Non tubular (stick) bodies and tractor motors.

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Senior Space Cadet

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I'm still intrigued by the idea of tractor motors. That is, motors toward the front of the rocket, eliminating the need for added weight in the nose and an inherent increase in stability (see arguments for FWD and bottle rockets).
The problems are, at least, two fold.
Problem one: At least two engines is nearly mandatory, unless your were making a glider. Any difference in power would result in a curved trajectory. As I said before, spinning would reduce that effect.
Problem two: The flame from the engines might start the body, or fins, of the rocket, on fire, but spacing the motors out from the body would reduce this risk but increases the likelihood of the first problem.

Possible solutions:
Don't use a central body tube. Instead, use stick balsa. This gets the engine thrust closer to the centerline. It would also give you a more solid way of attaching four fins (against the four sides of the square balsa stick).
Use heat resistant stove paint to paint the lower part of the rocket. Yes, color choices are limited (It comes in any color you want as long as it's black) and probably only comes in satin and flat. Hopefully I'm wrong about color selection.
Another possible design would be to use a rectangular balsa stick and use two fins, such that the motors don't point at the fins. Possible?

Potentially, you could use four motors. I'd have to experiment with how large the central balsa stick would need to be.
Something different to think about and experiment with.
As I said before, but didn't fully believe myself, it seems like everything has been done before. I'll be waiting for the photos of stick rockets you guys have.
 

dhbarr

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You'll want to think more about recovery, but there's no reason a 3-fin stick body shouldn't work.

Stainless tape or aluminum paint are two other things to try on the sides of your stick. And remember they make hollow FG or CF tubes, so your heat resistant stick could also be your lug.

Keep thinking new thoughts!
 

llickteig1

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Stainless tape or aluminum paint are two other things to try on the sides of your stick. And remember they make hollow FG or CF tubes, so your heat resistant stick could also be your lug.
Carbon fiber arrow shaft wrapped with Al tape.
 

Senior Space Cadet

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I certainly know where to get arrow shafts.
Considering the inherent stability of the tractor design, arrow vanes would make total sense. Might melt easily.
So, basically, a rocket powered arrow.
Seem like the Chinese did something like this a very long time ago.
Seems like there was something on Myth Busters.
 

Senior Space Cadet

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They also make aluminum arrow shafts.
One thing about arrow shafts, as a body, you know they are extremely straight.
Arrow shafts come in different diameters, including really fat ones for indoor competition.
 

mbeels

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That sort of reminds me of the rack rocket:

 

neil_w

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Stick body etc. should work, given due attention to recovery as dhbarr suggests above. That said, canting the motors away from the body is the most common approach for tractor motor designs.
 

125cc

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I can see it working. Fireworks have a stick that gives them some stability during ascent. Only problem I can think of having upper motors is setting fire to whatever structure is below them...
 

Kelly

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Problem one: At least two engines is nearly mandatory, unless your were making a glider. Any difference in power would result in a curved trajectory.
In practice, this isn't a problem. Pyrotechnic rocket makers use single, offset sticks all the time and don't see a curved trajectory.
Regardless, there's one other possibility that you didn't mention: Pyrotechnic rocket makers will sometimes use 2 sticks (for added stability), one on either side of the engine. That makes it symmetric, without going to two engines.
 

dhbarr

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In practice, this isn't a problem. Pyrotechnic rocket makers use single, offset sticks all the time and don't see a curved trajectory.
Regardless, there's one other possibility that you didn't mention: Pyrotechnic rocket makers will sometimes use 2 sticks (for added stability), one on either side of the engine. That makes it symmetric, without going to two engines.
Now I'm feeling a 2-stick 2-fin Space Ship Two kind of vibe, nice.
 

afadeev

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I'm still intrigued by the idea of tractor motors. That is, motors toward the front of the rocket, eliminating the need for added weight in the nose and an inherent increase in stability (see arguments for FWD and bottle rockets).
Like Nell, I suppose:

