Tire question

As both a mechanic and flight instructor, looking after six
airplanes, I can say that flat-spotting is normally a result of
improper approach speeds. The airplane shouldn't be landed until it's
ready to land, and for most lightplanes heavy braking shouldn't drag
tires if the landing speed was right. We get people in a 172
approaching at 65 or 70 knots, where 55 is often enough, then holding
that high speed until a sudden flare near the surface and touchdown, in
a really flat attitude, almost immediately. The end of the runway comes
up fast and they try to stop it using lots of brake, when there's still
no weight on the wheels. End of tires. Flaps make it worse.
As the textbooks say, use the recommended approach speed. You
won't stall and fall down unless you're not paying attention. At
anywhere from 15 to 30 feet, start the roundout (raising the nose to
check descent and get rid of the speed), getting the power off, and
touch down with the nosewheel well off the surface. Stall warning
should be honking before touchdown. Any heavy braking should be
accompanied by full up- elevator to place even more weight on the
mains.

Dan

As both a mechanic and flight instructor, looking after six
airplanes, I can say that flat-spotting is normally a result of
improper approach speeds.

This is all right and proper, of course -- but it doesn't address the issue.

Which is: Why is one tire flat-spotted, while the other is not?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Ron Natalie wrote in
m:

Margy and our mechanic blame me for anythign that breaks. And I
haven't broken any rudder pedals since I bought 4 spares at the
aeromart at Oskosh a decade ago.

Sign at the BBQ place I eat:

"I have a very responsible job around here."

"No matter what goes wrong, someone
always claims I was responsible."


Someone questioned earlier if you were always landing on one wheel vs. the
other. Quite possible. At my home airport, probably 90% of the time the
landing is with a quartering left front crosswind. So the landing is
almost ALWAYS left main first. Could be something similar, so "familiar"
that you don't even think about it.

Then again, could be that one wheel just needs alignment. G

jmk

Jay Honeck wrote:
As both a mechanic and flight instructor, looking after six
airplanes, I can say that flat-spotting is normally a result of
improper approach speeds.

This is all right and proper, of course -- but it doesn't address the
issue.

Which is: Why is one tire flat-spotted, while the other is not?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

One brake might have a bit more authority than the other. One
tire might have a slightly lower coefficient of friction. The pilot
might have a little stronger right foot. He might have a habit of using
a bit of unnecessary aileron in the landing roll, lifting one wheel a
bit. There are plenty of variables. If the brake isn't dragging more
than it should, and the bearings aren't too tight, there's no other
explanation for bald spots. The occasional sharp turn shouldn't do it,
though that can wear the tire more than usual. By the way, I've seen a
tire flat-spotted even when it was dragged on a wet runway.
A pilot should examine his technique when he notices excessive
tire wear, just as he should rethink engine management if his fuel burn
is too high or the airplane's belly is all black and sooty. We're often
too quick to blame the machinery.

Dan

Jay Honeck wrote:

As both a mechanic and flight instructor, looking after six
airplanes, I can say that flat-spotting is normally a result of
improper approach speeds.


This is all right and proper, of course -- but it doesn't address the issue.

Which is: Why is one tire flat-spotted, while the other is not?

You're heavier on that brake than the other. You may be riding that
brake during takeoff or landing without knowing it.

I spent 25 years maintaining larger aircraft. We didn't get flat
spots because they have anti-skid systems, but the right brakes and
tires always seemed to wear faster on my company aircraft. The reason
- most of our pilots were right handed. A right handed pilot will
have a stronger right leg and that is the side that got pushed first
and the hardest. You can watch the brake pressure gauge in the
cockpit and tell on the first landing if he is a lefty or not.

I spent 25 years maintaining larger aircraft. We didn't get flat
spots because they have anti-skid systems, but the right brakes and
tires always seemed to wear faster on my company aircraft. The reason
- most of our pilots were right handed. A right handed pilot will
have a stronger right leg and that is the side that got pushed first
and the hardest. You can watch the brake pressure gauge in the
cockpit and tell on the first landing if he is a lefty or not.

Interesting stuff. Thanks, Don!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"
"Don Hammer" wrote in message
...

Then again, could be that one wheel just needs alignment. G

You know, I was wondering about that. Can a fixed landing gear be "cocked"
to one side or the other? That would wear a tire out in no time. (Although
it wouldn't explain flat-spotting...)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:

You know, I was wondering about that. Can a fixed landing gear be "cocked"
to one side or the other?

One can be, but the effect would be to produce either excessive or insufficient
toe-in with a tendency for the aircraft to move a little sideways on the ground.
If bad enough, it will require noticeable rudder input. It would not produce
different wear patterns on the mains. Bending one axle either up or down *would*
produce an odd wear pattern on only that one wheel, but only a tendency for the
wear to be on either the inside or outside tread.

George Patterson
He who would distinguish what is true from what is false must have an
adequate understanding of truth and falsehood.

Jay Honeck wrote:
Then again, could be that one wheel just needs alignment. G

You know, I was wondering about that. Can a fixed landing gear be "cocked"
to one side or the other? That would wear a tire out in no time. (Although
it wouldn't explain flat-spotting...)

Cherokee main gear *can* be aligned. It's described in the maintenance
manual. You adjust it with shims that look like really big, but thin,
washers. They go in the upper and lower joints of the trailing links. By
shimming on one side of the link or the other, you remove any slop, and
tend to cock the axle in one way or the other. I've shimmed mine, but
we kinda' eyeballed which side the shim needed to go. It worked out OK.

Cherokee missalignments tend to show themselves in the common "inner"
tread wear. I "fight" that problem by unmounting and remounting my tires
backwards, after the start wearing the inner surface.

The type of flat spotting that you describe seems more likely to be a
brake problem.

--- Jay


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