Table of Contents

What is g force?

Colloquially known as a force, g force is a measure which determines the acceleration produced by Earth’s gravity on an object or individual.

Also, it’s also important to note that it’s represented by the lower case g in order to differentiate it from gravitational constance – G, and italics to differentiate it from the symbol of gram – g.

The best known g forces are 0 g, which is experienced in non-gravitational atmospheres; and 1 g, which is the force experienced by any object on Earth above sea level.

How does g force work?

To make it easier to understand, we will use a well known example such as travelling in a car.

When we travel sitting down in a car, we experience g forces every time there is a change of direction and/or speed. This way, when the car accelerates or brakes, our body experiences longitudinal g forces, (backwards, forwards or vice versa) while upon changing direction we experience lateral g forces.

The stronger the change, the higher the g force our bodies experience.

And what about g forces when flying an airplane?

For an airplane to fly, an amount of g force needs to be applied upwards equivalent to its weight. Sounds simple doesn’t it?

In reality, any change of speed, height or turn on any of the aeroplanes axels, new g forces will be provoked which can cancel out part of the weight or in contrast, increase it.

In fact, management of g forces is part of a pilot’s training, acquiring skills to manage them so you can have a cup of tea served to you upside down without spilling a drop. Would you like to see it? Don’t miss this video!

How to calculate the g-force

Now that you know what g-forces are, let’s dig a little deeper…

When a pilot starts a turn, the g-forces on his body increase, but how does the pilot know how many g-forces he is subjected to? Quite simply.

There is a formula that relates the degrees of pitch of the aircraft during the turn to the g-forces generated:

1/cos(alpha) = g forces.

where alpha is the aircraft’s degrees of pitch.

Substituting values into the formula, you can see that a 45-degree turn equals 1.41 g; while a 60-degree turn equals 2 g!

However, don’t think you have to do the calculations while flying, don’t worry! Most aircraft are already equipped with g-force meters.

G-forces and pilots

The g-forces have quite noticeable effects on pilots. For example, if the pilot weighs 80kg, in a 60 degree turn his weight will double to 160kg. So, suddenly, moving arms and legs will be more difficult. But don’t worry! Pilots are trained for this.

In cases of very strong g-forces, a so-called black out could occur, which is when the blood rushes to the lower part of the body causing loss of vision for a few seconds. If you have seen the movie Top Gun: Maverick, you know what we are talking about.

Although in commercial aviation g-forces are minimal, in military aviation, pilots are constantly confronted with them, which is why they are equipped with special suits that compress the lower body, making it less easy for blood to flow downwards.

With the right training and techniques, military and aerobatic pilots are able to withstand up to 10 g. Mind-blowing, isn’t it?

Training pilots to withstand g-forces

You know that tingling feeling you get in your belly when you go down in a fast lift? We’re sure you’ve felt it at some point – it’s the g-forces in your body! It’s the same when you ride a roller coaster or go down a ramp in your car.

The first time you might be shocked, but if you do it a few times, your body will get used to it and you’ll stop feeling it. Well, the same thing happens to pilots, and that’s the basis of training to withstand g-forces. As your experience increases with more and more flying hours, the effects of g-forces diminish.

In the Army, they have machines that rotate on themselves at high speed that allow pilots to simulate the effects of g-forces.

Positive g-forces and negative g-forces

And now that you know a bit more, let’s take it up a notch!

G-forces are classified into two types: positive g-forces and negative g-forces.

On the one hand, positive g-forces are those that are generated during turns or steep climbs; causing blood to pool in the lower parts of the body.

On the other hand, negative g-forces are produced when we operate the controls with forward force or on steep descents, and, unlike positive g-forces, they cause blood to circulate towards the head.

The most uncomfortable and difficult to bear are the negative g-forces, as we are not so used to them in our everyday life.

Categories of aeroplanes according to the g-forces they can withstand

As with people, not all aircraft can withstand the same g-forces. For this reason, there are several categories:

Normal

Maximum positive: 3.8 g
Maximum negative: -1.52 g

Utility

Maximum positive: 4.4 g
Maximum negative: -1.76 g

Acrobatic

Maximum positive: 6 g
Maximum negative: -3 g

Commercial aircraft

Maximum positive: 2.5 g (2 g if flaps extended)
Maximum negative: -1 g

It is important for pilots to know the limit of their aircraft to avoid excessive loads. In addition, the higher the g-forces to which an aircraft is exposed, the more specific its maintenance must be.

