Trim on final & bad habbits

[tomahawk1673]

The other day, I decided to trim on final, thinking it would make landing a little easier, and less exhaustive (C172). It worked too!!

However, my instructor did not teach me this... is this good practice, or one of these bad habbits I've heard him talk about.

Talking of bad habbits, what are common ones people get after gaining their PPL?

[essouira]

I'm interested in this one. If you've trimmed on base leg for your approach speed, why would you need to re-trim on finals.

[ShyTorque]

Depends on aircraft type. If you're using full flap, you may need to retrim on finals after it's selection.

If the aircraft isn't in trim, then the landing is hardly going to be easy. It needs to be done promptly and positively however; on final you need HOTAS as much as possible and should be looking outside.

[Whirlybird]

I was quite definitely taught to trim on final.

[englishal]

Some aircraft POH's recommend trimming on final. For example the Seneca II POH recommends that 'three turns of nose up trim on final will help achieve the proper flare' or words to that affect. Works too. Not so important for a simple single, but on a complex like the Seneca, when you retard the throttles, the props act like big air brakes and the nose tends to get quite heavy....


Cheers
EA:)

[javelin]

If you relax your already light hold on the stick/yoke and there is any residual force or the aircraft changes pitch - trim. You can't hold anything steady if you are out of trim. This is as important on a Cub as well as a 757. Airbus however, select pitch, pause, relax - Aaaaaaargh :D

[QDMQDMQDM]

However, my instructor did not teach me this... is this good practice, or one of these bad habbits I've heard him talk about.

There are many ways to skin a cat and fly an aeroplane, as a quick perusal of this forum will reveal!

It's tricky in training because you have to follow a single set of guidance fairly rigidly, otherwise you get in a pickle. Once you get your licence though it's worth flying with a number of different people and generally figuring out what works best for you. Eventually, you'll find a style which suits you and which you'll then develop. As long as you're safe, don't sweat minor issues like this one. I can't for the life of me see what's wrong with trimming on final. ;)

QDM

[FormationFlyer]

Hi all,

Yes I teach my students to trim on final approach - I do to - probably down to 200' I will trim...

Why need to trim on final approach? Because

1. You may change the aircraft configuration - u/c or flaps

2. if you alter the throttle one iota you need a trim change

3. approach speed and threshold speed are unlikely to be the same.....if you fly threshold speed on base you are endangering yourself...so a change in airspeed results in a change in trim.

4. if you change the attitude on the final approach its best to trim - if you hold the pitch change in then you are making a lot more work for yourself and the approach will not be as accurate.

Hope this helps.

[QDMQDMQDM]

This kind of teaching -- don't trim on final -- is what's wrong with much of flying training as it stands today, isn't it? Students taught to fly airliner-type, enormous circuits, often onto strips of tarmac onto which you could land the space shuttle. I learnt to fly like this the first time round at Hurn as it then was and you simply don't get the runway 'picture' fixed in your mind, because you don't have to. You have a mile and a half to land! Let's see much shorter, tighter, lower level circuits into small grass strips being taught to a much more frequent degree.

My advice to aspirant pilots is don't train at massive huge airports if you want to go on and fly little planes. Fine for airliners, but not anything else.

QDM

[foghorn]

Was taught in an FI course to trim on finals if required - in fact a part of the demonstration that I was taught was to briefly remove your hands from the controls to show how the aircraft is still in trim, descending at the required rate to the aiming point at the approach speed.

cheers!
foggy.

[nonradio]

3QDM: you born again cub pilot, you!

[undertheweather]

Off the thread slightly, but in agreement with QDMx3. I was doing a bit of circuit bashing at the weekend, and instead of honing my circuit flying skills, half of the time I was worrying about the Cessna 152 whose pilot appeared to think that when he lost sight of the airfield on the horizon over his shoulder was the appropriate time to turn downwind.

I always thought that circuits were supposed to be tight enough that if your engine failed at any time, that there was a reasonable chance of getting back to the runway.

Circuit bashing for the student (I remember) was about consolidating the critical takeoff and landing skills. Wide circuits mean fewer landings per hour. Are students being taken advantage of in a cynical exercise to generate more revenue for flying clubs?

