Today I christened my new plane launcher with success. I have built this as I have found the properties where I want to fly from have little or no adequate takeoff areas since the fields are full of waist high grass or lots of rough ground. Landing is OK by slowing down and dropping into the long grass but takeoff has been hazardous, to say the least.
The launcher is using an 900mm air ram to drive a 6:1 ratio pulley system that accelerates the launch trolley up the ramp. The ramp is made from 2 x 50mm x 25mm C sections welded together and bolted together in 2 x 3m sections that can be broken down for transport.
The trolley has a front wheel hold down that is released at the end of the ramp and hopefully this coincides with flying speed.
The speed is adjusted by altering the air pressure from the compressor. So far it is launching at approx 100 psi without ripping any wings off. As the compressor is rated to 150 psi it has some spare capacity for larger or heavy flying weights.
So far it costs about $300, the ram was an ebay special for $50. I sourced the pulleys from ebay by buying someone's unused gym weight machine, which has 125mm glass fibre pulleys complete with bearings (which to buy separately would have been $15-20 each.) I was also able to use some of the gym machine's steel for legs and some of the frame.