#1
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How deep to "nest" tubes for strength (HPR)
I'm starting to build my quarter scale Nike Ajax (single stage) This is a 4" dia Nike booster to a 3" dia Ajax. The rocket should end up just over 8ft and fly on 54mm motors. The two components will separate for transport but I'm trying to decided how deep into the Ajax the central tube should extend. The 3" Ajax tube serves as recovery gear compartment for the whole rocket so I need as much volume as possible.
My question, is how deep, in calibers, should the 54mm tube extend up into the 3"Ajax tube? This is pretty much where the strength is but it is also where the rocket separates for transport. Recovery separation is at the nose cone. To add more strength, the 54mm tube that extends out of the Ajax will have two centering rings and LOC coupler/stiffy that fits just inside the top of the 4" Nike booster. Screws/tee-nuts will hold the two together for flight. The 54mm tube has a very thick wall coupler that fits into the upper end of the 54mm motor tube proper in the Nike booster. Rocksim 8.0 file included for perusal. OF course, it's a rough drawing at the moment. Thanks for any advice or help Moe |
#2
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I am a firm believer that at a minimum 1.5 calibers is minimum. I usually use at least 2 calibers for coupler length. Allot of this depends on how well and what techniques are used for the coupler. Is it plain cardboard, phenolic or reinforced with composite materials.
Mick Kelly Last edited by Mick Kelly : 11-28-2008 at 10:00 PM. |
#3
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Hi Mick - thanks for the reply. All tubes involved are LOC heavy wall cardboard. For this project - the Nike Ajax, I'm probably going to go with 2 - 2.5 calibers for the 54mm tube nested inside the 3" tube. There is no coupler involved here - just a couple of 1/4" plywood centering rings. The coupler that phyisically joins the two rockets together is a LOC 6" long standard coupler with the "stiffy" inside and standard plywood centering rings at both ends to center the 54mm tube.
Moe |
#4
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Moe, sorry i didn't get a chance to answer your email on this...I got a bit side tracked.
If the model is only going to seperate for transport and it doesn't have to seperate at that point from ejection, then longer, at least 2 calipers is better. You probably should have some type of retension so it doesn't seperate at ejection. I'm thinking some type of srews. Something metal so they don't act like shear screws.
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"I'm a sandman. I've never killed anyone. I terminate runners when their time is up." Logan from "Logan's Run" http://sandmandecals.com/ |
#5
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No worries G - it was Thanksgiving weekend afterall...
The area where the nesting occurs is a solid bond... I'm thinking of 8 inches or so (over 2 calibers) for this area. The separation point for storage is at the top of the Nike booster and will have a LOC 4" diameter coupler plus six 10-24 threaed into tee nuts in the coupler to secure for flight. I'm gonna be ordering that nose cone by the way... |
#6
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Quote:
Thanks for understanding. My grandaughter was here and at 10 months she's very mobile now and quite a handfull. But fun!
__________________
"I'm a sandman. I've never killed anyone. I terminate runners when their time is up." Logan from "Logan's Run" http://sandmandecals.com/ |
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