I went out yesterday to fly for the first time in three weeks, but with the last flight's leftward-veering problem fresh in my mind. But I ended up cancelling my flight, and now I'm not sure whether I have a real problem or an imagined one.

As I was pushing the Pitts out of the hangar, I heard a slight grinding noise up by the main gear. I went around and listened to each main gear wheel as I slid the airplane back and forth. The left main seems to make the most pronounced noise, although both sides were making it to some extent. In addition, the left side makes a periodic squeak or chirp as the wheel rotates. I thought that the brakes might naturally be dragging ever-so-slightly, but I wanted to test things to see if there was any connection between this noise and my (real or imagined) left-veering issue.

I know already that, with the tailwheel unlocked, the airplane wants to turn left as it taxis. So to take the engine and turning prop out of the equation, I simply pushed the airplane at fast-walk speed along the ramp, got it tracking straight, then let it go. It does turn to the left as it drifts to a stop, regardless of which way I'm pushing it along the ramp, so I'd guess this is not just the result of a sloping surface or a weathervaning rudder. The left turn is enough to put the tail about three feet right of center by the time the airplane has stopped.

So, does a test like this show that there's really a problem? Significant enough to cause the excitement I saw last time on takeoff and landing? It's hard to imagine that some misalignment of the main wheels or tailwheel has suddenly appeared in the three flights I've had since the ferry pilot's problem free flight in November. But perhaps the cold weather has caused a sticky brake caliper or something.

Or maybe it's just me.

Tom P.

• RE: Brake Rub, a.k.a., Am I Nuts?,DHamblin, 18:03z, 01-27-03
• RE: Brake Rub, a.k.a., Am I Nuts?,Ben_Chiu, 21:27z, 01-27-03
• RE: Brake Rub, a.k.a., Am I Nuts?,Ninepilot, 06:27z, 01-28-03
  • RE: Brake Rub, a.k.a., Am I Nuts?,djpacro, 10:24z, 01-29-03
• RE: Brake Rub, a.k.a., Am I Nuts?,TomParsons, 13:26z, 01-29-03
  • RE: Brake Rub, a.k.a., Am I Nuts?,djpacro, 02:48z, 01-30-03
    • RE: Brake Rub, a.k.a., Am I Nuts?,TomParsons, 16:17z, 01-30-03

Perhaps the wheels need aligning? Not sure on a Pitts how this is done though.

As for the grinding, on our C150 (which has to sit outside for now) the rotors will get a fine layer of rust. The first couple brake applications or initial taxi will make a sort of grinding noise.

After a couple of applications its gone though.

There was an article on the American Aerobatics site that delt with wheel alignment for taildraggers. Not sure if it was on the guest or members side (joining is free if on the members side).

Its http://american-aerobatics.com/pubs/mp_taildragger.pdf if you want to take a look.

Dave Hamblin
(formerly DaveH on old site!)

Greetings Tom:

> I went out yesterday to fly for the first time in three weeks, but with
> the last flight's leftward-veering problem fresh in my mind. But I ended
> up cancelling my flight, and now I'm not sure whether I have a real
> problem or an imagined one.

I had a somewhat similar brake problem yesterday on a dual flight with two students. We were to fly in a Warrior and discovered during our brake check that the copilot side right brake was inop., the pilot side right brake was marginal, and the parking brake was inop.. Needless to say, the flight was scrubbed.

> So, does a test like this show that there's really a problem?

I'm not familiar with the Pitts braking system, but it's not uncommon for a brake to drag on other airplanes. The taxi test and brake test will usually be enough to indicate whether the aircraft is behaving abnormally, but I understand how your unfamiliarity with the airplane caused you to question this. Most of the time, a dragging brake pad (when observed while pushing the airplane) will sort itself out during taxi (the debris between the pad/shoe and the disc/drum will dislodge). Regardless, In no uncertain terms, you did the right thing by cancelling your flight. When it doubt, have it checked out.

Please keep us posted.

Ben

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Registered to: Ben Chiu
-OLR.PL v1.80-

Hey Tom--

I'm not sure what your swerving problem is, but I had a similar problem in my Eagle last summer, and I'll give you my story. Here's what happened to me.

I bagan to fly my Eagle for the first time last spring with Greg Poe, my instructor. Greg used to be Aviat's factory test pilot, so I trusted his judgement. We quickly found that my Eagle was a "wild child" on the ground, after landing. This thing scared the hell out of me on landing, as it would dive toward the weeds after touchdown, usually to the left...a few times, Greg saved my bacon (and my airplane), and I was beginning to wonder what I had gotten myself into. Greg's opinion was that my airplane was OK, but just a little "wild" on the ground. I hated that assessment, because I had little tailwheel time, and the last thing I needed was an airplane that was "a little wild". "Wild" was not my "thing".

After what seemed like a million landings, I decided that I needed to get to the root of the problem, so Greg and I decided to fly the Eagle to Afton, WY (the Aviat factory) to get the gear alignment checked. Since we were in Boise, ID, the flight wasn't too far...about 2 hrs. It was really fun to fly over the mountains of Idaho and Western Wyoming, and seeing the factory was like living a dream to an aerobatic novice like me. They gave me a personal tour of the place, and I was mesmerized....

Anyway, I told them of my problem, and they did a full check of the gear alignment, and they found the problem...but it was not what I was expecting..

Anyway, they found the gear to be within 1/4 inch of factory specs...they looked at it all day...test flew it several times...and in the end, found the tires to be bad..they were buckling under side-loads...they put two new tires on it, and it tracked beautifully....

So..look at everything...and don't overlook the obvious. Good luck...

Dan

The Biplane Hangar archives has a thread on checking and correcting main wheel alignment.
http://www.gf24.de/biplane/

Another item to check is the condition of the brake disc. They can corrode and crack at the inside corner.

Dan - say g'day to Greg for me.

Regards,
Dave Pilkington

Thanks for the responses.

I appreciate the suggestions regarding wheel alignment. But I am asking at the moment about the potential brake rub issue. I'm focusing away from alignment for now because I know the ferry pilot reported the airplane was tracking straight when he delivered it in November. Is it more likely that I've bashed the thing out of alignment in the 20 or so landings I've put on it so far, or that the cold has caused a sticky brake?

Since I posted last, a couple of local pilots have offered to taxi around and see whether they have a problem.

Tom P.

P.S. djpacro, I've been gobbling up that biplane hangar archive, including the 2001 and 2000 archives, since you pointed me there! It's in my regular rotation of places to check. I haven't joined, only because I'm not a builder.

I shud've expanded on my comment regarding the brake disc. Once cracked it can distort and I've heard sounds from one something like those you described. Take a close look at it.

Regards,
Dave Pilkington

Thanks very much, Dave. I'll take a good look at the disc at that inside corner. Also, I got some advice from the previous owner of the airplane to make sure the whole caliper assembly has some play in it relative to the disc.

To answer a previous question you had, I did confirm that my spring gear is aluminum, not spring steel. That "spring steel" misnomer somehow made it into the airplane's logbook.

Tom P.

P.S. I see that, unlike the ACRO list, you are able to post to this sophisticated board without resorting to any kind of time-travel! It's good to see that causality still rules in some corners of the universe.