Nozzle tricks?

[Asteroza]

Interesting post over at the Secret Projects Forum, outlining early J-2X nozzle extension concepts.

http://www.secretprojects.co.uk/forum/index.php/topic,16981.msg214887.html#msg214887

There is certainly the more conventional telescopic single piece nozzle extension concept, well demonstrated on ICBM's. Sea Dragon had a sorta pleated/folded metal nozzle extension that popped open like a jiffie-pop popcorn bag. The interesting bit in the above link is the inflatable airmat nozzle extension for the J-2X, filled via turbine exhaust. It's certainly unusual, using both turbine exhaust for maintaining inflation, plus possible film cooling via porosity of the internal airmat weave. I wonder if there are any opportunities for a TAN injector setup to line the main nozzle injector ring rather than the conventional injectors? Could the airmat concept be reversed for an annular aerospike?


For reference, what other major tricks are there to increase nozzle length? Physical extensions seem to revolve around some type of telescoping action. Non-physical methods creating virtual nozzles, such as a magnetic nozzle perhaps?

[john smith 19]

Interesting post over at the Secret Projects Forum, outlining early J-2X nozzle extension concepts.
For reference, what other major tricks are there to increase nozzle length? Physical extensions seem to revolve around some type of telescoping action. Non-physical methods creating virtual nozzles, such as a magnetic nozzle perhaps?

The linked item does a good job of showing a variety of extendible nozzle. They actual type used on the RL-10s (if you order one with it) seems to be a 2 piece design in RCC which has be to extended before ignition.

"Airmat" seems to have been proposed for various systems, including TPS and IIRC an inflatable wing aircraft.

There is another nozzle extension scheme I'm aware of. It originated with Bell Aerospace in the the early 70's. AIUI it worked like a kind of (refractory) metal foil "sock." A set of metal struts would sit round the engine and then extend downward. The tips of the struts had rollers the foil would gradually roll over them from the outside surface of the bell to the inside until fully extended. [EDIT Sort of like a Victorian "hoop skirt" turned inside out ]

[cordwainer]

I've always wondered if it might be technically feasible to use a variable geometry nozzle to control and throttle a pulse detonation ignition. In a pulse detonation jet engine the thermal wear and tear isn't as high as a rocket engine particularly if you use hydrogen or methane fuel so you might be able to use something like a ducted nozzle or a micro-actuated movable skirt. Could even be used in a small rocket engine in vacuum if you can get reliable pulse ignition with the right fuels.

[john smith 19]

I've always wondered if it might be technically feasible to use a variable geometry nozzle to control and throttle a pulse detonation ignition. In a pulse detonation jet engine the thermal wear and tear isn't as high as a rocket engine particularly if you use hydrogen or methane fuel so you might be able to use something like a ducted nozzle or a micro-actuated movable skirt. Could even be used in a small rocket engine in vacuum if you can get reliable pulse ignition with the right fuels.

What properties of the nozzle do you want to change?