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Extention of Motor Mount Tubes

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nosaj13

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Hi,
I bet this is a obvious questions but when your are building your engine motor mount is it wise to extend the tube that holding the engine up into the body? It seems to me that if the rocket was five feet tall (the height of the rocket im planning on for my scratch build) once the ejection charge was released it would not have enough power to blow the nose cone off the rocket. So with the tube extending up further into the rocket it would not lose presser but also increase the stability of the rocket. (If the centering rings also continued that far up.

J.I.

I have included a pic of what I think will happen

Thanks

View attachment rocket pressure.bmp
 

dedleytedley

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Forgive me if I'm wrong but it sounds like you don't have much experience designing rockets. Apogee(rocket vendor) has free tutorials for rocket designing and building. They also offer a free design and flight simulation program called Rocsim. You can design and fly your rocket with different motor configurations and flight conditions. The demo only lasts for a month however but it's fun while it lasts. Ted
 

MarkII

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nosaj13 poses a good, logical and legitimate question. He is using good engineering logic to think through a design, and is noticing important details like that. The issue of pressurizing large airframes with a motor's built-in ejection charge has long been recognized in the discipline. A stuffer tube (i. e., a tube within a tube) as Wayne mentioned has been the standard way to address the problem and it is still widely used. In the past 20 years, though, another way has also been utilized in rockets with large airframes: a separate recovery compartment and electronic firing of a deployment charge. The recovery system is packed into its own compartment which is sealed off from the rest of the airframe by bulkheads. Since it can no longer be activated by the motor's built-in charge, the charge is either removed or a plugged motor is used. Black powder is poured into a small ejection charge capsule that is sealed and placed inside the recovery compartment. Wiring is run through the bulkhead to an electronic device, either an altimeter or a timer, and the device electrically ignites the charge in the capsule at the appropriate or predesignated moment in the rocket's flight. The charge only has to pressurize the section containing the recovery system, which deploys out of the compartment by blowing off the nose cone, a hatch or another bulkhead.

MarkII
 
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Handeman

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One additional item you might want to consider is the number of centering rings you have in the rocket with the stuffer tube. You really only need the ones holding the motor in place, and the one that seals the top of the stuffer tube.

A common practice is to install a baffle in the foward end of the stuffer tube, or onto the forward centering ring at the top of the stuffer tube.

Just a few ideas you can think over as you work up your next design.
 
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