I hate the fact that phenomena worthy of proper scientific examination are often also massive nut-job magnets.
Seems to be possible in theory, but appears to require pretty extreme energies
Problem was, that was all the power you could get, and even then it wasn't enough to keep the cell afloat. Back then, we were using 10%-ish efficiency cells. Where I work now, we just toss 21+% monocrystalline cells which are 1/8th the mass of the originals around and don't care if they break, because as long as you can still put a bus ribbon on them all the way, they will produce full rated power, even if it looks like they were nailed with a sawed-off shotgun on the EL image.
“You want to play with 40,000 volts on an aircraft? That technology didn’t exist. Steve [Barrett] found a clever way to get that efficient conversion.”
So, the technology existed (when you do PWM with DC it mostly acts like AC so you can run it through a basic transformer) but they figured out the circuitry to make it efficient (nevermind solar efficiency now is enough to do what we want today without the basic transformer tech from almost 20 years ago.)
Still neat, but this really hints of amateurs that never checked some basic math which hinted at this possibility, and existed back in the 70s, which was before I was even born.
EDIT: added the second half after re-reading, edited again to make the PWM DC statement more clear.
(Edited for tone)
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.
http://jnaudin.free.fr/lifters/main.htm
So far their best result is 0.886 kW/kg (0.539 hp/lb), comparable to a helicopter, by using a pulsed DC power supply at 70 Hz:
http://jnaudin.free.fr/html/lftphv.htm
So a helicopter with that could lift 1.13 kg/kW (1.86 lb/hp).
A plane with a 10:1 lift to drag ratio would fly with 0.0886 kW/Kg (0.0539 hp/lb). It could lift 11.3 kg/kW (18.6 lb/hp).
A 200 kg (440 lb) helicopter, including human passenger, would take 177 kW (237 hp).
The same mass airplane would take 17.7 kW (23.7 hp).
Of course the pulsing would add a buzz which may not be desirable. It looks like the pulsed DC uses 17.72 RMS W vs 69.58 DC W, so is about 3.927 times more efficient than DC. Maybe a plane could have both silent and high efficiency modes for takeoff and cruising.
I have no idea how these numbers compare to the ones in the article, but they should be within the same magnitude. Please someone double check my math :-)