A few years ago a colleague of mine, a very experienced instructor/examiner asked me to fly with a friend of his with whom he shared a Cessna 210. His friend had been making awful landings, either coming down hard or touching down and bouncing. It was worse in a crosswind where he was making no rudder corrections to speak of. We flew and I observed first circuit and landing. On runway 26 there was a slight crosswind from the right. We touched down to the left of the centre line, bounced and went around. On the second approach I asked for control on final at about 250 feet. Straight away. The aircraft was not trimmed. I trimmed it and handed control back to him (which took all a few seconds). There followed a textbook landing, followed by two or three more, now with good trimming; problem solved. Because the aircraft was not trimmed, he was concentrating too much on keeping a steady trajectory, having to use constant input and didn’t have any capacity remaining. Once the airplane was trimmed however, the inputs he needed were smaller, lighter to the touch and didn’t require as much concentration.
All light aircraft I can think of have at least an elevator trim tab of some sort, and that is what I want to look at in this issue. It might be a servo tab on the elevator of a Cessna, or an anti-servo on the stabilator of a PA28. Whatever type of tab it is, it does the same thing. It sets the aircraft on a stable course and by staying on that course gives the pilot a capacity for other physical or mental tasks.
I can drive a student mad with incessant “are you trimmed?” questioning. Every time they change power setting or configuration, they learn that I am about to ask, “are you trimmed?” I randomly take control and if the nose goes up or down, I ask “why has the nose gone up? or down?”. I’m not actually that annoying and it is done with humor, but it gets the point across.
If you are at an early stage in your PPL, you should have started practicing trimming the aircraft. I start showing the use of trim on the very first lesson, if only to introduce the student to the idea of setting the aircraft on a stable course without having a constant input. I like to put the plane out of trim and challenge the student to maintain a stable nose attitude for a while. Then let them try the same thing with a well-trimmed plane. Recognising small changes in nose attitude can also be a challenge, and once these can be recognised, putting the nose back where it was is also a good exercise to start right from the beginning.
The first thing that has to be done before attempting to trim the plane is to understand that you are trimming for a stable configuration (a constant velocity). It can be straight and level, climbing or descending, base leg or final. By ‘stable’ I mean that the aircraft is not accelerating or decelerating. Being trimmed means that you can take your hands away from the control column and notwithstanding turbulence, the nose will stay where it is.
Trimming correctly for straight and level consists of making sure you have a stable nose attitude; if you are levelling off from a climb, choose your nose attitude, allow the airplane to accelerate then set the power you want. Then trim. Fly with a light touch (hold the column with three fingers, avoid the chicken strangling grip), release any pressure on the control column and watch the nose attitude. If the nose goes up (which it will when levelling off), put it back where it was as soon as you notice the change. Don’t watch the horizon while the nose attitude changes to the point the aircraft slows down and climbs. Put the nose back to where it was, then trim the aircraft so that when you release the control column again, there is no change in nose attitude. In this example the nose went up when the control column was released. In order to maintain straight and level a forward pressure was needed. Forward trim of the wheel is needed until the nose stays where it is on its own. The same principle applies to trimming for any configuration of power or flap. In short, for any configuration, once you have the power setting required, a stable nose attitude and speed, then you can trim.
Let’s say you are going to commence a climb at 80kts from straight and level at 100kts. In this instance you should apply full power first (with rudder), then choose a sensible nose attitude for the climb, hold it and then trim. Until you are more experienced it is a good idea to do this without looking at the ASI. Once you are trimmed, if you then look at the speed and find you are doing 85kts, simply raise the nose a touch more and re-trim back. Or if you are too slow, lower the nose a touch and re-trim forwards. Using this method, you should find the correct trim within two attempts. Try not to stare to at the ASI. Your attention should be on the horizon, then a quick glance, a snapshot of the speed is all you need.
A common error is trimming too soon or too late which leads to chasing the trim. Let me illustrate this by exaggerating what happens. Going back to levelling at a certain altitude from a climb. The first error is to lower the nose for the straight and level attitude, then almost immediately reduce the power and trim. You feel the control column and you think “Job done!”. But you didn’t give the plane enough time to accelerate, so what is happening now is the plane continues accelerating and the RPM will also increase. You have trimmed at about 85-95kts, and that is the speed the plane now wants to fly at. So the nose attitude starts to slowly rise as the speed and RPM increases, and you only notice this after maybe 100/200 feet or a glance at the VSI. So, you have to descend. You lower the nose. During the descent the aircraft accelerate to say 105kts. You get to your 2000ft, raise the nose, power seems fine and you trim. Job done! But now plane is going too fast, and as you trimmed at around 100kts, that is the speed it wants to do, so down goes the nose as aircraft slows and the RPM decreases. It might be another 100/200 feet of descent before you notice it (don’t worry you WILL do this a couple of times until it ‘clicks’). Dohhhhh! So, you need to climb again; up goes the nose, she slows down (unless you add a bit of power), you get to the correct height, nose to straight and level, power okay, trim. But the plane is still accelerating so——————————- enough. I would not let a student get into this never-ending wave. It is interesting how it can happen to PPL holders after not flying with for a while. It is one of the ‘habits’ people tend towards and I have watched it happening for a good 10 to 15 minutes before pointing it out.
Another erroneous use of the trim wheel is to use it not for relieving control pressure but for applying it. Trim should only be used following a change of pitch, power or configuration (gear or flap changes), not to make the pitch changes.
So, to practice trimming properly, understand what you are doing and why. Not trimming properly is like having a car that pulls to the left or right the whole time. It is a distraction. Trimming is like a good cruise control. It relieves control column pressure and allows you to fly with a light touch. In turbulence a well-trimmed plane means it is easier to notice updrafts and downdrafts. Trimming in turbulence is a matter of practice, and you will get there as long as you understand and can trim correctly on a smooth day.
Finally, on electric trim. Personally, I don’t like it for inexperienced pilots. It is too easy to be distracted while you trim and keep the pressure on the toggle. During a turn on to final it can be fatal. If you do like the electric trimmer and use it regularly, make sure you know how to pull the circuit breaker in a hurry. Also, try to use it only for large adjustments in trim, and then use the wheel for finer changes. This is because unless you use the electric trim a lot and are very used to it, you really don’t know how fast it is trimming for you, and it is easy to over-trim, and end up chasing it again.