B Model rocket physics: Why doesn't the motor go through the nose cone?

[LT72884]

For those who have built those small model rockets, please help me understand a very very simple physics problem that i for some reason do not fully get.
Why is it that the motor tube does not have a retention ring on it, to prevent the motor from flying out the nose cone? i know it cant be friction that holds the motor in place because the motor slides in pretty nice, but nothing to stop it from sliding further and eventually out the nose cone
Thanks
EDIT: i figured out my answer and yes, im an idiot today.... feel free to add whatever you want to this post

thanks.

 

[renormalize]

Why is it that the motor tube does not have a retention ring on it, to prevent the motor from flying out the nose cone?

The model rockets I built (decades ago!) all had retaining rings ("Engine Block/Ring (Internal)") glued to the interior to prevent engine motion.

(from here)

 

[russ_watters]

The model rockets I built (decades ago!) all had retaining rings ("Engine Block/Ring (Internal)") glued to the interior to prevent engine motion.
View attachment 323566
(from here)

...and for rockets with a body the same diameter as the motor, it's just a simple ring. If there wasn't enough friction in the body they could fall our before launch!

 

[Baluncore]

EDIT: i figured out my answer and yes, im an idiot today.... feel free to add whatever you want to this post

If you can ask the right question, and then answer it yourself, you are not an idiot. You are an engineer considering a complex multidimensional system.

 

[A.T.]

. feel free to add whatever you want to this post

Am I right to assume that the engine block accounts for most of the total mass? The friction/rings only have to transmit the force to accelerate the lightweight rest of the rocket.

 

[renormalize]

Am I right to assume that the engine block accounts for most of the total mass? The friction/rings only have to transmit the force to accelerate the lightweight rest of the rocket.

Well back in my day, the engine rings and body of a small model rocket were just sections of carboard tubing of almost negligible weight in comparison to that of the disposable rocket engine itself, the balsa wood fins & nosecone, and payload, if any.

 

[cjl]

As stated above, most small model rockets use an internal ring that the front of the motor butts up against to prevent exactly this from happening.

For larger model rockets, it's much more common for this to be missing, and instead the motors are designed with a slightly larger diameter section right at the rear of the rocket motor that butts up against the rear of the motor tube. The reason for this difference is because in larger models, a common way to change motor fuel capacity (and thus power) is to change the length of the motor, so having a forward stop would be problematic and would require a variety of spacers depending on motor length. Having the stop built into the rear of the motor instead completely solves this issue.

 

[marcusl]

It’s been over a decade since my last experience with model rockets (as a Scout leader), but I distinctly remember metal clips. Maybe they’re on some models but not others? Or maybe not used anymore?

 

[russ_watters]

It’s been over a decade since my last experience with model rockets (as a Scout leader), but I distinctly remember metal clips. Maybe they’re on some models but not others? Or maybe not used anymore?

It just depends on the diameter of the rocket. If the diameter of the rocket is the same as the motor they are held in place with just a thrust ring and friction. If the rocket is larger they use a mounting system with a separate tube, stand-off rings and a clip.