Briefing: Turning

Introduction

Aim: You will be able to roll the glider quickly, efficiently and safely

What do we know?
  • What steps do we take when rolling the glider?
  • When will we want to ‘turn’ instead of roll?
  • What’s different about turning, compared to rolling?
Turning is different because…

It involves a higher angle of bank,…

…which changes the dynamics involved.

Increased risk of spins, and these are potentially near the ground, or in close proximity to other gliders.

Theory

Refer to RJPLancaster.net for the full lectures on the principles of glider flight (and instruments).

Short version, relating to turns:

Forces in level flight

Lift supports weight, and acts perpendicular to the airflow.

Forces in a turn

Lift is perpendicular to the wings as viewed from the front.

When banked:

  • Lift is acting sideways as well as vertically, reducing the vertical component.
  • Hence, more lift is required, to generate the additional vertical lift needed to match the weight.

As the angle of bank increases, so does the need for even more lift.

Stall speed increases in a turn

Increasing the lift will increase the Load (or G, which acts opposite to lift).

To increase the Lift at any given speed, we must increase the Angle of Attack, potentially nearing or passing the Critical AoA, at which the wing will stall.

If the AoA is already close to the Critical angle, we can can only increase Lift by increasing Speed.

More detail? Iso-Gs
More G requires more Speed or increased AoA – exploring Iso-Gs

In a nutshell, steeper turns generate more G, increasing the Stall Speed:

Fly faster in steeper turns.

Bank AngleG LoadStalling Speed
0°1G40kts
30°1.15G43kts
40°1.41G47kts
60°2G56kts
Example of how stall speed increases in steeper turns.

Video: Five minutes of stalling in steep turns where two will do.

Changing effects and usage of controls

The impact on Pitch, Roll and Yaw when using the Elevator, Aileron and Rudder:

Elevator

Controls Pitch. When steeply banked it also:

  • increases the rate of turn
  • increases the load
  • increases the stall speed

Usage: Control the pitch (and speed). In steeper turns, over 45 degrees, the elevator does not raise the nose much or at all – roll out before adjusting pitch.

Ailerons

Controls the rate of Roll. When banked the outer wing

  • is flying faster
  • generates more lift than the inner wing.

Usage: Roll in, centralise the stick to stop the bank increasing – but you may then need some ‘out of turn’ stick to hold the desired bank angle.

Rudder

Controls Yaw. When in a well banked turn, it also raises and lowers the nose, causing slips and skids.

Usage: Coordinate with aileron to keep the string central.

Slips and Skids

Note: When powered off, the Turn & Slip indicator:

  • Needle does not work
  • Ball always works – “kick the ball”
  • The string always works (unless wet)
Over-Ruddered Turns

Why is over-ruddering tempting, but dangerous?

  • Over-ruddering causes the nose to drop, which looks safe, but…
  • The inner wing has slowed down, so will be nearer the stall.
  • The temptation, to be avoided, is to raise the nose with the elevator…
  • as it could stall the inner wing, causing a Spin.

Aileron and rudder should always be used in a coordinated manner, keeping the string central.

Making a Turn

Going In

A brief transitory phase

First action: Lookout! Where?

Then look over the nose, to monitor:

  • Attitude
  • Roll rate
  • Bank
  • Yaw String

Coordinated use of aileron, rudder and elevator, using an equal movement, or pressure:

  • Aileron: Rate of Roll
    • More aileron makes it faster, and requires more rudder.
  • Rudder: To overcome Adverse Yaw
    • Keep the nose pointing into the airflow (String straight back)
    • Proportional use
  • Elevator: To control Pitch
    • Increasing back pressure
Staying In (and correcting Slip and Skid)

  • Aileron: Hold the bank angle
    • Neutral stick position
    • Possibly a little ‘out of turn’
  • Rudder: No aileron drag in this phase
    • Less rudder required
    • Monitor the Yaw String (or Ball)
  • Elevator: Maintain Pitch
    • Track the horizon (assuming it is flat!)
    • Corrections: Adjust Bank, then Pitch
  • Trim: if staying in – e.g. Thermals
  • Lookout and Scan Cycle in the turn
    • Where are the threats?
      • Thermal Turns
      • In Circuit & Final Turns
Coming Out (onto a Heading)

Also a brief transitory phase

First action: Lookout! Why? Where?

Then look over the nose, to monitor:

  • Attitude
  • Roll rate
  • Bank
  • Yaw String

Approximately 30-40 degrees early, commence roll out.

Coordinated use of aileron, rudder and elevator:

  • Aileron and Rudder: centralise as wings come level
  • Elevator: reduce back pressure
  • Trim

Coming out on a heading takes a little practise:

  • Start by commencing the roll out when pointing at a reference, and see how far you have turned when the wings are level.

Video: Turning

Recap

  • What happens to the stall speed in steeper turns?
  • Why?
  • What is the first action when turning?
  • What is next?
  • Why is an over-ruddered turn dangerous?
  • How do you prevent an over-ruddered turn?
  • How do you exit on a heading?
TEM

  • Collision: Lookout!
  • Stall / Spin: Coordinated use of controls, to keep the string straight.