Design and development of a two-stage parachute system for delivery of troops from a high-speed aircraft

Abstract

The U. S. Army has a requirement to make undetected airdrop of small groups of special troops behind enemy lines in a high-threat environment. The drop aircraft must fly at high speed and low altitude to maximize aircraft survivability, and the troops must jump at these speeds and altitudes to prevent detection of the jump location. A two-stage parachute system was designed to meet this requirement. The first stage, a small drogue parachute. decelerates and stabilizes the jumper. A time delay pyrotechnic cutter then initiates deployment of the second stage. which is the main recovery parachute. The system must operate reliably, as no reserve parachute can be used, and must not produce forces which could injure the jumper, as he must be able to carry out a physically demanding mission. Initial prototypes did not meet all requirements. The first stage parachute and staging components were redesigned based on results of testing, and a modified system has successfully completed preliminary testing. Need and Requirement The U S Army has a need to conduct certain types of missions behind enemy lines. These specialized missions will be carried out by small groups of soldiers who will be airdropped into the area where the mission will be carried out. The airdrop must be made in a manner which will enhance aircraft survivability and ensure location of the airdrop remains undetected. The aircraft must fly at high-speed and low altitude to maximize survivability. The airdrop must be made at this speed and altitude to prevent detection of the drop location, which would be likely i f the aircraft slowed and climbed to normal drop speed and altitude. The general requirements of the system are listed below. These requirements are quite a bit different than those of other high-speed systems such as escape systems. There is just one set of primary operating conditions, which makes design of the system simpler, but this is offset by the high reliability required and the fact that the jumper cannot be injured in any way. rMrchanical Enqinmmr. Parachute Engineering Branch. Airdrop System. Division W e ~ b e r A I M Thi5 paper i* declared a work of the U.S. Government and is no1 wbjcct lo copyrighl protection in the United States. General Requirements: 1. Provide capability to make personnel airdrop at the speed and altitude the aircraft would normally fly while behind enemy lines. 2. Recover the jumper wlth no injury. This means the deceleration and opening forces must be relatively low, and the rate of descent must be low enough to prevent landing injuries. 3. The system must be very reliable because no reserve parachute can be employed under operational conditions. System Specifications The specifications for the system are listed below. These specifications were defined by the developer. U. S. Army Natick Research. Development and Engineering Center. (NRDEC), the customer. U . S. Army John F. Kennedy Special Warfare Center, (USAJFKSWC), and the U. S. Air Force. I . Exit conditions: a. Operational-250 KIAS 588 ' AGL 0 ' to 9000' Density Altitude b. Training120 to 250 KIAS 1000' AGL and higher 0' to 9000' ' Density Altitude