Langley’s Francis Rogallo is widely recognized as the father of the flexible wing concept known as the parawing. Rogallo conceived the idea of a flexible, diamond-shaped wing attached to rigid wing-forming members in 1947. His efforts to demonstrate the gliding potential of unpowered parawing configurations were followed by a growing interest in industry for broad applications to utility vehicles and cargo delivery concepts. When the space age dawned, NASA began to explore various candidate approaches for the recovery of its space capsules after exploratory space missions. A special interest was the possibility of extending the landing footprint to the point that recovery could occur on land or runways, thereby avoiding the
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Free-flight model of parawing utility vehicle during tests in the Langley Full-Scale Tunnel. Control was accomplished by tilting the para-wing relative to the pilot’s platform. After large adverse control effects were discovered using the technique, researchers conceived new roll control concepts using hinged keel members.
complexity and cost of ballistic water landings, which involved recovery ships and other complications. The search for recovery concepts that provided a degree of modification to the ballistic recovery flight trajectory included serious considerations of parawing/capsule applications. At the same time, free-flight studies were conducted to explore the use of packaged, deployable parawings for the recovery of rocket boosters, such as the Saturn rocket.
Before any of the foregoing parawing applications could be realized, significant research was required on the dynamic stability and control characteristics of the unconventional configurations resulting from parawing-vehicle combinations. In addition to traditional stability and control issues, such as how to provide sufficient levels of control without excessive adverse effects, researchers set out to explore problems associated with the deployment of flexible wings from other vehicles during flight.41 Free-flight model testing of the dynamic stability of parawing vehicles began with a series of studies of powered parawing utility vehicles in 1961.42 One of the major issues to be addressed in the design of parawing/vehicle combi-nations was the adequacy of longitudinal and lateral-directional control, because the relatively high position of the parawing relative to the center of gravity of the vehicle could create unconventional responses to inputs by the pilot.
During flight tests of dynamic models, it was found that shifting the center of gravity of the vehicle fore and aft for pitch control and side to side for roll control was satisfactory for some configurations. This control concept was implemented by banking the wing relative to the vehicle for roll control and by pitching the wing
67 for longitudinal control. However, other configurations using the same control technique exhibited marginal or unsatisfactory levels of control. In fact, some of the configurations would roll in a direction opposite to the pilot’s input because of excessive adverse yaw. Langley researchers conceived and demonstrated a revised lateral control concept, in which wing bank was still used for roll control, but the aft sections of the rigid lead-ing edge of the parawlead-ing were hlead-inged to reduce large hlead-inge moments produced by the original wlead-ing-bank control system. When modified with the revised control concept, the free-flight models all exhibited satisfac-tory characteristics.43
In the early 1960s, parawing recovery of large rocket boosters in the class of the Saturn rocket was explored by wind tunnel testing and outdoor drop-model studies at Langley’s Plum Tree test range.44 The concept used a folded rigid-member parawing that was stowed and deployed from the side of the booster after launch and booster burnout during an essentially vertical flight path at subsonic speeds. After deploy-ment, a small drogue parachute was used to maintain separation between the booster and the parawing until the parawing was fully deployed and producing lift for the recovery pullout maneuver. Suspension lines at the front and rear of the parawing were used for control inputs during the recovery flight. Although simple in concept, this recovery procedure had many potential pitfalls that were identified and eventually solved during the test program. Critical design
parameters such as the length of the sus-pension lines, the spacing between the side of the booster and the inflating para- wing, and the opening shock loads were all assessed using the drop-model testing technique, in which the booster and stowed parawing were released from a helicopter at altitudes of about 3,000 feet. Once a sat-isfactory deployment was obtained and the parawing/booster combination entered a glide, stability and control problems were noted, including an abrupt stall that some-times led to the test article pitching down and tumbling with the booster falling on top of the parawing. The free-flight model also exhibited relatively small constant-ampli-tude rolling and yawing motions.
Sequence showing deployment process for a free-flight model parawing recovery system for the Saturn rocket booster. Dynamic stability and control challenges were met after considerable research with a large free-flight model deployed from a helicopter.
Many organizations at Langley were also involved in wind tunnel testing of parawing/capsule combina-tions to assess aerodynamic characteristics for possible applicacombina-tions as gliding recovery systems. These activities included free-flight model testing in the Full-Scale Tunnel and outdoor drop-model testing.45 Once again, the parawing deployment process and an evaluation of the dynamic stability and control of the parawing/capsule arrangement was the major thrust of the research efforts. The drop-model used a tele-scoping rigid parawing in which the leading edges could be retracted into a small spanwise dimension and attached near the apex of a blunted cone suspended below the parawing. The lengths of the suspension lines were varied to shift the center of gravity of the vehicle fore and aft for pitch control and side to side for
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roll or lateral control. A drogue parachute was necessary to extract, open, and separate the parawing from the capsule. Dropped from a helicopter at near-zero airspeed and an altitude of approximately 3,000 feet, the 85-pound combination began the parawing deployment process at about 2,000 feet. After a series of exploratory test flights established the critical design parameters, results indicated that the free-flight model was stable and could be controlled during gliding flight by shifting the center of gravity. The deployment of the parawing, however, required a carefully controlled sequence that could not occur too quickly. In particu-lar, the parawing had to be slowly rotated to a lifting condition, or a tumbling motion ensued.
In addition to the foregoing studies, many more free-flight model investigations of parawing configurations were conducted at Langley with a variety of applications, including landing aids for high-speed aircraft and reentry vehicles.46