Back to Tubes – Theory & Shopping

This article is a follow up on our previous tube development covered here, here and here.

I had to remind myself on what we are trying to achieve here a bit and rethink it again. So for our actual project we need to develop a tube which will serve as a central duct and airship keel. It has to be ~6m long, roughly 6-7cm diameter, super-strong and also super-light. Yes, whole tube needs to be under 1kg to make it working, even better under 800 grams.

The idea is to end up with a scale-able jig which will allow us to produce continuous tube without a need to do some vacuum bagging or autoclave usage.

I made a simple draft on how that’s plan to work out.

So reading it sort of left to right there are two main parts, heater and mold pipe. For a heater we’ll get an 50′ aluminium tube, wrap it in Kapton tape, wind it in 18AWG 80m wire and apply two more Kapton tape layers.

Second part starts with another aluminium tube, now 60′ which will serve for the heat distribution and molding. First layer will be actually a set of decoupling wax layers (6) followed by a first carbon tape (200gms) clockwise winding, hand-applied resin, second carbon tape layer (200gms) counter-clockwise, finishing with very thick layer of office tape (1mm thread) to squeeze out excessive resin and air.

When done, the plan is to achieve a curing plan when on 3 Hours at 25˚C plus 2 Hours At 155˚C and attempt get tube parameters around as described in article Effect of Thermal Exposure on Residual Properties of Wet Layup Carbon Fiber Reinforced Epoxy Composites.

Translated in a table from here it practically says that we need to shoot for 90 minutes curing at 150C.

Percentage Change in Characteristics.

Unexposed66 °C93 °C121 °C149 °C177 °C204 °C232 °C260 °C
Tensile Strength
Increase from Initial5.42%33.91%37.66%31.83%54.42%36.37%34.12%26.82%32.95%
Decrease from Peak0.00%−23.85%−12.89%−20.52%−18.14%−17.67%−13.53%−11.25%−71.76%
Tensile Modulus
Increase from Initial14.61%58.59%42.70%20.53%33.34%27.94%29.88%30.91%13.24%
Decrease from Peak0.00%−24.00%−23.08%−21.54%−14.80%−17.26%−10.69%−20.83%−69.91%


In preparations we needed to do some additional shopping first. First thing on my list was a demoulding wax. Picked the best out of the best (and probably also the most expensive) TR-102 REGULAR PASTE WAX from Barnes.

Well, why not to get the best, when we have such a generous sponsors like Tam (huge thanks Tamara)!

Second essential was to order a Carbon Fiber tape – after some serious thinking, we ended up with 12k 200gsm 4″/10cm width Carbon Fiber Uni-directional Cloth UD Fabric Tap High strength Repair material Tensile strength 3400Mpa. It is on its way.

The final missing part is Epoxy, this is still to be decided on which one to use, secretly hoping to get our hands on EPOXY RESIN 4 HIGH TEMPERATURE FIBERGLASSING & CARBON FIBER PREPREG RESIN 80 as it seems to be perfectly what we need.

Next on the list is some CAD design and 3D printing as we need jigs to hold our tubes and operate them in general. I am splitting it into another post so it remains readable.

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