A Stability Analysis Of Tandem Parachute Mid Air Recovery Systems

The objective of this report is to present the derivation and application of an analytical technique to quantitatively predict and measure the performance/stability of a tandem parachute Mid-Air Recovery System (MARS). In this system, a main parachute is used to control the rate of descent of the payload and a smaller parachute, tethered to the apex of this main chute, serves as an engagement target for the recovery aircraft. Significant parameters relevant to the position and stability of the engagement parachute are identified and quantified. Those parameters relevant to system stability, as viewed by the pilot of the retrieval aircraft, are combined into a single numerically valued stability factor. Sensitivity of the stability factor to variation of its components is assessed. The stability quantification technique is applied to flight test data from two different systems. On one system, the performance of gliding and nongliding main canopy configurations is analyzed and compared. For the other system, an estimation is made of the potential change in performance obtainable through conversion from a non-gliding to a gliding main parachute. Potential refinements of the stability quantification technique to improve its sensitivity are presented. (Author).

This document serves as the third revision of the USAF Parachute Handbook which was first published in 1951. The data and information represent the current state of the art relative to recovery system design and development. The initial chapters describe representative recovery applications, components, subsystems, material, manufacture and testing. The final chapters provide empirical data and analytical methods useful for predicting performance and presenting a definitive design of selected components into a reliable recovery system.

The purpose of this manual is to provide recovery system engineers in government and industry with tools to evaluate, analyze, select, and design parachute recovery systems. These systems range from simple, one-parachute assemblies to multiple-parachute systems, and may include equipment for impact attenuation, flotation, location, retrieval, and disposition. All system aspects are discussed, including the need for parachute recovery, the selection of the most suitable recovery system concept, concept analysis, parachute performance, force and stress analysis, material selection, parachute assembly and component design, and manufacturing. Experienced recovery system engineers will find this publication useful as a technical reference book; recent college graduates will find it useful as a textbook for learning about parachutes and parachute recovery systems; and technicians with extensive practical experience will find it useful as an engineering textbook that includes a chapter on parachute- related aerodynamics. In this manual, emphasis is placed on aiding government employees in evaluating and supervising the design and application of parachute systems. The parachute recovery system uses aerodynamic drag to decelerate people and equipment moving in air from a higher velocity to a lower velocity and to a safe landing. This lower velocity is known as rate of descent, landing velocity, or impact velocity, and is determined by the following requirements: (1) landing personnel uninjured and ready for action, (2) landing equipment and air vehicles undamaged and ready for use or refurbishment, and (3) impacting ordnance at a preselected angle and velocity.

The stability of an aircraft equipped with an air cushion recovery system (ACRS) was investigated both in-flight and during the landing (slideout) phase of flight. Digital computer simulations were used to identify unstable tendencies of a specific aircraft (the Jindivik drone). Control system designs are proposed to eliminate the instabilities. A nonlinear, six degree of freedom, aerodynamic model is developed based on available wind-tunnel data. The model is used in a computer software package, EASY, to simulate the vehicle in flight. A model of the air cushion recovery system is also developed. The model is generated by matching experimental data obtained from an actual ACRS with 14 spring/damper units. the model is verified by computer simulation, and the slideout simulations are performed. These simulations reveal a lateral-directional instability in the slideout. An optimal control design is proposed and verified, after which it is shown that the stability of the system is dramatically exhanced by the addition of an optimal controller.

A selection of annotated references to unclassified reports and journal articles that were introduced into the NASA scientific and technical information system and announced in Scientific and technical aerospace reports (STAR) and International aerospace abstracts (IAA).