Aircraft with a 'lifting' tail

[Machdiamond]

Can you give more detail? It seems clear that it is in fact the angle of attack delta that is the key, as described above

Your example does not work at all. Let's assume that instead of starting from 3 degrees you start at 1 degree. You pitch up two degrees so now you have 3 degrees, do you really believe that suddenly the wing produces 3/1 or three times as much lift than it did before? And what happens if you start from zero degrees and you go to two, that's infinite acceleration to the stars now. Keep in mind that when dealing with dynamics, you are dealing with derivatives, not with static values.

[Machdiamond]

Rereading my prior posts, I have to confess that my attempts at explaining longitudinal dynamic stability are not good to be of any use. I should probably stick to what I know

Nonetheless, I stand by the rest. Tail lift, canard etc.

[photofly]

Your example does not work at all.

I think it does.

Maybe I should get one source of confusion out of the way, by saying the "zero" angle of attack is the angle of the airfoil that generates no lift. In that it differs from any other angle of attack definition by a constant angle it's just a convention as to the zero you measure from.

Let's assume that instead of starting from 3 degrees you start at 1 degree. You pitch up two degrees so now you have 3 degrees, do you really believe that suddenly the wing produces 3/1 or three times as much lift than it did before?

Yes, it does. For "sensible" values of alpha, lift is directly proportional to alpha.

And what happens if you start from zero degrees and you go to two, that's infinite acceleration to the stars now.

Zero angle of attack -> zero lift. Two degrees angle of attack, yes, the lift has increased "infinitely". You'd never be flying with angle of attack of the main wing though, you'd be accelerating towards the earth, because zero angle of attack -> zero lift.

Keep in mind that when dealing with dynamics, you are dealing with derivatives, not with static values.

The derivative of lift with respect to alpha is almost dead-on a constant value, reflecting their linear relationship, up to near the stall.

If you'd rather use a different definition of the angle of attack, say based on the chord, then define another quantity as the "angle of attack minus the zero-lift angle of attack". The analysis works just as well.

I have to say, it's not my treatment - it's John Denker's. I'm curious to see if you can fault it though.

[Machdiamond]

I can't, I was mistaken.

[18-Wheeler]

Interesting stuff guys, thanks.
Too much to reply to, so I'll just read most of it.

[18-Wheeler]

... and while we have some aerodynamic gurus here, would any of you like to have a go at this one please?
http://www.pprune.org/tech-log/45182...ctor-prop.html

[glhcarl]

What most of you are calling the tail is actually the "horizontal stabilizer". It could be on the aft end of the aircraft of the front (canards). Since its purpose is to stabilize the aircraft in the pitch axis sometimes it creates lift and sometimes it creates down force. Simple as that.