Sink and Glide angle

[Keith.Williams.]

Subsidence

Your statement that "The Rate of climb is the vertical component of the aircraft`s velocity and depends on the aircraft`s velocity and the climb angle" is true but if you are using speed relative to the air you must also use angle relative to the air.

A headwind increases climb or descent angle because the air is moving in the opposite direction to the aircraft. But if it is a steady wind it will not affect the airspeed, nor the angle of climb or descent relative to the air. So it will not affect the ROC or ROD.

To understand the situation in a glide for example, we should image that we are descending through a rectangular block of air. We start the glide at the top left corner and end it at the bottom right corner. The glide angle is the angle between our flight path and the top of the block. Our ROD is the height of the block divided by the time it take to reach the bottom. Let us suppose for example that it takes us 2 minutes.

Now consider the case where we descend with the same TAS and ROD as before, but this time with a headwind that is equal to half of our groundspeed. The block of air is now moving across the ground in the opposite direction to that of our aircraft. Because our TAS and ROD are unchanged, our dradient and endurance are unchanged.

But by the time we reach the bottom right hand corner of the block, the block itself has moved half a block to the left. So we have moved only half of the previous distance over the ground. From the point of view of an observer on the ground, looking from the side of our flight path, our glide angle appears to be greater because our ground distance is less. But the TAS and ROD were unchanged so the time taken will be unchanged. It will still have taken the same 2 minutes to reach the ground, but will have landed in a different place.

The problem with your argument is that glide angles are measured relative to space (the earth horizontla) whereas TAS is measured relative to the air. To do this calculation properly we must use our TAS, still air glide angle and windspeed to calculate our ground speed. Then using this and our ROD we could calculate our new glide angle.