This is probably the cheapest dyno to make and the most useful.
Not only will it measure your actual HP in the air on a
continuous basis but it will help greatly when optimizing
your propeller. It works the same way as a torque meter on
a PT6 turbo prop engine. It measures the un screwing force on a
helical gear set. It works best with a pressure
sensor and a digital read out but a 360 degree mechanical
pressure gage will also work. It is based on an invention
of mine 35 years ago that is now widely used through out
the world as a manual transmission clutch throw out system.
You are probably driving a car that has one in it. Consequently
The annular hydraulic cylinder could be scavenged from a junkyard.
Look for GM cars with V8's. Ideal if your building you own
PSRU.
-- 
Paul Lamar ...No rotor no motor.

I would really like a controllable pitch prop but will settle for a club for
now. The controllable pitch prop would enable good data for graphs.

I like the idea of the clutch throw out as torque meter. I will  look into
some kind of a data logging system for data collection. I got Linux
installed on my laptop, so all I need is a data collection system with a USB
interface. Maybe Tracy's EC and EM could be adapted. Do you have a
recommendation for a pressure sensor?

Doc Custer
Retired Software Engineer and sometime Audiologist


FreeScale from Digi Key 0-100 PSIG 0-5V out.
Same package Tracy uses in his EFI. About $18

The exact pressure range will be determined by
the area of the annular piston. The force is a function
of the gear helix angle (I think it is 37 degrees) and
the applied torque up to 225 ft pounds for a P-port.
More for a turbo. Tracy knows more about this as he has
already gone through a helical gear thrust bearing design
exercise with one false start :) See the pdf file.

Part number MPX 5700 DP-ND
http://www.digikey.com/

DigiKey web site sucks so request a catalog.
Also see the Free Scale pdf file.

-------------------------------------------------

BTW Doc even a controllable pitch prop will run into an
RPM brick wall about 6000 RPM static due to the tip velocity.

If you want to measure take off HP at 7500 RPM you will need some
sort of shortened prop. Variable pitch or other wise.

I guess you could put it in the back of your pick up
truck and let it push you at 100 MPH :)