The "Magic Prop" for any engine/airplane combo is the one that works best on YOUR airplane. What works for your flying buddy Charlie might not be the best for you and yours. The best way to find out is to get the model in at least pretty good trim, and then test fly props. Check them for pitch against what they are marked, and then balance them if needed. There are good starting points for each situation, and then go up or down on pitch/diameter from there. A lot depends on model weight, design and shape (drag.) A Rev-Up 10-6 EW would be wasted on a Ringmaster, but on Mike Gretz's Fierce Arrow it was what really made the airplane fly like I think it should. It's a fairly clean design, but weighs 50+ ounces. Planes that are smaller and lighter don't need as much prop. I have a pretty big collection of props I have accumulated over the years and was taught early on that if one prop did not feel right, try another. Different blade shapes work in different situations. Plastic props are heavier and can affect how an engine/airplane combo performs. I have a couple of Nobler ARfs that i finished up during my knee rehab, and one had a Brodak.40 on it. It was flying best with one of those grey plastic Thunder Tiger 11-4.5 props on it, but to get the best balance and turn I had to add some tail weight. I compared the TT prop to several other wood props and it's blade shape and arrangement is similar to the old Top Flight Power Props, I think they are called. I did not have one of those older wood props in 11" so I decided to make one using one of those Rev-Up 12-5 drone props that have been popping up hear and there over the last 30 years as blanks to cut one from. I measured the blade thickness at 3/8" increments from the tip to about 1" from the shaft hole and made notes. I made a blade template measure in length from the prop hole edge to the tip off of the TT prop, and transferred that shape to the Rev-Up. Then i set out to remove any wood that didn't look like a TT 11-4.5 prop, matched the thickness and airfoil as best I could, set the pitch, balanced it and put a clear finish on it. Next flying session, I put up 2 or 3 flights with t he B-40 Nobler to get ground RPM readings, lap times and engine run times recorded, then all I did next was change over to the wood copy I had made. At engine start up, the RPM matched the plastic TT prop almost exactly. Lap times were right where they needed to be and the plane felt just the same as it did with the Thunder Tiger prop. Engine run time was right there also within a few seconds of the plastic prop. I considered the whole exercise a success. Next I tried copying Rev-Up 10-6 and 10-6W props in the same manor and re-pitching them to 10-5 and find that they work well on smallish profiles also. Years ago, I got one of the first SIG Primary Force ARFS flying and eventually upgraded the engine to an OS.32F. I was trying every combination of 11-4 props that I had, and as a last resort, I tried a Zinger 11-4 PRO, and that tuned out to be the Magic Prop for that airplane/engine combo. I had never had any success using Zinger props of any kind but in this case it was just what the doctor ordered. You just never know what is going to work until you try it and give it a thorough flight test.
Type at you later,
Dan McEntee