Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Why Flaps On Airbus Dont Have A Gap Like Others  
User currently offlineAirIndia From United Arab Emirates, joined Jan 2001, 1656 posts, RR: 1
Posted (5 years 4 months 2 weeks 15 hours ago) and read 14931 times:

I was of the understanding that the gap in flaps is required for the exhaust flows to escape. It can be seen on widebodies by Boeings/MD in the pictures below.

747

View Large View Medium
Click here for bigger photo!

Photo © Bruno Tucci


777
View Large View Medium
Click here for bigger photo!

Photo © Bruno Tucci


767
View Large View Medium
Click here for bigger photo!

Photo © Anthony Jackson


DC10
View Large View Medium
Click here for bigger photo!

Photo © David Moore



But why the Airbus current widebodies do not have that gap, but olders ones do? examples

380
View Large View Medium
Click here for bigger photo!

Photo © Bruno Tucci


340
View Large View Medium
Click here for bigger photo!

Photo © Fyodor Borisov - Russian AviaPhoto Team


330
View Large View Medium
Click here for bigger photo!

Photo © Danny Fritsche


310
View Large View Medium
Click here for bigger photo!

Photo © Szabo Gabor


300
View Large View Medium
Click here for bigger photo!

Photo © Quinn Savit



18 replies: All unread, jump to last
 
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17190 posts, RR: 66
Reply 1, posted (5 years 4 months 2 weeks 11 hours ago) and read 14859 times:

Interesting question. The answer might be quite complex.

The gap is there, I believe, because there is otherwise quite a bit of strain on the flaps behind the engine. On newer planes with newer materials, the problem might have been "solved" from a materials standpoint.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineAirIndia From United Arab Emirates, joined Jan 2001, 1656 posts, RR: 1
Reply 2, posted (5 years 4 months 2 weeks 11 hours ago) and read 14844 times:



Quoting Starlionblue (Reply 1):
newer planes with newer materials, the problem might have been "solved

That could def be one of the reasons, but 777 is pretty recent too.

Would the wing design, size (area) or power of exhaust have to do something.

I dunno, have not tried analysing but what if the jet exhaust stream in Airbuses passes below the extended flaps maybe because the engine pods are lower.

Lets see, if we get other answers. It sure is interesting to know.

Thnks for your reply.


User currently offlineOly720man From United Kingdom, joined May 2004, 6849 posts, RR: 11
Reply 3, posted (5 years 4 months 2 weeks 10 hours ago) and read 14830 times:

Looking at this


View Large View Medium
Click here for bigger photo!

Photo © Mark H



the engine hot core does seem to be lower than the flap trailing edge, as it does with the C-17


View Large View Medium
Click here for bigger photo!

Photo © Georg Noack



Also, aren't the gaps in the flaps on the various Boeings and the A300/310 where the high speed ailerons are and Airbus with its flight control systems doesn't use them anymore?



wheat and dairy can screw up your brain
User currently offlineBuyantUkhaa From Mongolia, joined May 2004, 2915 posts, RR: 3
Reply 4, posted (5 years 4 months 2 weeks 10 hours ago) and read 14798 times:



Quoting Oly720man (Reply 3):

Also, aren't the gaps in the flaps on the various Boeings and the A300/310 where the high speed ailerons are and Airbus with its flight control systems doesn't use them anymore?

That is the correct explanation I think.



I scratch my head, therefore I am.
User currently offlineRoseflyer From United States of America, joined Feb 2004, 9836 posts, RR: 52
Reply 5, posted (5 years 4 months 2 weeks 7 hours ago) and read 14703 times:

I believe the basic reason is that Boeing tries to save weight while Airbus is willing to take the weight penalty to increase flap span. There is extra weight associated with having flaps behind the engine. Temperature and stress are higher, so you need more structural strength. Does the added lift counteract the need for more weight, or can the flap span be increased in other areas behind the wing instead?

