Skewed Logic: The RPRV Explores Jones’s Oblique Wing

In the early 1970s—a time when fuel prices were soaring—scientists at NASA Ames Research Center and NASA Dryden began investigat­ing an aircraft concept featuring a wing that could be rotated about a

central pivot. For low-speed flight, the planform would present a con­ventional straight wing, perpendicular to the fuselage. At higher speeds, the wing would be skewed to an oblique angle, with one side swept for­ward and the other aft to enhance transonic cruise efficiency by reduc­ing drag. Dr. Robert T. Jones, a senior scientist at Ames (and, early in his career, the American father of the swept wing), proposed the single­pivot oblique wing concept for a future supersonic transport. Studies indicated that such a plane flying at 1,000 mph would achieve twice the fuel economy of supersonic transports then operational, including the Concorde and Tu-144.

Jones built a 5.5-foot wingspan, radio-controlled model to test the configuration’s basic handling qualities. The wing, mounted atop the fuselage, pivoted so that the left side moved forward and the right side moved aft to take advantage of propeller torque to cancel rolling moment. Burnett L. Gadberg controlled the model during flight tests at wing angles up to 45 degrees and speeds between 50 and 100 mph. He found that the model remained stable at high sweep angles and could be con­trolled with decoupled aerodynamic control surfaces.40 In order to fur­ther investigate the aerodynamic characteristics of an oblique wing and develop control laws necessary to achieve acceptable handling quali­ties, a $200,000 contract was awarded for design and development of a subsonic, remotely piloted Oblique Wing Research Aircraft (OWRA). Rod Bailey at Ames led the design effort, originally conceiving an all­wing vehicle. Because of stability and control issues, however, a tail assembly was eventually added.

Built by Developmental Sciences, Inc., of City of Industry, CA, the OWRA had a narrow cylindrical fuselage tipped with a glass dome—like a cyclopean eye—containing a television camera. Power was provided by a McCullough 90-horsepower, 4-cylinder, air-cooled, reciprocating engine mounted in the center of a 22-foot-span, oval planform wing. The engine drove a pusher propeller, shrouded in a 50-inch-diameter duct to reduce risk of crash damage. To further ensure survivability and ease of repair, key structural components were constructed of fiberglass epoxy composites. A two-axis, gyro-controlled autopilot provided sta­bilization for pitch, roll, and altitude hold, but the vacuum-tube-based sensors resulted in a significant weight penalty.[919] By December 1975, following 3 years of development with minimal resources, construction of the OWRA was essentially complete. Engineers evaluated the vehicle in two rounds of wind tunnel testing to collect preliminary data. Tests in a 7- by 10-foot tunnel helped designers refine the basic layout of the aircraft and confirmed trends noted with the original subscale model.

Milton O. Thompson, chief engineer at Dryden, recommended flying the vehicle from a remote site such as Bicycle Lake, at nearby U. S. Army Fort Irwin, or Mud Lake, NV, in order to minimize any adverse pub­licity should an incident occur. Based on his recommendation, Bicycle Lake was selected for taxi testing.[920] During these preliminary trials, engineers discovered that the OWRA—designed to have a top speed of 146 knots—was considerably underpowered. Additionally, the air­craft was damaged when it flipped over on the lakebed following loss of signal from the control transmitter. After being rebuilt, the OWRA was tested in a 40- by 80-foot Ames wind tunnel in order to evaluate three different tail configurations and determine static aerodynamic characteristics at varying wing-sweep angles. The results of these tests provided data required for ground simulation and training for pilot Jim Martin.[921] In April 1976, the OWRA was delivered to Dryden for test­ing. Technicians spent the next several months installing avionics and instrumentation, conducting systems checkouts, and developing a flight plan through detailed simulations. Taxi testing took place August 3, and the first flight was accomplished 3 days later at Rogers Dry Lake.

The results of the 24-minute flight indicated insufficient lon­gitudinal stability because of a center of gravity located too far aft. Subsequently, the aircraft was modified with a 33-percent-larger vertical stabilizer, which was also moved back 3 feet, and a rede­signed flight control system, which alleviated trim and stability prob­lems. During a second flight, on September 16, stability and control data were collected to wing skew angles up to 30 degrees. Although severe radio-control system problems were encountered throughout the flight, all mission objectives were accomplished. A third and final flight was made October 20. Despite some control difficulties, researchers were able to obtain data at wing-skew angles up to 45 degrees, boost­ing confidence in plans for development of piloted oblique wing aircraft designs such as the Ames-Dryden AD-1 research airplane that was successfully flown in the early 1980s.[922]