RW Prouty - Helicopter Aerodynamics II
My Suggestion
Pilots use two terms "settling with power" and "power settling" - sometimes interchangeably and sometimes to represent
two different situations. One is the vortex ring condition discussed above. The other is simply entering into a flight condition
where the required power is more than the available power - for instance, finding it impossible to hover at the top of a
mountain that was no trouble to get to with forward speed. I propose dropping both terms and substituting "thrust instability"
for the vortex ring phenomenon and "running out of power" for the other.
A Final Word
I can't explain why re-ingestion comes stronger with rate of descent in the turbulent vortex-ring state, but I don't feel too bad,
knowing what famed aerodynamicist, Theodore von Karman, was reported to have said: "Only God understands turbulence"
It appears that "settling with power" is a generalisation used to cover two different phenomena which was possibly correct.
Was lucky enough to meet Mr Prouty on a couple of occasions - and if you didn't ask dumb questions he would casually talk to you all day.
Enough already?