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Forula for determining engine size?

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Forula for determining engine size?

Old 08-15-2016, 06:05 AM
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H5487
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Default Forula for determining engine size?

I've seen the info on RCU before but I can no longer find it. What are the formulas for sizing nitro and electric motors to an aircraft? I remember that the formulas were based on the model's weight vs the desired performance. This is something I need to print out for my Holy Binder of R/C Knowledge.

Thanks!

Harvey
Old 08-15-2016, 06:28 AM
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Rafael23cc
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Here's a little reading for ya:

https://www.google.com/webhp?sourcei...o%20calculator

And if you keep in mind that "WATT" is a unit of power, you could easily convert to nitro engines:
https://en.wikipedia.org/wiki/Watt

Rafael
Old 08-17-2016, 01:59 PM
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jester_s1
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Getting the watts/horsepower requirement right is the easy part. Determining how to use that power is what's tricky. Take my J3 Cub for example. The manufacturer suggested a .46 2 stroke engine for it. That engine was rated for about 1.6 HP, and realistically probably made 1.1-1.2 HP in actual use. It spun an 11x6 maybe 12k RPM and flew the plane ok. I then switched to a Saito .72 which is rated for a bit less HP, but has a lot more torque. It turns a 12x8 around 9600 RPM and flies the plane much better.

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