Following on from our trebuchet success, our next project had to be even bigger and better still, for which a hovercraft seemed the perfect choice. Construction started in the spring of 2010, and is still ongoing.
The base/undercarriage seemed the first logical step in the construction. It was made entirely out of roofing timber, with a thin sheet of plywood acting as the base. In hindsight the struts we used were excessively large, being a massive contributor to our weight issues. Ideally, if we were to do this again, the base would be made out of a material with a much better strength to weight ratio, such as aluminium. It would also have been a wise move to more thoroughly plan the design before we started, as later adjustments were required to fit the engine.
Finding two suitable fans was our next problem. However we managed to get very lucky after less than 30 minutes of searching, as we stumbled upon an old steel fan from an extraction unit dumped in a field. It was in pretty bad shape, and required quite a lot of welding to hold it together. We decided to use this with our larger 12HP engine looted from a broken go kart, mounting it on the rear of the vehicle to act as the forward thrust.
As for lift, some googling told us a centrifugal fan would be ideal, as they are more efficient when building up pressure. Again it didn't take us too long to find one, probably from an old air conditioning unit. However again it wasn't in the best condition we could have asked for, and looked like it would be difficult to mount.
Mounting the larger fan wasn't too difficult, as we had a spare CVT to fit to the engine, and plenty of drive chain to connect this to the fan axel. The CVT was required to isolate the fan from the engine while starting, and to act like a gearbox to spin the fan faster once the engine has reved up. Connecting the centrifugal fan was much harder, as we had to get a custom engine mount cut at a local workshop, which I will try to find the designs for. This was quite an expensive endevour, but thanks to my friends skill at online poker he was able to pay for the machining. We also welded on some mounts for a steering mechanism, and connected this via cable to a pair of old bike handlebars, which we also connected the rear engine throttle to via the brake cable.
Naturally after all this construction, we felt it was time to actually test the beast (video 1) 😀 Unfortunately due to the massive combined vibrations from the engine and the very poorly balanced prop, the fan axle kept shaking enough to allow the drive chain to jump off the upper gear when we reached a decent speed (you can see this at 0:11). Following a few hours of strengthening and reinforcing the supports, again increasing our weight, we managed to successfully run at full throttle 😀 (video 2)