Jet engines' thrust prediction is wrong
tsehao-hu opened this issue ยท 1 comments
The jet engines' thrust predicted by KER in VAB/SPH is wrong.
It seems that KJR use this fomular to calculate the thrust:
Thrust = maxThrust * k_a * k_v
where k_a is the multiplier from atmCurve, and k_v is from velCurve
However, the parameter flowMultCap and flowMultCapSharpness should also be taken into account.
If k_a * k_v > flowMultCap, then the multiplier should be reduced to
flowMultCapSharpness / ((flowMultCapSharpness-1)/flowMultCap + 1/k)
where k = k_a * k_v
By default flowMultCapSharpness = 2, therefore it just the harmonic mean of the original multiplier and the cap.
You may probably notice that, for example, the maximum thrust of RAPIER engine is 465.64kN at Mach 3.75, but KER gives 105kN * 8.5 = 892.5kN.
flowMultCap for RAPIER is 3.0, then the correct multiplier is
2/(1/3 + 1/8.5) = 4.435
105kN * 4.435 = 465.65kN
That is the correct answer.
