Prandtl-D

The Prandtl-D (Preliminary Research Aerodynamic Design to Lower Drag) is a family of unpiloted experimental gliders created by NASA, led by aerodynamicist Albion Bowers. The name honors German engineer Ludwig Prandtl, whose early 1930s work on bell-shaped lift distribution shaped the project. The goal was to reduce drag and improve aerodynamic efficiency without sacrificing stability or control, taking cues from birds that can turn and bank without the vertical tail fins found on conventional aircraft.

Design

The design uses a tailless flying wing, which offers the best chance for low drag and high efficiency. Sweeping the wings back helps maintain stability and control. The first two small-scale models had a 12.5-foot wingspan, built from machined foam core wrapped in carbon fiber.

The third aircraft, Prandtl-D No. 3, has a 25-foot wingspan, weighs 28 pounds, reaches a top speed of 18 knots, and a maximum altitude of 220 feet. It uses an Arduino flight control system from the earlier model and is made of carbon fiber, fiberglass, and foam. A key addition on the full-scale version is a Data Collection System (DAC) developed by the University of Minnesota.

Origins

The project drew on theoretical wing studies by Ludwig Prandtl, as well as glider concepts from the German Horten brothers, Reimar and Walter. It also incorporated findings from NASA pioneers R.T. Jones and Richard T. Whitcomb. Bowers, who served as NASA Armstrong chief scientist and project manager, worked with student interns to bring these ideas together. He believes the proven concepts may lead to a new aviation paradigm.

Development

The first full-sized model, Prandtl-D No. 3, flew on October 28, 2015, at NASA’s Armstrong Flight Research Center in Edwards, California. It was designed to test yawing without a vertical stabilizer, mimicking bird flight.

Though its wingspan doubled from earlier versions, the team reduced the glider’s drag by 11%. Early flights used a hobby-grade radio controller and a bungee cord launch system; later tests switched to a towed launch. The first two vehicles demonstrated that twisting the airfoil produced a bell-shaped lift distribution rather than the usual elliptical one, boosting efficiency and reducing wing strain.