Lift and induced drag...

[bookworm]

Is the increase of drag compared to zero-lift drag called "induced drag" in case of an infinite airfoil?

I think you'd need to be a lexicographer to get excited about this one.

If you take "induced drag" as being literally "the drag associated with the production of lift", then you would have to say yes.

If you prefer McCormick's version: "Induced Drag: The drag that results from the generation of a trailing vortex system downstream of a lifting surface of finite aspect ratio" then pretty much by definition, you'd have to say "no".

I prefer the latter.

[chornedsnorkack]

The AoA in the climb is about the same as it would be for the same speed in straight and level with an allowance for that proportion of weight that is being supported by part of the vertical component of thrust.

In a climb the thrust is angled upwards compared to the straight and level position.

Not only in climb.

Consider plane in a steady level flight. At some AoA, suppose that the thrust is exactly horizontal.

Since the flight is level, drag is exactly horizontal (and equal to thrust) while lift is exactly vertical (and equal to weight).

Now, pitch the plane up, increasing Cl, and slow it down, decreasing Vsquared, so that the plane is again in steady level flight.

Since the flight is again level, the drag must needs be exactly horizontal. But the thrust is now angled upwards, since we just pitched the whole plane with its engines. Therefore some of the weight of the plane is supported by the vertical component of the thrust. Lift must be smaller than weight - in level steady flight.

Indeed, as you pitch up to steady hover, both lift and drag must go to zero (because airspeed is zero) and thrust must be exactly equal to lift.

But when you go to steady vertical climb, lift and drag are no longer required to be zero because there is nonzero airspeed. Drag is opposed to airspeed, which means directly down. Lift must be at a right angle to airspeed, so horizontal. Thrust no longer needs to be directly vertical when there is lift present.

[27/09]

chornedsnorkack

You missed the condition I placed in my statement.

for the same speed in straight and level

My statement was about the fact that AoA doesn't really change from straight and level to a what it is in a steady climb so long as the aircraft flys at the same IAS in both cases.

You talk about varying speeds for straight and level and as a result are also talking about varying the AoA.

[hawk37]

Say it can't be so.....

Bookworm, you seem to be saying that an aircraft/airfoil combination with no wingtip vortices (consider the academic case of a perfect winglet) would have no induced drag. Or, an airfoil that stretched from one side of a windtunnel to the other (no wingtip vortices) has no induced drag. Am I understanding you correctly?

[bookworm]

Bookworm, you seem to be saying that an aircraft/airfoil combination with no wingtip vortices (consider the academic case of a perfect winglet) would have no induced drag. Or, an airfoil that stretched from one side of a windtunnel to the other (no wingtip vortices) has no induced drag. Am I understanding you correctly?

I didn't say "wingtip vortices" but "trailing vortex system" (or rather Barnes McCormick did). Vortices don't have to be shed at the tip. I have no idea what a "perfect winglet" might be -- if it's infinitely long then you might as well have an infinite span. As for windtunnels, there may be some practical effects that spoil the two-dimensional nature of the flow, but yes, perfect 2D flow means no induced drag. In a real wing of finite length, there must be vortices in order for there to be lift, hence there must be induced drag dependent on lift.

[cwatters]

I'm wondering if the OP wasn't after a much simpler answer...

On one level you can consider the lift produced by a wing to be more or less constant and equal to the weight of the aircraft even when climbing.

Increasing the angle of attack allows a wing to produce that amount of lift at slower speed but only within limits due to the stall.

Deploying flaps allows the wing to produce that amount of lift at an even slower speed to make landing and takeoff safer.

The extra drag produced by the flaps is worth it.