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Schweizer 1-36 in Flight - Controlled Rapid Descent Schweizer 1-36 in Flight - Controlled Rapid Descent

Photo Number: ECN-26845
Photo Date: 1983

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A Schweizer 1-36 sailplane, used by NASA for a series of deep-stall research flights, is shown here in a rapid, controlled descent during a flight test over the Mojave Desert in California.

In the early 1980s, a Schweizer SGS 1-36 sailplane was modified for the NASA controlled, deep-stall flight program. The aircraft, flown at the Ames-Dryden Flight Research Facility (ADFRF, both before and after that time called the Dryden Flight Research Center, Edwards, California), was used for controllability research in the deep-stall region at an angle of attack of above 30 degrees.

Schweizer modified the horizontal stabilizer (T-tail configuration) so that it could pivot as much as 70 degrees with the leading edge down. Once the aircraft arrived at ADFRF, it was further modified, including modification of the cockpit area to permit easier pilot egress and addition of a NASA instrumentation system in the fuselage. After the modifications were completed, radio-controlled-model and ground tests of the aircraft were performed prior to flight tests. These preliminary tests included use of a simulator.

In September and October 1983, the modified Schweizer SGS 1-36 was flown in the ADFRF’s high-angle-of-attack program. The Schweizer was chosen for the program because of its slow speed and because its high-angle-of-attack aerodynamics were dominated by long wings rather than a long, pointed nose or forward strake. The objectives of the program were to demonstrate the feasibility of piloted, controlled flight at very high angles of attack and to refine piloting techniques required to make a safe transition into, maneuver in, and recover from controlled flight at very high angles of attack. Of particular interest during the 20 flights of the sailplane were the stability-and-control derivatives, trim data, and piloting techniques required to safely enter and exit the very high-angle-of-attack flight regime.

For the flight test, the sailplane was typically towed to an altitude of 8,500 feet above ground level and released. Upon release the sailplane was decelerated to near-stall speed. The pilot then performed maneuvers to investigate handling qualities.

Flight data showed that piloting techniques for the sailplane allowed the pilot to safely make entry into, maneuver in, and recover from controlled flight within the 30- to 72-degree angle-of-attack range. Maximum likelihood analysis (parameter estimation) techniques were used to obtain aerodynamic derivatives from the flight test data. These data were compared to a predicted data set derived from wind tunnels. Generally, the agreement was fair to good, but the derivatives were used to refine the aerodynamic database at low and very high angles of attack. Analysis of the flight data was also used to better define the vehicle’s trim and operational performance envelope.

The Schweizer 1-36 sailplane is a single-place, mostly aluminum aircraft. The wingspan is close to 46 feet and the fuselage is nearly 21 feet long. The horizontal stabilizer is a T-tail configuration with a span of 7.9 feet.

Keywords: Schweizer SGS 1-36; Ames-Dryden Flight Research Facility; Dryden Flight Research Center; angle of attack; high-angle-of-attack program; parameter estimation.

Last Modified: February 6, 2002
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