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        Question high kV or low kV for plane with fat fuse?

#1 paulatgis Sep 14, 2010 09:00 AM

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.

#2 Alan Hahn Sep 14, 2010 09:32 AM

Quote:

Originally Posted by paulatgis (Post 16044984)
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.

#3 Bare Sep 14, 2010 12:10 PM

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.

#4 eflightray Sep 14, 2010 01:44 PM

1 Attachment(s)
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).

#5 Dr Kiwi Sep 14, 2010 02:44 PM

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.

#6 flypaper 2 Sep 14, 2010 09:40 PM

If I remember right, the outer third of the prop does most of the work.

Gord.


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