Quote from: Eka on 11/08/2019 04:33 am Quote from: Twark_Main on 11/08/2019 04:10 am Naturally the shorter nozzle trades off against Isp, so here a good designer will want to choose the optimum balance point to maximize whole-system performance.

Er, I'm not so sure. Make the outer nozzles have longer outside sides, say even vacuum length. All the inner nozzles will have their exhaust expansion constrained by neighboring Raptors. So they may be able to be really densely packed in the middle.



Packing density is ~90% for hexagonal circles, so you could pick up another 9+% by eliminating the inner sides of neighboring nozzles (seems simpler than the hexagonal nozzles proposed), but eventually you do want to retain the expansion ratio, if I understand correctly, so there would seem to me to be limits at which you lose efficiency to increase packing density.



Yeah, for the greatest efficiency, where is the limit? May even be less dense due to elevation issues. Yes they can be packed denser, but they will loose thrust and ISP and this gets worse as number of engines increases and as elevation increases. Also additional engine weight and fuel use will flip it negative sooner. Then there is the cost of making the different bell shapes. As I add in more stuff taken into account, I get the idea a simple hex grid of standard SL nozzles gets the job done with lower headaches. The big issue is due to exhaust interaction, how dense can they be? That center nozzle is pushing into more pressure than any further out ones. When does it's flow separate, and how much lower elevation does that force the SL engine to be optimized for? Even having the flame diverter on the launch pad too close could cause flow separation. What a quagmire... What a quagmire...Thrust vectoring can still be done, but engines must move in coordination. All could vector, but that's a lot of hardware, and what about failures. Centers could be fixed, and outer ones allowed to vector to the outside arc only. That can provide proper thrust steering including roll. Failures could be handled better.