Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
mxaxai
Topic Author
Posts: 1978
Joined: Sat Jun 18, 2016 7:29 am

Why no more multi-slot flaps?

Thu Sep 10, 2020 12:45 pm

Old airliners usually had multi-slot flaps. I think one of the first large aircraft with just single-slot flaps was the A320. Even some new models introduced in the 90s had multi-slot flaps, e. g. the 737NG and the 777. Airbus only added multi-slot flaps to the A321 later (which is reverting to single-slot for the XLR) and has used single-slot for everything else.

Nowadays, almost all new aircraft feature single-slot flaps. Even the 777-9 got some, and the 747-8 went from triple-slot to double-slot.

What has changed that makes multi-slot flaps obsolete? New airfoils? Better knowledge of flap design? Longer runways?
Could Boeing switch the 737 wing to a single-slot design (like Airbus is doing for the A321)?
 
tommy1808
Posts: 13478
Joined: Thu Nov 21, 2013 3:24 pm

Re: Why no more multi-slot flaps?

Thu Sep 10, 2020 1:24 pm

mxaxai wrote:
What has changed that makes multi-slot flaps obsolete? New airfoils? Better knowledge of flap design?


i guess guestimate a combination of those with better manufacturing tolerances and surface quality.

best regards
Thomas
Well, there is prophecy in the bible after all: 2 Timothy 3:1-6
 
User avatar
Starlionblue
Posts: 20092
Joined: Fri Feb 27, 2004 9:54 pm

Re: Why no more multi-slot flaps?

Thu Sep 10, 2020 2:07 pm

Vastly more powerful computational fluid dynamics have enabled much better modelling of airflow. This has led to the ability to design much more optimised airfoils.

Drooping ailerons have taken over some of the high lift workload.

New flap design features like the Airbus Adaptive Drooped Hinge Flap have been introduced. The spoilers deflect down to close the gap to the flap leading edge.

Longer runways are not really a factor. Runway performance is better now than 50 years ago, though some of that is due to more powerful engines.

Image
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Okcflyer
Posts: 667
Joined: Sat May 23, 2015 11:10 pm

Re: Why no more multi-slot flaps?

Thu Sep 10, 2020 3:39 pm

Single slot designs are lighter (less pieces, less material), cheaper, and less maintenance long term. They are the strong preference if the performance required can be achieved.
 
mxaxai
Topic Author
Posts: 1978
Joined: Sat Jun 18, 2016 7:29 am

Re: Why no more multi-slot flaps?

Fri Sep 11, 2020 11:39 am

Starlionblue wrote:
Drooping ailerons have taken over some of the high lift workload.

New flap design features like the Airbus Adaptive Drooped Hinge Flap have been introduced. The spoilers deflect down to close the gap to the flap leading edge.

Interesting. I did not know that the effect of adaptive spoilers was this large. Would it be correct to assume that this requires FBW (at least for the spoilers) since traditional methods have separate controls for spoilers and flaps? The 737MAX has FBW spoilers (viewtopic.php?t=773287), so I suppose they could use it to improve runway performance.

Starlionblue wrote:
Vastly more powerful computational fluid dynamics have enabled much better modelling of airflow. This has led to the ability to design much more optimised airfoils.

Does this imply that the original 777 wing was a conservative design? It's the only modern widebody with double-slot flaps, and also the only one to receive wingtip modifications within a few years after EIS. I guess this also made it worthwhile for Boeing to develop an all-new wing for the 777-9.

Interesting to note, the E-170/175 and E-190/195 both have partially double-slot flaps. However, the E-170 has the double-slot on the outer segment, wheras the E-190 has the double-slot on the inner segment. The E2 - much like the 777-9 - got a new wing and single-slot flaps.
 
unimproved
Posts: 204
Joined: Sun Jun 22, 2014 7:14 pm

Re: Why no more multi-slot flaps?

Fri Sep 11, 2020 12:19 pm

mxaxai wrote:
Starlionblue wrote:
Drooping ailerons have taken over some of the high lift workload.

New flap design features like the Airbus Adaptive Drooped Hinge Flap have been introduced. The spoilers deflect down to close the gap to the flap leading edge.

Interesting. I did not know that the effect of adaptive spoilers was this large. Would it be correct to assume that this requires FBW (at least for the spoilers) since traditional methods have separate controls for spoilers and flaps? The 737MAX has FBW spoilers (viewtopic.php?t=773287), so I suppose they could use it to improve runway performance.

