airlinebuilder
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Few Questions On Aircraft Mechanisms

Fri Sep 13, 2013 1:52 am

Hello All, I have a few questions on Aircraft mechanisms that I have periodically been dying to ask.

Airbus : Why is it that almost all airbus aircrafts except the A380 leading edge and trailing edge flaps are left extended when on ground? (is this a basic operational manual requirement?)

Why are airbus trailing edge flaps except the A380 span area when extended are quite small and during full landing configuration there seem to be just a small difference on the angle when taking off especially on the A330/340?

Boeing : Was wandering why the two inner leading edge flaps of the B747s retract during reverse thrust?

I know this has been covered before but a refresher, cant seem to find it. Thank you
 
AA737-823
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RE: Few Questions On Aircraft Mechanisms

Fri Sep 13, 2013 2:56 am

Quoting airlinebuilder (Thread starter):
Boeing : Was wandering why the two inner leading edge flaps of the B747s retract during reverse thrust?

Because the thrust reversers direct high velocity air up into the backside of the Krueger flaps if they are extended. To protect the mechanical mechanisms, the flaps are retracted, to prevent any debris from impacting the actuation works.

Quoting airlinebuilder (Thread starter):
leading edge and trailing edge flaps are left extended when on ground? (is this a basic operational manual requirement?)

No clue what you're talking about. I've never seen an Airbus that had the wings in anything other than a clean condition at the gate. ???

Quoting airlinebuilder (Thread starter):
Why are airbus trailing edge flaps except the A380 span area when extended are quite small and during full landing configuration there seem to be just a small difference on the angle when taking off especially on the A330/340?

Boeing has, for decades, built far more complicated and capable high-lift devices than any of their competitors, domestic or abroad. That said, there are drawbacks, and we've seen Boeing retreat from the maintenance-intensive, though very effective, designs. The 747-8 and 787, for example, have far simpler flaps than their predecessors.
The A320 flaps do their job, but aren't quite as fancy as some of the Boeing designs.
 
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Starlionblue
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RE: Few Questions On Aircraft Mechanisms

Fri Sep 13, 2013 4:07 am

Quoting AA737-823 (Reply 1):
Quoting airlinebuilder (Thread starter):
Why are airbus trailing edge flaps except the A380 span area when extended are quite small and during full landing configuration there seem to be just a small difference on the angle when taking off especially on the A330/340?

Boeing has, for decades, built far more complicated and capable high-lift devices than any of their competitors, domestic or abroad. That said, there are drawbacks, and we've seen Boeing retreat from the maintenance-intensive, though very effective, designs. The 747-8 and 787, for example, have far simpler flaps than their predecessors.
The A320 flaps do their job, but aren't quite as fancy as some of the Boeing designs.

One more reason. On widebodies, Boeing favors a high speed and a low speed aileron. With the low speed (outer) aileron locked out at high speeds, the wing can be made more flexible, and thus lighter without risking aileron reversal. The downside is that you lose flap area. Some of that is mitigated by using the high speed aileron as a flaperon.

Airbus, on the other hand, favors an unbroken flap line with only one aileron. This means more efficient lift creation since there is more flap and it is continuous from root to aileron. Thus it probably doesn't need to be extended as far.

Another reason Boeing is retreating is because of the weight of these devices. Setting aside materials, I bet the offset hinge flaps on the 787 are way lighter than the Fowler flaps on the 777.

Quoting AA737-823 (Reply 1):
Quoting airlinebuilder (Thread starter):
leading edge and trailing edge flaps are left extended when on ground? (is this a basic operational manual requirement?)

No clue what you're talking about. I've never seen an Airbus that had the wings in anything other than a clean condition at the gate. ???

  
"There are no stupid questions, but there are a lot of inquisitive idiots."
 
DeltaB717
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RE: Few Questions On Aircraft Mechanisms

Fri Sep 13, 2013 4:47 am

Quoting AA737-823 (Reply 1):
No clue what you're talking about. I've never seen an Airbus that had the wings in anything other than a clean condition at the gate. ???

Only thing I can come up with is the ailerons and elevators drooping once their electrical/hydraulic/whatever power is taken away. Which the A330 and A340 do, and pretty sure A32X also. Not sure on A380?
 
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Starlionblue
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RE: Few Questions On Aircraft Mechanisms

Fri Sep 13, 2013 4:52 am

Quoting DeltaB717 (Reply 3):
Only thing I can come up with is the ailerons and elevators drooping once their electrical/hydraulic/whatever power is taken away. Which the A330 and A340 do, and pretty sure A32X also. Not sure on A380?

