Originally Posted by CabinMaster
For Cost Index = 0, IAS Econ is maximum rate of climb.
Correct, and according to Airbus Perf 2.2.4, that speed is:
calculated by the FMGS as a function of the aircraft’s weight
I believe, but stand corrected, that the max rate of climb speed for constant thrust increases with increasing thrust-to-weight ratio. The FMGS in addition takes account of the change of thrust with airspeed. Shall we leave it to the FMGS to resolve our dispute?
regards,
HN39
P.S.(1) The question is discussed in more detail in 'Boeing Jet Transport Performance Methods', Chapter 30, page 30-6:
How about the speed for the best rate of climb?
(...)
For increasing weight the speed increases, as it did for the best angle of climb. However, the difference in time to altitude changes only slightly with speed, so it will be acceptable to use a single speed schedule for all weights.
P.S.(2) Just to satisfy my curiosity (and perhaps yours), I made
this graph. You will note that for T/W = 0 (a glider) the speed for max roc corresponds to Vmp (as defined by Keith on the other thread), and for level flight (T/W = minimum D/L) to Vmd. The speed for max roc increases with weight, but the rate of increase becomes very small when T/W is greater than 0.15, i.e. speed for max roc greater than 1.5*Vmd. (See
here).