well, you done did it now. First of all, as a Cloudster/Lucas fan, you're not only qualified in requisite nerdiness, you may have accumulated enough points just reading this thread to receive card carrying privileges. As to smart enough... well if that's a requirement it's due to ineffective communication on my part. This forum is about basic stuff we can relate to intuitively. Academicians will jargon it up later I'm sure.
People who truly appreciate motorgliders seem to be a rare breed. Thanks for carrying the torch. (I'd state for the record that glider pilots are real pilots and the rest of us haven't qualified. Flying around in 8:1 bricks, we may yet get the chance. Once.)
Since I was a kid I never could understand why putting an engine on an aircraft could destroy its L/D so completely. By the time of my student pilot training in high school I could recite the stock answer, but that doesn't mean I accepted it. There is no excuse for a powered aircraft being aerodynamically inferior to an unpowered aircraft, yet they typically are. So rather than cue off your desire to own a commercially extinct species, my brain goes to what the real options are.
Why not own something that does exactly what you want? Chances are it's on the drawing board already as a Synergy derivative; if not, it will be.
I can almost see the readers racing to fire off posts reminding all of us that airplanes are exercises in compromise and that we can't simply ignore the cherished limits of the past.
OK, why not? Referring us back to the black charts on post #12, why should we accept that there is no way to occupy the space above AEI =10 at any speed we desire to fly? Why not admit that there could be another path, a fork in the road we didn't take, long, long ago? One that leads, not to a dead end Aerodynamic Efficiency Index of 6, 7, or 8... but to double or triple those numbers. There is such a way. I'm racing to fly its full scale proof to OSH in 2011 via the CAFE Green Prize .
Every future aircraft comprehensively applying the lessons we're discussing here is a superb motorglider. They motor quickly up, and they glide slowly down, whenever we want and at whatever speed we design them to. In between times they zip smoothly coast to coast at twice the speed conventional wisdom allows for their horsepower. Since the catalyst is low induced drag in a stable and structurally robust package, high altitude performance and tremendous useful loads provide utility you'll never find in an older design. Ideal volumetric displacement waveform and assisted hybrid NLF takes care of the rest.
I can show you one if you want. The technology it takes isn't public yet, but it will be soon. When it is, kit manufacturers can license a simple, safe, inexpensive way to triple their fuel efficiency and double their speed in a quieter, roomier, slower-landing aircraft.
Regarding your prop question from post #1, it is one of mine. It's just a quick workup for the wake propulsion aircraft I designed as a conventional baseline to compare Synergy to, seen in post #43. It's not a finished product, but the visual design tool developed to model it parametrically now gives us the capability to quickly model and analyze real props for any application, using a novel system of priorities. This is what I spoke about at Oshkosh last year in the forum "Prop Design at the Bleeding Edge."
Awesome props are needed in order to deliver the kind of performance possible at this level. The prop you refer to is a quiet, constant Reynolds number, multi-blended, Mach-adapted, NLF airfoil wake prop of about 93% efficiency in the freestream. In the wake impeller role its efficiency exceeds that considerably. The reference pitch at each station is based upon inflow velocity variation due to fuselage effects.
Things that have advanced beyond this concept rendering include using a blade-and-hub design and new low-Reynolds NLF airfoils specifically designed for delivering super L/D over the unique AoA range of each prop station.
When you have a constant Reynolds number, each prop station is, as far as it is concerned, flying at the same speed. That takes a huge variable out of the equation and allows custom airfoils to be idealized into blendable families. In props that vary the Reynolds number, resulting non-optimum lift distribution is the source of excessive noise and poor efficiency. We need to be able to vary the lift of a blade along its length to optimize disk loading and lower induced drag, but the ideal means of doing this should consider not only pitch (angle of attack), but airfoil camber.
Near the hub, a highly cambered airfoil can be set at lower angles of attack, delivering the right lift (lots of it!) while minimizing rotational drag at runup. (The powerful inflow caused by the prop disk as a whole immediately reduces the actual AoA at the prop hub to a value that's not only reasonable, but is inside the stall range of the airfoil. That too reduces drag.) Outboard, camber is reduced, and at the tips it may be symmetrical or even reverse depending on the airfoil family. Compressibility effects with increasing Mach number toward the tips are considered in the airfoils for greatly reduced drag, instability, and noise.
Props need to be designed for engines and airframes together. Whether you can achieve the greatly desirable objective of direct drive depends on torque, RPM, and prop location. But as in post #43 above, a wake impeller is the way to go to get direct drive with high RPM engines.
My answer to your airfoil question is 180 degrees from the one I'd have given before starting to design airfoils. The bottom line is that for my own needs I can create airfoils at will that are far better than the ones you mention for a given application. I'd have gravitated toward Riblett and NASA NLFs previously depending on Reynolds range. A more complete graph comparing two Synergy airfoils to three common sections is attached as a .pdf below the one shown.
Regarding materials, for a quiet, efficient motorglider using your skills I'd go with wood. Bear in mind that wood is composite construction! Nothing stands in the way of designing and finishing it in a way that allows the final product to be comparable to a glass ship.
Reid, thanks for the post. 2593 more victims to go...
Files Attachment(s):airfoil graphs p2.pdf