Or am I just too cynical?

[LowNSlow]

I used to wind in full nose up trim on my L4 Cub and she would flutter down the approach at idle in a 3 point attitude. Made landings dead easy.

When I tried it in the Auster it felt as if I was trying to loop. Ooops, much more effective trim......Had to think about it then and just trim as appropriate. Ooooh these complex aeryplanes :D :D :D

Bad habits, I had plenty after flying the Cub from a grass strip. Took a bit of willpower to go out and pick out as many faults as I could before my bi-ennial flight test with the man from the CAA (which I passed I hasten to add) instead of just fannying around like I usually do :rolleyes:

[QDMQDMQDM]

you born again cub pilot, you!

Damn, you're right. I'm a 'Happy Clappy' cub pilot!

;)

QDM

[Circuit Basher]

Undertheweather - I'm with you on this one. I did half my PPL training in Canada and after about 4 hrs trg, my instructor would chop the throttle on me if he thought I was flying wide circuits and make me prove whether I could hit tarmac! Soon got me out of the habit of flying wide circuits! Got back to UK and was instantly slapped around the head for flying tight circuits (at Bournemouth!0 - these are nothing like as wide as Perth fly them!!

I always feel more comfortable if I feel I can land inside the airfield boundary after an in-circuit power failure - I currently fly a Fuji which glides like a brick - maybe I should never fly outside the airfield boundary ;) ;)

[QDMQDMQDM]

my instructor would chop the throttle on me if he thought I was flying wide circuits and make me prove whether I could hit tarmac

I was flying some very tight 500 foot circuits a week ago with about 10-15 knots down the runway. If I chopped the throttle on downwind it was instructive how much height I lost in the turn (supplementary lesson -- no turnbacks for me, I hope) and just how tight the circuit had to be to make it in if the engine failed.

QDM

[QNH 1013]

As far as I can see, if an aircraft is out of trim, then you trim it. It should be an automatic response. You will never manage to fly an ILS down to MDA unless the aircraft is in trim. The only time I don't trim is in turns (because the aircraft will then still be trimmed correctly when I roll out) and when I want a very short climb or descent followed by level flight (eg when changing from, say, 3000' on regional QNH to 3000' on aerodrome QNH).

Agree fully with QDM re learning at short fields for two reasons:
1. Its easier to make the change short-to-long than vice-versa.
2. You get practice at making go-arounds so you learn as second-nature to make a decision on every approach... are you going to land or are you going around? I think some people go through the far hedge because it never occurs to them to go-around.

I also agree with undertheweather that most circuits flown at airfields today are far too large. Sometimes this is necessary to avoid noise-sensitive villages, but often it there appears to be no reason other than a CFI once drew a particular circuit on the map. Perhaps its to give students "thinking time" during the circuit. I don't know.

I learnt at a small airfield and we weren't allowed to do touch-and-goes, plus the circuit was extremely large (for valid noise reasons). However, it took me a lot of time and money to learn to land because I only got four landing in each hour's lesson. At another airfield with a smaller circuit and touch-and-goes (plus a longer 418 metre runway) I could do twelve landings in an hour. What I am probably saying is that the optimum is probably to have a runway that is short, but not too short and a safe tight circuit. Pity we have to live and fly in the real world !

[HotCarb]

I was always taught to trim whenever I'm not flying a "transient manouvre" (e.g. turning, spiral dive ;) ).

I normally set carb-heat, power & flaps mid-way down base leg, then trim . Once turned onto final, make whatever adjustments are needed to make the picture out the front look right, re-trimming if necessary. Then - with about a mile to run, the carb-heat comes off and I don't worry about the trim any more. There shouldn't be any serious amount of back or forward pressure necessary on the CC at that time... If there is - then go around!!

[Final 3 Greens]

Tomahawk

Let's analyse what trim is for.

It's for removing the weight from the controls when the aircraft is at the appropriate attitude.

I don't know why your instructor did not teach you to trim on final and I won't try to second guess him.

Three points to bear in mind:

1 - when you remove power in the flare, the aircraft will start to decelerate and any sensible aircraft will pitch down to try and regain its trimmed airspeed.

