Trim Use During Approach Phase in Visual Patterns

[Topper Pimpi]

Hello everybody, I'd like to share with you an article I had recently posted on the IAFTP website. My thoughts are meant to be associated with light single prop training A/C. Please comments ... but don't be too cruel :}

Abstract:
Thanks to the fact that small SEPs are light, there’s no a real need for trimming all the time for every speed or flap setting. In this way the student has the chance to gain a “control/muscle memory” throughout the pattern, starting from the last time he trimmed the aircraft. He understand that now, the force he’s applying is due to the fact he is controlling the speed during the descent, managing the energy, instead of letting simply the nose down; in the same way he understand more easily how to control his rate of descent with power.
Details:
Once in downwind, memory items/flow are performed, entering slow flight condition at the required speed with the 1st notch of flaps, then a/c is trimmed to obtain a neutral feeling on the control column for that airspeed.
We are in a situation that require the a/c to cooperate with us and fly almost by itself, so we can spend a couple of seconds giving a glance to the checklist, deal with communications and stay focused on traffic avoidance, so trimming here is important.
When it’s time to turn on base, power is reduced to initiate a positive nose down tendency and base turn is started at max 20° of bank; during this maneuver the nose dipping movement is seconded applying a minimum back pressure on the elevator, this in order to obtain an initial deceleration to, lets say, 70 kts while descending.At this stage no trim is required, it’s an energy management phase therefore feeling how the airflow act on the elevator is very important, as well as maintain sensitivity over load changes.
Once on base the rate of descent is adjusted and flaps are set as required; even if 2nd notch of flaps is added no trim is really needed, as pitch changes are neglectable and flaps induced movements are absorbed with the joke while speed is kept constant, the attention is focused on final turn planning and height and energy management.
Final turn is achieved in the same way using the 20° bank and 70kt limitation, and then as soon as the a/c is stable and wings leveled, speed and flaps are set as required. Once on final trim is finally used to lighten up a little bit the loads on the elevator, but not to a neutral feeling.
Summary of Effectiveness:
In my opinion this practice help the trainees that tends to over control, and those who use too much trim in the wrong way, as it were a flight control.
Thanks to the fact that small SEPs are light, there’s no a real need for trimming all the time for every speed or flap setting. In this way the student has the chance to gain a “control/muscle memory” throughout the pattern, starting from the last time he trimmed the aircraft. He understand that now, the force he’s applying is due to the fact he is controlling the speed during the descent, managing the energy, instead of letting simply the nose down; in the same way he understand more easily how to control his rate of descent with power.
At the same time this help in dealing with go-arounds especially unexpected ones, where an excess of nose-up trim associated with flaps at slow speeds, can produce unhealthy climbing attitudes if power is suddenly applied; this is maybe not a problem for a seasoned pilot, but can be scary and hard to manage for a beginner.In addition, to give precise and simple parameters to comply with ( max bank, min airspeed) and avoid messing with the trim, will help in achieving a better initial stick&throttle feeling, while keeping him in a safe speed/attitude envelope.

[Piper.Classique]

Thank you for sharing your thoughts on this. I think I see what you are trying to say, but I am somewhat confused by

Once on base the rate of descent is adjusted and flaps are set as required; even if 2nd notch of flaps is added no trim is really needed, as pitch changes are neglectable and flaps induced movements are absorbed with the joke while speed is kept constant, the attention is focused on final turn planning and height and energy management.

Do you mean to say negligeable rather than neglectable? If so it makes more sense even if I think you are mistaken. The amount of pitch change is rather type specific, what are you using as an example? And I suppose joke is a typo for yoke?

I suspect most early students will be forgetting about the trim anyway, rather than conciously not trimming, maybe we should just let it happen? :)

[foxmoth]

IMHO this will not work well, if the aircraft is out of trim students are far more likely to allow the aircraft to trend towards its out of trim attitude and ends up with more problems.
Actually, what you are suggesting seems to be how many students ( and even some PPLs) fly the aircraft until they learn to trim properly and they struggle for exactly the reason that they ARE out of trim.

[Squawk_code]

My two pence...

