Hi can someone please summarise this attached graph in relation to ground effect.

I read theory but want to simplify of what the graph is essentially showing please

I would say , if you ignore forward airspeed, as you get closer to the ground there is a reduction In induced flow. So imagine a 20ft OGE hover, if you where to lower the collective just a small amount to initiate a gentle descent, as you got closer to the ground, as a percentage of rotor diameter, your angle of attack would increase without a change in power or blade pitch

Think of ground effect as the inability of the wing/aircraft airflow downwash to descend any further than the ground surface (stands to reason - the ground surface is a bit too hard for air to go through).

This has the effect of rotating the net lift vector a little towards the vertical (considering where it would be in the absence of the ground).

The physical (ie away from the ground) consequence of the aft-inclined net lift vector is induced (or lift-dependent) drag which is represented by the aftwards (ie drag) component of the vector.

So, if the vector rotates to a more vertical position, the aftwards component reduces, and the induced drag reduces.

The effect is very strongly dependent on the height of the wing above the ground.

In the graph you can see this very clearly as the wing height gets closer to the ground and the drag reduction starts to reduce much more rapidly -

(a) at, say, a full (100%) wing span height above the ground the drag reduction is only a couple of percentage points

(b) at, say, half (50%) wing span height above the ground the drag reduction is around 15%

(c) at, say, 1/5th (20%) wing span height above the ground the drag reduction is around 30-35%.

Hence the general observation that ground effect becomes significant once the aircraft wing is at a height of around 50% span above the ground surface.