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View Full Version : Max sustained rpm and gear ratios


eoosting
05-04-2004, 01:46 AM
I purchased a used Raptor50v2 from a guy at the field. This was a R30 that was upgraded, but it turns out that the pinion and main gear were never switched out. This means that the gear ratio is that of a R30v2: 9.55 instead of that of a new R50v2: 8.5

What this translates to is a higher sustained engine rpm at a given head speed. If I am flying with a headspeed of 1800, my engine is turning at 17200 instead of 15300.

Now I should say that it flies great, and looking at the specs of the OS50-sx, the max power is at 17000 and the rpm range goes up to 20000 so on the surface I see very little that could be wrong with this combination.

So my question is this ... Are there reasons to switch over to the manufacturer's suggested gear ratio of 8.5 for the os50? The only thing I can think of is that the lower RPM at the crank would be easier on the engine and gears, but that it might cost me in hp.

Eric

capebob
05-04-2004, 07:05 AM
If you are happy with it you should be OK. The advantages of changing to the 8.5 gear ratio include longer engine life, improved fuel economy, and less noise. A lot of us fly our 50s at 1850 to 1900. The R50 is a lot quicker at that head speed and the 8.5 gear ration keeps engine rpm reasonable.

Bob