Quoting Oly720man (Reply 3):
the engine hot core does seem to be lower than the flap trailing edge, as it does with the C-17

I believe that the C-17 has titanium plates on the section of the flap exposed to the engine.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlineVikkyvik From United States of America, joined Jul 2003, 10352 posts, RR: 26
Reply 6, posted (5 years 4 months 2 weeks 5 hours ago) and read 14653 times:



Quoting Oly720man (Reply 3):

the engine hot core does seem to be lower than the flap trailing edge, as it does with the C-17

While the exhaust opening of the core does seem to be below the flap, I'd wager good money that a not-insignificant part of the core flow is hitting the lower part of the flap, as the core flow expands behind the engine.

However, it'd also have slowed down a bit as it expands.



How can I be an admiral without my cap??!
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 7, posted (5 years 4 months 2 weeks 1 hour ago) and read 14530 times:

The newer Airbus's uses single slotted flaps. Boeing, uses double slotted flaps. Since the single slot flap creates less lift it has to cover a larger portion of the wing.

You may notice that the 777 use a double slotted flaps inboard of the engine, the area of the wing that produces the most lift and single slotted flaps outboard of the engine, where additional lift would cause excess wing bending.

Airbus A318/319/320 use single slotted flaps. The A321's have double slotted flap to compensate for the additional weight.


User currently offlineGST From United Kingdom, joined Jun 2008, 938 posts, RR: 0
Reply 8, posted (5 years 4 months 2 weeks 1 hour ago) and read 14518 times:



Quoting 474218 (Reply 7):
The newer Airbus's uses single slotted flaps. Boeing, uses double slotted flaps. Since the single slot flap creates less lift it has to cover a larger portion of the wing.

The single slotted system is strurally and mechanically simpler also. The lower lift created by the flap can be extrapolated to mean less lift dependant drag and less loads on the structure. Though the section behind the engine core will need to be reinforced, it may turn out that the overall structure required is less than a double slotted system, and therefore quite possibly lighter, all things equal. The mechanical compexity is deffiunately reduced so much less time needs to be spent maintaining it and the frequency of it failing should theoretically be reduced.


User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6546 posts, RR: 54
Reply 9, posted (5 years 4 months 1 week 6 days 21 hours ago) and read 14425 times:

Let me add some speculations...

In older days flaps in landing configuration mostly went down as much as 60 degrees. It was very practical in those days since it created a lot of drag which was countered by a rather high power setting on approach. Some old engine had a rather long spool up time in case of a go around, and the high power during approach helped a lot.

60 degrees was naturally impossible behind an engine.

Today a lot less flap angle is used, mainly in order to reduce noise during approach. That makes it possible to have the hot core below the trailing edge of the flaps.

Also with FBW the need for separate high speed ailierons disappeared.

The much reduced flap angle is compensated by full length flaps plus also drooped ailerons.

Final result is much the same lift from the flaps plus drooped ailerons as in old days, but much less noise and also reduced fuel consumption, since the approach is flown with much less power.

And with modern FADEC engines spool up time is not the same issue, even if it may still be slow. At least spool up from flight idle is no longer a delicate manual thing, but a fully predicable automated thing.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6546 posts, RR: 54
Reply 10, posted (5 years 4 months 1 week 6 days 20 hours ago) and read 14405 times:

Full length flaps with wing mounted engines was not "invented" by Airbus. The BAe-146 had it.

The BAe-146 was probably the very first airliner which was designed with noise reduction as a really critical design criterium. But it was also designed for short take-off and landing.

First of all it has no leading edge slats. They produce a not insignificant noise when extended. Instead it has a wing airfoil section which partially compensates for the lack of slats. It compromises cruise efficiency and cruise speed, but it was considered a bill worth to pay.

Max flap angle is only 35 degrees on the full length flaps and the hot core exhaust passes under the flaps trailing edge.

Together with the missing slats it all gives low drag and a low power setting for a stabilized approach.

For a less stabilized approach the power could therefore go critically low for a fast spool up. But then it has a speed brake in the tail which can be used without affecting lift, unlike the traditional combined speed brakes and lift dumpers (spoilers) on the upper surface of the wing. That makes it possible to keep a reasonably high power setting at all times allowing a not too slow spool up in case that is needed.

