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dravid kenyala

Trimming and how it is done.

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Hi all. At what point we do start trimming aircraft? When we will be knowing the aircraft is out of trim? When to stop trimming?

 

On what basis like either watching the fd bar to be on centre line of artificial horizon by trimming when it is not on the centre ( between blue and brown) of artificial horizon.

When you will know this time I have to trim up and k this time I have to trim nose down.

 

I know that I have to trim but I don't know when to trim and what to see to initiate manual trimming.

 

A lot of people said that to release the pressure on yoke and when you apply some force on yoke and when the aircraft is not responding as it should be we start trimming.

I haven't experienced with this. Even I trim or I don't trim I am manually landing the aircraft.

 

I have also seen the thread on trim on final? I couldn't find the answers.

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Take off and manually climb the 777. once established in a climb let go of the yoke. what happens? the nose will drop down because the plane has a tendency to reestablish straight and level flight

 

1. climb

2. let go of yoke

3. nose will drop (you dont want this) you want nose to stay up so it can climb but without pulling back on the stick 

4. apply elevator up trim and let go of yoke

5. when trim is applied correctly you can let go of the yoke and the 777 will climb by itself

 

do the reverse for descending

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Take off and manually climb the 777. once established in a climb let go of the yoke. what happens? the nose will drop down because the plane has a tendency to reestablish straight and level flight

 

1. climb

2. let go of yoke

3. nose will drop (you dont want this) you want nose to stay up so it can climb but without pulling back on the stick 

4. apply elevator up trim and let go of yoke

5. when trim is applied correctly you can let go of the yoke and the 777 will climb by itself

 

do the reverse for descending

This is going to sound very basic, but I tend to rely on autopilot way too much. When I turn off the auto pilot the plane stops its decent even if I idle the engines and I end up too high and having to force the nose down to drop for a hard landing. If I take the autopilot off at say 400ft do I need to adjust the trim to keep the plane on its decent path? I would love to do fully manual landings but always have difficulty getting the plane down in time. For takeoff I set my trim to the number in the FMC. At what point would I need to readjust my trim? Usually I just keep my hand on the yoke until I have climbed 1-2k and then switch on autopilot for the rest of the climb while I am raising flaps and running through radios/lights etc.

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the steps above are for use when not flying a flight plan. Its just for training.

 

In a flight with a flight plan the autopilot will trim the aircraft. If your established in a descent and you disconnect autopilot the plane in theory should be fully trimmed so you shouldn't need to touch the trim 

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For takeoff I set my trim to the number in the FMC. At what point would I need to readjust my trim?

 

Well as your speed moves up so does your lift and therefore as you speed up you should only have to trim down to counteract the lift produced from the speed.

 

For your question about landing.  On the NGX I use the trim a lot more then on the 777.  I takeover turning off A/P anywhere from 4000 to 2500 AGL for most my landings.  Sometime only once established on the LOC in lower visibility.  On the 777 I may only have to adjust trim just a few units during landing as the fly-by-wire is at work and seams to be modeled pretty well by PMDG.  Really for my 777 landing once I get the FD on point along with speed at Vref it takes little work and pretty much just holding it until flaring.

 

Of course if the speed moves +/- you may have to re-trim as speed and lift have a relationship together and therefore will always effect the other if you don't want a heavy/light yoke.

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Hi all. At what point we do start trimming aircraft? When we will be knowing the aircraft is out of trim? When to stop trimming?

 

On what basis like either watching the fd bar to be on centre line of artificial horizon by trimming when it is not on the centre ( between blue and brown) of artificial horizon.

When you will know this time I have to trim up and k this time I have to trim nose down.

 

I know that I have to trim but I don't know when to trim and what to see to initiate manual trimming.

 

A lot of people said that to release the pressure on yoke and when you apply some force on yoke and when the aircraft is not responding as it should be we start trimming.

I haven't experienced with this. Even I trim or I don't trim I am manually landing the aircraft.

 

I have also seen the thread on trim on final? I couldn't find the answers.

 

There are issues at the moment with the trim, and fly-by-wire.

 

PMDG have confirmed they are investigating.

 

It has been confirmed by real world 777 pilots on this forum, that the auto trimming phenomenon that occurs with elevator input is wrong. It shouldn't happen.

 

Manual trimming is tricky too. It should feel no different to trimming any aircraft. It does. 

 

As yet, nothing has appeared in PMDG's pinned bug list.

 

I'd say we are due an update on this issue.

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I was told by Support that the Autotrim/Trim System on the 777X is completely rewritten right now so you shouldn't try to cope with/get used to it right now too much. At the moment, there is actually no manual trimming necessary (except for TO of course) - just keep the pitch you want and the Autotrim will do the rest - might not be realistic but that is how it works for now....

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I was told by Support that the Autotrim/Trim System on the 777X is completely rewritten right now so you shouldn't try to cope with/get used to it right now too much.

 

Oh right, that's great news Chris. Glad to hear it.

 

Thanks for that.

 

:smile:

 

Would be nice if PMDG updated the pinned bug tracking list though to keep us in the loop.

