• 1MINUTE AVIATION

    Aviation facts explained in one minute

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.