How much metal is acceptable in model rocketry?

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Knuckledragger

TLAR Engineering hack
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Thinking about a couple of thermal and gas laws demonstrations I want to conduct with the kiddos at school. Part of the agreement with admin is that the students will conduct themselves under the NAR safety code. NAR stipulates:
  1. Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.
We have light metal pieces in recovery systems attachment, thrust plates, and payload bays so my questions are:
1. Is "body" open to interpretation and excluding internals
2. Would a 3" long, 3/4 piece of perforated (drilled) aluminum tubing joined at the lower end of a B-D motor, strictly as an exhaust duct, be a no-go

What is the prevailing consensus/interpretation?
 
  1. Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.

My interpretation would be: Don't use a metal pipe for your rocket or make your fins or nose out of metal. Lol

Within reason, I believe such small metal devices are permissible. Maybe if you explain your setup we'll understand what it's for better?

Heck I can ask the last 3 NAR presidents when they're down for Student Launch next week! :cool:
 
That non-metal stipulation is odd. You can’t, in practice, use metal for large structural parts simple due to the weight but presuming I could make a 5g “metal” nose cone out of some future expensivium alloy why not?

There are plenty of motor retainers that are aluminium or steel. Reloadable casings are metal... Sounds like your application isn’t much different than than either of those.



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Thinking about a couple of thermal and gas laws demonstrations I want to conduct with the kiddos at school. Part of the agreement with admin is that the students will conduct themselves under the NAR safety code. NAR stipulates:
  1. Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.
We have light metal pieces in recovery systems attachment, thrust plates, and payload bays so my questions are:
1. Is "body" open to interpretation and excluding internals
2. Would a 3" long, 3/4 piece of perforated (drilled) aluminum tubing joined at the lower end of a B-D motor, strictly as an exhaust duct, be a no-go

What is the prevailing consensus/interpretation?

Are you actually launching a rocket? if so why the exhaust duct? Why not just use a piece of paper tubing like the body tube?
 
Just be careful not to modify ( incl. permanently affix ) said motor. I presume you're wanting to demonstrate Krushnic?
 
To demonstrate Krushnic and Bernoulli Lock primarily without burning up the rocket body and setting the field on fire but just in case the rocket does go airborne I don't want our safety hawk stabbing a finger in anyone's face saying "I told you so." One of our members has been looking at a few slow motion videos of motor burns and the exhaust aft of the motor casing and asking what if you extend the nozzle... So for Spring break I directed him here to start with https://www.nar.org/pdf/TCR1.pdf
 
To demonstrate Krushnic and Bernoulli Lock primarily without burning up the rocket body and setting the field on fire but just in case the rocket does go airborne I don't want our safety hawk stabbing a finger in anyone's face saying "I told you so." One of our members has been looking at a few slow motion videos of motor burns and the exhaust aft of the motor casing and asking what if you extend the nozzle... So for Spring break I directed him here to start with https://www.nar.org/pdf/TCR1.pdf
I presume you're going to a) test several times before zero hour and b) use a firmly planted no-launch rod and/or hold-down?

Very excited to see video, will be nice for helping people get a gut feeling for the differences and what can prevent each.

Any plans to demonstrate one that's both highly-recessed as well as flat-and-flush?
 
My previous answer to this question:

Not enough metal:

Ratt.png



Perhaps a bit too much metal:

marduk18.jpg



Just the right amount of metal:

Ace-of-Spades.jpg


ssixsixsix
 
If I were an RSO making a ruling, I’d say that “joined at the bottom of the motor” would constitute motor modification, so I’d nix it.
 
I presume you're going to a) test several times before zero hour and b) use a firmly planted no-launch rod and/or hold-down?

Very excited to see video, will be nice for helping people get a gut feeling for the differences and what can prevent each.

Any plans to demonstrate one that's both highly-recessed as well as flat-and-flush?

First I have to find a drill press to angle bore the metal and determine how to test thrust generated while being held down. Gonna have to bribe the Science dept!
More to come...
 
So maybe if the motor was say, snugged, in to the tube without being fixed to the motor and the retainer was kept at the top?
 
That non-metal stipulation is odd. You can’t, in practice, use metal for large structural parts simple due to the weight but presuming I could make a 5g “metal” nose cone out of some future expensivium alloy why not?

There are plenty of motor retainers that are aluminium or steel. Reloadable casings are metal... Sounds like your application isn’t much different than than either of those.



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I has less to do with weight and more to do with rigidity or frangibility. You can make a rocket as heavy as you want as long as it does not exceed the max liftoff weight of the motor.

Pretty sure "Body" has a definition in the code somewhere though not sure where. Motor casings are not part of the body, fins, or nose cone, one would argue they are not part of the rocket at all. You can not make a metal nose cone for model rockets, no matter how light. Model rockets and high power rockets are different. High power allows the use of some metal parts. It is a debate that goes on and on...and on.
 
I has less to do with weight and more to do with rigidity or frangibility. You can make a rocket as heavy as you want as long as it does not exceed the max liftoff weight of the motor.

Pretty sure "Body" has a definition in the code somewhere though not sure where. Motor casings are not part of the body, fins, or nose cone, one would argue they are not part of the rocket at all. You can not make a metal nose cone for model rockets, no matter how light. Model rockets and high power rockets are different. High power allows the use of some metal parts. It is a debate that goes on and on...and on.

I understand that there need to be rules for low power and that those rules need to be clear and unambiguous (ie: defining them in terms of material vs some esoteric measure of rigidity that is impossible to validate without the RSO breaking your parts). If you want to be pedantically technical about it, everything except the hydrogen atoms in any rocket is a “metal” of course... :)

Frangibility and rigidity are as much a function of part design as they are material choice. A rigid solid ABS nose vs a thin foil one - for example. Both probably bad ideas, but not only because of the material. Thus the ongoing debate I assume...

I’ve been rethinking metal for things like shock cord mounts because they’re deceptively (and usually unnecessarily) heavy for mid power models.






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