Methods for determining air-breathing engine performance

[adamzl]

Hello, I was attempting to make a SSTO and learning the hardships of air-breathing engines losing power from lack of intake air. The question I wish to ask here is: aside from right clicking the engine part and looking at it's thrust value decreasing how can I determine if my engines are receiving their required intake air? The staging GUI seems to display the same value for air regardless so this does not seem useful.

[Mutex]

Should be pretty obvious if they aren't, they flame out. The staging GUI shows the same value for air for all engines because the air is shared between all the engines.

[Periple]

They will always eventually lose power when you go high enough.

The function is a bit complicated actually because different intakes perform differently at different altitudes and speeds, and different engines benefit more or less from the "ramjet effect" of going really fast. Turbofans don't like to fly very fast and the ramjet effect doesn't do much for them, the afterburning ones do. The Rapier benefits the most. 

The shock cone intake is the one to go for if you're building an air-breathing SSTO, it performs the best at high speed/high altitude.

[regex]

Off hand from my own testing the other night, use the box-looking intakes (F-14 style) and the Whiplash engine, that seems to allow the highest speed (less drag). Your engines will automatically flame out at ~22,000m because the intakes will produce 0 air. No idea if air-hogging still works because I didn't really test beyond @ ten (various) intakes for one engine.

E: You can get all the info from the right-click menu in flight, just scroll through to look for your intakes. Also, F12 brings up an aerodynamic display which might offer some additional insight.

Edited March 7, 2023 by regex

[adamzl]

Thank you for the replies everyone. I know the engines will flame out, but this also means they've reached some sort of below minimum point but what I seek to know through the GUI is how close I am to that point. At some point the engine is only 50% effective because of lack of air, but how does one know that from the UI?

Regex, thank you for the F12 hotkey hint. I loaded things up and took a look, it displays information about the air density but no per-part information like an intake's satisfaction.

Small followup on the F12 stuff, air density is certainly useful but air speed would also affect intake air and the different intakes have different levels of effectiveness at different speeds... so there are lots of complicated factors and I'm just trying to figure out if my engines are underfed through a gauge on screen of some sort.