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Flat Tire Landing...and a Mystery!

Ironflight

VAF Moderator / Line Boy
Mentor
Well, for a monent I thought I should post that in the "There I was..." section, but in fact, it wasn't all that bad....

After spending a couple hours out in New Braunfels (TX) this gorgeous afternoon, I had a nice tailwind back to Houston. A normal traffic pattern, no crosswind, and a normal approach was followed by a very small skip on touchdown (a good landing for me!). It was a nice wheelie, and as I lowered the tail, I started to get a bunch of skipping around just about the time the tail touched. There was a little pull to the right, but nothing the rudder couldn't handle. I was convinced I had a shimmying tailwheel until I got down to about 20 knots, when I started getting that lope, lope, lope feeling of rolling on a flat main. There was suddenly a lot of drag, and I could tell I better get off at the very first opportunity, becasue she was going to be stuck wherever I let it stop. If you've never had a flat on a light plane - there is no chock more effective than a flat tire! :eek:

Off the side of the taxiway, it was clear that the right wheel pant was holding up the airplane. Two of us got under the wing spar and lifted with our backs, while someone else (A nice day brings lots of people to the airport!) pulled the forward end of the pant and shot some air into the tire. First mystery - it held air! We set the plane back down on the tire, and couldn't believe it was still up, as flat as it had been. I hopped in, fired up, and quickly taxiied back to the hangar. There, I jacked it up, pulled the rest of the pant, and removd the wheel. Second Mystery - It was still holding air! The valve stem was bent in towards the axle a bit, but otherwise, it was normal. There were two sharp gashes - as if they had been made with a razor knife - in the sidewall of the tire, but they didn't go through the carcass. :confused:

So, I have a total mystery - the tire was totally flat from something that happened on a skip, and now it holds air. No, I am not going to fly with it again - I'm taking the opportunity to order leak-stop tubes and new tires (and I guess it will take a few evenings to fix the wheel pant...) I had checked the tires on Friday, and they were both at 35 psi, which is where I've been running them for 90 hours.....The slits in the sidewall of the flat tire suggest that the edge of the pant might have done the cutting. But nothing explains how it could have been flat and now hold air.... :confused:

OK, the floor is open for suggestions !

Paul
(New fiberglass on wheel pant setting up in garage...)
 
Sometimes when you check the tires or add air, the valve core doesn't reseat all the way and you have a small leak. The next time you depress it and release it, the leak stops. Try replacing the valve core and make sure it is tight.
 
Good thought...

I was trying to figure out if when I checked the air on Friday, I had somehow started a leak. But the tire was up when I preflighted in New Braunfels, and I also had a safety cap screwed on tight over the valve....

Paul
 
Double mystery

Paul,
I can match your tire mystery and oddly enough it also happened at New Braunfels! After attending Vans Homecoming in 2004, I flew South to visit my father in Tucson before heading East and home to NY. I stopped in New Braunfels to spend the night with a friend and retired co-worker. I gave him a ride before leaving the next morning. We had a nice flight and with the pressure on, I made the nicest wheel landing I have made to date. The rest of teh roll ouot reads exactly as yours, I too thought I had a tailwheel problem. By the time I was stopped, both mains were flat! They did not hold air for an extended time as yours did but we eventually got the plane to the ramp.

On inspection, both tubes (Michelan air stopers) had small punctures but there were no signs of punctures in the tires. We never did find an explanation for the punctures though there was some speculation that I picked up a thorn type seed from a plant that is common in the Oregon desert where I had stoped earlier. These weeds are known to puncture bicycle tires, I don't remember what they are called. Perhaps, they took several days to work themselves into teh tubes and both happen to let go on teh same landing. I don't think I'll ever know for sure.

The good news is that my friend and former co-worker is Brian Moline, now an RV-9A builder.

Scott A. Jordan
N733JJ
 
Whoah!!

Yeah, Scott, that is pretty weird!

The other "Whoah!" is that I just looked at the tire pressure chart on the Desser web site, and the recomended pressure for the 5.00x5 - 6 ply is 51 psi! I should know better than to assume that I know something based on previous experience. On my Grumman, we ran about 30 psi, and felt that was on the high end for 6.00x6's....I guess I'll a little more pressure in the next set on the -8!

Paul
 
Lots of good reading there!

I am still not sure how the air got out though....and why it is staying in now!!

I just downloaded my camera pictures - here's the wheel pant. I laid in the first layers of repair glass after I took this, and before I came home...

wheelpantdamage1jp.jpg


I'm going to open up the clearances a little more with this repair. I just wonder if, in my "skip" today, the sidewall contacted the edge of the wheel pant and started the process (whatever the process was...)

