Recent Advances & Current Concepts
In Ejection Seat Design
by
Gp Capt MM Dogra
Sr Adviser (Av Med)
IAM, IAF

In 1912, an ejection system from a flying aircraft was extracted by a small cannon launched parachuted dummy near Paris. This primitive system was not only a precursor but also had a lot of similarities with modern ejection systems. One of the important aspects being, it had a rudimentary skirt spreader gun for rapid parachute deployment, a system available in a sophisticated version in modern Stencel SIIIS seat. From that experiment to the present experiences like the very low altitude ejection just prior to ground impact of a MiG-29 aircraft in 1989 Paris Air Show or the unbelievable escapes by two pilots from a mid-air collided exploding aircraft in an air show in UK in 1993, the ejection seat development has come a long way.Over the period the ejection seats have been used over 15,000 times from aircraft.

Installment of 0-0 seat in an aircraft was a dream come true. However, pilots are still getting injuries during ejections. Analysis of various phases of the ejection sequence till parachute deployment indicates the following mechanism of injury production in successful ejections i.e. non fatal ejections which took place within the prescribed envelope :-

Sl No.	Cause	Injury
(a)	Ejection Seat 'G' forces	Spinal compression fracture
(b)	Fouling with seat/cockpit Structure	Extremity fractures/dislocations
(c)	Impact with canopy structure	Severe laceration Neck straining and cervical spinal fracture
(d)	Windblast	Petechial, retinal and conjunctival Hemorrhage
(e)	Flail & Wind drag deceleration	Fractures Dislocation/disarticulation of extremities Internal injuries to organs Head injury/LOC Subdural haematoma
(f)	Parachute opening shock	Cervical strain/vertebral dislocation fracture
(g)	Riser Strap	Facial injuries Concussion, Contusions & Lacerations

Modern ejection seat manufacturers are channeling their research activities in an effort to increase the safe envelope of ejection. This would entail that modern ejection seat manufactures further look in to amelioration of causes leading to injuries. Critical areas which are of interest in current ejection seats are :-

(a)	Ejection Seat propulsion   Rocket assisted seats for boost over longer duration
	Low seat weight-	K 36         - 100 Kg
		K 36L        - 95 Kg
		MB Mk-10  - 82 Kg
		MB Mk 14   - 91.4 Kg
		MB Mk 16    - 063.4 Kg
	Pilot Weight	5th percentile weight pilot experiences 18-20 G 95th percentile weight pilot experiences 14-16 G
(b)	Restraint System

Torso Restraint-		Conventional 'X' configuration with single   release point and inertia reel system
Arm Restraint-		Nets and lanyards
Leg Restraint-		Restricts lateral movements and lifts legs by 4   inches below the seat bucket
Head Protection-		Brim is essentially an airfoil to deflect   airflow over head. It is retracted prior to seat man   separation.
Inflatable Restraints     Restraint Net -		(4th Generation upgrade in ACES-II). A   Comprehensive restraint.

(c) Canopy Fragmentation

MDC (MB Seats)

Canopy breakers (MB MK-10, K-36, ACES-II)

Explosive Fragmentation (F-16)

Pyrotechnic for Canopy fragilisation (Dassault -Mirage)

Inflatable Restraints     Restraint Net -

(d) Wind Blast Protection

Wind blast flow deflectors (K-36 DM)

Head Protection Brim (AES-II)

CREST wind blast protection assembly

(e) Controlled Seat Deceleration (Aerodynamic Seat)

Electronic control system with roll attitude control rockets. (K-36)

Seat Drogue Chutes (K-36)

Digital Flight Control System with Four Thruster Geometry Pintle motors     to control yaw, roll and pitch (ACES -II upgrade)

CTAES (controllable thrust for aircrew escape system) for MDA seats

MAXPAC (Multiple Axis Pintle attitude control developed by Aerojet for     integration with NACES

2 Rigid Telescopic Booms with parachutes (K-36D) for seat stabilization

Flight Control System (FCS) being developed by MDA. This is an     attitude and trajectory controlled real time auto pilot function.

4TH GENERATION SYSTEM IN IAF
In the IAF, most of the ejection seats of the Russian as well as Western origin are so called 3rd generation seats. Only exception is K-36 DM presently available in MiG-29 and SU-30 aircraft. Its light weight variant K-36 DM-3.5L is being considered for installation in both LCA and HJT-36. The latter is being thought of as an Intermediate Jet Trainer for the IAF. This seat is probably the only 4th generation seat available off the shelf. Most other 4th generation seats are in the process of modifications by mainly McDonald Douglas aircraft (ACES II) and comparable Martin Baker variants of MK 10 and MK 16 seats.

