Revealed: How to be a fighter pilot

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How It Works visits the RAF’s High-G facility to see how fighter pilots prepare for their greatest battle – against the forces of physics itself

Royal Air Force pilots go through rigorous training to get their wings. Despite years of technical training for combat, one of the biggest hurdles to overcome as a fighter pilot are the forces of the Earth, in the form of gravity. HIW travelled to RAF Cranwell, Lincolnshire, to see first hand how a human centrifuge can prepare pilots for future military missions.

What is G-force?

As we’re all aware, gravity is the force keeping our feet firmly on the ground. Every particle of matter on Earth is subjected to its planetary pull. At sea level you will experience the force of gravity at one g, which is 9.8 metres per second squared and is equivalent to your body weight. As an object accelerates or decelerates it will experience different levels of g-force, categorised as either positive or negative force. The faster the rate of acceleration, the more gs or positive g-force is applied. Similarly, as a jet turns in flight, the acceleration increases dramatically and so greater amount of gs are experienced by the pilot. For example, if a pilot experiences three gs of positive force, that would equate to three times their body weight pushing down on their body during flight. The same is true for deceleration: the quicker the rate an object slows down the more negative g-force it will experience. For fighter jet pilots, this occurs during roll-outs or bunts (a spin and a half-loop). It’s these gravitational obstacles that have forced the invention of sophisticated training machinery, such as the human centrifuge, to put pilots through their paces in preparation for the real thing.

Out with the old, in with the new

This year saw the closure of the UK’s long-standing centrifuge facility at Farnborough, Hampshire. Here, the centrifuge had been giving pilots a gravitational glimpse into their flying future since 1955. However, as time has passed, the Farnborough centrifuge has reached its retirement and no longer meets the standards of the North Atlantic Treaty Organization (NATO). A new £44 million (approximately $57 million) training facility and human centrifuge at RAF Cranwell, Lincolnshire, is giving pilots the opportunity to experience flight simulation like never before.

Traditionally when using a human centrifuge to train pilots for high g-force exposure, trainees are strapped to a stationary gondola and sent spinning to reach levels of g-force comparable to those experienced during fighter jet flights. However, at Cranwell’s new facility the 39-ton centrifuge places a pilot into a virtual cockpit, where spinning sessions are carried out in a gondola that turns 180 degrees. The immersive experience is heightened by a digital simulation screen in place of a real glass window, delivering a digital flight programme similar to a flight simulator. As the motor-driven arm grasps the high-tech gondola, rapid acceleration replicates changes in g level. Rather than these levels being dictated completely by a control room, pilots strapped into Cranwell’s centrifuge are able to use one of three interchangeable fighter jet cockpits to steer and alter g levels while spinning. Pilots need to withstand a session in the centrifuge at nine gs for 15 seconds in order to progress to the real thing. This feat is gradually achieved over a period of a couple of days for experienced pilots seeking to transfer to faster fighter jets, such as a Tornado or a Typhoon. A centrifuge doesn’t only test the physical capabilities of future pilots, but also future equipment that will be placed in a jet cockpit. This allows engineers to evaluate how effective a radio, for example, will be under nine gs.

Feeling the force

Accelerating in gravity doesn’t come without its physical downfalls. Changes in g-force affects not only the pressure applied to the external body but also its internal workings. Without mechanical intervention, the blood in the body is pulled down towards the Earth, pooling in the pilot’s feet. This sudden relocation of blood results in the depletion of oxygen in the brain, which can render a pilot unconscious. Commonly known as ‘grey out’, G-LOC (gravity induced loss of consciousness) is a pilot’s main concern when carrying out turns

and rolls in the air, which can lead to potentially fatal accidents. The reverse, however, can occur when free falling and experiencing negative g-force, whereby blood rushes to the head causing ‘redout’. This is where the training on the human centrifuge comes in very useful. By exposing trainee pilots to varying levels of g-force, they can gain the skills and experience needed to combat the effect of G-LOC in the sky, while in a safe and controlled environment. During a test run on the centrifuge, should a trainee experience G-LOC or need medical assistance, the control room is able to execute an emergency stop, quickly reducing the centrifuge’s speed down to a single g. The centrifuge is programmed to place the gondola precisely outside the medical room door for fast extraction. Although there are no long-lasting health effects on trainee pilots, experiencing high levels of g-force can cause small bruises called petechiae. This is where capillaries along areas of the body, particularly the arms, rupture under the huge force, also known as ‘geasles’.

There are several ways in which pilots can combat the occurrence of G-LOC, including breathing and straining techniques. However, in order to safely reach the g demands of fighter jets, pilots are equipped with a flight suit which acts as a full body blood pressure cuff. These anti-g suits can afford pilots an extra few gs of protection during both a simulation and a real flight. A network of pipes fills each khaki-coloured suit, which is divided into a jacket, trousers and socks. During test runs, these pipes are connected via a single outlet to a gas supply feed into the gondola. As the pilot experiences increased gs, the suit will inflate to compress the body and prevent excessive blood pooling.

Anti-G Straining Manoeuvre

An anti-g-suit can greatly reduce the risk of a pilot experiencing G-LOC; however, there are a couple of techniques pilots can use to prevent themselves from passing out. Known as the Anti-G Straining Manoeuvre (AGSM), this method of G-LOC prevention involves pilots continuously clenching all skeletal muscles, such as the legs, arms and abdomen. In doing so, this helps retain blood in the head and chest. The manoeuvre also calls for pilots to adjust their breathing habits when experiencing heightened g-forces. Repeated at two- to three-second intervals, pilots will inhale, followed by a sharp burst of air to close a part of the larynx called the glottis. This increases the pressure in the chest and blood flow to the brain.

This article was originally published in How It Works issue 125

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