Starlionblue wrote:
Vastly more powerful computational fluid dynamics have enabled much better modelling of airflow. This has led to the ability to design much more optimised airfoils.

Does this imply that the original 777 wing was a conservative design? It's the only modern widebody with double-slot flaps, and also the only one to receive wingtip modifications within a few years after EIS. I guess this also made it worthwhile for Boeing to develop an all-new wing for the 777-9.

Interesting to note, the E-170/175 and E-190/195 both have partially double-slot flaps. However, the E-170 has the double-slot on the outer segment, wheras the E-190 has the double-slot on the inner segment. The E2 - much like the 777-9 - got a new wing and single-slot flaps.

The 777 is still an 80s design, computing power massively increased in the decade after it was designed.
 
OldAeroGuy
Posts: 3926
Joined: Sun Dec 05, 2004 6:50 am

Re: Why no more multi-slot flaps?

Fri Sep 11, 2020 2:43 pm

The 777 Classic has double slot inboard flaps. The outboard flap is single slot.

It has a design heritage related to the 767.

Reduction of flap slots helps approach noise by reduced landing flap drag (less thrust required) and less airframe noise (slots whistle).

As Starlionblue describes, using the spoilers to control flap slot geometry and drooping the ailerons greatly improves flap performance for later FBW airplanes such as the A350, A380, 787 and 777X.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
User avatar
Horstroad
Posts: 530
Joined: Thu Apr 08, 2010 8:19 pm

Re: Why no more multi-slot flaps?

Sat Sep 12, 2020 2:36 pm

mxaxai wrote:
Would it be correct to assume that this requires FBW (at least for the spoilers) since traditional methods have separate controls for spoilers and flaps?

FBW is not required. The MD11 lifts the spoilers slightly when the flaps are extended to prevent the upper surface of the flaps from rubbing on the spoiler trailing edges. The spoiler bias is linked to the aileron lockout system and purely mechanical with cables, pushrods, linkages and some black magic in the spoiler mixers.
 
User avatar
AirKevin
Posts: 625
Joined: Wed Apr 26, 2017 2:18 am

Re: Why no more multi-slot flaps?

Sat Sep 12, 2020 8:42 pm

mxaxai wrote:
Old airliners usually had multi-slot flaps. I think one of the first large aircraft with just single-slot flaps was the A320. Even some new models introduced in the 90s had multi-slot flaps, e. g. the 737NG and the 777. Airbus only added multi-slot flaps to the A321 later (which is reverting to single-slot for the XLR) and has used single-slot for everything else.

Nowadays, almost all new aircraft feature single-slot flaps. Even the 777-9 got some, and the 747-8 went from triple-slot to double-slot.

What has changed that makes multi-slot flaps obsolete? New airfoils? Better knowledge of flap design? Longer runways?
Could Boeing switch the 737 wing to a single-slot design (like Airbus is doing for the A321)?

Just to clarify, the 747-8 has double-slotted inboard flaps. The outboard flaps are single-slotted. Same with the 767 and the 777.
Captain Kevin
 
User avatar
crimsonchin
Posts: 565
Joined: Fri Feb 07, 2014 8:16 pm

Re: Why no more multi-slot flaps?

Sat Sep 12, 2020 9:42 pm

Seems like with the exception of the A321, Airbus has preferred the single slotted flaps from the start for all their planes?
 
texl1649
Posts: 1404
Joined: Thu Aug 02, 2007 5:38 am

Re: Why no more multi-slot flaps?

Tue Sep 15, 2020 12:20 am

crimsonchin wrote:
Seems like with the exception of the A321, Airbus has preferred the single slotted flaps from the start for all their planes?


Their first designs/widebodies (A300/A310) weren’t really heavy for the time; light twins, for relatively shorter routes. The next generation were essentially a half generation after the 777.

It’s amazing how well they did with the A320 wing design, which imho ranks up there with the 787 one as among the greatest of the past 40 years.
 
WIederling
Posts: 9346
Joined: Sun Sep 13, 2015 2:15 pm

Re: Why no more multi-slot flaps?

Tue Sep 15, 2020 9:25 am

texl1649 wrote:
crimsonchin wrote:
Seems like with the exception of the A321, Airbus has preferred the single slotted flaps from the start for all their planes?


Their first designs/widebodies (A300/A310) weren’t really heavy for the time; light twins, for relatively shorter routes. The next generation were essentially a half generation after the 777.

