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Jul 09, 2001, 06:41 PM
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Joe Elston's Avatar

Modeltech ME 109 Electric Conversion Which Prop?

Well I bought my ME 109 today and the specs are pretty close to what I had guessed. 45 inch wing and 360 inches of area. Weight with a 25 glow is supposed to be 3.2 pounds. The plane is pretty lightweight for an ARF. My question is that I will be using my AStro 805G Brushless 05 with Superbox. The Ratio is 3.3 to 1. What prop do you think I can use on the plane? Astro says to run a 12x7 but if I could get it down to a 10x8 that would be great on 8 RC 1900 cells and 2400's/
Thanks Joe
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Jul 09, 2001, 11:05 PM
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Old rule of thumb states:
Decrease diameter by 1" and increase pitch by 2" and it will turn the same rpm

Difference will be higher level flight speed with less vertical.

I'd guess you would need more like a 10/10 if you want to stick to that diameter.

An 11/9 would be the same ( see rule above ) as the 12/7

Jul 09, 2001, 11:46 PM
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rcastab's Avatar
I want to plug in your parameters into electricalc to see which is best. What turn is your motor, or what is the rpm/v?
Jul 09, 2001, 11:56 PM
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Originally posted by rcastab:
I want to plug in your parameters into electricalc to see which is best. What turn is your motor, or what is the rpm/v?
Stab my motor KV is 3500 RPM/Volt. I am not sure how many turns the motor is.
Thanks Much Joe
Jul 10, 2001, 12:31 AM
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rcastab's Avatar
If you want to use the 10x8, 10 cells is best. If you want to use 12x7, 8 cells will be fine. Assuming you end up with a 3.5lbs airplane after conversion, you can get 80 to 70 watts per lbs, respectively to the mentioned setup above. And your wingloading will be about 24-25 oz/sq feet, and about 19-20mph stall speed, so when you land you might have to fly it down. Also both setup will draw a maximum 29.5 amps, so it's okay.
And the figures are from electricalc version 2. Good luck and let us know how it goes.

[This message has been edited by rcastab (edited 07-10-2001).]
Jul 11, 2001, 12:21 AM
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Thanks allot Stab, I emailed Astro Bob last night and he also advised me to use the 10x8 or even 9x8 props. He also said to try an 11x8 and that I can add a cell with the 9x8 and 10x8 props. So I will try 8 cells on a 10x8 APC first and see what kind of performance I get. I also ran some numbers through E Calc 2 and got about the same as you.
Thanks Allot Joe
Jul 09, 2002, 07:34 PM
Registered User

ME-109 + 805G experience

I have been flying this plane with the 805G in it now for
about 6 months with a 12-8 APC prop on it and 10 2400mA
cells with no problems.

I did make new landing gear wires 1/2" longer an raked 1"
more forward than stock for the large prop and to improve
ground handling.

I also added an exaust scoop on the bottom of the fuse behind
the wing which really helps to cool the batteries and motor.
After a 5 minute flight at full power, the batteries are warm and
the motor is not too hot to touch.

Good luck!

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