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  #1  
Old 12-09-2012, 04:57 PM
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Ironflight Ironflight is offline
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Default Mystery Puncture

OK, so Tsam has a pretty benign tire history. With 188 total hours on the clock, she has that same amount of time on both Monster Retread tires and a pair of Michelin Air Stop tubes. Wear is nice and even, and based on what I saw during the condition inspection last weekend, she?ll go four times that in this set of tires. I noted that the pressures were down to 25 psi (hadn?t put air in for months), and I think we had started around 35, so I bumped them back up to 38 (where I run the other airplanes). First flight after that gave me a definite shimmy on the mains, so I bled them back down to 33 to see how they?d run there.

Today, Louise came back from a fuel run and had her usual great RV-3 landing (she lands Tsam better than anything in the inventory ? a perfect match!), and as she rolls out ? the left tire is flat ? she powers off the runway into our taxiway and we get the pant and wheel off. Disassembly reveals this:






A very careful inspection of the interior of the tire ? with a magnifier ? shows NO irregularities, bumps, hooks, or debris anywhere near the spot where this was resting ? and nowhere else either. Clean as a whistle. A new tube, a little fiberglass repair on the wheel pant, and she?s back in service.

But?.what the heck causes a wound like this? Anyone with years of airplane wrenching seen one like this before?
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  #2  
Old 12-09-2012, 05:28 PM
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AlexPeterson AlexPeterson is offline
 
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Maybe the Cleco that was in the tire???...

Actually, I wonder if you have the same phenomenon that we've seen in the nose wheel inner tube failures. My guess, in the case of the nose wheel flats, is that the tube sort of locally gets stretched progressively as the tire flexes on rolling. The first few years I had several flats. When I started putting obnoxious amounts of baby powder in, the flats stopped. The nose wheel flats were directly on the sidewall of the inner tube, and had a vaguely similar look to yours - looked cut. Put about a tablespoon of dust in the tire and see if it happens again.
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  #3  
Old 12-09-2012, 05:58 PM
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Good input Alex - so it has been seen before! Unfortunately, this one already had obnoxious amounts of baby powder - I remarked on it as I took it apart, wondering how I had installed so much in the first place....

Paul
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  #4  
Old 12-09-2012, 06:10 PM
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mannanj mannanj is offline
 
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Default Hole

Any chance that the schrader valve could have had some FOD hang up in there when you added air?

Then the tire could have leaked down as Louise was taking off, flying and landing and the damage might have been caused by moving the plane with the tire flat.

Just a guess.
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  #5  
Old 12-09-2012, 06:24 PM
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I like to put a lot of talc on the tube to allow it to move without binding on the tire. Dr. Scholl's foot powder is what I use. Keeping the tire pressure up around 45psi goes a long way in keeping this from happening as well.
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  #6  
Old 12-09-2012, 06:50 PM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by mannanj View Post
Any chance that the schrader valve could have had some FOD hang up in there when you added air?

Then the tire could have leaked down as Louise was taking off, flying and landing and the damage might have been caused by moving the plane with the tire flat.

Just a guess.
Yeah - that was the first thing I thought about - I had let air out two days ago, and thought that maybe the valve had hung up. But.....I always use a metal, gasketed cap as a redundant seal, and that was in place.

Paul
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  #7  
Old 12-09-2012, 06:51 PM
molson309 molson309 is offline
 
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This has happened on our RV-7A twice. Both times it occurred when the tire was low. The cuts in our estimation line up with the rim/bead area. Our theory is that a sharp turn while taxiing can cause the tire to "roll under" enough to where the bead pulls away temporarily and allows the inner tube to be pinched between the rim and the bead, causing the cut.

Keeping the pressure up and the turning breakout force at the right setting - not excessively tight - may help prevent this. We are trying to run 40 lbs to see if this will keep it from happening again.
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  #8  
Old 12-09-2012, 07:44 PM
Norman CYYJ Norman CYYJ is online now
 
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I had a similar experience. I found a proud string on the inside of the tire and it cut the tube. Faulty from the factory.
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  #9  
Old 12-09-2012, 07:56 PM
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Quote:
Originally Posted by molson309 View Post
This has happened on our RV-7A twice. Both times it occurred when the tire was low. The cuts in our estimation line up with the rim/bead area. Our theory is that a sharp turn while taxiing can cause the tire to "roll under" enough to where the bead pulls away temporarily and allows the inner tube to be pinched between the rim and the bead, causing the cut.
I'm an avid bicyclist and have seen my fair share of "pinch flats" mountain biking. They usually look like two punctures about 1/4" apart; sortof a snake bite. This doesn't look like a pinch flat to me, but certainly the tube material is way thicker than a mountain bike so I guess it could be.
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  #10  
Old 12-09-2012, 07:58 PM
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Geico266 Geico266 is offline
 
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Not related to Paul's picture, but I have had the white powder coating chips caused by mating the two wheels haves together cut the tube to the point where they slow leaked. I have patched these slow speakers and they have lasted for years.

BTW Paul, Louise is a -10.

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