It runs on batteries, has 10 engines, can take off like a helicopter and fly as efficiently as a fixed-wing. For now, the GL-10 – known in-house as Greased Lightning – may be a prototype, but it has now successfully be flown. NASA is hoping that its concept, initially seen as a drone, can take off in other areas of the aviation world, too.
NASA researchers at the organisation’s Langley Research Centre in Hampton, Virginia, designed and built the remotely piloted aircraft. It had already passed hover tests, flying like a helicopter, until the most recent tests (see video) proved that it is able to make the transition from hover to wing-borne flight.
The GL-10 is being envisaged at this stage as a potential unmanned aerial vehicle (UAV). “We have a couple of options that this concept could be good for,” said Bill Fredericks, aerospace engineer. “It could be used for small package delivery or vertical take off and landing, long endurance surveillance for agriculture, mapping and other applications. A scaled-up version — much larger than what we are testing now — would make also a great one- to four-person personal air vehicle.”
The GL-10 is currently in the design and testing phase. The initial thought was to develop a 6,1 metre wingspan aircraft powered by hybrid diesel/electric engines. The team started with smaller versions for testing, built by rapid prototyping.
“We built 12 prototypes, starting with simple five-pound (2.3 kilograms) foam models and then 25-pound (11.3 kilograms), highly modified fiberglass hobby airplane kits all leading up to the 55-pound (24.9 kilograms), high quality, carbon fiber GL-10 built in our model shop by expert technicians, ” said aerospace engineer David North.
“Each prototype helped us answer technical questions while keeping costs down. We did lose some of the early prototypes to ‘hard landings’ as we learned how to configure the flight control system. But we discovered something from each loss and were able to keep moving forward.”
As tested, it has a wingspan of 3,05 metres, eight electric motors on the wings, two electric motors on the tail and weighs a maximum of 28,1 kilograms at takeoff.
The idea of aircraft that can combine the best attributes of helicopters (hovering) and fixed-wing aircraft (efficient horizontal flight) has been proven. Overcoming the practical difficulties involved, though, has usually been too much of a challenge. The tiltrotor V-22 Osprey, for one, managed to show that it could be done successfully.
“During the flight tests we successfully transitioned from hover to wing-borne flight like a conventional airplane then back to hover again. So far we have done this on five flights,” said Fredericks. “We were ecstatic. Now we’re working on our second goal — to demonstrate that this concept is four times more aerodynamically efficient in cruise than a helicopter.”
Although it has ten engines it is reported to fly more like a three-engine plane from a control perspective. All four engines on the left wing are given the same command. The four engines on the right wing also work in concert. Then the two on the tail receive the same command.
One other advantage to the GL-10 besides its versatile vertical take off and landing ability is its noise or lack of it. “It’s pretty quiet,” said Fredericks. “The current prototype is quieter than a neighbour mowing the law with a (petrol)-powered motor.”
The next step in the GL-10 test program is to try to confirm its aerodynamic efficiency.