The radio-controlled (r/c) flying research model “Prandtl-D Ship 1” returned the first scientific data proving it is possible to design a wing with a bell-shape lift distribution that can generate favorable yaw. The NASA aerodynamicist responsible for designing, building, and testing the Prandtl-D Ship 1 flying research model is Albion H. Bowers (Chief Scientist, Armstrong Flight Research Center, ret.). Favorable yaw is the opposite of adverse yaw, the tendency of most fixed-wing aircraft to roll and yaw in the direction opposite to that which the pilot wishes to turn. Most conventional aircraft use the rudder mounted on a long moment arm, the fuselage, to allow the pilot to counteract adverse yaw. All-wing aircraft are particularly vulnerable to adverse yaw because they have no fuselage or rudder.

Wing Span 12 ft 4 in.

Length 4 ft 4 in.

Height 18 in.

Gross Weight 10 lb

The radio-controlled (r/c) flying research model “Prandtl-D Ship 1” returned the first scientific data proving that it is possible for a wing with a bell-shape lift distribution to generate favoroble yaw. A team led by NASA aerodynamicist Albion H. Bowers (..., ret.) designed, built, and tested Prandtl-D Ship 1. Favorable yaw is the opposite of adverse yaw, the tendency of most fixed-wing aircraft to roll and yaw in the direction opposite to that which the pilot wishes to turn. Most conventional aircraft use the rudder mounted on a long moment arm, the fuselage, to allow the pilot to counteract adverse yaw, however all-wing aircraft are particularly vulnerable to adverse yaw because they have no fuselage or rudder.

In a 1933 technical paper (Prandtl, L, “Über Tragflügel kleinsten induzierten Widerstandes.” Zeitschrift für Flugtechnik und Motorluftschiffahrt, 6 June 1933, 305-306), German Aerodynamicist Ludwig Prandtl derived a bell-shape wing lift distribution to minimize induced drag for a given wing weight. Prandtl was not aware that his lift distribution could also produce favorable yaw. The German designer of all-wing aircraft, Reimar Horten, realized that a bell shape lift distribution similar to Prandtl’s could generate favorable yaw although Horten did not prove it nor did he realize the drag savings that Prandtl had noted. NACA aerodynamicist Robert T. Jones also independently derived a solution similar to Prandtl’s theory, but Jones, failed to recognize that his solution could also counteract adverse yaw.

Beginning in 2013, NASA engineers, aerodynamicists, and interns used the Prandtl-D Ship 1 r/c flying model to collect the first known flight data proving that the Prandtl bell-shape lift distribution developed favorable yaw. This research is also significance in the following ways:

This flight data is consistent with the observed mechanics of bird flight, and confirms the methods birds use to achieve balanced, coordinated turning flight.

The data also provides insight into the aerodynamic effects of winglets such as those seen on many commercial aircraft.

The flight research data confirms how birds are able to have thin flexible feathers all the way out to their wingtips, which carry little or no load.

The flight research data confirms that despite the very narrow chord that birds have near their wingtips, they do not experience tip stall (or the resulting spin entry that follows tip stall).

The flight research data further confirms the reason that birds fly in formation with their wingtips overlapped, yet all the aircraft analysis predicts that birds should fly with their wingtips in-line. A multi-disciplinary peer-reviewed journal has just accepted for publication an article that details all of these findings and describes the potential for using the data to design a new class of more energy efficient aircraft.

The Prandtl-D Ship 1 flying model enhances the Museum collection of historic materials and original artifacts related to all-wing designer Reimar Horten. Horten’s role in further developing the Prandtl theory of the bell-shape lift distribution is described in Only the Wing: Reimar Horten’s Epic Quest to Stabilize and Control the All-Wing Aircraft (Smithsonian, 2011), by Russell Lee.

Wing Span 12 ft 4 in.

Length 4 ft 4 in.

Height 18 in.

Gross Weight 10 lb