Thankyou for your responses people, but the jury seems to be out! Is it related to prop speed(ie why a faster TAS means higher tip speed? -can you explain please?) or is it a control flutter issue.
Crash &Burn is your info from the manufacturer or elsewhere? Interesting none the less. Does anyone else have anything to offer on this issue?
In the Fokker example does anyone have any enlightening ideas?
What about the B1900 also?