It's all compromises, compromises and even more compromises.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 11, posted (5 years 4 months 1 week 6 days 16 hours ago) and read 14349 times:



Quoting Prebennorholm (Reply 9):
Also with FBW the need for separate high speed ailierons disappeared.



Quoting Oly720man (Reply 3):
Also, aren't the gaps in the flaps on the various Boeings and the A300/310 where the high speed ailerons are and Airbus with its flight control systems doesn't use them anymore?

Could you provide an explanation for FBW eliminating the need for the high speed aileron?

777 have high speed ailerons and they are FBW.

The L-1011 both the inboard and outboard ailerons were active at all times and they were not FBW?

The reason the outboard aileron was nulled in high speed flight is to reduce wing bending, which FBW would have no direct influence on.


User currently offlineDH106 From United Kingdom, joined Jun 2005, 626 posts, RR: 1
Reply 12, posted (5 years 4 months 1 week 6 days 15 hours ago) and read 14328 times:



Quoting 474218 (Reply 11):
Could you provide an explanation for FBW eliminating the need for the high speed aileron?

On the FBW Airbuses, the sidestick demands roll rate as an input to the computers which then 'decide' the relevant aileron deflection angle to supply that rate based on a range of other criteria including airspeed. Since the roll rate is restricted, there should never be enough aileron travel at high airspeeds to pose twisting/structural problems at the outer wing - a problem that inboard/high speed ailerons were designed to combat originally.
Strickly speaking I guess it's not the FBW that eliminated the need for high speed ailerons but the insertion of the computer into the loop to decide the deflection angles rather than it being a simple function of sidestick deflection.



...I watched c-beams glitter in the dark near the Tanhauser Gate....
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4073 posts, RR: 33
Reply 13, posted (5 years 4 months 1 week 6 days 14 hours ago) and read 14314 times:

Behind the engine exhaust the B777 has a flaperon. It droops with the flaps, but is used as an aileron as well. This is possible because of FBW.
Next time you fly a B777, get a window seat behind the wing and watch it during take off. When the flaps are extended for taxy, it comes down. When the engines are opened up for take off it goes up again and fluctuates in the engine exhaust. It is actually uncontrolled during this time and is pushed up by the exhaust. Then at about 80kts, it comes back down again. It is in the fan exhaust flow, but for as short a time as is necessary.

Quoting Prebennorholm (Reply 9):
And with modern FADEC engines spool up time is not the same issue, even if it may still be slow. At least spool up from flight idle is no longer a delicate manual thing, but a fully predicable automated thing.

Engine spool up is mandated by regulation. The engine must go from flight (or approach) idle to max thrust in 6 secs. This has been the case as long as I can remember. On older engines it was achieved by having a high flight idle to achieve this.


User currently offlineDocLightning From United States of America, joined Nov 2005, 20368 posts, RR: 59
Reply 14, posted (5 years 4 months 1 week 6 days 7 hours ago) and read 14192 times:



Quoting Prebennorholm (Reply 10):

First of all it has no leading edge slats. They produce a not insignificant noise when extended.

This is sort of OT, but I have noticed that when an A320 flies over on approach (and I live at SFO so we get a lot of them) it makes a characteristic "whistle" that other A/C don't make. I noticed that it seems to start at flap extension and so I think it's a product of the flaps.

Anyone know about that?


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 15, posted (5 years 4 months 1 week 5 days 16 hours ago) and read 14010 times:



Quoting 474218 (Reply 11):
Could you provide an explanation for FBW eliminating the need for the high speed aileron?

As DH106 noted, it's not really FBW that did it, it's the insertion of a mixer or lockout between the controls and the ailerons. It's just a lot easier to implement in FBW, so it tends to pop up there more often.

Quoting TristarSteve (Reply 13):
Behind the engine exhaust the B777 has a flaperon. It droops with the flaps, but is used as an aileron as well. This is possible because of FBW.

You can do it mechanically too, it's just much messier.

Tom.


