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 thecaliber 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 bySteve
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


FYI... According to my W&B figures, with pilot, no pax, and 50 gal fuel,
there is approx. 520# on the nose wheel and 707# on each of the mains.

Mark

A lot of weight is transfered to the nose gear under braking.
If I were building a high rotary powered STOL airplane like the
Zenair 801 with a nose wheel I would add braking to the nose wheel.

Paul Lamar



Hmmm.  There's 1414lbs on the mains.  I also think in this case, the
thrust of the prop doesn't cause any weigh transfer from the mains to
the nose.  Draw out the free body and I think the pivot is about the
main wheels.  With a u of 1, that means you should be able to generate
a maximum of 1414lbs of thrust before moving the airplane.  Assuming:

- Thrust line is parallel to the ground
- The wing generates no lift
- The airframe isn't bouncing around because of airflow over the
fuse, wing root, and tail (this is counter to my experience - most
airplanes bounce around when running how power sitting on the ground)

I think the reality is that the thrust line isn't parallel to the
ground, the inboard section of the wing is generating a bit of lift,
and the airframe is moving around some - adding some dynamic load.  I
could see 1000lbs of thrust sliding the airplane.

Matt-