The blades for the Aeromatic F200 are $3200 installed on a hub that needs no OH or repair. Check the new price installed on any other brand of variable pitch props like MT, Hoffman, Hartzell, McCaully.
The lag screw issue: The propellers made by those before me torqued the lag screws to 150 in/lb. I see no data in my engineering or procedures that told them to torque each screw at least 7 or 8 times. If they put 150 in/lb on each screw and mounted the blade on a prop they it is fairly certain that those props went on airplanes with less than half of the 15 screws carrying the centrifugal load. Since there is no history of blade failures then that whould be good indication that the lag screw method of retention is not an issue. Analysis and pull test prove that the failure of lag screws occurs at 4 to 5 times the calculated load. The FAR states that the blade shall be subjected to twice the calculated centrifugal load and it shall not fail. I doesn't say how much above twice the load it is allowed to fail. The calculated centrifugal load on a typical blade of a 74" prop turning 2800 rpm is about 19,000#. Pull tests have proven that the failure of 15 screws happens at between 90,000 and 120,000# of force.
I have found that each time I go around and torque all the screws that the screw will show some more "take". Typically, I torque all 9 bolts in the outside row, then torque the inside 6 bolts to 150"/lb, then go back to the outside row and find that they are not torqued to spec, so, I torque them to 150in/lb then go back to the inside row and find them not to spec, they "take" more torque. I do this on all screws until no screw "takes" any more torque. Now, that is the way to make all the screws do their job.
It is my judgement that all those broken screws I've found in old Aeromatic blades were not properly torqued.
I have one confirmed blade failure on a RV-4 with an 0-320 engine. One of my friends had an Aeromatic for many years. It looked very good, no dings in LE, pretty shinny paint, no rust. They put it on my other friend's RV-4 and flew it. Got only 2150 rpm, they landed, tweeked the counterweights, took off and climbed to about 2500' above his airport (which is above 4000' MSL). This time a blade separated, the pilot made a sucessful landing, broke the engine and firewall. They gave me the prop for analysis. The separated blade was never found.
The ferule was still in the hub. Of the 15 screws, 10 of them had old rusty breaks, two of them has fresh shinny breaks and 3 of them pulled out of the wood. So, it is clear that both flights were made on only 5 screws and it is most likely that those 5 were not sharing equally the load.
It then is logical that with the 15 screws properly torques that this would not happen. I would guess that there are a whole bunch of Aeromatics flying around out there with half the screws going along for the ride.
Early Messerschmidts, Hawker Hurricanes and Spitfires used this design of wood blades using lag screws to hold them together.
I am working on a patent that will allow higher rpm at high altitudes. This will allow the Aeromatic to give you everything a CS prop will give, it just will not have the closed loop control of rpm like the CS has.
The prop is approved for PA-12 and the PA-12S. Also the Aeronca 7AC, S7AC, 11AC, S11AC and 15AC.