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Engine basics => Engine set up tips => Topic started by: Larry Renger on July 30, 2013, 12:35:34 PM
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I have Cub .074 and McCoy .049 diesel engines. #^
Anyone have a clue as to the ideal prop sizes,first for break-in, and then for flying? ???
I understand that the McCoy has a fragile crankshaft, and needs careful handling. :X
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Hi Larry. These are iron p/c and of a certain age. Traditional running-in. 30% Castor fuel. Maybe 8 x 4 for the 049, and 9 x 4 for the 074? Short undercompressed runs of about 30 secs. - 1 minute, followed by cool down. See if they hold a full setting after about 1/2 hour? If not, another 1/2 hour?
As for flying, will depend on what the model is. For F/F I'd guess you could use a 7 x 4 for the 049 if it's a pylon job, but the 8 x 4 may be better, and probably best for sport F/F. It's surprising how a bigger prop can work wonders, even though it's further down the power curve. I expect you know all this. The larger props will be kinder to the shafts, but only if you don't overcompress!!!
For the 074 similar treatment? 8 x 4, or 9 x 4. For C/L 049-7 x 5? For 074-7 x 6?
All this is only ballpark thoughts. If ultimate performance is needed experiment will be required. Possibly drop the oil to 20% when fully run-in.
Good luck, best wishes.