Thrust
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Differences Between The Boeing And Airbus Wing

Fri Dec 31, 2010 10:26 pm

Hi there. I've noticed that all of Airbus' models and Boeing's models have wings that while each are different for different aircraft, there seem to be universal commonalities. To clear up what I'm saying:

Airbus for the A318/19/20/21, A330, A340, and A380 designed a wing in which similar spoiler types and flaps were used. The flaps essentially seemed to be one large flap, vs. Boeing which has two different sets of flaps on their aircraft (I'm talking about the ones that protrude from the rear of the wing). I guess my question was, Airbus and Boeing seem to have signature characteristics that universally apply to all of their models. What is the advantage of Airbus' flap design vs. Boeing's, and vise-versa? Let me know if I need to restate this to make it clearer. Thanks.
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PGNCS
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RE: Differences Between The Boeing And Airbus Wing

Fri Dec 31, 2010 10:37 pm

I can't speak aerodynamically, but I can say that the Airbus system is FAR easier to use from a transitioning, commonality, and mixed-fleet perspective. Flaps 0 (up), 1, 2, 3, Full as a standard is far better from this pilot's perspective than the mishmash of flap settings available on different Boeing models.
 
PapaChuck
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RE: Differences Between The Boeing And Airbus Wing

Fri Dec 31, 2010 11:49 pm

What is really interesting is the evolution of the Boeing flap philosophy over the decades. The 707 had large, double-slotted flaps separated by an inboard aileron.


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While effective in creating drag, they weren't the most efficient lift producers. This wasn't a major problem since the aircraft was designed to operate from large airports. Boeing's next offering, the 727, introduced more sophisticated triple-slotted flaps.


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These were much more efficient lift producers, and greatly helped the 727's runway performance. The drawback was that the system was much more complex and needed additional maintenance. This design philosophy carried on to the first two generations of the 737 and the 747. The 757 broke from the triple-slotted idea, doing away with the inboard aileron and returning to a double-slot design.


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This design is still an efficient lift producer, yet does away with some of the headaches associated with the previous triple-slot designs. This idea carried over to the 737NG series as well. The 767 broke again from that tradition, adding an inboard aileron, a double-slot flap inboard, and went with a single slot outboard.


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This design carried over to the 777 as well as the new 747-8. Boeing's latest offering, the 787, breaks off in an entirely new direction.


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While I guess it can technically be described as a single-slot design, it is augmented by the drooping of the spoilers. Bear in mind that each of these aircraft was designed for a specific purpose using the most advanced aerodynamics available at the time. Now, compare this brief history to the Airbus designs, and I guess you could say that Airbus likes to keep it simple.

On a side note, the A321 is the oddball of the airbus lineup, having double-slotted flaps.


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This was done primarily to offset the increased weight of the design while keeping the same basic wing profile as the rest of the A320 family. Anyway, hope this helps.

PC
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tdscanuck
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 1:03 am

Quoting Thrust (Thread starter):
What is the advantage of Airbus' flap design vs. Boeing's, and vise-versa?

Airbus's design is easier to build and maintain, and performs well enough to do the job its required to do. Boeing's design(s) tend to be higher performance but more complex and maintenance intensive.

Quoting PapaChuck (Reply 2):
While I guess it can technically be described as a single-slot design, it is augmented by the drooping of the spoilers.

Spoiler drooping is new, but the 787 flap is just an offset hinge, which is a feature that dates back to at least the DC-9. Very very simple...Boeing is headed more in Airbus's direction and, for the moment, has surpassed them in terms of flap simplicity with adequate performance.

Tom.
 
XT6Wagon
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 6:22 am

Quoting tdscanuck (Reply 3):
Airbus's design is easier to build and maintain, and performs well enough to do the job its required to do. Boeing's design(s) tend to be higher performance but more complex and maintenance intensive.

One might note that Airbus doesn't need as much lift from the flaps due to using a wing profile biased to more lift with higher cruise drag. Boeing uses wings optimized for cruise, but pays for it with needing more help from the flaps for lowspeed performance and a climb burn penalty.

I'm interested to see how the 748 turns out since its the first highly swept wing with a modern profile (in subsonic use). It looks to greatly improve the takeoff and climb performance over the older 747s while maintaining low cruise burn.

In the end I bet Airbus and Boeing profiles will lose the difference as they develop wing shapes with lower drag at cruise yet don't need as complex of flaps. Which is greatly aided by the industry standardising narrowbodies for "short-medium" and widebodies for "medium-long".
 
BMI727
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 7:53 am

Quoting PGNCS (Reply 1):
I can't speak aerodynamically, but I can say that the Airbus system is FAR easier to use from a transitioning, commonality, and mixed-fleet perspective. Flaps 0 (up), 1, 2, 3, Full as a standard is far better from this pilot's perspective than the mishmash of flap settings available on different Boeing models.

Aren't Boeing and Bombardier (at least on the Dash 8) just about the last two manufacturers still designating flap settings in degrees? And at least in the case of Boeing the designations are only approximate anyway.
Why do Aerospace Engineering students have to turn things in on time?
 
tdscanuck
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 8:15 am

Quoting BMI727 (Reply 5):

Aren't Boeing and Bombardier (at least on the Dash 8) just about the last two manufacturers still designating flap settings in degrees? And at least in the case of Boeing the designations are only approximate anyway.

In the case of Boeing, they're *really* approximate. They haven't been actual degrees for a long time.

Tom.
 
keesje
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 9:35 am

Quoting PapaChuck (Reply 2):
The 757 broke from the triple-slotted idea, doing away with the inboard aileron and returning to a double-slot design.

Never noticed. The inboard airlerons also kept the flaps out of engine exhaust, but that probably was less of an issue because the 757 is high on its wheels. They made the flap a bit shorter to prevent engine exhaust jet blowing on the flaps.

http://cdn-www.airliners.net/aviation-photos/photos/0/8/5/1197580.jpg

I found a presentation on the A380 high lift devices development process. Some iteresting pictures / grahs on the trade-offs between the different alternatives considered.
http://www.dlr.de/as/Portaldata/5/Re...aero-design_of_high-lift-wings.pdf
"Never mistake motion for action." Ernest Hemingway
 
PapaChuck
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 3:08 pm

Upon further review, it seems as if the A321 isn't the only oddball from Airbus. It looks like some of the earlier versions of the A300 had a double-slot design.


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Later versions ditched that idea in favor of a single-slot design.


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The A310 split the difference with a double-slot inboard and a single outboard.


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Just a few more examples of different solutions to the same problem. Still, it seems as if Airbus favors simplicity over fancy aerodynamics.

PC
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474218
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 3:37 pm

Quoting PGNCS (Reply 1):
I can't speak aerodynamically, but I can say that the Airbus system is FAR easier to use from a transitioning, commonality, and mixed-fleet perspective. Flaps 0 (up), 1, 2, 3, Full as a standard is far better from this pilot's perspective than the mishmash of flap settings available on different Boeing models.


There is no difference in a flap setting of 0, 1, 2, 3 , etc and 0, 5, 15, 25 degrees etc.

On a Airbus aircraft If you position the flap handle to flap 1 the flap must move to a specific degree plus or minus the tolerance allowed.

On a Boeing aircraft when the flap handle is moved to 15 degrees the flap must move to a specific degree pulse or minus the tolerance allowed.

The use of flaps 0, 1, 2, 3 etc, follows the Airbus philosophy that the on board computers are really in command of the aircraft and the pilot does not need to know specifics of what the aircraft is doing.
 
2H4
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 3:47 pm

Quoting 474218 (Reply 9):
There is no difference in a flap setting of 0, 1, 2, 3 , etc and 0, 5, 15, 25 degrees etc.

The Airbus method seems far, far more logical. I can conceive of no practical advantage to memorizing actual degree settings...particularly when there are so many other, more useful things to be memorized.
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XT6Wagon
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 4:15 pm

Quoting 2H4 (Reply 10):
The Airbus method seems far, far more logical. I can conceive of no practical advantage to memorizing actual degree settings...particularly when there are so many other, more useful things to be memorized.

whats the difference? Flaps 1,2,3,4,5 is the same now as 5,10,15,20,25 In some ways I much prefer the larger numbers as then you can use a gap to indicate importance. If you say skip 25 so it goes 20, 30... It places extra importance on the 30 being different than just a bit more flap. As others have said these are not the actual flap angles anymore so you can use the numbering system to help pilots instinctively understand.
 
2H4
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 4:32 pm

Quoting XT6Wagon (Reply 11):
whats the difference? Flaps 1,2,3,4,5 is the same now as 5,10,15,20,25

The difference is ease of memorization. It's easier and more intuitive to simply memorize the sequence of flap positions. Having to memorize specific degree settings isn't an overwhelming task, but when going through systems ground school, the little things can add up in a big way.