I found that the practice of course trimming initially to remove the pressure on the elevator to maintain the attitude, followed by a fine trim to correct for small changes in attitude, worked well. By doing it this way, the student will have at least got the aircraft more or less trimmed to an acceptable level prior to the fine trim taking place. I found that some students got predicated on the need to trim (overly) accurately in the approach attitude and especially at the early stages meant that airmanship, circuit planning , speed/attitude control went out the window as the work load increased. I'd personally prefer someone to be slightly out of trim but fly a safe and accurate circuit than get fixated on trimming and let the fore mentioned go out the DV panel!

[Topper Pimpi]

For Piper Classique, thank you.

Those thoughts are referred to a light SEP training a/c, like a C150/C152, I'm sorry about my "Itanglish" but difference between neglectable and negligeable is not very clear for me at the moment (I'll do some research now :-) ).
What I meant was that, passing from flap1 to flap2, pich changes are small and considered
that we are slow and descending with a nose down attitude, this changes are hardly
visualized and sensed by the pilot. So, once the pilot knows about the effects that flap
produce on that particular a/c (nose up or down moment), he will compensate for it
using the yoke (thanks again) but without acting on the trim. The pilot will rather
concentrate on mantaining the required speed and descent slope.

For Foxmoth

Well, the a/c is not really out of trim, the a/c is trimmed for a speed, lets say 75 kts on
downwind. On downwind the a/c is trimmed at that particular airspeed in order to
mantain level flight, so you can do all your stuff etc... yes, in downwind I need a nicely
trimmed airplane. When turning on base power is reduced, a/c will naturally put the nose
down looking for that 75 kts he wants, here the pilot stop the nose drop just by means
of the elevator in order to obtain a lower airspeed, lets say 70 kts.
The difference is just 5 kts, not very much out of trim. In this way, using a little muscle, the pilot will have immediately a better understanding on what is going on about lift and gravity, about energy balance while trading altitude for speed and, most important, load factor.

Thank you again for your comments

[mad_jock]

I disagree with letting the sods ever fly out of trim.

They should be taught what attitude they should be holding for every configuration change and power setting.

Then trim after the aircraft has settled.

Once its in trim they can then have the over controlling habit beaten out of them.

Use what you like one hand on the power and one hand on the stick if they still have to firm a grip stick a pencil across there fingers so they can only grip with there middle finger.

The trick is not to let them wander with the attitudes even in transition periods they should be holding a attitude and not just letting the nose pick its own.

TO/climb thats your attitude.

Down wind thats your attitude

Base thats you attitude

Approach thats your attitude

Go-around thats your attitude

All done and practised away from the circuit. The only thing you should be teaching in the circuit is the last 10 ft.

If you teach them right they should be able to do it with no instruments at all and the speeds etc will be bang on the numbers.

[pulse1]

Another factor which should be considered when trimming on final approach is the possible need for a go around. Having an out of trim a/c is not very helpful when you are close to the ground and trying to reconfigure for best climb, reducing flap and trying to stay on the centre line in a Xwind. On the other hand, if a student is used to having an out of trim a/c it may be less of a problem.

[mad_jock]

On the other hand, if a student is used to having an out of trim a/c it may be less of a problem.

So your going to train them to fly in a manner which encourages unstable approaches and increases the chance of a go-around so that they are used to flying in a configuration which is not normal.

Instead of teaching them set that power, nail that attitude reconfigure while maintain that attitude and trim as required.

Its no wonder trimming an aircraft seems to be a forgotten art these days.

[Duchess_Driver]

...all the time, for every config change, wherever you are. So much easier in the end.

If they can't trim the aeroplane by this stage, take them back out of the circuit and do some more exercise 4!

My 2p.

DD

[Sillert,V.I.]

Personally I detest flying out-of-trim & think this is a bad idea for the reasons expounded by MJ & others. I'd have thought at the circuit bashing stage it would just make it that much harder for the student to nail attitude/airspeed & flying with neutral stick/yoke force down to the flare just seems to me to be the right way of doing things.

On the occasions I've flown gliders I've found most BGC instructors teach flying the last part of the approach 'out-of-trim'; this feels unnatural to me (as does speeding up for the approach!) & if I don't retrim I really have to concentrate to prevent the airspeed bleeding off on short final.

In addition, learning to feed in some forward pressure (and hopefully a bit of rudder correction too) when advancing the throttle for the go-around will engender good habits in students that will help prevent nasty incidents if they ever transition to more powerful types.

