SpanWise,
The speed to use when calculating ROC is definitely GS.
The answer is no. When calculating ROC we have to use TAS. I will try to explain why:
The climb angle of the aircraft has to do with its performance in still air:
(1) sinφ = tanφ = (Thrust - Drag) / Weight (sinx = tanx, in small angles)
So it is a function of excess Thrust and Weight, nothing with speed to do and wind is ofcourse not a factor.
If
φ is the angle of climb in still air ,
and
ψ is the angle of the aircrafts flightpath in a windy day
Simple math and geometry:
ROC= TAS*tanφ = GS*tanψ , but we do not know this angle ψ yet, so we are not able to use it in relation to GS to find ROC.
The Rate of climb has thus the same value for 2 different gradients/angles and 2 different speeds. As I have said before, since Climb Gradient, tanφ is a measure of performance in still air we have to use TAS. So,
(2) ROC=TAS*tanφ
Now that we know ROC if we want to calculate the Flightpath Gradient, tanψ, for our aircraft performance in case of wind and mountains ahead. We know our ROC we know our GS
(3) tanψ= ROC/GS ,
This is our Flightpath angle, Flightpath gradient! Now we can use this equation for our performance calculations...
If you now still want to call Flightpath gradient as Climb gradient I dont mind, I only find it confusing..
Jetpipe.