chopper wake

frosty

hi guys,
this is my first post..been a reader of the forum for some time. heres an argument i had with someone today. suppose a helicopter is hovering still over a lake/deep enough pool of water. also, it is wide enough. the chopper is close to the water (for eg...dropping a swimmer or a marine....basically close!)
will the chopper cause any depression (i.e cavity) of certain depth? or will it just set waves. i feel there is going to be a certain depression and also waves and that i can analyse the problem as a uniform airflow impinging on a wall of water with a central line from the center of the chopper to a "stagnation" point on the water surface. my friend feels that the assuming of the wall is not justified and that it is just going to set of waves.
comments? not a well defined problem. maybe to make it well defined: what is the depth of the cavity?? (:

chroot

It will cause a depression. You can solve Bernoulli's equation to figure out how much.

- Warren

russ_watters

Hint: the downwash force is equal to the weight of the chopper. This divided by the area gives pressure.