While we are pernickety – it is the gravitational acceleration in vacuum near the surface of the earth, and defined as 9.80665 m/s2. As has been pointed out before, to arrive at the actual force you need to multiply it by the mass of the thing subject to gravitation.
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The reason we can’t quite decide why it is weight and balance or mass and balance is that the way we do it, it really only works if mass and weight are interchangeable so it really does not matter at all.
There are some aspects of flying that depend on mass. For example acceleration and hence take-off and landing performance.
There are some aspects of flying that depend on weight. For example climb rates and induced drag and hence sustained speeds (e.g., cruise performance).
There are some aspects where it makes no difference. For example the centre of mass and centre of gravity (leaving alone flying aircraft several dozen miles long, or flying close to a neutron star)
All this “it is really mass” and “it is really weight” is fun from a purist physics point of view, but it is completely irrelevant when flying on Earth alone, and neither is correct.
just to add a little clarity G (capital) is the universal gravitational constant (circa 6.67×10^-11 m^3 kg^-1 s^-2) . Which does not change.
g (lower case) is the gravitational force at the earth’s surface.
Mass will be equal on earth and mars, weight will differ.
gallois wrote:
What does the G stand for? I always thought it stood for gravity and surely gravity is a force.
I guess G stands for “Gravity”.
Gravity is acceleration (ref. general theory of relativity). It causes a force but the force itself depends on the mass of the objects involved.
What does the G stand for? I always thought it stood for gravity and surely gravity is a force.
G is force per unit mass. Force per unit mass is an acceleration measure.
G (in N/kg) times Mass (in kg) is the force (in N), which is weight (in N)
Pilots confuse weight with mass in their MnB calculations, it should as it should be WnB calculations 
What does the G stand for? I always thought it stood for gravity and surely gravity is a force.
Forces are in newtons (N) not in newtons per kilogram!
1G force is 9.81 N/Kg and causes an acceleration of 9.81 m/s if unopposed, I thought.
It doesn’t measure force. I measures acceleration along the yaw axis. (Vertical when the aircraft is flying straight and level.) 1 G being approximately 9.81 m/s^2. But as acceleration is caused by the lift on the wings, indirectly the G measurement also gives the ratio of the lifting force to the gravity force acting of the aircraft.
