Sine wave, yep.
Let's track the red blade - say (for illustration only) at 90 degrees it is about to reach the top of its upflapping curve. That means that the rotorhub at the 270 degree position (where the other blade would be on a 2-bladed system) is reaching the bottom of its downflapping curve. It also means that ANYTHING attached to the hub more than 90 degrees away from that upflapping blade is also flapping down, so the yellow blade at 330 is flapping down and the blue blade at 210 is also flapping down. Remember that even though Dave's design is a CV joint, the hub is rigid in the flapping plane, therefore the blades are not free to flap independantly. Put another way, you are trying to impose split-phase dynamics on a three-phase system (or vice-versa).
Take a conventional fully-articulated 3-blade system. The red blade at 90 is reaching maximum upflap, the yellow blade at 330 is on the way down, the blue blade at 210 has passed maximum downflap (which occured at 270) and is on the way back up. The blades are free to operate independantly in the flapping plane.
Only a 2 or 4-bladed system will remain in proper "flapping phase", but the problem of the underslung configuration (required to reduce/eliminate the Coreolis effect) remains for the 4-bladed system.
(I am using the maximum flapping positions of 90/270 for convenience - I realize they occur at different places depending on where the air is coming from.)
Last edited by Flingwing207; 15th October 2004 at 18:49.