Probably the same. Gravity is a harsh mistress...
"There are no stupid questions, but there are a lot of inquisitive idiots."
 
PhilBy
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RE: Few Questions On Aircraft Mechanisms

Fri Sep 13, 2013 7:44 am

Quoting airlinebuilder (Thread starter):
Why is it that almost all airbus aircrafts except the A380 leading edge and trailing edge flaps are left extended when on ground? (is this a basic operational manual requirement?)
Quoting DeltaB717 (Reply 3):
Only thing I can come up with is the ailerons and elevators drooping once their electrical/hydraulic/whatever power is taken away. Which the A330 and A340 do, and pretty sure A32X also. Not sure on A380?

Ailerons will droop with no power but slats and flaps will remain retracted.
The only time an Airbus should have slats and flaps extended on the ground is for maintenance.

Quoting airlinebuilder (Thread starter):
Why are airbus trailing edge flaps except the A380 span area when extended are quite small and during full landing configuration there seem to be just a small difference on the angle when taking off especially on the A330/340?

Not forgetting the double-slotted flaps on the A321. They're as large as they need to be to do the job. Any extra would just add weight.
Compared to Boeing, Airbus wings tend to be less flexible and therefore by implication have a deeper section. This may lead to an apparent difference.
 
mandala499
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RE: Few Questions On Aircraft Mechanisms

Fri Sep 13, 2013 10:27 am

Quoting airlinebuilder (Thread starter):
Airbus : Why is it that almost all airbus aircrafts except the A380 leading edge and trailing edge flaps are left extended when on ground? (is this a basic operational manual requirement?)

In hot weather, for A320 family to the A340, the manual requires you leave the leading edge slats extended (therefore the trailing edge flaps too) to prevent a temperature misread for I think the bleed air system. This is for above 33C I think... *can't remember correctly*

Quoting airlinebuilder (Thread starter):
Why are airbus trailing edge flaps except the A380 span area when extended are quite small and during full landing configuration there seem to be just a small difference on the angle when taking off especially on the A330/340?

Different wing design to Boeing... Yes, the clean flap lines with no inboard aileron as previously mentioned.
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
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DarkSnowyNight
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RE: Few Questions On Aircraft Mechanisms

Fri Sep 13, 2013 12:49 pm

Quoting airlinebuilder (Thread starter):
Airbus : Why is it that almost all airbus aircrafts except the A380 leading edge and trailing edge flaps are left extended when on ground? (is this a basic operational manual requirement?)
Quoting AA737-823 (Reply 1):

No clue what you're talking about. I've never seen an Airbus that had the wings in anything other than a clean condition at the gate. ???
Quoting PhilBy (Reply 5):
Ailerons will droop with no power but slats and flaps will remain retracted.
The only time an Airbus should have slats and flaps extended on the ground is for maintenance.

This done most commonly on the 330 & 340, to setting one. The reason is that in warmer locales, like DFW, PHX, DXB, etc, enough heat will generate an ECAM msg, and will most likely delay the flight considerably, as there is no relief (eg, you cannot just clear out the message, it has to go away for real after troubleshooting, and a call to MX Control; there is no MEL for this).
You Sir, are a very funny lady.
 
Pihero
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RE: Few Questions On Aircraft Mechanisms

Fri Sep 13, 2013 2:54 pm

Quoting AA737-823 (Reply 1):
Boeing has, for decades, built far more complicated and capable high-lift devices than any of their competitors, domestic or abroad.
Quoting AA737-823 (Reply 1):
The A320 flaps do their job, but aren't quite as fancy as some of the Boeing designs.

I beg to differ : The technology has tremenduously evolved and the simple single slotted flap of, say, an A320 is far superior to the triple slotted TE flap of a 727 or a 732.
See the evolution
The 732 :

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Photo © Serge Bailleul - AirTeamImages



vs the 738 :

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Photo © Laszlo Gyori



the 742 :

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Photo © Jochen Thoma



vs the A333

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Photo © Hardy Springborn



the A320 :

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Photo © Allan Martins Antunes



compared to the A321 double slotted TE Flap :

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Photo © Felix Roitsch

Quoting PhilBy (Reply 5):
Not forgetting the double-slotted flaps on the A321. They're as large as they need to be to do the job. Any extra would just add weight.

There is very little gain in coefficient of lift on the A321 : The reason for it was to have a flatter body angle at rotation and landing. The A321 is still one of the fastest approaching airliners around.

Quoting Starlionblue (Reply 2):
On widebodies, Boeing favors a high speed and a low speed aileron.

That solution is the reason Boeing did away with the single slotted flap for the 777.
For the 767, this configuration is exactly due to the same reason as the A321.
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