Looking at different rocket engines, L/D(CC_length/CC_diameter) ratio of combustion chamber is very much less compared to Rocket labs. Even the modern age engines like Merlin 1d and Raptor engines seem to have lower L/D.

Also, with reference to this lecture notes, having lesser combustion chamber diameter/ lesser contraction ratio[Ac/At], will subsequently increase the velocity in the chamber making it difficult to maintain the chamber pressure.

How do the length of combustion chamber is designed usually? Is there any specific reasons why rocket labs have went with higher L/d

  • $\begingroup$ What is the length and diameter of the Rocket Labs engine? $\endgroup$
    – Hobbes
    Sep 26, 2018 at 12:16
  • $\begingroup$ Not sure of the dimensions, but we can actually get it from the pictures ! They are having higher L/D $\endgroup$
    – Vasanth C
    Sep 26, 2018 at 12:22
  • 2
    $\begingroup$ But that's just the outside, we don't know what the cross-section looks like. If they use a thick injector plate, the size of the combustion chamber may be normal. $\endgroup$
    – Hobbes
    Sep 26, 2018 at 12:37
  • $\begingroup$ interesting discussion on how to derive the combustion chamber size from other parameters: forum.nasaspaceflight.com/… $\endgroup$
    – Hobbes
    Sep 27, 2018 at 9:01


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