In seeking a compromise between helicopters and fixed-wing aircraft, engineers in recent
years ШУУД ҮЗЭХ have opted for tilt
rotors, but NASA has dusted off and improved on a tilt wing aircraft design that takes off and lands like a helicopter and flies like an airplane. Called the Greased Lightning, or GL-10, the unmanned prototype made a successful vertical takeoff and transition to horizontal flight at Fort A.P. Hill, not far from NASA's Langley Research Center in Hampton, Virginia.
One of the major challenges for aviation engineers is combining the
vertical takeoff and landing (VTOL) and hover capabilities of a
helicopter with the speed and range of a fixed-wing aircraft. The V-22
Osprey and similar aircraft achieve this by rotating their engine
nacelles while keeping their wings fixed because it's mechanically
simpler and reduces crosswind drag. However, the GL-10 is an unmanned
hybrid-electric aircraft that uses 10 electric motors for propulsion and
NASA believes that a tilt wing is the better option for handling so
many nacelles at once.
Currently in the design and testing phase, the composite construction
GL-10 has four motors on either wing and two on the tail section. These
motors are powered by two 8 bhp (6 kW) diesel engines, which charge the
craft's lithium-ion batteries. The Unmanned Air Vehicle (UAV) has a
wingspan of 20 ft (6.1 m), a dry weight of 55 lb (24.9 kg), and a
takeoff weight of 62 lb (28.1 kg).
"All four engines on the left wing are given the same command," said
Zack Johns, the GL-10's primary pilot. "The four engines on the right
wing also work in concert. Then the two on the tail receive the same
command."
The
GL-10 was developed using a rapid prototyping process, with NASA saying
that a series of 12 prototypes were made. It started with modified foam
before working up to hobby planes weighing 5 to 25 lb (2.3 to 11.3 kg)
that suffered a number of "hard landings" as the engineers worked to
improve the flight control system.
According to the space agency, the GL-10 can loiter for 24 hours in
horizontal flight and is described as being as quiet as a petrol lawn
mower. The UAV is expected to eventually find applications in small
package delivery and long endurance aerial surveillance for agriculture,
mapping, and other survey tasks. A much larger version could one day
carry one to four passengers.
"During the flight tests we successfully transitioned from hover to
wing-borne flight like a conventional airplane then back to hover
again," says Bill Fredericks, aerospace engineer. "So far we have done
this on five flights. 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."
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