With Airbus, one only has to know that there are five flap settings. Because the specific settings are sequential, they are instantly and automatically known with no further effort.

Boeing flap settings are not only spaced unevenly (737 classics - five degrees apart, then ten degrees apart, then five degrees apart in the sequence), they are also inconsistent from one type to another. For example:

737 3/4/500 - Up-1-5-10-15-25-30-40
757 - Up-1-5-15-20-25-30

This requires a minor, yet an unnecessarily complicated memorization task to transition training.

Again, I will happily stand corrected, but I can find no practical advantage whatsoever to presenting the flight crew with nonsequential numbers that may or may not have any actual relevance to the actual angle of the flaps.
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Klaus
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 4:33 pm

If the 757 only has outboard ailerons, how have they handled low speed / high speed control authority in pre-FBW days? Is there a ratio changer in the control chain or does yoke roll control "just" become progressively more sensitive at higher speeds?

I've looked around but haven't found any information on that.
 
A342
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 5:21 pm

Quoting tdscanuck (Reply 3):
Airbus's design is easier to build and maintain, and performs well enough to do the job its required to do. Boeing's design(s) tend to be higher performance but more complex and maintenance intensive.

I recall reading in an article that Airbus' single slotted flap on the A320 provides the same additional lift compared to the clean wing as the triple slotted flap does on the 727.
According to the author, this achievement was rendered possible not only through advances in technology over more than 20 years, but also due to the fact that all newer (FBW) Airbuses have aerodynamically uninterrupted flaps, i.e. the flap may or may not be split into several segments, but there is no significant gap between those.

Quoting 474218 (Reply 9):
There is no difference in a flap setting of 0, 1, 2, 3 , etc and 0, 5, 15, 25 degrees etc.
Quoting XT6Wagon (Reply 11):
whats the difference? Flaps 1,2,3,4,5 is the same now as 5,10,15,20,25

I believe one advantage PGNCS and 2H4 are trying to explain is that all Airbus aircraft have the same "0, 1, 2, 3, Full" scheme, so there is no need to memorize DIFFERENT settings. They're all the same, no matter if you fly an A318 or an A380.

However, I think that at least on certain Airbuses, setting 1 deploys only slats and there is an additional 1+F setting which adds a little bit of flap deployment.

Maybe PGNCS could chime in here?
Exceptions confirm the rule.
 
BMI727
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 5:36 pm

Quoting 2H4 (Reply 10):
I can conceive of no practical advantage to memorizing actual degree settings...particularly when there are so many other, more useful things to be memorized.

It was practical on McDonnell Douglas planes, where the flap designation was the actual angle, particularly since their planes use Dial-A-Flap.

Quoting XT6Wagon (Reply 11):
Flaps 1,2,3,4,5 is the same now as 5,10,15,20,25 In some ways I much prefer the larger numbers as then you can use a gap to indicate importance. If you say skip 25 so it goes 20, 30...

Perhaps, but then you have things like the 737 having the same flap detents (I think) throughout its entire history despite having a completely new wing and flaps now, which probably causes the angles to make less sense.

Quoting 2H4 (Reply 12):
they are also inconsistent from one type to another.

Lots of things are inconsistent from one type to another. I don't see how that is a problem.

Quoting 2H4 (Reply 12):
This requires a minor, yet an unnecessarily complicated memorization task to transition training.

It is minor, heck I managed to memorize the 737 flap settings just from playing flight simulator, but is it really less trouble than trying to switch naming systems at this point?
Why do Aerospace Engineering students have to turn things in on time?
 
tdscanuck
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 6:25 pm

Quoting A342 (Reply 14):

I recall reading in an article that Airbus' single slotted flap on the A320 provides the same additional lift compared to the clean wing as the triple slotted flap does on the 727.

That's certainly possible, given the design gap between the two aircraft.

This paper is my all-time favorite for discussion of what high-lift devices are on which aircraft:
http://www.soton.ac.uk/~jps7/Aircraf...h%20lift/high%20lift%20systems.pdf

Tom.
 
mandala499
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 6:58 pm

Quoting Klaus (Reply 13):
If the 757 only has outboard ailerons, how have they handled low speed / high speed control authority in pre-FBW days?

Roll spoilers... the 737 does not have inboard ailerons either.

Quoting PapaChuck (Reply 8):
Still, it seems as if Airbus favors simplicity over fancy aerodynamics.

Well... with Airbus... the fancy aerodynamics in the wing design enabled the simplicity !

The difference on 737-CL then -NG and 320 on the wing is that the 320 was a cleansheet airframe. the Classics and NG weren't. Boeing had to come up with something to make a 737 still a 737 (the constraint) yet meet the objective of keeping the aircraft competitive... it's one heck of a challenge they've so far not failed on (winning it is a different matter though).

Hence the advantage lies with those coming up with clean sheet designs. The 320/330/(and in a lot of aspects)340 can go with the same/similar set up in many aspects including wing stuff, and other systems. Boeing didn't have that luxury. The 707/727/737 all had very different requirements if you live in the 60s. However markets and technology continue to develop and by the time Airbus came to the 320, things like runway performance requirements and infrastructure proliferation has entered the mature phase... and everything they do (except for the 380) can have the same minimum performance basis. Boeing didn't have that when they came with the 747. The 757/767 entered at a later stage but the drive for commonality on 2 very different aircraft require a non-uniform solution.

The flap settings on the Boeing is a tell-tale sign of this legacy/circumstance. Then the HYD/ELEC systems naming and flow... and it goes on.

Now... Airbus did have to go through this stage... but on the A300/310... which comparing with other Airbuses... is as different as the 737/747/757/767/777...

Electronics and computers have also enabled a more similar set up on the 320/330/340. Now the 787/380/350 is on the next generation of computing power and (except the 380) aircraft engine and systems capability... noticed how different the 350/380 flight deck is from the 320/330/340?

Quoting 474218 (Reply 9):
The use of flaps 0, 1, 2, 3 etc, follows the Airbus philosophy that the on board computers are really in command of the aircraft and the pilot does not need to know specifics of what the aircraft is doing.

Indeed. Take off is 1+F... it's different from 1... but then... all you need to do is put the lever to 1.

Quoting XT6Wagon (Reply 4):
One might note that Airbus doesn't need as much lift from the flaps due to using a wing profile biased to more lift with higher cruise drag. Boeing uses wings optimized for cruise, but pays for it with needing more help from the flaps for lowspeed performance and a climb burn penalty.

Then why can Airbuses getaway with no VGs? Sticking to the 320 and 737s... the 320 has a supercritical wing and therefore have a lower cruise drag due to much less/delayed shockwave separation and a thinner boundary layer. The NG has a more supercritical wing than the CL... hence a cleaner wing and doesn't require as much "flap" to generate lift at lower speeds for the same gross weight as the CL.

Quoting tdscanuck (Reply 16):
That's certainly possible, given the design gap between the two aircraft.

Aaah! that's the term I was looking for... "Design gap"...
Cheers!

Mandala499
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Klaus
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 8:51 pm

Quoting mandala499 (Reply 17):
Quoting Klaus (Reply 13):
If the 757 only has outboard ailerons, how have they handled low speed / high speed control authority in pre-FBW days?

Roll spoilers... the 737 does not have inboard ailerons either.

That doesn't really answer my question: How is the speed dependency of the aerodynamic controls handled?

With Airbus FBW the controls are deflected differently to achieve the same commanded roll rate depending on airspeed. The speed dependency is almost completely compensated by the flight computers.

Some Boeings lock out their outboard ailerons at higher speeds for at least some rough compensation. Is there any speed compensation in the 757 (or 737) where control deflection would normally be directly proportional to yoke deflection? Or does the pilot simply need to be (much) more cautious with the controls at higher speeds?
 
tdscanuck
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RE: Differences Between The Boeing And Airbus Wing

Sat Jan 01, 2011 9:45 pm

Quoting mandala499 (Reply 17):
Then why can Airbuses getaway with no VGs?

It's not a matter of "getting away with"...it's a trade. Boeing chose to incurr the (relatively small) drag penalty for the VG's in return for slightly improved performance. The wing VG's are there for high speed performance, as far as I know, not low-speed. Airbus chose the other side of the same trade study. This happens a lot...Boeing used intermediate-diagonal-tension floor beams, Airbus used shear-resistant floor beams (for equal generation aircraft). Neither choice is right or wrong, it's just different.

Quoting Klaus (Reply 18):
How is the speed dependency of the aerodynamic controls handled?

I think it's rolled into the aileron feel & centering unit...variable deflection based on speed. Of course, with cable-driven hydraulically boosted flight controls, like the 737 and 757 have, you automatically get lower deflection at higher speed because of the increasing aerodynamic loads.