 

That's what it's there for.

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I was told by Support that the Autotrim/Trim System on the 777X is completely rewritten right now so you shouldn't try to cope with/get used to it right now too much. At the moment, there is actually no manual trimming necessary (except for TO of course) - just keep the pitch you want and the Autotrim will do the rest - might not be realistic but that is how it works for now....

 

You mean PMDG just done an airbus :P 

Airbus X auto trim sucks........hope PMDG will do an airbus oneday~

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Boeing does not embrace the Airbus auto-trim philosophy. Neither the 777 or 787 fly by wire systems have auto-trim. In all my flights, trim has worked as expected by adding "bias" to the control input such that pitch would remain as desired without control input. Don't know what you guys are talking about.

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Boeing does not embrace the Airbus auto-trim philosophy. Neither the 777 or 787 fly by wire systems have auto-trim. In all my flights, trim has worked as expected by adding "bias" to the control input such that pitch would remain as desired without control input. Don't know what you guys are talking about.

 

What we are referring to, and why PMDG has "apparently" rewritten the code, is in regard to the following...

 

Configuration changes in the real T7, for example flap deployment and thrust increases, are trimmed out automatically by the fly-by-wire. However, just like any other aircraft, speed changes need to be trimmed out manually by the pilot.

 

In the PMDG 777 the above is not the case. It's possible to hand fly, change speed, and not bother to trim at all. As speed changes, and elevator input is used to maintain flight path, we find ourselves magically in trim as soon as the new speed is established. This is wrong. Speed changes should  require manual trimming when hand flying.

 

In addition, when we do trim manually, nothing happens initially, and then it over trims. Trimming should feel just the same as trimming any airliner.

 

Rob, a real world 777 pilot, on a previous flight, hand flew the real aircraft and confirmed that in reality, it doesn't function the way the T7 does in the sim.

 

This should help you see the issues.

 

http://forum.avsim.net/topic/419407-hand-flying-tips/page-7

 

Post 20 from Rob.

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This is so weird. Ever since the release there's a group of people saying that PMDG is wrong, and another group saying the PMDG is right... and there are real 777 pilots in both groups!

 

So now I hadn't been flying the 777 very much because I'm afraid to learn it incorrectly.

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I have flown about a hundred hours in the PMDG 777. Except for the first couple of hours I have not touched the trim button except to set initial trim setting. 

 

I apply gentle yoke pressure in the appropriate direction depending on take off or landing. The aircraft trims and will remain so until I command otherwise with the yoke.

 

Judging from the discussions indicating that it may not be correct or that it is being rewritten, this may be an incorrect procedure. Currently, it seems to work. 

 

I await definitive and authoritative information from PMDG.

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This is so weird. Ever since the release there's a group of people saying that PMDG is wrong, and another group saying the PMDG is right... and there are real 777 pilots in both groups!

 

So now I hadn't been flying the 777 very much because I'm afraid to learn it incorrectly.

Just go by the manuals as they are the final authority a forum is not the best place to learn about this plane unless the poster is a VERIFIED rw pilot.

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the steps above are for use when not flying a flight plan. Its just for training.

 

In a flight with a flight plan the autopilot will trim the aircraft. If your established in a descent and you disconnect autopilot the plane in theory should be fully trimmed so you shouldn't need to touch the trim 

 

I have to ask: Where did you find connection between flight plan and trimming an aircraft?   :blink:

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Just go by the manuals as they are the final authority a forum is not the best place to learn about this plane unless the poster is a VERIFIED rw pilot.

Well, that's the confusing part. There's a group saying that PMDG doesn't fly like what is described in the manual, while there are a few real pilots saying it does!

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My philosophy regarding trim is this: Trim is used to reduce pilot fatigue by reducing the need for control input once establishing stable flight. That means getting your power settings and aircraft attitude more or less settled before trimming regardless of climb, cruise, or decent. Attempting to trim while not in stable flight often results in chasing the trim and adding to the workload instead of reducing it.

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Well, that's the confusing part. There's a group saying that PMDG doesn't fly like what is described in the manual, while there are a few real pilots saying it does!

If the real pilots are saying its good then its good, when you think about it half of the "bugs" reported here are the result of user error or ignorance.

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Well, that's the confusing part. There's a group saying that PMDG doesn't fly like what is described in the manual, while there are a few real pilots saying it does!

 

The only real-world 777 pilot that I know of here, agrees that the FSX behavior is wrong. On a recent flight he tested the trim behavior, and he *HAD* to manually trim the real aircraft for speed changes. The sim however, will auto-trim, which is incorrect.

 

Note carefully that where the sim is wrong is with auto-trimming of speed changes. It correctly handles config changes.

 

Best regards,

Robin.

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If the real pilots are saying its good then its good, when you think about it half of the "bugs" reported here are the result of user error or ignorance.

 

There are real 777 pilots here who say it is not good. Maybe the ones who claim it is ok, have not tested thoroughly this issue and just skimmed over. There is pilot in particular, very experienced on the T7, a captain, who has carefully tested all this on the REAL airplane, and he finally stated that, as I also think, the simulation is not ok. I firmly trust what this pilot says.

