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PAPER PRESENTATION ON SEAT EJECTION SYSTEM IN AIRCRAFTS PRESENTED BY: PRASAD PUNAGE 8th Sem, E & E E-mail: [email protected] SEAT EJECTION SYSTEM IN AIRCRAFTS CONTENTS TOPIC PAGE NO. 1. Abstract ……………………………………………… 2 2. Introduction………………………………………….. 3 3. History……………………………………………….. 4 4. Definitions…………………………………………… 6 5. Operating principle…………………………………... 8 6. Evolution of ejection seats…………………………… 10 6.1 Application of rocket motors…………………… 12 6.2 More recent applications to escape system…….. 18 6. Timing an ejection……………………………………. 19 7. Modes of ejection……………………………………. 20 9. Conclusion…………………………………………… 21 10. References…………………………………………….. 22 GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 1 SEAT EJECTION SYSTEM IN AIRCRAFTS 1. ABSTRACT: A brief history of the use of propulsive elements in aircrew escape systems is presented. For the purposes of this history, both closed propulsion elements (catapults), as well as rocket motors are considered since early ejector seats depended solely on catapults for their motive source. Applications of rocket motors other than for providing the main impetus to the escape system are also considered in more recent systems. Information contained in this history was obtained from all types of literature both published and unpublished, as well as from discussions with individuals who have been involved in the escape system arena from its infancy. The use of an ejection seat is always a last resort when an aircraft is damaged and the pilot has lost control. However, saving the lives of pilots is a higher priority than saving planes, and sometimes an ejection is required in order to save a life. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 2 SEAT EJECTION SYSTEM IN AIRCRAFTS 2. INTRODUCTION: Early escape equipment consisted of a recovery parachute only. As aircraft performance rapidly increased during World War II, it became necessary to assist the crewmen in gaining clear safe separation from the aircraft. This was accomplished with an ejector seat, which was powered by a propellant driven catapult - the first use of a propulsive element in aircrew escape. Since then, this collection of componentry has evolved through several generations into today's relatively complex systems, which are highly dependent upon propulsive elements. Today, propulsive elements (rocket motors, specifically) are used to stabilize the ejected mass, provide trajectory steering, jettison aircraft canopies, provide positive separation of the ejected seat from the crew member, generate the force necessary to rapidly extract a parachute from its container, all in addition to the basic function of providing clear safe separation from the aircraft. Since the first operational ejections from aircraft, nearly 6,800 successful non-combat ejections have taken place from US Navy and US Air Force aircraft alone. In savings to the taxpayer that amounts to over 8 billion dollars based on the current average training cost of 1.2 million dollars per aircrew member. Ejecting from an aircraft moving at speeds greater than the speed of sound (mach 1: 750 miles per hour / 1,207 kph) can be very dangerous. The force of ejecting at those speeds can reach in excess of 20 Gs -- one G is the force of Earths gravity. At 20 Gs, a pilot experiences a force equal to 20 times his or her body weight. Most military aircraft, NASA research aircraft and some small commercial airplanes are equipped with ejection seats to allow pilots to escape from damaged or malfunctioning airplanes. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 3 SEAT EJECTION SYSTEM IN AIRCRAFTS 3. HISTORY: Generations of Seat Designs First Generation - (1940-1965) These seats were purely ballistic operation with a compressed air, mortar, or rocket cartridge providing a single force to remove the seat and occupant from the aircraft. In early generation 1 seats, the occupant had to deploy the parachute manually. In later seats this became an automatic function. Examples of first Generation seats would be the Saab Mk 1 and the Martin Baker Mk 1-5 seats. Second Generation - (1965-1975) Accumulated information had shown that a catapult alone would put too much force/acceleration on the occupant to survive an ejection without significant injury. Also, the end users of the seats were looking for zero/zero performance and performance at high speed. To accomplish this, a rocket sustainer was added. The catapult would operate from 0.15 to 0.25 seconds to keep the initial acceleration under 10G. The rocket sustainer would then act for an additional 0.20 to 0.40 seconds. The Martin Baker Mk 7 and the Douglas Escapac seats would be