Flying wing CG
07-24-2002 | 02:23 AM
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From: Lee\'\'s Summit,
MO
Flying wing CG
I have never been able to figure out a "formula" I usually make a model of foam in the same proportions and shift the weight until the thing flies then I balance the big one the same and everything works.
07-24-2002 | 09:01 AM
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From: Punta Gorda, FL
CG
A tailless model must have the CG ahead of the aerodynamic center of the wing to provide pitch stability ( unless a gyro is used to provide pitch stability). The aerodynamic center (AC) is near 25% of the mean aerodynamic chord (MAC) of the wing. For straight taper planforms, there is a simple geometric construction that will give the MAC. See:
http://www.usrcjc.org/howto/MAC.htm
There is also a free download of a MAC calculator at:
http://www.dchobby.com/airfoil/maccal.html
There are conflicting objectives involved in selecting how much ahead of the AC to place the CG. As the stability is increased (CG is moved forward), more and more up trim is required and the increase in up trim is acompanied by decreases in lift and increases in drag. Putting the CG at the AC and using a gyro is a solution with fewer performance penalties.
At model sizes and speeds the AC location may vary a bit with angle of attack. This complication can be delt with by choosing a safe, forward CG to begin flight testing and gradually moving the CG back and retrimming to a point which is the best compromise between stability and efficiency for the type of aircraft and the skill and flying style of the pilot.
http://www.usrcjc.org/howto/MAC.htm
There is also a free download of a MAC calculator at:
http://www.dchobby.com/airfoil/maccal.html
There are conflicting objectives involved in selecting how much ahead of the AC to place the CG. As the stability is increased (CG is moved forward), more and more up trim is required and the increase in up trim is acompanied by decreases in lift and increases in drag. Putting the CG at the AC and using a gyro is a solution with fewer performance penalties.
At model sizes and speeds the AC location may vary a bit with angle of attack. This complication can be delt with by choosing a safe, forward CG to begin flight testing and gradually moving the CG back and retrimming to a point which is the best compromise between stability and efficiency for the type of aircraft and the skill and flying style of the pilot.
