Briefing: Spins & Spirals

Introduction

Aim: You will:

  • recognise when spins can occur
  • recognise a spin’s characteristics
  • learn and apply the correct recovery action with the minimum loss of height
  • avoid inadvertent spins by developing safe flying habits
  • recognise the difference between the spin and spiral dive, and apply the correct recovery action
What do we know?

So, you can see a lot of green, not much blue, and the world is going round…

How would you feel in this unusual attitude? What would you do? Look at the string, vario and ASI!
  • How might a glider get into a spin or spiral dive?
  • Why are we bothered?
  • What would you do?
A little Theory

What is a Spin?
  • A spin is “a stall with autorotation“
  • The autorotation can be in all three axis
  • “Autorotation” indicates a steady state

How do Spins occur (in gliding)?

A Spin develops from a Stall with Yaw. Autorotation follows.

  • A wing will stall, then drop, and hence become more stalled, with more drag, increasing the yaw.
  • The upgoing wing will have decreasing drag.
  • The rotation accelerates, leading to autorotation.
The most common situations where they occur
  • Over-Ruddered Turn
  • Final Turn
  • Thermal Turn
  • Turn in a Winch Launch Fail Recovery
  • Misuse of ailerons

What is a Spiral Dive?

A spiral dive is “a steeply descending turn”

A spiral dive can result from:

  • allowing the nose to drop when entering a turn
  • a partially recovered spin, when the glider unstalls
Why differentiate?

Recovery actions differ

Recognition

Spin
Spiral Dive
Recovery

Spin

Spin Recovery:

  • Establish Direction of Rotation.
  • Full Opposite Rudder
  • Centralise Ailerons
  • Ease Stick progressively forwards, until the rotation stops.
  • Centralise Rudder when the rotation stops.
  • Ease out of dive, to normal attitude
Rudder: why fully opposite?
  • That is the design criteria!
  • Reduces Yaw
  • Helps to pitch the nose down.
  • Airflow at speed will make this feel (very) heavy.
Stick: why centrally?

To remove differential drag from the ailerons

Stick: why ease?
  • To avoid a steep dive.
  • Minimise height loss.
Stick: why forward?

To unstall the wings.

Spiral Dive

Spiral Dive Recovery:

  • Level the wings with a coordinated roll
  • Ease out of the dive
The importance of knowing the difference
  • Recovery differs
  • One won’t work in the wrong situation
  • The other is dangerous if used incorrectly
Speed may build rapidly during a spiral dive
  • Max Manoeuvring Speed is easily exceeded
    • Take recovery action immediately
  • Take care with control usage:
    • One control at a time,
    • used cautiously…
    • One control may be used up to full deflection, on its own – usually the elevator.
Use of Airbrakes

Do not use the Airbrakes:

  • Opening the airbrakes will reduce the acceptable loads:
    • From 5.3G to 3.5G
    • Weakening the wings in the centre section
  • Accept the G and pull hard, without exceeding the range of control usage permitted

Four minutes of spins and spiral dives. Which is which?
Play, then press [f] to view in Full Screen
Prevention

Always keep the String central – especially when turning.

The Scan Cycle: Lookout, Attitude, Instruments (String).

Factors that may encourage a spin

Aside from those which will initiate a stall (such as contamination, or gusts, etc), some are implicated in the occurrence of spins:

Centre of Gravity

  • A rearwards CoG increases the tendency to spin, and makes recovery harder.
  • Light pilots: read the placard – use ballast.
  • May be glider-specific: Refer to the Flight Manual.
  • BGA advice is for early solo pilots, and pilots new to type:
    • to fly at least 15Kg above the placarded minimum weight.
Pilot Error
  • Distraction
    • e.g. A busy thermal
  • Inattention
    • e.g. Looking elsewhere instead of over the nose during the final turn.
Flaps
  • Flaps change the stall speed.
  • Spin characteristics may be affected: Read the Flight Manual
  • Neutral setting is probably required for recovery, and to avoid a subsequent stall!

Further Spinning
An exploration of circumstances in which spins occur

Changing effect of Rudder at the Stall

  • The secondary effect of rudder is more pronounced near the stall:
    • causing a sudden wing drop.
Steep, or Thermal Turn

  • The glider will spin well above the normal stall speed (for the angle of bank) if the controls are not coordinated e.g.:
    • Steeply banked – perhaps when working a tight thermal,
    • Excess rudder,
    • Excess elevator to hold the nose up – which may be happening as a result of pulling up into a thermal from a high speed inter-thermal cruise.
In a normal Approach Attitude, following a winch launch failure

  • During the recovery push-over, the glider will briefly be in the Approach Attitude. If the glider is held in this attitude, rather than continuing to a more nose-down attitude, it will be:
    • at less than 1G, and
    • below the normal flying speed.
  • It may be flying like this at that moment, but… 1G will return.

If in this configuration:

  • the stick is held back (to return to the normal attitude), the glider will mush stall.
  • a turn is commenced, a wing will drop and the glider is likely to spin.
Spin to the opposite direction of the intended turn
e.g. Spin Left off a Right Turn

  • If a wing drops during a turn, and Full Opposite Rudder is applied before a spin develops, it may cause a Spin in the opposite direction.
Recap
  • Which gliders can spin?
  • How does a glider spin?
  • How do you recognise a spin?
  • How do you recognise a spiral dive?
  • What is the recovery technique for a spin?
  • How do you prevent a spin?
TEM
  • Loss of height
  • Risk of over-stressing the aircraft during recovery
  • Collision
  • Loss of control

Prevention

  • Scan Cycle
  • Standard Recovery
  • HASSLL

When will you jump?

  • 2,000′