I was in charge of marketing for the company who created the CFD software illustrated here. There are several counterintuitive fluid dynamics phenomena which occur during VTOL. These were only fully understood by the use of this program.
How sad that the UK failed to maintain its lead in this field and is now buying US derivatives.
The company itself was technically unrivalled but, despite my best efforts, it was commercially hobbled by an autocratic MD. I have encountered this scenario more than once since, but never to the same extent.