Outwash velocity prediction

[skiddriver]

I've combed my old FTMs and texts, but cannot find what I would have thought would have been done and dusted formulas to predict idealized maximum outwash velocity at given distances from a hovering helicopter.

The downwash velocity is simple, but no luck on outwash. Any help?

[richatom]

Outwash modelling is actually relatively simple to determine approximately enough for most purposes (eg heliport planning, environmental considerations) using fairly basic fluid mechanics which is why you might not find too many references. But here is a lead to a more advanced study:
http://www.nlr.nl/eCache/DEF/268.html

[skiddriver]

Thanks, I'd actually seen that site. I just find it difficult to believe that there isn't a relatively simple set of formulae developed to provide theoretical outwash. I mean, induced velocity is simply a function of disc loading with standard formulae for at disk and remote wake velocities. An idealized outwash velocity can't be that difficult (he says having forgotten all the math he learned that would have helped him determine it himself).

I'm just looking for something relatively simple to plug and chug out a rough order of magnitude velocity.