User currently offlineHAWK21M From India, joined Jan 2001, 31712 posts, RR: 56
Reply 16, posted (5 years 4 months 1 week 5 days 13 hours ago) and read 13971 times:



Quoting TristarSteve (Reply 13):
Engine spool up is mandated by regulation. The engine must go from flight (or approach) idle to max thrust in 6 secs. This has been the case as long as I can remember. On older engines it was achieved by having a high flight idle to achieve this.

Slam Acceleration check is carried out on B737/757 during Grd run post major Mx or unscheduled related Mx.
regds
MEL.



Think of the brighter side!
User currently offlineGST From United Kingdom, joined Jun 2008, 938 posts, RR: 0
Reply 17, posted (5 years 4 months 1 week 5 days 13 hours ago) and read 13967 times:



Quoting DocLightning (Reply 14):
I have noticed that when an A320 flies over on approach (and I live at SFO so we get a lot of them) it makes a characteristic "whistle" that other A/C don't make. I noticed that it seems to start at flap extension and so I think it's a product of the flaps.

The less clean an aircraft (or any vehicle or object) is aerodynamically, the more noise it will make as air passes over it. Is the whistle similar to wind on telegraph wires on a blowy day? If so I'd say it deffinately could be linked to the flaps, as there will be an ammount of airflow that goes between the main wing and the flap, or between the two main flap surfaces.

You would be amazed how much whistling noise an ultra clean glider will make if it goes over you at 500 feet or so, even at speeds of 55kts! Now imagine it at 50 feet doing a near VNE beatup/competition finish just to the side of you. This is a very clean aircraft, moving at quite similar speeds to an A320 approach, and it makes a hell of a racket, the addition of large flap surfaces into the airflow will by definition make a massive racket.


User currently offlineRheinwaldner From Switzerland, joined Jan 2008, 2289 posts, RR: 5
Reply 18, posted (5 years 4 months 1 week 5 days 11 hours ago) and read 13935 times:

Single slotted flaps weight less and cost less for maintenance. It's a matter of "can we achieve the needed high lift without double slotted flaps"? If yes single slotted flaps are preferable. Airbus pioneered this approach that is followed by Boeing with recent new developments (787).

It is interesting that the mindshift at Airbus happened at the same time when they went from a low-wingarea-approach to a high-wingarea-approach.

The A300 and A310 had complex double slotted high lift devices. The A310 was famous for its performance in relation to the abnormal small wingarea. Wingarea+span was small, wing loading high.

The A330 and A340 simply reversed each of those paradigms. They had much simpler high lift devices. And yet the low speed and gliding capabilities are exeptional because of the large wings. The A330 is famous for its performace and efficiency due to the enourmous wing area.

The A330/A340 family founded the current trend of large wingspans+wingareas. The switch to simple high lift devices is a positive side effect. Double slotted flaps simply were no longer required.


Top Of Page
Forum Index

Reply To This Topic Why Flaps On Airbus Dont Have A Gap Like Others
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Why Do Airbus Tails Have A Bump On The Bottom? posted Sun Apr 29 2007 18:49:29 by Kaitak744
Why The Up-Curve Of Windows On Airbus Widebodies? posted Mon Aug 29 2005 04:16:58 by Web
Why Does Airbus Not Have C/n Numbers? posted Sun Jan 2 2005 15:29:23 by DeltaWings
Shaking Flaps On Tire Touchdown - Why? posted Thu Nov 25 2004 15:01:20 by Boeing nut
No Flaps Takeoff On Airbus 300? posted Sun Sep 5 2004 05:53:18 by N229NW
Why 40° Flaps On The Cessna 150? posted Fri May 14 2004 20:48:04 by Bragi
Why AA's B738 Dont Have Winglets? posted Mon Jul 21 2003 19:36:49 by B752fanatic
Small Flaps On Helicopter Rotor Blades - Why? posted Fri Jun 20 2003 20:05:31 by Mr Spaceman
Certification On Airbus A330 And A340 For Cabin Cr posted Sun Aug 9 2009 13:33:11 by LaPaige
Why 'eyebrows' On Aircraft? posted Thu Apr 16 2009 19:59:33 by Jetplaner

Sponsor Message:
Printer friendly format