Thrust
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Gear Retraction For Airbus Giants: Why So Slow?

Tue Apr 12, 2011 4:39 pm

Hi there. I just felt like I had to ask this because it seems like a very defective characteristic. The A330 and A340 have the SLOWEST gear retraction process I have ever seen. I'm trying to figure out why this is. Was it factored into the design? Are the electrical motors that retract the gear weak? Are there advantages to having a slower gear retraction? Even with the largest Boeing jets, the gear seems to retract relatively quickly. Thanks.
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sprout5199
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Tue Apr 12, 2011 5:59 pm

Quoting Thrust (Thread starter):
A340 have the SLOWEST gear retraction process I have ever seen. I'm trying to figure out why this is. Was it factored into the design? Are the electrical motors that retract the gear weak? Are there advantages to having a slower gear retraction?

You need a positive rate of climb to retract them and we know how well the A-340 climbs. Gives the Aircraft a fighting chance.            

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roseflyer
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Tue Apr 12, 2011 6:57 pm

I have never worked on the A330/A340 so my knowledge is based on other planes, so correct me if wrong.

Quoting Thrust (Thread starter):
The A330 and A340 have the SLOWEST gear retraction process I have ever seen. I'm trying to figure out why this is. Was it factored into the design?

Gear retract time is figured into performance calculations for engine out performance. One assumption is that the gear will be able to be retracted on single engine operations as soon as positive climb is achieved. This is required because the gear causes a lot of drag and engine out performance can be critical in payload capability. Gear retraction time is one factor that goes into building performance charts for engine out operation. In fact every airplane built has a functional test done to make sure its gear retraction system performs correctly and meets minimum retract times.

One side note is that gear extension is often slower than retraction since extension time is not factored into performance charts.

Quoting Thrust (Thread starter):
Are the electrical motors that retract the gear weak?

I would expect that they are hydraulic actuators. On most airplanes the main landing gear retract actuator is the largest hydraulic actuator on the entire airplane and are important in sizing the pumps in the hydraulic system.

Quoting Thrust (Thread starter):
Are there advantages to having a slower gear retraction?

Less hydraulic demand has an advantage as it allows a smaller actuator and lower powered hydraulic pumps (if the landing gear retraction is the critical factor in sizing the hydraulic system).
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474218
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Tue Apr 12, 2011 7:04 pm

Quoting Thrust (Thread starter):
Are the electrical motors that retract the gear weak?


The A330 and 340 along with every other current airliner use "hydraulics" actuators to retract the landing gear!
 
KELPkid
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Tue Apr 12, 2011 7:36 pm

Quoting 474218 (Reply 3):
The A330 and 340 along with every other current airliner use "hydraulics" actuators to retract the landing gear!

Not an airliner I know, but lots of GA planes use an electric motor turning a hydraulic pump for the gear system   Don't know why you wouldn't drive the hydraulic pump directly off of the accessory drive of the engine(s).
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474218
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Tue Apr 12, 2011 8:16 pm

Quoting KELPkid (Reply 4):
Not an airliner I know, but lots of GA planes use an electric motor turning a hydraulic pump for the gear system


And the Mooney Mite used the Armstrong* system to retract the gear.

* A lever and a strong arm!
 
DiamondFlyer
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Tue Apr 12, 2011 9:17 pm

Quoting 474218 (Reply 5):
And the Mooney Mite used the Armstrong* system to retract the gear.

Not just the Mooney Mite. The Mooney M20 A,B & C models had the same thing. I believe they went to the electric gear retracts on the E model, and the D model was a fixed gear model.

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Fly2HMO
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Tue Apr 12, 2011 10:53 pm

Quoting DiamondFlyer (Reply 8):

Not just the Mooney Mite. The Mooney M20 A,B & C models had the same thing. I believe they went to the electric gear retracts on the E model, and the D model was a fixed gear model.

        

I have about 10 hrs on an M20B. That johnson bar is a bitch. But apparently it is a nearly unbreakable and very reliable system.
 
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Tue Apr 12, 2011 11:23 pm

Quoting Fly2HMO (Reply 9):
I have about 10 hrs on an M20B.

I have about 80 hours in a M20J. Not very relevant to the subject but the gear was electric and it's the most exciting airplane I ever flew. A Cirrus is not as much fun for instance (to me at least). My flying club sold it years ago. Those were good times!!!
 
tdscanuck
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 4:18 am

Quoting KELPkid (Reply 4):
Not an airliner I know, but lots of GA planes use an electric motor turning a hydraulic pump for the gear system   Don't know why you wouldn't drive the hydraulic pump directly off of the accessory drive of the engine(s).

All large jets I can think of run hydraulic pumps off the gearbox and have some other non-mechanically driven hydraulic pumps as well...typically electric or pneumatic.

Tom.
 