Tom.
 
rcair1
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RE: Differences Between The Boeing And Airbus Wing

Sun Jan 02, 2011 12:34 am

Quoting XT6Wagon (Reply 11):
whats the difference? Flaps 1,2,3,4,5 is the same now as 5,10,15,20,25 In some ways I much prefer the larger numbers as then you can use a gap to indicate importance. If you say skip 25 so it goes 20, 30...

In human factors testing - where you want the person to be able to interpret the behavior of they system they are controlling - a linear scale should not be used to represent non-linear response. That means that if the 'performance effect" of different flap settings is not linear, the numbers representing them should not be linear.

Assuming the "effect" ( eg. increase in lift, decrease in stall speed) changes exactly the same way when changing from 1-2, then 2-3, then 3-4, etc. - a linear scale is appropriate.

If the "effect" is non-linear - then a non-linear scale is better.

The point is the 'change' in the number should relate to the change in effect. If going from 2-3 is provides twice the effect than going form 1-2, it is not what people intuit. A scale that is 5-10-20 would be better. (or 1, 2, 4)

In human factors design/testing, we actually spend a lot of effort in trying to match the 'movement' of the control to the 'effect' being controlled.

That is why brightness/contrast controls don't work - we don't see in brightness and contrast. Same with RGB.

Quoting 2H4 (Reply 12):
Boeing flap settings are not only spaced unevenly

That would imply to the user that the moving from each setting is not "even". If that is true - the B's approach is better for B.

To be clear - I have no idea if the 1,2,3,4,5 settings on A, which would imply equal effect from each step match the response. If the effect is equal. Then 1,2,3,4,5, and 10,20,30,40,50 are equal.

If the effect is non-linear - not equal for each step, then it is bad.

Perhaps A designs for this and B designs for a different result.

I have no idea of the behavior of either A or B aircraft in this regard. I know how my cessna's react.

This assumes, of course, that the pilot is actually trying to understand how the aircraft is flying/behaving versus pushing buttons.

It does fit with the "pilots are just accessories to the computers" that some have claimed is A's approach. It also fits with the fact that A's have non-haptic feedback (no change in feedback to simulate control feel) whereas B's do attempt to model the feedback to non-FBW controls (IIRC).

I actually prefer B's approach than A's in this particular. Tactical feedback is one channel to our brain - why should we ignore it?

(Of course, on a.net - I'll probably be immediately labeled a Abasher and Blover since I dared to disagree with something A did)
rcair1
 
Klaus
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RE: Differences Between The Boeing And Airbus Wing

Sun Jan 02, 2011 2:28 am

Quoting tdscanuck (Reply 19):
I think it's rolled into the aileron feel & centering unit...variable deflection based on speed.

So there's a mechanical ratio changer in there?

Quoting tdscanuck (Reply 19):
Of course, with cable-driven hydraulically boosted flight controls, like the 737 and 757 have, you automatically get lower deflection at higher speed because of the increasing aerodynamic loads.

How so? A mechanical coupling of any kind with a positioning servo should normally produce the same control surface deflection on the same input deflection (plus/minus minor unwanted deviations due to mechanical elasticity).

In this context I would expect mechanical feel to be realized through a directly or artificially induced force at the control column, but the direct positioning link should still be preserved (as modified by a ratio changer, if present).

Quoting rcair1 (Reply 20):
That is why brightness/contrast controls don't work - we don't see in brightness and contrast. Same with RGB.

Pardon? I've used all these for years and somehow never noticed they actually didn't work...
 
Quoting rcair1 (Reply 20):
It does fit with the "pilots are just accessories to the computers" that some have claimed is A's approach. It also fits with the fact that A's have non-haptic feedback (no change in feedback to simulate control feel) whereas B's do attempt to model the feedback to non-FBW controls (IIRC).

In the Airbus system the resulting roll/pitch movement of the plane is the feedback to the sidestick command.

It is a different philosophy, but as far as I can see the pilot should subjectively have more direct control of the aircraft in a sense – (s)he's not commanding the deflection of some control surface which then indirectly controls the behaviour of the airplane, but instead directly the behaviour of the airplane without needing to think about the additional indirection in between because the airplane transparently takes care of that indirection.

That has absolutely nothing to do with making the pilot "just accessories to the computers" – the command hierarchy is still the same, just with a bit less overhead to deal with.
 
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Web500sjc
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RE: Differences Between The Boeing And Airbus Wing

Sun Jan 02, 2011 4:19 am

Quoting Klaus (Reply 21):
How so? A mechanical coupling of any kind with a positioning servo should normally produce the same control surface deflection on the same input deflection (plus/minus minor unwanted deviations due to mechanical elasticity).


The feed back comes directly from the control surface.

at 0kts it takes 10kg of force to move an airline 20 degrees- but at 100kts it takes a whole lot more force to move the controll surface because the air is trying to keep the contoll surface "neutral".

It's like sticking your hand out the window of your car on the highway. If you rotate your hand around, youl find it a lot easier to keep it even with your body if your had is parallel to the road
Boiler Up!
 
Klaus
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RE: Differences Between The Boeing And Airbus Wing

Sun Jan 02, 2011 4:44 am

Quoting web500sjc (Reply 22):
at 0kts it takes 10kg of force to move an airline 20 degrees- but at 100kts it takes a whole lot more force to move the controll surface because the air is trying to keep the contoll surface "neutral".

As I said: The feedback would be force-based, but the deflection angle would apparently still be coupled directly.

Is that the only speed-dependent change on the 757 and 737 or is the deflection angle ratio also changed the way many models do it with the rudder at higher speeds?

Airbus FBW effectively eliminates airspeed from the roll/pitch equation as far as the pilot is concerned, so there it wasn't difficult to go with just the outboard ailerons and let the flight computers deal with the different response; My question was how (and if) Boeing dealt with the same effect in their very different control regime and at a much earlier time.

That aspect is similar as far as the wing layout is concerned, but the effect of airspeed on control behaviour is apparently a different one. Exactly how that difference manifests in practice would be interesting to know.

[Edited 2011-01-01 21:04:55]
 
rcair1
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RE: Differences Between The Boeing And Airbus Wing

Sun Jan 02, 2011 3:28 pm

Quoting Klaus (Reply 21):
Pardon? I've used all these for years and somehow never noticed they actually didn't work...

   Yes - of course they work - as in operate. And you can learn to use them - particularly if you know what is going on in the tone maping behind the scenes. However they do not relate naturally to what people expect them to do. There are other controls that do map to the response of the HVS (human visual system) that 'work' much better. Also - brightness and contrast are linear functions (brightness changes the intercept, contrast the slope). Sometimes you need a non-linear transformation (commonly called gamma, but really just a power function).

Quoting Klaus (Reply 21):
In the Airbus system the resulting roll/pitch movement of the plane is the feedback to the sidestick command.

Really - I was misinformed. Yes - I knew that if you pulled the stick further it was harder, but not that the feedback was related to the aerodynamic forces on the aircraft as is the case in other systems. So - in other words, the force required to deflect the side stick a certain distance will vary based upon the aircraft's config. And buffet in the ailerons or elevator will be felt in the controls?
rcair1
 
474218
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RE: Differences Between The Boeing And Airbus Wing

Sun Jan 02, 2011 4:25 pm

Quoting web500sjc (Reply 22):
The feed back comes directly from the control surface.


Only on an aircraft "without" powered controls.

Quoting web500sjc (Reply 22):
at 0kts it takes 10kg of force to move an airline 20 degrees- but at 100kts it takes a whole lot more force to move the control surface because the air is trying to keep the control surface "neutral".


Not on aircraft with boosted or powered controls.

With hydraulically powered control surfaces the pilot only positions an input to a servo, the servo then ports fluid to the actuator (actuators). The actuator, using hydraulic power, then moves the control surface. It takes no more effort to move the input lever on the servo at 0 kts than it does at 400 kts. So to prevent the pilot from putting too much control surface movement, either "artificial feel" is added to the system or hydraulic power in regulated to prevent over control.
 
Klaus
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RE: Differences Between The Boeing And Airbus Wing

Sun Jan 02, 2011 4:53 pm

Quoting rcair1 (Reply 24):
Yes - of course they work - as in operate. And you can learn to use them - particularly if you know what is going on in the tone maping behind the scenes. However they do not relate naturally to what people expect them to do. There are other controls that do map to the response of the HVS (human visual system) that 'work' much better. Also - brightness and contrast are linear functions (brightness changes the intercept, contrast the slope). Sometimes you need a non-linear transformation (commonly called gamma, but really just a power function).

Well, I think there's still quite a difference between "don't work" and "don't match the perceptional linearity as well as one would like"...

People have been using these kinds of controls for many years and they've been relatively easy to understand and operate intuitively even so.