It’s amazing how well they did with the A320 wing design, which imho ranks up there with the 787 one as among the greatest of the past 40 years.


A progression of improved supercritical designs starting with the first A300 wing progressing quite a bit with the A310 wing.
Then A320, A340/330, A380 lastly A350.
and a drive towards clean wings with closed flaplines. ( no thrust gate or similar discontinuities.)
The A340/A330 wing predates the 777 by a couple of years ( mid 80ties to early 90ties.).
Going by a NASA report neither the 777 wing nor the 737NG wing reach the aerodynamic achievements of the airbus products.
The 787 seems to be the earliest comparably capable design.

supercritical design property:
traditional profiles show a lift concentration in the first third of the wing area.
evening out the lift distribution over much more of the wing area to avoid going transsonic in the airflow
should allow higher wingloading for the same wing real estate.
Murphy is an optimist
 
Wacker1000
Posts: 233
Joined: Tue Jan 07, 2014 6:36 pm

Re: Why no more multi-slot flaps?

Tue Sep 15, 2020 9:30 am

crimsonchin wrote:
Seems like with the exception of the A321, Airbus has preferred the single slotted flaps from the start for all their planes?


It isn't a case of single vs multi. They had to get more flap into an existing area and adding the tab was a way to do it.
 
LH707330
Posts: 2353
Joined: Fri Jun 15, 2012 11:27 pm

Re: Why no more multi-slot flaps?

Wed Sep 16, 2020 1:45 am

WIederling wrote:
texl1649 wrote:
crimsonchin wrote:
Seems like with the exception of the A321, Airbus has preferred the single slotted flaps from the start for all their planes?


Their first designs/widebodies (A300/A310) weren’t really heavy for the time; light twins, for relatively shorter routes. The next generation were essentially a half generation after the 777.

It’s amazing how well they did with the A320 wing design, which imho ranks up there with the 787 one as among the greatest of the past 40 years.


A progression of improved supercritical designs starting with the first A300 wing progressing quite a bit with the A310 wing.
Then A320, A340/330, A380 lastly A350.
and a drive towards clean wings with closed flaplines. ( no thrust gate or similar discontinuities.)
The A340/A330 wing predates the 777 by a couple of years ( mid 80ties to early 90ties.).
Going by a NASA report neither the 777 wing nor the 737NG wing reach the aerodynamic achievements of the airbus products.
The 787 seems to be the earliest comparably capable design.

supercritical design property:
traditional profiles show a lift concentration in the first third of the wing area.
evening out the lift distribution over much more of the wing area to avoid going transsonic in the airflow
should allow higher wingloading for the same wing real estate.

Do you have a link to that NASA report?
 
TTailedTiger
Posts: 2588
Joined: Sun Aug 26, 2018 5:19 am

Re: Why no more multi-slot flaps?

Wed Sep 16, 2020 7:11 am

WIederling wrote:
texl1649 wrote:
crimsonchin wrote:
Seems like with the exception of the A321, Airbus has preferred the single slotted flaps from the start for all their planes?


Their first designs/widebodies (A300/A310) weren’t really heavy for the time; light twins, for relatively shorter routes. The next generation were essentially a half generation after the 777.

It’s amazing how well they did with the A320 wing design, which imho ranks up there with the 787 one as among the greatest of the past 40 years.


A progression of improved supercritical designs starting with the first A300 wing progressing quite a bit with the A310 wing.
Then A320, A340/330, A380 lastly A350.
and a drive towards clean wings with closed flaplines. ( no thrust gate or similar discontinuities.)
The A340/A330 wing predates the 777 by a couple of years ( mid 80ties to early 90ties.).
Going by a NASA report neither the 777 wing nor the 737NG wing reach the aerodynamic achievements of the airbus products.
The 787 seems to be the earliest comparably capable design.

supercritical design property:
traditional profiles show a lift concentration in the first third of the wing area.
evening out the lift distribution over much more of the wing area to avoid going transsonic in the airflow
should allow higher wingloading for the same wing real estate.


I thought the wing of the 737NG being newer than the A320 was one reason why the 738 outperformed the A320 on transcontinental flights? I'm not sure how you can claim the A320 wing is superior. It all depends on which details you are looking at.
 
tommy1808
Posts: 13478
Joined: Thu Nov 21, 2013 3:24 pm

Re: Why no more multi-slot flaps?