Viscount724
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 4:46 am

Quoting KELPkid (Reply 4):
Quoting 474218 (Reply 3):
The A330 and 340 along with every other current airliner use "hydraulics" actuators to retract the landing gear!

Not an airliner I know, but lots of GA planes use an electric motor turning a hydraulic pump for the gear system Don't know why you wouldn't drive the hydraulic pump directly off of the accessory drive of the engine(s).

As a sidenote, the Fokker F27 had pneumatic landing gear, but the license-built Fairchild F-27 had hydraulic gear.
 
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DocLightning
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 6:01 am

I've often wondered about the OP's post.

When you compare the A380 or A340/30 gear retraction sequence to, say, the 747, the 747 is positively speedy.

Why such a discrepancy between manufacturers? And if gear retraction time is figured into engine-out performance, the 744 has much more sprightly engine-out performance than the A340 (the running joke is that the A340 climbs by the curvature of the Earth). So what gives?
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DH106
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 7:55 am

The A380 has a fair few fillet doors to sequence - perhaps that slows it down.
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474218
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 12:51 pm

Quoting tdscanuck (Reply 12):
All large jets I can think of run hydraulic pumps off the gearbox and have some other non-mechanically driven hydraulic pumps as well...typically electric or pneumatic.


But those non-mechanical pumps are auxiliary or back-up pumps. They would have a hard time actually retracting the landing gear.

The L-1011 actually used the pneumatically powered Air Turbine Motor (ATM) at assist the Engine Driven Pump (EDP) in gear retraction. When the gear was selected up the flow of hydraulic fluid to the landing gear actuators that the pressure would drop and the ATM would run automatically to assist the EDP. As soon as the pressure stabilized the ATM shut off.
 
tdscanuck
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 1:43 pm

Quoting 474218 (Reply 16):
Quoting tdscanuck (Reply 12):
All large jets I can think of run hydraulic pumps off the gearbox and have some other non-mechanically driven hydraulic pumps as well...typically electric or pneumatic.

But those non-mechanical pumps are auxiliary or back-up pumps. They would have a hard time actually retracting the landing gear.

Not necessarily...the 787 center hydraulics are responsible for gear retraction and the center system doesn't have any mechanically driven pumps.

Tom.
 
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zeke
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 2:47 pm

Quoting Thrust (Thread starter):
The A330 and A340 have the SLOWEST gear retraction process I have ever seen.

Can I ask how you came to this conclusion ?

A380 around 16 seconds (starts at 2:25) http://www.youtube.com/embed/0PVizo6XuEo?rel=0

777 gear swing around 20 seconds http://www.youtube.com/embed/HhWKxJGfS3U?rel=0

A340-600 gear swing around 20 seconds http://www.youtube.com/embed/x7B-ooWZsdY?rel=0

747 gear swing around 45 seconds http://www.youtube.com/embed/AOekRQBmQzM?rel=0

767 gear swing around 50 seconds http://www.youtube.com/embed/2tFgNP5cJHM?rel=0

Quoting Thrust (Thread starter):
Are the electrical motors that retract the gear weak?

The electric hydraulic motor on the A330 is used as a backup during gear retraction only in the event of an engine failure.

Quoting DocLightning (Reply 14):
And if gear retraction time is figured into engine-out performance, the 744 has much more sprightly engine-out performance than the A340 (the running joke is that the A340 climbs by the curvature of the Earth).

A.net myth, the A340-300 has better engine out and climb performance than the 747-400.
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Pihero
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 3:59 pm

Quoting RoseFlyer (Reply 2):

Gear retract time is figured into performance calculations for engine out performance.

Please provide proof of that statement as I have never heard of it. If someone buids an aircraft with a 30 min gear retraction time, no one is going to object   but the climb / obstacle performance is going to be interesting, with a long first segment requiring a climb gradient of...0% !

Quoting RoseFlyer (Reply 2):
In fact every airplane built has a functional test done to make sure its gear retraction system performs correctly and meets minimum retract times.

Same as above, please provide references

Quoting sprout5199 (Reply 1):

You need a positive rate of climb to retract them and we know how well the A-340 climbs.
Quoting DocLightning (Reply 14):
And if gear retraction time is figured into engine-out performance, the 744 has much more sprightly engine-out performance than the A340 (the running joke is that the A340 climbs by the curvature of the Earth). So what gives?

What gives ?
Just uninformed prejudiced so-called jokes that used to be fun 15 years ago... and which forget the slowest climber of all : the 747 in all its versions, bar the SP.
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roseflyer
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 5:02 pm

Quoting zeke (Reply 18):
Can I ask how you came to this conclusion ?

