Ground effect
Hi Guys,
I have seen over and over how difficult it is to explain behaviour of a Helo (to pilots if you allow me...).
It is maybe plausible to say, looking at the airflow (the whole tube of air that is acted upon by the rotor), and derive that because of the blockage by the ground, precisily at the ground level the static air pressure probably will be higher than the static pressure measured in the same tube of air without the ground.
But even trying to explain it with pressure, I think one should make a difference between static and dynamic pressures, and also look at the pressure just above the rotor with and without ground effect. I am shure this could be developped into a model, but the pressure under the rotor would only be part of the story (pressure above the rotor could also be higher).
My simulator tries to model the helo based on the fundamental dynamics and aerodynamical rules. In that model the pressure at the ground does not come into play, in the same way as the pressure measured at the runway does not directly come into play when studying the influence of the ground on a wing of a airplane.
What the rotor sees and acts upon is a moving air mass.
It is the speed of that air mass that counts. The ground just changes that speed (making abstractions of more detailed vortex effects) : it reduces the speed, making the rotor more efficient in exactly the same way as forward speed makes the rotor more efficient.
Delta3
Last edited by delta3; 12th Jun 2005 at 22:22.