Why Lift-induced Thrust Required(Tr) decreases and Zero-Lift Tr increases with the increase of velocity? As the minimum Tr is at the point where L/D (lift/drag) ratio is the most. And Lift-induced Tr depends on the Coefficient of Lift, (Cl)^2 and Dynamic Pressure (q) which also increases as velocity increases. But why it is decreasing?
And how Zero-Lift Tr depends on velocity and is affected that much when its coefficient is a constant?
This happens because Angle of Attack required to maintain flight at a given weight decreases with the increase of speed.
As for the zero-lift Tr, also known as &quot;parasitic drag&quot;, while its coefficient is a constant, its formula is not: it actually has a cube of velocity.