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Quite a few incident free runs after the last article I noticed erosion on the leading edge of the thrust prop at the outer end.  One of the other hovercraft's had noticed little puffs of water from the thrust prop and we concluded that water was coming over the edge of the craft and entering the thrust prop.  To repair this I did two fixes.

  Water shield and flexible coupling.jpg  Prop End 2.jpg

I put a rubber shield across the safety screen to stop the water and epoxied aluminium ends on the propellor. 

I was then ready for the Australian National Rally at Lake Coolmundra about 2 hours drive west of Brisbane (www.qhover.com for details).  On the day before the Rally I was cruising around the Dam and firstly noticed that my exhaust had become very loud and then there was a bang from the back.  When we got back one of the aluminium strips had let go, put holes in the thrust duct and ripped a hole in the safety screen.  The stainless steel flexible exhaust coupling (seen above) has rusted and ripped in half leaving a large hole.  I took the other strip off the propellor to try and balance the prop and continued.

The next day I installed the wings for the first time and attempted to take off.  I must admit that it was fun doing the high speed runs.

Wings.jpg

Unfortunately after about 8 runs I was not able to leave the water surface.  At 84km/h I did lift the front slightly but could not accelerate the engine over 5500rpm and so could not go faster.  I will admit that my craft is heavier than what the factory intend, many layers of paint to look nice and covering on the inside of the cockpit.  We had a good Rally but then the work started.

The next weekend I did a thrust test -

3000rpm   99 lbs

4000rpm   264lbs

5500rpm  330 lbs ( about half of the thrust in the manual)

A static thrust calculation shows that the prop was using only 70HP and the lift prop would be about 25HP so the engine was lacking power, it should be 130 to 140 HP.  I also realised that the water guards covered a good deal of the air inlet and would be staving the prop of air.

Further investigation showed that the almininum raditor had cracked mounts and the oil scavenger had cracked mounts.  It amounted to a lot of small stuff but it has taken a few months to fix.

Radiator.jpgOil Coppector.jpg

The exhaust needed a new flexible coupling and I was not going to put another Chinese one on to fail again.  I purchase a US built spherical joint from Magnaflow exhausts, the only down side is the delivery to Australia.  The engine was serviced and as well as the exhaust the fuel filter was blocked.  We did identify corrosion on the spark plugs so I did some research and have covered all the electricals and metal parts with ACF50 an aircraft corrosion inhibitor so we will see how that goes.  The welding is all done and the exhaust has an aluminium shiel because we felt that the fiberglass wrap was keeping salt water on the exhaust.

Exhaust.jpg

The only down side was that this exhaust is a little lower than the original and the steering wire hit the exhaust so a small deflector had to be installed.

The prop was stripped and sanded back to original.  I have used JB weld to repair any erosion damage and put a layer of JB weld on the outer leading edge.  I hope this works.  I then balanced the prop.  I usually put a pipe through the center hole and balance it on two angle irons.  I had done this but it was suggested to use a bearing so I purchased a plastic sliding door wheel with ball bearings the correct diameter. I drilled a hole through my bench to support the axel for the bearings and was able to closely balance the propellor.

Prop Leading Edge.jpg

The craft is now all back together so will take it for a run in the next week or so.  Hopefully it will all hang together

 

 

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Author / Member : lazza

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