More of the Same IV
I totally accept the line vortex theory of lift, this vortex "contained" in the wing cannot just end, and does leave the wing as the trailing vortex we all know and love from a wing tip (well as a sheet vortex which has increasing strength to the tip, which all bundles up as one just behind the wing). Ground effect can be explained by the mirror image of this vortex system in the ground, as I think I have mentioned earlier.
The effect of the mirror image trailing vortices is to push the real trailing vortices further outwards, this has the effect of increasing the aspect ratio of the wing, reducing downwash, and induced drag hence producing the efficiency improvement we are all talking about. Also by effectively increasing the aspect ratio we also reduce the strength of the vortex, as previously mentioned.(Lift/unit span is proportional to vorticity and airspeed, so longer span same lift and airspeed give less vorticity)
There you go all explained without even mentioning pressure!
BUT air will continue in its state of rest or constant linear motion unless a force is applied to it. Pressure is the force that makes air deviate around an aerofoil, if we are to change this flow field we must also change the pressure distribution. So despite vortices being able to explain ground effect, there must be pressure changes if there is to be a different flow pattern. So I say the pressure directly under a wing is increased by ground effect. I am not saying that this pressure on the underside of the wing makes more lift, but it does resist downwash hence reducing induced flow, reducing induced drag, and for our helo allowing a lower pitch angle for given alpha, bringing the lift vector closer to the vertical and reducing the power requirement.
I will produce diagrams if it helps.
Light photons behave according to probability, which is apparently a great explanation! To who?
PS I did not go to Sunday school for very long so again Nick you are mistaken.
Last edited by DeltaFree; 22nd Nov 2002 at 19:46.