Experiments at Stanford University in the USA using fuel grains made from simple candlewax are going well. The advantages of candle wax are simplicity of moulding the grain using traditional candlemaking techniques, and also a much higher regression rate (see our 'Introduction to hybrid design' paper in our Technical Papers).
Aspirespace have joined the growing band of amateurs trying to emulate Stanford's successes.
Firstly we contacted rocketeer and candlemaker Stuart Liddell for advice on moulding the fuel grains: after some experimentation, we discovered that the use of a porous cardboard liner allowed the wax to flow into the cardboard; this anchored the wax to the card, and prevented it shrinking radially as it cooled.
We discovered that using a highly heat-conductive copper tube as the central mandrel prevented the port from increasing in radius as the wax shrank upon cooling. Removing this metal tube just as the wax was setting produced a smooth central port.
We then modified our H0engine to use wax grains; we wound our own liner tubes using brown paper and wood glue.
Unfortunately, the results of our firings were less than encouraging. The majority of them just caused unburnt melted wax to spew out of the nozzle like water from a hose. The regression rate (speed of liquid wax production) was far too high for our H0 to handle.
A video of one of our firings can be viewed below (double-click on the icon):