voiceofgoa
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A380 Landing Speed

Tue May 31, 2011 2:42 am

I flew the Lufthansa A380 from SFO-FRA a couple of days ago for the first time. I noticed that the speed before landing was around 170 mph. Every 747 flight I have been on usually has it at over 210 mph. Is the A380 speed lower because it generates more lift at lower speed?
 
vikkyvik
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RE: A380 Landing Speed

Tue May 31, 2011 3:49 am

Quoting voiceofgoa (Thread starter):
I flew the Lufthansa A380 from SFO-FRA a couple of days ago for the first time. I noticed that the speed before landing was around 170 mph. Every 747 flight I have been on usually has it at over 210 mph. Is the A380 speed lower because it generates more lift at lower speed?

How soon before landing are we talking about? 210 mph (182 kts) seems pretty high, even for groundspeed. Especially since landing is typically done with a headwind. But I'll defer to 747 experts.

The short answer to your question is yes - keeping everything else equal, to land at a slower speed, you have to generate as much lift at that slower speed as you would at a faster speed.

Since flying slower gives you less lift, you have a few other options for slow flight: increase lift coefficient, increase wing area, increase air density.

Increasing lift coefficient is done by going to a higher angle-of-attack. There's a limit, though, since you don't want to stall, and don't want to have a tailstrike upon landing. Flaps and slats also increase the lift coefficient, by increasing the camber of the wing. Slats, specifically, allow you to get to higher AOAs before the wing stalls.

The wing area is designed into the airplane from the beginning.

Increasing air density is rather impractical.  

So whatever combination Airbus used seems to work pretty well. I'd guess it has something to do with the enormous wing.
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tdscanuck
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RE: A380 Landing Speed

Tue May 31, 2011 4:22 am

Quoting voiceofgoa (Thread starter):
Is the A380 speed lower because it generates more lift at lower speed?

Yes. Giant wing (sized for the future A380-900) means the A380-800 can generate enough lift at a lower speed.

Quoting vikkyvik (Reply 1):
How soon before landing are we talking about? 210 mph (182 kts) seems pretty high, even for groundspeed. Especially since landing is typically done with a headwind. But I'll defer to 747 experts.

182 kts is really really fast for a 747 approach. Even a fully loaded freighter doesn't need to do an approach that fast unless you've got the flaps stuck up too high.

Tom.
 
bond007
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RE: A380 Landing Speed

Tue May 31, 2011 4:38 am

Quoting voiceofgoa (Thread starter):
I noticed

How??
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wilco737
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RE: A380 Landing Speed

Tue May 31, 2011 5:47 am

An approach speed of 210mph (which would be 182knots) happens at a landing weight around 390 tons, which would be 10 tons below max TAKE OFF weight. So this seem to be wrong.
At max landing weight the approach speed is around 152 knots hich is 175mph...
So I guess the A380 will be somewhere near that speed as well.

wilco737
  

[Edited 2011-05-30 22:52:49]
 
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Starlionblue
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RE: A380 Landing Speed

Tue May 31, 2011 8:52 am

Quoting bond007 (Reply 3):
Quoting voiceofgoa (Thread starter):
I noticed

How??

Probably looking at AirShow, which shows ground speed and is thus a highly inaccurate indication of landing speed, which is an airspeed.
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InnocuousFox
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RE: A380 Landing Speed

Tue May 31, 2011 2:18 pm

Quoting bond007 (Reply 3):

Quoting voiceofgoa (Thread starter):
I noticed

How??

Or someone had their GPS fired up.  
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Starlionblue
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RE: A380 Landing Speed

Tue May 31, 2011 2:28 pm

Quoting InnocuousFox (Reply 6):
Quoting bond007 (Reply 3):

Quoting voiceofgoa (Thread starter):
I noticed

How??

Or someone had their GPS fired up.

Well, that still doesn't tell you airspeed.
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baroque
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RE: A380 Landing Speed

Tue May 31, 2011 2:38 pm

Quoting tdscanuck (Reply 2):
Giant wing

Not sure about the name for a "Giant wing" but a "Big wing" is now technically known as a "Bader".
 
voiceofgoa
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RE: A380 Landing Speed

Tue May 31, 2011 3:39 pm

In response to "How I noticed the airspeed" -

Yes, via the flight display - which was a fairly responsive and new piece of display software. (Incidentally, we also get live views from 3 cameras positioned at various points on the plane.)

Of course, as someone has noted, what the flight display in the passenger cabin reveals might be different from the actual readings the pilots have access to at that instant.
 
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Starlionblue
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RE: A380 Landing Speed

Tue May 31, 2011 11:10 pm

Quoting voiceofgoa (Reply 9):
In response to "How I noticed the airspeed" -

Yes, via the flight display - which was a fairly responsive and new piece of display software. (Incidentally, we also get live views from 3 cameras positioned at various points on the plane.)

