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22nd of September 2018

Automotive



A New Ejection Seat Makes Rocketing out of a B-2 Bomber Surprisingly Safe

The American military has a funny way of thinking about size. Some ground vehicles are sized not necessarily for battlefield functionality, but rather to fit inside the cargo airplanes that will take them to said battlefield. And pilot size and weight restrictions aren’t written to limit who can stuff themselves inside a tight cockpit, but who can be blasted out of one.

In fact, ejection seat capabilities have been limiting pilot selection for decades, to the disappointment of countless would-be aviators and the frustration of military commanders desperate to fill increasingly empty cockpits. The situation improved a few years ago with the Martin-Baker MK 16 seat, which allows pilots weighing as little as 103 pounds and as much as 245 pounds to eject from the F-35 fighter jet at 65,000 feet.

Now, another new ejection system meets even stricter safety standards, works with today’s gear-laden helmets, and further expands the pool of eligible pilots climbing into the B-2 stealth bomber and future airplanes that will also use the system. “In the past, simply surviving an ejection was considered a good enough standard. Now the Air Force expects its pilots to be able to walk away from an ejection, start training again, and be back in action right away,” says John Hampton. He’s the head of aircraft escape system engineering at UTC Aerospace Systems, the defense contractor that built this latest system, called the ACES 5.

To ensure that pilots are ejected safely no matter their size, UTC’s engineers created a system that automatically modulates the thrust based on their weight.

UTC Aerospace Systems

The ACES 5, which could also see use in the forthcoming T-X trainer jet, uses everything from nets to gyroscopic rockets to carry pilots from a plane that flies 50,000 feet off the ground at near supersonic speeds to the ground with minimal risk.

It starts with a helmet support system that automatically extends and retracts during an ejection, catching the heavy helmet like a ball in a baseball glove. That lets it accommodate the larger high-tech helmets like those used in the F-35 as well as accessories like night vision goggles. “Just 15 years ago, helmets were spherical and aerodynamic shells,” says John Fyfe, UTC’s director of Air Force programs. (The former F-16 pilot still goes by his callsign, Barney.) “It’s not spherical anymore, thanks to all the technology inside of it. If we don’t have that helmet stabilized and protected from the airstream, there will be an immediate neck injury and probably a fracture.” With the ACES 5, you can feel free to shoot out of your plane at 690 mph.

That high-speed airflow, you see, can force an ejecting pilot’s head off the headrest, exposing him or her to injury (as if riding a rocket chair out of a jet weren’t bad enough). The system mitigates this risk with a head and neck restraint that deploys during the ejection sequence to temporarily catch the pilot’s head and support it as the g forces stack up. (They can range between 9 and 12 g’s with a UTC seat during the 200-millisecond ejection sequence. Other systems have subjected pilots to up to 20 g’s.) The restraint maneuvers the helmet to transfer the load to the seat itself. The system is spring-operated and instantaneous, and it can be retracted before the parachute deploys, so the pilot regains his or her full range of motion as they drift to Earth.

The rocket seat also protects crewmembers who may not be fully prepared for an ejection, such as in a multi-crewmember aircraft, where one might be distracted when the other initiates the exit. Along with the head holder, nets deploy to pull the pilot’s arms toward the seat, and restraints keep their legs in place. (Martin-Baker’s system uses tethers to achieve the same thing for the arms, and a similar passive system for the legs.)

To ensure that pilots on the lighter and heavier side are ejected safely, UTC’s engineers created a system that automatically modulates the thrust based on their weight. “If a pilot is on the heavier side, the seat will encounter resistance as it’s firing, so it will add in more thrust to accommodate,” Hampton says. “If the pilot is lighter, the thrust is dialed back so they aren’t injured by excessive forces.” The key is a chamber underneath the rocket that measures the pressure during the launch. “As the pressure goes up, so does the burn rate,” Hampton says. “So it maintains constant acceleration on the way out.”

Since heavier pilots tend to make the seat pitch forward and lighter ones pitch back, the seat incorporates a second, gyroscope-controlled rocket that corrects those movements. Everything’s controlled by a small, triple-redundant computer that measures airspeed, altitude, and seat angle. Finally, the new seat also has a new parachute that can handle up to 330 pounds—plenty for a pilot and all the survival gear they carry. It’s designed to prevent oscillations in the descent, to angle the pilot so they don’t risk falling backwards on impact, and provide a slower and more controlled landing. This matters: 43 percent of ejection injuries occur at contact with the ground.

The ACES 5 system was actually approved about eight years ago but is only now being introduced in the B-2. You can thank the typically protracted development and evaluation process that governs military systems. As it makes its way into more aircraft, it will accommodate a greater range of pilots, helping the military fill seats that it hopes will stay firmly in place.

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