In the case of the glider I don't know if my reasoning is correct but I would interpret the pulling force of the tug as the thurst of the glider.
It doesn't matter to me who is providing the force but the force is there beacause without it it won't move.
Besides that when you talk about an endless runway, I could disagree with that because if we have a symmetric airfoil the airplane will never climb no matter the speed it's rolling at.
Even if we have a symmetric airfoil, accelerating to the point that the aircraft needs an AoA of 0.5 degrees to lift off doesn't seem to me the usual take off technique so please lets stick to the real world.
Last edited by AirGek; 29th Oct 2012 at 11:42.