Wed Sep 16, 2020 10:23 am

TTailedTiger wrote:
WIederling wrote:
texl1649 wrote:

Their first designs/widebodies (A300/A310) weren’t really heavy for the time; light twins, for relatively shorter routes. The next generation were essentially a half generation after the 777.

It’s amazing how well they did with the A320 wing design, which imho ranks up there with the 787 one as among the greatest of the past 40 years.


A progression of improved supercritical designs starting with the first A300 wing progressing quite a bit with the A310 wing.
Then A320, A340/330, A380 lastly A350.
and a drive towards clean wings with closed flaplines. ( no thrust gate or similar discontinuities.)
The A340/A330 wing predates the 777 by a couple of years ( mid 80ties to early 90ties.).
Going by a NASA report neither the 777 wing nor the 737NG wing reach the aerodynamic achievements of the airbus products.
The 787 seems to be the earliest comparably capable design.

supercritical design property:
traditional profiles show a lift concentration in the first third of the wing area.
evening out the lift distribution over much more of the wing area to avoid going transsonic in the airflow
should allow higher wingloading for the same wing real estate.


I thought the wing of the 737NG being newer than the A320 was one reason why the 738 outperformed the A320 on transcontinental flights?


Nope, the reason why the NG outperformed the A320 on that mission is ~3000L more fuel volume.

I'm not sure how you can claim the A320 wing is superior. .


because it is supercritical vs. only being partially supercritical on the NG (and 757/767). Iirc the wing root still got a conventional airfoil.

best regards
Thomas.
Well, there is prophecy in the bible after all: 2 Timothy 3:1-6
 
WIederling
Posts: 9346
Joined: Sun Sep 13, 2015 2:15 pm

Re: Why no more multi-slot flaps?

Wed Sep 16, 2020 4:24 pm

LH707330 wrote:
Do you have a link to that NASA report?


one ref:
https://www.nasa.gov/pdf/89232main_TF-2004-13-DFRC.pdf

89232main_TF-2004-13-DFRC p3 wrote:
Boeing's 757 and 767 jetliners, and the new
generation of 737 aircraft, also have wings designed
with some form of applied supercritical technology


In a way semantics what is tagged as "supercritical wing".
Only full hog acceptable or just steps in the right direction?
Beginning with the first research from Göttingen during WWII
continued in Britain long before that NASA guy invented it anew
this feature has been developed in a long progression.

This is a bit like the laminar flow nacelle for the 787:
Extending laminar flow from ~~25% along the nacelle
to slightly beyond 30..% created a
"(fully?) laminar flow nacelle, a global first on Dreamliner" in PR parlance.
Murphy is an optimist
 
LH707330
Posts: 2353
Joined: Fri Jun 15, 2012 11:27 pm

Re: Why no more multi-slot flaps?

Thu Sep 17, 2020 12:04 am

Thanks, I'll take a gander at it!
 
tomcat
Posts: 598
Joined: Thu Sep 28, 2000 4:14 am

Re: Why no more multi-slot flaps?

Thu Sep 17, 2020 3:15 pm

WIederling wrote:
texl1649 wrote:
crimsonchin wrote:
Seems like with the exception of the A321, Airbus has preferred the single slotted flaps from the start for all their planes?


Their first designs/widebodies (A300/A310) weren’t really heavy for the time; light twins, for relatively shorter routes. The next generation were essentially a half generation after the 777.

It’s amazing how well they did with the A320 wing design, which imho ranks up there with the 787 one as among the greatest of the past 40 years.


A progression of improved supercritical designs starting with the first A300 wing progressing quite a bit with the A310 wing.
Then A320, A340/330, A380 lastly A350.
and a drive towards clean wings with closed flaplines. ( no thrust gate or similar discontinuities.)
The A340/A330 wing predates the 777 by a couple of years ( mid 80ties to early 90ties.).
Going by a NASA report neither the 777 wing nor the 737NG wing reach the aerodynamic achievements of the airbus products.
The 787 seems to be the earliest comparably capable design.

supercritical design property:
traditional profiles show a lift concentration in the first third of the wing area.
evening out the lift distribution over much more of the wing area to avoid going transsonic in the airflow
should allow higher wingloading for the same wing real estate.


The A300 and A310 wings also had less sweep (28°) than their closest Boeing equivalent, ie the 767, which had a 31.5° sweep. Less sweep is beneficial for the low speed characteristics and that helps to keep a simpler flap design (other things being equal).
 
