Under study for six years, Lockheed Martin’s Hybrid Wing Body (HWB) concept is designed to carry all of the outsize cargo now airlifted the Lockheed C-5 while burning 70% less fuel than the Boeing C-17. Over-wing nacelles make it easier to install large-diameter, fuel-efficient very-high-bypass engines.
The HWB configuration combines a blended wing and forebody for increased aerodynamic and structural efficiency with a conventional aft fuselage and tail, which maintains compatibility with existing airlift infrastructure and operations, including airdropping paratroops.
The HWB retains a circular pressurized fuselage, with additional unpressurized cargo bays in the inboard wing sections that are accessed from the main cargo hold. This hybrid design allows conventional cargo loading and unloading equipment and procedures to used.
Wind-tunnel tests confirm over-wing nacelles reduce drag by 5% compared with conventional under-wing engines. Retaining after fuselage and tail incurs less than a 5% penalty, Lockheed says, and provides robust flight control compared with a pure blended wing-body configuration.
In addition to the airlifter configuration, Lockheed is studying a multi-role tanker/transport variant of the HWB that would be 15% more fuel-efficient than the Boeing KC-46A. The design would allow a single aircraft type to replace today’s separate airlift and tanker fleets, the company argues.
Tests of a 4%-scale semi-span model in the National Transonic Facility at NASA Langley Research Center have validated the predicted aerodynamic efficiency of the HWB with over-wing nacelles, says Lockheed. Low-speed testing of the high-lift system was also accomplished.
Lockheed plans to fly a 4%-scale unmanned version the HWB early in 2016, and is funded by AFRL to study a large-scale manned demonstrator to fly around 2020. To reduce cost, this could be based on a business jet, possible a Gulfstream V, fitted with a new wing and forebody fairing.
If pursued, Lockheed Martin’s HWB airlifter could enter service around 2035. Under NASA contract, the company is also studying an HWB commercial freighter, from 747- down to 757-size, that could enter service in the same timeframe – raising the potential for dual-use development.
With wind-tunnel tests confirming the expected efficiency benefits of Lockheed Martin's Hybrid Wing Body airlifter, Aviation Week takes a closer look at the latest transport design.
