I would love to find someone that could give me some info on building a simple dyno. One horse power is something like 460 watts, don't take that to the bank but for what I'am asking it will do. If I take an altenator and hook up my engine and it puts out 920 watts will that mean it has two horse power or is there a serten type of configuration that must be used.I'am sure that a large alternator would take more power to spin than a smaller say kabota stile would need. So does anyone know anything about this?

1 horse power is 745.7 watts or 33,000 foot pounds per minute .

If your alternator put out 14 volts at 52 amps...that would =728 Watts. Volts X Amps = Watts Does that help Capt,n

This is a cute idea, that unfortunately is fraught with problems. It's just not as simple as it seems on the surface. Too many variables, and unknown in-efficiencies to work out. How much power does it take to turn the alternator itself when it isn't generating power for example? Unknown. I once made up a homemade battery charger for use where I didn't have electricity. I used a 53 amp, 12 volt alternator and a 3.5 horsepower Briggs and Stratton engine. It was all the engine could do to turn the alternator when it was putting out full power, and after a while it would overheat trying. So obviously the alternator was sucking up more energy than it was literally making!

The other problem is the gearing needed. Horsepower is a function of torque and revs. Our engines don't have a lot of torque, but they make that torque many "times" or revs, and that equals horsepower. You would have to rig gearing to enable the low torque of our motors to turn the alternator.

Lastly, our motors usually have a "dyno" bolted onto them; a propellor! If you are after actual numbers, they could be calculated from the prop loading, or for comparisons just bolt props to different engines or different props to the same engine.

AV8TOR

AVATOR: where can one find a chart online for propeller RPM,S with size and Horse Power produced. Wold it be possible to start a new Tread with the most acccurate data from people who post on RCU? Thanks Capt,n

Well, there's always the Thrust HP program. It does exactly what you mentioned. Plug in the prop size and rpms, and it will give the horsepower. It's notoriously inaccurate, but fun to play with. The rcfaq.com site has a huge chart with props, rpms, etc. of various motors.

AV8TOR

A Dyno measures torque not HP. A little math gives you HP.
Just think of a motor mount mounted on bearings that are inline with the crank center. A 1' arm and an digital scale would give you the torque. Change props to give you WOT at different RPM and you would have a HP curve.

I am thinking a setup wherein thrust is measured directly from the motor would be more accurate. The motor needs to be mounted on linear bearings and the slide on which its mounted needs to press on a digital scale. From the thrust and prop size HP at the known RPM can be calculated. By throttling the engine a HP curve is obtained.

I think you have the right idea. If the engine could be mounted on a ball bearing that is centered with the shaft and a torque arm connected to a digital scale, the torque transmitted into the engine from the prop could be measured. That and an accurate rpm reading would allow precise measurement.

Take a look at the thrust measurement system on this page:

http://www.gas-turbines.com/nt5/

http://www.gas-turbines.com/nt5/mount.gif

Sounds doable.

What about this, make a clutch disk to mount as the prop would be and another to be mounted to a dail type tourqe rench . Rench would be mounted to the test bench on a track to alow it to ingage the engines disk. this would give you say inch pounds for smaller moters and you take the reading as you time it,(33,000 fp per min.) and do the math for the hp.

How do the people that sell all these engines measure the the Horse power?..They must have a way to test for Horse power? YA How about that!!!! Capt,n

They use inertia dynos...miniature ones though.

I'm with the guy who said the prop is the dyno.

Contact APC props and ask them how much Horsepower / torque it takes to run their props.

There is a free program called ThrustHP Calculator, it gives a rough idea of the power it takes to turn a prop
at at certain RPM.