T7 pitching to rapidly after changing the trim reference speed ? ? ?

[cmbaviator 5]

Hi all

 

After watching this video : https://www.youtube.com/watch?v=K9MRlFFXPL8&list=UU8_bi6SOITpwzhcZ_DdXzAQ

 

you can see that during rotation and acceleration alttitude, the Captain didn't trim at all, I think only once,( using the blip trim function, I reckon).

 

but at acceleration altitude, we can see him pressing gently the nose DN trim switch, but what shock me is that we can see that the pitch response is Very Smooth, with the current version, even if you change the TRS by +- 8-10 kts, the plane will pitch up/Down quite severly, thus lots of pressure required to try maintaing the flight path.

 

acceleration starts at : 3:45

 

Am I the only one having that feeling ??

 

regards

 

CMB

[777simmer 117]

Hi all

 

After watching this video : https://www.youtube.com/watch?v=K9MRlFFXPL8&list=UU8_bi6SOITpwzhcZ_DdXzAQ

 

you can see that during rotation and acceleration alttitude, the Captain didn't trim at all, I think only once,( using the blip trim function, I reckon).

 

No, not even once....he thought he had to trim for a split second and then decided it was not necessarry after all.

 

Why did he not to trim?

 

Because the FMC calculates the take off trim.....and this take off trim setting is set during the "before start setup".

 

If you rotate correctly during take off then you end up with a speed of V2+15 to V2+25kt and it is exactly that speed the STAB trim was set for.

So you are in trim if you rotate correctly and no or verry little trim is required untill acceleration.

[scandinavian13 5,192]

Also, you have to consider that the FMC is assuming a "perfect" environment, which may not be the case at all.  The FAs and airline dispatch software give the pilots generic numbers of approximately how much weight will be in each area to come up with generic weights and a CG value.  These weights are built off of the assumption that people all weigh the same and bags all weigh the same (except "heavy" bags, which also all weigh the same, but are counted at a heavier weight).  Since this not actually true, there is error inherent in the calculation.

 

What you're seeing in your ZFW and CG isn't exact.  It has error in it.  That error will manifest in the calculated trim value being more or less correct.  What you're seeing in the video is a day where the numbers worked out to be mostly correct.  Everyone must've actually weighed about 185 pounds, and brought bags that were all about 35 pounds... (at least according to FAA guidance).

 

More with pretty pictures here:

[777simmer 117]

Yes, I did not even think of that one......good addition Kyle!

[paulyg123 135]

I am surprised he hand flew this for 7+ minutes.

[FlyBoyMike 38]

I am surprised he hand flew this for 7+ minutes.

 

If that was me I would TOTALLY be hand flying for as long as possible before turning on the AP. Unlike the sim where we have to do everything ourselves plus talk to ATC if online he actually has someone in the right seat to back him up which makes it more manageable.

 

Hand flying the 777 especially since SP1b is absolutely sublime.

[Arnold Bruce 0]

 

 

with the current version, even if you change the TRS by +- 8-10 kts, the plane will pitch up/Down quite severly, thus lots of pressure required to try maintaing the flight path.



acceleration starts at : 3:45



Am I the only one having that feeling ??

 

 

No, you are far from the only one.    What you are seeing is the aircraft not responding to trim reference speed setting until you neutralize the controls, then pitching wildly either up or down towards trim reference speed when you release pressure from your joystick.     You do not have a problem with your hardware, nor are you doing anything wrong.   

 

The 777 SP1b version manual pitch trim is erratic and unpredictable.    

[whoispankaj 51]

I am uploading videos where i flew with A/P and A/T on to 15000ft and speed 250knots. I then disconnect the A/p.In one video i change from 250 to 270 and second 270 to 290.I have both the PFD and FCTL page open.You can see as i am pushing up and down the elevator and trimming, the trim is being applied and not applied at once when in neutral.

 

1. Speed Trim from 270 to 290

 

http://youtu.be/QIghaOQYIVg

 

2. Speed Trim from 250 to 270

 

http://youtu.be/Xdbp623erRs

 

Trim is being applied while I am still pulling/pushing the yoke to maintain level flight.

