SCALE JET ENGINES

Also known as miniature gas turbines or micro-jets.

Many model engineers relish the challenge of re-creating the grand engineering feats of today as tiny working models. Naturally, the idea of re-creating a powerful engine such as the jet, fascinated hobbyists since the very first full size engines were powered up by Hans von Ohain and Frank Whittle back in the 1930s.

Recreating machines such as engines to a different scale is not easy. Because of the square-cube law, the behaviour of many machines does not always scale up or down at the same rate as the machine's size (and often not even in a linear way), usually at best causing a dramatic loss of power or efficiency, and at worst causing them not to work at all. An automobile engine, for example, will not work if reproduced in the same shape at the size of a human hand.

With this in mind the pioneer of modern Micro-Jets, Kurt Schreckling, produced one of the world's first Micro-Turbines, the FD3/67. This engine can produce up to 22 newtons of thrust, and can be built by most mechanically minded people with basic engineering tools, such as a metal lathe. Its radial compressor, which is cold, is small and the hot axial turbine is large experiencing more centrifugal forces, meaning that this design is limited by Mach number. Guiding vanes are used to hold the starter, after the compressor impeller and before the turbine. No bypass within the engine is used.