### Airfoils for Tailless Airplanes: Design and Selection

Airplane Types and Moment Coefficient
Moment Coefficient and Airfoil Shape
Reflex and Moment Coefficient
Reflex and Lift & Drag
Location of Camber and Moment Coefficient
Velocity Distribution and Boundary Layer
Dangers everywhere
Airfoil Design for Light Tailless Airplanes
Conclusions

## Moment Coefficient and Airfoil Shape

The shape of an airfoil can always be thought of being composed of two parts: a camber distribution (camber line) and a thickness distribution, which is distributed along the camber line. The requirements for the three classes of tailless planes can be translated in corresponding airfoil shapes and wing twist distributions. The only way to achieve a positive moment coefficient and the required amount of lift is to use a S-shaped camber line, which is also called a reflexed camber line.

• wing without sweep (plank)
A positive moment coefficient results in a reflexed camber line. A twist does not help for stability, but can improve the stall characteristics of the wing.
• swept wing
Low moment coefficients and a small amount of twist can be achieved by airfoils with little camber and a neutral or slightly reflexed camber line.
• wing with a low position of the center of gravity (parafoil)
The moment coefficient poses no strong restriction on the airfoil shape.

Classes of tailless airplanes and their typical airfoil shapes.

Airfoils with strongly reflexed camber lines are usually not used on conventional airplanes - they are unique to tailless airplanes. From the aerodynamicists view, airfoils with `reflex´ are quite difficult and very interesting to develop, because they are very sensitive with respect to changes in Reynolds number.

Thus the following sections will concentrate on airfoils with reflexed camber lines, as they are used in tailless planes with no or little wing sweep.

Airplane Types and Moment Coefficient
Moment Coefficient and Airfoil Shape
Reflex and Moment Coefficient

Last modification of this page: 21.05.18

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