safe rpm limits for Cox gray props

[diesel_don]

Anyone know where such data is published? Particularly for from smallest diam up to say 8X4-,9X4. TIA,Cheers; diesel don

[Jim Thomerson]

I've blown blades off two Cox grey 8 x 4's at around 14,000 on an ST G20-15 diesel. On the other hand I've run them up to 17,000 with no problem on a Cox 15 special. The 7 x 3.5 is fine at 15,000 on a TD 09 and I've run them at 17,000 for short periods without failure. I think diesels and glow engines put different stresses on props, but that's opinion rather than fact. I don't know if there is published limit data.

[ffkiwi]

The 7x3.5 Cox grey used to have an rpm limit of 19,000 embossed on the blade-but I don't recall whether this was the case for the others. Hobby Lobby, who stock Graupner props, used to have something in their (IC)prop section which was a formula for calculating the rpm limit for each size of Graupner prop (the grey ones)-I suspect that somewhere on the APC prop site there will also be something on prop rpm limits-alternatively you could ask them thru the 'query' function on the website
'ffkiwi'