2 - on most light singles, this pitch down is countered unconciously by the pilot and the control forces are light enough for this to be practical - however some heavier singles (e.g. PA32R) require trim to be added in the flare ro reduce the back pressure to manageable proportions; this is not an old wives tale, its in the POH

3 - if you sit on the flight deck of a jet or a jet sim and watch an autoland, the a/p in the models I've observed tends to slightly over trim nose up before the flare

Having said all of this, trying to fly the a/c using the trim instead of the yoke as a low hours pilot is not good and I could understand why an instructor may feel it better to encourage a pilot to develop a feel of the plane by using the yoke properly.

On training type aircraft this forces allow this, but as you have discovered the trim, used sensibly, is a wonderful aid!

Enjoy your flying. :)

[G-SPOTs Lost]

We need to remember....

Trim is a function of Airspeed and not attitude.

Therefore if you fly an approach in a cessna 172 at say 70 knts and do not change the trim from say the trimmed state speed which is of course 70knts then ssais 172 will gladly stick 2 fingers up at you as it floats 1/2 way down the runway.

A good landing comes from a good approach, in any airplane you have a Vapp and Vref approach at one speed, touch down at another.

I teach accurate speed control down finals and at the height of a double decker bus - Pitch Up - Retrim to the revised speed of eith er 60 or 65 knots and the airplane will then dissipate energy and give a cushioned touchdown on the runway.

Energy is a function of Airspeed squared.

Try and land at 70 knots = 4900 units of energy

Try and land at 60 knots = 3600 units of energy

a 25% decrease in energy for a 10 knot speed reduction.....

Hey presto ace QFI landing every time.

The trim wheel helps maintain the correct selected speed

[tomahawk1673]

Thanks guys, I've decided to keep trimming on final.

However, what about on takeoff and climbout? This is the part I find quite difficult, as the forces are quite considerable on the 180hp 172. My instructor always told me to be on the throttle till circuit height, then A-P-T, turn downwind etc.

[Tinstaafl]

Use trim. If the trim isn't correct then correct it. After take off OR final.

It should be a semi-automatic response...

[QDMQDMQDM]

However, what about on takeoff and climbout? This is the part I find quite difficult, as the forces are quite considerable on the 180hp 172. My instructor always told me to be on the throttle till circuit height, then A-P-T, turn downwind etc

I believe, if memory serves me correctly, that you have the luxury of a throttle friction nut on the 172, so what's the problem with one second off the throttle and on the trim wheel? The aircraft is not going to fall out of the sky.

QDM

[Final 3 Greens]

G-Spot

Trim is a function of Airspeed and not attitude

Could you explain more?

e.g. Power & Pitch = Performance ...the golden rule of attutude flying.

Trim an aircraft to an airspeed without considering pitch/power and surely you do not necessarily get the required performance ... just accurate speed control.

e.g. trim to approach speed with too little power and you get excessive sink - you land in the undershoot unless you correct.

Therefore shouldn't we set the attitude (picture), set the power to give us the airspeed and sink rate required to maintain the glidepath and then trim to remove the control forces so that the aircraft is stabilised?

[Loony_Pilot]

Hi,

Regarding trimming... the aircraft should be in a trimmed state for all phases of flight... and by that I will simplify it to Climb, Cruise, Descent, Approach. No trimming in turns.

I dont teach my students to trim before 300ft QFE on the climbout unless the the aircraft is a long way out of trim. Then.. hand back on the throttle until at circuit height.

Trimming on approach is a must... its hard to land well without a stable approach.. if you havent got the speed stabilised and approach stabilised with the aircraft in trim by 300ft then go around and try again.

[Aussie Andy]

Loony - always wondered why the hand on the throttle? I was also taught this and always do it - the reason I was given was so that "when the CFI does an EFATO on you you will notice when he grabs the throttle!" but I suppose there's another reason!?

[G-SPOTs Lost]

Cerpently

You are flying downwind in the circuit, aeroplane perfectly trimmed for straight and level say 95knts/2350rpm in a warrior, assuming there is nothing below you lower the nose to increase speed to 110 knts then reset the attitude.

Nose climbs due to increased dynamic pressue on the trim tab, now with this new found increase in altitude raise the nose to say 65knts and reset the attitude to S & L. Nose drops away as you would now expect.

