Briefing: Use of the Trimmer

Introduction

Aim: You will understand why and how to make use of the trimmer.

What do we know?
  • Does anyone here use the trimmer?
  • What are the benefits?
  • And if you don’t use it, how do you cope?
Which Control is it, and Where is it?
  • Green
  • Location depends on the make of glider:
    • Left side
    • Right side
    • On the stick
  • Type of control varies: Lever, Knob, Trigger
How does it work?

Spring Trimmer:

  • GRP gliders – affects the elevator circuit, and hence the stick’s neutral position

Aerodynamic Trimmer:

  • ‘Wood’ gliders – moves a trim tab, which alters the elevator’s position, and hence the stick’s neutral position
What effect does it have?
The glider is stable in pitch

If you were to let go of the stick in level flight, the glider would settle in an attitude which balances the effects of weight, lift from the wings and the tailplane, and any trim forces. The stick would assume a ‘neutral’ position for this attitude.

Adjusting the trim moves the stick’s neutral position fore and aft.

  • So there is no stick pressure for the selected attitude (and speed).
  • Trim forward: trimmed fast
  • Trim backwards: trimmed slow
Why do we use it?
  • Continuously pulling or pushing against a stick force is tiring
  • Having no stick pressure is easier to manage than holding ‘just the right amount’
  • Less effort needed to hold a speed
  • Easier to hold an attitude in a turn
  • One less thing to do
  • Safer, especially at lower heights
How do we use it?
Illustration of Pitch Loads

It a complex situation, balancing three different pitch loads:

To increase speed, pitch down…

  • Angle of Attack is reduced – so Lift is reduced
  • Glider falls – so Speed increases
  • Lift increases again – so Centre of Pressure moves forward – which raises the nose

More forward pressure is then required to hold the same attitude.

  • The Trimmer removes this load from the stick.

The trimming method, associated with changing speed:

  • Change Attitude, Hold (Adjust), Trim, (Adjust):
    • Set the attitude for the desired speed (a guess)
    • Wait
    • Adjust attitude if necessary, for the desired speed
    • Hold this attitude
    • Trim to remove the out-of-trim load on the stick
      • Coarse setting
      • Fine tune

When do we use it?

All the time.

Whenever a speed is to be held for more than a short while:

  • Between thermals
  • On the ridge
  • In wave
  • In thermal turns
  • In circuit, notably for Approach Speed

Recap
  • What colour is the trimmer?
  • Does it affect Pitch, Roll or Yaw?
  • Why do we use it?
  • Which direction do we move it and why?
  • How does pilot weight and ballast affect it?
TEM
  • Distraction from more important tasks, such as Lookout: leave your left hand to deal with it while you carry on flying.
  • Stall / Spin: if trimmed fully back, the glider is likely to be close to the stall.