Graupner Speed Props
 

I know guys are spinning these up in the 30's on NovaRossi .15's, .21's etc. in the speedcup circuit overseas. I have few in the prop drawer, the 6x5.5 being a particular favorite for perky .15's.

But doing the math on the safety limits in the Graupner instructions - 3438/(dia in meters) = max rpm, for this prop at 152.4mm dia, I get 22,560rpm and m=0.53 at the tip which seems pretty conservative. Hardly a "speed prop" if the 6" caps out under 23k.The large hub 6" APC's are 31.6k.

I don't think I've ever seen one of their speed props.
There tolerance for liability / risk is driving whatever their safety factor is.
It would take a pretty healthy .15 to blow the blades off a APC 6x5, I think.

I know they spin the snot out of them on Novarossi's ad the like overseas and say they work great. These props don't show up on shelves everywhere, but they have a 6x5.5 and 6.5 x 6.5 that are great .15 - .25 zippy props.

Now knowing what else to do I'd stick with the APC rule 190k/dia in inches. That pegs the 6" at a hair over 30k max, I can believe that.

http://static.rcgroups.net/forums/at...g?d=1281227986

I wonder if that 30,000 is true number? I wonder if those props are going flat at higer rpm. MJD can you take a APC put it next to this one. then take some picture and post on here. take one over head shot and one with the hubs held together so we can see the pitch of both props at the saem time.