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CF airframe + alu skin on a supersonic rocket?

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136472 makemake

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Hey everyone! First poster here. I'm an absolute newbie to this subject who just learned about it a few days ago, so have mercy on me if I'm wildly off the mark here with my question:

In the search for a lighter rocket, has anyone built a supersonic rocket which has a carbon fiber skeletal airframe for the main body, wrapped in a very thin non-structural layer of aluminum (or something else) for the "skin" to preserve aerodynamic qualities?

I envision the airframe as rings spaced out every so often, connected with 3-4 "columns" to join them all, as opposed to a full CF tube, most likely capped with a conventional CF nosecone and fin can.

I read that on the SR-71 flying at Mach 3+, temperatures could get up to 315 C / 600 F, and the melting point for these materials is much higher, so I'm assuming nothing would melt or deform significantly?

Thanks to all who reply.
 

tfish

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cardboard rockets are capable of going "supersonic" And cardboard is a fairly good insulator.

Tony
 

Xrain

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The SR-71 traveled at mach 3.2 for many, many hours on end. That is why the skin would get so hot, it was operating supersonic in a steady-state condition. Rockets on the other hand, especially amateur ones only spend a few brief seconds supersonic. Because of this you don't get much heating of the airframe.

Just like you can take your finger and if you are quick enough, wave it through the flame of a blow torch and not even feel warm; rockets can get some pretty high heating levels and not need much to deal with it. It's only when you start going Mach 4 to Mach 5 on your rockets at low altitudes you have to start contemplating taking measured to deal with heating issues. So as Tony said, you can do supersonic rockets with cardboard and other "not so great" materials. Just depends on how you design it.

As for your idea otherwise. Carbon Fiber isn't really the best material for compressive strength. So it isn't really the best material to make a superstructure out of. Aluminum is also highly thermally conductive, so it would quickly transfer heat to the composite superstructure below it; which would ruin most of the point of why you wanted it in the first place. Something it would do well, is the surface of the aluminum would not get roughened up like composites do when you go high supersonic.

I like that you are putting quite a bit of thought into things like this. You missed the mark a bit this time, but that is pretty normal for just starting out in a field. Only difference between someone starting out, and someone who is experienced, is one asked a lot more questions and made more mistakes.

Keep at it!
 

boatgeek

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I don't know for sure, but I suspect that by the time you got the aluminum thick enough (or CF elements close enough together) to hold up to aerodynamic forces, you'd be at or more than the weight of a basic CF airframe. It's definitely an interesting thing to think about.

Another complication is that if you are launching under NAR or Tripoli rules, you can't have major airframe components made out of metal. I believe that Tripoli will relax that if you show a good reason, but that might be difficult to prove in this instance since other airframe materials are available.
 

dhbarr

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The lightest rocket is none at all, just motor, fins, and recovery gear. Anything that makes it fatter, rougher, or massier is going to slow you down.
 

136472 makemake

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Thanks a lot for the input everyone, it's given me a lot to think about! Some really good info here.
 
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