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Old Sep 14, 2010, 09:00 AM
Registered User
United States, FL, Melbourne
Joined Apr 2009
431 Posts
Question
high kV or low kV for plane with fat fuse?

im making a halls bull dog with a 7 inch diameter fuselage, wing span about 3 foot, weight about 1 1/2 to 2 lbs. The fuse is similar to a Gee Bee fat fuse. Should i fit it with a low kV or high kV motor? Im just planning on flying it slow and easy, but i think it requires extra speed for all that wind resistance.
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Old Sep 14, 2010, 09:32 AM
Registered User
Chicago 'burbs
Joined May 2006
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Quote:
Originally Posted by paulatgis View Post
im making a halls bull dog with a 7 inch diameter fuselage, wing span about 3 foot, weight about 1 1/2 to 2 lbs. The fuse is similar to a Gee Bee fat fuse. Should i fit it with a low kV or high kV motor? Im just planning on flying it slow and easy, but i think it requires extra speed for all that wind resistance.
It is important to know, or remember, that the actual running of a motor is dependent on both the kV AND the pack voltage. There is basically no difference in efficiency. So a 1000kV motor on a 3s pack will behave identically to a 1500kV motor on a 2s pack. In both cases I assume the same motor family (e.g. Scorpion 3020-xx) and that the battery pack capacities scale as the kV--so if the 3s pack is a 1000mAHr pack, the 2s pack is a 1500 mAHr pack. That's so you are carrying the same energy, and if the "C" is the same, the current capability will also be the same.

The only difference is the 2s system needs to have an ESC with a higher current capability-since the watts will be the same.
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Old Sep 14, 2010, 12:10 PM
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Canada
Joined Nov 2000
6,980 Posts
Your logic is flawed :-) Gee Bee exampled has a Very streamlined/ sophisticated fuse/shape.. despite all shade tree opinions.
It was a successful, purpose designed race machine built for max speed.
Gee Bees don't fly slow happily... wing loading is wayyy too high. IF memory serves wasn't the Bulldog a racer?
If so it's needing a.. much.. lower weight/ wing loading to float about.
Only thing of concern is the amount of prop extending beyond the engine cowl.. as there are views that only the outer edges of props actually do the 'heavy lifting'. Size the prop accordingly, then decide what motor is indicated.
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Last edited by Bare; Sep 14, 2010 at 12:17 PM.
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Old Sep 14, 2010, 01:44 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,166 Posts
If you're looking at fitting a scale size prop, and the cowl is 7" diameter, that's one fair sized scale prop at 13.5".

For that you would need a fairly low kv outrunner, (or inrunner and a gearbox).
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Old Sep 14, 2010, 02:44 PM
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Chattanooga, Tennessee, United States
Joined May 2003
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A KEDA TR2837/16 (~920Kv) swings a 13x6.5 at 21A/220W on 3s... that gets you 43oz thrust but only 37mph... you might be better with a 12x8.
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Old Sep 14, 2010, 09:40 PM
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Kingston, Canada
Joined Jun 2004
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If I remember right, the outer third of the prop does most of the work.

Gord.
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