Re: Measurements.camber

Bob Farnam <bfarnam@...>

The thing that has always bothered me is that all spring gear airplanes - C120,
C140, C170, C180, C195, RV's, Christen Eagle, to name a few have considerable
camber change under different conditions of load. You can include in that list
bungee gear types like all of the ragwing Pipers. This has never, to my
knowledge, been identified as causing a directional stability problem. My
thinking is that camber, at least a few degrees either + or -, doesn't have
much effect. I have felt all along that the primary problem was that the
airplane as originally designed, lacked the full complement of steering tools
present on other taildgraggers.

Here's another point to think about. David G, in his original analysis,
referenced a race car dynamics book which said that toe was about 5 times as
effective in producing side thrust at the wheel as is camber, per degree. So we
have airplanes which produce about -3 degrees of camber due to canard deflection
which would make the left wheel, for example, produce right side thrust. Now if
you divide 3 degrees by 5, you get 0.6 degree, which is exactly the toe out
(left side thrust) set for the left wheel. Is is possible that Quickie
understood this relaionship and that the 0.6 degree toe out was deliberately
done to counteract the negative camber? Or is it just a coincidence? I don't
know the answer to this, but the numbers do agree exactly.

I'll say this. The negative camber does cause tire wear to be off center to the
inside of the tire. I don't know whether that's good or bad. I let the tire wear
on one side, then turn them around and wear the other side. I am getting about
175-200 hours per set of tires. I should go back and count the landings made in
that time to get a better comparison with other airplanes. The Gall alignment
should even out the tire wear, but maybe should include removing the toe out
when it is done. Has anyone experience with a "zero-zero" setting for toe and

Bob F.

"David J. Gall" wrote:

Neither am I!

However, I still stand by my earlier notes that +ve camber is good. Several
people have made the +ve camber change and reported an improvement in ground
handling from this one change alone. On the other hand, some have not made
the change all the way to positive camber, but have still reported better
handling just reducing the negative camber. Maybe there's a "magic number"
for negative camber -- go more negative and the handling gets really bad,
but stay on the positive side of that number and things are OK. I had
thought the magic number was zero, but Jim and Bob make a strong argument
for -3 degrees. I just don't know. It's a lot like finding the aft CG limit.
When you have positive stability, there's a whole range of CG locations that
all offer positive stability, but when you go aft of the aft limit, there's
a whole range of CG locations that are ALL unstabile. Maybe Bob Hoover can
fly in this range on some airplanes on some test flights, but can Joe
average pilot do that on all flights all the time? I'm not saying Jim and
Bob are in this range, I just don't know where that range starts. I do think
that range includes zero camber and small positive camber angles, so that's
what I wrote. I entertained the possibility that some negative settings were
okay when the first person to take my alignment advice, Michel Royer,
advised that he had good results even though the brake mechanism made it
impossible for him to get zero camber. Jim and Bob are reinforce that

The bottom line: +ve is better than -ve. The question now seems to be, what
is the -ve limit?

David J. Gall

-----Original Message-----
From: Jim Patillo [mailto:patillo@...]
Sent: Sunday, December 30, 2001 10:00 PM
To: Q-LIST@...
Subject: Re: [Q-LIST] Measurements.camber


Better ask David that question as I am not an eng gin eer.

Jim Patillo N46JP Q200

----- Original Message -----
From: "Neil Jepsen" <jepsen@...>
To: <Q-LIST@...>
Sent: Sunday, December 30, 2001 6:08 PM
Subject: Re: [Q-LIST] Measurements.camber

This means you have -ve camber. Davids original notes recommended +ve
camber so does this mean camber is not all that important, or is -ve
better than +ve?

Jim Patillo wrote:

David Gall,

We checked Farnams' axle heights yesterday. They are exactly the same
as mine. What a coincidence! The floor to center of axle measurement
is 3/8" lower on the inside as compared to the outside of the wheel
pant. (full fuel and no pilot/pax/bags).

We set our axles using the " 2" forward of the original axle hole
sighting method". Thus we believe our planes both have .6 degrees toe
out and - 3 degrees camber. Incidentally, they both handle the same,
which is right down the center line on take off and landings.

What does this suggest to you regarding your thinking on this matter?


Jim Patillo N46JP Q200
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