foam Mirco disk help

[jmezzio]

I am working on a foam disk 11" dia and using 2 mm thick foam. My servos are the Micro Jeule type and work great. I need some pics or drawing on small disk or oval shaped aircraft with 10" or lower WS. How do I calculate the CG on a disk?

I am having some control problems with this one. It uses a 3 cell Lipo and a small GWS direct drive motor. It has elevon control. I basicly flyes all over the place on it's own and even hovers. It's fun but I would like to be able to make it fly more stable and controled.

Jack

[Dave Robelen]

Hi,
It sounds like you are having CG issues, most likely tail heavy. With no seperate horizontal tail, the CG will need to be 10-15% of the chord behind the LE. Propery rigged, it should take a significant amount of up elevator to trim level.
How about making a mock up glider with the same layout, but with a weight to represent the equipment. Some tossing, and shifting things about should help establish a workable CG, and suitable control sizes and settings. Can be fun too.
Regards, Dave

[jmezzio]

Hi,
It sounds like you are having CG issues, most likely tail heavy. With no seperate horizontal tail, the CG will need to be 10-15% of the chord behind the LE. Propery rigged, it should take a significant amount of up elevator to trim level.
How about making a mock up glider with the same layout, but with a weight to represent the equipment. Some tossing, and shifting things about should help establish a workable CG, and suitable control sizes and settings. Can be fun too.
Regards, Dave


Dave what about Dihedral? I have a silight one. Also how big should the elevons as a percentage? I made mine too big I think. They are around 25% of the area.

I want to make my next one less than 8". What is the formula for wing surface to weight ratio? and what is the lowest that will fly with a 3 cell lipo 250mh and that direct drive GWS motor.

Thanks again

[Dave Robelen]

Hi,
I would leave out the dihedral. A stubby flying wing of this type has ample dihedral effect without adding more. As far as the control surface size, 25% is not too large if you limit the movement while you are learning the flight characteristics.
I doubt that your question about minimum size for a given battery and motor can be answered without testing. When you are dealing with unconventional designs, and especially at such small sizes, there are no real decent guidelines to work from.
Regards, Dave