And on a tapered wing PA-28, the trim change that accompanies the first stage of flap extension/retraction would make this decidedly uncomfortable.

[Piper.Classique]

The trick is not to let them wander with the attitudes even in transition periods they should be holding a attitude and not just letting the nose pick its own.

Of course. This I think is where the OP has a point about muscle memory.

On the occasions I've flown gliders I've found most BGC instructors teach flying the last part of the approach 'out-of-trim'; this feels unnatural to me (as does speeding up for the approach!) & if I don't retrim I really have to concentrate to prevent the airspeed bleeding off on short final

Well, this ITP doesn't teach approach out of trim. But the approach speed is usually higher than thermalling speed.


All done and practised away from the circuit. The only thing you should be teaching in the circuit is the last 10 ft.

Halleleuja!

Absolutely!

For the OP neglectable means you can forget about it, it isn't important. Negligeable means it is small, which is not the same as not important.

On a go around the out of trim forces can be large.....so you do need to be able to hold an attitude despite the best or worst efforts of the aircraft.

Type specific comes in here. Rallye, super cub, spring to mind.

Interesting thread which links to the question of things we could teach better

[Big Pistons Forever]

I am totally with MJ on this issue. The most important skill required to fly a proper circuit and landing is to by looking out the window be able to set thr correct attitude for what ever you want the aircraft to do. If the student goes immediately to the right attitude and holds it, an out of trim condition will be obvious and they can apply a bit of grim in the appropriate direction.

I see a continuing widespread problem in flight training with students going to the circuit before they have truly mastered ex 5 to 9. That IMO is invariably the root cause of students who are not progressing in the circuit.

Finally the last thing I do before starting in the circuit is to at altitude, have the student practice the 4 legs of the circuit in the practice area. This gets them used to the rhythm of the circuit, reinforces attitude and speed control but without the pressure of landing and since each final will, of course, end with an overshoot in this exercise it reinforces this often neglected part of circuit training.

[sevenstrokeroll]

Throughout the pattern the student or any pilot should have the aircraft in proper trim (elevator/stab). One should be able to release the controls having the plane maintain speed and attitude.

I allow a bank up to 30 degrees from downwind to base and 15 degrees from base to final.

Once the plane is in trim on final, no application of trim to make the flare should be done...here is where the muscles can actually feedback speed info to the pilot...the heavier the yoke the slower you are going towards touchdown speed (vref minus 5 or so...down to a full stall landing).

Trimming into the flare might give you a grease job once in awhile but you are not ''feeling'' the speed as outlined above. This is for all planes, not just small GA stuff.

and Gosh I hate the C150/52. Much prefer piper cherokees and even the tomahawk. Better visiblity!

[Ascend Charlie]

On the crew room wall at 1FTS at Point Cook were the words:


TRIM OR FAIL

[BEagle]

Topper Pimpi, please do the world a favour and stop teaching such utter rubbish!

[DB6]

The sooner a pilot learns to:
1) select and maintain a visual attitude
2) accurately trim to maintain that attitude (and retrim for every power, configuration and speed change)
3) maintain a good lookout while doing the above,
the sooner you can start teaching them to fly.
Essential building blocks, not to be modified according to whether you are in the circuit or not. Topper, you are describing how to thoroughly confuse a student, not teach them!

[foxmoth]

I think Beagles post says all that needs saying really :D- I was trying to be too polite!

[Whopity]

I wondered how some schools were managing a 4 day FI Course, now we know!

[Piper.Classique]

Come on, people. The OP, who is not a native english speaker, has at least done some thinking about what he is trying to achieve, which is a pilot who has some feel for the aeroplane.
He doesn't suggest not teaching correct trim, or at least I don't think this is what he is advocating. As far as I can interpret his post, and I agree it is not entirely clear, he is saying that he does not advocate trimming out a transient load, and is emphasizing the need to be able to hold a required attitude.

Sevenstrokeroll says it better...

