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# Calculating Nozzle Width2

## Calculating Nozzle Width

(OP)
So I'm not very experienced in terms of aerospace design (at all), but I've been looking for a formula to help me estimate nozzle thickness given temperature at the throat, exhaust area, and choice of nozzle material (which I still have yet to decide) etc.. I have found the general guideline that the nozzle thickness is roughly the same as the thrust chamber thickness, but I'm looking for something a bit more specific; this is in case for say my choice of nozzle material differed from that of the thrust chamber et al.. I'm really approaching this from more of a theoretical point of view and so am light on the details. Anyway I was wondering if anyone knew of a formula or could point me in the right direction. Thanks.

### RE: Calculating Nozzle Width

icevail...

Some references that may be useful...

MIL-HDBK-762 DESIGN OF AERODYNAMICALLY STABILIZED FREE ROCKETS ... has some info on rocket nozzle design.

http://www.nakka-rocketry.net/

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

### RE: Calculating Nozzle Width

Might also want to check-out...

AMCP 706-242 ENGINEERING DESIGN HANDBOOK. DESIGN FOR CONTROL OF PROJECTILE FLIGHT CHARACTERISTICS.
http://www.dtic.mil/dtic/tr/fulltext/u2/801509.pdf

AMCP 706-285 Engineering Design Handbook. Elements of Aircraft and Missile Propulsion
http://www.dtic.mil/dtic/tr/fulltext/u2/861082.pdf

AGARD-CP-194 Small Solid Propellant Rockets for Field Use.

NOTE.
A Solid propellant rocket's stability/accuracy/trajectory are uniquely dependent on the solid-propellant/nozzle/exhaust-flow alignment/physical-interactions... and of-course fin/component symmetry/alignment... etc. Hard to get a 'bunch' of small tactical rockets to follow the exact-same standard/accurate trajectory shot-after-shot.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

### RE: Calculating Nozzle Width

iceveil-

The nozzle wall (beyond the throat) does not not see the same temps/pressures as the chamber, and the gas temps/pressures steadily decrease towards the nozzle exit. Most applications involving rocket engines are usually extremely weight sensitive, so a huge effort is made to minimize the weight of large components like the nozzle. However, you did not mention what type of rocket engine you are considering (liquid fuel, solid fuel, etc.).

At one end of the spectrum there are large liquid engines like the F1. The F1 used regenerative cooling of the chamber and nozzle walls, and the inner walls were surprisingly thin in order to provide efficient heat transfer. I've seen one of these massive engines up close, and the thousands of hand-welded cooling tubes lining the chamber and nozzle walls is a very impressive sight.

There are also un-cooled ablative nozzles like used on the RS-68 liquid engine. This nozzle is made of a phenolic material that develops a protective char layer on the flow surface after initial exposure to the high-temp propellant gas. While not quite as lightweight or efficient as a regeneratively-cooled nozzle, it is cheaper, less complex and more reliable.

Lastly, the link provided in your last post describes an extendable nozzle design. This type of nozzle is commonly used on the upper stage of launchers that place payloads in high orbits, and they operate in vacuum conditions. This application requires a high area ratio nozzle that is usually far longer than can be easily fit in the space available, thus the use of extendable nozzles. The extended portion of the nozzle is usually not cooled.

The NTRS website has lots of great tech references for rocket nozzle design.

Good luck to you.
Terry

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