A380 around 16 seconds (starts at 2:25) http://www.youtube.com/embed/0PVizo6XuEo?rel=0

777 gear swing around 20 seconds http://www.youtube.com/embed/HhWKxJGfS3U?rel=0

A340-600 gear swing around 20 seconds http://www.youtube.com/embed/x7B-ooWZsdY?rel=0

747 gear swing around 45 seconds http://www.youtube.com/embed/AOekRQBmQzM?rel=0

767 gear swing around 50 seconds http://www.youtube.com/embed/2tFgNP5...rel=0

Ground swings unless they are using ground hydraulic carts rated at higher than airplane capability are not reflective of actual gear retract times especially if they are using airplane electrical hydraulics.

Quoting Pihero (Reply 20):
Quoting RoseFlyer (Reply 2):

Gear retract time is figured into performance calculations for engine out performance.

Please provide proof of that statement as I have never heard of it. If someone buids an aircraft with a 30 min gear retraction time, no one is going to object but the climb / obstacle performance is going to be interesting, with a long first segment requiring a climb gradient of...0% !

Pihero, it is in there. I can't provide the information because it is not public data, but having the ability to have gear retracted is a requirement for engine out minimum performance obstacle clearance. You'll have to trust me as I am an engineer with intimate subject knowledge regarding gear performance.

If an airplane had a 30 minute gear retraction time, then it is perfectly certifiable, but it won't be able to take credit for having a clean configuration for engine out obstacle clearance and thus would have to have other capabilities to handle it.

Quoting Pihero (Reply 20):

Quoting RoseFlyer (Reply 2):
In fact every airplane built has a functional test done to make sure its gear retraction system performs correctly and meets minimum retract times.

Same as above, please provide references

Trust me after the gear is rigged when an airplane is built it is timed to ensure proper performance. I think I have a high enough respect rating to show that I don't make things like that up.

[Edited 2011-04-13 10:06:42]
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Pihero
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 6:11 pm

Quoting RoseFlyer (Reply 21):
You'll have to trust me as I am an engineer with intimate subject knowledge regarding gear performance.
Quoting RoseFlyer (Reply 21):
Trust me after the gear is rigged when an airplane is built it is timed to ensure proper performance. I think I have a high enough respect rating to show that I don't make things like that up.

Sorry, I can always back my statements with a reference. We're in Tech Ops and we should be able to get accurate info to one another.
As I've done quite a bit of teaching performance and I have never heard of a *Maximum retraction time* as per FAR /JAR or EASA regs.
As I wrote on that previous post, the penalty for a lengthy retraction time is built in the performance requirements, and such an airplane will have great difficulties getting any load aloft.

Quoting RoseFlyer (Reply 21):
it is not public data

Sorry, first time I hear that certification regs are Top secret.
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roseflyer
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 6:23 pm

Quoting Pihero (Reply 22):
As I've done quite a bit of teaching performance and I have never heard of a *Maximum retraction time* as per FAR /JAR or EASA regs.
As I wrote on that previous post, the penalty for a lengthy retraction time is built in the performance requirements, and such an airplane will have great difficulties getting any load aloft.

I think we agree. Retraction time is built in to the performance requirements and type design. It is not a FAR/EASA reg. Any airplane can have whatever values its design constitutes, but in order to take credit for a clean aircraft configuration, the airplane must have gear up capable within the designed time period. It has to either have a primary system redundant enough on single engine operations or a backup (on demand pump, power transfer unit between hydraulic systems, etc) capable of meeting certain reliability requirements.

Quoting Pihero (Reply 22):

Sorry, first time I hear that certification regs are Top secret.

Please point me to a public source then for how the performance charts are created and what formulas are used (I'd be curious to see it). From what I know the exact calculations are proprietary information at the manufacturer and can only be shared with proper agreements and is not posted in the public domain. I'd love to be proved wrong. The regs are available, but I haven't seen detailed certification reports and deliverables made public.

[Edited 2011-04-13 11:26:50]
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Pihero
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 6:41 pm

Quoting RoseFlyer (Reply 23):
Please point me to a public source then for how the performance charts are created and what formulas are used (I'd be curious to see it).

That's not what I asked.
What I 'd like to see is , somewhere in the FAR 25.1XY, a regulatory text defining the aviation authority certification requirement for a given part which as we can see, could have a major impact on aircraft ability to carry load.
That is all. What belongs to the manufacturer is of course their own;
I myself, have never posted an information which wasn't in the public domain.
FAA / EASA regs are in the public domain.
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wingscrubber
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Wed Apr 13, 2011 8:57 pm

A moderator deleted my post, for quoting something which was then deleted....??

Repost (minus quotes):

Gear retraction speed is determined by the flow capacity of the hydraulic system. Slower retraction allows a lower flow rate which means pumps can be smaller/lighter, and take less shaft horsepower from the engine accesory gearbox.