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What is g force?

Colloquially known as a force, g force is a measure which determines the acceleration produced by Earth’s gravity on an object or individual.

Also, it’s also important to note that it’s represented by the lower case g in order to differentiate it from gravitational constance – G, and italics to differentiate it from the symbol of gram – g.

The best known g forces are 0 g, which is experienced in non-gravitational atmospheres; and 1 g, which is the force experienced by any object on Earth above sea level.

How does g force work?

To make it easier to understand, we will use a well known example such as travelling in a car.

When we travel sitting down in a car, we experience g forces every time there is a change of direction and/or speed. This way, when the car accelerates or brakes, our body experiences longitudinal g forces, (backwards, forwards or vice versa) while upon changing direction we experience lateral g forces.

The stronger the change, the higher the g force our bodies experience.

And what about g forces when flying an airplane?

For an airplane to fly, an amount of g force needs to be applied upwards equivalent to its weight. Sounds simple doesn’t it?

In reality, any change of speed, height or turn on any of the aeroplanes axels, new g forces will be provoked which can cancel out part of the weight or in contrast, increase it.

In fact, management of g forces is part of a pilot’s training, acquiring skills to manage them so you can have a cup of tea served to you upside down without spilling a drop. Would you like to see it? Don’t miss this video!

How to calculate the g-force

Now that you know what g-forces are, let’s dig a little deeper…

When a pilot starts a turn, the g-forces on his body increase, but how does the pilot know how many g-forces he is subjected to? Quite simply.

There is a formula that relates the degrees of pitch of the aircraft during the turn to the g-forces generated:

1/cos(alpha) = g forces.

where alpha is the aircraft’s degrees of pitch.

Substituting values into the formula, you can see that a 45-degree turn equals 1.41 g; while a 60-degree turn equals 2 g!

However, don’t think you have to do the calculations while flying, don’t worry! Most aircraft are already equipped with g-force meters.

G-forces and pilots

The g-forces have quite noticeable effects on pilots. For example, if the pilot weighs 80kg, in a 60 degree turn his weight will double to 160kg. So, suddenly, moving arms and legs will be more difficult. But don’t worry! Pilots are trained for this.

In cases of very strong g-forces, a so-called black out could occur, which is when the blood rushes to the lower part of the body causing loss of vision for a few seconds. If you have seen the movie Top Gun: Maverick, you know what we are talking about.

Although in commercial aviation g-forces are minimal, in military aviation, pilots are constantly confronted with them, which is why they are equipped with special suits that compress the lower body, making it less easy for blood to flow downwards.

With the right training and techniques, military and aerobatic pilots are able to withstand up to 10 g. Mind-blowing, isn’t it?

Training pilots to withstand g-forces

You know that tingling feeling you get in your belly when you go down in a fast lift? We’re sure you’ve felt it at some point – it’s the g-forces in your body! It’s the same when you ride a roller coaster or go down a ramp in your car.

The first time you might be shocked, but if you do it a few times, your body will get used to it and you’ll stop feeling it. Well, the same thing happens to pilots, and that’s the basis of training to withstand g-forces. As your experience increases with more and more flying hours, the effects of g-forces diminish.

In the Army, they have machines that rotate on themselves at high speed that allow pilots to simulate the effects of g-forces.

Positive g-forces and negative g-forces

And now that you know a bit more, let’s take it up a notch!

G-forces are classified into two types: positive g-forces and negative g-forces.

On the one hand, positive g-forces are those that are generated during turns or steep climbs; causing blood to pool in the lower parts of the body.

On the other hand, negative g-forces are produced when we operate the controls with forward force or on steep descents, and, unlike positive g-forces, they cause blood to circulate towards the head.

The most uncomfortable and difficult to bear are the negative g-forces, as we are not so used to them in our everyday life.

