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Eject! Eject! Eject! – Current Ejection Systems

Technological advancements in the design and development of ejection systems have resulted in significant improvements in the ejection seat and life support systems. Some of the advancements in ejection seat related sub-systems are discussed here.

Harness System.  This has seen several changes from the conventional 5-point harness system to the newer concept of integrated harness assembly. Integrated harness assembly consists of lower and upper torso restraint system along with Passive Arm Restraint System (PARS), which is activated on ejection. This provides in-flight retention of aircrew with full mobility, vision and ability to control the aircraft. The lower torso restraint system provides protection at all times where as upper torso restraint is needed when exposed to a maximum of 30 G in the forward and downward axis. The distribution of the ejection forces, crash loads and parachute opening shock are distributed evenly over a larger area of contact provided by this integrated harness assembly.

Powered Inertia Restraint Device (PIRD).  The gas initiation mechanism of PIRD, initiated on ejection, helps in restraining the pilot into the seat prior to ejection. This concept has been introduced in the newer ejection seats.

Directional Automatic Realignment of Trajectory (DART). DART action during the rocket burn stage provides stabilising force based on the center of gravity and aerodynamic movements. It is composed of 2 lanyards, a disc brake and a DART bridle. As the seat moves up, the lanyard plays out under minimal line tension and once fully stretched helps rotate the bridle downward for realignment of trajectory.

STAPAC.  The gyro-stabilised thrust vector control helps in stabilising the pitch through rockets.

Wind Oriented Rocket Development (WORD). WORD is fired by a lanyard operated firing mechanism. During development of the drogue chute the direction of the WORD trajectory is aligned with the relative air streams thus facilitating early deployment of the chute.

Miniature Detonating Cords (MDC).  MDC connected through thin layer explosive (RDX) lines facilitate fragmenting the canopy for early exit. There are two types – In-flight Egress System (IES) wherein the MDC is placed over inside or about the midline of the canopy and Ground Egress System (GES) wherein the MDC is located at periphery.

Automatic Inflation Modulation (AIM).  This concept of parachute deployment is being made available in the ACES, SIIS and MB 16 seats. The size of the parachute is from 28-29 ft with maximum rate of descent at 7 m/sec (22.96 ft/sec). Automatic inflation of parachute reduces the parachute opening shock. Aero conical parachutes are now being used on MB XIV and later versions of MB seats.

With the advent of computerisation in every field, the modern seats e.g. MB 16 have a microprocessor-based control. This is continuously updated with the various parameters of flight (attitude, altitude, airspeed etc.) and has increased the overall capabilities and safety of ejection seats. Thus an inverted aircraft will withhold firing of rocket, motors and pass on to the next stage of operation.


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Reference

1. Ernsting’s Aviation Medicine. Rainford DJ, Gradwell DP (Editors). 4th Edition. Hodder Arnold, London 2006.

2. Fundamentals of Aerospace Medicine. DeHart RL, Davis JR (Editors). 3rd Edition. Lippincott, Williams & Wilkins, Philadelphia 2002.

Acknowledgement.  Image courtesy Wikimedia Commons

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