Saturday, July 17, 2021

Carbon Fever

Carbon-fibre tubing has its advantages in constructing drones. It certainly goes some way to explain the price-rise once you shift from the injection-moulded plastics used in domestic quadcopters toward commercial types dedicated to surveys or to filming for the likes of the BBC.

When it comes to using it ~ as I clearly could ~ for personal air vehicles however, it is much like the choice between buying a Maclaren instead of a Mustang (or in my case a seventeen year old Suzuki Jimny).

For your benefit, here's a rough formula I use to remind myself of its properties:

3 : 7 : 21

This is because compared to (non-aviation) aluminium tubing it is three times lighter, seven times stronger, but twenty-one times more expensive... even given the recent hike in global non-ferrous metal prices.

You could argue that because of that superior strength I could reduce the dimensions of the various struts involved (and therefore the cost) but to some extent that process is self-defeating. For as Brunel discovered whilst building London railway bridges using timber, doubling the depth of material involved alone quadrupled its strength.

In fact it was while I was flying for an airline in Germany, with leisure time invariably spent designing and building, that I was first introduced to a length of carbon-fibre tubing at a light-industrial concern of the kind that the country has in abundance.

I was astonished... light as a feather and unbendable despite being only wafer-thin. It is though useless for the rapid-prototyping on which until now I have been engaged, in which I've used and re-used the same sections of sheet and tubular alloy constantly.

It will happen at some stage, however, if only because carbon-fibre and my airframes were meant for each other:

                                            All I want is a room somewhere

                                            Far away from the cold night air

                                            With one enormous chair

                                            In a carbon-fibre airframe

                                            Oh, wouldn’t it be loverly?