Rocket Engine: Centripetal Force to Vector thrust

[Jack Oswald]

Hey guys,

I'm new to the forum and I have a question that has stumped several of the professors at my school. My idea is to use an electric motor with a solid rocket engine on a thrust stand to spin the exit cone. The concept would make use of centripetal force to increase the pressure of expanding gasses against the diverging cone. The spin would be precisely controlled and could allow micro adjustments of thrust in larger engines. Additionally, if enough centripetal force is created, the exit cone could be lengthened increasing thrust by means of an electric motor rather than more propellant. Please let me know if this idea is feasible and any literature that would help me find the solution.

Regards,
Jack Oswald

 

[berkeman]

Hey guys,

I'm new to the forum and I have a question that has stumped several of the professors at my school. My idea is to use an electric motor with a solid rocket engine on a thrust stand to spin the exit cone. The concept would make use of centripetal force to increase the pressure of expanding gasses against the diverging cone. The spin would be precisely controlled and could allow micro adjustments of thrust in larger engines. Additionally, if enough centripetal force is created, the exit cone could be lengthened increasing thrust by means of an electric motor rather than more propellant. Please let me know if this idea is feasible and any literature that would help me find the solution.

Regards,
Jack Oswald

Welcome to the PF.

Do you have some sketches that you can share? Have you done efficiency calculations that compare the extra weight of the battery and electric motor and extra mechanical complexity, versus the same weight of adding more propellant?

 

[anorlunda]

I'm not sure I understand your question. Do you want to generate electric power using a rocket?

Can you post a sketch of your idea? It sounds like a fireworks helicopter.

 

[Jack Oswald]

Welcome to the PF.

Do you have some sketches that you can share? Have you done efficiency calculations that compare the extra weight of the battery and electric motor and extra mechanical complexity, versus the same weight of adding more propellant?

Thanks berkeman,

I have not, not yet. My interest lies not in necessarily how practical the application is in the present but simply in whether the centripetal force would allow further control over the thrust of a solid rocket engine (and hypothetically liquids) and/or increase the pressure and allow the lengthening of the exit cone. I am only a high school student, I am on the road to fluid dynamics but it is still a year of calculus away.

Jack Oswald

 

[Jack Oswald]

I'm not sure I understand your question. Do you want to generate electric power using a rocket?

Can you post a sketch of your idea? It sounds like a fireworks helicopter.

I think this is a recurring theme; I'll try to draw something up.

 

[Nidum]

This is a non viable project . No analysis needed .

 

[Jack Oswald]

This is a non viable project . No analysis needed .

Nidum,

I would appreciate it if you could elaborate.

 

[Jack Oswald]

It's ugly, hope it gets the idea across.

I'm not sure I understand your question. Do you want to generate electric power using a rocket?

Can you post a sketch of your idea? It sounds like a fireworks helicopter.

 

[RogueOne]

Converting that linear thrust into tangential thrust around a circumference that is perpendicular to the rocket's direction of travel will decrease the amplitude of the net force propelling the rocket on its forward vector. Also, an equal and opposite amount of force would be needed in order to counteract the rocket's spin that would be caused by the momentum transfer while imparting spin onto the thrust itself. Both of these concepts are due to Newton's third law. You start out with all of the particles imparting force to the rocket 180 degrees away from the rockets intended path of travel (forward). Thus, equal and opposite reaction causes the rocket to move forward. If the particles apply that force at any angle less than 180 degrees from the intended path of travel, the rocket will not be able to use all of that particle's energy to move forward. If the particles symmetrically departed from the system at 90 degrees from the ipot, then the rocket would have no motion.

However, it does have the potential to give adjustability by incrementally reducing the amount of effective thrust being applied to the rocket.

 

[Jack Oswald]

Converting that linear thrust into tangential thrust around a circumference that is perpendicular to the rocket's direction of travel will decrease the amplitude of the net force propelling the rocket on its forward vector. Also, an equal and opposite amount of force would be needed in order to counteract the rocket's spin that would be caused by the momentum transfer while imparting spin onto the thrust itself. Both of these concepts are due to Newton's third law. You start out with all of the particles imparting force to the rocket 180 degrees away from the rockets intended path of travel (forward). Thus, equal and opposite reaction causes the rocket to move forward. If the particles apply that force at any angle less than 180 degrees from the intended path of travel, the rocket will not be able to use all of that particle's energy to move forward. If the particles symmetrically departed from the system at 90 degrees from the ipot, then the rocket would have no motion.

However, it does have the potential to give adjustability by incrementally reducing the amount of effective thrust being applied to the rocket.

If I am understanding correctly, you're saying the spinning of the exit cone of the nozzle will result in the exhaust particles applying force in a less than 180 degree direction from the forward position. However, my question is would this loss of thrust be made up for by the longer exit cone made possible by the centripetal force.

 

[RogueOne]

Not unless the longer cone increases the energy release of the engine enough to overcome that loss in net force thrusting the rocket forward.

 

[Jack Oswald]

Not unless the longer cone increases the energy release of the engine enough to overcome that loss in net force thrusting the rocket forward.

To make sure, it would be an electric battery supplying the energy to spin the nozzle not exhaust gas. I wouldn't think that spinning the nozzle would actually reduce that much thrust being produced due to an incomplete angle.

 

[JBA]

Due to the propellant exit velocity through the nozzle at Mach 1 or above, I doubt that the nozzle could be spun a sufficient rate to significantly alter the exhaust vector.

 

[Jack Oswald]

Due to the propellant exit velocity through the nozzle at Mach 1 or above, I doubt that the nozzle could be spun a sufficient rate to significantly alter the exhaust vector.

Great, thanks for the info everyone.

 

[berkeman]

Great, thanks for the info everyone.

Glad to help. Your interest in STEM going forward is great. Keep on thinking and asking questions.

 

[berkeman]

BTW, do you have a rocketry club where you are? If not, maybe you should find a Mentor and start one...

 

[Nidum]

Nidum,

I would appreciate it if you could elaborate.

The gas flow dynamics of a rocket nozzle is complex and just saying ' increase the pressure ' is not very meaningful .

Since simple rocket nozzles are always optimised for their purpose anyway adding complex systems to them is unlikely to result in any improvement in performance .

There is no mechanism for transfer of any significant amount of energy from a spinning rocket nozzle to the contained gas flow .

To significantly increase the pressure of the gas flow would require compressor like components inside a much modified nozzle and a huge input of power .

This input power would have to have a source . Basically more fuel and an auxiliary engine . Batteries and electric motors are not a realistic proposition .

The proposed system would add considerable weight and complexity and reduce reliability for no obvious gain .

Your interest in STEM going forward is great. Keep on thinking and asking questions

+5 to that .