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I'm taking inspiration from phased array antennas, which can match the function of a directional dish antenna with several omnidirectional antennas.

The objective is to simplify engine construction by eliminating the highly shaped nozzle.

While a single nozzle-less chamber would be inefficient, I would expect the plumes from adjacant chambers to interfere constructively, hindering, sideways dissipation while permitting backwards acceleration.

So why not cluster several small combustion chambers like this?

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    $\begingroup$ Mechanically speaking, diverging nozzles add thrust by increasing the surface area upon which the exhaust pressure can act. If performance were to be gained by clustering truncated nozzles, there would need to be an increase of pressure acting on some other surface (which is possible, but not an obvious result of this idea). $\endgroup$ Commented Aug 20 at 16:56
  • $\begingroup$ @AMcKelvy the pressure on the forward of the nozzle is removed $\endgroup$ Commented Aug 20 at 17:08
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    $\begingroup$ aerospikes cluster somewhat like you're talking about, but of course the spike is important $\endgroup$ Commented Aug 20 at 18:05
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    $\begingroup$ @ErinAnne I immediately thought about Aerospikes - but, 18 hours after you did :-) . $\endgroup$ Commented Aug 21 at 12:33
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    $\begingroup$ @AbdullahisnotanAmalekite No matter what fancy things you do with exhaust gas, after it leaves the rocket at supersonic speed, its history of interactions with the rocket (...including accelerating it) ends. The nozzle allows to extend the interaction, as expanding gas pushes on the nozzle, accelerating the rocket. Remove the nozzle and all accelerating interactions end at the combustion chamber, and whatever you do after the gas exits the throat has no impact on the rocket. $\endgroup$ Commented Aug 21 at 12:45

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Interesting concept, but unfortunately this would not be expected to work. Ultimately engines are not antennas.

The key differentiating factor is that the flow from an engine is not (to first order) time-varying the way a radio wave is. Phased arrays are great, but they only work on things that have a phase, which means time-varying wave fields. A constant operating engine does not produce this.

The other thing is that a nozzle is not simply a directionality-improving device the way a radio dish is. A nozzle is really more of an energy conversion device. Put simply: the combustion chamber is full of hot gas, and a nozzle converts hot gas into fast gas. That conversion from thermal to kinetic energy is critical and is the chief purpose of a nozzle. Two gas plumes interacting will not have the effect of energy conversion that we're looking for.

Keep coming up with neat ideas! But unfortunately this one doesn't work since radio waves and combustion flows aren't as comparable as you might hope.

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  • $\begingroup$ For a phased-array antenna, the ability to change direction is important, and THAT needs a phase/wave to exist in the first place, but possibly not for uni-directional thrust, which is what is desired from a rocket. $\endgroup$ Commented Aug 21 at 12:55
  • $\begingroup$ @MikeB Wait, did you just invent gimbal-less thrust vectoring using a phased array of omnidirectional "engines"/pulsed fireball generators? Hurry up and you might still be able to make big money on a patent. (But designing engines with sufficiently fast throttle response might be a little hard.) $\endgroup$ Commented Aug 22 at 10:12
  • $\begingroup$ @TooTea No, this would not be a phased array effect, it would be as simple as "push harder on the right than the left". Phased arrays rely on controlling constructive and destructive interference of the phases of waves. Rocket plumes are not waves, do not have phase, and do not destructively interfere. $\endgroup$ Commented Aug 22 at 11:34
  • $\begingroup$ @TJM but pulsating plumes would be! $\endgroup$ Commented Aug 22 at 20:32
  • $\begingroup$ Conventional nozzles do not have phase ... but rotary detonation rocket engines do. Hmmm... a cluster of counter-rotating detonation engines with phased injectors and synchronized detonations ... the stuff of sleepless nights. $\endgroup$ Commented Sep 13 at 2:42
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Partial answer:

Shortly after I posted this question, I realized that you can only eliminate the subsonic part m, since the suction front cannot travel faster than the speed of sound.

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    $\begingroup$ If you are saying the nozzle is needed to accelerate the flow, I agree that is the answer. $\endgroup$ Commented Aug 21 at 0:45

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