I'm having grave concerns, with what is a safe speed for the "Scale Props" we now see on the new generation of "Foam Warbirds". I just witnessed a prop failure at my field. The propeller was of a construction that is new to me. It is where the individual blades are held on to a plastic disk (spinner back plate) with small sheet metal like screws. I’d like to learn what is the safe operating speed for this style of propeller?
I did a search on the AMA’s site and only came up with restrictions for a propeller made with metal blades and some topics addressing tip speed and noise. I fully understand the restriction on metal blade as metal tends to work harden and crack when subjected to cycle loads.
I think we all as safety conscious modelers would want to know what is the safe tip speed for this type of prop. I’m looking for information like what Graupner supplies with their Super Nylon prop, that is the tip speed must be kept below 180 meters per second. They also supply a formula to derive this limit K/D=RPM. Where “K” = 3438 and “D” is the diameter of the prop in meters. Landing Products (APC Props) offer a site that address this issue for the various types of props they manufacture http://www.apcprop.com/Articles.asp?ID=255
. As the distributors, I’m thinking MotionRC through their upgrade page and their forum Hobby Squawk, often post performance enhancing upgrades to the base product they sell, knowing the safety limits of the prop is critical to a safe and happy experience for all at the flying field.
I’d like to know what is the safe speed (tip speeds) for these component props that come with the Freewing, FMS and Flight Line models? I’ve asked MotionRC for this data and they don’t seem to have the engineering breadth to answer this fundamental safety question. Not that they should but the OEMs should provide the importer and distributors this information. I’d like to ask does anybody here have a link or know what the safe limits are for this type of prop?
BTW, I’ve asked for the AMA’s stance on this subject. I’ll let you all know what if anything the AMA says on the subject.
All the best,