Building a streamliner (from scratch!)

Typhoon is a streamlined bicycle I built alongside my teammates from the Human-Powered Vehicles Design Team (HPVDT). It involved performing numerous carbon fibre layups.

Process and Design

Typhoon is made almost entirely of carbon fibre. This includes the wheels, wheel well, and the fairing. The general process we followed to perform a wheel layup is as follows:

Preparations
1. Coat mold with several layers of frekote to prevent the layup sticking to the mold when trying to extract it
2. Prepare your carbon fibre, considering the angles needed for each layer. My team cut layers of carbon fibre that ran 45 degrees to each other, for a stronger wheel
3. Measure out the appropriate amount of resin and hardener and mix well

Performing the layup
1. Saturate carbon fibre layers with a thin layer of epoxy. Layer these pieces inside the mold, along with foam pieces
2. Reinforce the edges of the layup with strips of uniaxial carbon fibre
3. Vacuum seal

The process for creating the wheel well is similar, except that the foam pieces must be chamfered. We did some layups with perforations in the foam and some without, and it didn’t seem to make a difference in the result. For our fairing layups, we used layered carbon fibre in a 0 30 60 configuration instead of a 0 45, since we decided that the fairing would consist of three layers of carbon fibre instead of two, and wanted the change in angles to occur evenly across the three layers.

Some things I learned

Epoxy cures faster under warm conditions, and the chemical reaction that occurs while it is curing is exothermic. I didn’t know this at first. Then I performed a layup and wondered why the solo cup of epoxy I was using seemed to be rapidly heating up and getting stickier and more difficult to work with. Turns out, it was feeding off of its own heat which was accelerating the cure time exponentially.

I was surprised by this - after all, when I chose an epoxy hardener and resin to mix together, I had accounted for the cure time and thought we’d be safe. But it turns out that the cure time listed on the labels of epoxy resin and hardener containers is valid for a 1mm-thick layer of epoxy, and a solo cup full of epoxy is… not a millimetre-thick layer. Now I know to dump out the epoxy on a (covered) table or keep it in the fridge to keep it from curing while we’re still trying to work on it - that’s something to keep in mind for next time.

The result of that particular wheel and wheel well layup turned out pretty well, even though there was a mad rush towards the end to finish quickly when my teammates and I realized our situation. I do feel like that wheel is slightly heavier than the other one we made, and this makes sense - we weren’t able to spread the epoxy in thin layers on the carbon fibre since it was partially cured, which means we used a little more than on the other one which ended up contributing more mass.

We don't anticipate that this layup issue will cause problems, but we'll know for sure when we test-drive Typhoon.