stunthanger.com
Engine basics => Engine set up tips => Topic started by: EF on October 16, 2007, 01:11:39 PM
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Is there a reason against locking an RC carb in the fully open position, and flying it in a CL model?
Must I use an engine with a simple venturi?
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No. There has always been a lot of hub-bub S?P about airleaks in rc carbs, but I say, look at the big hole going straight down the carb and compare its area with that from some little micro gaps---the air is smart enough to go the easy way. The main issue with airleaks in rc carbs have to do when the throttle is set to idle speeds, then the gaps can become significant compared to the small opening. However if you are running an rc engine in idle mode for CL, that must be some powerful engine!
The main downsides to the rc carb is the extra weight. The upside is that you can look at it as an adjustable venturi!
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It works fine for me.
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Carbs wired open often work o.k. for a period of time. With engines used heavily, in competition stunt planes, for instance, the carbs tend to eventually loose their setting. They can lack the dead on repeatability needed in a competition plane. A club member who is a top 20 flier, went to a venturi/needle valve on a Saito 72. He wasn't satisfied with the way the carb kept it's setting from practice session to practice session. Carbs had been o.k. on his sport planes. Tuning in a comp plane is different. Variations in a sport plane engine run may not even be noticed. A little more or less power, a slightly longer or shorter run time, isn't an issue when messing around. Comp planes need as much consistency as possible. Handling weather conditions, temperature fluctuations, humidity shifts, air density etc. is enough to deal with. Simplifying the variables helps.
There are after market folks who convert RC engines to control line, popping in venturis using easy to obtain needle valves. Also many engines are a straight forward conversion from RC to dedicated control line, using factory parts. OS fps and LAs were made (LAs are still being made) in control line and RC models. Needed parts can be bought from Tower and elsewhere.