N1120A
Posts: 26574
Joined: Sun Dec 14, 2003 5:40 pm

Re: Why no more multi-slot flaps?

Thu Sep 17, 2020 7:29 pm

TTailedTiger wrote:
WIederling wrote:
texl1649 wrote:

Their first designs/widebodies (A300/A310) weren’t really heavy for the time; light twins, for relatively shorter routes. The next generation were essentially a half generation after the 777.

It’s amazing how well they did with the A320 wing design, which imho ranks up there with the 787 one as among the greatest of the past 40 years.


A progression of improved supercritical designs starting with the first A300 wing progressing quite a bit with the A310 wing.
Then A320, A340/330, A380 lastly A350.
and a drive towards clean wings with closed flaplines. ( no thrust gate or similar discontinuities.)
The A340/A330 wing predates the 777 by a couple of years ( mid 80ties to early 90ties.).
Going by a NASA report neither the 777 wing nor the 737NG wing reach the aerodynamic achievements of the airbus products.
The 787 seems to be the earliest comparably capable design.

supercritical design property:
traditional profiles show a lift concentration in the first third of the wing area.
evening out the lift distribution over much more of the wing area to avoid going transsonic in the airflow
should allow higher wingloading for the same wing real estate.


I thought the wing of the 737NG being newer than the A320 was one reason why the 738 outperformed the A320 on transcontinental flights? I'm not sure how you can claim the A320 wing is superior. It all depends on which details you are looking at.


The 738 is a larger airplane that holds more fuel, but has similar costs and burn. That is why it outperforms the A320.
Mangeons les French fries, mais surtout pratiquons avec fierte le French kiss
 
LH707330
Posts: 2353
Joined: Fri Jun 15, 2012 11:27 pm

Re: Why no more multi-slot flaps?

Thu Sep 17, 2020 10:42 pm

WIederling wrote:
The A340/A330 wing predates the 777 by a couple of years ( mid 80ties to early 90ties.).
Going by a NASA report neither the 777 wing nor the 737NG wing reach the aerodynamic achievements of the airbus products.
The 787 seems to be the earliest comparably capable design.

I checked out the report you linked, but could not find a passage about the respective comparisons on these designs. You recall where else you may have seen it?
 
744SPX
Posts: 254
Joined: Mon Jan 27, 2020 6:20 pm

Re: Why no more multi-slot flaps?

Fri Sep 18, 2020 1:23 pm

The 747SP has single slotted flaps
 
User avatar
ElroyJetson
Posts: 837
Joined: Fri May 26, 2017 5:04 am

Re: Why no more multi-slot flaps?

Fri Sep 18, 2020 3:04 pm

Starlionblue wrote:
Vastly more powerful computational fluid dynamics have enabled much better modelling of airflow. This has led to the ability to design much more optimised airfoils.

Drooping ailerons have taken over some of the high lift workload.

New flap design features like the Airbus Adaptive Drooped Hinge Flap have been introduced. The spoilers deflect down to close the gap to the flap leading edge.

Longer runways are not really a factor. Runway performance is better now than 50 years ago, though some of that is due to more powerful engines.

Image



As I recall triple slotted flaps on the 727 were mostly about field performance as the 727 was replacing many turboprops (Electra as an example) that did not use long runways. I know Eastern told Boeing in order for them to purchase the 727 it must be able to take off from LGA with a full load. Those Krueger flaps were complex but worked beautifully.

Today engines are more powerful, runways are often longer, and wing performance has greatly improved. Why add the complexity and weight of it is unnecessary.
707 717 727 72S 737 733 737-700 747 757 753 767-300 764 A319 A320 DC-9-10 DC-9-30 DC-9-50, MD-82 MD-88 MD-90 DC-10-10 DC-10-40 F-100
 
GalaxyFlyer
Posts: 6239
Joined: Fri Jan 01, 2016 4:44 am

Re: Why no more multi-slot flaps?

Fri Sep 18, 2020 3:10 pm

The only reason for triple-slotted flaps is field performance. KLGA didn’t have the runway pier extensions then, either.
 
DH106
Posts: 634
Joined: Wed Jun 15, 2005 5:32 pm

Re: Why no more multi-slot flaps?

Fri Sep 18, 2020 3:13 pm

ElroyJetson wrote:
Those Krueger flaps were complex but worked beautifully.


