to take up the space in the oblong hole so the gear leg can not rotate in the mounting bracket tube. The gear leg is 2 inches thick and will not oblong as easily as the thin wall of the tube while turning the 7.9mm bit in the bracket and leg while twisting the leg.
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Strasnuts
Joined: 10 Feb 2009
Posts: 502
Location: Salt Lake City, UT
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| Posted: Wed Dec 12, 2012 2:22 pm Post subject: Main gear vibration |
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I agree Gordon, but over time when 90% of your taxiing is straight ahead I believe you would wear one tire quicker than the other. As far as the shimmy goes I believe toe in or out doesn't make much difference. It would get worse when braking causing the wheel to track out when there is brake pressure. This didn't happen in my case.
Vans told me a larger bolt holding the gear would work fine. Personally I wouldn't oval the weldment. I aligned mine for tire wear and hoping it would help the shimmy that others have had. Not sure if it helped for shimmy because it hadn't flown before I aligned mine. I do know the gear stiffeners fixed my shimmy.
My .02
Sent from my iPhone
On Dec 12, 2012, at 16:22, Gordon Anderson <mregoan(at)hispeed.ch (mregoan(at)hispeed.ch)> wrote:
[quote]Hope this isn't a late night dumb question, but here goes. Since most of my landings are somewhat unstraight anyway, I am wondering why an unequal toe-in on left and right gears would matter? Presumeably the aircraft will just track in the direction giving equal side forces from the wheels (plus or minus crosswinds) which would be a degree or two off fuselage centerline. Is the critical issue causing vibration perhaps the total toe-in, rather than the inequality?
Having been instructed by the plans to drum up a peculiarly (under)sized drill-bit to ensure there is minimal bolt clearance, it seems questionable to enlarge the holes in any way which might introduce (more) slop in the system (which already exists with the 7.9mm hole).
Just my 2 centimes.
Gordon Anderson
41014 Switzerland
On Dec 12, 2012, at 9:55 PM, Carroll L. Verhage wrote:
| Quote: | Lew, I think it is easier to oblong the thin walled mounting bracket tube than drill out the bracket and leg. This is some hard steel and I would be afraid of weakening the landing leg by drilling it's hole bigger. The gear fixation bolt is 3/8 inch. A 3/8 inch washer has the right inside curvature. You will have grind the eliptical moon shape on the out side of the washer. It will be small, perhapes only 1/32 to 1/16 inch thick by 3/8 inch. None-the-less, You need to take up the space in the oblong hole so the gear leg can not rotate in the mounting bracket tube. The gear leg is 2 inches thick and will not oblong as easily as the thin wall of the tube while turning the 7.9mm bit in the bracket and leg while twisting the leg.
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Lew Gallagher
Joined: 04 Jan 2008
Posts: 402
Location: Greenville , SC
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| Posted: Wed Dec 12, 2012 7:32 pm Post subject: Main gear vibration |
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Hey Carroll,
Thanks. Got it. I also thought of landing on the mains would equalize the toe in ... until the nose wheel contacts, and I seem to remember someone saying the shimmy didn’t start for them until nose wheel was down and roll out around 35 mph – which would make sense (as well as wondering about the nose wheel itself – tension/air pressure).
Later, – Lew
do not archive
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cv93436(at)windstream.net
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| Posted: Thu Dec 13, 2012 6:48 am Post subject: Main Gear Vibration |
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Gordon, Since the vibration occurs at about 40 knots taxi speed, my theory is that the tires are skipping sideways at that speed. I have balanced my tires 2 times, checked the swivel tension of the nose gear, etc. as noted in Van's Airforce forums. This did not help the vibration. Aligning the wheel travel stopped the vibration. As I mentioned earlier, my total toe in with both wheels was 6 inches in 13 feet. That means the tires had to slide 50 feet sideways in 1300 feet of travel! My RV10 is noticeably easier to push on pavement now. If nothing else, parallel tracking should help your tire wear. There is no play of the gear leg in the original 7.9 mm. hole. Consequently, you must shim the hole to prevent the leg gear from twisting in the gear mounting bracket. I suppose you could weld the bracket hole partially shut and redrill it to 7.9 mm.
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