[Graham Boak]

[If we hold AoA constant and increase weight, speed MUST increase.

Lift has to increase to meet the amount required. Crumpp[/quote]

AoA is Angle of Attack, the angle an aircraft makes with the airflow, for anyone still with us who doesn't know the term.

Ah. I begin to understand. However, there is no need to hold AoA constant. Why should you want to? Yes, lift has to increase to allow for the extra weight. This is done by flying at a slightly higher AoA giving a slightly higher CL, and hence a higher drag. Higher drag = lower speed. QED. However, this increase in drag is insignificant, for the reasons explained.

If, for some reason, you wanted to fly at the same AoA (bearing in mind that no machines of the period had the instruments to do this) then yes, an increase in weight would have to be balanced by a higher q, or speed. But you are already flying at maximum power, so you can't do this.

This flying at constant AoA would, I think, be relevant to cruise, where a heavier aircraft does indeed require a higher speed. This is because the optimum cruise point is where the induced dag (which reduces with the square of the speed) equals the zero-lift drag (which increases with the square of the speed). An increase in weight needs an increase in lift, which creates an increase in induced drag. A new optimum, induced drag = zero lift drag, requires a higher zero-lift drag which is found at a higher speed. The resulting AoA will be close to, if not identical to, that of the previous weight.

Your equation may hold at cruise conditions, if AoA is held constant. It does not apply to flying at maximum power, where additional lift can only be found by increasing AoA.