The Fighter Pilot's Arsenal - part 2

G-Suit: Defying Gravity’s Wrath

Over the years, I’ve often been asked how I feel - what happens in my body - when I fly supersonic, soar at high altitude, or pull high – G turns, climbing and descending in a jet fighter.

It’s clear from these questions that people are fascinated by the world of fighter pilots. And it’s also understood that profession is not just physically demanding, but mentally exhausting as well.

At the beginning of this century, I had the luxury to fly the F-104, an aircraft from a different era, later transitioning to the F-16 and ultimately the Typhoon. The common denominator to conduct the mission effectively was not only the skills to survive the demanding environment - high speeds, extreme G-forces, and intense combat scenarios – but the use of advanced gear which enhanced the pilot’s abilities.

Understanding G-Force and Its Effects on the Human Body

If you have never flown on other than airliners the closest experience, you might have with G-force is on a roller coaster. That feeling of being pressed into your seat is similar to wearing a weighted vest (exactly your weight multiplied by the number of Gs you experience). Duration of that exposure is just few seconds, and it ends with the end of the ride with the blood flowing in your body normally again.

“G-force (gravitational force) is the acceleration experienced as a ratio of Earth's gravity (9.81 m/s²). It quantifies the stress on a body due to acceleration or deceleration. For example, 1G equals Earth's gravity, while 5G means five times that force. Fighter pilots endure high Gs, requiring countermeasures to prevent G-LOC (G-force-induced loss of consciousness)”¹.

To translate the above definition, when subjected to high-G maneuvers, blood is forced to the lower extremities leaving the brain without sufficient oxygen. Aviation history is filled with incidents of lost fighter aircraft lost due to loss of consciousness. There are two key factors which contribute to this phenomenon: the magnitude of sustained Gs and the rapid onset with which we reach high sustained Gs. Since the brain has a minimal reserve of oxygen lasting only moments, a pilot who is not applying the correct countermeasures is going to be in trouble².

Combating G-LOC: The Anti-G Straining Maneuver and G-Suits

To prevent G-LOC, pilots must use a breathing technique called the Anti-G Strain Maneuver (AGSM) and are aided by individually fitted equipment, generally called anti-G suit.

When I started pilot training in 1993, young pilots were equipped only with a helmet and a parachute they would take with them on the shoulders. The SF 260, an Italian Air Force basic trainer aircraft, did not require the use of G-suits.

I remember with a smile (now) my first flight, struggling to maintain level flight at 2-3000 ft, trying to tame the almighty SF 260, while my instructor, frustrated by my lack of finesse, swearing at me, pushed and pulled the stick to what I estimated to be plus or minus 3 Gs (just guessing here, but probably more like a plus or minus 1,5 Gs). That was my first real encounter with gravity. Not pleasant, but effective enough to like it and to understand that being in the air was a serious business.

Later, during my training at the ENJJPT (Euro Nato Joint Jet Pilot Training) program, I finally received structured instruction on acceleration, what happens to the body and how to counteract G-forces.

Even though the SF 260 was capable of an admirable maximum acceleration of 6 Gs, on the other hands it was underpowered, and it could not sustain them for more than few seconds. However, the T-37, “Tweet” also known as “the noise converter”, had one of the quickest Gs onset to 6,67 in less than a second. Since pilots did not wear the G-suit, they had to perform a mandatory breathing technique paired with lower body muscle tightening, aka Anti-G Strain Maneuver (AGSM).

I remember seating on the Tweet like you seat in your dining table chair and feeling the accelerations much heavily than in the SF 260³.

After completing the block of training on the Tweet, I transitioned to the T-38s and I was equipped with a well fitted anti G-suit.

This piece of “clothing” which pilots wear on top of the coverall, is connected to the aircraft oxygen system and it’s designed to inflate during positive accelerations compressing the legs and the abdomen preserving cerebral blood flow.