Categories of aeroplanes according to the g-forces they can withstand

As with people, not all aircraft can withstand the same g-forces. For this reason, there are several categories:

Normal

Maximum positive: 3.8 g
Maximum negative: -1.52 g

Utility

Maximum positive: 4.4 g
Maximum negative: -1.76 g

Acrobatic

Maximum positive: 6 g
Maximum negative: -3 g

Commercial aircraft

Maximum positive: 2.5 g (2 g if flaps extended)
Maximum negative: -1 g

It is important for pilots to know the limit of their aircraft to avoid excessive loads. In addition, the higher the g-forces to which an aircraft is exposed, the more specific its maintenance must be.

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Share this entry

You may be interested in…

UPRT: This is how a pilot prepares for a loss of control

What is the ground effect and how to handle it

The Kármán Line, the border with outer space

Lift principle on aircraft

Turbulent wake: What is it? Is it dangerous?

What is Venturi’s effect?

Cookie and Privacy Settings

We may request cookies to be set on your device. We use cookies to let us know when you visit our websites, how you interact with us, to enrich your user experience, and to customize your relationship with our website.

Click on the different category headings to find out more. You can also change some of your preferences. Note that blocking some types of cookies may impact your experience on our websites and the services we are able to offer.

These cookies are strictly necessary to provide you with services available through our website and to use some of its features.

Because these cookies are strictly necessary to deliver the website, refusing them will have impact how our site functions. You always can block or delete cookies by changing your browser settings and force blocking all cookies on this website. But this will always prompt you to accept/refuse cookies when revisiting our site.

We fully respect if you want to refuse cookies but to avoid asking you again and again kindly allow us to store a cookie for that. You are free to opt out any time or opt in for other cookies to get a better experience. If you refuse cookies we will remove all set cookies in our domain.

We provide you with a list of stored cookies on your computer in our domain so you can check what we stored. Due to security reasons we are not able to show or modify cookies from other domains. You can check these in your browser security settings.

Check to enable permanent hiding of message bar and refuse all cookies if you do not opt in. We need 2 cookies to store this setting. Otherwise you will be prompted again when opening a new browser window or new a tab.

We also use different external services like Google Webfonts, Google Maps, and external Video providers. Since these providers may collect personal data like your IP address we allow you to block them here. Please be aware that this might heavily reduce the functionality and appearance of our site. Changes will take effect once you reload the page.

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You can read about our cookies and privacy settings in detail on our Privacy Policy Page.

All About G Forces

What’s behind gravity forces, and how much of them can we take?

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Airplanes: Designing for Stealth

A few summers ago I took my then nine-year-old daughter on a glider ride. Midway through, as we soared over a coastal landscape, I casually asked the pilot whether he could do any tricks. Without a word, he threw the plane into a dive. We were accelerating straight towards the ground. My daughter and I shouted and grabbed the armrests. Suddenly we were hit with that thrill-inducing pressure familiar from rollercoasters—tensed facial muscles, light-headedness, a sense of altered reality.

The pilot pulled up, and all we could see through wide-open eyes was sky. We zoomed straight up until the glider ran out of pizzazz, then the pilot tipped it over into another sheer drop. Again, squeezed faces, dizziness, otherworldliness. After two or three loop-the-loops, the thrill became dread: Would he ever stop? My daughter was laughing, but I thought I would pass out.

What was going on? What happens to us physiologically when we start “pulling G’s,” as pilots label what we were feeling? Why was the sensation most pronounced as we swooped out of a dive? Might the glider pilot, I wondered at the time, pass out himself?

glider in flight

If you’re sensitive to G forces, aka gravity forces, think twice before going up in a glider and asking the pilot if he knows any tricks.

“Fainting in the air”

Before the advent of airplanes, which could accelerate the human body like nothing before, people rarely experienced G forces. So-called gravity forces first became a concern during World War I, when pilots began mysteriously losing consciousness during dogfights. As early as 1919, a doctor wrote up this strange phenomenon for the literature, calling it “fainting in the air.”

With the development of faster and more maneuverable planes, G forces became more dangerous. Based on rates of survival (or lack thereof) during crashes, it became accepted wisdom that no pilot could withstand more than 18 G’s, or 18 times the force of gravity at sea level. So cockpits were designed to withstand only 18 G’s. Yet pilots sometimes walked away from crashes in which the G forces were calculated to have been much higher.

