Sunday, 30 June 2013

Success - allbeit limited.

I'm still struggling with the carburetor and the design in the previous blog won't do. The bends in the pipework from the carburetor to the cylinder heads are too tight and it's not possible to make them. So this time I've gone for twin carbs and they each attach directly to the cylinder heads.

It works! That propeller is an 16 x 8 Master Airscrew

After a lot of thinking and research on the internet I thought that the fuel was not burning correctly. I've put it down to the glow plugs not protruding far enough into the combustion chamber so I've made the plug recess 2.3mm deeper on the outside.

Seems to be more reliable and controllable with two carbs.

There is still some work to be done, it won't run to full power, it seems to lean out so I think perhaps I need to enlarge the fuel passages in the carburetors. This was probably the cause of the tightening that occurred at half throttle where the air flow increased and the fuel flow stayed the same. The result was a hotter burn and swelling of the pistons and creating more friction = more heat = more swelling = more friction = more heat. You can see where I'm going with this. I closed the throttle at this point and the engine stopped abruptly. I turned it over by hand and it was tight so I let it cool down and it became free again. If I can cure the the fuel starvation I think the overheating problem will be solved. I'm pleased with today's testing, a good result.

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