Slow Flight and Stalls

The objective of this lesson is to save your life. We often want to fly slowly to save height. Too slow though and we can fall out of the sky. It is essential that you recognise the symptoms of a potential stall, and instinctively react to recover from one. This lesson focuses on “1G” or “unaccelerated” stalls, at the slowest speeds of flight. “Accelerated” stalls will be described later.

A mushing stall, or the start of something else?

Learning Points

Slow flight is inevitable. Minimum sink is typically only just above the stall speed, so we must be on our guard. It can also catch us out descending through a wind gradient, often close to the ground as we approach to land. A stall here needs to be avoided, or else recognised and dealt with immediately. The symptoms of an impending stall are well known and easily recognised. You’ll always see one or more these conditions before a stall:

Symptoms of the Stall

Note, you may not see all of these symptoms, as they may not all be present or obvious in any given stall. Treat any single symptom as a pre-stall warning.

  • The nose is high
  • Airspeed is low, or reducing
  • The sound of the airflow will become much quieter
  • The ASI reading may be oscillating
  • Buffeting of the airframe can be felt, heard and possibly seen
  • Elevator, aileron and rudder control may become sloppy (or worse, and precipitate a wing drop)
  • The controls may be in unusual positions for the phase of flight, such as lots of out of turn aileron
  • The elevator will not raise the nose. If this is the case, you’re already stalled. If you haven’t fallen out of the sky, you’re about to do so
  • Sink is increasing and may be higher than expected for the current attitude.

Types of Stall

Mushing Stall

The glider is dropping, wings horizontal, and nose high. An example is shown in the image above.

Stall with Nose Drop

The glider is dropping, wings horizontal, with the nose down. There is an example of this in the lesson ‘Effect of Controls – Elevator’.

Wing Drop Stall

Possibly the most exciting variant: One wing drops first, resulting in the start of a spiral dive. There is an example in the demonstration.

Recovering from a Stall

You’ve probably understood that the stall is associated with flying too slowly. The real underlying cause, common to all stalls, is that the angle of attack is too steep, typically around 15 degrees. The solution is obvious: lower the angle of attack. How? 

The response is always:

Move the Stick centrally forward to get the nose down.

As speed increases, as it will quite quickly, make coordinated use of aileron and rudder to level the wings and ease back on the stick to recover some height.

As your speed decays in the climb, ease the stick forward again to adopt the required attitude for a safe speed – with the nose slightly lower than normal to avoid a second stall.

Scenario and Demonstration

This demonstration shows the glider flying at best L/D, then slowing to Min Sink. We then slow some more, and with the nose high we try the elevator to see if it picks the nose up any further. It doesn’t, and the result is a stall with wing drop. A simple recovery, followed by a second example showing the stick more clearly. This is recovered and a third example is seen from the outside with a smoke trail, to visualise the mush stall before the wing then drops.

You’re flying a Standard Cirrus, and the air is calm, so you’re fully in control.

Stall with wing drop

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

Get a feel for flying slowly, at say 40kts. Then ease the stick back to settle at 38 knots. Note any changes in sink, the vario sound, the sound of the air, and feel for stability. Try holding it for a while. Look out for pre-stall buffet. Hold it there if you can, before easing back a little more. Can you fly any more slowly? With practice, you can hold the nose high while sinking. A wing drop will come more easily… Recover as above. Aim to do so with the minimum of height loss. Practise lots.

The sim is a great place to practise stalls and recovery.

Further Reading and References

Gliding From Passenger to Pilot, 2nd Edition: Page 92-94

BGA Instructors’ Manual, 4th Edition: Section 5, Chapter 18 Pages 1-5 (Accelerated stalls follow on)

BGA Instructors’ Reference Cards: Ex 9a and 9b

BGA Gliding Basics