Propeller revolutions

[Greybeard]

Often propeller specification consists of diameter, pitch and revolutions. E.g.: 8.5' - 7.5' - 1300 rev.

I wonder what means that RPM: max allowable, max efficiency or what else?

Any help much appreciated.

GB

[GabiLaser]

From what i've read, the RPM specified for the propeller should match the standard RPM of the engine where the propeller is fit. Many rotary engines could not be throttled up or down and had [almost] fixed RPM values (changed only by mixture control(s)). I think the propellers where designed at least at first of war to have highest efficiency (and not break) for a specific, known RPM, engine.

Regards,
Gabi

[Greybeard]

Uhm! I agree almost completely, but I think that, whilst it should be max allowable RPM for prop, not necessarily could be max engine RPM, since I've evidence of a 1300 rev. prop mounted on a 1200 RPM Le Rhone.