The Krueger flaps are actually quite simple, on the inner leading edges. Are you referring to the triple slotted trailing edge flaps perhaps?
...I watched c-beams glitter in the dark by the Tanhauser Gate....
 
User avatar
ElroyJetson
Posts: 837
Joined: Fri May 26, 2017 5:04 am

Re: Why no more multi-slot flaps?

Fri Sep 18, 2020 3:26 pm

DH106 wrote:
ElroyJetson wrote:
Those Krueger flaps were complex but worked beautifully.


The Krueger flaps are actually quite simple, on the inner leading edges. Are you referring to the triple slotted trailing edge flaps perhaps?



Yes, I mentioned the triple slotted feature and that is what I was referencing. Some dubbed it the canoe for how it folded out at full extension. And the poster above is correct, initially the triple slotted wing feature was all about field performance.

A standard runway length for many airports in the 1960's was around 5500 ft. With existing engine tech of the era a single slot design on a 727 would not have worked to get it in the air with a full load. The Krueger flaps were an ingenious solution. Now most intermediate airports have a 9000 ft runway so field performance, along with improved wing and engine tech is not so much an issue.
707 717 727 72S 737 733 737-700 747 757 753 767-300 764 A319 A320 DC-9-10 DC-9-30 DC-9-50, MD-82 MD-88 MD-90 DC-10-10 DC-10-40 F-100
 
User avatar
ElroyJetson
Posts: 837
Joined: Fri May 26, 2017 5:04 am

Re: Why no more multi-slot flaps?

Fri Sep 18, 2020 3:33 pm

WIederling wrote:
texl1649 wrote:
crimsonchin wrote:
Seems like with the exception of the A321, Airbus has preferred the single slotted flaps from the start for all their planes?


Their first designs/widebodies (A300/A310) weren’t really heavy for the time; light twins, for relatively shorter routes. The next generation were essentially a half generation after the 777.

It’s amazing how well they did with the A320 wing design, which imho ranks up there with the 787 one as among the greatest of the past 40 years.


A progression of improved supercritical designs starting with the first A300 wing progressing quite a bit with the A310 wing.
Then A320, A340/330, A380 lastly A350.
and a drive towards clean wings with closed flaplines. ( no thrust gate or similar discontinuities.)
The A340/A330 wing predates the 777 by a couple of years ( mid 80ties to early 90ties.).
Going by a NASA report neither the 777 wing nor the 737NG wing reach the aerodynamic achievements of the airbus products.
The 787 seems to be the earliest comparably capable design.

supercritical design property:
traditional profiles show a lift concentration in the first third of the wing area.
evening out the lift distribution over much more of the wing area to avoid going transsonic in the airflow
should allow higher wingloading for the same wing real estate.


I have never heard this. I do not disbelieve you but I would love to see the data. I know the 707 had a more efficient wing than the DC-8 which is why it ultimately sold better. But that was not fully known and understood until quite a few years after EIS.

If the A320 family has a more efficient wing it is not reflected in fuel burn as both the 737 NG and A320 are extremely close depending on mission. Anyway, I would love to see the data.

Regards.
707 717 727 72S 737 733 737-700 747 757 753 767-300 764 A319 A320 DC-9-10 DC-9-30 DC-9-50, MD-82 MD-88 MD-90 DC-10-10 DC-10-40 F-100
 
WIederling
Posts: 9346
Joined: Sun Sep 13, 2015 2:15 pm

Re: Why no more multi-slot flaps?

Sat Sep 19, 2020 10:06 am

LH707330 wrote:
WIederling wrote:
The A340/A330 wing predates the 777 by a couple of years ( mid 80ties to early 90ties.).
Going by a NASA report neither the 777 wing nor the 737NG wing reach the aerodynamic achievements of the airbus products.
The 787 seems to be the earliest comparably capable design.

I checked out the report you linked, but could not find a passage about the respective comparisons on these designs. You recall where else you may have seen it?

NO comparison.
Statement about Boeing details only. ( elements of but not fully.... )
Murphy is an optimist
 
mxaxai
Topic Author
Posts: 1978
Joined: Sat Jun 18, 2016 7:29 am

Re: Why no more multi-slot flaps?

Sat Sep 19, 2020 11:20 am

tomcat wrote:
The A300 and A310 wings also had less sweep (28°) than their closest Boeing equivalent, ie the 767, which had a 31.5° sweep. Less sweep is beneficial for the low speed characteristics and that helps to keep a simpler flap design (other things being equal).