Bear in mind ground gear swings can be longer than gear swings in flight - if the electric motor pumps are used on the ground to perform the gear swing it can take longer because they produce a lower hydraulic flow rate than the engine-driven pumps can produce at 100% N 2 on takeoff. If a hydraulic ground cart is used however, these can closer emulate EDP performance, but they also have variable flow control.
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astuteman
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Thu Apr 14, 2011 4:29 am

Quoting RoseFlyer (Reply 17):
Ground swings unless they are using ground hydraulic carts rated at higher than airplane capability are not reflective of actual gear retract times especially if they are using airplane electrical hydraulics.

But to give Pihero his due, at least he had a go at providing tangible evidence of landing gear retraction times, something which everyone else on the thread has signally failed to do.

I've not even seen any evidence presented yet that the large Airbus retraction times are actually slow, compared to other large aircraft.

In a tech-ops thread, it would be nice to see something factual presented, or at least some attempt at analysis.

And the running jokes about A340 climb rates, which are also based on an incorrect premise, don't count in that respect either......   

Rgds
 
tdscanuck
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Thu Apr 14, 2011 5:26 am

Quoting Pihero (Reply 16):
Please provide proof of that statement as I have never heard of it.

The proof is that you don't get the certified climb performance if you don't pull the gear up...that would only be true if the gear retraction was factored into the performance.

Quoting Pihero (Reply 18):
As I've done quite a bit of teaching performance and I have never heard of a *Maximum retraction time* as per FAR /JAR or EASA regs.

Of course not. Just as you don't have the FAR/JAR/EASA specify what your maximum or minimum speed must be...they just say that, once you know what your min/max speeds are (an OEM design choice), that becomes the basis for your required performance.

In similar vein, the OEM's can choose any retraction time/system the like, but they have to be able to meet the required climb gradients. It's up to the OEM whether they choose to meet those gear down or gear up...for obvious reasons, all OEMs choose to do it gear up, require the crew to retract gear on a go-around, and include the gear up time into the obstacle clearance calculations.

Quoting Pihero (Reply 20):
What I 'd like to see is , somewhere in the FAR 25.1XY, a regulatory text defining the aviation authority certification requirement for a given part which as we can see, could have a major impact on aircraft ability to carry load.

You're not going to see such a thing, and I think you know that. Gear retraction time is an *input* to FAR compliance, not a result.

Tom.
 
Pihero
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Thu Apr 14, 2011 7:58 am

Tom and RoseFlyer,

Quoting tdscanuck (Reply 23):
You're not going to see such a thing, and I think you know that. Gear retraction time is an *input* to FAR compliance, not a result.

That's what I wanted to hear

Quoting tdscanuck (Reply 23):
The proof is that you don't get the certified climb performance if you don't pull the gear up...

Not really : one could stay in the first segment, whiuch stops, IIRC when the gear is up, but of course all the obstacle-clearing performance would be messed up.
Now, I understand why it was manufacturer's confidential data : (By the way, one could go to any obstacle-clearance graph and deduce the origin of the 2nd segment, therefore inducing the first segment characteristics, i.e gradient and retraction time).

Regards
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Pihero
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Thu Apr 14, 2011 8:00 am

Quoting astuteman (Reply 22):
But to give Pihero his due, at least he had a go at providing tangible evidence of landing gear retraction times, something which everyone else on the thread has signally failed to do.

And give Caesar what belongs to him, and here what was posted by Zeke to Zeke.
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Gingersnap
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Thu Apr 14, 2011 5:11 pm

Can't remember where, maybe it was on here...but I remember someone mentioning that an A340 has superior climb performance up to 10,000ft over a 744.

Seems wrong, but I did read that somewhere. Probably BS but hey  
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Aircellist
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Thu Apr 14, 2011 6:17 pm

If I may, I will propose this:

747-122: http://www.youtube.com/watch?v=OBqo0qPVmh8 (>15')

http://www.youtube.com/watch?v=T2RoG9gjS1k

http://www.youtube.com/watch?v=_DcoVBj7pyU

777-300ER: http://www.youtube.com/watch?v=u1pubVJP2VM (ca. 16')

Alas, not so much clear views of Airbus, apart from the A380's first flight, in Zeke's post...
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Pihero
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RE: Gear Retraction For Airbus Giants: Why So Slow?

Thu Apr 14, 2011 7:13 pm

Quoting gingersnap (Reply 26):
Can't remember where, maybe it was on here...but I remember someone mentioning that an A340 has superior climb performance up to 10,000ft over a 744.

Superior climb, at all altitudes. Full stop.
Compare the initial cruise alts 330 FL + for the 340.... 300 - FL for the 744, which is, by very far the best climber of that series (except the SP).
A very good friend of mine who used to be a Mirage reco pilot called the 744 l'"avion hippie", because it was, in his eyes a "tree hugger".
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