1: Make a stand to mount the motor on similar to some of the rotating engine
rebuilding stands, only use a small truck wheel that uses 2 timken bearings,
and a hollow axle---mount the axle rigid to the stand.
2: Attach a big plate or framework to the wheel, using the lug bolts as attach
points.
( I made my framework motor mount points the same as the mount points on
my fuselage, to allow testing different engines)
3: The motor mount MUST hold the engine with it's PROPELLER center line-
centered on the wheel hub.
4: extend an arm---horizontally-if you want to use a bathroom scale--with a
single ball(from a large ball bearing) welded to the bottom of the arm at a
precise
distance from the center of the wheel hub.You will want a smooth plate of metal
on the scale platform to make the contact point constant & little friction.--I
used
a little pneumatic cylinder with an accurate pressure gage, & air pressure
regulator
to hold the tork arm in the center of the travel of the cylinder.
If you have a conventional Rt. Hand prop, --the arm should project out to the
left,
as you stand behind the engine--
which is where I mounted a panel with all the usual engine instruments.

Run the engine, measure the pressure on the scale(subtracting any tare wt.)
Multiply by the length of the torque arm-(in feet).--This is your torque in Ft.
Lbs.

Measure the PROPELLER RPM--which equals engine rpm divided by
the ratio of the PSRU ( if you have one)
Then your HP =
Torque X RPM X 2pi 2pi= 3.14159 X 2 =
6.28
------------------------
33,000 1 HP = 33,000 ft lbs
per minute
( the 2pi X arm length gives the distance the arm would move, if the propeller
were held still--)
NOTE: record the temp, & actual barometric pressure----when your figures seem
a little puny, you can correct them to sea level, std baro, & temp (68 OR 70
DEG.F) I fergit which.

Note: this makes a nice club project where everyone can test their engines.
If you get real interested, I can send a pic of mine .

Andre wrote:




So now I'm thinking...
How do I measure the Horsepower of my Sonerai's 1835cc VW motor?
Or do I just make a couple of assumptions?
Prop 52" dia. 42" pitch motor can turn it 3000rpm static at WOT and a ground
elevation of 5000 feet and temperature of 31 degrees Celsius or 87.8 degrees
F.
Assuming that the prop is more or less efficient (guess 80%???) where does
that leave me?