Preliminary Research Aerodynamic Design to Lower Drag, or Prandtl-D was an unmanned experimental glider-aircraft developed by

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. The acronym is a reference to early German

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Ludwig Prandtl Ludwig Prandtl (4 February 1875 – 15 August 1953) was a German fluid dynamicist, physicist and aerospace scientist. He was a pioneer in the development of rigorous systematic mathematical analyses which he used for underlying the science of ...

. The Prandtl-D was a tailless glider that is based on the flight of birds. Birds turn and bank without vertical tails that are required for such maneuvers on traditional aircraft. It was intended to provide for future low drag and experimental aircraft designs, which previously have had issues of controllability. The program reinforced similar wing designs by Ludwig Prandtl which were conceptualized a century before. The Prandtl-D's designs were also based on glider concepts of German brothers Reimar and Walter Horten and incorporate the conclusions of NASA aerodynamics pioneers R.T. Jones and Richard T. Whitcomb. The Prandtl-D1 and the Prandtl-D3 models were featured in the

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and the

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, respectively. Albion Bowers, NASA Armstrong chief scientist and Prandtl-D project manager, brought together the theories and has led the effort with help from student interns. He believes that with the concepts proven under the Prandtl-D "the time may be coming for a new paradigm in aviation."

Development

The first full sized model of these to fly was designated "Prandtl-D No. 3", and flown in a series of tests on October 28, 2015 at the Armstrong Flight Research Center in

Edwards, California Edwards (formerly, Muroc and Wherry Housing) is an unincorporated community in Kern County, California. It is located east-southeast of Mojave, about northeast of Lancaster, east of Rosamond, and south of California City at an elevation ...

. The aircraft is centered around the testing of yawing without a vertical stabilizer. The manager of the project, Albion Bowers, said that the aircraft is based on the flight of a bird. The Prandtl-D No. 3 first flew Oct. 28, 2015, with double the wingspan of the earlier versions, however, through development, the team managed to reduce the final glider's drag by 11%. Initially, each aircraft was radio operated with a hobby-grade controller and launched with a

bungee cord Bungee cords equipped with metal hooks A bungee cord (sometimes spelled bungle; also known as a shock cord) is an elastic cord composed of one or more elastic strands forming a core, usually covered in a woven cotton or polypropylene sheath. The ...

system. Later flight tests switched from a bungee launch method to a towed launch system. The first two vehicles of the program showed twist of the airfoil in providing an bell shaped lift distribution instead of the elliptical distribution. This feature gave an efficiency boost and reduced strain on the wings. PRANDTL D 3c on bungee during launch with center cover and FOSS

PRANDTL D 3c on bungee during launch with center cover and FOSS

In March 2016, Bowers published a technical paper entitled, “On Wings of the Minimum Induced Drag: Spanload Implications for Aircraft and Birds,” NASA/TP – 2016-219072. Detailing the aerodynamic properties and mathematics associated with the project, Bowers discusses in depth the science behind altering the span load distribution on aircraft wings and the data gathered from experiments that demonstrated validation of its critical principles.

Influence

The Prandtl-D led to the Preliminary Research Aerodynamic Design to Land on Mars (Prandtl-M) program designed for Mars Exploration. It has been tested in upper atmosphere of Earth and is designed to take topographic photos of the Martian surface. It also has provided a valuable platform for the Weather Hazard Alert and Awareness Technology Radiation Radiosonde Glider (WHAATRR) that will be used for atmospheric weather testing on Earth.

Museum aircraft

In 2019, two of the aircraft, D1 and D3, were transferred to the

Smithsonian National Air and Space Museum The National Air and Space Museum of the Smithsonian Institution, also called the Air and Space Museum, is a museum in Washington, D.C., in the United States. Established in 1946 as the National Air Museum, it opened its main building on the Na ...

in Washington, D.C., and

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, respectively, for their display following a successful review of the program. The Smithsonian specifically requested the aircraft because of its innovative proverse-yaw design.{{Cite web, date=2019-08-14, title=Prandtl-D’s next mission: Smithsonian Institution, California Science Center, url=https://www.aerotechnews.com/blog/2019/08/14/prandtl-ds-next-mission-smithsonian-institution-california-science-center/, access-date=2021-12-06, website=Aerotech News & Review, language=en-US

Specifications

The first two subscale Prandtl-D aircraft had a 12.5-foot wingspan and were constructed of a machined foam core wrapped in a skin of carbon fiber. The Prandtl-D No.3 has a wingspan of 25 ft, weight of 28 lbs, top airspeed of 18 kt, and a maximum altitude of 220 ft. The aircraft also has the Arduino flight control system used in the second Prandtl-D subscale model and is constructed of carbon fiber, fiberglass and foam. A key difference in the Prandtl-D full scale model is an addition of a

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developed Data Collection System (DAC).

List of vehicles

* Prandtl-D1 * Prandtl-D2 * Prandtl-D3 * Prandtl-D3c

References

External links

“On Wings of the Minimum Induced Drag: Spanload Implications for Aircraft and Birds,” NASA/TP – 2016-219072.
NASA 2010s United States experimental aircraft Glider aircraft Unmanned aerial vehicles of the United States Aircraft first flown in 2015 Tailless aircraft