 

 

ts, the plane will pitch up/Down quite severly, thus lots of pressure required to try maintaing the flight path

No .Lots of pressure is not required to maintain the flight path.In my above videos I did not have to put in lots of pressure.A best guess would be arnd 15% of my yoke travel length is what I might have used. Now this would differ from yoke to yoke depending on how you calibrate it.

[cmbaviator 5]

the thing I'm wondering, is that :

 

Is it normal that after setting a new TRS, the plane will pitch agressively ?

[scandinavian13 5,192]

No, you are far from the only one.    What you are seeing is the aircraft not responding to trim reference speed setting until you neutralize the controls, then pitching wildly either up or down towards trim reference speed when you release pressure from your joystick.     You do not have a problem with your hardware, nor are you doing anything wrong.   

 

The 777 SP1b version manual pitch trim is erratic and unpredictable.    

 

It really isn't.  Your efforts to resolve cognitive dissonance are rather impressive, though...

[BluRay 7]

Great video representing W&B Kyle.

 

The wide disparities between airline SOPS never cease to amaze me, though. I've been doing W&B on the 77W for over seven years now; and my specific airline utilizes a mere 155 pounds per passenger (in the summer; 160 in the winter). Additionally, there is no extra weight factored in for carry-on baggage. If they checked in a bag, the weight assumption for that bag would be 40 pounds.

[scandinavian13 5,192]

Great video representing W&B Kyle.

 

The wide disparities between airline SOPS never cease to amaze me, though. I've been doing W&B on the 77W for over seven years now; and my specific airline utilizes a mere 155 pounds per passenger (in the summer; 160 in the winter). Additionally, there is no extra weight factored in for carry-on baggage. If they checked in a bag, the weight assumption for that bag would be 40 pounds.

 

Thanks!  Yeah, I was always amazed at how different everything was between the airlines, particularly because one of my jobs offered me the opportunity to work with so many of them simultaneously.  Luckily the airline's regional line that I was contracting for was somewhat standardized through a Ground Ops agreement between the carriers.

 

...but 155 and 160???  Man, and I thought the FAA suggestion was low.  Went in for a pre-employment physical for ATC (equivalent of a Class II medical with ECG in FAA-land) this week and my weight was 185.  That's on the pretty low end for me, given my body type.  Then again, my body type isn't quite average since I'm a cyclist, so I have awkwardly-sized (and therefore weighted) legs...haha.

[BluRay 7]

Thanks!  Yeah, I was always amazed at how different everything was between the airlines, particularly because one of my jobs offered me the opportunity to work with so many of them simultaneously.  Luckily the airline's regional line that I was contracting for was somewhat standardized through a Ground Ops agreement between the carriers.

 

...but 155 and 160???  Man, and I thought the FAA suggestion was low.  Went in for a pre-employment physical for ATC (equivalent of a Class II medical with ECG in FAA-land) this week and my weight was 185.  That's on the pretty low end for me, given my body type.  Then again, my body type isn't quite average since I'm a cyclist, so I have awkwardly-sized (and therefore weighted) legs...haha.

 

Exactly. I've always had the feeling my airline was undershooting these estimates. I'm not even sure how these estimatesl were derived anyway, perhaps it was through a massive study where they took the grand average of all passengers surveyed? I would certainly hope there is some scientific evidence backing up these estimates. Whenever we have an MTOW (~500 LBS within MTOW) day, I would always be extremely curious to know what the absolute actual TOW weight of the aircraft actually is...

 

When I worked the 767F however, I was always comfortable knowing the maximum disparity is typically at maximum around 100 pounds.

[PerWel 23]

I have no problem with severe pitching when changing the trim!? I even sometimes trim ahead during acceleration after takeoff, no strange pitch up or down. I tried a couple of times to handfly up to 10 000 without any problem. Smooth as silk and only small changes with the yoke was needed.

 

So this whole thread is something I have never seen.

 

/Per W

[Arnold Bruce 0]

Your efforts to resolve cognitive dissonance are rather impressive, though...

 

 

"I suppose it is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail."    -Abraham Maslow

 

 

 

Signed,

 

Bruce Arnold