examples of this generation. Third Generation - (1975-present) Automated features had been added to seats such as drogue chutes, parachute deployment based on altitude, and automatic deployment of survival gear since the first generation. But the advances in electronics GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 4 SEAT EJECTION SYSTEM IN AIRCRAFTS allowed a computer to be placed into the seat and control the functions based on readings from sensors. Pitot - static systems, gyroscopic stabilizers, and pilot weight indicators were added to give information to the seat computer, extending the ejection envelope and improving crew survivability. Representative examples of the third generation are the Martin Baker Mk 14, The McDonnell Douglas ACES II, and the Stencil S4S. Fourth Generation - (present) Research continues on expanding the envelope for the systems. Martin - Baker Aircraft, Boeing (McDonnell Douglas), and the former Soviet Union have either tested or placed into service seats featuring vectored thrust, flow generators, or variable thrust rockets. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 5 SEAT EJECTION SYSTEM IN AIRCRAFTS 4. DEFINITIONS: Bucket - This is the lower part of the ejection seat that contains the survival equipment. Canopy - This is the clear cover that encapsulates the cockpit of some planes; it is often seen on military fighter jets. Catapult - Most ejections are initiated with this ballistic cartridge. Drogue parachute - This small parachute is deployed prior to the main parachute; it designed to slow the ejection seat after exiting the aircraft. A drogue parachute in an ACES II ejection seat has a 5-feet (1.5-m) diameter. Others may be less than 2 feet (0.6 m) in diameter. Egress system - This refers to the entire ejection system, including seat ejection, canopy jettisoning and emergency life-support equipment. Environmental sensor - This is an electronic device that tracks the airspeed and altitude of the seat. Face curtain - Attached to the top of some seats, pilots pull this curtain down to cover his or her face from debris. This curtain also holds the pilot's head still during ejection. Recovery sequencer - This is the electronic device that controls the sequence of events during ejection. Rocket catapult - This is a combination of a ballistic catapult and an under seat rocket unit. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 6 SEAT EJECTION SYSTEM IN AIRCRAFTS Under seat rocket - Some seats have a rocket attached underneath to provide additional lift after the catapult lifts the crewmember out of the cockpit. Zero-zero ejection - This is an ejection on the ground when the aircraft is at zero altitude and zero airspeed. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 7 SEAT EJECTION SYSTEM IN AIRCRAFTS 5. OPERATING PRINCIPLE: Ejecting from an airplane is a violent sequence of events that places the human body under an extreme amount of force. The primary factors involved in an aircraft ejection are the force and acceleration of the crewmember, according to Martin Herker, a former physics teacher. To determine the force exerted on the person being ejected, we have to look at Newton's second law of motion, which states that the acceleration of an object depends on the force acting upon it and the mass of the object Newton's second law is represented as: Force = Mass x Acceleration (F=MA) Regarding a crewmember ejecting from a plane, M equals his or her body mass plus the mass of the seat. A is equal to the acceleration created by the catapult and the under seat rocket. Acceleration is measured in terms of G, or gravity forces. Ejecting from an aircraft is in the 5-G to 20-G range, depending on the type of ejection seat. As mentioned in the introduction, 1 G is equal to the force of Earth's gravity and determines how much we weigh. One G of acceleration is equal to 32 feet/second2 (9.8 m/s2). This means that if you drop something off of a cliff, it will fall at a rate of 32 feet/second2. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 8 SEAT EJECTION SYSTEM IN AIRCRAFTS It's simple to determine the mass of the seat and the equipment attached to the seat. The pilot's mass is the largest variable. A 180-pound person normally feels 180 pounds of force being applied to him when standing still. In a 20-G impact, that same 180-pound person will feel 3,600 pounds of force being exerted. "To determine the speed of the [ejection] seat at any point in time, one solves the Newton equation knowing the force applied and the mass of the seat/occupant system. The only other factors that are needed are the time of the force to be applied and the initial velocity present (if any). Herker provides this equation for determining the speed of the seat: Speed = Acceleration x Time + Initial speed V (f) = AT + V (i) Initial speed refers to either the climb or the sink rate of the aircraft. It may also be determined by the initial step of the ejection process in a seat that combines an explosive catapult and an under seat rocket. The seat speed must be high enough to allow separation of the seat and person from the aircraft as quickly as possible in order to clear the entire aircraft. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 9 SEAT EJECTION SYSTEM IN AIRCRAFTS 6. EVOLUTION OF EJECTION SEATS: All the early seats were a collection of components including a parachute, a seat structure to which the aircrew and parachute were firmly attached, and a propulsive element, which forcibly separated the seat and its contents from the aircraft. This early propulsive element has been called a gun or catapult and, is in essence, a closed telescoping tube arrangement containing a propellant charge to forcibly extend the tubes, thereby imparting the necessary separation velocity to the "ejector seat" and its contents. The first British emergency ejection occurred from an out-of-control flying wing on 30 May 1949. The first operational British aircraft with a propellant GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 10 SEAT EJECTION SYSTEM IN AIRCRAFTS driven ejector seat was the Meteor. The first operational ejection from it occurred on 11 November 1951 over Korea. Meanwhile, in the US the first US Navy operational ejection occurred on 9 August 1949, while the first operational USAF ejection occurred from an F-86 fighter on 29 August 1949. While many different catapults were designed, developed, qualified, and produced, they all basically fell into two design categories: the short-stroke catapult, and telescoping tube catapult. The former is a two-tube device, one of which is attached to the aircraft, and the other attached to the seat. The two tubes are nested one inside the other and are attached to each other by some type of locking device. A propellant charge is contained in one of the tubes which when fired, unlocks the two tubes from each other and then provides the necessary gas pressure to accelerate and separate the two tubes, thereby ejecting the seat from the aircraft. Typical stroke to separation of the tubes was about 30 inches, and separation velocity was as high as 50 feet per second. The factor limiting separation velocity was acceleration and rate of acceleration change or onset rate as seen by the aircrew's spinal column. The second category of catapults utilized three tubes nested one inside the other to achieve separation velocities as high as 83 feet per second from a total of 72 inches of stroke Typically, the US catapults of this type used a single propellant cartridge and provided separation velocities closer to 60 feet per second, while the British catapults (Martin-Baker) utilized a primary and two subsequently staged cartridges to achieve the higher velocity. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 11 SEAT EJECTION SYSTEM IN AIRCRAFTS 6.1 APPLICATION OF ROCKET MOTORS The jet engine continued to increase the performance of post World War II aircraft, and it was not long before the limitations of the simple ejector seat become apparent. Two such areas of limitations were: (1) Inability of the ejected seat to clear the aircraft's vertical tail at high speed, and (2) The potential for windblast injury to the aircrew forced to eject under high "Q" conditions. Propulsive elements were involved in the solutions to these problem areas. The problem of achieving tail clearance was approached in several ways. As indicated earlier, the German approach was to jettison the vertical or dorsal surface. One approach taken in the US was to eject the seat downwards, rather than upwards. This approach had serious shortcomings when the ejection occurred at low altitudes. Another approach was to increase the catapult output sufficiently to provide adequate tail clearance. While successful in clearing the tail, this approach was also very successful in inducing spinal injury to the aircrew. The problem was finally addressed successfully by combining a rocket motor with the catapult to form a two-stage propulsion system for the seat. The catapult remained as the initial booster to get the seat/man mass clear of the cockpit, while the rocket motor came on line, once clear of the cockpit, to act in a sustainer mode. When combined into a single unit, this propulsive element was termed the rocket catapult. The first USAF rocket catapult, the TALCO Engineering Co. 1057, was installed in the F-102 in 1958. Shortly after this, the first USN rocket catapults, the RAPEC I for the A-4 and the TALCO Engineering Co. 1192 for the T-2, became operational. Propellants used in GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 12 SEAT EJECTION SYSTEM IN AIRCRAFTS the RAPEC were double base, as were most previous escape propulsion units. The 1057 and 1192 units were unique in that they used a composite propellant. This basic rocket catapult configured seat is illustrated in figure 1. Martin-Baker in England took a slightly different approach. The catapult was maintained as separate component, and the rocket motor was located separately under the seat bottom. This configuration is illustrated in figure 2, and is, if not unique, certainly rare in its use of multiple propellant tubes feeding into a single nozzled manifold. Propellant is double base. This propulsion concept was extensively tested, culminating in a live static (zero airspeed and zero altitude) test on 1 April 1961. The test was repeated at the Paris Air Show of the same year. The Stencel Aero Engineering Company of Asheville, North Carolina, likewise utilizes separate catapult and rocket motors. However, their system consists of twin catapult tubes, which also do duty as the main seat structural beams. Rocket motors are located on both sides of the seat at the aft extremity, and they are termed "SBR's" for "Seat Back Rockets." figure 3 illustrates this variation. Composite propellant is used. In summary, then, the next major step in escape propulsion evolution was the addition of the rocket motor to the ejection seat to compliment the catapult. In general, the first rocket catapults were categorized as "low impulse" units, indicating that the rocket motor delivered from 800-1,000 pound-seconds of impulse, in addition to that provided by the catapult. This additional impulse was sufficient to provide tail clearance GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 13 SEAT EJECTION SYSTEM IN AIRCRAFTS at high speed and to provide recovery from ground level at speed, when used in conjunction with other ejection seat improvements. Emphasis was initially placed, however, on high-speed recovery. As time progressed it became obvious that many ejection fatalities were occurring at low speed close to the ground. Hence, in the mid-1960's, the "high impulse" rocket/catapult system was put into service to provide static (zero airspeed, zero altitude) recovery capability in conjunction with the current seats. High impulse generally designated that the rocket motor portion of the system provided approximately 2000 pound-seconds of impulse. Function time of the rocket was 0.5-0.6 seconds, and the increase in impulse compared to the low impulse unit generally provided additional trajectory height, which translated into additional time available for all of the automatic ejection seat functions to occur. Today the advent of high performance aircraft operating at very high speed and very close to the ground have necessitated that the escape system designer reduce the total time from ejection initiation to full parachute to the absolute minimum consistent with human physiological tolerances. This has necessitated shortening rocket function time and hence impulse. Current generation rocket propulsion units are again sized to deliver 1000-1100 pound-seconds of impulse. When combined with much faster parachute systems, the low impulse units can still provide zero-zero recovery capability while at the same time provide greatly improved adverse attitude recovery capability. Another interesting escape system propulsion concept is that of the Stanley Aviation Yankee (now produced by Stencel Aero engineering and called the GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 14 SEAT EJECTION SYSTEM IN AIRCRAFTS Ranger extraction System. This system utilizes a tractor rocket, which is ejected or catapulted away from the aircraft above the cockpit. It is attached to the crewmember by a pendant. When the rocket motor reaches pendant line stretch, It Is fired and tows or extracts the crewmember clear of the aircraft. This concept is illustrated in figure 4. High-speed windblast protection was originally addressed by providing some type of encapsulation for the aircrew. This approach was heavier than the open seat, necessitating larger propulsion systems. The first such capsule was developed by Douglas Aircraft Company under contract to the US Navy for the F-4D Skyray. While this capsule never was installed in the aircraft, it was tested at China Lake. The propulsion system was developed by AeroJet Engineering and provided approximately 9000 pounds of thrust for 0.3 seconds. It also provided bleed gas for drogue parachute deployment and fin extension. Testing was accomplished in 1951 - 1952. Other capsules, encapsulated seats, etc., were designed and tested, including a separable nose section for the F-104. Rocket motor impulses ranged from under 1000 pound-seconds, all the way to 40800 poundseconds for the proposed Boeing ADO-12 airplane nose capsule. Other propellant powered devices evolved during post World War II to assist the aircrew in achieving safe escape. Their functions included limb positioning and restraint, torso positioning and restraint, seat positioning, canopy jettison, seat/man release and separation, and aerodynamic stabilization. