G Force
Human body is an accelerometer: it captures the strenght and the direction of the imposed G forces.
Of course it can't really measure those forces in a detailed way (because of this we find mechanical accelerometers in many planes).
Here's is a way to display it to the player:
Neutral G:
Right turn climb (Light G):
Right turn climb (Medium G):
Right turn climb (Heavy G):
For a full 3D accellerometer:
A better version, more recognizable, is this one:
Where the red area is blinking.
Of course it should be resizable.
But why should this be important? Fatigue simulation.