Originally Posted by NinerVictor
The dangly bits do affect induced drag. There is a relation between Lift and Induced drag.
Cdi = Cl^2/Pi*e*AR
Cdi = Coefficient of induced drag
Cl = Coefficient of lift
Pi = 3.14...
e = Oswald Efficiency Factor
AR = Aspect Ratio
Indeed - no arguament there, induced drag is all about lift. however, the lift required remains the same, dangly bits or no. The dangly bits only affect HOW that lift is generated...
Originally Posted by NinerVictor
By changing slats and flaps configurations, the coefficient of lift changes and so will the coefficient of induced drag.
Instantaneously, yes - but if Cl increases, we've destroyed the equilibrium and all bets are off. In order to maintain equilibrium, the lift force L must remain the same - the amount of L required for a given flight path is constant, irrrespective of the wing configuration.
Now, considering that Cl = L/half rho Vsqared A
Rearranged, L = Cl half rho Vsquared A
rho (air density) will not change appreciably, nor will A (wing area), so L is proportional to Cl * vsquared.
In order to restore equilibrium, we can nose down, reducing AOA, hence returning Cl to it's original value, Or, if not, the aircraft will pitch up and slow down, Vsquared will reduce and we will find a new equilibrium where L is the required amount. The induced drag there will have increased, but due to the reduced airspeed, NOT the flaps.
So, I maintain that flaps do not *directly* affect induced drag.