Whirlybird vs. whale-y-bird

[deleted-190112]

I completed my science fair experiment and I found that the whirlybird with straight edged wings flew longer than the whale-y-birds with curvy or jagged edge wings when I dropped them off a balcony. That confused me because all the wind tunnel studies comparing wings with tubercles with regular wings showed that wings with tubercles had more lift and less drag. When I thought about it, I could see how the straight edged wings could have more drag to make it go slower. I also guessed that lift could be responsible for it flying longer, but in the wind tunnel studies the whale fin had more lift. Am I right in thinking that the drag and lift are both working in the same direction when you drop a whirlybird (to slow it down when falling)? Am I right in thinking that with a swimming whale the lift and drag are working 90 degrees from each other? Could the surface area have something to do with the lift? For example, if I made sure that all the wings had the same surface area would that control for lift more? Is there any other way I should be thinking about this problem? Thank you

[rmarz]

dominicman - You have unearthed a very unique question about the aerodynamics of this whirly-bird. Conventional wisdom would try to analyze the components of lift considering Bernoulli's Principle of observing the flow of air over an airfoil. That would also be the basis of any wind tunnel observations on the various shapes you noted (whale fin, tubercle etc). In this case you have more of a situation where the blade is falling through the air where the angle-of-attack, and relative wind is very different than an airfoil following Bernoulli's principle. It is very analogous to a helicopter in auto-rotation, where positive lift isn't being generated by the rotor, but the falling rotor is converting potential energy (altitude) into kinetic energy (blade rotation). In this case, it appears that the longer flight (slowness in falling from the release height) is slowed by significant drag, and an airfoil that performed more efficiently (less drag) in a wind tunnel is producing less drag as it falls, so falls faster to ground. This seems to cause the more efficient airfoil (when in normal flight) to actually fall faster to ground producing a shorter 'aloft time'. Look up auto-rotation for more information. Although I'm a private pilot and understand the traditional Bernoulli Principle pretty well, perhaps another expert with helicopter or other aerodynamic experience can shed more light.

Rick Marz