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Old 11-03-2005, 05:51 PM
  #24  
Rotaryphile
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Default RE: Why Lifting Stab?

Just to get my two bits worth in, any stable airplane must have its CG ahead of its overall center of aerodynamic pressure. The center of aerodynamic pressure on the wing is at about 25% of the mean chord behind the leading edge. If, as is nearly universal, the CG is aft of 25% of mean wing chord, you have to have lift from the stab, or the model would pitch up violently, requiring corrective a stabilizing upward force from the stab. That is all there is to it. It's just simple physics.

A lifting stab does not have to have camber - i.e. - flat bottomed; a symmetrical section will do just fine, and produce less drag too boot, since stabs seldom develop a very high lift coefficient, and can't take much advantage of a cambered section.

I used to build free-flight duration models with 50% stabs that had their CG close to the trailing edge of the wing. These very clearly had lifting stabs, or they would have been radically unstable in pitch. Having rather long tail moments, their stabs developed at least half the lift coefficient of the wing, and the large stab helped to control high power in the rapid climb.