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If I stick out a flat board from a moving car window, and hold it at an angle, it will "lift up". So indeed, airfoil shape does not matter. Angle of attack matt
by bruce343434 2y ago
If I stick out a flat board from a moving car window, and hold it at an angle, it will "lift up". So indeed, airfoil shape does not matter. Angle of attack matters more, because that dictates the path of least resistance.
Planes fly by slicing through a lattice of air, with blades (wings) that only slice easily in directions that lie on a single plane. Orthogonal tail fins means that the vehicle doesn't go from side to side as easily, so it mostly keeps flying on a line. Take a `+`-shape and elongate it so you get a "dentastix" like shape, then hold that out the car window. It will go in whichever direction you point it.
Same idea of a boat rudder. And yet with boat rudders, we don't say "force of lift". The angle of attack changes, which means it now cuts through the water in a different direction (and the rudder piece wants to go straight in the direction it is pointing, since that way has comparatively little resistance in the water), which changes the way the rear of the ship moves which ultimately steers the ship.
- NovemberWhiskey 2y ago>So indeed, airfoil shape does not matter. ... what do you mean by that? If you mean "you can demonstrate the aerodynamic force using a flat plate", then yes you can do that. If you mean "a flat plate is a good tool to explain the aerodynamic force", then that's much less true. If you mean "in the real world, airfoil shape is irrelevant to aerodynamics" that's obviously false.
- bruce343434 2y agoI was being a bit facetious, sorry. It matters, but I think what I was getting at is often simply overlooked in favor of airfoil shape and the pressure difference explanation. The situation of gravity no longer being a factor such as with vertical rudders seems often missed. Then, it's suddenly called "rudder force". Even though it's the same thing as "lift". It seems the field of physics has trouble with isolating this concept/phenomenon and coming up with an apt name for it. Rudders are symmetric, i.e. don't have camber to create high/low pressure on one specific side all the time, and yet they work in redirecting (the relative) flow and thereby through Newtons 3rd redirecting the vessel!
- NovemberWhiskey 2y agoThe pressure difference explanation is the basic explanation, though. The name of the force is "the aerodynamic force", and there's not really any confusion on that point. The difference of shape between hydrofoils and airfoils is determined by the properties of the masses in which they move, explained by the same theories of fluid dynamics, rather than any fundamental difference.
- bruce343434 2y agoThat's just because when you angle the sheet, more molecules of air hit one side imparting part of their kinetic energy, and fewer molecules on the other side to counteract this. I do realize I'm explaining pressure on a molecular level here, but to me it's still "slicing through" and "pushing against" a lattice of molecules.