I just stick my fingers and let them go "thum thum thum" on the blade grips, heh, when I had my aluminum shaft on, one of my friends wasn't thinking all to well and decided to stick his hand into the blades while they were going at about 50 rpm. even at the low speeds he got a good wack (no injury, just a little supprised) and bent the main shaft. stupid aluminum...


I too was wondering about that little knob, the only thing I could think of was a low restance zone for all your super low inverted flying needs!