Hovercraft Mk II
This is the successor to Hovercraft Mk I, as the name implies. My aim this time was to use the knowledge gained from Mk I to build a self-propelled hovercraft that's more stable than its predecessor.
A major difficulty in this design was the rectangular nature of the craft. Because Mk I was circular, the skirt worked fairly well. However, because Mk II is a rectangle, the air cushion would cause the skirt to bulge out on the sides in an attempt to be as circular as possible. To counter this, I had to run strings from the bottom of the craft to the bottom edge of the skirt. This would help keep the skirt in shape. Initially, I installed too few strings, and lift capabilities suffered. The addition of more strings dramatically increased performance.
Making the skirt was also tricky. It is made from 4 sections, each cut at a half of a sine wave at each short end. This allowed me to curve the skirt segments into half tubes and have the ends match up. If you cut a tube at an angle and then unravel it to make it flat, the result will be a sine wave where it was cut. I used that phenomenon to make my half tubular skirt fit together. Overcomplicated, yes, I know.
The lift engine is mounted such that the fan blades are under the plywood which composes the craft. Then holes were cut in the plywood around the engine to allow the air to blow under the craft. The engine was then raised on stacked washers in order to make the fan as close to the plywood as possible to make it as efficient as possible.
The thrust engine was a string trimmer, which, unlike the lift engine, is meant to be held when operated, not mounted. Thus, it soon became apparent that attaching the engine to the hovercraft would be a challenge. In the end, I removed part of the casing and bolted it to the hovercraft via the places where the front casing was meant to attach. Unfortunately, by doing so, the pull start was lost. Therefore, to start the engine, I need to wrap a rope around the drive shaft and then pull on it. It works very well, actually, and the only time the rope ever got caught in the fan was when I was using barn string. That got entangled when the rope frayed. Then I switched to a nylon rope, and it has never become caught since.
The rudder control is a control stick attached to the rudders via nylon rope, with turnbuckles for adjustment. I attached the stick to the rope under the pivot point so that moving the stick right will cause the craft to turn right. The throttle control was originally going to be a trigger mechanism attached to the engine with bike cabling. However, the bike cabling proved to be difficult because the cable had the wrong fittings on the end for the trigger and engine. Finally, I decided to abandon the trigger throttle, and opted for a pull throttle. Now, to the right of the seat, there is a rope with a handle that the pilot pulls on to increase throttle. The rope is attached to the throttle plate of the carburetor, and then travels through eye hooks to reach the pilot.
The cushioned chair was not included in the original design. Originally, the pilot was meant to sit directly on the red stool. I was at a garage sale, and they just gave it to me for free! I then spraypainted it black and put it on the hovercraft.
The thrust engine doesn't appear to produce significant thrust. On full throttle, the craft doesn't even budge. It only moved in the downloadable video when my father gave me a push. This is one of the problems I'm most concentrating on fixing in Mk III.