FBW Yoke Sensitiviy

[Westnest]

Ok chaps,

We already know that 777 first came as the FBW Narrow Body A/C with a yoke. But I was never get used to idea using the FBW without the auto-trimming, especially with a yoke.

You have a feeling of depth, bank, pitch and even the wind when using a HYD yoke(maybe not as the manual reversion but still), as when the control surface move, it moves the actuator, puts pressure and moves the yoke. At point of larger G, it becomes harder to move so it can point the limits to pilot. Thus you can have the correct trim on yoke. Airbus I suppose does this making restrictions on banking, even with non-A/P "hand flying". Trim is done automatically while in Normal and Alternate laws. Correct me if it's not exact.

But does the T7 also features that?? "Simulating" the way yoke acts in a HYD/Mechanical system, and allowing pilot to trim as its done in the "classical" way. Not just the T7, also the B748, and B787.

Also another little question, Airbus uses autothrust and there is no react on levers(as far as I know), Boeing does it in the autothrottle way and levers move. T7 has which one?

[Rick777]

The B777 trim switch is only used for speed changes. There is no need to trim for turns, configuration changes, or power changes. The thrust levers move in response to autothrottle power changes just as if you were hand flying. All Boeing autothrottle systems are like that. A lot of pilots prefer this as it gives them another cue as to what the autoflight system is doing.

[misd-agin]

The 777 works. You can debate FBW vs hydraulics, A vs B, but the 777 is a great flying airplane where the FBW is an invisible system. It just works. No mode shifts that catch you out. It just works.

[SMOC]

Westnest,

FBW vs Cables and pulleys makes no difference to the yoke feel it's exactly the same, both are completely artificial. Under the floor is a mechanical set up just the same as any Boeing yoke which at some point connects to springs to provide artificially feel and some additional hydraulic/electromechanical resistance when required.

The trick with FBW is to make sure the 1cm, 1 inch or whatever amount of movement under the floor translates to the corresponding hydraulic actuator movement and resulting flight control movement and pitch/roll rate plus provide the visual yoke movement feedback.

As stated FBW can take advantage of the fact that the lack of mechanical connections between yoke and actuators means the flight controls can be commanded to move without having to feedback to the yoke and therefore remove the requirement to trim as it's being done behind the scenes with no feedback.

[stilton]

Since when is the B777 a narrowbody :confused:

[roulishollandais]

The 777 works. You can debate FBW vs hydraulics, A vs B, but the 777 is a great flying airplane where the FBW is an invisible system.It just works. No mode shifts that catch you out. It just works
I don't share your non scientific concept of invisibility for a control system who just works....until the failure and crash ! Your invisible banker never puts his money on your acount ! Human are not devil but are not more angels. Confidence and reliability needs to put things on the table before you sign.
Did Russian pilots in Kazan had working invisible licenses too ?

[misd-agin]

What 777 crash due to FBW are you referring to?

[Westnest]

Since when is the B777 a narrowbody :confused:
I was a bit preoccupied:ugh:

AF Flight 296 was one of the famous FBW incidents, though it wasn't about the control surfaces or the airframe. The thrust levers was just a decoration instead of controlling the fuel flow, or the Captain Michel Asseline was trying to commit suicide with his passengers on board.

What if 777's overintelligent computers disagree with the pilots commands just as in the AF296?

If everything is simply is on the computer's determination, that would make no sense to try a yoke to be tweaked as its feeling like a hydraulic yoke. Because in fact aircraft decides on its own pitch and bank angle.

So 777 has a bit less strict FBW system than what found in buses?

[flyboyike]

Aren't thrust levers "just a decoration" on any FADEC-equipped aircraft?

[SMOC]

What if 777's overintelligent computers disagree with the pilots commands just as in the AF296?

What are you talking about, AF296 crashed because TOGA thrust was applied to late, the plane didn't climb over the trees because it was already at max alpha for the slow fly-by and the engines took around 4 sec (which was normal) to get to any decent amount of thrust, they were around 90+% when they began ingesting the trees! Had it been a Boeing exactly the same thing would have happened except the stick shaker would probably been going off intermittently indicating they were near the stall as they tried to climb over the trees with insufficient speed and waiting for the engines to spool up.

