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Brake Fire

J

Jim Wright

Well Known Member
Had a bad experience with my RV-8A. I purchased a low time (200 hrs) 8A and have about 5 hours in it . I was taxiing out from the hangar with about a 12 knot quartering tailwind, and was experiencing difficulty steering down the taxiway, having to use brakes to keep it straight. I experienced the same thing on previous days. As I turned up wind on the run-up pad I smelled something hot which was obviously the brakes. Then smoke began filling the cockpit. I jumped out to investigate and saw that the left wheel pant was on fire and dripping burning resin on the asphalt. I grabbed the small fire extinguisher and sprayed the pant trying to get as much agent into the burning area as I could. The fire went out and the extinguisher was empty. Smoke continued to pour from the pant and I was afraid that it would reignite. I called for help on CTAF without much response. There is no fire department on PWT . I used my cell and called 911. My buddy finally came to my rescue and we towed the 8 back to the hangar. Curiously the smoke entered the cockpit from the MLG fairing. It acted as a chimney allowing the smoke to enter the cockpit and there was a lot of it!
There seems to be adequate air circulation between the brake assembly and the fiberglass pant so it is difficult to believe that the fiberglass would ignite. We are thinking that the overheated brake caliper may have leaked brake fluid on the disk and that the fire started in that manner We are replacing the Vans Cleveland brakes with the upgraded heavy duty assemblies from Cleveland .
I would greatly appreciate hearing from anyone who has experienced brake fires with their RV?s and what you have done to eliminate this hazard. Please give me your suggestions and comments.
 
Hmmm

With some experience in brake fires, I'm trying to figure this one out.

Generally, one way we see brake fires when the friction material is saturated with oil - so a caliper seal MAY do it, or the oil, usually suspended in a thixotropic blend of schmutz(tech term) from a wheel seal, may be source. Plan on doing bearings too, and replace the seals!

Bottom line, is heat was needed, which means not releasing. A single stop shouldn't do it. My recommendation is to GET TO ROOT CAUSE before just replacing stuff. It could be a hanging MC. Or a kinked line. Or . . . .

And as a brake systems engineer, I'd go with Grove rather than Parker - It's what I've done. Robby has his poop in a pile, if you know what I mean.

Rick 90432
 
A number of Cirrus aircraft have had brake fires because of a long period of taxiing with a brake dragging. It is believed that the cause is from the caliper getting hot enough to cause the O-ring to fail which allows fluid to leak out causing a fire.
Cirrus began offering a heavy duty brake upgrade to owners but is continuing to equip airplanes with the original brakes (they felt they did the job if not abused).

While working on your brakes I would suggest you also look at two other things (particularly since you didn't build the airplane).

1 - Disconnect the brake peddles form the master cyl and verify there is no friction at the pivot point of the peddle that could be causing the brake master cyl to not fully extend after releasing the brakes.

2 - Check the brake out resistance of the nose fork for the proper 22 lbs when pulled from the side at the axle. If it is not correct (it does change over time, particularly during the first 50 hrs) it will allow the airplane to weathervane much more easily.
 
Lots of info in the archives.

Short version; caliper reaches 300F or more, nitrile o-ring gets baked and leaks 5056 fluid. The fluid flash point is only 215F (Aeroshell 4). Both the caliper and the disk are already much warmer, and there isn't much air circulation in the wheel pant. The results are predictable.

Mil-H 5056 fluid:
http://www.shell.com/static/aviation-en/downloads/safety_data_sheets/within_usa/AeroshellFluid_4.pdf

Mil-H 83282 fluid:
http://www.shell.com/static/aviatio..._data_sheets/within_usa/AeroshellFluid_31.pdf
 
First, im glad you got out ok Jim, and you got the fire put out also !
Now I dont know what to do, as I will need a finish kit soon for my 7A.
If I use 83282 I still have a problem with the O-ring. Can someone please post the grove assy part number , that I could use on my 7A so I can do a bit of reading.
 
I remember reading (when I was building) about the gentleman who flew his -8 around the world, and got stranded in Southeast Asia for a couple of weeks due to a brake fire - scared the heck out of me then, and still does now! I'd hate to lose an airplane because of a simple failure down in the undercarriage - very glad you got it out and saved both you and the aircraft Jim!

Lots of good advice above already. One minor additional thing to consider is that for some people's geometry, the RV-8 pedal design can allow you to put brake on when you don't want to. You might check to see how your feet are riding on the pedals, and if you think you may be applying brake when you don't need it, there are several mods people have developed as a fix, like a bolt across the bottom of the pedal, or pedal extensions.

Good luck on the repairs - get 'er back flying!

Paul
 
Some info

http://www.vansairforce.com/community/showthread.php?t=9267

Lots of info on this thread. It was started after a brake failure resulted in loss of control on the ground on a 7A. Overheating and failure was due to a dragging master cylinder. Further investigation showed some other reasons for hot brakes.

The springs shown in the thread took care of the binding problems for us.

Grove 56-1A (aluminum wheel) or 56-1M (magnesium) are what Grove recommends for the 7A and have a bit more than twice the kinetic rating as the standard Clevelands. Grove has a calculator on his site that tells the tale.

http://www.groveaircraft.com/wbproducts.html

Check out Aeroshell fluid 31 for the fluid.

A buddy is flying this setup with a 7A. A recent condition inspection showed virtually no heat-related issues with the brakes. They look like new. He also reports vastly improved ground handling due to the more powerful braking available.
 
I have seen RV brakes on fire after a long taxi at SnF. The owner rode the brakes way too much and did not "get off them" until it was too late. Use your brakes sparingly. Make sure you are not riding the brake when turning, or just going straight. If you can turn without using them then don't use them.

It takes a conscious effort to place your feet on the sides or bottoms of the RV peddles to avoid riding the brakes. I know, I cooked the o-ring on my -10. I came back to a puddle of brake fluid after a aborted take off and heavy brake use. I was riding the heck out them and learned the hard way. Ever since I changed techniques I have not had any problems at all.

I'm not looking for a argument, but I think it has more to do with pilot technique than the brakes themselves.

JMHO.
 
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Brake pedal geometry

Early on in my 8 I had brake problems. On my taxi tests, I lost brakes on one side by overheating them and the O-ring melted. I'm sure I was close to a fire as well because my wheel pant was so hot it deformed.

It turns out that in the RV-8, the pedals are designed in such a way that any pressure on the pedal at all -- even just to use rudder -- exerts a force on the brake cylinder. This is true for every 8 built to plans. Get in there and look at the pedal. All of the pedal is above the pivot point (the bolts at the bottom of the pedal). So pushing on the pedal for whatever reason gives you a force on the brake cylinder.

A friend of mine came up with a fix that worked great for all of us at our airport. We replaced the bolts at the bottom with a piece of cold rolled steel that goes all the way across the pedal. In other words, we moved the "push point" aft of the pedal itself thereby removing force from the pedal and brake cylinder. (So just to elaborate, you would remove the two bolts at the bottom of the pedal and then replace with a piece of steel rod that goes all the way from side to side....and that's what the foot pushes on)

I can send photos of this. It's a very easy install and really does solve the problem. It has worked for me for 600 hours now.

This problem is all about the geometry of the rudder pedal.

Safe flying and braking!!

-- Rich Wilson
 
<<It turns out that in the RV-8, the pedals are designed in such a way that any pressure on the pedal at all -- even just to use rudder -- exerts a force on the brake cylinder. This is true for every 8 built to plans.>>

Totally true, and if you have big feet it is worse. I've done the "rod mod" before. I seem to recall a more elaborate pedal mod also. Anyone have pics? I'm going to do something with the new bird's pedals even if I have to weld up a new assembly. The catch to the rod mod is that it steals 3/4" of legroom, and concentrates pressure across your foot if you wear soft shoes.

Dan
 
When I installed my brakes from Vans, I modified them by replacing the standard Nitrile O-rings with Viton (sometimes refered to as Flourocarbon) O-rings of the same size, the Viton has an upper temperature limit about 100-125 degrees F higher than Nitrile, however it is only good down to about -15 degrees F (I'm not too worried about that in Calif.). The other modification i intend to make is to use either the Mil-H 83282 hydraulic fluid or Mobile one Synthetic automatic transmission fluid for an increased flash point temperature. (the temperature at which the fluid will burn in an open container.) If you compare the specification data between the Mobile One synthetic Automatic transmission fluid and the Mil-H 83282 hydraulic fluid, you will find that they are very similar and the I have found that the Mobile one trans fluid is more readily available.

I hav found the best source for O-rings (if you don't need tracability or special compounds) to be Mc Master Carr.

Mike Warfel
RV-8
Finishing
 
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DanH said:
Totally true, and if you have big feet it is worse.
Click to expand...

I can stay off the brakes by using the sides of the peddle "frames", and I have # 12 EEE's. It's a little awkward at first, but it beats the heck out of replacing o-rings, or running for the fire extinguisher. :eek:
 
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Part of the problem is people mount their rudder bars completely vertical. Ideally they should be sloped away from you a bit so your toes aren't hitting the brakes when you're working the rudder. This is part of the problem with people dragging brakes. If you shorten the rudder cable 'links' and mount the rudder bars a little more forward there's no problem. I have had no problems so far in 160 hours and my pads look like they can go another 160 or more. I also installed auxiliary return springs on the master cylinders which I feel helps with brake life.
 
DanH said:
I seem to recall a more elaborate pedal mod also. Anyone have pics? I'm going to do something with the new bird's pedals even if I have to weld up a new assembly. The catch to the rod mod is that it steals 3/4" of legroom, and concentrates pressure across your foot if you wear soft shoes.

Dan
Click to expand...

Here is a picture of the "pedal extension" mod (scroll down to my first panel picture, and you can see the pedal extensions). It is pretty easy to do, and gaurentees that you are taking pressure OFF the brakes, as long as you have your toes low on the pedals. But....it doesn't fit everyone's ankle geometry, so I don't consider it a universal solution. I like it, but have flown -8's without it as well.

It's important to remember that the -8 pedals are different from those on the side-by-sides (and the -4's, and the -3's...), so what works for them might be different than what works on an -8.

Paul
 
burning brakes

during my search for a airplane (rv) i came across an article about brake fires and i believe it was on this site, anyway the solution was to use automotive dot fluid , it is non-flamable-- but here is the critical part-- you must use o-rings compatible with the dot fluid. i will try to find the contact info for this guy as he had to buy a pretty large quantity. good luck
 
m_warfel said:
When I installed my brakes from Vans, I modified them by replacing the standard Nitrile O-rings with Viton (sometimes refered to as Flourocarbon) O-rings of the same size, the Viton has an upper temperature limit about 100-125 degrees F higher than Nitrile, however it is only good down to about -15 degrees F
Click to expand...
Hi Mike - did you change the O-rings in the master cylinders also? I'm planning on running the "other" milspec fluid and am thinking of changing O-rings. Is the Viton only for heat or for fluid compatibility?

I've flown a C150 at -15F, so that might actually be a problem... BRRRRR :eek:

dave
 
Brake fire

Hi Rich,
Thanks for your reply. I would greatly appreciate you pictures of your brake pedal modification. I feel that this is definitely a part of my problem.
Many thanks for your reply.
Jim
 
Brak Fire

Just want to thank all of you for responding to my inquiry. You supplied me with a wealth of information and suggestions. At this point in time we will go to the Grove 56-213 wheel and brake assemblys and change from 5606 to mil spec PRF 8382D if we can find it. Guess my only other question is... where can we find it and is the 8382 fluid compatible with the master cylinder 0 Rings. Grove says their 0 Rings are compatible and that you can flush the 5606 through the system with the 8382 and everything is compatible.
Any other thoughts or suggestions??
Many thanks,
Jim
 
Jamie said:
Part of the problem is people mount their rudder bars completely vertical. Ideally they should be sloped away from you a bit so your toes aren't hitting the brakes when you're working the rudder. This is part of the problem with people dragging brakes. If you shorten the rudder cable 'links' and mount the rudder bars a little more forward there's no problem. I have had no problems so far in 160 hours and my pads look like they can go another 160 or more. I also installed auxiliary return springs on the master cylinders which I feel helps with brake life.
Click to expand...

A quick clarification - they should be sloped up and away from you such that the bottom of the pedal is closer to the top. This is how I've set my -6A pedals up after seeing a bunch of others, including the vertical mounting.
 
IowaRV9Dreamer said:
Hi Mike - did you change the O-rings in the master cylinders also? I'm planning on running the "other" milspec fluid and am thinking of changing O-rings. Is the Viton only for heat or for fluid compatibility?

I've flown a C150 at -15F, so that might actually be a problem... BRRRRR :eek:

dave
Click to expand...
I only changed the O-rings in the calipers for increased heat resistance, there should not be any compatability problems with the standard Nitrile O-rings. The -15 degrees F is a conservative number in a dynamic application, if you expect to spend hours below -15, I would either look for special viton compound rated for lower temps or stick with the nitrile and change them at every annual condition inspection. They get brittle after high temp exposure for extended periods of time. Anything above 275 degrees F gets them close to melting.

Y.M.M.V

Mike Warfel
RV-8 finishing
 
-8 Rudder Pedal Mod

As Paul said, the -8 has different rudder pedals than all the other RVs so the solution for the others may not work (probably wont work) for the -8.

The -8 actually has rudder pedals mounted to the floor, not hanging from above. The cables are on the outside of each pedal making it difficult at the very least to keep your feet on the edges instead of on the pedals.

The mod that Paul was talking about (if I remember correctly) was the same mod that Randy Lervold did, not sure who was first. Seems like a pretty straight forward mod that helps get the pressure away from the top of the pedals.

You can see his mod on his -8 site.
-8 Pedal Extensions
 
RatMan said:
The mod that Paul was talking about (if I remember correctly) was the same mod that Randy Lervold did, not sure who was first. Seems like a pretty straight forward mod that helps get the pressure away from the top of the pedals.

You can see his mod on his -8 site.
-8 Pedal Extensions
Click to expand...

For the record, I stole the idea from Randy - he gets the credit! And it takes about an hour to make and riivet on the extensions - very simple.

Paul
 
Suggest you call Ed Anderson...he's an expert on brake fires. 704-821-7585 in NC. He will explain his incident w/ his 6-A.
 
What to do when it catches fire.

Friend Reg ran out of left brake under the same circumstances, in his Glasair. I have no sympathy for Reg or anyone who mucks about with sticky resins, but I do have sympathy for what followed.

Out of brakes, Reg stopped to let the brake cool.
He then heard a loud pop and got out to investigate.
I was apparent that the left tire was on fire, so he grabbed his fire extinguisher to put it out.
However, the wheel fairing was on the ground due to the flat tyre and he could not get the extinguisher in to spray onto the hot bits.
He tried to smash the fairing, but it had gone all rubbery with the heat and just bent.
As the fire progressed (Lots of resin) Reg ceased fighting it when he heard the fuel boiling in the wing tank and retreated to safety to watch his pride and joy turn to black smoke.
Fortunately there was no argument from the insurance company. and Reg has a new Glasair

Lesson; Have a way of getting the extinguisher inside the wheel fairing.
I used the 1" diam spring loaded plates designed for inserting the hose to inflate the tyres. Available from Aircraftspruce.

One ounce of prevention . . .

Pete.
 
fodrv7 said:
I used the 1" diam spring loaded plates designed for inserting the hose to inflate the tyres. Available from Aircraftspruce.
Pete.
Click to expand...

Pete, what's the Spruce part number for that doodad. And did it allow you to easily inflate the tyre without removing the wheel pant. Did you also need a special extention.

ps. Are you having another grandfinal bash again this year.
 
Dunno! No! Yes!

FO Avgas,
I can't remember the part number and, I must confess, I never fitted them, but just left the hole for the fire extinguisher.
I think I still have the parts; if you want them; but you should just drill a couple of holes and get on with finishing that thing.

And, yes, having an Aussie Rules footy bash. All welcome, but if you don't barrack for Geelong, bring a bodyguard.

Pete.

my.php



Pete, what's the Spruce part number for that doodad. And did it allow you to easily inflate the tyre without removing the wheel pant. Did you also need a special extention.

ps. Are you having another grandfinal bash again this year.[/QUOTE]
 
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Dragging brakes

Jim Wright said:
Then smoke began filling the cockpit. Curiously the smoke entered the cockpit from the MLG fairing. It acted as a chimney allowing the smoke to enter the cockpit and there was a lot of it!
Click to expand...

Good point for the RV's where the MAINS enter the cabin (Model A's and I guess RV-8, RV-10?). SEAL IT UP TIGHT.

Great posts on how heat, o-ring, brake fluid leak, flash point happens.

We all have small brakes and tight wheel pants. This is NOT a RV problem. There have been MANY airplane brake fires recorded in all kinds of planes in the NTSB records.

When a large airliner is certified, they do RTO's (rejected takeoff) at max speed to stopped.

http://www.youtube.com/watch?v=wXpjBxD0Rhg

The brakes glow red and the tires blow out due to over pressure. Inevitably a fire starts. The certification regulations require the plane sit for several minutes before fire fighters can put the burning rubber and grease fire out! They just let it burn! I have seen videos of planes sitting there stopped after an RTO with the tires burning. Not pretty. :eek: Of course successes is the fire does not spread and they put to fire out after a few minutes. If you get something hot enough, anything will burn.

Glad it worked out OK.

Lets all be aware of brake dragging. Its best to use the brakes intermittently, if taxi speed is too fast, check speed to a very low speed and let the brakes go completely. If the speed builds again, check speed again and repeat brake application. This is BETTER than dragging the brakes continuously.
 
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Ironflight said:
Here is a picture of the "pedal extension" mod (scroll down to my first panel picture, and you can see the pedal extensions). It is pretty easy to do, and gaurentees that you are taking pressure OFF the brakes, as long as you have your toes low on the pedals. But....it doesn't fit everyone's ankle geometry, so I don't consider it a universal solution. I like it, but have flown -8's without it as well.

It's important to remember that the -8 pedals are different from those on the side-by-sides (and the -4's, and the -3's...), so what works for them might be different than what works on an -8.

Paul
Click to expand...
As Paul (and others have) said, *modify your pedals* and go fly!! Fix the heat damage too, of course. No need for hi-temp fluid or special o-rings, unless you just want to go through the motions. RV-8 pedals are different. Make the mods and go. I've got 1035, plus or minus a few, happy hours not riding the brakes with my own variant of the rod mod.
 
Brake fire

We're working on it. Pulled the Clevelands and replaced them with Grove Kit # 56-113. Having to modify the wheel fairing brackets a bit for clearance.
I seem to remember that one member mentioned a modicication to provide the brake bleeder valve more clearance in the wheel pant. Would appreciate any suggestions on this.
Every thing going back together nicely thanks to the efforts of some really great friends.
Many thanks,
Jim
 
Check the tightness of the peddle mounts

I talked with Van's about brake peddles and they commented to be sure they are mounted so they are VERY loose as in almost sloppy. No drag on the return. This too can cause break drag and heat 'em up.
 
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