July 2004
 

June was another busy month - it must be close now ???

Make a throttle control cable
Fit the skirt
Fire up the engine
Hope for the best!


Sealing the hull

The HCGB regulations require racing hovercraft to be able to float if the engine is stopped while on water. As the underside of the hull is made from aluminium panels screwed onto an aluminium frame, the chances of this producing a water tight seal are pretty low! Therefore I needed to include some sort of filler between the frame and the panels to keep the water out. The usual choice for hovercraft is Sikaflex, and the latest marine grade sealant is Sikaflex 291. So I bought a couple of tubes from Sea-Screw to test it out. I stuck two pieces of bare alulinium together and left it for a few days - wow what grippiness. This stuff sticks better than sh*t to a blanket, is water proof (so it doesn't wash off your hands), and its also very flexible when cured. I  ran a bead of sealant around the edges of the lower panels before screwing them back onto the frame.


Buoyancy

The HCGB regulations also require that the craft contains buoyancy, so that in the event of it becoming holed or swamped, it will still float - remember the hull has air holes to inflate the skirt but these can also allow water in.

buoyancy foam in hull
I used slabs of expanded polystyrene stuck in with aerosol foam. K&M supply 4 inch thick foam, and Wickes do it in 2 inch and 19mm.
 




Conduits and cabling

wires emerging from hull
Left: wires emerging from conduit next to engine.

Right: wires emerging onto deck below instrument pod.
wires emerging through deck

The cabling runs between the control box and the instrument pod via electrical conduit inside the sides of the hull. These need to be fitted before the buoyancy foam is fitted. The ends of the conduit are fitted with adaptors which fix onto the aluminium panels. At the engine end they prevent any water inside the hull chambers from getting into the cockpit, and at the instrument pod end they prevent air and water being blown up into the pod. The battery lives on the cockpit floor inside the steering box.


Finishing off the tank cover

tank cover clasp

To hold the seat/tank cover down I used a pair of rubber toggle catches from Vehicle Wiring Products. These were excellent value.



Throttle linkage

The throttle is operated using a converted bicycle brake lever (with extended pull distance)

steering

The main problem was that the cable bends had to be kept fairly slack (to avoid too much friction), but the whole handlebar assembly clearly had to turn, which meant that the cable needed to flex, and attaching the end of the cable to the throttle lever was then a little tricky. A cable-end bracket from one of the TZRs was perfect.


Fitting the skirt

Back in the Winter I had made up some skirt clamps from plastic gas pipe, but these didn't look like they would hold the edge of the skirt firmly enough so I decided to screw through the skirt clamps and through the skirt edge, and put a bit of sealant on it for good measure. The holes in the hull frame were drilled via a template so almost any skirt segment will fit in almost any location (except for the segements underneath the grab handles which use the M8 bolts that hold the handle webbing on.

Most of the skirt segments are "pressure segments" which have an internal flap to maintain pressure when ground contact ios lost. The segments at the back and rear corners are chip bags.The rear segments are prone to picking up water and these allow the water to drain out easily.

The bottom of each skirt segment is attached via a cable tie to a P-clip screwed into the hull panel.


IT FLIES !!!

So on the evening of July 24th 2004 it was ready to fly...

The hovercraft was raised up about 2 feet in the air on crates. I started the engine (with difficulty) and warmed it up. The new throttle linkage worked well and it revved up to 8,000 with a little help from the power valve.

I felt underneath the hull, but I couldn't feel much air flow. It was worth seeing if it flew though. I switched off the engine, lowered the craft to the floor of the garage, and started the engine again. This time it started much more easily. I got in and revved the engine. The hull lifted off the floor a little. I revved it a bit more and we slid out of the garage and onto the unsurfaced track at the back of the house. The track was far too narrow to turn using the rudders so Sharon (the wife) pulled the hovercraft around to point up the alley and off I went. It went reasonably straight and I manged to avoid hitting the cars as I flew about 80 metres, then with the end of the alley fast approaching I pulled the lanyard switch to cut the ignition and the bottom of the hull ground out.

It flew at last! After 19 months and around 1000 hours it finally flew!

I looked back and all I could see was dust, and when that cleared the neighbours appeared wondering what all the noise and dust was from.






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