Quoting rcair1 (Reply 24):
Really - I was misinformed. Yes - I knew that if you pulled the stick further it was harder, but not that the feedback was related to the aerodynamic forces on the aircraft as is the case in other systems. So - in other words, the force required to deflect the side stick a certain distance will vary based upon the aircraft's config. And buffet in the ailerons or elevator will be felt in the controls?

No, there is no artificial feedback whatsoever. The acceleration of the aircraft is the feedback. The sidestick just has a progressive centering spring which provides a reset force proportional to the resulting acceleration.

The margins are not maintained by the pilot looking out for signs of turbulent airflow but by the control computers limiting control surface deflections to stay (just) clear of these limits according to the conditions at the moment.

The pilot can safely command even extreme maneuvers (full sidestick deflection) and the plane will follow as closely as aerodynamically possible at the time. Airbus has demonstrated this numerous time at airshows with takeoffs which would have been too risky to undertake in a conventional plane but are quite safe in a FBW Airbus (in the absence of windshear or other complications).

YouTube - A340 600 Demo Flight Le Bourget 2001

As many pilots around here have attested numerous times, both control systems are safe to fly, but either of them needs a specific way of handling the controls and a different way of thinking about how "flying works" with each system.

The Airbus FBW system is more abstract and takes some technical details out of the loop for the pilot to monitor and standardizes as much of the handling as far as possible across all models, the traditional (Boeing) model requires the pilot to deal with more of those details hands-on, inevitably exposing more of the individual model differences.

And how exactly airspeed influenced (particularly) roll handling on the 757 was my question...
 
tdscanuck
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 1:26 am

Quoting Klaus (Reply 21):
Quoting tdscanuck (Reply 19):
I think it's rolled into the aileron feel & centering unit...variable deflection based on speed.

So there's a mechanical ratio changer in there?

I believe so, but I haven't been able to pull down the documentation to confirm.

Quoting Klaus (Reply 21):

Quoting tdscanuck (Reply 19):
Of course, with cable-driven hydraulically boosted flight controls, like the 737 and 757 have, you automatically get lower deflection at higher speed because of the increasing aerodynamic loads.

How so? A mechanical coupling of any kind with a positioning servo should normally produce the same control surface deflection on the same input deflection (plus/minus minor unwanted deviations due to mechanical elasticity).

Hydraulically boosted systems saturate when you're applying maximum pressure. Aerodynamic load comes into the control loop as a disturbance force, which offsets the force balance point in the servo. So, as you increase speed, your maximum deflection is capped by the maximum force the actuator can supply. Since it's a pressure-based system, the maximum force point moves around with airspeed.

The most extreme case I know of is if you get a 737 up above about M=0.95 or so with a nose-down attitude...there isn't enough actuator force available to get enough elevator deflection to pull out of the dive.

Tom.
 
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 2:01 am

One thing I cannot understand is why A flap track fairings are so voluminous compared to B's. I recall reading somewhere that there was an area ruling angle to this but am not fully convinced of this argument. In general, B's fairings seem to be smaller and more compact although the difference is not as manifest on the 737NG and 747. I suspect that B's fairings are simply -and I can find no better qualification than this- better designed. The A380's fairings in particular are simply *massive*, even compared its own, outsize wing.

Faro

PS: In the case of the 767, I believe B's flap retraction mechanism is patent-protected. Maybe that's part of the explanation...
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 5:57 am

Quoting tdscanuck (Reply 27):
The most extreme case I know of is if you get a 737 up above about M=0.95 or so with a nose-down attitude...there isn't enough actuator force available to get enough elevator deflection to pull out of the dive.

At those speeds would deflecting the elevator do any good anyway?
Why do Aerospace Engineering students have to turn things in on time?
 
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 6:13 am

Quoting BMI727 (Reply 29):
Quoting tdscanuck (Reply 27):
The most extreme case I know of is if you get a 737 up above about M=0.95 or so with a nose-down attitude...there isn't enough actuator force available to get enough elevator deflection to pull out of the dive.

At those speeds would deflecting the elevator do any good anyway?

If you could get enough deflection to get a nose-up pitch moment, you might be able to keep the thing together long enough to bleed off speed to gravity. However, with the available actuator power, the aerodynamic load is too high to get nose-up pitch. The maximum-deflection point decreases with increasing airspeed because the hydraulic servo actuator is force limited.

Tom.
 
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 6:17 am

Quoting tdscanuck (Reply 30):
However, with the available actuator power, the aerodynamic load is too high to get nose-up pitch. The maximum-deflection point decreases with increasing airspeed because the hydraulic servo actuator is force limited.

But going that fast would shockwaves over the horizontal stabilizer render the elevators useless even if they could deflect enough?
Why do Aerospace Engineering students have to turn things in on time?
 
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 6:39 am

Quoting BMI727 (Reply 31):
But going that fast would shockwaves over the horizontal stabilizer render the elevators useless even if they could deflect enough?

Airfoils still work at supersonic speeds, and the basic trends are all the same (the detailed aerodynamics are different). Deflecting an elevator nose-up at supersonic speed will create another shock at the elevator/stabilizer joint on the upper surface and an expansion fan at the joint on the lower surface (both required to turn the flow to follow the elevator surface), increasing the pressure differential across the elevator and causing a nose-up pitching moment.

Tom.
 
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 8:15 am

Quoting tdscanuck (Reply 32):
Airfoils still work at supersonic speeds, and the basic trends are all the same (the detailed aerodynamics are different).

Transonic isn't exactly the same thing as subsonic and supersonic. Its a very nasty and complex area for areodynamics.

Oh yah, ask P47 pilots how well it worked in high speed dives. Go too fast and you lost all pitch control... which makes pulling out of a dive rather... difficult.
 
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 8:19 am

Quoting tdscanuck (Reply 32):

Doesn't that assume that there is no flow separation aft of the shockwave? Otherwise there would be no need for supersonic aircraft to use all moving tailplanes. I know that when the DC-8 was taken supersonic the pitch trim was placed almost full up and the pilots held the dive by pushing forward on the yoke and simply let go to pull out of the dive, creating a pseudo-all moving tailplane.
Why do Aerospace Engineering students have to turn things in on time?
 
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 9:22 am

Could one use trim instead of elevator to get out of the dive? If it was good enough for Chuck Yeager...
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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Aesma
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 10:51 am

Quoting Klaus (Reply 26):
The pilot can safely command even extreme maneuvers (full sidestick deflection) and the plane will follow as closely as aerodynamically possible at the time. Airbus has demonstrated this numerous time at airshows with takeoffs which would have been too risky to undertake in a conventional plane but are quite safe in a FBW Airbus (in the absence of windshear or other complications).

YouTube - A340 600 Demo Flight Le Bourget 2001

The day I started to like airliners ! Before that I was only into fighters   That move was incredible to see from the grass area at the show.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
tdscanuck
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 2:24 pm

Quoting BMI727 (Reply 34):
Doesn't that assume that there is no flow separation aft of the shockwave?

Yes, but even then separation isn't binary. Even with some flow separation, you can get some effect. Otherwise Concorde would have no pitch control when it was going supersonic.

Quoting BMI727 (Reply 34):
Otherwise there would be no need for supersonic aircraft to use all moving tailplanes.

There is no *need* for supersonic aircraft to use all moving tailplanes (Concorde, Bell X-1, Blackbird, etc.).

Quoting Starlionblue (Reply 35):
Could one use trim instead of elevator to get out of the dive?

Only if you haven't already burned up all the trim trying to counter Mach tuck.

Tom.
 
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 4:24 pm

Quoting tdscanuck (Reply 27):
Hydraulically boosted systems saturate when you're applying maximum pressure. Aerodynamic load comes into the control loop as a disturbance force, which offsets the force balance point in the servo. So, as you increase speed, your maximum deflection is capped by the maximum force the actuator can supply. Since it's a pressure-based system, the maximum force point moves around with airspeed.


Simply not true!

Example: The L-1011 rudder is powered by three (3) 3000 psi hydraulic systems. To prevent excessive rudder inputs over stressing the rudder and attaching structure "rudder limiting" is used. From 0 to 164 kts all three system provide full 3000 psi. Above 164 kts and below 230 kts two (2) of the three (3) hydraulic systems are shut down leaving one (1) system operating at 3000 psi. Above 260 kts the one (1) remaining hydraulic system is regulated down to 2000 psi. In addition on the very early L-1011's there were mechanical stops that extended when the the hydraulic pressure was regulated to physically prevent the rudder from moving to a point where damage could occur. Without these protections full rudder travel could have been accomplished at any speed, just like full aileron and elevator travel is available through the entire flight spectrum.

Quoting tdscanuck (Reply 37):
There is no *need* for supersonic aircraft to use all moving tailplanes (Concorde, Bell X-1, Blackbird, etc.).



The Concorde and SR-71 (and A-12 and YF-12) used fuel transfer to accomplish high mach trim.

