Currently the nozzle size scales with expansion of the nozzle only depending nozzle length, not with nozzle throat size. A result is that a 1st stage rocket engine - with relatively short nozzle, optimized for sea level - is oddly small compared the engines of higher stages on the same rocket.
In reality when nozzle throat size is increased (while nozzle expansion remains the same), the entire nozzle becomes larger.
@bspawn sorry to be 2 months late, you didn't ping me in the previous one.
I should've explained my point better reading back:
In the throat size slider you are changing the value between less than 100% and 100%. In real life you can achieve this by clogging the throat, for example making the walls thick to reduce the internal section, without any external change. The diameter of the throat section can be the max throat size plus the minimum wall thickness and changes to the throat size can keep the old throat section diameter and just increase the wall.
@pedro16797
"You aren't increasing the throat size"
How do you mean that? I'm talking about the "throat size" slider in the part properties panel of some of the rocket engines. How is it that moving the throat size slider to the right and have the % number increase, does not increase the throat size?
"you're reducing it or keeping it open"
Two of the standard rocket engines have a bell- or delta nozzle and they have throat size at 75%, so throat size can be reduced and increased, not only "reduced or kept open".
The throat is inside the ingine, but internal dimensions do affect extrernal dimensions.
For a given throat expansion ratio, increasing the nozzle throat size does mean that the entire nozzle (bell) increases in size, and the diameter of the engine mounting also increases.
The game does not reflect that fundamental reality and it results in engines that are just visually wrong.
Maybe scaling the size of the exhaust with throat size is not the correct solution, but there is a problem:
In the game a cone or bell with minimum nozzle length (for optimal efficiency at sea level) results in an tiny engine size that is disproportionally small for its large thrust.
Also it is odd that for Omega and Bravo engines the nozzle length can not be adjusted, even though those engines are essentially just bell nozzles. The expansion rate can still be adjusted but only by nozzle throat size, which greatly affects thrust (by a factor of about 4) without visual representation in the game (same engine size).
I think part of the problem is that nozzle length can be changed from 0% to 200%, where (for bell and cone) 0% is visually extremely short. Maybe part of the solution is to limit minimum nozzle length to 100%.
I think that all rocket engines should have the same adjustments wrt nozzle throat size and nozzle length, and that there should be proper visual representation of those.
You aren't increasing the throat size, you're reducing it or keeping it open, that doesn't have to affect the bell necessarily
@pedro16797
"sorry to be 2 months late, you didn't ping me in the previous one."
No problem.
"In the throat size slider you are changing the value between less than 100% and 100%."
No, all the standard rocket engines that can have their throat size adjusted have a default throat size of 75%.
So in the game the nozzle throat can in fact be increased and engine thrust increases with it; 100% gives almost double the thrust of default throat size, not just a little bit - but the size of the engine remains the same.
I think the fix is easy: in a way throat size is redundant and already covered by engine size (a bit higher up in the part properties panel) - just remove throat size and maybe move "engine size" down in the panel and rename it to "throat size".
I do concede that part of the cause of these visually stumpy little (and relatively unrealistically powerful) rocket engines is not in fact that throat size is not visually represented, but is also caused by the fact that throat length can be made unrealistically short.
"In real life you can achieve this by clogging the throat, for example making the walls thick to reduce the internal section, without any external change. "
I very much doubt that in reality a rocket engineer would ever do that. Seems like rather far-fetched reasoning to make it seem as though this 'bug' in the game is in fact intentional design.
It is not unusual for a game in early beta to not only be incomplete but to also have faults in content that is already released. I just worry a bit that the dev may lose sight of little 'visual bugs' like this (there is similar issue with exhaust plume expansion) - it would not be the fist time such a thing happens with an indie game, which is a shame because these sort of bugs are low-hanging fruit in terms of effort required to fix it.