RE: How to Correct Measured Thrust for Density Altitude?
Remember on Gilligan's island when Gilligan would hear and argument and agree with both sides?
I think that Dr. Honda is saying that it's hard to compute thrust for a specific turbine design just from basic parameters like inlet diameter, rpm, etc. That seems reasonable, they are complex beasts and there is so much art in the combustion chamber and NGV to name two that seem a little spooky .. you would not expect to take the mechanical drawings of a model turbine and make an accurate prediction of thrust with hobbyist-level math and computations.. if you had access to supercomputers and hydrodynamics codes as P+W does .. well different story .. but sadly we don't :-(
But rctech2k7 (resistor code username? geek! :-) ) is saying that for a given specific engine, you can pretty accurately scale its own performance (not compare to any other) by ratio of density altitude for the two test sessions that are to be compared, e.g. one at done at standard atmosphere, plus any other. Again, pretty sensible to me. I'll bet its close enough for any needs we have. I believe it's what most of the testers actually do but perhaps they will comment.
Regarding people's natural fascination with specs .. I have learned over the last several years of climbing the turbine learning curve that small performance differences are insignificant in determining actual utility and enjoyment in our hobby, and what really matters is reliability, predictability of operation, and great service when you need it.
Dave