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 above 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.)
NASA's Greased Lightning, design diagram
Hybrid-electric aircraft designs could change all that, however. Electric propulsion, as with electric cars, allows for much more efficient designs. No longer do you have to worry about where to put the large fossil fuel-powered engines, or how to manage the mechanical stress across the airframe -- instead, you can have a bunch of smaller, more efficient, optimally placed electric motors. Without the mechanical complexity of big (jet) engines, it suddenly becomes a lot easier to have wings and propellers that can swivel between horizontal and vertical. [Read: Terrafugia TF-X: The vertical take-off flying car.]
While pure-electric aircraft do exist (quadcopters!), hybrid-electric designs with longer range are generally of more interest to military and commercial groups. In the case of NASA's Greased Lightning, there are two small diesel engines in the body of the aircraft that turn electric alternators that constantly recharge the lithium batteries. While a battery-powered quadcopter might be able to stay in the air for 30 minutes, a hybrid-electric aircraft like Greased Lightning could theoretically have the same range and duration of a modern plane -- while also having VTOL capability.
GL-10 Greased Lightning, on the ground
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(Opens in a new window) [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. [Read: DARPA is building an autonomous vertical takeoff transport for troops, cars, and more.]
For now, Greased Lightning only has a wingspan of 10 feet (3 meters), and its first test flight(Opens in a new window) (National Aviation Day, August 19) was tethered. Untethered flights are planned for later in the year -- and hopefully we'll then get some awesome videos of it flying around, too.
