This lesson demonstrates that spins and spirals are difficult to demonstrate – you never know quite what you’re going to get. It is important to recognise which one you are dealing with so that you can recover quickly – one key thing they have in common is the rapid consumption of height.
Spins and spiral dives tend to result from erroneous use of the rudder and/or ailerons during an uncoordinated turn – notably the under-banked, over-ruddered variety. They are a real problem if you’re near the ground at the time, as is often the case in a Final Turn, or a recovery from a winch launch. Gusty conditions can contribute, as can being out of practise for a field landing. The initial symptom is that one wing becomes stalled, drops, increases its angle of attack and so the problem compounds. Different gliders are more or less prone to spin. Some are benign, others bite. Get to know your glider! A glider that doesn’t spin will enter a spiral dive, bypassing the spin stage. Whilst training, the Puchacz and K13s will spin, whereas K21s rarely do. In any case, you’re most likely to be pointing at the ground, going round in circles quite quickly. In some countries they are considered so dangerous that they are not practised. Given they can occur unexpectedly, it is as well to recognise and recover from them instinctively, and even better to learn to avoid them.
Symptoms of a Spin
Whilst spinning, one or more wings are stalled. This may not be obvious, but it affects the recovery. You will see:
- Nose down (mostly), with rapid rotation.
- The rate of rotation and pitch attitude may vary greatly if the spin is unstable.
- Airspeed may be low, and/or flickering.
- The rate of descent is very high: “30+kts Down” in the image above.
- No increase in G.
- Controls may be unresponsive (the glider is stalled whilst spinning…).
All modern gliders are designed to recover from a spin with a specific set of control inputs. Behaviour will still depend on loading, C of G, contamination of the wings, and the like, so read the glider’s Flight Manual. It may be normal to have to hold the inputs for a couple of turns before recovery occurs. Hence the need to know the glider.
- Apply Full Opposite Rudder.
- Centralise the Ailerons.
- Move the stick progressively and centrally forwards until the rotation stops.
- Centralise the rudder when rotation stops.
- Recover from the dive, before speed builds significantly.
Symptoms of a Spiral Dive
Whereas in the Spin, where one or more wings are stalled, in the Spiral Dive the glider is “flying” and will respond to the controls.
- Speed increases rapidly, but may stabilise (fast).
- The nose will be down.
- G-force sensations increase if the stick is moved or held back.
- Controls are heavy due to the speed, but are responsive.
Recovery can be summarised as “fly out of it”. To be precise:
- Make a coordinated turn to bring the wings level.
- Ease back on the elevator to come out of the dive, regain some height, and level out before stalling.
- When recovering, be aware of the airspeed limits, initially as you approach Max Rough Air speed – use the controls gently.
Scenario and Demonstration
This demonstration shows the glider in level flight, slowing until little faster than the stall speed. Then we attempt a turn with a bit too much rudder, resulting in a spin, with pitch attitude, sink and speed changing markedly. After recovering, we make another over-ruddered turn close to the stall, resulting in a spiral dive: steady nose down attitude and increasing speed until it stabilises close to Max Rough Air speed. We recover and have another go – notice how quickly we can lose 1,000 feet.
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 make an over-ruddered turn or two to see what happens. In the demonstration, the controls were held for quite some time to see what developed. Recovery is rapid if you respond to the stall and wing drop quickly.
You’re flying a Blanik. They stall a little more slowly, around 34kts, and will spin.
The sim is a great place to practise these exercises.
Further Reading and References
Gliding From Passenger to Pilot, 2nd Edition: Page 95-97
BGA Instructors’ Manual, 4th Edition: Section 5, Chapter 19
BGA Instructors’ Reference Cards: Ex 10a