a380900
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Airbus = Single Slotted Flaps?

Wed Sep 22, 2004 12:36 pm

I just took a virgin A340-600 and I was surprised because the flaps are single slotted. They are a lot less spectacular than on the triple slotted 747.

On such a big plane, I would have assumed that it would have been at least double slotted. So I am wondering, is a single slotted flaps an airbus trademark (I know that the A321 has double slotted flaps but is it the only one in the family?).

Even the A380, due to its oversize wing, will be single slotted. Is it an application of the "keep it simple, stupid!" principle?

Anyway, it's a lot less impressive than watching a 747 extending its flaps. It looks like a Swiss watch.

 
wilax
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RE: Airbus = Single Slotted Flaps?

Wed Sep 22, 2004 2:46 pm

In a nutshell, a slightly cracked one, the more swept back the wing, the higher the cruise speed, the less the low speed lift; thus the need for more flap area. Modern airframes such as all Airbus have less swept wing design mostly for field performance; shorter runways needed. You get more lift at slower speeds but also more drag at higher speeds. The A321 does not really have enough wing for such a large aircraft, so Airbus remedied that by slotting the flaps so that it could have a slightly larger wing when necessary.
 
ASalo
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RE: Airbus = Single Slotted Flaps?

Wed Sep 22, 2004 4:27 pm

I once read in an article that 50% (or so) of the sound an average modern airliner creates on approach is not from the engines, but from the aircraft body itself. Thus the flaps are naturally a big source of noise on approach, and to my understanding the single slotted flaps are quieter than double slotted ones. This is probably one reason Airbus has started to use single slotted flaps.
 
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Starlionblue
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RE: Airbus = Single Slotted Flaps?

Wed Sep 22, 2004 6:11 pm

There's also, as A380900 suggested, the KISS principle. Triple slotted flaps=complicated mechanism=higher maintenance costs and bigger risk of breakdown.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Q330
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RE: Airbus = Single Slotted Flaps?

Wed Sep 22, 2004 7:49 pm

Thus the flaps are naturally a big source of noise on approach, and to my understanding the single slotted flaps are quieter than double slotted ones. This is probably one reason Airbus has started to use single slotted flaps.

I suppose the flaps can contribute lots of noise on approach, but would noise really be a more important factor in design than things like complexity?

-Q
Long live the A330!
 
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Starlionblue
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RE: Airbus = Single Slotted Flaps?

Wed Sep 22, 2004 8:01 pm

I suppose the flaps can contribute lots of noise on approach, but would noise really be a more important factor in design than things like complexity?

It would. All the maintenance savings and fuel savings in the world are sort of pointless if you can't land at certain airports. And noise regulations are getting mighty strict.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Q330
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RE: Airbus = Single Slotted Flaps?

Wed Sep 22, 2004 8:29 pm

All the maintenance savings and fuel savings in the world are sort of pointless if you can't land at certain airports. And noise regulations are getting mighty strict.

Ohh, I wasn't even thinking about external noise! I'd assume that something like the number of landing gear bogies would be much more of a factor than the flaps...

-Q
Long live the A330!
 
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Starlionblue
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RE: Airbus = Single Slotted Flaps?

Wed Sep 22, 2004 9:01 pm

Ohh, I wasn't even thinking about external noise! I'd assume that something like the number of landing gear bogies would be much more of a factor than the flaps...

Ah, I get your thinking. Well if you've lived under the landing path to 27R at LHR you would know that the engines aren't so bad, but the airframe noise is quite significant.

Not that I minded. Nice spotting was had. Big grin
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
a380900
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RE: Airbus = Single Slotted Flaps?

Thu Sep 23, 2004 4:42 am

Is the noise on approach an issue anyway? Isn't it very low when compared to a take-off?
 
QantasA332
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RE: Airbus = Single Slotted Flaps?

Thu Sep 23, 2004 4:57 am

Is the noise on approach an issue anyway? Isn't it very low when compared to a take-off?

Not at all - in fact, quite the opposite. Very counter-intuitively, approach noise can be as much as 10 EPNdb greater than that of takeoff. Airframe and flap generated noise has much more of an impact than you'd think!

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QantasA332
 
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Starlionblue
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RE: Airbus = Single Slotted Flaps?

Thu Sep 23, 2004 5:54 am

Is the noise on approach an issue anyway? Isn't it very low when compared to a take-off?

Not at all - in fact, quite the opposite. Very counter-intuitively, approach noise can be as much as 10 EPNdb greater than that of takeoff. Airframe and flap generated noise has much more of an impact than you'd think!



As QantasA332 says.

It's also important to remember that it's not noise in absolute terms, ie how loud the plane is objectively, that really counts. It's perceived noise on the ground. When an airliner is climbing out, it does so rather steeply, and thus the noise on the ground has a limited footprint. Coming in for landing at a shallow angle keeps the plane close to the ground longer, waking up more NIMBYs.

This noise footprint issue is the reason why more modern aircraft do not derate as much at SNA, for example. By using higher power settings they can get up to altitude faster. While they objectively make more noise, they make a larger proportion of the noise further from the NIMBYs, and thus the perceived noise on the ground is less.

Same with winglets on the 727. These allow the 727 to be certified for takeoff at airports where it would normally be banned for noise. The winglets don't make the airplane any quieter but allow it to climb out of hearing range faster.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
320tech
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RE: Airbus = Single Slotted Flaps?

Thu Sep 23, 2004 12:39 pm

As far as I am aware, the only reason the A321 has double slotted flaps is to ensure that the flight characteristics are sufficiently similar to the A320. I forget what the flaps extend to (35 degrees, I think), but on the A320 it's 35 degrees and the A319 is 40 degrees for the same reason.

There're a lot of advantages to having simple flaps, noise, ease of maintenance, lighter, etc. Guys are already cursing the 321's extra flap mechanism, since we have to take off the fairings during inspection. A bit of a pain.
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
 
oly720man
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RE: Airbus = Single Slotted Flaps?

Thu Sep 23, 2004 6:35 pm

The 321 has double slotted flaps to get extra lift at the same rotation angle (or less) than on the 320. Longer fuselage = tail strike if the flaps were the same.
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