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  #1  
Old 09-15-2007, 12:59 AM
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Solomoriah Solomoriah is offline
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Default My "Spike" -- would it be stable?

I'm considering a rocket stabilized by drag surfaces; it was inspired by a "nail" rocket built by another forum member (sorry, don't remember who). Take about 12" of BT-20, an ogive nose cone like the one in the Wizard kit, a thrust ring (duh) and three or four CR-2060's (and a recovery system, probably shock cord and streamer). Space the centering rings every half inch or so starting at 1/2" from the tail of the body tube. I'm assuming/hoping that they would provide adequate drag to make the rocket fly straight, similar to the spool rocket design.

I dreamed this up a while back, but when my trial of RockSim couldn't figure out the stability of it, I gave up on the idea. Now I'm thinking about it again...

Would it be stable? If not as described, perhaps with nose weight?
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Old 09-17-2007, 10:22 PM
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Well, that was a resounding silence.

I have two designs on the drawing board that RockSim couldn't handle... one is the Spike, and the other is a cone-shaped model. I wish I knew how to figure them out. Guess I'm going to have to actually learn the math.
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Old 09-17-2007, 10:55 PM
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Quote:
Originally Posted by Solomoriah
Well, that was a resounding silence.

I have two designs on the drawing board that RockSim couldn't handle... one is the Spike, and the other is a cone-shaped model. I wish I knew how to figure them out. Guess I'm going to have to actually learn the math.


Solo,

I tried working your "Spike" up and couldn't get the margin without some additional work, like a paper shroud...

My suspicion is that you can get the idea to fly, using a set of rings that get progressively larger toward the tail. It might generate the same slipstream as the shroud, and thus create a similar drag. RockSim might just not be able to compute the air flow correctly...

One thing that will help: Use 13mm motors instead of 18mm. All you want for this prototype is to fly, say, no more than 400'. An A3-4T would be more than sufficient.
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Old 09-17-2007, 11:26 PM
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I'm more inclined to wonder if RockSim can even simulate either rocket properly. I was unable to get any sort of cone rocket to be stable when I was trying it out (a few months back) and yet there I was looking at the article from MRM discussing such a rocket. One thing I never tried was the "Finless" rocket (the one with the conical shroud at the aft end) but frankly I'm not sure it would make a difference. I don't think RockSim can simulate a rocket that gets stability from something that doesn't look like a fin.
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Old 09-18-2007, 08:19 PM
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IIRC, the CP of a cone is 2/3rds of the distance from the nose tip, so you can use that as a figure for determining if the rocket is stable. Moving the motor forward also helps to compensate.
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Old 09-19-2007, 11:19 PM
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Quote:
Originally Posted by Solomoriah
I'm considering a rocket stabilized by drag surfaces; it was inspired by a "nail" rocket built by another forum member (sorry, don't remember who). Take about 12" of BT-20, an ogive nose cone like the one in the Wizard kit, a thrust ring (duh) and three or four CR-2060's (and a recovery system, probably shock cord and streamer). Space the centering rings every half inch or so starting at 1/2" from the tail of the body tube. I'm assuming/hoping that they would provide adequate drag to make the rocket fly straight, similar to the spool rocket design.

I dreamed this up a while back, but when my trial of RockSim couldn't figure out the stability of it, I gave up on the idea. Now I'm thinking about it again...

Would it be stable? If not as described, perhaps with nose weight?


I actually have something very similar to what you are describing. I took an 18" BT-50 tube, 1 CR 5060, 1 CR 5070, and finally 2 CR 5080's. They are spaced 1" apart. It uses 13mm motors. The complete rocket (minus paint) weighs .8 ounces.

Don't get all carried away mounting your CR's....each one has to be drilled for the launch rod or I guess you could use stand offs and a launch lug....either would work. I like the "no lug" look myself.

Have fun!

Bo
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Last edited by Bohica : 09-23-2007 at 01:34 AM.
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Old 09-20-2007, 12:27 AM
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Quote:
Originally Posted by Bohica
I actually have something very similar to what you are describing. I took an 18" BT-50 tube, 1 CR 5060, 1 CR 5070, and finally 1 CR 5080. They are spaced 1" apart. It uses 13mm motors. The complete rocket (minus paint) weighs .8 ounces.

Don't get all carried away mounting your CR's....each one has to be drilled for the launch rod or I guess you could use stand offs and a launch lug....either would work. I like the "no lug" look myself.

Have fun!

Bo


Bo,

Would you want to post something on the new BARCLONE thread for that rocket? I'd like to see it, and I think others would, too.
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Old 09-20-2007, 06:48 AM
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Quote:
Originally Posted by CPMcGraw
Bo,

Would you want to post something on the new BARCLONE thread for that rocket? I'd like to see it, and I think others would, too.


Sure...let me slap a little paint on it and I will post the specs and a pic.
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  #9  
Old 09-20-2007, 08:06 AM
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Quote:
Originally Posted by Bohica
Don't get all carried away mounting your CR's....each one has to be drilled for the launch rod or I guess you could use stand offs and a launch lug....either would work. I like the "no lug" look myself.

I did actually think about that. I figure I'll stack the CR's and drill them on my drill press.

I'm curious whether a design with same-size CR's can be stable. My "gut" says yes, but RockSim said no. I think I may build the darn thing just to find out.
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  #10  
Old 09-20-2007, 10:30 PM
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Quote:
Originally Posted by Solomoriah
I did actually think about that. I figure I'll stack the CR's and drill them on my drill press.

I'm curious whether a design with same-size CR's can be stable. My "gut" says yes, but RockSim said no. I think I may build the darn thing just to find out.


That's what I do! If I have a design...I build it and tweak it until it works. I have at least 3 designs that fly great that certain Sim programs said would never be stable. Of course just like with any program the "garbage in, garbage out" rule applies.

Bo
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