This lesson demonstrates that the stall speed increases in turns. The steeper the turn, the higher the stall speed. Fly fast to turn steep.
We have seen the stall in level flight. The pre-stall buffet became apparent at about 37kts in the Cirrus, and we were able to avoid the impending stall by easing the back pressure on the stick. So what happens if the wings are not level? As the angle of bank increases, the vertical component of the lift generated by the wings reduces. It reduces significantly as we bank beyond 45 degrees. With less vertical lift being generated at any given angle of bank, it is obvious that we are going to fall out of the sky sooner, i.e. at a higher stall speed. We can avoid these stalls by easing the back pressure on the stick. In the event of a stall, the recovery will be the same as a stall with a wing drop.
Scenario and Demonstration
This demonstration shows the glider in level flight, slowing until the pre-stall buffet. This is at around 37kts. Easing the back pressure on the stick is enough to avoid the stall.
We then make a series of turns at various angles of bank, and slow the glider until we see the pre-stall buffet. It takes a few moments to get there. As we do, note the angle of bank, and the speed at which the pre-stall buffet occurs. In the steepest turn, the pre-stall buffet occurred above 50kts. Use the pause key if it helps.
The video is best viewed in YouTube in HD in Full Screen mode, to easily see the on-screen messages and instruments during the demonstration. Use view, pause and rewind as needed to grasp the content and timing of the messages displayed, then focus on the action.
Performing the Exercise
Start by confirming the speed at which you see pre-stall buffet in level flight. Then speed up a little and try a steady turn of around 20-30 degrees of bank at 45kts – then ease back on the stick while maintaining the bank angle. Note the speed at which the buffet occurs. Recover, and increase your speed to 50kts and make a turn with 45 degrees of bank. Hold this and slow down, noting when the buffet occurs. If you are practised at turning steeply, go for 60 degrees and repeat. If you drop a wing, recover as usual: stick centrally forward, gain speed, make coordinated use of controls to level the wings, ease back and level out.
You’re flying a Standard Cirrus, and the air is calm, so you’re fully in control.
The sim is a great place to practise stalls and recovery. In more tubulent air, such as thermals, you can experience sudden wind sheer. This means that while you were happily circling above the stall speed, a moment later the airspeed has dropped away and you’ve stalled as a result.
Further Reading and References
Gliding From Passenger to Pilot, 2nd Edition: Page 95-96
BGA Instructors’ Manual, 4th Edition: Section 5, Chapter 18