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 15 SEAT EJECTION SYSTEM IN AIRCRAFTS GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 16 SEAT EJECTION SYSTEM IN AIRCRAFTS GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 17 SEAT EJECTION SYSTEM IN AIRCRAFTS 6.2 MORE RECENT APPLICATION OF ROCKET MOTORS TO ESCAPE SYSTEMS A typical ejection sequence includes the following functions, which occur generally in the order listed, following initiation by the crewmember 1. Canopy or hatch jettison. 2. Crewmember torso positioning and restraint 3. Clearance of workstation equipment from ejection path 4. Seat ejection/crewmember extraction. 5. Seat stabilization 6. Seat trajectory control 7. Drogue parachute deployment 8. Seat man separation 9. Recovery parachute deployment and inflation 10. Survival gear deployment GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 18 SEAT EJECTION SYSTEM IN AIRCRAFTS 7. TIMING AN EJECTION: 0 seconds - Pilot pulls cord; canopy is jettisoned or shattered; catapult initiates, sending seat up rails. 0.15 seconds - Seat clears ejection rails at 50 feet (15 m) per second and is clear of surrounding cockpit; rocket catapult ignites; vernier motor fires to counteract any pitch changes; yaw motor fires, inducing slight yaw to assure man-seat separation. (Burn time of all motors equals 0.10 seconds.) 0.50 seconds - Seat has lifted to about 100 to 200 feet (30.5 to 61 m) from ejection altitude. 0.52 seconds - Seat-man-separator motor fires; cartridge fires to release crewmember and his equipment from seat; drogue gunfires parachute. 2.5 to 4 seconds - Main parachute is fully GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 19 SEAT EJECTION SYSTEM IN AIRCRAFTS 8. MODES OF EJECTION: In the ACES II ejection seat produced by Goodrich Corporation, there are three possible ejection modes. The one used is determined by the aircraft's altitude and airspeed at the time of ejection. The environmental sensor and recovery sequencer in the back of the ejection seat measure these two parameters. The environmental sensor senses the airspeed and altitude of the seat and sends data to the recovery sequencer. When the ejection sequence begins, the seat travels up the guide rails and exposes pitot tubes. Pitot tubes, named for physicist Henri Pitot, are designed to measure air-pressure differences to determine the velocity of the air. Data about the airflow is sent to the sequencer, which then selects from the three modes of ejections: Mode 1: low altitude, low speed - Mode 1 is for ejections at speeds of less than 250 knots (288 mph / 463 kph) and altitudes of less than 15,000 feet (4,572 meters). The drogue parachute doesn't deploy in mode 1. Mode 2: low altitude, high speed - Mode 2 is for ejections at speeds of more than 250 knots and altitudes of less than 15,000 feet. Mode 3: high altitude, any speed - Mode 3 is selected for any ejection at an altitude greater than 15,000 feet. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 20 SEAT EJECTION SYSTEM IN AIRCRAFTS 9. CONCLUSION: The rocket motor has proven to be the only stored energy source, which can provide the needed force versus time output consistent with both the human physiological limitations and the necessity to decrease escape system total functioning time to the absolute minimum. Since the human physiological limits are not likely to change as rapidly as the performance envelope of the next generation of combat aircraft, it seems likely that the rocket motor will continue to be a key part of future escape systems. The use of an ejection seat is always a last resort when an aircraft is damaged and the pilot has lost control. However, saving the lives of pilots is a higher priority than saving planes, and sometimes an ejection is required in order to save a life. GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 21 SEAT EJECTION SYSTEM IN AIRCRAFTS 10. REFERENCES: 1. http://www.globalsecurity.org 2. http://www.instituteofarmamenttechnology.com 3. http://www.howstuffworks.com GOGTE INSTITUTE OF TECHNOLOGY BELGAUM 22