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Differences Between The Boeing And Airbus Wing  
User currently offlineThrust From United States of America, joined Sep 2003, 2690 posts, RR: 10
Posted (3 years 8 months 3 weeks 6 days 7 hours ago) and read 17532 times:

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.


Fly one thing; Fly it well
74 replies: All unread, showing first 25:
 
User currently offlinePGNCS From United States of America, joined Apr 2007, 2825 posts, RR: 45
Reply 1, posted (3 years 8 months 3 weeks 6 days 6 hours ago) and read 17566 times:

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.

User currently offlinePapaChuck From United States of America, joined Aug 2010, 136 posts, RR: 0
Reply 2, posted (3 years 8 months 3 weeks 6 days 5 hours ago) and read 17529 times:

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



In-trail spacing is a team effort.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 3, posted (3 years 8 months 3 weeks 6 days 4 hours ago) and read 17456 times:

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.


User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3409 posts, RR: 4
Reply 4, posted (3 years 8 months 3 weeks 5 days 23 hours ago) and read 17357 times:

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".


User currently offlineBMI727 From United States of America, joined Feb 2009, 15745 posts, RR: 27
Reply 5, posted (3 years 8 months 3 weeks 5 days 21 hours ago) and read 17316 times:

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?
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 6, posted (3 years 8 months 3 weeks 5 days 21 hours ago) and read 17303 times:

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.


User currently offlinekeesje From , joined Dec 1969, posts, RR:
Reply 7, posted (3 years 8 months 3 weeks 5 days 19 hours ago) and read 17280 times:

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


User currently offlinePapaChuck From United States of America, joined Aug 2010, 136 posts, RR: 0
Reply 8, posted (3 years 8 months 3 weeks 5 days 14 hours ago) and read 17112 times:

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



In-trail spacing is a team effort.
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 9, posted (3 years 8 months 3 weeks 5 days 13 hours ago) and read 17086 times:

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.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 10, posted (3 years 8 months 3 weeks 5 days 13 hours ago) and read 17074 times:
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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.



Intentionally Left Blank
User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3409 posts, RR: 4
Reply 11, posted (3 years 8 months 3 weeks 5 days 13 hours ago) and read 17057 times:

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.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 12, posted (3 years 8 months 3 weeks 5 days 12 hours ago) and read 17025 times:
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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.



Intentionally Left Blank
User currently offlineKlaus From Germany, joined Jul 2001, 21470 posts, RR: 53
Reply 13, posted (3 years 8 months 3 weeks 5 days 12 hours ago) and read 17026 times:

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.


User currently offlineA342 From Germany, joined Jul 2005, 4682 posts, RR: 3
Reply 14, posted (3 years 8 months 3 weeks 5 days 12 hours ago) and read 16979 times:

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.
User currently offlineBMI727 From United States of America, joined Feb 2009, 15745 posts, RR: 27
Reply 15, posted (3 years 8 months 3 weeks 5 days 11 hours ago) and read 16961 times:

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?
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 16, posted (3 years 8 months 3 weeks 5 days 11 hours ago) and read 16935 times:

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.


User currently offlinemandala499 From Indonesia, joined Aug 2001, 6878 posts, RR: 75
Reply 17, posted (3 years 8 months 3 weeks 5 days 10 hours ago) and read 16912 times:

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



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineKlaus From Germany, joined Jul 2001, 21470 posts, RR: 53
Reply 18, posted (3 years 8 months 3 weeks 5 days 8 hours ago) and read 16815 times:

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?


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 19, posted (3 years 8 months 3 weeks 5 days 7 hours ago) and read 16759 times:

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.


User currently offlinercair1 From United States of America, joined Oct 2009, 1323 posts, RR: 52
Reply 20, posted (3 years 8 months 3 weeks 5 days 4 hours ago) and read 16670 times:
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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
User currently offlineKlaus From Germany, joined Jul 2001, 21470 posts, RR: 53
Reply 21, posted (3 years 8 months 3 weeks 5 days 3 hours ago) and read 16614 times:

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.


User currently offlineweb500sjc From United States of America, joined Sep 2009, 740 posts, RR: 0
Reply 22, posted (3 years 8 months 3 weeks 5 days 1 hour ago) and read 16555 times:
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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!
User currently offlineKlaus From Germany, joined Jul 2001, 21470 posts, RR: 53
Reply 23, posted (3 years 8 months 3 weeks 5 days ago) and read 16533 times:

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]

