ORIGINAL: ww2birds
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 :-(
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Dave
Exactly.
The thing is... if someone has done some EXPERIMENTS on power with different temps, humidity, altitude.... etc. Then we can build some "Curve fitting" equations. With experimental data... we don't need the "True Physics"... we just need a generalization. And... for hobby related info... it's close enough. I was un-aware of anyone doing good, back-to-back/comparison data, with altitude, on our engines. And to be accurate/usable data... it has to be THE SAME ENGINE AND TEST RIG used in all the tests. Saying... "my K80 made 18lbs of thrust ast sea level... and Joe-Bob's K80 made 17lbs at 4000' MSL" insn't usable data. That thrust change is still within the error of the engine, and the people operating it... and in the test rig.
BUT......... to have an accurate, generalized equation for thrust lost in a pure jet.... it's impossible.
Oh... did I mention that I have a Degree in Physics... worked in an R&D lab for 8 years.... and now own my own shop, and I build engines??? (lol)