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Old Apr 02, 2012, 04:59 PM
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CM Analysis in Aerofoil Selection

Hi All,

I've been told before that a Clark-Y on a delta wing configuration RC-aircraft is unstable due to the presence of a strong CM (pitching moment). It was suggested to use another aerofoil (I've forgotten off the top of my head what the substitutes are) or the Clark-YH which is a Clark-Y with a Reflex @ TE

My Q...

1) Looking at Cl-Alpha curves please explain (in layman terms aswell) how to know what is a strong Cm value and what isn't.

2) Can pitching moment not be corrected by relocating the CG of the battery etc (electrical componenrts within the fuselage cavity of the aircraft) rather than choosing another completely different aerofoil?

3) I need calculations to carry out in an 'Aerofoil analysis', I've done calc's on Re # of my design comparing CL's at that design-Re for a number of diff aerofoils but i havent even looked at CD or Drag values nor have i looked at Cm's...which now seems to be a concern because the kind members here have prev pinted out that Clark Y on A delta wing config is unstable... hence why i NEED calc's to back this up...

4) Is a reflex aerofoil easy or hard to's a college project... we dont have state of the art machines just milling/CNC machines etc.
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