Of course, as someone has noted, what the flight display in the passenger cabin reveals might be different from the actual readings the pilots have access to at that instant.

Again, this is NOT airspeed. It is ground speed. Wings don't care about ground speed. Approach speeds are air speeds.

Say you were landing with a 10 knot tailwind (I believe that is an acceptable component). The ground speed would be about 12 mph higher than the airspeed. So you see how ground speed is an inaccurate indication if how fast the aircraft is flying through the air.
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vikkyvik
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RE: A380 Landing Speed

Wed Jun 01, 2011 12:00 am

Quoting Starlionblue (Reply 10):
Again, this is NOT airspeed. It is ground speed. Wings don't care about ground speed. Approach speeds are air speeds.

Not only that, but aren't approach speeds indicated airspeeds? Which, depending on your pressure altitude, will differ more and more from true airspeed.

So the difference could be more than 10 kts/12 mph.

Though 182 kts still seems high for groundspeed to me, but obviously I'm not an expert.  

The other factor may simply be that the speeds shown on the flight display are not that accurate. I doubt anyone really cares whether the passengers are getting an accurate speed and location.

On JetBlue, I've noticed that when the moving map switches between different zoom levels, our position sometimes appears to change significantly. Wouldn't be surprised if the speed isn't accurate either.
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tdscanuck
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RE: A380 Landing Speed

Wed Jun 01, 2011 5:22 am

Quoting Starlionblue (Reply 10):
Say you were landing with a 10 knot tailwind (I believe that is an acceptable component).

It's operator specific, but 10 is usually OK. Many operators allow 15. The airplane is usually capable of considerably more than that.

Quoting vikkyvik (Reply 11):
Not only that, but aren't approach speeds indicated airspeeds? Which, depending on your pressure altitude, will differ more and more from true airspeed.

Yes, approach speeds are indicated. Although, unless you're at a high-altitude airport, that should be close to true when you're landing.

Tom.
 
HiJazzey
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RE: A380 Landing Speed

Wed Jun 01, 2011 8:00 am

I have a recollection that when the A380 was in flight testing, Airbus announced that the wings performed better than expected and that consequently the landing speed was reduced. Don't know how it fares against the B747 in absolute terms though.
 
Pihero
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RE: A380 Landing Speed

Wed Jun 01, 2011 9:33 am

Quoting Baroque (Reply 8):
Not sure about the name for a "Giant wing" but a "Big wing" is now technically known as a "Bader".

There he goes again !.?.. with or without sir Keith Park ?
     
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Starlionblue
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RE: A380 Landing Speed

Wed Jun 01, 2011 1:41 pm

Quoting HiJazzey (Reply 13):
I have a recollection that when the A380 was in flight testing, Airbus announced that the wings performed better than expected and that consequently the landing speed was reduced. Don't know how it fares against the B747 in absolute terms though.

The design brief from the very beginning was that the 380 had to have better field performance than the 747. And it does. Not that this should surprise anyone given the difference in age.
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baroque
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RE: A380 Landing Speed

Wed Jun 01, 2011 3:17 pm

Quoting Pihero (Reply 14):
with or without sir Keith Park

With of course, or you will not have anywhere to put the Big Bus once it has stopped. Trying to work in Dowding there, but the nearest I can get is that you would feel Dowdy if someone bumped into an unfortunately Parked bus and anyone doing the bumping should feel Stuff(y)ed. How is that Skipper?

Back on the A380 landing, those wings are just incredible in the last part of the approach.
 
Fabo
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RE: A380 Landing Speed

Wed Jun 01, 2011 10:01 pm

Quoting Starlionblue (Reply 15):
And it does. Not that this should surprise anyone given the difference in age.

I for one dont think this has one thing to do with age. I believe that if Boeing wanted to make 744 better in short field situations, they could have, only they did not (unlike Airbus with A388)
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Starlionblue
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RE: A380 Landing Speed

Wed Jun 01, 2011 11:45 pm

Quoting Fabo (Reply 17):
I for one dont think this has one thing to do with age. I believe that if Boeing wanted to make 744 better in short field situations, they could have, only they did not (unlike Airbus with A388)

It has everything to do with age. The 747 was originally designed in the late 60s and the -400 in the mid 80s. The 380 was designed in the early 00s. Decades of aerodynamic and engine improvements. Also, the wing is sized for the A380-900 so has a lot of lift given the weight of the -800.

Of course Boeing could have made the 744 better, but this would have required significant rework and this hypothetical new variant would have been as young as the 380.

BTW we're hardly talking "short field" in either case.  
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Aaron747
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RE: A380 Landing Speed

Thu Jun 02, 2011 1:05 am

Quoting Starlionblue (Reply 18):
BTW we're hardly talking "short field" in either case.

Perhaps not, but I would venture for their size and inertia, both aircraft have quite impressive landing field performance. Having all those brakes sure helps.
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