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A solar car compromises to get power from a solar array, so the teardrop needs to be flattered or have a flat portion added. Bullet designs tend to add a streamlined large surface for the solar array to a general teardrop shape, where catamaran’s are example of where a teardrop is flattened to accommodate the solar array.
Near the ground there is a “ground effect” caused by an airfoil. When there is an aerodynamic shape moving near near the ground, there is a low pressure area created. This is because the flow under the must pass through a minimum ground clearance, as the area the flow can pass through opens up toward the rear, air cannot replace it, which causes low pressure and induced drag. This is fixed with camber, and I believe it can also be applied to the space between two fairings on a catamaran. Camber is a bending of the centerline for an airfoil.
Side Profile of an Airfoil
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Camber: A measure of the curvature of the airfoil
The camber of the upper surface is more pronounced than the camber of the lower surface (usually somewhat flat).
Leading Edge: Forward facing end that is rounded
Trailing Edge: Rear facing end that is narrow and tapered towards the rear
Chord Line: Reference line drawn from the centre of the leading edge straight through the wing till the trailing edge.
This reference line is used to find the magnitude of the upper or lower camber at any point along the wing (by measuring the distance between the chord line and the upper and lower surfaces of the wing).
Mean Camber Line: Another reference line drawn from the leading edge to the trailing edge.
However, unlike the chord line, this line is equidistant at all points along the wing from the upper and lower surfaces.
Airfoils are designed in such a way that the shape takes advantage of the air’s response to certain physical laws. Hence, two actions from the air are developed as the wing passes through. A positive or high pressure lifting action from the air mass below the wing, and a negative pressure lifting action from low pressure above the wing.
Teardrop wing profile results in the speed and pressure changes of the air passing over the top and under the bottom to be the same.