We already know, that the moment coefficient Cm and the shape of the camber line are closely connected. If we examine airfoils with a reflexed camber line more closely, we find, that the shape of the rear part of the camber line has a big influence on Cm. In fact, it is possible to adjust the shape near the trailing edge to achieve nearly any desired Cm. The figure below shows how Cm can be controlled: starting from a symmetrical airfoil, a flap is deflected smoothly upwards by 5° and 10° - the moment coefficient follows the deflection.
The plot of moment coefficient vs. angle of attack shows,
how cm depends on the amount of reflex.
Using this trick, the problem seems to be solved. We simply bend the trailing edge upward until we achieve the moment coefficient necessary to stabilize our tailless plane and there we go...
But we probably prefer an airplane, which not only flies safe and stable, but also performs with a low sink speed, a high penetration speed and a good L/D ratio - that's where all the trouble begins.
Last modification of this page: 16.02.08
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