Parachute Technology

The use of tail-mounted parachutes for emergency spin recovery has been common practice from the earliest days of flight to the present day. Properly designed and deployed parachutes have proven to be relatively reliable spin recovery device, always providing an antispin moment, regardless of the orientation of the aircraft or the disorientation or confu­sion of the pilot. Almost every military aircraft spin program conducted in the Spin Tunnel includes a parachute investigation. Free-spinning model tests are used to determine the critical geometric variables for parachute systems. Paramount among these variables is the minimum size of parachute required for recovery from the most dangerous spin modes. As would be expected, the size of the parachute is constrained by issues regarding system weight and the opening shock loads transmitted to the rear of the aircraft. In addition to parachute size, the length of parachute riser (attachment) lines and the attachment point location on the rear of the aircraft are also critical design parameters.

The importance of parachute riser line length can be especially crit­ical to the inflation and effectiveness of the parachute for spin recov­ery. Results of free-spin tests of hundreds of models in the Spin Tunnel has shown that if the riser length is too short, the parachute will be immersed in the low-energy wake of the spinning airplane and will not inflate. On the other hand, if the towline length is too long, the parachute will inflate but will drift inward and align itself with the axis of rotation, thereby providing no antispin contribution. The design and operational implementation of emergency spin recovery para­chutes are a stringent process that begins with spin tunnel tests and proceeds through the design and qualification of the parachute system, including the deployment and release mechanisms. By participation in each of these segments of the process, Langley researchers have amassed tremendous amount of knowledge regarding parachute systems and are called upon frequently by the aviation community for consultation

before designing and fabricating parachute systems for spin tests of full-scale aircraft.[514]