Paul,

Slide-throttle update: I received the 1/32" teflon from McMaster and
made a
piece to fit between the teflon slide and the inner aluminum plate.
While I
had it apart, I milled about .040" off the height of the slide to
allow for
expansion. I'm happy to report that the actuation forces are now very
acceptable, even after a good heat soak. This is one powerful engine.
During tuning at about 3/4 throttle, the brakes could no longer hold
it. I
guess I need to find a big tree. I've been told that the exhaust
tone isn't
louder, just throatier. Cooling system appears to be up to the task.
Stay
tuned...

Mark S.

If the brakes do not hold it you probably have static thrust about
equal
to the gross weight.

Some where between 1500 and 2500 pounds. What is the weight?

Paul Lamar



2080 lbs empty.

Mark in Texas

Wow! Here is a physics question for everybody. How much
net out of the prop HP is Mark's engine generating? Assume
the coefficient of friction between tire and pavement is one.

Paul Lamar

Are the wheels turning or are the tires sliding? I got the impression
that the wheels are turning in which case the force is unknown.


Matt-

If you are pushing as hard as you can and the brake pedal
or master cylinder is bottoming out then your brake lines
are too flexible. Your caliber could also be deflecting
excessively.

The brake lines can be fixed with steel lines and
double braided -3 Teflon flexible brake lines.
If the caliber is deflecting excessively then you have
more serious problems. You should be able to lock the wheels.
You may need to go to a larger diameter master cylinder.

Paul Lamar

Actually, to increase the hydraulic pressure, you need to DECREASE the
master cylinder piston area for a given amount of applied pressure on the
piston. Pressure (psi) equals force (lbs) divided by area/

Joel

True. But I am assuming Mark can apply more pressure on the brake pedal
and the system needs more volume to compensate for system deflection.
If the master cylinder bottoms out no more pressure or fluid are possible
and
there may not be enough fluid to expand all the things that need
expanding such as brake lines and calibers.

We identified this problem years ago and started designing calibers
based on deflection. Rubber brake lines were changed to double braided
Teflon lined -3 AN to reduce expansion.

BTW I helped write a book on Racing Braking systems published by Steve
Smith
Autosports wherein all this was discussed.

Race Car Braking Systems book
by Paul Lamar and Steve Smith
Steve Smith Autosports
1975

Paul Lamar


One would need to assume a few things:

- The thrust line is parallel to the ground. If the thrust line is
angled upward it reduces the weight applied to the tires, reducing the
friction available.

- The airflow over the inboard section of the wing is negligible, and
hence the lift generated by the inboard section of the wing is also
negligible. If the wing is generating significant lift, the weight
applied to the tires is again diminished, reducing the friction.

- The weight on the nose gear is negligible. This is the big one
because the nose wheel isn't braked. The weight the nose gear takes
again reduces the friction available.

None the less, the friction: f=Us * Fn : The coefficient of static
friction times the normal force.

Am I on the right track or have I exposed my ignorance?


Matt-

Results in a few days :)

Paul Lamar

Sorry if it's already been mentioned and I claim no expertise. But is it
possible he just needs bigger brakes?

http://www.groveaircraft.com/brakedesign.html

Jay

Depends on what you mean by bigger brakes.
The disk size is limited by the wheel size.

Paul Lamar


It's not actually critical that an airplane be able to remain
stationary during a full power run up. Lots of airplanes generate
enough thrust to either roll the wheel or slide (skid) the tires when
full power is applied (most modern jets, many WWII fighters, some
sport planes).

The more critical things are whether the airplane has enough braking
power to adequately slow during a landing roll out, and that the
brakes can dissipate/store heat well enough during roll out so that
the braking power is maintained.

A side issue on aircraft with caster wheels (either nose or tail) is
that they may have problems taxiing for long distances with a
crosswind blowing as differential braking is required to maintain
directional control. In such a circumstance, the brakes may heat to
the point that they become damaged, or cause damage to other parts of
the airplane. Airplanes with tight fitting wheel pants and plastic
gear legs (most EZ's and Cozy's) need to consider this

Adding pucks/pistons to the caliper can increase the braking power -
good for big tires. More pucks/pistons doesn't particularly help in
dissipating heat. Going to a larger wheel/disk increases the amount
of energy that can be dissipated/absorbed.


Matt-

All true but it still does not answer the question.

Paul Lamar