Airfoils

Parts of an Airfoil

Leading Edge

The leading edge of an airfoil is the first part of the airfoil in the free stream. It will change with the angle of attack (AoA) of the airfoil.

Trailing Edge

The trailing edge is the furthest rearward edge of the airfoil.

Chord

The chord of an airfoil is the distance from leading edge to trailing edge. It is measured by drawing a straight line from the LE to TE.

Camber

The camber of an airfoil measures its shape. The camber line is drawn from the leading edge to the trailing edge, staying equidistant from the top and bottom surfaces of the airfoil at each point. The camber at each point is thus the distance from the camber line to either the top or bottom surface of the airfoil. For a symmetric airfoil, the camber line and the chord line are the same.

Airfoil Selection

Airfoils are available in various shapes and forms and the right airfoil may not even exist for your application. To get an understanding of the variety of airfoils you should check databases such as airfoiltools.

Airfoils can be compared by different key parameters such as $C_{l}$, $C_{d}$, $C_{m}$ and the change of these parameters over the angle of attack. To compare an airfoil, the Reynolds number gives an insight on the ratio of chord length to airspeed (simplified). The Reynolds number is given as:

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): Re = \frac{\rho u_\infty C}{\mu} = \frac{u_\infty C}{\nu}
, where Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle C} is the chord length, Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \nu} is the kinematic viscosity, and Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle u_\infty} is the free stream velocity. To check the Reynolds number on your design visit airfoiltools Reynolds number calculator.

Additional Parts

Endplates

In a standard wing with no endplates, the wing experiences induced drag due to the high pressure region above the wing coming around the edge to the low pressure region below the wing. This creates vortices and adds extra drag to the vehicle. In a plane, the aspect ratio of the wing can be increased to limit this effect (think about a glider, they frequently have really long wings with a short chord, increasing wing span while limiting wing area).

For our vehicles, we cannot extend our wings outside of our wheels, and thus need to find a different solution to limit our induced drag. Adding endplates physically prevents the high pressure and low pressure region from interacting, thereby reducing the drag generated from this effect. Sadly, endplates can generate their own drag through similar effects. The high pressure ambient air can "spill over" into the low pressure region captured inside the endplates, creating vortices and drag.

There are a few different methods to reducing this drag:

Louvers

Louvers are small cuts in the endplate, generally found above the mainplane and in front of the flaps. These cuts allow some of the high pressure air in this region to escape, which lowers the overall pressure in this area. Lowering the pressure can reduce the downforce generated, but can also reduce drag by limiting the strength of the created vortices.

Slats

Slats are generally found below the flaps and behind the mainplane, toward the rear bottom corner of the endplates. These slats allow some of the low pressure air to escape, thereby reducing the downforce and drag generated, similar to the louvers.

Supports

When designing supports, it is important to take into account deflection and adjustablity