[Denti]

Isn't QF72 one of the famous incidents where a FBW system disagreed with the pilots? Probably a better example than AF296.

[CONF iture]

Once again Habsheim is mentioned.
I will reply here (http://www.pprune.org/tech-log/528034-habsheim.html).

[Westnest]

Aren't thrust levers "just a decoration" on any FADEC-equipped aircraft?
Cool kind of decoration. While Boieng/MD FADEC is making sure of the fuel flow and keeping the engine at the safe levels, thrust levers still have movement while dependent on the A/T, while in Airbus FBW they're static to Max N1 when A/THR is active. I wonder if 777 went through the traditional A/T way or the futuristic A/THR way.

[Mac the Knife]

"....therefore remove the requirement to trim as it's being done behind the scenes with no feedback"

Hasn't this created a few problems lately when the aircraft has significant amounts of trim in that the aircrew will only be aware of if they specifically look for it?

Is this not confusing when modes change or the AP drops out?

:confused:

[tdracer]

Aren't thrust levers "just a decoration" on any FADEC-equipped aircraft?


Perhaps on Airbus, but not on Boeing.
On ALL Boeing FADEC-equipped, the thrust command is directly linked to the throttle position. Baring some sort of mechanical failure that would prevent the engine from responding, on a Boeing if you set the throttle at idle, you'll get idle. Set the throttle at part power, and you'll get part power, set high power, well, you know... On Boeing, there is no aircraft computer between the throttle and the FADEC - it's a basic design philosophy.

[DozyWannabe]

The 777 works. You can debate FBW vs hydraulics, A vs B, but the 777 is a great flying airplane where the FBW is an invisible system. It just works. No mode shifts that catch you out. It just works.

Same as with the Airbus implementation - Airbus Flight Law changes exist purely to provide the pilot with as close to "Normal" response and handling as possible in the event of damage or systems failure. Boeing opted to use a servo-operated and software-driven PFC setup on the B777 and B787 as opposed to the passive Airbus setup, however this added complexity and made the manual bypass (the oft-cited 'Big Red Button') a mandatory inclusion in the system.

FBW vs Cables and pulleys makes no difference to the yoke feel it's exactly the same, both are completely artificial. Under the floor is a mechanical set up just the same as any Boeing yoke which at some point connects to springs to provide artificially feel and some additional hydraulic/electromechanical resistance when required.

Exactly - tactile response has been, either in whole or in part, artificial since just prior to the Jet Age. The last jetliners to have purely manual reversion mechanisms were the B737 and DC-9. Manual reversion was impossible on widebodies because the flight surface resistance was way beyond the ability of human muscle power to counteract.

The only difference FBW makes on the B777 and B787 is that the artificial resistance is software-controlled as opposed to mechanical.

I don't share your non scientific concept of invisibility for a control system who just works....until the failure and crash ! Your invisible banker never puts his money on your acount !

It's not invisible - at least no more "invisible" to the pilot than the equations behind the mechanical artificial feel systems used since the '40s.

Thus far there have been no accidents on the line put down to errors in FBW implementation - none.

On ALL Boeing FADEC-equipped, the thrust command is directly linked to the throttle position.

On Airbus, the actual thrust setting feedback is visual via the "donut". People will argue 'til the cows come home, but IMO there have been enough incidents and accidents on aircraft with moving thrust levers that the perceived issues with the passive Airbus design aren't reflected in the real-world record.

On Boeing, there is no aircraft computer between the throttle and the FADEC - it's a basic design philosophy.

Same with Airbus. The FMGC can order thrust to assist control inputs, but it augments the original settings rather than overriding them.

What are you talking about, AF296 crashed because TOGA thrust was applied to late, the plane didn't climb over the trees because it was already at max alpha for the slow fly-by and the engines took around 4 sec (which was normal) to get to any decent amount of thrust...

Spot on. With the way the aircraft was positioned and configured, the only thing the flight control computers could do was keep the aircraft flying by preventing a stall. The A/THR system couldn't command more power (as they were below 100ft RA - though that was supposed to be manually disabled), and as such, the only aspect they could control was AoA, by keeping it as close to theoretical Alpha Max as the conditions would allow.

"....therefore remove the requirement to trim as it's being done behind the scenes with no feedback"

Hasn't this created a few problems lately when the aircraft has significant amounts of trim in that the aircrew will only be aware of if they specifically look for it?

Is this not confusing when modes change or the AP drops out?

If you're thinking of AF447, the AP had already dropped out, and it was the PF's inputs that caused the autotrim to move the THS to an abnormal position. When we tested the scenario in an A320 sim, the THS would be held well shy of maximum deflection - it may be that the A330 was implemented differently. Regardless, the trim's movement and position is not invisible - it is clearly visible via the movement of the wheel and the gauge inset at the trim wheel's hub.

[Pub User]

Same with Airbus. The FMGC can order thrust to assist control inputs, but it augments the original settings rather than overriding them.

I was under the impression that Airbus thrust-levers don't move during normal flight, is that not the case?

[Reverb_SR71]

Hey guys, a bit of an old thread but here goes .


Artificial feel unit simulates the air pressure loads on the yoke so the pilot does not end up over controlling the aircraft ,as powered flying controls are not back driven .

Does this apply to FBW as well ? ( A320 ) because from my understanding the FBW systems have flight envelop protections so there is no fear of over controlling the aircraft . you can have a simple spring centered yoke/stick and call it a day .

If that indeed is the case then how is it handled when the protections are lost ?

SO in short , does the A320 have an artificial feel unit or q feel ?

I am sure the 737 has this .

[DozyWannabe]

FBW Airbus types (as in A32x/A330/A340/A380) have passive spring feel in the sidesticks in all modes. As far as I can tell it's not an issue and hasn't been now for around 25 years.

[FLEXPWR]

No mode shifts that catch you out. It just works.

Some Asiana crew might disagree on this.

[Cool Guys]

Thus far there have been no accidents on the line put down to errors in FBW implementation - none.



The lack of statistical evidence does not mean that someone cannot not have a valuable contribution or opinion.

The less statistical evidence there is, the more value the opinions of experienced professionals becomes.

Experience in the subject, as well as statistical evidence, contributes to understanding and decisions made in the subject being discussed.

[DozyWannabe]

The lack of statistical evidence does not mean that someone cannot not have a valuable contribution or opinion.

I don't believe I was inferring otherwise in any way - it was a while ago, but I'm pretty sure I wasn't saying that.

Experience in the subject, as well as statistical evidence, contributes to understanding and decisions made in the subject being discussed.

Sure - however this thread definitely unearthed some examples of how the use and purpose of technology on the flight deck has been misinterpreted, and that those misunderstandings have become an accepted part of piloting lore.

Same with other threads - I recently read a post claiming that FBW was primarily intended to replace the flight engineer with technology, when in fact there were several jetliners from the '60s onwards that were well pre-FBW, yet deleted the FE station from the flight deck.

I know there's a romantic attachment to the days of yore, and that's not just true of piloting - but I suspect that were one to offer E.K. Gann and his contemporaries a control system that worked incredibly reliably, and also helped them stay out of the brown stuff by working against stalls and spiral dives, they'd have been rather thankful on those nights when the weather and visibility were against them!

[Piltdown Man]

...and the there's the Embraer. The pitch and rudder control is pretty good. It feels very conventional and compensates for flap and thrust changes so well that you don't feel it. It appears to have a conventional elevator trim and it too works well. The then there's the :mad: ailerons. Complete and utter sh!te. Allegedly these are not "fly-by-wire" but are just cable actuated (fly-by-wire?). But their loading is purely synthetic and done by wacking great springs. And this is poorly designed because the spring feedback unit appears only provides a single load, no matter what the displacement is. There is also no "fight back" from the ailerons. I also reckon a different person designed the loading on the ailerons resulting in the controls feeling totally un-harmonised. So the thing is difficult and un-pleasant to fly in a gusty cross-wind - but it could be so much easier. Or there again, that's my excuse!

[cosmo kramer]

What is a thread like this doing in Techlog? Move to Questions or Spotters corner....