Expansion ratio - altitude?

[HattoriHanzo]

Suppose we want our rocket fly(vertical) to an altitude(within the atmosphere but not in "space") were ambient pressure is, for example, 1Pa.
What expansion ratio of the nozzle is best to choose?

Is it possible to calculate a mean number of the atmospheric pressures at any given altitude between 1.103e+5Pa to 1Pa and use this pressure as a reference when designing the nozzle?


A variable expansion nozzle would be very helpful. Are there any commercial or known experimental "spacecrafts" that use rocketengines with variable nozzles?

[HattoriHanzo]

Maybe its best to optimize the expansion ratio(> thrust) for a lower altitude(and higher pressure) because the gravity are stronger and more thrust is requried?

[Ray]

Nozzle expansion is a tough one. It depends on many different variables...chamber pressure and ambient pressure being the primary factors.

Decide what altitude you want it to work best at, choose a chamber pressure you want to operate at, then calculate what its going to take to return the chamber pressure to the altitude pressure. At a chamber pressure of around 800psi (5.5 megapascal) a nozzle expansion of around 6.5 (just a wild assed guess) works for sea level.

OR you could use an aerospike nozzle.

[HattoriHanzo]

Nozzle expansion is a tough one. It depends on many different variables...chamber pressure and ambient pressure being the primary factors.

Decide what altitude you want it to work best at, choose a chamber pressure you want to operate at, then calculate what its going to take to return the chamber pressure to the altitude pressure. At a chamber pressure of around 800psi (5.5 megapascal) a nozzle expansion of around 6.5 (just a wild assed guess) works for sea level.

OR you could use an aerospike nozzle.

I have read about the aerospike nozzle. And Boeing-Rocketdyne linear aerospike nozzle with "inside out" flow. Very interesting stuff! Hard to understand however...

If you have any literature recommendation on this subject I would be grateful.

[Ray]

I did a quick search on Google (aerospike nozzle) and came up with a bunch of referances...

Try this one, go to the referance page. He has a ton of papers that he has published about the Aerospike nozzle. Unfortunately for me, they are in Japanese, however, you are from Okinawa, I assume that you speak Japanese, that's good for you.

Another one here

Good luck, let us know your results.

[MJD]

AIAA 2005-3797 describes aerospike flight tests conducted by NASA Dryden using solid rocket motors with aerospike nozzles built by our company. We built the nozzles to NASA's profile, and also designed and built the solid rocket motors. These are "O" class motors based on our commercial 168mm motor.

It's easy to build something that looks a bit like an aerospike and several amateur motor makers have done so, but to build a properly designed aerospike that does what it is supposed to, and have it hold together is a serious engineering challenge.

Mike D.

[HattoriHanzo]

I did a quick search on Google (aerospike nozzle) and came up with a bunch of referances...

Try this one, go to the referance page. He has a ton of papers that he has published about the Aerospike nozzle. Unfortunately for me, they are in Japanese, however, you are from Okinawa, I assume that you speak Japanese, that's good for you.

Another one here

Good luck, let us know your results.

Thanks
Unfortunately I am not japanese, just a big fan of Kill Bill :wink:

[HattoriHanzo]

AIAA 2005-3797 describes aerospike flight tests conducted by NASA Dryden using solid rocket motors with aerospike nozzles built by our company. We built the nozzles to NASA's profile, and also designed and built the solid rocket motors. These are "O" class motors based on our commercial 168mm motor.

It's easy to build something that looks a bit like an aerospike and several amateur motor makers have done so, but to build a properly designed aerospike that does what it is supposed to, and have it hold together is a serious engineering challenge.

Mike D.

I can only get the first side of that papers.
Where do you work? Sounds like the place to be.

[MJD]

Where do you work? Sounds like the place to be.

Yeah, it's okay.. :wink:

www.cesaroni.net - company website
www.pro38.com - hobby solid rocket motor site
www.hypertekhybrids.com - hobby hybrid rocket motor site (needs updating)

Check out the news section on the first link, you can see the nozzle and a quick video of a static firing there.


MJD

[Ray]

Hey MJD, were you in Lethbridge this summer for LDRS? I think I may have met you there...in Tsolo's coach? Last day of the launch...