The X-1 had a movable horizontal stabilizer with separate elevators! The ability to trim the horizontal stabilizer is what allowed it to exceed Mach 1.
 
Pihero
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RE: Differences Between The Boeing And Airbus Wing

Mon Jan 03, 2011 11:04 pm

Quoting tdscanuck (Reply 3):
Airbus's design is easier to build and maintain, and performs well enough to do the job its required to do. Boeing's design(s) tend to be higher performance but more complex and maintenance intensive.

Thats a very simplistic -and false statement-, if I knew one, as this one shows:

Quoting tdscanuck (Reply 16):
This paper is my all-time favorite for discussion of what high-lift devices are on which aircraft:
http://www.soton.ac.uk/~jps7/Aircraf...s.pdf

This paper has a funny way of reappearing once in a year for discussions of this type.
Excerpts :
"The Boeing 767-300 and 777 have virtually identical CLappr performance because their high-lift
configurations are virtually identical.
Why does the Airbus A330/340 with single-slotted flaps show CLappr performance very close to that
of the Boeing 727? Not only does the 727 have a discontinuous trailing-edge flap, but the major
factor here is technology level. The 727 was designed about 1960 and the A330/340 about 1991,
a difference of over 30 years, in which aerodynamic technology made tremendous progress.
Technology level, however, does not answer the question why contemporary airplanes like the
Boeing 777 and the Airbus A330/340 do not have similar performance; i.e., why the Airbus
airplanes are doing better with simpler high-lift systems
. The reason is not easily explained, and
any attempt to do so is politically charged, but the author presents some facts and opinions in the
following paragraphs.
The Boeing 777 has a thrust gate/high-speed aileron between the double-slotted, inboard and singleslotted,
outboard flaps. Even though the inboard aileron is slotted as well as drooped during lowspeed
operation, this design is probably not as good as a continuous Fowler flap. Another difference
is that the A330/340 has two outboard aileron panels, and the inboard panel is drooped during lowspeed
operation. A third difference could be the slat planform: The A330/340 has tapered slats,
while the Boeing 777 (with the exception of one inboard panel) has constant-chord slats. It is hard to
determine whether this difference accounts for the entire variation in performance or whether there
is also a difference in aerodynamic technology, such as better optimization for flight Reynolds
number."


Quoting mandala499 (Reply 17):
Well... with Airbus... the fancy aerodynamics in the wing design enabled the simplicity !
Quoting PapaChuck (Reply 2):
Boeing's latest offering, the 787, breaks off in an entirely new direction.
Full span slats,no thrust gate, full span single slotted Fowler flaps with drooped ailerons....Smells of an Airbus solution, doesn't it ? (as a matter of fact, it's just following th recommendation of the NASA study Tom linked us to.)


[quote=XT6Wagon,reply=4]One might note that Airbus doesn't need as much lift from the flaps due to using a wing profile biased to more lift with higher cruise drag. Boeing uses wings optimized for cruise, but pays for it with needing more help from the flaps for lowspeed performance and a climb burn penalty.

That's bull. See in the NASA study the comparative performances of all the Jetliners'wings, prior to the latest generation (i.e the 787, the A380 and the A350) and see that the Clappr -that's the lift coefficient, mark of a wing efficiency in this configuration is systematically better on an Airbus wing for comparable aircraft types. See Mandala's research on a comparison between 738 and the 320. Might change your idea on that subject, and take a further look on studies made by LAXDESI in this forum.
they are quite enlightening, too .

Quoting web500sjc (Reply 22):
at 0kts it takes 10kg of force to move an airline 20 degrees

As there is no aerodynamic force, because the relative wind is nil, there won't be any flight control effect on the aircraft.
Contrail designer
 
rcair1
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RE: Differences Between The Boeing And Airbus Wing

Tue Jan 04, 2011 2:54 am

Quoting Klaus (Reply 26):
Well, I think there's still quite a difference between "don't work" and "don't match the perceptional linearity as well as one would like"...

People have been using these kinds of controls for many years and they've been relatively easy to understand and operate intuitively even so.

Just because people can learn to use a non-intuitive control does not make that the best solution. Brightness and contrast controls were designed by engineers (like me) who understood the electronics being used - but had little or no experience in how those interactions would relate to how the effect of the control related to expectations of a non-engineer user.

We used to laugh at when people struggled with making a 'fill in the blank' work - 'error 299: dumb a** user'. But in fact it is 'error 399: dumb a** engineer.' When you have a chance to actually work on human factors testing and watch people struggle with one control - while picking up another and just "using it", it becomes very clear. You do have to leave your ego at home as an engineer tho - and that is not something that many engineers are good at.

Quoting Klaus (Reply 26):
No, there is no artificial feedback whatsoever. The acceleration of the aircraft is the feedback. The sidestick just has a progressive centering spring which provides a reset force proportional to the resulting acceleration.

So - in fact, I was not misinformed. The airbus sidestick does not have active (haptic) feedback. Unless that centering spring you mention is really relating to acceleration - then it is. However, I believe that it is, in fact, related only to side stick position - not aircraft acceleration.

That would not be my preference. However, I can see how, for budgetary and certification reasons, it was forgone in the Airbus.

The most commonly known form of haptic feedback in aircraft is the stick shaker.
----- From Wiki ----
One of the earliest forms of haptic devices is used in large modern aircraft that use servomechanism systems to operate control systems. Such systems tend to be "one-way" in that forces applied aerodynamically to the control surfaces are not perceived at the controls, with the missing normal forces simulated with springs and weights. In earlier, lighter aircraft without servo systems, as the aircraft approached a stall the aerodynamic buffeting was felt in the pilot's controls, a useful warning to the pilot of a dangerous flight condition. This control shake is not felt when servo control systems are used. To replace this missing cue, the angle of attack is measured, and when it approaches the critical stall point a "stick shaker" (an unbalanced rotating mass) is engaged, simulating the effects of a simpler control system. This is known as haptic feedback. Alternatively the servo force may be measured and this signal directed to a servo system on the control. This method is known as force feedback. Force feedback has been implemented experimentally in some excavators. This is useful when excavating mixed materials such as large rocks embedded in silt or clay, as it allows the operator to "feel" and work around unseen obstacles, enabling significant increases in productivity.
----

It is interesting to note that this is an area of philosophical difference between Boeing and Airbus in some controls.

For instance, in the 777 there is a backdrive actuator which will 'fight' the pilot as he/she reaches envelope protection limits. The pilot can override the envelope protection by pushing/pulling/turning harder. In AB FBW - there is no tactile equivalent, to override envelope protection the pilot changes the control law from normal to alternate to direct to override protections.

Similarly in the 777, the control feel does change with airspeed - designed to mimic the effect on conventional controls (if not replicate it).

Another example it the auto throttle backdrive on the throttles in Boeing and Airbus. In Boeing, the throttles move in response to auto throttle commands- as if the pilot was moving them - in Airbus, they do not. Obviously - even this visual clue did not keep the 737 crew in Amsterdam from missing the decaying airspeed.

It is clearly a matter of opinion (differing) on which approach is "better" - I certainly know of no 'hard data' to back up either position in aircraft. There is lots of data in other fields.

Personally - and professionally (no I'm not an aircraft designer - consumer electronics/software), I prefer to make use of all the human senses when financially possible.
rcair1
 
tdscanuck
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RE: Differences Between The Boeing And Airbus Wing

Tue Jan 04, 2011 5:47 am

Quoting 474218 (Reply 38):
Simply not true!

Example: The L-1011 rudder is powered by three (3) 3000 psi hydraulic systems...Without these protections full rudder travel could have been accomplished at any speed, just like full aileron and elevator travel is available through the entire flight spectrum.

It's not true *if* you have so much actuator power that you can achieve full deflection at maximum aerodynamic load. Obviously, from your description, the L-1011 is in such a situation (otherwise you wouldn't need to much rudder protection in the first place). However, this isn't a generally true situation for all aircraft.

It is absolutely true that hydraulically boosted flight control surfaces are force limited, that the aerodynamic force increases with speed, and that the aerodynamic force enters the control loop as a disturbance force. As a result, *if* you saturate your actuators, your maximum deflection point moves with airspeed. If you never reach actuator saturation, as with the L-1011, then you retain full control surface range throughout the speed envelope, which is why you need extra rudder protections on an L-1011.

Quoting 474218 (Reply 38):
Quoting tdscanuck (Reply 37):
There is no *need* for supersonic aircraft to use all moving tailplanes (Concorde, Bell X-1, Blackbird, etc.).

The Concorde and SR-71 (and A-12 and YF-12) used fuel transfer to accomplish high mach trim.

The X-1 had a movable horizontal stabilizer with separate elevators! The ability to trim the horizontal stabilizer is what allowed it to exceed Mach 1.