Paul
 
My guess is a cut where the valve stem enters the tube. Once the wheel stopped spinning, the stem found a postion that sealed. I'm thinking the skip caused the tire to rotate slightly on the rim, cutting the stem. Just my guess, but if I'm right what's the prize?
 
Mystery...solved?

IronFlight said:
OK, the floor is open for suggestions !
Paul, Just the other day you were commenting that you didn't have anything to do on your airplane - you forgot to knock on wood after saying that! :)
 
Mystery

Thats the purpose of the nut and washer on the tube, to prevent what happened to you from happening
 
Tire pressure

I generally pump up to 35 PSI and let it bleed to 30PSI before I refill (Don't have airstoppers now because they didn't have any at New Braunfels when I was there). Ever try those carnival games with the over inflated basketball?Anything over 35 is like trying to land on an overinflated basketball.

Scott A. Jordan
N733JJ
 
Nut and washer...

Well, I had the nut and washer in place on mine, so it was either the right thing to do, or the wrong thing to do.... ;)

I inflated the tube on the workbench last night, just nice and firm, and this mornig, it is just as firm....put another layer of glass on the pant before work this morning - it should survive.

I have no answer to any of this - but like Mickey say, always have a piece of wood (this is aviation - it would have to be Sitka Spruce...) handy to knock on.

Thanks for all the ideas guys - I am begining to lean towards an alien encounter at 9,000 feet...

Paul
 
Paul,

You might want to increase your tire pressure in increments. The increased pressure may change ground handling in unexpected ways. I found this out in a Starduster several years ago after I increased pressure from the usual 35 psi to something around 55 psi per A&P recommendation. On the very next flight it took me fourteen landing attempts to bring it to a safe stop. That's right, fourteen. It wanted to enter a high speed ground loop immediately on touchdown. Two old timers pulled up chairs to watch the show about half way through. All they said afterwards was, "Heh, heh. We thought you wuz gonna bust yo a..." I guess I would have done/said the same if I weren' t the one in the cockpit. :D

And this was in an airplane I had been flying for years and had never before explored the edges of a runway with. I can understand it wanting to bounce more, but not go straight any more? Needless to say I reduced the pressure.

Kelly
 
More good commens - thanks!

Yes, definitely I am going to increase tire pressure incrementely (if at all) - my mention of the 51 psi was really that I was amazed that the upper limit (on the tire/tube combination) was that high.

I think that the comment on altitude accelerating the leak has significant merit. I had checked the tires on Friday (and actually put a little air in the one that went flat yesterday). Suppose that the valve did not fully seat, and had a very slow leak. When I flew out to New Braunfels yesterday morning, I stayed down at 2000', becasue of headwinds. When I came back, I did so at 11,500, pick up the tailwinds (45 knots!). It might be that the slow leak turned into a faster leak on the return trip, and got below the critical value to support the landing. We have had several "engineering discussions" here at work this morning as we hashed over our weekends, and this is the leading theory.

However, new tires and Michelin tubes are on the way from Desser in any event!

Paul
 
Yeah....the Cap....

When I put that cap back in place on Friday, it didn't want to thread on right - had a lot of drag. It did screw on about the right number of turns, and it snugged up, but still - I'm just not sure it was doing a good job. It's easy to talk myself into that conlcusion at this point...

I'm going to submerge the entire tube tonight, just becasue I'm curious, but it's not going back on the airplane - regardless! Way back when, I did a lot of test flying in the shuttle simulator doing failed tire cases - inboards, outboards, left, right...at 190 knots, they get really exciting! Yesterday's landing was much more well behaved, but still, not something I have any desire to repeat...

Paul
 
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Another thought

Other things to consider in this flat tire scenario are moisture content of air used to inflate the tire and OAT at cruise alt. I know from experience that not using a dry air source to inflate tires then flying above the freezing level the valve core will unseat due to the moisture freezing.
 
air pressure based on wheel rating!

Check the rating on your wheels. My Clevelands from Van's specify 30psi or so. I usually put in 31.5 and it gets me a little farther along till I need it again.

Now, as to the flat tire, I once had a main go flat when turning, slowly even, in my -4, because the pressure was too low, allowing the tire to roll off the rim. I suppose it's possible that landing could do the same thing.