In the mid-1940s, an Air Force physician named John Stapp began to suspect that it was the mangling effects of a crash and not the G’s that killed pilots. Hoping to improve cockpit safety, Stapp set out to determine just what humans could take in the way of G forces. He built a rocket-powered sled, the “Gee Whiz,” which accelerated a tightly strapped-in body—initially a dummy but soon Stapp himself—to extraordinarily high speeds along a track before coming to an almost unimaginably abrupt stop.

By the late summer of 1948, Stapp had done 16 runs himself and withstood up to 35 G’s. He lost dental fillings, cracked a few ribs, and twice broke a wrist, but he survived. Still he was not satisfied. Eager to know what pilots ejecting at high speed could endure in terms of sudden deceleration, Stapp built a new sled called “Sonic Wind” in the early 1950s.

Film strip of man

John Stapp riding the “Sonic Wind” during a 421-mph ride in March 1954

On what became his final run, in December 1954, Stapp decided to pull out all the stops. Firing nine solid-fuel rockets, his sled accelerated to 632 miles per hour in five seconds, slamming him into two tons of wind pressure, then came to a stop in just over one second. A witness said it was “absolutely inconceivable anybody could go that fast, then just stop, and survive.” But Stapp did—in fact, he went on to live another 45 years, dying quietly at home in 1999 at the age of 89—and he experienced a record-breaking 46.2 G’s. For an instant, his 168-pound body had weighed over 7,700 pounds.

Stapp’s efforts put him on the cover of Time, and he was called “The Fastest Man on Earth.” More importantly, his work led to greatly improved safety in both planes and cars, and he gave us a much-improved understanding of human tolerance to G forces.

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A matter of acceleration

Even before Stapp it was well-known that G forces have less to do with speed than with acceleration—the change in speed over time. If speed alone could cause the thrill that comes from feeling G forces, then simply driving on the highway would suffice.

There is a limit to what anyone can take. Princess Diana tragically proved that.

When most of us think of acceleration, we think of, say, a Jaguar doing 0 to 60 in six seconds. But acceleration is technically any change in the velocity of an object: speeding up, slowing down, and changing direction are all types of acceleration. That’s why, on a rollercoaster, you feel G forces when you round tight bends and are thrown against the side of your seat (a change in direction) as much as when you plunge from the heights (accelerate) or grind to a halt (decelerate).

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You feel the thrill, but don’t black out, because the coaster’s creators designed it to be well within the G-force tolerance of the average person. The amount of G forces that are tolerable differs by individual. But for all of us it depends on three factors: the direction in which the G forces are felt, the amount of G’s involved, and how long those G’s last.

woman and child riding rollercoaster

Roller coasters are precisely calibrated so average people can enjoy the spine-tingling effects of G forces and few of the ill effects.

Blood pressures

Depending on which way your body is oriented when it accelerates, you can feel G forces front-to-back, side-to-side, or head-to-toe. (Or, in each case, vice versa—for example, toe-to-head.) Each of us can tolerate the two horizontal axes a lot better than the vertical, or head-toe, axis. Facing forward in his seat on that final run, Stapp felt front-to-back G forces as he accelerated and back-to-front G forces as he decelerated, and as we’ve seen, he endured well over 10 times the G’s my daughter and I encountered in the glider.

But vertical forces are another matter, and it has everything to do with blood pressure. At sea level, or 1 G, we require 22 millimeters of mercury blood pressure to pump sufficient blood up the foot or so distance from our hearts to our brains. In 2 G’s, we need twice that pressure, in 3 G’s, three times, and so on. Most of us would pass out with head-to-toe G forces of just 4 or 5 because our hearts can’t summon the necessary pressure. Blood pools in our lower extremities, and our brains fail to get enough oxygen.

Fighter pilots can handle greater head-to-toe G forces—up to 8 or 9 G’s—and for longer periods by wearing anti-G suits. These specialized outfits use air bladders to constrict the legs and abdomen during high G’s to keep blood in the upper body. Fighter pilots can further increase their G-tolerance by training in centrifuges, which create artificial G’s, and by learning specialized breathing and muscle-tensing techniques.

