Exhaust/thrust being blocked by parts

[Dobelong]

Is there any clear way to see if engine exhaust is being blocked by a part and heating it up rather than producing thrust that is moving the craft forwards? I know that sometimes this change in temperature will show up on the F11 indicator but I feel like I have experienced situations where this change in temperature has been negligible. In these cases, is there some way to check if a part is blocking an engine's exhaust and reducing effective thrust?

[swjr-swis]

1 hour ago, Dobelong said:

is there some way to check if a part is blocking an engine's exhaust and reducing effective thrust?

What you see can be deceiving, because the KSP code doesn't check the visual model to decide on blocking. Also, some engines have an offset added to their exhaust effects. Visually, it can look like the exhaust is going right through another part, and yet to KSP, the engine is not considered 'blocked' and the other part is not getting heated. On top, there are different multipliers for the exhaust heat some engines produce, which makes them more/less likely to show heating effects.

Unfortunately we've been given no way to see directly whether the thrust is considered blocked. The PAWs, even the debug windows, will all merrily continue to show full thrust being produced, even when you have none.

Once upon a time it used to show in the logs when engines were heating another part, and that's how we could tell. I haven't seen such entries anymore in a long while though, I think they were removed; possibly it was part of the old engine module. Or it was some undocumented setting that I forgot along the way, I'm not sure.

So, all we got to go on now is this: if you can notice the engine is producing thrust, ANY thrust, it's not blocked. The way it works, it's an all or nothing thing.

Obviously this is per individual engine, so if you have more than one, you have to account for that. Note also that you do need to check this per exhaust nozzle, if the engine has multiple. Engines like the RAPIER, Mammoth, and others, will still produce thrust from the unobstructed nozzles, which will affect torque and total effective thrust produced.

[fourfa]

I’ll just add - I’ve had situations where thrust was not obstructed while not steering, but was blocked when gimballed over while steering.  That can seem to the pilot like an intermittent, hard to diagnose overheating problem.  But yeah, no way to find out except trial and error.  Maybe something like a static fire test, where you start engines but don’t release launch clamps, and try every combination of steering inputs