Also had a main on a -6A go flat because of a large slit in the tube, tire was fine!!! Holding the tube in your hands, you couldn't even see the slit, it was such a fine line. If you squeezed the tube, you could then see a 4 to 5 inch slit, like cut with a razor, as you said. This happened inside the tire! Wierd.

Apparently the tube for nose tire types is a wierd size, most guys around here carry a spare with them. Just a thought...

Jeff
 
More interesting ideas!

If nothing else, this thread is building up a lot of good things for the search engine!

Just came back from the airport where I was working on the wheel pant - another couple glass sessions, and it will be ready (again) for Grady to paint in May...

Inner tube from the flat tire is still holding air - leak checked in water just fine. Ocam's Razor says it had to have been something in (or having to do with) the valve. There are just no holes in the tube rubber!

Oh, I had also heard that the nosewheel uses a funny tube...but it's not my problem - I fly with the little wheel in the back... :p

Paul
 
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Found it! Mystery Solved!

OK, I just couldn't stand it anymore, so this morning I took a magnifying glass, some soapy water, and my air compressor, and went one-on-one with that stupid tube! Sure enough, if you put enough pressure into it...right along a seam, there was a very fine cut line, like it was done with a razor (as mentioned by someone above). It matches farily close to the cuts in the sidewall of the tire, but becasue it didn't leak at low pressure, and was right along a seam, I missd it before. But there are bubbles!

So here's what I'm going to call a final solution...In my landing, the stars aligned wrong, and the narrow opening of my wheel pants allowed the tire to be cut by the edge of the pant (I guess it was the origianl touchdown, or the skip, who knows!?). The pressure pulse of landing was enough to blow the air out htrough the cut. When we re-inflated the tire on the ramp, we just put enough pressure in to make it round to taxi, and the tube was held against the sidewall in such a way to let it seal (like putting your hand over a wound).

So what was the lesson learned ? There are no NEW lessons! Open up the wheelpant clearance some more, dummy!!

Oh,and in closely examining the tube, I read the label - the tubes Van supplied with my kit are the Aero Classic Leakguard's. They are the ones that Desser sells for just about as much money as the Michelin AirStops. So they aren't the cheapest on the block, as I kinda assumed...but now I can do my own comparrison with leak-down to the Michelins, which should be here today....

Thanks again for all the replies and ideas !

Paul
 
Sorry, you're not off the hook yet...

Now, after you've opened up the wheel clearances, you're going to have to do some detailed documentation on how your cruise speeds are affected so the rest of us can learn from that as well.

I think we'd all like to know a definitive answer as to how much wider pants gaps change things like airspeed, and maybe even handling too?.

Get back to work. ;)
 
tube slice

"right along a seam, there was a very fine cut line, like it was done with a razor"


Ocam's by chance??


Sorry, I just couldnt pass that one up.

Mike
 
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Leaking tube

Our club Cessnas go through a lot of tires. Apparently applying the brakes while still flying and at touchdown slow the airplane down. It also flat spots the tires very quickly :mad: . Guess who gets to change the tires :mad: . One trick I found to check the inner tube is to apply a small amount of spit into the valve stem. You will know immediately if there is a leak there. I may even do it more than once during the tire changing process. Sounds gross using spit? It is cheaper than buying glycerin and readliy available.

Dave Nellis
 
Gross? No!

truflite said:
One trick I found to check the inner tube is to apply a small amount of spit into the valve stem. You will know immediately if there is a leak there. I may even do it more than once during the tire changing process. Sounds gross using spit? It is cheaper than buying glycerin and readliy available.

Dave Nellis


I was diving in the big fancy swimming pool at work this morning, and they offered me this wonderful chemical mask de-fogger...."That's OK", I said, as I spit in my mask," I'll just do it the old fashioned way!" :D

Young whipper-snappers with their fancy, expensive stuff..... :rolleyes:

Paul
 
Yeah, I'd thought about that...

Highflight said:
I think we'd all like to know a definitive answer as to how much wider pants gaps change things like airspeed, and maybe even handling too?.


I was wondering the same thing, and since I have a lot of fresh data from Phase 1, I should be able to make a decent comparison!

Paul
 
Tire Deflection

Neal Willford created a series of Excel spreadsheets as companions to his excellent Sport Aviation articles. They are available for download at the EAA site. One of them is for landing gear design, specifically flat spring and tapered rod legs. Sound familiar?

If you want some perspective on just how much your tire sidewalls deflect, use this easy spreadsheet to model your gear legs, tire and wheel sizes, tire pressures, and landing G's. Output will include both gear deflection and tire deflection. You might be surprised....

Dan
 
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