There are aspects of this discussion that disturb me, including dangerously incorrect statements by some posters, so a few bullet points to ponder:
A wing stalls when the critical angle of attack (stalling angle) has been exceeded on that wing. In the training situation, the classical focus is on the situation where both wings stall at the same time. A wing drop at the stall is invariably caused by one wing stalling before the other. This “uncommanded roll” may have been caused by:
- Yaw being present as the stall was approached. This could be perhaps be due to change of engine torque. In a training situation, students (and instructors) often fail to correctly balance with rudder when reducing power to enter a clean stall or when applying power during recovery. I also see lots of pilots controlling direction on finals by over-use of rudder, rather than using it correctly to balance the aircraft.
- Differential condition of the wing(s) e.g. ripples in the surface; dents in the leading edge; rigging differences in the wing or the flaps / slats; on a laminar flow wing (such as a glider) even bug squash on a leading edge that results in airflow breaking away (stall) at a lower angle of attack that on the other wing.
Teaching recovery from a stall with a wing drop has classically involved what came to be known as the “standard stall recovery”:
· Ailerons neutral
· Reduce the angle of attack with elevator (stick forward)
· Simultaneously apply full power (if available)
· Sufficient rudder “to prevent further yaw”
Over the years, in some quarters, this last point has been translated into “pick up the dropped wing with rudder”. To “pick up the wing” requires yaw in the other direction and as the aircraft is still close to the stall, it may well result in the opposite wing stalling. The technique is used in certain aerobatic manoeuvres such as the “falling leaf” where the aircraft angle of attack is held just off the stall and the pilot applies rudder one way and then the other to stall one wing then the other. As a basic stall recovery technique, it is potentially dangerous.
Significantly, the military moved away from using rudder “to prevent further yaw” years ago as it was “negative training” for future aircraft types. Extensive trials were conducted on light piston training aircraft as well as on turboprop and pure jet trainers to look at height loss during stall recovery. Interestingly it was discovered that use of rudder to prevent further yaw had absolutely no effect on height loss – and even could distract the pilot from simply using elevator to un-stall the wing or wings and then using aileron to level the wings when the aircraft was no longer stalled.
A number of modern aircraft – some of which are used for training (e.g. Cirrus) have design features that allow ailerons to be used at the stall (such as marked washout or chord twist that causes the inboard section of the wing to stall well ahead of the outboard section containing the ailerons). However, the licencing system allows a pilot to fly any type of light aircraft and I'd suggest that the concept of “primacy” will prevail in a startle / surprise situation that would almost certainly be present in an inadvertent stall. This would result in a pilot reverting to whatever had been drummed into them during training. If this involved use of aileron, it is likely to lead to very bad outcomes in an aircraft that does not have the design feature.
Bottom line is that elevator is the primary control to un-stall the wing(s). Use of aileron or rudder can be problematic near the stall – more so in some types than others. Teaching use of rudder to “pick up a wing” at or close to the stall is dangerous.
Fly Safe
PJ88