Why use a canopy/transparency removal system?
When a military aircraft ejection is imminent, removing the canopy by jettison or fracturing is advisable to avoid the elevated levels of head and neck load on the aircrew member ejecting. Those higher head and neck loads can result in injury to the aircrew during ejection. Also, if choosing to go through the canopy, the canopy ‘glass’ material will be limited to either cast or stretch acrylic. Other materials like polycarbonate or laminates with acrylic and polycarbonate may increase the head and neck loads resulting in a higher potential for aircrew injury.
How is the canopy or hatch removed from the aircraft prior to the seat ejecting?
There are two main methods. The first is jettison. This is accomplished by either severing or unlocking the mechanism securing the canopy or hatch to the aircraft’s structure. Once released rocket motors or a thruster are used to move the canopy away from aircraft, creating a clear path for the ejection seat. The second method is canopy fracturing. This method is possible with canopies that are either acrylic (cast or stretched), polycarbonate (less than 0.3-inch) or acrylic/polycarbonate laminate. The canopy material is severed or fractured to open a clear escape path during seat ejection or emergency ground egress from the aircraft. This can be accomplished with Mild Detonating Cord (MDC), Flexible Linear Shaped Charge (FLSC) or Expanding Tube Assembly (XTA).
How are the seat and canopy sequenced to occur in the proper order?
Sequencing of the escape system is accomplished through a network of Explosive Transfer Lines, interconnected to ensure a specific sequence of events. Additional components, including but not limited to, Time Delay Initiators, One Way Initiators, Mechanical Pull Initiators, Seat Mode Selectors, Actuators, Pin Pullers and Gas Generators can be incorporated into system to execute a safe canopy / hatch removal and seat ejection in the proper sequence.
Is canopy fracturing better than canopy jettison?
Each has their advantages and disadvantages. The aircraft platform’s mission, configuration, flight parameters and many other factors will determine which method is best. One of the advantages of canopy fracturing is a faster sequence time with no delay waiting for the canopy to jettison.