Stephen, think about it this way: For a helo to hover, it needs to
generate a thrust which is equivalent to the weight of the helicopter
(the rotor needs to move the same weight of air as the weight of the
helicopter). If gross weight is increased, the thrust must increase,
and since the area of the is not increased, the velocity of the air
must. What has occured is an increase in the disc loading, which can
also be accomplished by changing the size of the rotor. So the
velocity of the down wash is directly linked to weight & disc loading.
You can use a simple formula to calculate the velocity of your own
downwash.



Yes, but that downwash is not able to continue unabated. Immediately on
leaving the disc it is compressed against surrounding air which slows it
considerably.

Your assertion was that for a large helicopter to get into SWP it would take
"considerably higher" speed than a brisk walk down the stairs. Yet, in all my
training, I have never heard any other reference used. Please define
"considerably higher".

You mention a simple formula for calculating downwash velocity yet you didn't
post it. I'd be interested in knowing this too.


Stephen Austin
Austin Ag Aviation
Charleston, Missouri