Hi guys,

What is the best way to determine thrust for a given engine with a given propellor size? I've tried a couple of Javascript converters, but got dramatically different results.

Is there a formula? Is there a good way to hook up the engine to a scale of sorts to measure thrust?

Thanks in advance!

There are inaccuracies in most of the thrust formulas particularly with the bigger prop sizes.

The only accurate way is with a fish scale.

Enjoy,

Jim

Every engine is slightly differrent from the next, as is every prop. Actual testing is the only accurate way to measure. Many companys are marketing thrust measuring engine stands. You can build your own and use a fish scale to measure thrust. I have found however that my digital fish scale may not be accurate enough to derive very accurat readings.

Thanks, guys. Do any of you have any design pictures of how something like that can be set up? Regarding the mounting of the engine, the connecting of the engine to the scale, and so forth.

nothing complicated, just a fish scale connected to the back of your plane.

But wouldn't the weight of the plane interfere with the thrust as shown on the scale? Or would one add the weight of the plane to the final thrust? I may be way off on this...[&o]

Scub:

All you can measure is static thrust, and the weight of the plane has no effect beyond the rolling friction of the wheels. As the engine is running at speed, push the plane forward until the scale reading goes up, then gently stop pushing and note the reading just as your hand comes off the plane. Then pull the plane back against the thrust, and carefully let the engine slowly pull it back. Again noting the scale reading when you let go of the plane.

Ideally the two readings will be the same, but if there is a difference it's caused by rolling friction, the true thrust is the average of the two indications.

Bill.

Ah, I see. Thanks for the explanation.