Brake Failure on an "A"

As you know if you don't have brakes on an "A" model RV you can't steer it. I have now had both the static and dynamic failure experiences and they produced a couple of lessons learned. Earlier in the year I went out to the plane after visiting a friend in Panama City Beach, FL. I saw a wet area on the ground in the area of the right main gear. I didn't think much of it and I've had brake failures before and I have been able to touch the good brake for speed control and steer with the nose gear. I wanted to get home... I started the engine, applied a little power to overcome inertia and applied the left brake to come out of the tie down. The castering nosegear pivoted and the plane spun around the left main gear. The right brake was totally gone!There was no way to break the turn and all I could do was cut the power and hold it in its spinning location until the kinetic energy was overcome by rolling friction. My friend and I fixed the right brake problem with a lot of creative work but the line was disconnected several times in the process.

Fast forward several months until this past Sunday. I was flying out to Southern California and was making a fuel stop at Prescott. I landed on 21L and was well into the right turn off onto taxiway C-5 when the right brake went out instantaneously. When the aircraft is rolling it has some stability and the nosegear will not pivot over to the stop (limit). The remaining brake does work in a semi-normal fashion. I was headed for a colision with the first taxi light after the taxiway identifier sign and I was able to stear to the left of it by applying the left brake. When I released the brake, as you might expect, the the force of the moving airplane returned the nose gear to the center and I rolled out into the "grass" between the runway and the parallel taxiway (C). I had previously noticed the fitting on the right brake line was wet but it wasn't dripping so I did nothing about it. I now have a basic tool kit in the plane as a result of my Florida experience. After getting the plane towed to the ramp, I removed the fairing and found that the aluminum line was broken at the AN fitting. When I removed the AN fitting I found the flare still inside. I have a generous service loop so I was able to borrow a miniature tube cutter, a flare tool, a pump and hydraulic fluid from an aircraft service company on the field and fix it. The final lesson learned (there are several here) was, if the AN filling is wet, it is leaking and is not reliable.

Bob Axsom

What can happen...

.. when you can't avoid obstacles when a brake fails.

Bent tank

Bent spar

Ugly story..
Av Consumer had a sidebar article about a Cirrus fire when the right brake failed. They hit upon the fact that you hit the right brake a lot to counteract Pfactor even on the ground. More wear and tear on the RH brake.

Same thing happened to me at 30 hours

It was with my first passenger in the plane (naturally). We were coming back from a lunch fly-in, and I was showing off how I could land it short enough to make the first turn-off. I used a lot of brake, but the landing was fine. Then I taxied to my hangar's apron and mashed the left brake to spin it around. The pedal went to the floor. I shudder to think what would have happened if it had failed a couple of minutes earlier!

Just like you, I found that the flare had failed at the AN fitting.

I've mentioned this before. That 3003-0 tubing that Van's supplies is a problem. It's so soft that it's difficult to get a good flare in it without getting a crease where the two halves of the tool come together. The crease causes it to leak. So then you tighten it down till it quits leaking. But that grade of aluminum is so soft that you can actually flatten the flare paper thin by just tightening the flare nut. Then all it takes is a heavy foot and you've got a brake failure -- and possibly a fire.

The solution is so cheap I don't understand why it's not in the kit: 5052-0 tubing. I think it cost me about $20 to replace all the 3003-0 in my plane. It flares beautifully and you can't torque a flare nut hard enough to crush it. And it's no more difficult to bend and shape than 3003-0.

The lesson learned should be that brake calipers slide back and forth, and occasionally chatter and sometimes an out-of-round tire will make them move around on the pins.

All this suggests that the connection from gear leg to caliper should be made with flexible braided brake line hose, and not solid aluminum tubing.

Good Point

You're right of course John but this has to be thought out and done right to avoid a sub-optimum fix. A clamp securing the hose part of the line downstream of the aluminum tube seems desirable. There could probably be an attach point made on the wheel fairing aluminum mounting plate some way. As indicated by my past mistakes, I am a strong proponent of the "If it ain't broke don't fix it" school but this one is on the back burner of my mind for sure.

Bob Axsom

Bob Axsom said:

You're right of course John but this has to be thought out and done right to avoid a sub-optimum fix. A clamp securing the hose part of the line downstream of the aluminum tube seems desirable. There could probably be an attach point made on the wheel fairing aluminum mounting plate some way. As indicated by my past mistakes, I am a strong proponent of the "If it ain't broke don't fix it" school but this one is on the back burner of my mind for sure.

