The objective of this lesson is to teach you how and why we use the trimmer in flight.
In the previous lesson (Airspeed Monitoring) we learnt that we should always “fly by attitude” appropriate to our chosen speed. During the exercise, your goal was to hold the glider at various attitudes, to achieve a variety of different speeds. You probably found that the glider was happy to settle at one of those speeds, but the more you tried to deviate from it, increasing amounts of pressure (aka stick force) were required to move and hold the stick. The same is true in real life. Step forward the Trimmer.
There are two types of trimmer, both operated by the left hand and controlled by a small lever, or knob, which moves fore and aft. If in doubt, it is the green one. The aerodynamic trimmer is linked to a moveable tab on the elevator, which moves the elevator up or down into the airflow for any given stick position. These are usually found on ‘wooden’ gliders. The spring trimmer works directly on the elevator circuit, and these are usually found on the more recent gliders. The spring trimmer may also be linked to a lever (it looks like a bicycle brake lever, mounted vertically) on the front of the stick. The effect in all cases is to eliminate the stick force at the chosen position. Hence when flying at your chosen speed, any stick force can be eliminated by adjustment of the trimmer. This makes flying less tiring, and it is much easier to apply the small control movements otherwise needed to stay in balance. For these reasons our aim is to always fly in trim. Moving the lever forwards trims the glider nose heavy. This reduces the forward pressure that you need to apply. Moving the lever backwards trims the glider tail heavy. This reduces the back pressure that you need to apply. The method of use is always the same: move the stick to achieve the required attitude, then operate the trimmer to eliminate the need for any pressure on the stick.
This is one exercise that cannot be shown very well by a pre-recorded demonstration. You have to feel the force! This demonstration is over flatlands, in calm conditions, flying a Standard Cirrus.
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
This is your opportunity to experiment with the trim control. If your simulator is linked to a glider cockpit, the trim function should be linked to the trim lever. If you are using a joystick, Condor’s Set-up gives you the option to assign the controls to your joystick or keyboard. It is recommended that you assign it to a lever type of control, so that you have infinite adjustment available within the range of movement.
In the exercise, adopt the attitude that gives you 50kts. When you’re there, hold it, and operate the trimmer to see what happens. In an ex-glider cockpit simulator, you may well find that it affects the stick force, as in real life. Using a joystick, you’re more likely to see the stick move on the screen, and for the speed to change accordingly. This is your cue to ease the pressure on the joystick, and to find the balance of moving the trimmer while you ease pressure on the stick. Small movements are best. Test your setting by letting go of the (joy)stick. In either case, when the trim is set correctly the attitude and speed will remain unchanged. And your flying will be easier.
Further Reading and References
Gliding From Passenger to Pilot, 2nd Edition: Page 46-47, 80, 85-86
BGA Instructors’ Manual, 4th Edition: Section 2, Chapter 8