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Author Topic: A couple of old diesels - what props to use?  (Read 459 times)

Offline Larry Renger

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A couple of old diesels - what props to use?
« on: July 30, 2013, 12:35:34 PM »
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
Think S.M.A.L.L. y'all and, it's all good, CL, FF and RC!

DesignMan
 BTW, Dracula Sucks!  A closed mouth gathers no feet!

Offline rustler

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Re: A couple of old diesels - what props to use?
« Reply #1 on: July 30, 2013, 03:47:24 PM »
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.
Ian Russell.
[I can remember the schedule o.k., the problem is remembering what was the last manoeuvre I just flew!].


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