Bob Axsom

Click to expand...

Bob, sounds like it is broke. You could keep the al tube that runs down the gear leg, and put a bulkhead fitting on a small piece of angle that is clamped to the leg or part of the wheel pant brace or something. The flex hose could be only 10" long or so, and just go from the fitting to the caliper. It would be inside the wheel pant.

As you pointed out, brakes are very important, especially with castoring nose wheels. I think you have been lucky so far, but I don't want anything to happen to your airplane...I need my racing buddies!!

Gary Bricker

I am building a 7A and have already installed flex brake lines. You can have them made any length at any good hydraulic hose shop. Mine are true brake rubber brake line material with the correct fittings.

This is mostly related... I just want to add a bit of clarification regarding the need for brakes to steer the -A models. I have found that about the only time I need to tap a brake on my 6A is when I want to make a sharp turn. General taxiing in straight lines or in gentle turns does not need any brakes. It may, however, need full rudder. A strong crosswind may also require the use of brakes, but again, don't ride them but just tap them from time to time. Anything above idle power gives the rudder quite a bit of authority, even the small -6 rudder.

I have used about 1.25 sets of brake pads in 814 hours and about 1100 flights. The average taxi distance per flight is around 1 to 1.5 miles at my airport.

I don't go easy on them

I think in my normal operation I would go through the right brake pads every year and a half. They are fairly cheap (in airplane terms) and easy to change so my current procedure is to just use them in a way that seems natural and change them at each annual. When I go to full right rudder on takeoff it is difficult to tell if there is any brake pedal deflection or not. I suspect that I catch some brake although I consciously try to avoid it because of the affect on acceleration.

Bob Axsom

Flex all the way down?

My brake-bitten buddy is going over to Parker AirQuip at KADS this week to get some custom, absurdly high pressure, full length (fuze fitting to caliper) hose made up. I'm tagging along cuz brakes 'R me.

Can't see why this wouldn't address all issues on the gear leg. Maybe a skosh heavier?

John

lucky333 said:

My brake-bitten buddy is going over to Parker AirQuip at KADS this week to get some custom, absurdly high pressure, full length (fuze fitting to caliper) hose made up. I'm tagging along cuz brakes 'R me.

Can't see why this wouldn't address all issues on the gear leg. Maybe a skosh heavier?

John

Click to expand...

2 RV9As and a Mustang II at my home 'drome have steel braided brake lines from the fuse to caliper. My RV has'nt flown with them yet but my buddy's has-approx 100hrs with no problems so far. I've gone with the steel braided lines mainly because I didn't trust my flares,and also another buddy who is building a 7 and flying a Grumman had a factory aluminum line crack and leak. I made some zip-tie standoffs to keep the lines from chafing the gear legs. I'll pay the minor weight penalty for a little peace of mind. Greg RV9A N4603X res.

I'll sell my 9A braded lines

I made steel braded lines for my 9A when it was first built. They cost about 70 dollars and where very easy to make. I have taken them off the plane because they are too short for my new 9 gear legs. They are still assembled. If anyone is interested in them, send me a PM.

Greg Dillon said:

I made some zip-tie standoffs to keep the lines from chafing the gear legs.

Click to expand...

Try some poly tubing the whole length of the gear leg. It allows the lines to move up and down the gear legs and you can fiberglass the gear stiffers over it.

I had a similar experience recently with a brake tube cracking.

On landing I only had right a brake on a 7A Directional control is fine while there is still airflow over the rudder and the problems only start when you try to taxi.

The problem was obvious as there was fluid all over the leg of the aircraft. The first time we found a small hole/crack in the tube just below the fitting (not the flange). A temporary repair was made by filling the hole with an epoxy type flue and binding it with some rubber and locking wire. The temporary repair did not last and almost immediately started to leak again. On removal of the fairings the second time we were surpirsed to se that the temproary repair was fine but that there was a further larger rack lower down.

A picture of the crack can be found at http://www.avcom.co.za/phpBB3/download/file.php?id=63084 The temp repair can be seen above the crack.

Any ideas why it would crack like that? The only two suggestions I have had are that the tubing had a defect and that the tube was fixed to the gear leg and could have been stretched at the break.