1) This is meant to go on the propeller hub. Thus, the rpm should be
3,000 or less. If you are planning to use the engine in an airplane, you
will have to get a propeller to spin something like 3000 RPM, so it is
the most sensible way to connect the brake dyno. You get to load test
the PSRU while you are at it.

2) The disk is never going to get hotter than boiling water. If it does
get too hot, pause the test and let it cool down. Turn up the water flow.

3) Trailer disks are made of stainless steel.

4) I think a large diameter chunk of wood is more likely to come apart
than a small diameter stainless disk.

5) A long lever will make the side loads small. Put the lever on the
side that pushes down so it tends to counter act the weight of the brake
mechanism. It will also hit the floor if something goes wrong. Make the
lever 4 or 5 feet long to get the side load down to a hundred pounds or
so. The PSRU should be able to take a hundred pounds of side load. If it
won't, you would want to find this out on the ground. You can put on a
second arm to make the side load zero if it is important to you, but you
will have to put on a second load cell (or scale).

6) You can easily adjust the hydraulic pressure by closing a closing a
"line lock" valve and then operating the handle of a second valve closer
to the caliper. As you twist the valve stem in and out, you will
displace fluid and move the brake pucks quite nicely. Nice for fine
tuning. Use a porta-power hand pump to set the starting pressure.

7) A trailer brake has all the parts you need and nifty mounting bolt
holes to boot.

8) A 12 inch steel disk with a 5 inch hole spinning 3000 rpm would
experience a maximum stress of about 4500 psi. Obviously no problem.

   At 7000 rpm, this maximum stress goes up to about 25000 psi.
Annealed stainless steel has a yield strength of 30,000 psi minimum.
Thus, 7000 RPM is on the edge. If you were to go with a 10 inch disk
brake instead, this would drop the stress down to 20,000 psi. Probably a
smarter move if you want to go to 7000 rpm. I wouldn't stand next to it,
regardless.

Bill Dube'

-------------------------------------------
Thanks Bill.

What size trailer are we talking about?

I think you are assuming a simple disk. Most truck brake disk
I have seen recently have vent holes and the outer mass is displaced
from the plane of the disk as in this 3D. If so there will be a bending stress
tending to deflect the disk backwards into a cone shape. This will
then vector add to the stress caused by the centrifugal forces.

Also the thermal stresses of spraying water on a red hot disk
are not going to help the stress distribution. No doubt it
will cool the disk.


Paul Lamar

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