You know, some people seem baffled why our airfoils can be flat plates and work so well. And some seem to think that because so many almost flat airfoils work on our planes that the same would be true of our props.

It's actually very obvious why plate airfoils work. Same reason symmetrical ones with almost no max thickness (or WITH no thickness at all) work. The wing loadings our models produce is so far under what full scale sees, it isn't funny. Max coefficient of lift is a function of airfoil thickness. When you got virtually no payload, you don't need no stinking CL, much less what would be called "max". So our models don't need appreciable lift. And some don't need appreciable structural strength. Foamies weigh comparitively nothing and not virtually or comparitively but really don't need max CL or max strength.

But don't confuse how the wings can be with how the props can be.

Fact is, our engines produce finite power, gas, glow, or electric. And the airframes wind up producing drag that fits that power (or vice versa, depending on how you look at it). So we wind up with demands on our props that our wings will never have a hope of seeing. Unless we start building with wrought iron. Our structural materials also give our airframes some advantage in the payload area, btw.

And our props don't see the Reynolds our airplanes do. Airspeed is a major player in Reynolds effect. And our props can see all the way up to the speed of sound. So don't assume that the blade's chord or thickness is not doing something. Or it's width/chord. Want to see a prop that just might owe it's somewhat outstanding performance to either it's chord or wing area? Test a couple of Graupners if you can find them. Or just ask MinnFlyer what he thinks of 'em. They prove that chord and/or area means something with our models. And they might also prove that maybe some of the other prop mfgs have missed a trick or two. Or shaped their blades to catch this market's eye. But not seeing the same Reynolds isn't exactly a positive. Or really a negative. It just puts our props into a somewhat different world. For this discussion it really just backs up the idea that we can't cut out a foamboard prop and fly an IMAC whale with it.

We really shouldn't be to quick to blow off things we think aren't needed for model props. At least blow 'em off as a general rule for all model props. Chord doesn't matter if something else takes it's place. Truly thin blade thickness does work, but not over the whole span. And we don't have matching props with thicker blades to compare. Truth is, even the mfg's probably didn't.

The guys who "carved" their own back in the day really did learn a lot about props. Control Line in particular is one of the best, most accurate test setups anyone could hope for. Our speed planes used that to huge advantage, but thousands of guys racing rats did too. And the precision aerobatics boys weren't exactly wandering about in a daze. Both the rat and stunt guys discovered that "wing area" really did matter. But it had to be balanced with diameter. You USUALLY got your rpm range by adjusting diameter. And you didn't do it by buying the next size prop down at the LHS. (There were lots more LHSs back then too.) That next longer or shorter one was so far different it wasn't even funny. Why? Because the "wing area" was a different world as were so many other things. Experienced stunters could change their performance by changing radius by 1/8". And by thinning a half mm. And they could prove it. With a watch for one. Lap times and run time. (Are those affected by the "weather"? Yeah, and some of us recorded temp/pressure/humidity and worked from standard day.) They called Precision Aerobatics that for a reason. And it was more than just how the maneuvers were flown. And racers put them to shame. At least a few of the ones who won all the time did.

Lot's of guys took larger props and made smaller ones. You didn't just cut the diameter. You trued the bottom of the airfoil on a pitch gauge. Trued the top profile with a set of pattern forms that you'd made yourself, while at the same time setting whatever thicknesses you wanted. And there are a few other details..... Why did we do that? It was fun for one thing. And you learned who was BSing about his props and who wasn't. And you might win more often. But mostly it added to the fun. For them what did it.

Something that most learned along with all those details? Ain't no magic prop design or mfg.