It might look like some kind of crazy machination that adorned the cover of Popular Aviation back in the ’60s, but the flying machine pictured is the real deal.
Developed by NASA, the GL-10 Greased Lightning is an unmanned hybrid-electric aircraft that can swivel its wings and engines – into the vertical position for vertical takeoff and landing (VTOL), and then horizontal for conventional flight.
The fairly recent advent of electric propulsion – thanks in large to the growing power and energy density of batteries – allows for some very efficient hybrid-electric aircraft designs that could finally replace the current (massively inefficient) king of VTOL: the helicopter.
While it’s not particularly hard to create an aircraft capable of VTOL, it has so far proven to be very tough to create an aircraft that can also efficiently cruise through the air after taking off vertically.
Without getting into the rather messy mechanics and physics of it all, it’s just really hard to create a single machine that can produce downwards thrust and then efficiently switch over to forwards thrust. The helicopter is the only common example of a VTOL aircraft that can also cruise acceptably, but its design is essentially a shopping list of compromises.
An everyday helicopter has a lift-to-drag (L/D) ratio of just 4.5 — compared to the Boeing 747 with a L/D of 17, or a modern sailplane glider with a L/D of 40 or more. This basically means that a helicopter has to try a lot harder to achieve a decent cruise speed — which basically means it needs to have a bigger engine (which in turn means it burns more fuel, has a lower range, has less space for cargo, etc.)
Interestingly, NASA also says that such a hybrid-electric design is “scale free” — meaning the same principles could be used to revolutionize everything from helicopters, to military UAVs, to massive jetliners. There doesn’t seem to be a specific target for NASA’s research [PDF], only that it thinks our current crop of aircraft designs could be a lot more efficient than they currently are. I’m sure the US military is interested in drones and helicopters with improved VTOL and cruise capabilities, though.
Source: Extreme Tech