Opting for the lower speed, let's say 230 KIAS climb to allegedly reach higher levels sooner. At your CAS/Mach changeover height for 280/M0.6 at FL200 feet, TAS at ISA is 370 Kt. At 230 KIAS at the same level, the TAS is 306 Kt, some 64 Kt slower at the same fuel flow. My low CI friends will need to find 64 Kt of Tailwind that you don't have just to remain equal. In the reverse direction, flying into a headwind, the faster climb wins again, as a given headwind component has a lesser percentage penalty upon KNM per unit of fuel at high speed than at low speed.
Last edited by jimmyg; 3rd Sep 2012 at 12:55.