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Mystery Puncture

Ironflight

Ironflight

VAF Moderator / Line Boy
Mentor
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:

P1020107.JPG


P1020108.JPG



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?
 
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.
 
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
 
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.
 
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.
 
mannanj said:
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.
Click to expand...

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
 
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.
 
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.
 
molson309 said:
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.
Click to expand...

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.
 
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. ;)

:D
 
When it comes to tube type tires: LOW PRESSURE = FLAT TIRES

Personally I run 40-45 PSI all around and check them at least once a month.
 
That cut looks identical to one I induced in my brand new Leakproof tube when I did not notice that the tube was trapped between the wheel halves I was reassembeling. I cut mine all the way through, so it was obvious very quickly. I wonder if your tube was cut part way through at some point, and finally let go.

Jim Berry
RV-10
 
Tube cut

Lots of good ideas. One other might be that tube was damaged
Prior to you receiving it. I once received a tube that got pinched
By other stuff in the shipping box.
A caution on using (talc or foot) powder- use only enough to mist
The inside of the tire. Using excess could cause the powder to turn
Into a muck that acts like 800 grit against your tube.
Blue skies
Ralph
 
Look your tires and tubes over very carefully before installing them. I changed my Air Tractor tire and in two days it looked half flat...had 26 psi from a starting 50 PSI the book calls for, so I added air. Same thing the next day, so I disassemble it and see that the valve stem had separated from the tube, half way around and leaking.

I called Desser and they said that a new, free tube was on the way and to please send the other one back...great folks to do business with.

I run their recaps and always put new tubes in. Recaps...$160, new tires twice that or more.

Best,
 
I don't want to get too far from the OP but the new wheels I put on the 9 are drilled for bead screws. I don't believe I saw anything in the instructions about them and have not heard anyone else mention them. We used to put screws in the bead of our drag racing wheels to keep them from spinning off the rim when run low on air. Seems like a good idea for a tire that goes from 0 to 60 on a landing. It might keep the valve stem from seperating from the tube like it sound like happened to Pierre. Does anyone use sidewall screws?
 
Lots of good discussion here for the archives folks, but I still don't think I'm any closer to a good answer on this funny-shaped puncture. Since the tire/tube/wheel had been fine for a year, I think the probability of an installation problem is low. Could have been a leak induced by the recent pressure change, and then a "pinch" cut...but given that a careful examination of the interior of the tire showed no irregularities, well - this is just another weird one.
 
Ironflight said:
Very close Dan....so I want to hear THIS theory! :D
Click to expand...

I don't really have a theory. I was struck by the roundness of the cut, so I started thinking about damage a long time ago, back when that tube was one of many bouncing around in a big bin of tubes at the tube factory, poking each other with their little stems.......or something like that.

Never mind. Maybe I should quit drinking ;)
 
DanH said:
I don't really have a theory. I was struck by the roundness of the cut, so I started thinking about damage a long time ago, back when that tube was one of many bouncing around in a big bin of tubes at the tube factory, poking each other with their little stems.......or something like that.

Never mind. Maybe I should quit drinking ;)
Click to expand...

Oh, drinking something good is never a problem! ;)

When you asked the question, that was the first thing I thought you might be thinking - it sure DOES look like it could have been cut well before installation, maybe by how it was packed in a box...

Too chilly here to worry about now - the airplane is flying, and the hangar is cold! (for Houston, that is...)

Paul
 
Bead screws

Mark, the Cleveland wheel/brake kits (Grove kits also) come with hub caps that mount to the 3 threaded holes in the rim, which we discard when mounting wheel pants.
Bead structure is much smaller in our 500x5 tires than automotive tires, I wouldn't try disturbing then with screws.
 
aerhed said:
Paul, is that cut opposite the stem & could the butt of the stem have cut it?
Click to expand...

No, that's a good thought, but it is about a third of the way around the tire. It is on the opposite side, but I can't see any way that it could have touched the valve from there- unless it was when it was folded in the box.
 
Ralph,
Thanks for the answer. I was afraid it would go unanswered.
I will leave the holes empty.
 
Ironflight said:
When you asked the question, that was the first thing I thought you might be thinking - it sure DOES look like it could have been cut well before installation, maybe by how it was packed in a box...
Click to expand...

Can you reasonably bend and twist the tube to make the puncture match the valve stem? If so does the size match well?
 
Forensics?.

OK, so given the clues above, I deflated the tube completely, and folded it in half – this put the end of the valve on the same side as the “wound”.

P1020109.JPG


I then folded the tube the way it might have been in the box – see how the end of the valve touches the tube rubber?

P1020114.JPG



And guess what fell in that exact spot when I moved the valve away?

P1020113.JPG


Yup – the wound!! While we can’t say for absolute certainty, a likely scenario would have been undiscovered damage during shipping that finally let go with an overstress for some reason – the tube had a weak spot due to the damage. Now all the new tubes I have in stock (only one to a box Gil) have valve caps on them – but I seem to remember that in the past, they sometimes didn’t. If your new tube doesn’t have a cap installed, check to make sure that the sharp edge of the valve hasn’t done any damage.

Paul
 
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Wow, that is really amazing

They say it takes a village! You guys are amazing, except now I'm worried about my tubes

Thanks Paul
 
Impressive!

Wow, I am impressed with your detective work Paul and team. Nice hypothesis and analysis.

Paul, I sure am glad you are watching over our spaceflight efforts. Gene Kranz would be proud ;)
 
Ironflight said:
While we can?t say for absolute certainty, a likely scenario would have been undiscovered damage during shipping that finally let go with an overstress for some reason...........l
Click to expand...

Overstress, you say! :eek: Really, it was a nice landing! :mad:

I think Dan Horton wins the prize on this one....
 
tubes and tires

Just got new tubes and tires from Desser for my 6a.....the tubes were folded and crammed into the rim openings in the tires! I wish I'd taken pics of the packing job. Not surprised to see tube damage if they pack everything like this. Tubes did have caps installed though..
 
Tire tubes

Maybe add some air to the tube out side of the tire and give it a good QC look over.
I would think Paul defective tube might have shown that blemish.
What ya think of do that?
Bill J
 
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