That's a good point. The original 777 had a sweep of 31.6°, which is reduced to 28° for the 777X. The A380 also has less than the 747 (33.5° vs. 37.5°), and the A350 has slightly less than the 787 (31.9° vs 32.2°). So one could argue that modern supercritical airfoils allow for less sweep at the same cruise speed, which improves low speed characteristics and flap design. On the other hand, both the A350 and 787 went up compared to their predecessors (the A330 has 29.7° and the A340NG got pushed to 31.1°).

However, the 737 and A320 both feature a sweep of 25°. The 737 prior to the NG had triple-slot flaps whereas the A320 had single-slot flaps already in 1988. That's less than the 727 at 32° - which was built for high cruise speed and short runways - but it still doesn't explain why the 737NG retains a relatively complex flap design.
 
WIederling
Posts: 9346
Joined: Sun Sep 13, 2015 2:15 pm

Re: Why no more multi-slot flaps?

Sat Sep 19, 2020 4:01 pm

DH106 wrote:
ElroyJetson wrote:
Those Krueger flaps were complex but worked beautifully.


The Krueger flaps are actually quite simple, on the inner leading edges. Are you referring to the triple slotted trailing edge flaps perhaps?


Image
ref: https://forums.x-plane.org/uploads/mont ... db4340.jpg

not in every case. :-)
( on the 747 this seems to have been a rather complex design.)
Murphy is an optimist
 
tomcat
Posts: 598
Joined: Thu Sep 28, 2000 4:14 am

Re: Why no more multi-slot flaps?

Sat Sep 19, 2020 5:48 pm

mxaxai wrote:
tomcat wrote:
The A300 and A310 wings also had less sweep (28°) than their closest Boeing equivalent, ie the 767, which had a 31.5° sweep. Less sweep is beneficial for the low speed characteristics and that helps to keep a simpler flap design (other things being equal).

That's a good point. The original 777 had a sweep of 31.6°, which is reduced to 28° for the 777X. The A380 also has less than the 747 (33.5° vs. 37.5°), and the A350 has slightly less than the 787 (31.9° vs 32.2°). So one could argue that modern supercritical airfoils allow for less sweep at the same cruise speed, which improves low speed characteristics and flap design. On the other hand, both the A350 and 787 went up compared to their predecessors (the A330 has 29.7° and the A340NG got pushed to 31.1°).

However, the 737 and A320 both feature a sweep of 25°. The 737 prior to the NG had triple-slot flaps whereas the A320 had single-slot flaps already in 1988. That's less than the 727 at 32° - which was built for high cruise speed and short runways - but it still doesn't explain why the 737NG retains a relatively complex flap design.


Besides the wing aerodynamics optimisation comprising the airfoil selection, the slats and flaps kinematics and the quality of its surface finish, I would list the following factors driving the flaps design:
- the wing loading
- the wing sweep
- the aircraft thrust to weight ratio
- the targeted takeoff and landing performances
- the available angle of attack upon takeoff and landing

These factors are all interdependent and are the results of tradeoffs carried out during the early design phases.

I don't have an table available to compare all these factors for all the aircraft you mentioned but on top of my head I would say that the 737 starting from the -400 and longer is penalized by its low landing gear which limits the angle of attack during takeoff and landing. This is probably one of the reasons, if not the main one, explaining why the NG retains this fairly complex flap design.
 
GalaxyFlyer
Posts: 6239
Joined: Fri Jan 01, 2016 4:44 am

Re: Why no more multi-slot flaps?

Sat Sep 19, 2020 8:57 pm

Another comparison in high-end Bizjets. The G650 uses a rather simpler wing generous wing area and single slotted flaps, no slats. The Global 7500 uses more sweep,slats and double-slotted flaps that extend aligned with the flow rather than normal to the sweep angle to achieve somewhat field and cruise performance at 10,000 pounds heavier gross and a heavier wing loading. It is all about trade-offs.
 
WIederling
Posts: 9346
Joined: Sun Sep 13, 2015 2:15 pm

Re: Why no more multi-slot flaps?

Sun Sep 20, 2020 8:09 am

A comparative look at high lift devices and arrangements, unfortunately ending in 1996:
https://ntrs.nasa.gov/citations/19960052267 ( go for the pdf download link at the bottom. )
Murphy is an optimist

Who is online

Users browsing this forum: No registered users and 37 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos