RV-6 Incident

[jetjok]

Saw this on the web today. Dragging Brake?
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IDENTIFICATION
Regis#: 109RJ Make/Model: EXP Description: RV6
Date: 09/29/2009 Time: 1740

Event Type: Incident Highest Injury: None Mid Air: N Missing: N
Damage: Unknown

LOCATION
City: ENGLEWOOD State: CO Country: US

DESCRIPTION
AIRCRAFT ON TAXI, REPORTED RIGHT MAIN GEAR CAUGHT FIRE, ENGLEWOOD, CO

INJURY DATA Total Fatal: 0
# Crew: 1 Fat: 0 Ser: 0 Min: 0 Unk:
# Pass: 0 Fat: 0 Ser: 0 Min: 0 Unk:
# Grnd: Fat: 0 Ser: 0 Min: 0 Unk:

WEATHER: 1753Z 10SM FEW090 27/M03 A3002

OTHER DATA
Activity: Pleasure Phase: Taxi Operation: OTHER


FAA FSDO: DENVER, CO (NM03) Entry date: 09/30/2009

[craigvince]

Contradicting report?

Highest Injury: None

INJURY DATA Total Fatal: 0
# Crew: 1 Fat: 0 Ser: 0 Min: 0 Unk:
# Pass: 0 Fat: 0 Ser: 0 Min: 0 Unk:
# Grnd: Fat: 0 Ser: 0 Min: 0 Unk:

No injuries or 1 Fatal ?

[Radomir]

No injury... that "1" is referring to "Crew" not to "Fatal"... (and it's not contradicting... just hard to read)

[craigvince]

Got it. Thanks!

[flyeyes]

This appears to be a -9A, and the right brake is typically the one to fail.

This is a known issue with castering nosewheels, since the brakes are required for ground steering, and the right brake gets more use. There are multiple reports in RVs, Cirrus, and other aircaft with tight wheel pants and castering nosewheels.

There was an AD issued on Cirrus SRxx aircraft which required bigger brakes, a hole in the wheel pants, and a "telltale" thermal sticker on the caliper to determine if there had been an overtemp.

This is avoidable with careful technique (Our Cirrus, which is only flown by three pilots, had the original factory brake pads when we complied with the AD at 800 hours TT) but the record suggests it continues to bite people.

There are some simple, cheap steps you can take to IMHO reduce the likelihood of this problem. I have no data to support this, but I think the theory is sound:

"Standard" MIL-5606 red brake/hydraulic fluid is a very old glycol-based fluid with a relatively low flash point. It is flammable. It is used in light GA aircraft mainly for historical reasons I think. Larger aircraft have long since abandoned it for other alternatives.

MIL 83282 (a.k.a. Royco 782) is a red, glycol based, hydraulic fluid that is completely compatible with 5606. The two may be mixed in any proportion, and changing your fluid out only requires draining and refillling. You can top of with either fluid in a pinch. 83282 has a much higher flash point, although it is still flammable. Its downside AFAIK is that it performs poorly at very low (like -50 degrees) temps.

83282 is not Skydrol, which is nasty stuff.

The standard O-rings in the brakes we use will soften and deform at relatively low temps. This is what causes the brake fire--an overtemped o-ring loses its ability to seal, and allows brake fluid to escape onto the very hot brake disc. Viton o-rings tolerate much higher temps, and cost pennies.

Changing the brake fluid and o-rings (you only need to do the ones in the calipers if you are changing to mil-83282) takes maybe a half hour and $30. My belief is that it lowers the risk for this type of problem.

[Jamie]

Originally Posted by flyeyes

This is a known issue with castering nosewheels, since the brakes are required for ground steering, and the right brake gets more use.

True, for the most part. I would like to add though that the brakes are not the only method for ground steering. The large rudders on our airplanes are surprisingly effective.

With 300 hours on my -7A now I have discovered that I never need to use the brakes to taxi straight in calm to breezy (< 10kts) winds. On long straight taxis I can keep it on the centerline using the rudder with zero problems and even make most gradual turns using the rudder (especially if going uphill...uphill = more power = more prop blast over the rudder). For what it's worth, I have the newer, larger rudder (same as the -9A).

The only time I really ever have problems keeping the airplane on the centerline during taxi is with a tailwind. A direct tailwind means little or no air over the rudder OR if the tailwind is blowing faster than my taxi speed the rudder essentially becomes reversed and messes me all up.

Going around tight turns, etc. of course requires brakes.

[AlexPeterson]

Originally Posted by flyeyes

snip

This is a known issue with castering nosewheels, since the brakes are required for ground steering, and the right brake gets more use. There are multiple reports in RVs, Cirrus, and other aircraft with tight wheel pants and castering nosewheels.

snip

I have the small tail 6A, and I almost never use any brakes when taxiing. With any power setting that will get the plane to move, the rudder is quite effective. The only exceptions are hard turns from one taxiway to another, and even those are usually just a jab, and strong (>15 knots) crosswinds.

I would not call it an issue with Van's nose wheel designs. The issue might be when people do not use the rudder to its full stop prior to using brakes. Taxiing with a strong tailwind will also require brake jabs. Something is wrong with a technique that requires anything other than jabs.

[flyeyes]

Originally Posted by AlexPeterson

I
I would not call it an issue with Van's nose wheel designs. The issue might be when people do not use the rudder to its full stop prior to using brakes. Taxiing with a strong tailwind will also require brake jabs. Something is wrong with a technique that requires anything other than jabs.

Philosophically I agree with you, and we have a lot of experience in a Cirrus SR22, which has developed a reputation among some for "eating brakes" although others with identical airplanes seem to have excellent brake life. We got 800 hours on the original brake pads, and only changed them to comply with the AD. I'm not at all shy about using the brakes on landing, and typically turn off at midfield (1700'). I just don't use them to taxi much.

However, the record suggests that, for whatever reason, as a group we don't do this very well. I'm also bothered by the idea that a single episode of carelessness can result in a brake failure or fire. As an example, I recall the gentleman who flew his RV-8 around the world--He had a brake fire after a single bad landing with excessive brake use. The tailwheel airplanes don't have this history AFAIK, but a single landing was enough to fail the system and almost cost him his airplane. Better o-rings and brake fluid would have given extra margin for abuse.

I'd rather have my airplane as robust as possible, especially when a potential fix is this easy and cheap

[Ron Lee]

A year ago I replaced all the O-rings in my brake system. The caliper o-ring was replaced with one made of Viton. I don't recall what brake fluid I used but at least the o-ring should not fail.

I got the parts from Ace Seal in Santa Clara CA and got beaucoup extra o-rings.

[plehrke]

Originally Posted by AlexPeterson

I have the small tail 6A, and I almost never use any brakes when taxiing. With any power setting that will get the plane to move, the rudder is quite effective. The only exceptions are hard turns from one taxiway to another, and even those are usually just a jab, and strong (>15 knots) crosswinds.

I concur as this matches my experience with my RV. I have always been taught that brakes are only to be used around the gas pumps. I do not even use brakes on landing. I hold the nose up for aero braking until I turn off the runway (RV have lots of elevator authority). Aircraft flying and ground operations require technique. (not going to even start the nose wheel landing technique debate.) You can get by with brute forcing things but eventually you may encounter issues.

Also, get your engine idle set as low as possible.