The problems are, at least, two fold.
Problem one: At least two engines is nearly mandatory, unless your were making a glider. Any difference in power would result in a curved trajectory. As I said before, spinning would reduce that effect.
Problem two: The flame from the engines might start the body, or fins, of the rocket, on fire, but spacing the motors out from the body would reduce this risk but increases the likelihood of the first problem.
Or, option #3:
 

jhartman009

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I'm still intrigued by the idea of tractor motors. That is, motors toward the front of the rocket, eliminating the need for added weight in the nose and an inherent increase in stability (see arguments for FWD and bottle rockets).
The problems are, at least, two fold.
Problem one: At least two engines is nearly mandatory, unless your were making a glider. Any difference in power would result in a curved trajectory. As I said before, spinning would reduce that effect.
Problem two: The flame from the engines might start the body, or fins, of the rocket, on fire, but spacing the motors out from the body would reduce this risk but increases the likelihood of the first problem.

Possible solutions:
Don't use a central body tube. Instead, use stick balsa. This gets the engine thrust closer to the centerline. It would also give you a more solid way of attaching four fins (against the four sides of the square balsa stick).
Use heat resistant stove paint to paint the lower part of the rocket. Yes, color choices are limited (It comes in any color you want as long as it's black) and probably only comes in satin and flat. Hopefully I'm wrong about color selection.
Another possible design would be to use a rectangular balsa stick and use two fins, such that the motors don't point at the fins. Possible?

Potentially, you could use four motors. I'd have to experiment with how large the central balsa stick would need to be.
Something different to think about and experiment with.
As I said before, but didn't fully believe myself, it seems like everything has been done before. I'll be waiting for the photos of stick rockets you guys have.
I tried a tractor design that was similar to the Nell model for an altitude contest. It worked but did not produce the results I wanted. The distance between the motor nozzle and the trailing balsa nose cone was about an inch. The cone was successfully protected by a thin layer of epoxy. Another alternative is a model called the Bifurcon (Model Rocketry, March, 1969). The motors are canted 15 degrees and there is little to no damage to the trailing body tube. Not the most efficient, but it is a great design.
 

Dotini

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Here's a rocket I've been playing with for a couple of weeks. I've launched and recovered it 5 or 6 times with different motors and ballast, and done some swing testing. I'm trying to get it to come down tail first.

DSC00117.jpg
 

Dotini

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Nice. Are those dowels? Is it an 18mm?
Yes sir, those are I/8" birch dowels from Canada, and is indeed 18mm. There are 48 tiny lead balls glued around the base, but yet are insufficient to get it to come down tail first, even with ejection of the motor. My attention has been diverted from playing with this rocket, but my plan is to perhaps add even more weight, or better yet reduce the length of the base ring. There may also be needed an adjustment in the overall length of the model. It's an experimental attempt to achieve a form of tumble recovery with the bell rocking back and forth on descent.
 

Aeronerd

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Yes sir, those are I/8" birch dowels from Canada, and is indeed 18mm. There are 48 tiny lead balls glued around the base, but yet are insufficient to get it to come down tail first, even with ejection of the motor. My attention has been diverted from playing with this rocket, but my plan is to perhaps add even more weight, or better yet reduce the length of the base ring. There may also be needed an adjustment in the overall length of the model. It's an experimental attempt to achieve a form of tumble recovery with the bell rocking back and forth on descent.
Oh wow that must put the CG really way back. And it's still stable?
How about keeping the motor and popping a streamer? The drag from the streamer and the extra motor weight should bring it down tail first.
 

Dotini

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Oh wow that must put the CG really way back. And it's still stable?
How about keeping the motor and popping a streamer? The drag from the streamer and the extra motor weight should bring it down tail first.
At present it seems over stable, though doesn't seem to weathercock. One of my personal priorities is to research tumble recovery and avoid chutes and streamers, thus ejection of the motor becomes highly useful in this regard. There is no room in this model for a conventional recovery system, so in that case it would have to be a new model, completely redesigned.

In swing testing this model, if started facing backwards it will not turn around and go nose first. So I may be very close to getting it to descend tail first.
 
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