Once the plane is in trim on final, no application of trim to make the flare should be done...here is where the muscles can actually feedback speed info to the pilot...the heavier the yoke the slower you are going towards
touchdown speed (vref minus 5 or so...down to a full stall landing).I certainly take issue with

When turning on base power is reduced, a/c will naturally put the nose
down looking for that 75 kts he wants, here the pilot stop the nose drop just by means
of the elevator in order to obtain a lower airspeed, lets say 70 kts.If he means that is the last time he expects the trim to be used, which would imply nose heavy on base leg and final approach. Or is he trying to say trim after the turn from downwind to base? As the base leg and the final approach are not transient phases, yes of course the aircraft should be trimmed correctly. As indeed it should for all steady states. But once the attitude and power are set on final or anywhere else would you expect a retrim for every gust?

I don't think we need to be rude to each other here, there is enough of that elsewhere on the forums.

I wondered how some schools were managing a 4 day FI Course, now we know!Seriously, Whopity? Four days? Please name and shame!

[ShyTorque]

I was always taught (and in turn taught others) to trim any aircraft properly, at all times.

If a pilot is taught to routinely fly the aircraft out of trim, at any stage of flight, it seems obvious to me what might go wrong. Especially on final approach to an unfamiliar airfield in poor visibility, where some of the pilot's attention might get diverted away from the proper priority of poling the aircraft. If you're not flying the aircraft, it will fly you. You know where I'm going with this....

[Whopity]

Seriously, Whopity? Four days? Please name and shame!It appears the CAA issued a FI Certificate on the basis of a FI course conducted at a Spanish FTO in 4 days! There are not enough hours in 4 days to match the course hours requirement!

[Topper Pimpi]

WoW, I'd never expected such response to this post, I'm receiving so many
suggestions that I can only thank you all for this, even if there is someone a little too rough in his comments ;-) I want to thank especially Piper.Classique, sevenstrokeroll, Big Pistons Forever and mad_jock, which are helping me to understand even myself :-D and are trying to be constructive.

I know the importance of mantain the right attitude for every phase of flight, and the importance of a correct use of (elevator) trim tab to obtain this. Teaching to my students what the trim wheel is for is very important to me, to trim for an airspeed, an attitude or for just relieve the force on the yoke.

In the past I came across some pilots who made me concerned about this matter: some of them where used to really overtrim (nose up, slow speed), so when it happened we had to go-around on base or final, the nose was so light that he struggled visibly completing the maneuver . Another one was an abituè of overshooting the final, so he was fine with doing steep turns at low speed to regain the centerline, using too much rudder and messing up with the ailerons. Thats why I came up with those mumblings over handling sensitivity and use of trim and so on... thoughts wich are meant for the initial phase of the circuit pattern training: after having demonstrated all the primary and secondary controls effects, climb and descents, slow flight and stall, in this phase I try to make them mix everything to perform a pattern safely as part of a teaching strategy.

When it comes the time to hit the pattern, I think it's useful if the student learn how to do it with stic and throttle, whit just little help from the trim: learning how to mantain that descent angle and that speed mixing pitch and power by his own, can definitely help in my opinion, when he will use the trim on heavier planes (or autotrim, autopilot maybe in the future), being more aware of what is going on under his hands. So, if we have the a/c fine trimmed for a downwind speed and then we start the approach reducing power, we just make the a/c have a healthy nose down tendency, wich is nice to understand energy management in the pattern, here the pilot will act to obtain the right speed and the right descent angle.

Again, this isn't done with a complete out of trim a/c, but just the amount to keep on the hands of the students the responsability of the landing, and just until necessary. Nobody here is teaching to land with an a/c trimmed for a dive as well nobody should stress too much about trimming to a complete neutral control feeling in approach, at least on a vfr approach! Training aircraft are built to naturally lower the nose when short on energy, even the full automated airbus leaves to the pilot the job of round up the descent, level off and flare. Overtrimming on base or final, at low speed/high AOA and low altitude, can turn out to be more dangerous than the opposite I think.
About go around, the priorities are stop the descent, increase speed and then climb. Stop losing altitude/energy should be an instinctive all-in-one maneuver of level flight attitude+full power; if to do it I have to keep the nose down in order to regain energy because of a nose-up over-trimmed a/c, well it's everything but instinctive.

