Trimming

[K1200Sagian]

Help please,

I am 5 hours into a NPPL, but having major problems with trimming the 152. I am sure it is just practice, but da**ed if I can get it right.

My FI has tried to explain, every which way and he is getting as frustrated as I am.

I belive it is a common problem, but any tips appreciated.

[topcat450]

Hold it at the datum attitude....using the cowling and horizon for reference. If you can't feel if you're pushing or pulling - simply let go of the controls briefly.... what does the nose do? If the nose tends to rise you need to trim more nose down... ie wind the wheel forwards. If the nose drops you need to wind the wheel backwards.

It only requires you to momentarily let go of the wheel - just to work out what the nose of the a/c wants to do left to it's own devices.


It'll come to you - just takes a bit of practise. It's also far easier to work out on a smooth day.

[maxdrypower]

yeh man keep at it its all practice you will undoubtedly find something you cant get to grips with at some satge in your training , mine was increasing airspeed on steep turns , and I still cant get it right .
Try flying straight and level for five mins or so out of trim , once you feel like your weight training trim the aircarft you will soon know when its trimmed as you ll stop panting

[Saab Dastard]

The idea is to fly the plane at the attitude you want, then use the trim to take the load of the stick / yoke.

Be careful not to fall into the habit of flying with the trim wheel! I got into a bad habit on a Cherokee 180 that had electric trim... :O

SD

[Awesome_Welles]

Make sure your eyes are focussed on the horizon.

Remember to keep the aircraft where you want it, don't let it pitch up or down whilst trimming.

As far as which way to trim, imagine you have a cannon ball in the aircraft. If the aircraft is out of trim, where is the cannon ball? Pushing forward = heavy tail, cannon ball in the back. Pulling back = heavy nose, cannon ball in the nose.

You want to move the cannon ball into the middle of the aircraft. Using the trim wheel, move the wheel in the direction you want to 'roll' the cannon ball. You need to relate the movement of the trim wheel to the decreasing pressure on the control column. Move the cannon ball too far and you've gone too far!

Lastly, don't hold onto the controls too tightly. Flying your C152 is all about what you see out of the window and what you feel on the control column.

I hope that makes sense. I would suggest telling your instructor that you want to work on trimming, might be worth flying S+L for a while, each time the instructor giving you the aircraft out of trim at various extents, sometimes grossly out of trim, sometimes very slightly.

Please note:Don't actually put a cannon ball in your C152, goodness knows what it would do to the W&B. No cannon balls were harmed in the creation of this post.

[davidatter708]

Just practise you will end up doing it without thinking. It is very useful. I remember on my skills test when i wanted to get my sunglasses out my examiner said let go if you got it trimmed correctly itll fly itself so i did. Also when you do VOR bits to find your position you need 2 hands to use the ruler. and if you do let go remember rudder induces roll so you can fly it perfectly happily with feet.
David

[Gertrude the Wombat]

let go if you got it trimmed correctly itll fly itself
For many seconds, yes. And the entry into the eventual spiral dive is slow and gentle (as far as I've ever let it develop!) and not a problem to recover from.

[High Wing Drifter]

I found the key technique with trimming, as with any other element of aircraft control, is small adjustments. People say take the load of the stick, but the stick force is virtually imperceptible in a 152 when it is still a couple of hundred FPM away from being trimmed. Once you have a feel for getting it sorted with small adjustments, the knack will follow.

[sternone]

I also train on the C152, if you have pressure pulling stick where you have it, trim down, if you push the weel forward trim the wheel up.

Just trim the force away, most of the time it will be very very gentle, only a few centimeters if you ask me.

Basics: first put the airplane where you wan't to have it THEN trim, if you need to lower the nose a little, DO NOT trim a little down, push the stick a little forward and trim

Don't worry at all, you will be into the art of trimming in no time

[K1200Sagian]

Thank you all,

I like the idea of the cannon ball, makes sense to me...........

Got another lesson booked for thursday, will try and find a cannon ball.

Sat here and the household thinks I have been glue sniffin...............

left arm out straight with hand going up and down, and right hand working the imaginary trim wheel.

[BackPacker]

The other thing in learning to trim is to understand is what you're trimming for.