Classic mistake or (back to the thread) "BadHabit" is student or novice PPl'er who from crosswind in the circuit lowers the nose at circuit height, doesn't give the airplane a chance to accelerate properly and trims for straight and level at 80knts - turns downwind and due to the aircraft accelerating in the turn increases altitude to cct hght +100

Had the privilige of checking out a retd. grp commander in the RAF who's last job was flying F3's. You'd think it would be very straightforward to sort out a PPl for somebody with such experience but he would happily admit it was actually reasonably difficult.

How did he get through it

Old RAF adage at every phase of flight "TRIM, TRIM, TRIM"

If its good enough for the RAF doing 7 miles a minute its good enough for us spam can drivers doing 1.5!

And to answer the second part of the question, on approach the speed is maintained by the elevator and the trim tab. Think of the throttle as a rate of descent/climb leve. It either gives 0fpm rate of climb/descent or a positive or negative figure. Large throttle movements will give a variation in airspeed, subtle changes in power wil not, they only modify the rate of descent sufficiently to remain on your intended glide path to the runway. This is assuming of course that you are at the right height turning finals.

I always advocate getting into the "letterbox" which is an imaginary slot at approximately 1.5 miles out at approximately 550-600 feet.

If you get into the letterbox and set the power that your instructor told you to set the first time you flew the aircraft in the circuit when you were getting checked out, then the subtle changes in power on an average day (wx wise) are tantamount to the instructor figure plus/minus 250 rpm.

This will give the the dearly sought after stable approach you can clearly see that the good approach comes from a good base leg - getting you into the letterbox....

[MLS-12D]

Here's a link that may assist with another bad habit that most of us tend to develop over time:
www.avweb.com/articles/profiles/mcollier/lazyrudder.html

[Final 3 Greens]

G-Spots

I understand where you are coming from now, but for some of us the stick controls rate of descent and power the airspeed.

In this scenario, the two factors are adjusted to give the required performance and then the trim is used to take the weight off the elevator.

When you think about it, the actions and results are the same, but the conceptualisation is different.

[InFinRetirement]

Just noticed this thread and find the subject matter interesting. Certainly some of the answers are interesting.

But what is more interesting than all the above, is that it is fundamental to ensure that your aircraft is in trim - in ANY phase of it's flight.

But for landing it must be correctly trimmed, and I would always expect to have it 'finalised' by 200' or thereabouts. But........it is still possible that further trim might be required down to around 100'. Trim cannot, however, be ignored. It must be adjusted, and there NO rules to say that it should not be adjusted at ANY time.

[QDMQDMQDM]

I understand where you are coming from now, but for some of us the stick controls rate of descent and power the airspeed.

The elevator controls the angle of attack of the wing. All else stems from that and all roads lead back to angle of attack.

;)

QDM

[Final 3 Greens]

QDMx3

All I am saying is that Power & Pitch = Performance. Pretty standard stuff really - basic attitude flying technique.

The the airline constituency uses the stick to control sink and power to control speed. Thus you adjust an input and monitor the relevant indicator. (you will also understand that P&P=P also allows the stick to be used for speed and power for sink.)

BTW, the US Navy uses the same technique.

[G-SPOTs Lost]

Finals three greens

What are you flying? It sounds probably like you are flying an aircraft with a reasonably broad speed range.

In this case then yes I would agree with your theory and of course if it works for you then fine. Exercising my diploma in diplomacy if you are flying a "normal" single i.e. 2/4 seats fixed pitch prop etc then I think that your technique would go against current and historical instructional technique.

Having said that I would reiterate if it works for you then fine..

Also I'd be interested to know if you fly IMC because I think you would have trouble flying a stable ILS with your technique.

I havn't thought that through completely but it just sprung to mind :rolleyes:

PS RAF have a technique called point and power anybody care to explain?

IFRet Indeed a healthy topic!

[Them thar hills]

How about long flat drag it in type approaches for being NBG ?
OK for counting hedgehogs but not good for much else.

Landing with carb heat in HOT is very good for killing off the go-around option should it arise (it will, and when you least expect it)
How many pilots have three hands ??!!

TTH