The other day, I flew night circuits in a C152 with an instructor towards my NFQ.
He would frequently remind to to trim, telling me that I don’t trim enough/not at all/making life difficult for myself.
I’m wondering if that is really the case.
It’s true that I don’t trim the C152 much in the circuit – because I don’t “feel” the need to. I find that I’d make life more difficult for myself if I focused a lot of time on the perfect trim if in a light aircraft such as this one, the control forces aren’t strong enough to initiate my own sense of “I need to trim”. Sure enough, I flew more circuits this week with a different aircraft (C172) and a different instructor, too – and here you’d obviously be more active on the trim tab as the control forces are stronger and very certainly, when I fly circuits in the C182, I’m VERY actively trimming.
I guess my question is: Does the instructor have a point or is he stuck in his “PPL training scheme” where they need to instill the very concept of trimming into their students, who mostly fly C152 anyway? I feel that after almost 4 years of flying, I have developed a sense when I need to trim and when I don’t (personally) and regard it as a bit of a flying-style kind of thing and I see nothing wrong with more or less leaving the trim tab as is during circuits with a 152 or the like.
If you are happy with some control forces while flying manually then you can trim as much (or as few) as you like. The problems start when you need to let go of your yoke for a moment, i.e. to search for a chart while flying alone, or have some distraction like talking to ATC, taking note of something or looking outside for traffic. Your aircraft will inevitably start to climb or descend because we humans are not really multi-trasking capable. And since you write that you did those patterns as preparation for night flying, where inadvertent climbs and even more descends can get unnoticed and really cause bad trouble, I can perfectly well understand your instructor for wanting you to keep your plane perfectly in trim. I would do exactly the same as him.
Once again: did you have to constantly push or pull in order to maintain your desired flight path, or not?
If not, then tell the instructor. If yes, then you should not get yourself used to that, even if the pressure is light.
It all depends on the way you fly circuits as well. If you climb out at say 75 knots, then level off and (as is sometimes done) select a very reduced power setting for the level portion of the circuit (say 2100 RPM or so), then the aircraft will fly level at just that, 75 knots, and obviously no trim is required. For descent, 75 knots works just fine, too. You might then only have to trim up a little for the final which is flown slower, at about 60-65 knots.
However, if you want to fly the level portion at “normal” cruise speed (90-95 knots, say 2300-2400 RPM), the you will have to trim, otherwise the aircraft will just want to continue to climb.
If you are anything like myself, perhaps you do not feel any reason/need for trimming because your attention is too much with other matters. On my longer flights, whenever I sufficiently relax from look-out for traffic and navigation and R/T and watching altitude and speed and what not, the first thing I realise is often that a bit of trim might make life easier.
If such be your case, I think your instructor is fighting phenomena, rather than wondering where they come from.
The airplane should be trimmed to you can fly it with two fingers of one hand and not have to exerce constant pressure one way or the other to maintain your attitude. Otherwise you are making it difficult for yourself.
Frankly it’s a question of good airmanship, and control of your aeroplane. You don’t say how many hours you have, but away from the circuit, how do you fly? If flying the 152, or any other type, how do you climb, how do you descend? How do you fly?? How do you settle in cruise config? Do you power, attitude, trim?
Answer these questions, correctly, then apply as to how you fly your circuits. It will make you a more proficient aviator.
My view, your instructor is entirely correct.
I retrim in pitch for every phase of flight. Other than in the flare on landing, it would drive me crazy to push on the stick continuously.
I think your instructor is correct. While a C152 in the pattern (circuit) may not need much/any trim, heavier airplanes to which you will progress, do. And sometimes a lot of it. It’s a good habit to form and, as what_next says, can save your life, especially at night. The trim wheel is your friend!
Trimming was not really covered in my PPL. I started on a PA38 Tomahawk whose “trim” was a crude mechanism, usually seized up due to corrosion (not to mention a litre of water in the fuel tanks, due to perished seals; the company held a charter AOC – see G-OMAR – so didn’t need to do maintenance 
) and it didn’t really do anything obvious. Later I walked out of there and finished off in a C152, which had a proper trim mechanism.
But still trimming was not taught as to what it actually does. It was taught as being a means of removing pressure from the yoke. It should have been taught as a device which controls the speed at which the plane flies, and the engine power just changes the rate of climb.
Eventually it “clicked” in my head, and the workload went down by a factor of 10x 
But as noted above if you fly at say 70kt all the time then you can trim for 70kt and never touch the trim. Just change the power (for a certain RPM) That sort of thing works until you move to something a bit quicker.
One should trim for each phase of flight, and do so more or less immediately upon entering that phase of flight, once the desired speed is reached.
Peter wrote:
One should trim for each phase of flight, and do so more or less immediately upon entering that phase of flight, once the desired speed is reached.
That’s the one little point where I envy the fly-by-wire colleagues: All they have to do is press down on the “coolie hat” trimmer button on their sidestick and the aircraft is instantly trimmed in pitch and roll.
