LeSving wrote:
and have to be included every time.
I agree if you want to reach the limit of the x axis on cobalt’s graph.
Almost all applied aerodynamics ignores one or more things, for example viscosity was never considered in the calculations in the design of almost all GA aircraft. The calculations are so difficult that experts still argue about their mistakes (fictitious or real).
In the vein of peter’s three line summary to have lift (and for the ailerons to work):
You need to:
with the first being the easiest concept to actually ‘apply’
Isn’t it sufficient to move it from up to down for what moved to have a force up? (The other ones merely being means to achieve that goal)
Noe wrote:
Isn’t it sufficient to move it from up to down for what moved to have a force up? (The other ones merely being means to achieve that goal)
Yes, you can pick the one you like the best 
as long as it is properly applied. I could have added energy and momentum (both being transferred) to the list but was constrained by three. 
Almost all applied aerodynamics ignores one or more things, for example viscosity was never considered in the calculations in the design of almost all GA aircraft
The classical way is to use the Kutta condition. You apply rotation in enough amount to cause separation at the trailing edge. Then you don’t have to bother with overly complex equations. It’s kind of voodoo magic that lifts the whole thing up from the x-axis
Digging up this old topic…
It has often been said that the understanding of subsonic aerodynamics has not really improved since the 1940s.
How is it possible to design a new wing, for an airliner, which produces the same lift with say 20% less drag, than was possible 50 years ago?
Peter wrote:
How is it possible to design a new wing, for an airliner, which produces the same lift with say 20% less drag, than was possible 50 years ago?
I think we already know how to make a very efficient wing in theory. To get rid of the induced drag make is very high aspect, to get reduce the transonic shock wave drag, sweep the wing (for an airliner at mach .8 etc). The trouble with the former is that is very heavy, and or bendy. Sweep is also is not without problems.
Using winglets etc has many of the advantages of high aspect ratio foil, but without the same structural penalties. To reduce the shock wave drag, special air foil shapes are used, with the bottom of the wing having a concave section, rather than convex like on most light aircraft.
So I think the trick is make a wing that is as efficient as an idealised shape that is very light and practical from a structural point of view.
For your TB20 where induced drag is not significant at your typical cruise altitude you could just make the wings area smaller, but now your stall speeds will be much higher… Which maybe you could fix with the right kind of flaps, made of composite materials etc, but that will have some weight penalty…
Peter wrote:
It has often been said that the understanding of subsonic aerodynamics has not really improved since the 1940s.
That is definitely not correct. Turbulence, laminar to turbulent transitions etc, and in particular general 3D effects was not at all understood in the 1940s.
Subsonic aerodynamics are researched constantly and understood in the world of formula 1. That doesn’t mean that things can’t be learnt and improved. The only real difference is that the aerofoils used on the cars are upside down to those used on aircraft.
It’s not the speed of the air over top and bottom of the aero foil but the distance it has to travel that makes the difference between lift or stick and drag.
Peter wrote:
It has often been said that the understanding of subsonic aerodynamics has not really improved since the 1940s.
Not that much understanding of turbulent airflow and aerodynamics at slow speeds: having an airframe that produce substantial lift at very slow speeds with controlled transition in turbulent airflow is still an unsolved problem
For cruise speeds, as @Ted mentioned you can do a lot for cruise performance, but only if you accept higher stall speeds, bringing that down while maintaining stability require lot of innovative engineering in geometry (e.g. right kind of flaps, active winglets, vortex generators), then passing stall/spin certification with it is a whole story, if you can’t, at least make sure it has CAPS attachment points
Wake me up when someone has +240kts cruise aircraft with -35kts stall speeds !