Positive vs. Negative G-Forces

I mentioned positive accelerations, but we also must be aware of negative Gs given by a maneuver which will make you feel “floating”. The blood will flow towards the head, with some dramatic effects on the vision and deteriorating the capability of breathing due to the lack of blood in the lungs, ergo passing out.

In general, pulling the stick = positive Gs, pushing the stick = negative Gs.

The absolute numbers of negative Gs are heavier on the body than positive Gs leading to "redout", where blood is forced into the head, potentially causing vision impairment, discomfort, or even loss of consciousness. Fighter pilots with the right training and right gear can sustain up to 12 Gs, but anything more than -3Gs will cause significant physiological issues, including capillary ruptures in the eyes and brain.

Unlike positive Gs, where pilots use the AGSM and G-suits, negative Gs require different countermeasures, in primis limiting time exposure, and using controlled exhaling while resisting to head movement.

High-G Environments in Advanced Fighter Jets

Back to the T-38, I had the real exposure to aerial combat exploring the G envelope of a jet trainer very similar to a fighter aircraft.

During BFM (Basic Fighter Maneuvering) pilots make tight turns at high speeds, experiencing extreme G-forces within the envelope of the aircraft. To maximise performance each pilot must study the Energy Maneuverability (EM) Diagram which defines the aircraft’s capabilities and constraints setting the boundaries the man-machine synergy.

Boyd stated:

“…to win in battle a pilot needs to operate at a faster tempo than his enemy”.

Mastering AGSM and using a G-suit effectively are essential for staying lethal in combat.

After getting my Silver Wings I was assigned to the F-104 and apart from sporadic moments where the aircraft was configured without external stores (less stores = more Gs available), most of the flights did not expose me to a High Gs environment.

The G-suit was a mere pair of pants where I stored instrument approach publications, checklists, and the mobile phone.

That changed in 2003 when I transitioned to the F-16, a true 9G jet. Before being deemed suitable to fly the “Viper” I had to perform the centrifuge.

The centrifuge training at Lemoore Navy Base resulted in an c eye opening experience, where I learned more about my body and my G tolerance, with or without Anti-G Straining Maneuver (AGSM).

I still recall the instructor’s voice under 9 Gs:

“Breathe…legs…butt… relax your shoulders…”

And that is what I tell myself every time I fly a combat training mission.

As mentioned in my previous article about the helmets, the F-16 was equipped with Combat Edge, which included not only an inflatable bladder in the helmet, but pressure breathing under Gs and a vest for the upper body.

All these features combined helped the pilot not only to achieve maximum Gs, but also to recover from fatigue quicker.

Typhoon, by contrast, does not have Combat Edge, but features an improved G-suit and a smoother pressure breathing schedule that activates from engine starts.

Studies “suggest that if the oxygen concentration in the brain tissue is increased, prior to the onset of Gz, additional time of useful consciousness may be realized”.

The Aerospace Physiology studies in this field of military aviation have made tremendous progress in the last 50 years allowing pilots to perform to their maximum. G-suits are the most prominent equipment that pilots use to edge their game, but they are not the only one.

Physical conditioning, mental preparedness, and continuous advancements in flight equipment all contribute to enhancing a pilot's ability to withstand high-G environments. In a future article, we will explore the role of physical training in reducing reliance on G-suits and further enhancing combat performance.

1. NASA (2016). The Effects of G-Forces on the Human Body. Retrieved from https://www.nasa.gov

McGowan, D. G., et al. (2007). Acceleration Effects on Fighter Pilots: G-LOC and Countermeasures. Aviation, Space, and Environmental Medicine, 78(3), 235

2. Cramer FS. Oxygen and acceleration. Mil Med. 1991 Nov;156(11):608-11. PMID: 1771009.

3. https://www.safety.af.mil/News/Features/Display/Article/434555/t-37-gloc-syndrome/#:~:text=First%2C%20it%20has%20one%20of,of%20this%20fully%20aerobatic%20jet.