User currently offlinercair1 From United States of America, joined Oct 2009, 1323 posts, RR: 52
Reply 24, posted (3 years 8 months 3 weeks 4 days 14 hours ago) and read 16343 times:
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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
25 474218 : Only on an aircraft "without" powered controls. Not on aircraft with boosted or powered controls. With hydraulically powered control surfaces the pil
26 Post contains links Klaus : 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
27 tdscanuck : I believe so, but I haven't been able to pull down the documentation to confirm. Hydraulically boosted systems saturate when you're applying maximum
28 faro : 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
29 BMI727 : At those speeds would deflecting the elevator do any good anyway?
30 tdscanuck : 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 grav
31 BMI727 : But going that fast would shockwaves over the horizontal stabilizer render the elevators useless even if they could deflect enough?
32 tdscanuck : Airfoils still work at supersonic speeds, and the basic trends are all the same (the detailed aerodynamics are different). Deflecting an elevator nos
33 XT6Wagon : 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 wel
34 BMI727 : 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
35 Starlionblue : Could one use trim instead of elevator to get out of the dive? If it was good enough for Chuck Yeager...
36 Post contains images Aesma : 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.
37 tdscanuck : 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 w
38 474218 : 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
39 PIHERO : Thats a very simplistic -and false statement-, if I knew one, as this one shows: This paper has a funny way of reappearing once in a year for discuss
40 rcair1 : 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
41 tdscanuck : 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
42 Aesma : Don't forget all the delta fighters without horizontal stabilizer at all.
43 Post contains images PIHERO : A sidestick input is a rate demand on moddern Airbus, whether in pitch or in roll. That's a new one. Congratulations, nobody before you has had the c
44 tdscanuck : Important caveat I forgot...unless your servo (the PCU, usually) has integral control, there will always be some steady state position error in the p
45 Post contains images mandala499 : For the aileron... for the 757/767: The above wording is identical on the 757/767 FCOM/AOM. BUT... for the 767 (and not 757) it adds: The reasons for
46 Post contains images travelavnut : Mandala, thank you for this extensive reply! Very informative So what is your preference?
47 Post contains images rcair1 : If I wanted to be "cheeky" I would call it a rate request, not demand. What does my cheek have to do with it? Seriously - what are you talking about.
48 PIHERO : 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
49 Post contains images mandala499 : 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! It
50 Post contains images mandala499 : I've always thought the airflow behind the shockwave in relation to the airframe is subsonic (at perpendicular angle to to the shockwave) The problem
51 Post contains images PIHERO : Funny enough, I have the same preference ! To illustrate what I said earlier about perceived Airbus idiosyncracies and Boeing superiority, an excerpt
52 rcair1 : I specified my preference, I did not claim superiority. I leave that to you. And the instance I gave was example where the "superiority" (your word,
53 SEPilot : Well, according to the sales statistics it's not been competitive for quite a while.
54 tdscanuck : A great deal of gain changing (ratio changes, etc.) is to improve the feel to the pilot...it's entirely possible to have ratio changers that still le
55 Starlionblue : Saying "you had the cheek to..." is britspeak for "how dare you?" more or less.
56 PIHERO : Oh Great. It's not the first time this argument comes back on this subject, and no one has ever contradicted me on this scenario. The situation is qu
57 PIHERO : Sorry, I missed this part . I , of course totally disagree with you. Good ergonomics are about making the tasks simpler and easier to perform. In the
58 tdscanuck : The only instructions I've ever heard from any instructor pilot are fly to the pitch limit indicator (this is for Boeing, I'm not sure what the Airbu
59 BMI727 : For what it's worth, I think I was partially misunderstanding why elevators might become less effective by neglecting the effect of the shockwave on
60 PIHERO : There is no PLI for the 'Buses other than the +30° / -15° that are solidly cast in the PFD. That's of course because of the envelope limits definit
61 Post contains images Klaus : Just to set the baseline: I'm an IT developer, so I understand system design, user interfaces and perception principles pretty well. I'm not flying my
62 Post contains images PGNCS : I have flown and instructed on both A and B products (McD and Lockheed, too.) I recognize the merits on both sides of this conversation, and come out
63 tdscanuck : Agreed, but pre-FBW hydraulic PCU's aren't digital, and aren't even particularly good analog servos...they're fast and powerful, but position accurac
64 PGNCS : That is exactly correct in the real world, and you stated it much more clearly than I could have. It's a great theory to be able to eke out a bit mor
65 Max Q : You raise a good point Klaus. Without inboard Ailerons the roll response on the B757 is quite sluggish and nowhere near as responsive as the 727 / 74
66 PIHERO : PGNCS : The cavalry has arrived. Many thanks for the gentlemanly manner you solved that situation with. I have to confess that I cannot be as serene a
67 CALTECH : What about the anti-B boys who for so long claimed the A-320 was so perfect it didn't need winglets/sharklets ? That the B-737 wing was flawed so it
68 Post contains images 2H4 : I love that argument. It ignores the fact that any wing can benefit from a span extension.
69 Pihero : You have flown ON the 'Bus. I have flown the 'Bus (and the 73 too, btw) Very strange as the Lufthansa seating is both wider and with a longer pitch t
70 Post contains images PGNCS : You are most welcome, sir! It is difficult sometimes to respond unemotionally, and I am far from perfect in this regard. On this one I, like you, am
71 Post contains images Aaron747 : LOL hilarious. I *heart* this forum - can learn just so much in a few scrolls of the mouse wheel. So what I basically take from the above is: you hav
72 747400sp : I did not know 737s had triple-slotted flaps.
73 Post contains images ferpe : If one tries to return the subject of the thread: "Differences Between The Boeing And Airbus Wing" and one looks at their latest designs, 787 vs 350:
74 Starlionblue : I think we may be fooled by visual clues quite a bit. LH always gave me a bit of cramped impression, though it has been a while since I flew them. I
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