Instrument Ranting
Canberra Fin Stalling.
Good question.
Firstly fins are just double sided aerofoils that will stall given enough alpha. Not a new phenomenon.
Some aircraft in flight test come close to fin stall under the worst conditions and this is often corrected by adding more fin area which may then require a change to rudder design.
Then there is sometimes an additional complication which may occur at high fin alphas where the rudder force does a rapid decline at high rudder angles leading to rudder overbalance.
Given that this can be followed by a lock over of the rudder requiring a large force to unlock, TPs are very wary of this condition and approach the condition very warily. Often with a deployable tail chute
In my experience with multiple Mks of Canberra including flying all of the conventional aerobatics not involving negative g I feel I have never come close to stalling the fin. Flight test instrumentation would be required to determine how close and this would have been checked by English Electric and or Boscombe Down..
If I am right then the only time one will definitely get fin stalling will be following departure from a high thrust asymmetric and a slow reaction in pulling off the thrust.
This is sometimes demonstrated by a QFI showing Vmca (min speed to retain control following an engine failure) It is a normal test procedure in establishing that speed to fail an engine and wait an obligatory 2 seconds before taking any recovery action. If one does this procedure at too low a speed in the Canberra you rapidly roll inverted with an extreme angle and rate of yaw which can only be possible with a stalled fin. The fin will quickly unstall as thrust comes off leaving you to revover in the safe height you have allowed.
It's really not all that much fun.
Can someone expand on this?