Originally Posted by
john_tullamarine
And, as an additional curiosity (minor for fixed wing but perhaps not so for rotary), there is a phenomenon described as high speed stall associated with VERY high pitch rates (scratchy memory suggests in excess of around 70 deg/sec). A stable vortex can form along the leading edge and angle of attack values significantly in excess of "normal" stalling angles are possible.
As I recall I first read of this in an RAeS tech report ?
The limited research done on tumble aerodynamics of tailless aircraft has shown something like this - the vortex tends to form above the leading edge which is pitching nose-down (or vice-versa), with a nominal diameter around 2/3 of the root mean chord. In the tumble it tends to travel towards the trailing edge sustaining the pitching motion.
This certainly occurrs at pitch rates in excess of 200°/s (tumbling aircraft have been observed to show over 400°/s), but intuitively lower pitch rates in the order of 60°/s will almost certainly do the same - indeed this is probably part of the tumble initiation mechanism.
If you can handle a 5Mb pdf,
this contains some pretty pictures of it about pages 6-10.
G