 Copyright ©2019 by Paul Niquette. All rights reserved.  ingsuit
flying is a sport that dates back to the
'90s. It features gliding
flight in the sky-diving experience.
The ratio of Lift-to-Drag
L/D determines the glide angle. With
training, an angle of about 20 degrees to the
horizon can be achieved, which means that for each
meter of vertical descent through the sky, the
flier moves about 2.5 meters horizontally. The Wingsuit Aerodynamics puzzle calls for a comparison between the two wingsuit designs depicted above, with one question: Which wingsuit has the better glide ratio? As shown in the sketches, the surface area of the suit on the right is 25,775 cm2, which is 41% larger than the surface area of the suit on the left. One might think that that answers the question. Best keep thinking... The key parameter for gliding flight is Aspect Ratio AR, and AR is defined for a rectangular wing as the ratio of span to chord. An alternative definition can be used for a wing with a complex planform: Divide the square of the span by the surface area of the wing. We see above that the suit on the right has an aspect ratio of 1.12, which is 41% less than the AR of the suit on the left. To answer the question in the puzzle, we need to compare glide ratios. The glide ratio of a wing foil is equal to the Lift-to-Drag ratio L/D, which is proportional to the square-root of the Aspect Ratio AR. We observe that the L/D for the wing on the right divided by the L/D for the wing on the left = 1.06 / 1.26 = 0.84-to-one. Surprised?
If the wingsuit on the left moves forward 2.5 meters for each meter in descent, the wingsuit on the right will move forward only 2.1 meters. Its angle of descent of 25 degrees is five degrees steeper. Care to explain why? Glide Angle in Ski Flying
 Photograph © Daniel Karmann/picture alliance by Getty Images
Gazing
at this 2018 Bing
Wallpaper photograph taken at a ski flying event in
Innsbruck, Austria, your puzzle-master
observed the positioning of the competitor's
skis during the 'flight phase'. The
technique is called V-style.
Inasmuch as the skis are acting as wings, one might suppose that the approximation for glide ratio used in the solution for Wingsuit Aerodynamics puzzle might be useful here... Aspect Ratio (AR) for both skis based on these assumptions: Span = 2 x 185 cm, Width = 15 cm: AR ≈ 25 Assuming
that the skis comprise half the 'wetted
area' of the whole, then the L/D
≈ 3.5, which may still be
better than the wingsuit since it implies
an angle of descent of about 16 degrees
(versus 25 degrees) during the stable part
of each flight.
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