Honeycomb or Foam Core Body Tubes

botscott08 said:

I have a little side project I'd like to try using very light construction to build an 8" diameter or larger low power rocket. I've considered a carbon/honeycomb/carbon tube and a balsa stringer and dope construction and don't much fancy the complexity of all those stringers even with a laser cutter handy. I've seen John Coker's honeycomb rocket article so that seems promising but the times I've tried honeycomb cores for fin stock they came in way over weight as the honeycomb absorbed a lot of excess epoxy. A divinycell foam core should solve that problem at the expense of weight since I can't find anything lighter than 3 lb foam. Does anyone know of a source for lighter flexible foam sheet or have tips for reducing epoxy over the honeycomb? I should mention I'm shooting for a one wrap of 4 oz 1K per layer but I'll build a practice tube or two using 5.9oz 3K just because I already have tons of it. I'm comfortable with prepreg too but couldn't find light 1k fabric.

Thanks,
Scott

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CarVac said:

If your goal is low-power, I think you should just use a few layers of 1k carbon instead of trying to increase the thickness; the thickness of the honeycomb gives weight benefits only when you need a certain minimum strength which I believe is more than necessary for low power.

Alternatively, you can try using an open balsa frame and simply wrap that with paper for appearance. That's probably the lightest.

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botscott08 said:

I really don't want to go the balsa stringer route. I mentioned that in my OP.

The problem with really thin wall tubes is thin shell buckling. Sure, in compression even a cardboard tube may have a factor of safety of 500 but the slightest asymmetry to the load and it buckles. I have 8" tubes with a .040" wall which have been fine for several HPR builds but I'd need less than a 0.020" wall to get the weight down enough to fly class 1. I finally found some 1k 4oz prepreg but I'll have to buy a whole roll of it. I suppose I'll just do that.

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CarVac said:

Not balsa stringers: a truss.

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