To conclude, if in vfr patterns the most important thing is to look out, basically I want make them learn how to keep the correct attitude just with external references, keeping rwy and aiming point under control while cross-checking the airspeed, this until the pilot freezes the big picture in his mind. After that, in my opinion, is far more easyer to show how with that specific picture/power setting we can obtain safe approaches even without airspeed indication, or how to fixate that particular attitude on the artificial horizon to obtain the same performance when visual conditions are poor, etc... Again sorry about my non-native english, I'm just trying to do my best, maybe everything it's just mental mastubation. I'm not trying to reinvent anything cause nothing more new can be invented about flight, that's just an effort to find my way in it, for sure I miss a standardization course :ugh:.
Thanks for your comments.

[mad_jock]

Forget about anything big when you are doing intial training. Any changes in flying style are dealt with in type ratings and line training.

Your only job is to teach people how to fly single engine piston aircraft properly.

And all the points you have been making arn't for the circuit they should have been taught and practised well away from the circuit. Hitting the pattern maybe something you strive to do as quickly as possible but it is counter productive and you just spend hours hammering out circuits with the student working at the max never quite getting in front of the aircraft which reduces thier learning rate. The reason why people over control and do daft things is because they are completely maxed out with no time to think. They react and because they don't have the previous exercises understood and hardwired in yet their reaction is the wrong one. If they know what they are doing and have spare capacity they see situations before they need aggressive control inputs to recover and there isn't a problem. The plane does the flying and the work load is decreased.

The only time you don't want the student trimming all the time is in the flare, below Vs+20 during stalling and the verdict is out on trimming during steep turns mainly because some people don'y have the brut force to do it without trimming a little bit.

I work as a line trainer on a manual turboprop I have to spend rather alot of time with new FO's and some of the more experenced ones teaching them how to trim properly and how to let the aircraft do the flying. I must admit a few years ago thought maybe I was a bit long in the tooth and away from regular instructing to comment on threads like these. But then I realised hang on here I am teaching new FO's the basics every day. Some of them arrive thinking you trim for a flight level not an airspeed. Secondary effects of controls is a mystery. And the power levers are up and down like a fiddlers elbow and approaches are completed inspite of the pilots inputs not because of them. The only way to tackle this is at the grass roots level of intial flight training.

And one of the big problems is people training for the future using pesudo airline ops and techniques. In the main the instructor thinks this is the way things are done in airlines when it isn't and also the student doesn't have the correct foundations to build the next step onto which they will be taught when it comes to actually flying that particular hardware. If they don't have the foundations there when the poo really hits the fan eg Buffalow or AF477 they don't have anything to go back to.

[Big Pistons Forever]

I second everything MJ says. For ab initio I teach 500 feet AGL to the flare should be the same for every landing. Therefore the first thing they want to work on is getting the aircraft to the 500 foot spot on speed, trimmed, lined up with the centreline and at a point back from the runway to give the correct flight path. If the aircraft is not in good shape at the 500 foot point we go around as if they were not able to stay ahead of the aircraft to this point it will not get better the closer we get.

Also working on getting a consistent stabilized approach first, makes teaching the flare and hold off much easier.

Towards the end of my time as a full time instructor I got all the problem and not progressing students. If the student was stuck in the circuit the first thing I did was go to the practice area and re teach Attitudes and Movements. Invariably the problem was the fact that their instructor had rushed though the foundation ex 5 to 9 and the student did not understand the basics of aircraft control.......

[Piper.Classique]

I think that says it all, Big Pistons. No point whatever trying to fly circuits when the student is already working full time at basic handling.

Instructor's best friend, a packet of post-its to cover instruments......

[sevenstrokeroll]

teaching the circuit/pattern...

in a modern circuit/pattern, there is actually littletime on final...the most important part if you ask me

so, why not take your student to a place where final can be five miles long and DO trim so that you can let go of the controls and still have your vref maintained at the proper rate of descent.

practicing ground reference maneuvers like turn about apoint and rectangular course over the ground is important

but the real aid in landing is ''slow flight'' or flight at minimum controllable airspeed.

you can't learn how to land in the few seconds of final in an average traffic pattern.

also...have the student fly a low pass over the runway at a few feet, not touching down...(full landing configuration) and then without warning, reduce the throttle and they will end up with the niceest touchdown you can imagine

(use a good long runway for this)

[KAG]

Always trim.
However as an instructor it's not bad to simulate a trim failure from time to time.