Baron, I don't think this figures are any where near V min drag. Also, way out of the flat rating
range. And 20% loss in thrust available with a 5 deg C rise sound WAAAAAAY too much. Was that a published number?
For Keith, I have found a thrust vs mach graph for the Garret 731 at sea level, 59 deg F. Its a 2.79
bypass fan. The graph has thrust in lbs on the y axis, and mach on the x axis. The curve starts at
3700 lbs at zero mach, and slopes down to the right. Other values are 2800 lbs at mach .3, and 2200 lbs at mach .6.
Concerning thrust decrease with tas near V min drag, say mach .3, about 198 ktas, if I draw a
tangent, the slope of the line works out to be 3.4 lbs of thrust per knot.
So with a 10 ktas increase near V min drag, the decrease in thrust from the engine is 34 lbs.
Based on the 2800 lbs it is producing, this is a 1.2 percent decrease in thrust available. Regarding the excess thrust available, this percent would be considerably higher, of course.
Now it you had a model to calculate drag, the decrease in excess thrust due to tas increase could give you the decrease in climb gradient. I’ll leave that up to Baron to calculate