# 2-Cycle power curves... want more thrust

Discussion in 'RC General & Getting Started' started by imarocktscientst, Jun 8, 2004.

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1. ### imarocktscientstNew Member

Does anyone have accurate power curves for airplane engines in the .40 to .90 range? I have some ideas to get more thrust out of them, but I need the curves to test my theory.

Thanks
2. ### iluv2boostNew Member

I dont know What A Power Curve is, What is it?
3. ### imarocktscientstNew Member

A power curve is a graph that shows you how much power an engine produces over its entire operating range of RPMs.

For example, suppose you have an engine that produces 2 HP at 16,000 RPM (according to the manufacturer) but you and just about everybody else run props that only allow the engine to turn at 12,000 RPM. How much power are you actually getting out of your engine? If you had the graph of the power curve, you could find the RPM your running at and then find how much power your engine produces at that RPM from the graph (and probably be disappointed that it is much less than 2).
4. ### imarocktscientstNew Member

Here are some more details about what I'm doing:

I wrote a script for designing and analyzing the performance of propellers. I've tried to reproduce the shape of commercially available propellers and compare their performance to test data I've obtained (static thrust). The results from the program come very close to the actual performance in terms of static thrust vs. RPM. Now I want to see if the power requirements for the propeller (as predicted by the program) match the output of the engine.

WHY SHOULD ANYONE CARE?... Suppose you're running a .60-size engine on your plane. First, the propeller efficiency (how well it turns power from the engine into thrust) is about 50%, although it varies a lot. Second, you're probably turning somewhere in the neighborhood of 12,000 RPM. If you're using the O.S. .61 FX rated at 1.9 BHP at 16000 RPM but only spinning at 12,000, (and this is what I need to confirm) the engine is only producing about 0.85 BHP. This means that only about 0.43 HP (50% of 0.85), or about 22% of your engine's rated HP, is actually turned into thrust.

If the power curves for these 2-cycle engines are shaped as I suspect, then it is possible (in theory) to increase thrust by over 60%.