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Krushnick Effect and rockets

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#1 Karl


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Posted 02 November 2005 - 12:06 AM

This is a question that has been playing on my mind for a good while now!

I've read about the Krushnick Effect in model rocket motors, and have been wondering why doesn't the same theory expand into Rocket Motors in fireworks?
The Krushnick Effect if you didn't know is;

Krushnic Effect: A very dramatic phenomenon where your rocket makes a tremendous amount of noise and smoke but doesn't go anywhere! This happens when the motor is recessed into the body tube by more than one tube diameter. If so recessed, the cylindrical volume below the motor forms a secondary expansion chamber which allows the exhaust gasses to expand below atmospheric pressure before leaving the rocket. Surrounding air aspirated into the exhaust stream causes turbulence which negates much of the thrust, along with creating the characteristic roar. A multi-stage model that ejects its booster motor, but not the airframe, is a perfect example. Very damaging; it almost always destroys the lower body tube beyond use. Named for Richard Krushnic, the rocketeer who characterized the effect in the late '60s. Not to be confused with "Suction Lock" (q.v.).

The majority of large display rockets use a plastic motor tube, wrapped in a cardboard outer layer. This would reenact the bodytube around the motor. Now, I've seen motors in rockets that have had the carboard tube atleast extended over the motor by one tube diameter! Why do rockets seem unaffected by this?

Edited by Karl, 02 November 2005 - 12:07 AM.

#2 fishy1



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Posted 05 November 2005 - 11:15 AM

got any vidoes of the effect?

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