Simon Elliott wrote:

What prevents those contra-rotating rotors from touching?

The blades are rigid, far apart , but, most importantly, they are kept
about the same distance from each other by the centrifugal force.
Sometime they do touch, however. This happened with the Ka-50 when the
pilot exceeded the maximum G load during testing. Ka-50 crashed and the
pilot had no time to eject. Since then Kamov use a different material
for the blades and moved them further apart.

--
Regards,

Venik

Visit my site: http://www.aeronautics.ru
If you need to e-mail me, please use the following subject line:
?Subject=Newsgr0ups_resp0 nse