JR wrote:Erm being not even a diletant in physics i have a question on that. I read through wikipedia result for parasitic drag and all the hyperlinks in all the resulting pages and man things get complicated, when you move beyond basic Bernoulli principle, which does not seem to work for gases, more accurate for liquids. And yes the old mantra of liquids and gases being both the same in fluid dynamics does not hold true in aerodynamics. thoughts? I am wondering it the bubbles change the shape of the disc and the surface. If there are changes i wonder about parasitic drag changes and real world inplications. I guess nobody knows before we get flight time on these.
"Parasitic drag" is exactly what I mean when I say that the forces acting on a disc in flight depend only on its shape, both at large (form drag) and small (skin friction drag) scales.
Air vs water is a question of which dynamical regime you're talking about. Bernoulli's principle works for incompressible fluids with negligible viscosity. In air, in this condition is satisfied only at speeds much less than the speed of sound. Once you approach the speed of sound, the compressibility of air becomes important, and since air is vastly more compressible than water, differences arise. Above the speed of sound the dominant forces are in the shock wave. In water, on the other hand, under extreme flow conditions you can get different effects such as cavitation.
But the hand-thrown disc flies much slower than the speed of sound, and the assumption of incompressibility works fine. And air has a very small viscosity, you can only feel the resistance of the inertia of air, not the viscosity of it. In which case, everything works fine.