Although slow-motion reviews of pilots and navigators ejecting from their aircraft at hundreds of miles an hour are a near-beautiful spectacle, fragile dangling limbs too frequently get in the way of aircraft frames and other VERY solid items. The two ejection seat series known as MINI-PAC II and ACES-II have been designed to keep flyers and navigators as safe as possible.

Let's take a brief look at what they do:

Abstract: The McDonnell Douglas MINI-PAC II lightweight ejection seat had just completed a zero speed/zero altitude test in the USA. During the test the seat was fired from a stationary sled and propelled to a height of 160 feet, with the main parachute opening at the top of the trajectory. The seat is designed for use in turboprop powered trainers, helicopters, and other low- to medium-speed aircraft and uses technology developed for the ACES II Advanced Concept Ejection Seat used in the F-15, F-16, A-10 and B-1.

Although the MINIPAC II seat is fully automatic, it retains an ‘over the side’ bail out option in which the pilot leaves the aircraft with his parachute while not using the ejection seat.

ACES II Seat History

The Advanced Concept Ejection Seat (ACES) was developed to provide a standard Ejection seat to be utilized in all United States Air Force jets from the mid-1970s. It was first flown in a A-10 Thunderbolt II from the Fairchild Republic Co. at the Farmingdale Long Island (N.Y.) plant in April 1978. The driving reasons for the development of the ACES II were to standardize on one type of ejection seat that would lead to reduction in training of both mechanics and pilots. The design was also  intended to provide better performance in low altitude/adverse attitude conditions, as well as to improve high speed seat stablity. It also allowed the government to purchase larger lots of spare parts.

The initial ACES II production contract was awarded to McDonnell-Douglas Corp. (MDC) in November 1976. The contract was a 'Leader/Follower' type contract which meant that MDC would be the Leader and would train the Follower to build the seat as well. Weber Aircraft Co. (WAC) was selected and trained as the follower. Thereafter, each additional contract from 1982-1990 was bid upon by both MCD and WAC, with the competition helping keep the unit cost low. In 1990, with fewer seats to be ordered, the entire production was awarded to McDonnell-Douglas Corp. Soon thereafter Weber Aircraft Co. ceased manufacturing ejection seats and concentrated on the manufacture of crew seats.

Production of the seats totaled about 8000 as of May 1997, with some 416 non-combat and 10 combat ejections worldwide. The official USAF success rate is 94.4% in envelope, and 89.9% including out of envelope ejections. MCD manufactured some 6500 and WAC the remaining 1500.

Since its development it has been used in various forms in the following aircraft: F-15 Eagle; F-16 Fighting Falcon; A-10 Warthog; B-1B Lancer; T-46A; B-2 Spirit; F-22 Raptor.

The ACES II is a third-generation seat, capable of ejecting a pilot from zero-zero conditions up to maximum altitude and airspeeds in the 600 KEAS range. The peak catapult acceleration is about 12g, with a extra 2g pulse from a stabilizing rocket.

The ACES II has three main operating modes, one each for the low speed/low altitude, medium speed, and high speed/high altitude. In Mode 1, which includes 0-0, the parachute is inflating in less than two seconds. In Mode 2 the chute is inflating in less than 6 seconds. Mode 3 deployment is delayed by the sequencer until the seat-man package reaches either Mode 2, or Mode 1 conditions, whichever comes first.

Note: Prior to the ACES II becoming standard, most aircraft manufacturers manufactured their own seats, or had one manufactured to their specifications. This lead to a wide variety of seats in use, with a wide range of operating envelopes. It also meant that the mechanics working on the seats had to be familar with the individual seats mechanisms and specifications. Spare parts would have to be purchased in lot sizes determined by the number of aircraft in the inventory. With a standard seat, the lot sizes for many of the parts would be larger, allowing for some savings in purchase price.

The ACES II (Advanced Concept Ejection Seat) is considered a smart seat because it senses the conditions of the ejection and selects the proper deployment of the drogue and main parachutes to minimize the forces on the occupant. The seat is a derivative of the Douglas Escapac seat.

Removal from the aircraft is by a three part pyrotechnic sequence. A gun catapult provides the initial removal of the seat from the aircraft. A rocket sustainer provides zero/zero capability to the seat. To prevent the seat from tumbling when the aircraft is in a roll maneuver or there is a center of gravity imbalance, another (smaller) rocket called a STAPAC is attached to a gyroscope. This senses the motion and attempts to keep the seat from spinning by automaticly providing a correcting force.
Once clear of the aircraft, the pitot - static system on the seat measures the conditions and selects one of three operating modes depending on the conditions present at egress.

Mode 1 - Low speed (<250 knots) and low altitude (<15,000 feet) operation.
The main parachute deploys as the seat clears the rails. Drogue parachute remains undeployed to prevent line tangle.

Mode 2 - Moderate speed (250-650 knots) and low altitude (<15,000 feet) operation.
Drogue parachute deploys as the seat leaves the rails. Main parachute deploys 0.8 to 1.0 seconds after the drogue. Drogue chute is then released to prevent line tangle.

Mode 3 - High speed (250-650 knots) and high altitude (>15,000 feet) operation.
Drogue parachute deploys as the seat leaves the rails. The pitot-static system senses the conditions and delays the main parachute until mode 2 conditions are met. Then the main parachute deploys after 0.8 to 1.0 seconds. Drogue chute is then released to prevent line tangle.

ACES II is a rugged, light-weight, easy-to-maintain ejection seat. It provides optimum performance across an escape envelope from 0 to 600 knots equivalent airspeed and 0 to 50,000 feet altitude, and is designed to safely eject a crew member under zero-zero condition. At low speed, the ACES II produces a parachute 1.8 seconds after initiation. A unique gyro-controlled system - STAPAC - stabilizes the seat during ejection.

Advanced Sensor Control

ACES II provides trajectory divergence allowing two crew members to eject in tandem or side-by-side with no interference. A drogue parachute is used for stabilization and deceleration in high-speed escapes and for stabilization during descent from high altitudes. The recovery parachute is mortar-deployed to assure positive consistent deployment, and is reefed for additional crew member protection. Sensors on the seat detect altitude and airspeed and send the information to the recovery sequencing subsystem, which then directs the operation of the seat according to the situation.

The seat is equipped with an emergency oxygen supply for high-altitude ejection, a survival kit and a harness release mechanism to release the crewman from the seat during automatic recovery.

With more than 8,000 seats delivered to date, ACES II is currently used on F-15A/B/C/D/E, F-16 A/B/C/D, B-1B, B-2, A-10 AND F-117A aircraft, as well as on F-15s and F-16s of 16 other nations. An advanced version has been selected for the F/A-22 Advanced Tactical Fighter.

This guide was assembled by booksuncommon.  Any errors are mine. For those I apologize.

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