Something doesn't quite add up. Cessna 172 and Robinson R44 use similarly powered engines for similar payload, same on the the heavy end of transport planes vs transport choppers.
In general, the lift to drag ratio (L/D) of an airfoil is proportional to the square root of the aspect ratio (AR). For airplane wings, this hits a limit of about 60 simply due to the difficulty of reinforcing a long wing while keeping weight down.
A helicopter rotor spins, so has different requirements (like greater strength near the hub) so can have a higher aspect ratio. Unfortunately the inner third of the rotor turns too slowly to contribute much lift, and the tips shed large toroidal vortices that diminish efficiency. The tips also encounter turbulence near the speed of sound which diminishes efficiency. So rotors (even on wind turbines) can't really get higher than 60% efficiency:
There has probably been more research in helicopter rotors over the years than increasing the L/D ratio of light aircraft, which explains how they reduced some of the discrepancy between the two.
When I was doing research for the Sikorsky human powered helicopter competition (unfortunately someone already won it haha), I did a lot of napkin calculations for this sort of thing:
There are many ways of increasing lift using winglets, vortex generators, EHD devices, etc (a few other keywords to look for are boundary layer and Reynolds number):
Personally I don't think we've even scratched the surface of what's possible in L/D ratios. With modern materials science and computer simulation at our disposal, I'd like to see someone break 100. Probably by using an array of airfoils and some EHD effects. I don't think anyone is seriously looking at it though other than maybe Bigelow Aerospace (JP Aerospace) and their defunct airships-to-orbit project:
I think this idea has merit and is one of the only ones that can compete on price with a space elevator. But it's not sexy enough, and people are still stuck on the idea of using helium instead of hydrogen, which sabotages it from ever succeeding (due to the limited supply of helium).
I would love to work on revolutionary ideas like this, but like most of you, I'm building SPA CRUD apps on the web to pay the mortgage. Sorry there's a lot of info here, but hey it's black friday on HN. What else are we gonna do.
zackmorris|7 years ago
https://en.wikipedia.org/wiki/Aspect_ratio_(aeronautics)
https://en.wikipedia.org/wiki/Lift-to-drag_ratio#Theory
https://en.wikipedia.org/wiki/Helicopter_rotor#Overview
In general, the lift to drag ratio (L/D) of an airfoil is proportional to the square root of the aspect ratio (AR). For airplane wings, this hits a limit of about 60 simply due to the difficulty of reinforcing a long wing while keeping weight down.
A helicopter rotor spins, so has different requirements (like greater strength near the hub) so can have a higher aspect ratio. Unfortunately the inner third of the rotor turns too slowly to contribute much lift, and the tips shed large toroidal vortices that diminish efficiency. The tips also encounter turbulence near the speed of sound which diminishes efficiency. So rotors (even on wind turbines) can't really get higher than 60% efficiency:
https://en.wikipedia.org/wiki/Betz%27s_law#Betz's_law_and_co...
There has probably been more research in helicopter rotors over the years than increasing the L/D ratio of light aircraft, which explains how they reduced some of the discrepancy between the two.
When I was doing research for the Sikorsky human powered helicopter competition (unfortunately someone already won it haha), I did a lot of napkin calculations for this sort of thing:
https://en.wikipedia.org/wiki/Igor_I._Sikorsky_Human_Powered...
Success came down to having the fewest, longest, thinnest, lightest rotor blades possible:
http://www.pitt.edu/~jdnorton/Goodies/TE-antiTE/
There are many ways of increasing lift using winglets, vortex generators, EHD devices, etc (a few other keywords to look for are boundary layer and Reynolds number):
https://en.wikipedia.org/wiki/Wingtip_device
https://en.wikipedia.org/wiki/Vortex_generator
https://sbir.gsfc.nasa.gov/content/aerodynamic-efficiency-dr...
Personally I don't think we've even scratched the surface of what's possible in L/D ratios. With modern materials science and computer simulation at our disposal, I'd like to see someone break 100. Probably by using an array of airfoils and some EHD effects. I don't think anyone is seriously looking at it though other than maybe Bigelow Aerospace (JP Aerospace) and their defunct airships-to-orbit project:
https://rimstar.org/space/jp_aerospace_balloon_airship_to_or...
https://en.wikipedia.org/wiki/JP_Aerospace
https://en.wikipedia.org/wiki/Bigelow_Aerospace
I think this idea has merit and is one of the only ones that can compete on price with a space elevator. But it's not sexy enough, and people are still stuck on the idea of using helium instead of hydrogen, which sabotages it from ever succeeding (due to the limited supply of helium).
I would love to work on revolutionary ideas like this, but like most of you, I'm building SPA CRUD apps on the web to pay the mortgage. Sorry there's a lot of info here, but hey it's black friday on HN. What else are we gonna do.