Hi Russell, On Tue, Apr 29, 2008 at 9:26 AM, Apptech wrote: > 45 degrees AOA as max lift is as per sites quoted BUT > stalling usually occurs well below that. Maybe not for flat > plates. NASA sim I quoted allows you to model a flat plate > well. Doesn't allow my "bent plate" rotors and it's not > obvious how to handle them analytically and easily. 45 deg AOA for max lift is ONLY for flat plates. Typical light aircraft airfoils have max lift at just below stall AOA, around 15 or 20 deg. Delta winged high performance aircraft often have a much higher usable AOA (35 deg or so), and in fact will often also have significant, decreasing lift at AOA higher than stall. (This can lead to the paradoxical situation that pulling "up" on the stick results in less lift, without the characteristic "break" at stall which would warn you of what is going on) Flat plates are always "stalled" in the sense that their behavior at any AOA is like that of a normal airfoil NEAR its stall AOA. > > With the flat-bent plate rotor machines the plate goes > through 0-180 degrees of aoa and back again so analysis may > be "difficult". Do you have a drawing or photo of what you are trying to model? Yes, I think it would be difficult. If you could assume that there is enough time for the turbulent air to get out of the way before the AOA changes significantly, then you could probably model it in a stepwise fashion (two regions - simple geometrical flat plate (where lift is just airflow times drag times sin(angle)) and airfoil-like, where L/D is greater than one and dependent on AOA squared, like a normal wing) > > I'm contemplating just measuring torque for a locked rotor > at various aoa's and air speeds which should give me easy > empirical > results and then vary variables (blade to bent section > ratio and bend angle) and see where that takes me. Would probably be worth it even just to develop some more insight into the problem. Sean > > > Russell > > -- > > > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist