Another way to explain why Vx is a function of excess thrust is simply to look at what happens to the component of weight opposing the direction of flight in a climb (ie: resolve weight into a component opposite to lift and a component opposite thrust / with drag).
As the angle of climb is increased the component of weight opposing the direction of flight increases. As a result thrust must be increased.
This is quite simple but clearly shows that there is a direct relationship between thrust and the angle of climb.
The more thrust you have in reserve (excess thrust), the steeper you can make the angle.
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Great explanations Keith. I've got a question(s) you might be able to answer re: the actual speed for Vx -
Based on the fact that the thrust produced from a prop is maximum at low speeds,
AFAIK the speed Vx is set at the lowest possible 'safe speed' to take advantage of this maximum excess.
So I was wondering how the speed for Vx is actually set in the flight manual?
Is it simply determined through flight testing?
Is there any requirement that it maintain a certain buffer above the power on/off stall speed?
Would it be true to say that the best AoC could be achieved right on the stall speed or would the maximum excess more likely be found at a speed just a bit below minimum drag (where drag has increased only slightly but the thrust has increased further at the lower airspeed)?
Cheers
