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  #1  
Old 06-14-2021, 02:40 PM
DavidHarris DavidHarris is offline
 
Join Date: May 2018
Location: Upland, CA
Posts: 152
Default Brake / tire issue

I had a wheel lock up while taxiing at Tuscon yesterday afternoon about 3:30 pm.

The weather forecast indicated 110 degrees. My OAT gauge read 120, and the temperature on the tarmac was probably 150. I had a 2-mile taxi from the FBO to the departure runway. I was behind a slow-moving airplane and had to apply occasional braking even at low thrust, and also some braking for differential steering in a modest crosswind. I was concerned about overheating brakes and mentioned it to my son.

Shortly before reaching runup area, the plane made a hard turn to the right and came to a complete stop. I tried starting again and the plane continued turning right, so I shut down the engine on the taxiway, notified ground control, and got out to investigate. I found the wheel fairing resting on the ground, with the tire completely flat. I was able to remove the fairing, and found the tire pulled off the rim, the tube flat, and the brake locked. The right wheel would not turn when I pushed the airplane. I removed the brake pad, pushed the airplane off the taxiway, and had a 2-hour adventure with the facility manager and three FBOs getting the plane to an FBO. I'm grateful to a bunch of kind people at TUS. This morning the mechanic replaced the tire and I reattached the brake pad and did a ground test, then ferried the aircraft back to KCCB in SoCal, thankfully with a short taxi to the crosswind runway and all before it got too hot.

I'm looking for ideas about the root cause. I have standard Vans RV7A Matco wheels and Cleveland brakes. I think the most likely reason is that the brake locked. I don't know too much about brake failure, but the temperature and length of taxi are both much higher than usual so I suspect it could be heat related. It is also conceivable that something such as unseen debris on the taxiway could have popped the tube, and then the tire deflated, and somehow this led to stresses that locked up the brake. In any event, the brake behaved normally when I reassembled it this morning.

As another possible clue, I've been dissatisfied with my right brake. The plane started flying 15 months ago and I have about 200 hours on it. The brake pad squealed frequently until I replaced it, and occasionally still squeals. The braking action is less effective than I'm accustomed to in a Cessna or Bonanza, and I usually brake gently and have a rollout of more than 1000' before coming to a complete stop. The brakes generate a lot of fine dust that needs cleaning. I'm also not wild about the tube design; I think I follow all the directions about talc powder and repeatedly inflating and deflating but I've had to replace two failed tubes so far on the airplane.

I'm also looking for feedback on a remedy. I've worked on the tires enough times already that I'm feeling fed up, as well as concerned about a ground loop if it fails on landing. It looks like the Beringer wheel and brake system is more reliable, and possibly has better braking action. It's fairly pricey, but I'm considering replacing all three wheels and two brakes with Beringer. Any thoughts or alternative suggestions?

Thank you,

David Harris
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David Harris
Vans RV-7A N47HM
First Flight March 2020

Last edited by DavidHarris : 06-15-2021 at 03:20 AM.
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  #2  
Old 06-14-2021, 03:49 PM
gasman gasman is offline
 
Join Date: Mar 2007
Location: Sonoma County
Posts: 4,098
Default

What tire pressure are you running? ....... mains and nose.
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  #3  
Old 06-14-2021, 03:52 PM
BH1166 BH1166 is offline
 
Join Date: Nov 2017
Location: Eatonton Georgia
Posts: 513
Default My 2 cents

If brakes, why just one side? I suspect tube slipped under low pressure, tube was compromised, you got a flat. Flat Tire rolling on rim will not roll, thinking brake not locked. Continue enjoying your efforts…. don’t over think. Beringer good stuff, most have a version of your setup with no issues. Go fly !
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  #4  
Old 06-14-2021, 04:17 PM
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koupster koupster is offline
 
Join Date: Dec 2013
Location: SLC, UT (KBTF)
Posts: 301
Default

David,

I suspect your right brake may have locked up because your right master cylinder did not fully retract. This will trap the fluid in the line, caliper, and master cylinder. When the fluid heats up, it has nowhere to go besides extending the piston in the caliper (thus applying the brake).

There are fixes in the archives including retract springs and one long brake pedal pivot bolt instead of two short ones. It's also possible to trap fluid by never completely taking one's toe off the brake pedal while compensating for a crosswind, for instance.

If it helps, consider yourself lucky that the brake locked up and ruined the tire rather that starting a brake fire.

Did you replace the right brake pads only, or both sides? How does the wear compare side to side?

Like gasman, I'm wondering about your tire pressures.
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  #5  
Old 06-14-2021, 07:41 PM
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flytoday flytoday is offline
 
Join Date: Jun 2011
Location: Houston, TX
Posts: 448
Default Trim the wheel pants?

