Why a new acronym?
I think you might want to drop this Vz term and revert to ROC (Rate of Climb) and ROD (Rate of Descent), S.F.L.Y. That way all of us can be clear about whatever it is you want to tell us. When you stated in a previous post that there was a "high Vz" then it was unclear, to me at least, not just what was meant by Vz but also whether you were referring to ROC or ROD , since the Z axis does have a vertical extent in both directions, positive and negative.
It is not that we are too stupid to understand your prose, just that what you have written is both non-standard and ambiguous and I am happy to share that insight with you as, for one thing, an FAA-licensed Ground Instructor. You, on the other hand, are perfectly free to reject this insight of mine should you so choose, this being just one of the really neat things about PPRuNe.
These axes, X, Y and Z, are more commonly used theoretically to define roll, pitch and yaw respectively around an aircraft in flight's CG (Centre of Gravity) than, as you are using one of them in isolation, some sort of flight path. (Of course an aircraft in flight, free to move in space as it is, rarely moves purely around one axis; it is simply easier to teach the principles of flight by considering them in isolation.) It's fortunately rare to experience motion along the Z axis alone so that Vz as a flight path is generally not a valid description. Instead we usually combine forward speed and vertical speed to arrive at a flight path vector, not the same thing as what you choose to call Vz at all. You may be using an ROD of 2500 fpm but with a TAS of 400 knots for a very different flight path than what an ROD of only 1500 fpm but 80 knots yields, when what matters to us as pilots is the flight path vector (and perhaps the pitch attitude if we want to avoid those thumping noises the trolleys make as they smack into the cockpit door) and not the ROD alone.
In other words, I want to know the energy state of my aircraft, not just its IAS and ROD. If both are high or if just the IAS is high then I have an aircraft with lots of energy stored. If both are low but steady then I have an aircraft without much stored energy but perhaps not much need for energy. If I have an aircraft with a low and diminishing IAS or a low IAS and a high ROD then I need to be thinking ahead to putting some energy into it using either gravity (assuming altitude to spare) or else engine thrust or perhaps both together because sooner or later I am going to need to alter its flight path. We will need to read this accident report to discover the reason for this accident crew having overlooked this very obvious first principle many have already cited here, what we teach a beginner as simple awareness of airspeed as a top priority.
Last edited by chuks; 1st February 2010 at 06:55.