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A380 Landing Speed  
User currently offlinevoiceofgoa From United States of America, joined Feb 2011, 20 posts, RR: 0
Posted (3 years 1 month 3 weeks 6 days 1 hour ago) and read 26269 times:

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?

19 replies: All unread, jump to last
 
User currently onlinevikkyvik From United States of America, joined Jul 2003, 9773 posts, RR: 27
Reply 1, posted (3 years 1 month 3 weeks 6 days ago) and read 26247 times:
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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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User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 2, posted (3 years 1 month 3 weeks 5 days 23 hours ago) and read 26226 times:

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.


User currently offlinebond007 From United States of America, joined Mar 2005, 5397 posts, RR: 8
Reply 3, posted (3 years 1 month 3 weeks 5 days 23 hours ago) and read 26216 times:

Quoting voiceofgoa (Thread starter):
I noticed

How??



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User currently offlinewilco737 From Greenland, joined Jun 2004, 8968 posts, RR: 76
Reply 4, posted (3 years 1 month 3 weeks 5 days 22 hours ago) and read 26188 times:
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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]


It it's not Boeing, I am not going.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16993 posts, RR: 67
Reply 5, posted (3 years 1 month 3 weeks 5 days 19 hours ago) and read 26102 times:

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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineInnocuousFox From United States of America, joined Dec 2003, 2805 posts, RR: 14
Reply 6, posted (3 years 1 month 3 weeks 5 days 13 hours ago) and read 25937 times:

Quoting bond007 (Reply 3):

Quoting voiceofgoa (Thread starter):
I noticed

How??

Or someone had their GPS fired up.  



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User currently offlineStarlionblue From Greenland, joined Feb 2004, 16993 posts, RR: 67
Reply 7, posted (3 years 1 month 3 weeks 5 days 13 hours ago) and read 25931 times:

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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineBaroque From Australia, joined Apr 2006, 15380 posts, RR: 59
Reply 8, posted (3 years 1 month 3 weeks 5 days 13 hours ago) and read 25922 times:

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".


User currently offlinevoiceofgoa From United States of America, joined Feb 2011, 20 posts, RR: 0
Reply 9, posted (3 years 1 month 3 weeks 5 days 12 hours ago) and read 25868 times:

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.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16993 posts, RR: 67
Reply 10, posted (3 years 1 month 3 weeks 5 days 5 hours ago) and read 25691 times:

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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently onlinevikkyvik From United States of America, joined Jul 2003, 9773 posts, RR: 27
Reply 11, posted (3 years 1 month 3 weeks 5 days 4 hours ago) and read 25664 times:
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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.



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 12, posted (3 years 1 month 3 weeks 4 days 22 hours ago) and read 25578 times:

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.


User currently offlineHiJazzey From Saudi Arabia, joined Sep 2005, 864 posts, RR: 1
Reply 13, posted (3 years 1 month 3 weeks 4 days 20 hours ago) and read 25540 times:

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.

User currently offlinePihero From France, joined Jan 2005, 4389 posts, RR: 76
Reply 14, posted (3 years 1 month 3 weeks 4 days 18 hours ago) and read 25513 times:
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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 ?
     



Contrail designer
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16993 posts, RR: 67
Reply 15, posted (3 years 1 month 3 weeks 4 days 14 hours ago) and read 25442 times:

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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineBaroque From Australia, joined Apr 2006, 15380 posts, RR: 59
Reply 16, posted (3 years 1 month 3 weeks 4 days 12 hours ago) and read 25409 times:

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.


User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 17, posted (3 years 1 month 3 weeks 4 days 6 hours ago) and read 25286 times:

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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User currently offlineStarlionblue From Greenland, joined Feb 2004, 16993 posts, RR: 67
Reply 18, posted (3 years 1 month 3 weeks 4 days 4 hours ago) and read 25251 times:

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.  



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineAaron747 From Japan, joined Aug 2003, 8021 posts, RR: 26
Reply 19, posted (3 years 1 month 3 weeks 4 days 3 hours ago) and read 25227 times:

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.



If you need someone to blame / throw a rock in the air / you'll hit someone guilty
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