 

I'm a real pilot. I do not fly or have flown the 777. I actually fly the 737 but, with my experience as a pilot and in studing FCOMs, etc, testing the handling characteristics of the PMDG 777 I can say that PMDG does not fly as per documentation regarding this issue of FBW. The first thing I do when purchase and FSX aircraft, is to hand-fly it extensively to see how it feels and behave because I love hand-flying. I inmediately felt something was not ok. I then studied the FCOMs, everything regarding FBW, handling charateristics, etc and I concluded the FBW is not correct.

 

Some others fellow simmers, very experienced and knowledgeable, and real pilots who love flight simulation just like me,  have felt the same issue themselves and agreed there is some kind of bug here.

 

And finally, you got it some posts upwards. PMDG became aware of this, they must have tested themselves, and finally concluded that we were right and fixes were to be carried out, and so they have, which I find fabulous....Don't we forget this is PMDG, and they are absolute professionals. If something is worng they do their best to fix it and for this one it seems it was wrong. In the same way if something is working ok though there are people who think it isn't, PMDG let them know why and authoritatively.

 

Cheers.

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I have to ask: Where did you find connection between flight plan and trimming an aircraft?   :blink:

He wont be doing much manual trimming if he hits the autopilot at 1000ft and then does an Autoland.  you would need a flight plan for that

 

But if he fires up FSX and just does trim training he wont need a plan lol. I did make that clear in an earlier post

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Trimming only happens when the autopilot is off. If you try to trim manually with the autopilot on, the autopilot will actually turn itself off (and then the big warning sound will start till you press the Autopilot Disconnect button on the yoke/stick, or turn the autopilot back on).

 

Assuming you are manually flying your descent/glidepath/approach it's pretty simple, use the yoke (hereby called "Stick" because, whatever)

 

Getting too high? Push the stick forward.

 

Are you pushing the stick forward to maintain the attitude you want without moving? use trim so that you can release that pressure on the stick.

 

So, lets say I have let the stick go. The aircraft is pitching up which is causing it to reduce it's descent rate, (or climb) and also loose speed. I don't want it to climb, or slow down, so I push the stick forward, enough to maintain the pitch I want.

 

Now I don't like holding the stick forward all day, so I push the "trim aft (for me this is Joystick Button 3, or numpad number 7)" button enough so that I can release the stick, and keep the pitch I want at the same time.

 

pushing the trim button and moving the stick back to 'neutral' at the same rate using hand/eye co-ordination. Once the stick is released again, use the trim to make the last fine adjustment. If the adjustment gets out of hand, push/pull the stick again and start the process over.

 

Push stick first. Establish the attitude you want, then trim out the stick back to neutral.

 

It's more a feel than an adherence to numbers. You don't want to be using too much muscle to keep the status-quo. Neutral stick should = not much movement in pitch attitude. Use the trim to set up that Neutral stick.

 

If you want to change the pitch (to change your rate of decent/climb or in response to speed changing your rate of descent/climb) then pull/push the stick, and then trim the forces out once you're happy with the new pitch.

 

It's possible to use the trim without moving the stick to adjust the neutral point, but I'd only use that to "keep" the current attitude as you change speed, not to initiate a change in attitude, which should be done on the stick first.

 

If the air is turbulent, and the pitch is moving around a lot, use the stick more than the trim. You should 'feel' that there is a 'centre' somewhere around which you are yodelling the stick around in response to turbulence. Moving the trim will move that 'centre' point forward or backward in the movement range of the stick. Use the trim to put this where you want it, but be ready to move the stick forward/backward to counter the turbulence at any time. You have quicker control over the stick input than the trim, so resort to that first.

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I'm really really impressed by the extremely relevant issues you guys arise in this forum.

Trimming in the 777 is actually not at all as trivial as some may think.

The fly by wire system in the 777 introduced some very new concepts to the trimming techniques as well.

 

The concept of "put the aircraft where you want it, then trim out the residual forces" thing, is still valid in the 777 just like in most other planes BUT on this plane the pilot needs to

 

TRIM ONLY FOR SPEED CHANGES

 

Once trimmed for a specific speed, any changes in attitude (level off; climb; turns; descends...) DO NOT REQUIRE any trim adjustments.

 

Trim System in the 777 trims at a constant rate of 10kts per second throughout the flight speed envelope SO, if you need to accelerate from say 250 to 300kts, manually push the controls down to achieve that speed and trim the plane down for 5 seconds. You should now be right in trim.

 

Trim "Blip" function.

Once your Trim Reference Speed is within 5kts from your Actual speed, a blip will synch to the Actual speed.

If at your first attempt to trim the aircraft for a 300 kts attitude, you managed to trim it at say 296, a "blip" on the trim will synchronize your Trim Reference Speed to the Actual one.

 

This is just a quick recap of another very complex system, but I hope I gave you some kind of useful explanation

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Trimming only happens when the autopilot is off.

tl;dr. The above is wrong though, the AP will trim when in use.

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