At this point, you are learning to trim for straight and level flight, which is good. As said, best check is to let go of the stick/yoke altogether and see if the aircraft maintains the proper attitude. If it doesn't, don't try to correct the trim straight away but first use the stick/yoke to regain the proper attitude, then adjust the trim again and try again.

As others have said: a properly trimmed aircraft can be flown (and is flown, actually) hands-off, where you use rudder to initiate or check a small turn. This leaves both hands, and your lap, free for charts, rulers and other navigation stuff.

But in the course of your training, eventually you may or may not have to or want to trim for other attitudes as well. For instance, are you going to trim the aircraft for a long climb (from take-off to 3500' - which is a long climb in a 152), or for a long descent, or for other attitudes? Are you going to re-trim the aircraft on downwind, and again on final?

To answer these questions, go back to the beginning. The reason for trimming an aircraft is to reduce or eliminate permanent control forces. Either with the objective to fly the aircraft hands-off, or with the objective of making your controls more sensitive. So I tend to trim the aircraft during a climb, during straight and level flight, and again for the descend & downwind. I normally do not retrim on final, unless it's some kind of precision/short field landing and I want the sensitivity in the stick. In fact, even on short final, when doing a precision landing, I try to nail the speed first, then trim the control forces out and then quickly let go to see if the trim is correct. I then fly the aircraft onto the runway with throttle alone, with maybe just a tiny bit of pressure from my thumb or index finger. But that pressure is more to anticipate the effect that an altered throttle setting has on the attitude than anything else. (Until the flare of course.)

But I'm also doing an aerobatics course right now. Before starting the aeros we trim for a fast cruise, but then leave the trim wheel alone. Slow flight, stalls, spins, inverted flight, but also 4g loops are all done by heaving on the stick without retrimming. Because the amount of force on the stick tells you to what extent you are forcing the aircraft into doing something it doesn't naturally want to do.

So eventually you're going to have to work out for yourself when to retrim and when not to. Basically, you retrim for any attitude that you will want to keep for a longer period of time, and you don't retrim for short, transient manoeuvres.

[Runaway Gun]

SELECT - HOLD - TRIM. Think of that when you do something new (like levelling out, entering a climb, or descent etc).

Select the attitude you need, Hold the force on the column, and trim (forwards if holding forwards, and vice versa).

And whenever you have more than 10 seconds and find yourself enjoying the scenery, think about trimming again :)

[IO540]

The reason for trimming an aircraft is to reduce or eliminate permanent control forces.

That's true but I would say the primary purpose of the elevator trim system is to set to aicraft angle of attack which (for a given w&b configuration) sets the speed at which it will fly.

The likely reason so many people stall and spin (and kill themselves) is because nobody told them to trim for the desired speed.

Once one discovers this little secret, flying suddenly becomes so much easier because one is no longer fighting the aeroplane. The trim sets the cruise speed, and the engine power merely controls the rate of climb/descent.

Of the 10 or so instructors I had, only one came up with this explanation. All the rest would just say the trim is to take out the elevator control force.

[effortless]

I was lucky enough to have an instructor in the dark ages who told me to practice flying using trim only. I soon got the hang of it.

[BackPacker]

The likely reason so many people stall and spin (and kill themselves) is because nobody told them to trim for the desired speed.

Yep. And they just keep heaving on the control column on final until they get into a stall. Good argument for trimming for final approach speed on final. If you are properly trimmed and nevertheless find yourself pulling back on the stick, alarm bells should be going off everywhere in your mind.

The following would be a nice exercise (at altitude and with sufficient engine power on) to become familiar with an aircraft type. Reduce speed to below flap deployment speed. Bring the aircraft in landing configuration (full flaps, gear down if relevant, prop full fine if relevant.) Now trim for the desired final approach speed as listed in the POH - but it does not matter whether you are climbing or descending at this point, so use whatever power you need to stay level. Then pull the flaps up, DO NOT retrim but let go of the controls and let the aircraft settle itself on a new speed. Remember this speed. If you fly this speed on downwind (no flaps and properly trimmed) then you don't have to retrim the aircraft while putting the flaps down. As if by magic, the aircraft will arrive at the proper speed on final. As long as you don't fight the aircraft, that is.

Now mind you that this trick will not always work, depending on the quality of the aerodynamic design of the aircraft. You might get totally unsuitable or unsafe speeds on downwind. And in fact, it might even be so that the whole situation changes with actual weight or actual center of gravity. Nevertheless, I have found that if you fly 80 knots on downwind, nil flaps in a PA-28-161, and let out the flaps, you are almost perfectly trimmed for 65 knots on final.

