This will raise some eyebrows or increase someone’s blood pressure. A while back I made a comment to Nick Lappos indicating that the field of engineering is in a constant state of change. I further stated that sometimes the new kid on the block would change the rules and redefine a problem in opposition to the facts as taught to the older guys. I don’t dispute what Nick is saying in his explanation. But, I also feel that based on what is taught to most helicopter pilots and this includes the older guys with no engineering training there is such a thing as a ground cushion and by implication the cushion exists due to an increase in the localized pressure field. It takes a long time to reshape a persons perception when it comes to learning a new theory while discarding the old theory. There is a possibility that new helicopter pilots will get Nicks explanation in their POF courses but until the last of the old breed dies off they will still believe in a “Ground Cushion” and an increase in pressure.
Even the FAA Helicopter book is in support of Nicks' theory.