The argument was about whether the aerodynamics of supersonic flight would allow an elevator to work...the Concorde, Bell X-1, and Blackbird all show that you can have a moveable surface at the trailing edge that still functions properly above Mach 1. They do use other trim mechanisms to increase pitch authority, but it's not like any of those aircraft just quit using their elevators above Mach 1.

Tom.
 
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Aesma
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RE: Differences Between The Boeing And Airbus Wing

Tue Jan 04, 2011 6:31 am

Quoting tdscanuck (Reply 37):
(Concorde, Bell X-1, Blackbird, etc.).

Don't forget all the delta fighters without horizontal stabilizer at all.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
Pihero
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RE: Differences Between The Boeing And Airbus Wing

Tue Jan 04, 2011 1:17 pm

Quoting rcair1 (Reply 40):
The airbus sidestick does not have active (haptic) feedback. Unless that centering spring you mention is really relating to acceleration - then it is. However, I believe that it is, in fact, related only to side stick position - not aircraft acceleration.

A sidestick input is a rate demand on moddern Airbus, whether in pitch or in roll.

Quoting rcair1 (Reply 40):
That would not be my preference. However, I can see how, for budgetary and certification reasons, it was forgone in the Airbus.

That's a new one. Congratulations, nobody before you has had the cheek to call the Airbus solution "cheap"   
As a matter of fact, that cheap solution is the one that allows airplanes with vastly different sizes, weights, balance, to feel exactly the same, making the concept of communality a really new one. Of all the Airbii I've flown, the only one that has unmistakable characteristics is the smallest, the 318 which is twitchier than all the rest of the family in roll.

Quoting rcair1 (Reply 40):
The most commonly known form of haptic feedback in aircraft is the stick shaker.

Apparently, the British CAA did not find it obvious or safe enough as it refused to certify the Boeing 727 without a *stick pusher*.

Quoting rcair1 (Reply 40):
For instance, in the 777 there is a backdrive actuator which will 'fight' the pilot as he/she reaches envelope protection limits. The pilot can override the envelope protection by pushing/pulling/turning harder.

Yes, there is, and as a pilot, I certainly do not consider that characteristic a bonus, as were the pilot to find himself with a very high AoA and wanted out, the maneuver will be made a lot more difficult as the control forces will be increased tremenduously, making the already difficult task of accurately piloting the damn thing just inside the stick shaker speed that much more arduous.
On the 'Bus, just pull back on thre stick and firewall the thrust levers : You'll get every time the optimum performance to get you out of trouble....and I, for one, know which philosophy I prefer.
You said "designed to mimic the effect on conventional controls ? Sorry, but that statement died a long time ago when hydraulic-boosted flight controls arrived.... some sixty years ago....And pray tell me why we should pretend we're still flyind Ford Trimotors and DC-4s....and that their flying characteristics are still valid - and linear - inside thre transsonic domain...
What is amusing is that the people who are against the 'Bus philosophy are people who have never flown them ( and those who never will).

Quoting rcair1 (Reply 40):
Another example it the auto throttle backdrive on the throttles in Boeing and Airbus. In Boeing, the throttles move in response to auto throttle commands- as if the pilot was moving them - in Airbus, they do not.

Please explain how that would help you during takeoff, all throttles forward and then you have an engine failing you. Remember that you're the pilot of a modern aicraft, equipped with an automatic yaw input to counteract the induced turn toward the *dead* engine. So, the visual cue is dead wrong and the sensory clue has been removed...Oh ! Dear ! Shall we become an Airbus ?
  
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tdscanuck
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RE: Differences Between The Boeing And Airbus Wing

Tue Jan 04, 2011 2:26 pm

Quoting tdscanuck (Reply 41):
the aerodynamic force enters the control loop as a disturbance force.

Important caveat I forgot...unless your servo (the PCU, usually) has integral control, there will always be some steady state position error in the presence of a disturbance force. Servos should have high DC gain, which means the error should be small, but it's always going to be there. This is a second-order effect that's much smaller than the magnitude of actuator saturation, but in most non-FBW systems you'll see some deflection that scales with aerodynamic force even within the actuator's normal range of force.

Quoting PIHERO (Reply 43):
A sidestick input is a rate demand on moddern Airbus, whether in pitch or in roll.

I thought Airbus used a modified C* law in pitch, in which case they're commanding a blend of pitch rate and normal acceleration.

Quoting PIHERO (Reply 43):
Congratulations, nobody before you has had the cheek to call the Airbus solution "cheap"

It's a true statement that dynamic force feedback is a more expensive technology than a fixed spring rate. He didn't say Airbus was cheap, he said that they may have taken expense into consideration (which is certainly true). You don't stay in business as an OEM without considering cost-vs.-benefit of your systems.

Quoting PIHERO (Reply 43):
Quoting rcair1 (Reply 40):
The most commonly known form of haptic feedback in aircraft is the stick shaker.

Apparently, the British CAA did not find it obvious or safe enough as it refused to certify the Boeing 727 without a *stick pusher*.

Which is totally irrelevant to whether a stick shaker is the most common known form of haptic feedback in aircraft. You're setting up a straw man argument.

Quoting PIHERO (Reply 43):
I certainly do not consider that characteristic a bonus, as were the pilot to find himself with a very high AoA and wanted out, the maneuver will be made a lot more difficult as the control forces will be increased tremenduously, making the already difficult task of accurately piloting the damn thing just inside the stick shaker speed that much more arduous.

If you have a very high AoA and want out, you have to nose-down. The elevator feel shift doesn't impact your ability to put in nose-down command (in fact, it helps you)...it's not a symmetric feel shift.

Quoting PIHERO (Reply 43):
You said "designed to mimic the effect on conventional controls ? Sorry, but that statement died a long time ago when hydraulic-boosted flight controls arrived.... some sixty years ago...

Except it's just as true today as it was sixty years ago. An enormous amount of effort (for both Boeing and Airbus) goes into the FBW systems to make them fly how the pilots "think airplanes should fly." The whole point of C* pitch control (which *Airbus* started using first in commercial jets, not Boeing) is that it's an easily implemented pitch control law that makes an airplane fly the way "pilots think it should"...i.e. like conventional controls.

Quoting PIHERO (Reply 43):
Quoting rcair1 (Reply 40):
Another example it the auto throttle backdrive on the throttles in Boeing and Airbus. In Boeing, the throttles move in response to auto throttle commands- as if the pilot was moving them - in Airbus, they do not.

Please explain how that would help you during takeoff, all throttles forward and then you have an engine failing you.

It's not supposed to help you during takeoff. The throttle position shows *commanded* thrust, not actual, therefore has nothing to do with engine failure cases.

Tom.
 
mandala499
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RE: Differences Between The Boeing And Airbus Wing

Tue Jan 04, 2011 3:24 pm

Quoting Klaus (Reply 18):
Some Boeings lock out their outboard ailerons at higher speeds for at least some rough compensation. Is there any speed compensation in the 757 (or 737) where control deflection would normally be directly proportional to yoke deflection? Or does the pilot simply need to be (much) more cautious with the controls at higher speeds?
Quoting tdscanuck (Reply 19):
I think it's rolled into the aileron feel & centering unit...variable deflection based on speed.

For the aileron... for the 757/767:

Quote:
Roll Control
An aileron is located on each wing on either side of the outboard trailing edge flap. Aileron surface deflections are proportional to control wheel displacement. Spoilers begin to extend to augment roll control after several degrees of control wheel rotation. Control wheel forces increase as control displacement increases.
The control wheels are connected so that, if one control wheel jams, using significant force causes the control wheels to override. Roll control is then available using the free control wheel.

Ailerons
Aileron positions are shown on the EICAS status display. A full–scale indication corresponds to maximum aileron deflection.
Dual aileron trim switches located on the aft aisle stand must be pushed simultaneously to command trim changes. Hydraulic power from one of the three hydraulic systems is necessary to accurately set aileron trim.
The amount of aileron trim is indicated on a scale on the top of each control column.

The above wording is identical on the 757/767 FCOM/AOM.
BUT... for the 767 (and not 757) it adds:

Quote:
The aileron lockout control system permits full travel of the outboard ailerons at low speeds and locks out the outboard ailerons at high speeds. This provides the required roll authority at low airspeeds and prevents over controlling at high airspeeds.

The AIL LOCK light illuminates and the EICAS advisory message AILERON LOCKOUT displays to indicate aileron lockout actuator disagrees with the commanded position. At high airspeeds it may indicate that one or both of the outboard ailerons failed to lockout. When the message and light appear at low airspeeds it may indicate that one or both of the outboard ailerons failed to unlock.

