lateral trimming

[Ton van Bochove]

Flying with real weather is a great experience but it also brings new questions.

I fly FL310 and have a crosswind of 104 knots. The direction of my route is 128 and the direction of the nose is 139. Should this be trimmed or just left alone?

[Jeroen Hoppenbrouwers]

Don't "trim" the heading, as this would drive you off the intended ground track. You really need this crab angle into wind.

However you do not want a slip or skid, as this means more fuel burn. Look up page 303, the Slip and Skid Indicator. Here you can actually trim something, though it often is taken care of by the autopilot.

In most cases, there won't be a slip or skid unless you have asymmetric thrust or do something with the rudders. Many airframes have slightly misaligned rudders, so it is good form to assure that there is no slip or skid at all during straight flight. You can nudge the rudder trim for this.

Hoppie

[Will]

It's like a ship... if the current is coming from the left, then you have to steer a little to the left to keep going towards your destination, but you want the deck to be flat with the water so nobody leans to one side, and so the plates and wine glasses don't slide off the tables.

When you have a crosswind, what that means is that you are in an airmass that is carrying you along in a direction other than exactly where you want to go. So you steer into the wind to compensate, and your ground track ends up taking you where you want to go, even if your nose is pointed off a few degrees. But the floor stays level (in the left-to-right direction) and your plates and wine glasses stay on your seat back table.

If you were to use rudder or differential power to align your heading with your ground track, then one wing would always be down, and your dinner service might slide off the table to the left or to the right.

This is what the slip indicator* on the PFD is telling you: how much of a tilt you have to one direction or another. When the slip indicator is centered, then no matter what the bank angle of the wings, the gravity vector is pulling you down into your seat (and pulling your wine glass onto your table). When the slip indicator is out of center, the gravity vector is pulling you to one side or another, which is uncomfortable and hugely fuel inefficient.

In sum: fly with the slip indicator centered, and wings level, and point the nose wherever it needs to point to deliver a ground track that takes you where you want to go.

*) The slip & skid indicator is sometimes called the "ball," because prior to electronic attitude indicators, it was an actual little black ball that could move freely within a U-shaped glass tube full of oil. When the gravity vector was pulling directly "downwards" through the floor, the ball was pulled to the base of the U and was centered there. When slipping or skidding, the ball would slide out of center... it basically showed you the direction of the gravity vector. You should always have the gravity vector going straight through the floor (i.e., "fly with the ball centered") unless you have asymmetric thrust due to engine problems, and that's true whether in level flight, or climbing, or turning.

[Ton van Bochove]

Thanks guys for this extensive explanation. Asymmetric trust is the next thing on my list, but in prior attempts I really made a mess of it: all the plates and wine glasses were on the ground!

[Jeroen Hoppenbrouwers]

Pro tip: when an engine fails, just also shut down the other symmetrical engine, and flying in trim becomes a lot easier.

[localiser]

Ton,

What hoppie said..... 

At top of climb, once at cruise thrust one of the things we do is take a look at the aileron trim indicator (the index lines on the top of the control column). There may be some misalignment in the rudder for example, and this can cause the yoke to be out of the horizontal position. We can use the index as a guide to add a bit of rudder trim. It's not really something you can do in PSX though (on a laptop at least) as there is no yoke as a reference.

Pro tip: when an engine fails, just also shut down the other symmetrical engine, and flying in trim becomes a lot easier.

But going around gets a bit harder 

[Ton van Bochove]

Localiser, thanks for the input!

and this can cause the yoke to be out of the horizontal position.

But what could cause this misalignment? Cables, pulleys?

[RogerH]

... as there is no yoke as a reference.

If you have the >>Preferences/Screen/show info tags<< checkbox filled, the little icons for the controls show at the top right of the screen. Any control which is not in the centre becomes highlighted and moves with the control - this could perhaps help?

EDIT - top _left_ of the screen - doh!

[Ton van Bochove]

Hi Roger, Thanks! I have it checked, that is a very good info tool

[Hardy Heinlin]

But what could cause this misalignment? Cables, pulleys?

I guess Localiser means the autopilot commanded aileron position. At top of climb, at FL290 or higher, you usually have the autopilot engaged.

When there is a constant yaw moment to the left or right, the autopilot needs to set a constant aileron deflection to stop that yaw. When just a single autopilot is engaged, the autopilot will not control the rudders.


Regards,

|-|ardy

[Jeroen Hoppenbrouwers]

But what could cause this misalignment? Cables, pulleys?

Yes, airframe out of rig, small building deficiencies, etc. It's a machine. It warps.


Hoppie