First few years of flying my -6A I had some unexplained flats. Hole in tubes with nothing penetrating the tire. EAA friend recommended looking at clearance between wheel pants and main gear tires.

Recommendation was having a thumb-width clearance between tire and wheel pants. Got out a Drem**l tool and carved up some fiberglass to increase the clearance.

No more unexplained flats….

Carl
..
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  #6  
Old 06-14-2021, 08:03 PM
Taltruda Taltruda is offline
 
Join Date: Oct 2017
Location: Las Vegas, NV
Posts: 871
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I have had a brake drag, get hot, and not release. It doesn't sound like what you described. In my case, the brake slowly dragged more and more, not suddenly like you experienced. Of I were to guess, could your tire have been low to begin with? And the heat of taxing, may have caused the tube to fail? The lock up may have been the tire jamming in the wheel pant or into the caliper and brake pad? How did the wheel turn after you reassembled things? I imagine the mechanic set the wheel bearing, spun the tire to check bearing drag, then torqued the brake pad, spun the tire again to check drag. .If the brake disk gets warped, I've made shims to space out the outer pad.

Another concern is that you mentioned previous tube failures. In almost 13,000 hours, I've had 2 flats. One on a tubeless Caravan tire, and one on a dry rotted Cessna tube that the valve stem fell off while in the hangar. None while in motion. Is it possible that you are pinching the tube between the wheel halfs? Try putting a tiny bit of air in the tube when you assemble the rim, check that the rim makes a metal to metal sound that indicates you don't have a tube getting pinched. Then do the 3 inflate/deflate cycles before you go to final pressure. What PSI do you run, and how often do you check them?
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  #7  
Old 06-15-2021, 03:20 AM
DavidHarris DavidHarris is offline
 
Join Date: May 2018
Location: Upland, CA
Posts: 152
Default

Thanks to all these ideas.

I've been running my main tires at about 25-30 psi and my nose wheel at 30-35 psi. I visually inspect the tires at each preflight but only have been removing the wheel pants to check pressure when the tire looks low. My last check would have been in March. I measured my left tire after the event and it was still reading 26 psi.

Last fall I did increase the clearance of my wheel pants to at least 3/4" all around.

I'm fairly confident the right brake was locked. When I tried pushing the plane off the taxiway, the right wheel wouldn't budge with three of us pushing. The airplane just wanted to go in circles. Once I removed the brake caliper, three people collectively were able to push the plane back, though the right wheel was of course more reluctant. I don't know what else would have explained that. It is conceivable that a flat occurred first and then something about the flat or sudden stop cause the brake to behave locked, but I can't explain exactly how that would happen.

After reinstalling the wheel, I spun it while the plane was jacked up. The disk doesn't seem significantly warped. There was a very light rubbing of the brake pad on the disk, which I think is normal, and the rubbing varied slightly as the wheel turned, but not much.

I haven't checked the left brake pad since March, but the right has a lot of life in it today and the left brake was in good condition in March.

I thought I was careful about inflating and deflating and avoiding pinches the first time I put the tires in, and I've reread the instructions carefully and been even more careful on my subsequent tires, but I realize I'm more than capable of error.

I know I was not riding the brake continuously; I was very aware of the risk of riding brakes in this situation and was tapping the right brake briefly every few seconds as required for directional control, then fully releasing.
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Vans RV-7A N47HM
First Flight March 2020
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  #8  
Old 06-15-2021, 05:24 AM
BH1166 BH1166 is offline
 
Join Date: Nov 2017
Location: Eatonton Georgia
Posts: 513
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I think you have your main tire pressure too low. You’d be surprised how much better it rolls with say 30-35lbs. Strange how the tube slips inside tire, and pin holes appear.
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RV6A Purchased N72TX
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  #9  
Old 06-15-2021, 06:29 AM
WingsOnWheels WingsOnWheels is offline
 
Join Date: Mar 2009
Location: Plano, TX
Posts: 2,231
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I run my mains at 50psi. 25 is pretty low, remember, they have to spin up from 0-60 in an instant. When you assemble the wheel, make sure the bead is clean of talc (you are using talc on the tube right? You want to tube to be able to move in the tire and the tire to not move on the rim. After you assemble the wheel inflate and deflate the tube a little a few times to make sure there is no twist in the tube.

If the brake did lock up then, as noted before, the pedal not retracting (master not extending) all the way is the most likely culprit. There is a mod to add springs on the brake master and improve the pedal pivot. These are easy to do and super worthwhile.
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  #10  
Old 06-15-2021, 07:07 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,537
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Loose bearings can create brake dragging. 25 psi is way too low IMHO. Possible that tube blew and the now deflated tube was causing an excessive bending moment on the wheel , due to the loose bearings, and that allowed that bending to cause pressure against the pad.

Larry
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