The reasons for it are obvious... over control at high speed. For the 757, like the 737... there's no need for the lockout/limiter or ratio changer (less wing bending)... anything more that risks excessive wing bending will begin to deploy the roll spoilers (through the spoiler mixer) which spreads out the rotational forces of the wings (same with almost all modern passenger jets). Another reason why the 767 has the aileron lockout and the 757 is "conventional" is that the maximum aileron deflection on the 767 only needs 45deg roll input on the yoke but over 90deg on the 757 (and 737 IIRC).

The aileron lockout on the 767 is interesting for those who'd like to know...
On the 767 the aileron lockout is operated by an electrocal actuator which aligns the pivot points of the aileron inout and output cranks. when the lockout is in place correctly, any rotation on the input crank does not produce any movement in the output crank. The left and right electric actiators are driven by 2 Stabilizer Trim/Aileron lockout modules (SAMs) with one (Usually the left) operating both ailerons and the other in standby (usually the right). A logical cross-feed provides autoselection of the controlling SAM (again, usually the left). Each of the SAMs are fed with CAS data from the onside Air Data Computer via an ARINC429 Databus. The controlling SAM generates discrete lock commands to both the outboard aileron lockout electrical actuators. It also monitors the lockout actuator position for fault announciation (and also control switching to let the other SAM have a go). This closes the loop on the aileron feedback circuitry with respects to the lockout (any non-reversible system needs to have feedback/warnings of resultant position difference/lockouts that is not the desired output).

The lockout is done when the speed is
- 275KCAS; OR
- 0.5M to 0.58M AND speed equal to 235KCAS; OR
- Mach = or >0.58M
The tolerance band is 0.2M or 6KCAS to allow for lag time/recomputation. The lock/unlock time is about 15secs I think.

So... it's locked or not locked. No ratio change from the way I understand it (see above quote from the FCOM/AOM)

Quoting Klaus (Reply 21):
So there's a mechanical ratio changer in there?

The wording of the manual does not say so for the ailerons. The spoiler mixer is a ratio changer. The ratio changer also exists in the rudder.

Quoting Klaus (Reply 21):
A mechanical coupling of any kind with a positioning servo should normally produce the same control surface deflection on the same input deflection (plus/minus minor unwanted deviations due to mechanical elasticity).

And it's true for the 757/767 for the ailerons.

Quoting Klaus (Reply 21):
In the Airbus system the resulting roll/pitch movement of the plane is the feedback to the sidestick command.

It's only springloaded to center. Roll stick displacement = a particular roll rate (except in direct law where it is directly proportional to aileron displacement). Pitch stick displacement = a particular g-load command produced through the aircraft's vertical trajectory/acceleration changes... the computer sorts out the elevator displacements (again... except in direct law).

Quoting web500sjc (Reply 22):
at 0kts it takes 10kg of force to move an airline 20 degrees- but at 100kts it takes a whole lot more force to move the controll surface because the air is trying to keep the contoll surface "neutral".

For the 737/757/767, "yes" (0kts = zero aerodynamic load)... due to articial feel unit providing simulated "resistance".
On the 737, get a total HYD fail and U're on manual reversion and it's a lot heavier.
On the 737/757/767, get an artificial feel unit failure and U won't feel the resistance force (that's when the roll index on the yoke is used!... and on pitch the yoke is springloaded to center).

Well on pitch on 767... loss of HYD L & C loses your elev feel computer... the yoke is springloaded to center/neutral.

Quoting Klaus (Reply 23):
Airbus FBW effectively eliminates airspeed from the roll/pitch equation as far as the pilot is concerned, so there it wasn't difficult to go with just the outboard ailerons and let the flight computers deal with the different response; My question was how (and if) Boeing dealt with the same effect in their very different control regime and at a much earlier time.

On the Bus FBW... pilot makes input... computer processes it... and commands the actuators to move... and then monitors the result ("did the stuff move to the position I want?" and "am I getting the result I want?")

Pre-FBW Boeing goes about with the "pressure feedback" on the pitch and the spoiler mixer on the roll. It does NOT throw away the airspeed from the equation as far as the pilot is concerned, however, it dampens the speed related difference in reactions.

Quoting Klaus (Reply 26):
No, there is no artificial feedback whatsoever. The acceleration of the aircraft is the feedback. The sidestick just has a progressive centering spring which provides a reset force proportional to the resulting acceleration.

Correct. On the Bus the feedback (closing the control loop in the non-reversible control system to which the FBW is one type) the feedback loop is done on the flight computers and downstream... it doesn't go back upstream from the computers to the pilot except for opening the F-CTL page on the ECAM or an ECAM warning saying there's a FCTL problem (again... "disagreements downstream from the computers" or "the computers themselves disagreeing"). It then lets the crew know and if required, degrades the modes automatically.

Quoting Klaus (Reply 26):
The Airbus FBW system is more abstract and takes some technical details out of the loop for the pilot to monitor and standardizes as much of the handling as far as possible across all models, the traditional (Boeing) model requires the pilot to deal with more of those details hands-on, inevitably exposing more of the individual model differences.

Again... The mixers, feel computer (and now with the FBW)... reduces all that "differences"... but yes... different !

Quoting Klaus (Reply 26):
And how exactly airspeed influenced (particularly) roll handling on the 757 was my question...

Apart from the spoiler mixer... none I think... But the stuff I wrote above should explain the answer.

Quoting Starlionblue (Reply 35):
Could one use trim instead of elevator to get out of the dive?

Speedbrakes anyone?   
Reduce your speed and create some drag above the chord line. Bernoulli be damned! Time to rely on Newton in situations like those!    And same logic with the pulling the elevators... if the shockwave is already affecting it... the shockwave on the more curved surface is going to be more severe and appear earlier than the flatter surface... the flatter surface on the stabilizer is on top... U're more likely to get the upper surface of the elevators playing rather than the bottom surface (shockwave and boundary separation). But whether that's enough... I don't know! Your elevators might have detached by then!

Quoting PIHERO (Reply 39):
That's bull.

LOL! U know the simple answer is that the Airbus are almost always clean sheet designs and therefore doesn't carry the "legacy constraint baggage" that Boeing operators continue to demand from Boeing.

Quoting tdscanuck (Reply 41):
It's not true *if* you have so much actuator power that you can achieve full deflection at maximum aerodynamic load. Obviously, from your description, the L-1011 is in such a situation (otherwise you wouldn't need to much rudder protection in the first place). However, this isn't a generally true situation for all aircraft.

It is not unique to the L-1011. Otherwise why would you need rudder ratios and rudder limiters? Why did the elevators of the Adam Air 737-400 that plunged to the ocean is suspected to have detached much earlier than the aircraft breakup? Why did rudder hardover suspected to this date on that Silk Air 737 that went down 23yrs ago? Why do the Airbus FBW need to have G-demand protection in normal (and ALSO in alternate law?)? Those ailerons, elevators and rudders (when rudder ratio fails) are more likely to detach before the aerodynamics overcome the HYD Actuator power... heck... if I remember correctly some did become detached in high speed dives.

Quoting PIHERO (Reply 43):
Yes, there is, and as a pilot, I certainly do not consider that characteristic a bonus, as were the pilot to find himself with a very high AoA and wanted out, the maneuver will be made a lot more difficult as the control forces will be increased tremenduously, making the already difficult task of accurately piloting the damn thing just inside the stick shaker speed that much more arduous.

The major difference in the philosophy mon ami.
Boeing non-FBW's philosophy is "I'll give you all the tactile cues you need to keep you out of trouble. If that still don't get your attention (stick shaker, overspeed clicker, throttles moving to whichever end stop the A/T has gone) then you deserve to be in trouble."
Boeing's FBW philosophy goes further in that after all the above, "If you want to kill yourself then you got to fight me!" And in the case of trying to maintain Alpha-CLmax to get out of trouble in the miniscule chance that it is needed... "I'll give you hell for putting me there in the first place!"
Airbus FBW' philosophy is simple. "I fly this thing, you tell me what to do and I'll keep both of us out of trouble. If I can't do my job (critical systems for computer inputs failing) then I'll give it back to you! But if you want to kill both of us with me still protecting you... am not going to let you! Kill me first!" (Switch off the FACs!)   

Both philosophies work (most of the time anyways!) but my personal preference goes one way.

Quoting PIHERO (Reply 43):
Congratulations, nobody before you has had the cheek to call the Airbus solution "cheap"

In the words of a colleague working for an Airbus operator (and he reads this place a lot): "it's cheap redefined"   

Quoting tdscanuck (Reply 44):
I thought Airbus used a modified C* law in pitch, in which case they're commanding a blend of pitch rate and normal acceleration.

It's G-demand on pitch (Stick neutral = 1.0G trajectory). Roll is roll rate. The only time where there's a pitch rate involved is in flare mode to induce a nose down so that the pilots pull the stick back and assists a smoother transition from flight mode to ground mode (direct law).

