SSTO Spaceplanes in FAR: How exactly does air-breathing engines losing thrust work?

[RunaDacino]

Hello!

 

I'm using procedural wings and near-future propulsion, OPT (J fuselage) (SCIMITAR, like Rapier but a bit stronger). My plane has 4 engines like this. According to KER, my engines receive air well into 25 km high and yet - depending on my ascent profile I either start losing thrust at 1200 m/s or go well into 1400, almost 1500 m/s. This is a pretty significant difference for deltaV due to efficiencies and I'm trying to figure out how to best reproduce the 1400/1500 ascent profile.

 

My observations have been, given I'm using a Delta-wing lifting body fuselage with canards and V tail fins is... My best bet is to fly up to ~8 km high and point with a barely 5 degree angle of attack if not less. The body/wings will cause me to ascend still and somehow I'll hit and maintain 1400/1500 m/s until 27 km high when I swap to rocket mode.

 

When I rise to 20 km then do level flight, I'll never go higher than 1200 m/s.

 

Is this some sort of a feedback loop going on? That you need to break the velocity barrier when there's more air to maintain it higher?

 

My ascent profile works either way, and I can return/launch reliably. I'm just trying to figure out how it works exactly and why.

Edited April 26, 2024 by RunaDacino