I am an owner/operator of a C90B King Air considering an upgrade to the newer C90GT. The only difference between these two aircraft are upgraded engines that are flat-rated to exactly the same 550 SHP as the original engines. Everything else is the same, including the props. Now here is the question. Raytheon made the change because the new engines have larger compressor sections and therefore perform better at high density altitudes. My question is why does this aircraft perform better at low altitudes. My 90 climbes at 1500 fpm and 160 knots. The new one at over 2000 fpm also at 160 knots. To me, horsepower should be directly related to thrust. However, clearly there is more going on. There is one important note, the newer design runs the props slower (1900 vs 2200) rpm during the climb. So, the newer design is taking a bigger bite of air. That said, if my assumption that shp is directly related to thrust is right (and it may not be), then what has changed.
Dave
Dave
