Why is trimming so difficult?

[Jambo Buana]

Taking a handful of rudder trim until the cow horns are level is not the right way to trim. You've also got to disengage the AP and correct for the lateral trim forces using aileron trim, after you have achieved zero heading change using the rudder trim.
This basic technique is so difficult to find in very many pilots, some of which have a hell of a lot of time. Are trainers out there actually overlooking this simple lesson when they are teaching because it is so simple, or what?

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Any chance of a flightdeck visit?

[411A]

Quite correct, many pilots do not trim properly, yet it is not that difficult. However, I find during training that many pilots are reluctant to disengage the autopilot for the brief time required to achieve proper trim. Suspect also that on the new EFIS types, most of the time during training is spent on the FMC that trim is ignored. This is a great disservice to the younger guys, IMHO.

[captmu2]

If you want to talk trim...work your way into a flight in an MU-2 without the a/p. There you are always trimming...in fact it makes for somewhat of a dance...pilots have no choice but to learn how to trim an a/c.

[HugMonster]

Jambo sana. Habari?

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Breeding Per Dementia Unto Something Jolly Big, Toodle-pip

[airforcenone]

Back on the 737 ..... (yawn)

Technically, it's correct to trim the rudder until there is no heading change. However, on the 737, we trimmed to get the column level in order to keep the ailerons in their neutral position to minimise drag.

[HighSpeed]

airforce1,

i'm afraid i have to disagree. having the control wheel neutral and aircraft in-trim are two different thing... i believe thats the point Jambo was trying to make.

ideally, when the aircraft is in-trim, the control wheel should be neutral. if i'm not mistaken, the b737 books says the spoilers will start to deploy if control wheel is greater the 1.6 units displaced. the correct thing to do, IMHO, is to send the aircraft to the hanger where it should be re-rigged. if i recall correctly, the books also mention about entering in MR when displacement is > 3/4 units.

i used the following technique to achieve 'perfect' trim:

1. Select HDG SEL
2. Trim Rudder TOWARD 'wing-low' side
(take as much time you need)
3. Disengaged A/P
4. Trim off any aileron force
5. Re-engage A/P

I teach this to all my F/Os... it works much better than trying to hand-fly wings level and looking for a heading drift.

HS

[OzExpat]

And in the B200, you also need to disconnect the Yaw Damp, or you end up trimming against it. The result? Well, part of the pre-ldg checks is Yaw Damp Disengaged.

If you're too busy to check trim manually at that stage, you're gunna need huge amounts of rudder when you close the throttles! Yeeehaaa! http://www.pprune.org/ubb/NonCGI/eek.gif

So... why don't pilots disconnect the YD, as well as the a/p? Beats the stuffing out of me! Especially if the pilot hasn't thought to get the trim right before sticking the YD and a/p on. The only thing I can think is that some pilots might be a bit overawed by a manual that says things like ... yaw damp is required ... yada yada yada.

Yes, it really IS required. But that don't mean it has to be engaged every GD moment! Now, I just KNOW there's gunna be other aircraft types out there, fitted with YD... http://www.pprune.org/ubb/NonCGI/eek.gif

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Once a king, always a king.
But once a nite's barely adequate!

[JBravo]

Trimming? Bus drivers don't even know what that means ;) (unless it is the A300/310 ofcourse)

[airforcenone]

HighSpeed,

It was a long time ago ........... I'm sure you are quite correct.