[Pitts2112]

All good stuff that's been posted here. I normally fly the trim and only use the stick to maneuver. And don't worry too much about not trimming the C152 exactly. I've got 100 hours in the thing and I don't think I ever managed to trim it just right. Get it as close as you can and worry about other stuff. Otherwise you can drive yourself crazy tryig to get it perfect.

Pitts2112

[homeguard]

Much debate goes into this;
Are you trimming attitude or are you trimming speed? If you trim for attitude and before the speed is stable then within a short period of time, as the speed changes, you will become out of trim. You must be at the required speed to 'fine' trim.
Also remember the fixed pitch propellor rpm varies with speed and cannot be finally set until speed is stable.
So, you must achieve the required speed and have set the correct rpm before you can then fine trim. If you do not do this you will be always be chasing your tail.
You MUST therefore know the speed to be achieved, the power (RPM) required together with the correct attitude before a successful trim can be done.
Top of climb;
1) Adopt the correct S&L attitude and maintain height with elevator.
a) Maintain balance (ball in the middle).
2) achieve the correct speed.
3) Set RPM (maintain ball in the middle)
4) TRIM ( if you allow the attitude to change while trimming then the speed will change and you will therefore trim for the wrong speed and the wrong attitude - the RPM will also have changed. If this happens then stop trimming adjust attitude to re-establish the correct speed and retrim - re-check the RPM and adjust the trim as required)

[FullyFlapped]

... and most importantly, relax ... ;)

As in life, constantly chasing the trim will bring you nothing but grief .... :eek::p

Once you've flown a particular aeroplane quite a lot, you know how it will react to changes in attitude, power, etc - and what you'll need to do to co-ordinate with these changes. That's why you will see more experienced pilots trimming almost as soon as they've changed the flight parameters - they are anticipating the aeroplane's reaction to their inputs. Comes with practice.

But at your stage of the game, I think you need to learn to wait a little ... set your attitude and power, and then wait a little to see what the aircraft does - then trim your yolk forces away. As time goes by, your anticipation skills will become honed and, as has been said, you'll be doing it in automatic mode.

But for now, put a "WAL" (wait a little) in those PAT and APT acronyms ... and relax ..... ;)

FF :ok:

[Fright Level]

I used to fly Budgies (HS748). I got so in tune with the trim that I could tell which one of the two hosties we had were walking up from the back of the cabin, the fat one or the thin one, simply by the amount of trim needed to keep the nose up when they arrived at the flight deck!

[negativeG]

but the stick force is virtually imperceptible in a 152 when it is still a couple of hundred FPM away from being trimmed

I feel exactly the same...the darn thing doesn't fight back enough for my liking:}

[K1200Sagian]

Just had two trips this afternoon,................

Getting there, using the cannon ball, rolling it up and down the plane.

Put the attitude where you want it, feel the pressure, then trim to move the cannon ball, then check...............

And, did the two takes offs on my own..................smiling from here to next week!

[sternone]

Thats great, and did you trimmed during climb-out ?

[Awesome_Welles]

I'm glad the ol' cannon ball is working. :) All the best with your training.

[K1200Sagian]

Yep, trimmed for the climb out, and did all the trimming on both sorties, and even trimmed the C152 down to downwind for finals.

Can I keep the cannon ball for a bit longer, will then pass it on to the next student who needs it?

Thank you all, still along way to go, but there has been a good steep learning curve this week.

[tmmorris]

Surely all instructors teach trimming for speed...don't they? It was part of the 'patter' for all the instructors I've flown with - 'trim for 60kts...'

Otherwise, what do you do when the engine fails? The immediate action I was taught was : trim for XXkts. Or is that shorthand for 'attitude for XXkts, then trim'?

Tim

[BackPacker]

Actually, the routine for an engine failure, how I learned it, was to trim two notches up (in a PA-28-161). That gave you roughly best glide speed (assuming trimmed for normal cruise speed), leaving you time to deal with other issues without looking at the ASI too much. Fine tuning the trim/speed was done after the other checks.

Unless you were very low of course (EFATO for instance). In that case don't worry about anything except finding a landing spot and setting up the approach.