VTOL Rides Again

Why Not Be Able to Do Everything?

- Peter Garrison

The idea was to blow high-speed air over the wing during takeoff and landing, augmenting lift and allowing the wing area (and weight, and drag) to be reduced by two-thirds. In cruise, 16 of the motors would shut down and their propellers would fold flush with the sides of their nacelles; thrust would then be provided by two motors at the wingtips. These would rotate top-blade outward, weakening the tip vortices and shaving off some induced drag. A full-scale piloted test item is now being built, using the fuselage and empennage of a Tecnam P2006T, an Italian-built light twin. It is expected to fly in 2018 or 2019, and will, as NASA modestly states, “allow engineers to compare the performance of the flight demonstrator with that of the original P2006T.”

In the meantime, another NASA group, this one at the Langley Research Center in Virginia, has been developing a concept that is similar in some respects to LEAP Tech, but in others more radical. It is called GL-10. The GL stands for Greased Lightning, not because it is expected to be exceptionally fast, but because in its final form it will use a hybrid power system consisting of an internal combustion engine burning fossil fuel or discarded French-fry oil — hence the “greased” — and driving a generator to supply power to electric motors — hence the “lightning.”

The 10 stands for the number of motors and propellers. Each wing has four motors, spread out so that the entire wing is bathed in prop wash; in that respect, its technology is similar to LEAP Tech’s. Two more motors are on the tail. One project engineer described it as a tandem-wing design, as opposed to wing-and-stabilizer, because the CG is somewhat farther aft than it normally would be and so the horizontal stabilizer/aft wing contributes about a sixth of the lift in cruising flight. The reason for this design choice will become apparent shortly.