Indoor News and Views

Substituting Carbon Tow for Boron

In the summer of 2012 Bill Gowen introduced me using single threads from Mike Woodhouse’s 0.08mm thick Russian Unidirectional Carbon Cloth. The tow is easier to work with than boron and provides sufficient structural reinforcement for most F1D applications. The carbon tends to have better adhesion characteristics than boron due to its rougher texture and ability to be flattened against the balsa. I have since equipped my current F1D program with this material including, my 2014 AMA Cat I record model.

The Russian Unidirectional Cloth is different from other unidirectional products I have worked in that it is more like a knitted blank. The cloth is made up of 0.08mm threads running in the longer direction with 0.08mm interwoven orthogonally every few centimeters. Thus, making it easy to separate the individual threads. I start at one corner of the cloth and pull outermost thread away from the cloth. Take care to pull gently because the product has exceptionally short fibers and it is easy to fray the threads.

Separating carbon tow

Once a thread has been separated from the cloth, it will need to be pretreated with 1:10 Ambroid or Duco diluted with acetone. I hold the thread up with one hand and gently run a paintbrush loaded with diluted glue along the length of the thread. The thread will not necessarily be straight when it is dry. The thread is now ready to be attached to any structure boron would have traditionally been used to reinforce.

Carbon tow being pretreated with Ambroid solution

I recommend experimenting with different glue dilutions, using your experience with gluing boron as a guide, to determine how much glue to use for proper adhesion. Start by gluing a small segment of thread down and then pull enough tension into the thread to hold it straight. Glue the thread to the structure a few centimeters at a time pressing it flat before the glue dries. When finished gluing, cut the thread off with a razor blade or scissors and tack down the loose ends with glue.

Carbon thread being applied to the underside of an elliptical F1D stabilizer spar

The bottom thread has been trimmed and the top has not

Elliptical F1D stabilizer spars after carbon reinforcement has been added

I have found the carbon tow to be a feasible alternative to boron and I am looking forward to seeing future work expanding its applications.

~Nick Ray