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Wetted Area, Frontal Area, and Parasitic Drag

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Aerowerx

Well-Known Member
Joined
Dec 1, 2011
Messages
6,092
Location
Marion, Ohio
This is a spin-off of the poll thread on tailless aircraft pod/cabin location. I was trying to find a way to see just how much difference there was between tandem and side-by-side seating. My results were interesting enough that I thought they deserved its own thread, and the results have a general application anyway.

Many of the methods for calculating parasitic drag involve dividing the surface (wetted) area by some reference. As a good first approximation to a pod, I used an ellipsoid (football, or rugby ball for those outside the USA) shape.

For tandem seating, an ellipsoid 12 feet long, 3.5 feet high, and 2.4 feet wide was used. The formula for the surface area of an ellipsoid gives an area of 89.95 ft^2

For side-by-side seating a 8ft by 3.5ft by 4ft ellipsoid was used, and the surface area came out to be 39.92 ft^2 This is less than half of the tandem configuration.

But what about the reference area? While searching around, I came across a reference to using the frontal area in this situation, which is simply the cross section of the ellipsoid at the largest dimensions. So the tandem arrangement gave a frontal area of 6.597 ft^2 and the side-by-side 11.00 ft^2.


The result is that the Swet/Sref=13.63 for the tandem case and 3.63 for the side-by-side. These numbers can then be used to calculate the parasitic drag.

In this simple analysis, then, it is clear that side-by-side is the winner.
 
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