On manual flight on decaying speed and no stick input... the nose slowly pitches up to maintain the 1.0G trajectory. IMHO in the eyes of the pilot, whether pitch rate is part of the G-load demand law or not, using it in the explanation, would just be confusing. If someone can point out the part where it says pitch rate (except for flare mode) on the Bus FBW FCOM then I'd gladly read up what I've missed.

Quoting tdscanuck (Reply 44):
It's a true statement that dynamic force feedback is a more expensive technology than a fixed spring rate.

Dynamic force feedback in a G-load demand and Roll rate normal law is not needed due to the hard limits and other protections given in the Bus FBW... unless the crew wants to try funny things on a degraded mode. But yes... should Airbus feel that it needs to be put in... it's not going to be impossible.

Now 767s... something utterly wonderful from Boeing. I'm still amazed that it's still competitive today after what? almost 30 years of no wing change except for the blended winglets which makes it even more of a wonder? The 767 to the 332 is like the 320 to the 738! An amazing older competitive design!   

Mandala499
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
travelavnut
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RE: Differences Between The Boeing And Airbus Wing

Tue Jan 04, 2011 4:02 pm

Quoting mandala499 (Reply 45):
Mandala499

Mandala, thank you for this extensive reply! Very informative  
Quoting mandala499 (Reply 45):
personal preference goes one way

So what is your preference?
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rcair1
Crew
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RE: Differences Between The Boeing And Airbus Wing

Tue Jan 04, 2011 4:12 pm

Quoting PIHERO (Reply 43):
A sidestick input is a rate demand on moddern Airbus, whether in pitch or in roll.

If I wanted to be "cheeky" I would call it a rate request, not demand.   

Quoting PIHERO (Reply 43):
had the cheek to call the Airbus solution "cheap"

What does my cheek have to do with it? Seriously - what are you talking about.

Quoting tdscanuck (Reply 44):
He didn't say Airbus was cheap,

Thanks Tom.

Quoting rcair1 (Reply 40):
for budgetary and certification reasons,

What I said is that Airbus may have decided the benefit to the pilot was not worth the cost of building and certifying haptic feedback into the sidestick. A perfectly rational argument.
I also don't like the fact that my FBW truck throttle does not have the 'feel' of the old cable driven throttle - but I can understand why.
Nor do I like how some power steering cars don't have good feedback regarding approaching skid.
On the other hand - I don't like how MUCH feedback that 35,000 lb 6x6 firetruck with no power assist in the steering has. Keep those thumbs outside the wheel.   

Quoting PIHERO (Reply 43):
Apparently, the British CAA did not find it obvious or safe enough as it refused to certify the Boeing 727 without a *stick pusher*.

Which has nothing to do with what I said.

Quoting PIHERO (Reply 43):
Please explain how that would help you during takeoff, all throttles forward

Why would I explain something irrelevant that you came up with?
In fact, I gave an example of where the added feedback in the Boeing, which should have been and addition clue, did not help the TK crew recognize the impending disaster. I'm surprised you did not lock on to that as proof that the auto throttle feedback in Boeing is not worth the cost.

Quoting mandala499 (Reply 45):
The major difference in the philosophy mon ami.
Boeing non-FBW's philosophy is "I'll gi

Nicely stated mandala499

Quoting PIHERO (Reply 43):
What is amusing is that the people who are against the 'Bus philosophy are people who have never flown them ( and those who never will).

The only Boeing I've ever flown was a Stearman - and only once - and a long time ago. BTW - it most certainly had a real "feel" in the stick.
I never have, and never will, fly either a Boeing or an Airbus transport category aircraft as anything but a passenger   

So - I guess that means, in your book, I'm not allowed an opinion about anything to do with them? Even in an area I do have experience in (haptic feedback and human factors testing). Maybe I'll understand after more   , but somehow I doubt it.
rcair1
 
Pihero
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RE: Differences Between The Boeing And Airbus Wing

Tue Jan 04, 2011 4:32 pm

Quoting tdscanuck (Reply 44):
If you have a very high AoA and want out, you have to nose-down. The elevator feel shift doesn't impact your ability to put in nose-down command (in fact, it helps you)...it's not a symmetric feel shift.

Try a windshear situation close to the ground....and your theory, albeit true at higher heights goes down the drain : You have to check your descent rate at the same time you need to nurse your AoA around max alpha So please, don't shove that control column forward, you'll kill yourself !..and , you said it, the elevator feel shift is CERTAINLY NOT HELPING YOU (it's not shouting, just an emphasis on what's happening)

Quoting tdscanuck (Reply 44):
He didn't say Airbus was cheap

He certainly came so close as to make no difference at all.

Quoting tdscanuck (Reply 44):
Except it's just as true today as it was sixty years ago.

Certainly not. Just look at the private discussion ypu"re having on this thread, transsonic aerodynamics are different, involving all sorts of phenomena linked to the presence of a set of shock waves. If it wasn't why a Mach tuck repositioning of the con trol column, then?

Quoting tdscanuck (Reply 44):
An enormous amount of effort (for both Boeing and Airbus) goes into the FBW systems to make them fly how the pilots "think airplanes should fly."

I agree with you, but the great majority of the Boeing fan population thinks that their champion is the one that promotes a natural piloting feeling wheras those Airbus people are just making the computrer fly the damn airplane instead of humans.

Quoting tdscanuck (Reply 44):
It's not supposed to help you during takeoff. The throttle position shows *commanded* thrust, not actual, therefore has nothing to do with engine failure cases.

Sorry, I'm not letting this bone go that easily : the idea is that "moving throttles are much better because they give you at all times a visual / tactile cue on your engines and aircraft behaviour...you started a much better statement, using the word *commanded*... but it doesn't change the fact that it is about useless and misleadiung everytime there's an engine problem, witness the China Airlines 747SP (engine flameout) and the Kegworth 734 (engine surge) among other instances.
So, if I understand well, that visual cue given by the moving throttles is only worthy of confidence when everything is OK ?, which puts it's usefulness into some perspective, doesn't it ?

Quoting tdscanuck (Reply 44):
Apparently, the British CAA did not find it obvious or safe enough as it refused to certify the Boeing 727 without a *stick pusher*.

Which is totally irrelevant to whether a stick shaker is the most common known form of haptic feedback in aircraft. You're setting up a straw man argument.

Errrrr.... Don't think so, when the purpose of the previous post is to introduce a very simple and efficient way of notifying the humans on board of the system behaviour, that Airbus was too cheap to implement. That was obviously the idea as the insistence on clues and cues, even for excavators, shows.
The whole pâragraph is thus :"The airbus sidestick does not have active (haptic) feedback. Unless that centering spring you mention is really relating to acceleration - then it is. However, I believe that it is, in fact, related only to side stick position - not aircraft acceleration.
That would not be my preference. However, I can see how, for budgetary and certification reasons, it was forgone in the Airbus.
The most commonly known form of haptic feedback in aircraft is the stick shaker..."

Therefore, I was quite entitled to challenge the beauty -and the choice - of so called *haptic* feedback, probably for *hapless* people. 'sorry, couldn't resist )
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mandala499
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RE: Differences Between The Boeing And Airbus Wing

Tue Jan 04, 2011 5:19 pm

Quoting PIHERO (Reply 48):
but the great majority of the Boeing fan population thinks that their champion is the one that promotes a natural piloting feeling wheras those Airbus people are just making the computrer fly the damn airplane instead of humans.

Excuse my simplistic sarcasm but...
One's honest about making the computer fly the damn plane... the other pretends that it's the human flying it!   

Quoting PIHERO (Reply 48):
So, if I understand well, that visual cue given by the moving throttles is only worthy of confidence when everything is OK ?, which puts it's usefulness into some perspective, doesn't it ?

It's useful only BEFORE you get into trouble (Boeing)...

and when the system (when working fine most of if not almost all the time) keeps you away from trouble then there's no point in having the tactile clues. And if the FCTL smart boxes can't do it's job properly... it'll disable what CAN get you into trouble and tells you... so that you know it can't keep you out of trouble (Airbus)...

Quoting travelavnut (Reply 46):
So what is your preference?

I prefer the one that only needs the throttles/thrust levers being whacked to the front most stop and just pull the stick and keep it pulled if I see cumulus granitus in front of me... to hell with everything else when I need to go-around... Coz I don't want all the extra hassles when it's my life on the line... All the talk about tactile clues or "it's nice to be able to eat a meal on a table while flying" can go to hell! They're just bonuses and none of them are perfect! (If buses are perfect then I shouldn't have to hear "clic clic clic... stall" if someone's hand or chewing gum got stuck on the trim wheels at the wrong time... and if Boeings are perfect... why the hell do I have to press a button instead of "hell! I want power NOW otherwise we're all dead" if I need to go around?)   

Mandala499
When losing situational awareness, pray Cumulus Granitus isn't nearby !

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