All of us, fighter pilots included, can handle only far lower toe-to-head, or negative, G forces. Facing a mere -2 or -3 G’s, many of us would lose consciousness as too much blood rushed to our heads.

NASA's 20-G research centrifuge

Spinning at high speed, NASA’s 20-G research centrifuge at California’s Ames Research Center can simulate up to 20 times the normal force of gravity we feel at sea level.

Too much and too long

Magnitude and duration are as critical as direction. While John Stapp showed that people can withstand much higher G forces than had long been thought, there is a limit to what anyone can take. Princess Diana tragically proved that. Experts estimate that, in the car accident that killed her, the G forces on her chest were about 70 G’s (and 100 G’s on her head). That acceleration was enough to tear the pulmonary artery in her heart, an injury almost impossible to survive. If Diana had been wearing a seatbelt, the G forces would have been in the neighborhood of 35 G’s, and she may have lived.

Astronauts in orbit are still subject to about 95 percent of the gravity we feel on Earth.

Diana’s death notwithstanding, Stapp proved that people can often survive high G forces for very brief periods. We’re all familiar with this to a certain degree. According to a 1994 article in the journal Spine, the average sneeze creates G forces of 2.9, a slap on the back 4.1, and a plop down into a chair 10.1. If you jump from three feet up and land stiff-legged, write the authors of the book Physics of the Body, you’ll feel about 100 G’s momentarily.

We suffer no ill-effects from these everyday events because they’re so brief. The trouble starts when G forces linger. That’s why I began feeling worse with each dive the glider made. It’s also why, during launches of the space shuttle, controllers keep the acceleration low—no greater than what generates about 3 G’s—so as not to unduly stress the astronauts.

Zero G’s

Of course, once the shuttle goes into orbit, astronauts no longer feel G forces. They’re in a zero-G environment, right?

Well, not exactly. There’s no such thing as zero G’s. Even the two Pioneer spacecraft, launched in the 1970s and now the most distant man-made objects, experience a tug of one 10-millionth of a G from the solar system they’ve now left. Astronauts in orbit are still subject to about 95 percent of the gravity we feel on Earth. It’s just that they’re in a constant free fall. They’re falling towards Earth, but their speed—up to 25 times the speed of sound—means that the planet is falling away from them just as fast. Better to say they’re in a microgravity, or weightless, environment.

astronaut in space

Even though the force of gravity is still very much in effect, astronauts in orbit do not feel it because they’re in a constant free fall. Here, astronaut Ed White during the first U.S. spacewalk in 1965.

Weightlessness may be a gas, but it comes at a cost, because our bodies are used to a 1-G environment. Each of us here on Earth is actually accelerating towards the center of the planet at roughly 32 feet per second squared. We don’t feel we’re accelerating because the ground holds us in place. But without that customary pressure, our bodies take a beating. Over time, our cell walls collapse, our muscles atrophy, our bones decalcify. (The opposite happens in hypergravity: A 2001 study found that Australian fighter pilots who routinely felt G forces of 2 to 6 experienced, over the course of a year, an 11 percent increase in the bone mineral content and density of their spinal columns.)

These health effects of microgravity are of concern to NASA as it contemplates sending astronauts to Mars, a trip that could take three months one-way. On the way there, astronauts would need a centrifuge or other means to create artificial gravity to ensure that any “small step for a man” onto the Red Planet didn’t result in a broken ankle. Visionaries are already wondering whether people born in potential future colonies on Mars (38 percent of Earth’s surface gravity) or the moon (17 percent) could ever safely come to Earth.

Give me gravity

Coming safely to Earth was just what my glider-riding daughter and I began to wish for in the worst way. (Later she admitted to feeling increasingly queasy, adding, “I felt like my whole body was collapsing.”) Fortunately, after four figure-eights, the pilot tired of his sport and leveled off, and we returned to the airport without further ado. One G never felt so welcome—good old 32 feet per second squared.

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Source https://www.grupooneair.com/what-is-g-force/

Source https://www.grupooneair.com/what-is-g-force/

Source https://www.pbs.org/wgbh/nova/article/gravity-forces/

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