The 4th Generation seats ability to monitor environmental factors allows better control inputs, improving seat stability and consequently reduced ejection injuries. The dramatic escapes by MiG-29 pilots in Paris (1989) and Forford, UK (1993) airshows brought the K-36D seat into limelight. Conventional seats are safe up to speeds of 350K EAS and injury potential increases exponentially to a high probability of fatal injuries at about 600 K EAS. Successful K-36D operational ejections have been reported at speeds of 720 K EAS and Mach 2.6. The designer of seat Prof. Guy Severin, a member of the Prestigious Russian Academy of Sciences has claimed safe escape up to 755 K EAS.

Scientists from Air Force Research Laboratory (AFRL) and US Navy's Air and Surface Warfare Centre evaluated the K-36D seat. The seat was ejected from the rocket sled at speeds of 730 K EAS and from a MiG-25 at speeds of Mach 2.5 and altitudes of 56,000 ft. 17 successive successful ejections forc1ed the Americans to accept that the K-36D seat was superior to ejection seats in US aircraft. It is interesting to note that Zvezda has developed an ejection seat test bed consisting of a cockpit mounted on the tail of an AN-12 aircraft. A contract between Boeing North America (BND) and Zvezda was signed for technology development for K-36 variant ejection seat, for American aircraft. Some of the salient features of K-36 DM seat are :-

• Telescopic booms for seat stabilization till recovery parachute deployment.



• Wind blast deflector during ejection at speeds above 430 K EAS,



• Leg lifting devices and arm and leg restraints, such that do not restrict limb movements during normal operation.



• K-36D - 3.5L is 50 lbs lighter than K-36DM and accommodates larger range of occupant weights.



• Increased vertical adjustment range and option of variable tilt back of the seat.



• Smaller head rest/parachute container to improve mobility to check six and to reduce head injury reported at high-speed ejections causing probable whiplash concussion/amnesia/LOC as suspected in a few unexplained cases

Ejection catapult and rocket designed to work with wider range of occupant weights. Electronic control system to maintain attitude in high-speed descents and a set of small, attitude control rockets.

Some of the newer areas of concern in injury potential are helmet/head box interactions and helmet/parachute-riser interaction. A few cases of LOC, neck laceration, cervical spinal injures and concussion/amnesia, have been reported to be related to these mechanisms. This has led to smaller head boxes and defining combined helmet/head box impact attenuation.

EJECTION SEAT OPERATION IN K-36D SERIES
With ejection handles pulling out, the ECM microswitches are engaged and electric power from the onboard system and PS (back-up) is supplied to the electric pyrocartridges of the restraint system pyroinitiator and the MDC gas generator; besides an electric signal is sent for APS actuation. The restraint system pyroinitiator gases initiate the shoulder and waist restraint mechanisms which retract and restrain the pilot's shoulders and waist. Leg elevators rise the pilot's knees by 120 mm. Arms arresters come into action, pressing the pilot's arms to his body and preventing arms flailing. The automatic system connected with the onboard data bus selects the operation mode for the CG and MRM (depending on the aircraft flight mode and pilot weight) and sends commands to the thrust control mechanism. After a delay of 0.2 s for operation of the restraint system, electric power is supplied to the electric pyrocartidges of the CG. When the ejection speed exceeds 900 km/h, the command is also sent to the electric pyrocartridge of the deflector deployment system and the wind blast shield is deployed to protect the pilot's head and chest against the airflow. As the seat moves along the guide rails, the following events take place

• Destruction of the canopy by two canopy breakers mounted on the seat head rest (if it has not been destructed by the MDC);
• activation of the barostatic time delay hammer
• disconnection of the electric connectors mating the seat with the aircraft;
• separation of the combined service connector;
• activation of the emergency oxygen supply;
• deployment of the stabilizing booms;
• restraint of the pilot's legs;
• sending of command for the MRM activation.

At the moment of disconnection in of the electric connectors mating the seat with the aircraft, the automatic system stores the last values of the flight parameters, and proceeding form this values, it selects the seat operation mode. In the trainer the TDMs operate sequentially approximating the set trajectory to the vertical one and the seat performs flight on the trajectory in the stable "face - to - incoming flow" position. The stabilizing booms terminated with parachutes provide the seat stabilization. The parachute deployment mechanism (PDM) is actuated with maximum allowable rate of the recovery parachute deployment at 650 km/h. If the seat ejection is performed at an altitude o