Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
A340NG - Why Does It Have 4 Engines?  
User currently offlineCygnusChicago From United States of America, joined Mar 2007, 758 posts, RR: 1
Posted (7 years 8 months 1 week 1 day 6 hours ago) and read 7280 times:

(I did a quick search and can't find this discussed recently)

My understanding is that the A340 original and A330 are basically the same aircraft with a different wing. By the time Airbus started the A340NG project, ETOPS was in place for many routes, powerful engines were available, and the 777 had proved itself in service both in reliability and unbeaten economics.

Why then didn't Airbus design a two engine version of the A340NG, seeing as they had to redesign the entire wing?

[Edited 2007-04-19 21:19:23]


If you cannot do the math, your opinion means squat!
34 replies: All unread, showing first 25:
 
User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3598 posts, RR: 66
Reply 1, posted (7 years 8 months 1 week 1 day 6 hours ago) and read 7239 times:

Quoting CygnusChicago (Thread starter):
Why then didn't Airbus design a two engine version of the A340NG, seeing as they had to redesign the entire wing?

Years of marketing that you needed "4 Engines 4 Long Haul"?



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineTugger From United States of America, joined Apr 2006, 5785 posts, RR: 10
Reply 2, posted (7 years 8 months 1 week 1 day 6 hours ago) and read 7219 times:

Probably would have required a redesign of the landing gear, bays, and everything related as the original design was not tall enough to hang the engines it would need under those wings.

Tug



I don’t know that I am unafraid to be myself, but it is hard to be somebody else. -W. Shatner
User currently offlineAreopagus From United States of America, joined Sep 2001, 1373 posts, RR: 1
Reply 3, posted (7 years 8 months 1 week 1 day 6 hours ago) and read 7182 times:

To Tugger's list, I would add that the 4 engines distribute their weight more evenly along the span of the wing, relieving bending loads. To hang one much bigger engine on each wing would probably have required strengthening the wing.

User currently offlineFlyDreamliner From United States of America, joined Jan 2006, 2759 posts, RR: 15
Reply 4, posted (7 years 8 months 1 week 1 day 5 hours ago) and read 7057 times:

Quoting Areopagus (Reply 3):
To Tugger's list, I would add that the 4 engines distribute their weight more evenly along the span of the wing, relieving bending loads. To hang one much bigger engine on each wing would probably have required strengthening the wing.

A set of GE90s weight less than the 4 RR Trent 500s on A340NG. Moreover, RR's Trent 800's are not THAT much heavier than the CF6's available on A330. Add to that that in fact to carry the outboard engines - the A340 wing had to be upgraded with a bulge like feature on the wing between the inboard and outboard engines.

Had they gone 2 engines and called it A330-400 and A330-500 instead i'm sure they'd be selling much better right now.

I am all but certain you could get 2 RR Trent 895s or PW4090's under the A330/340 without having clearance issues, and even if you did, you'd be within a few inches.

The other major problem though that even a 2 engine A340NG would have is that fuselage. Because it is so narrow and needs to be structurally bolstered to such a degree to be stretched to 247 feet long, it would still be heavier than 773ER and be able to carry less payload.

And because it is heavier, it would need engines at least as big as 773ER.... and while you could get the Trent 895's from 773 and 772ER under an A330 wing, I am nearly certain a GE90-115b wouldn't go under there without really substantial changes to the wing and undercarriage.



"Let the world change you, and you can change the world"
User currently offlineConcordeBoy From , joined Dec 1969, posts, RR:
Reply 5, posted (7 years 8 months 1 week 1 day 4 hours ago) and read 6678 times:

Quoting FlyDreamliner (Reply 5):
A set of GE90s weight less than the 4 RR Trent 500s on A340NG. Moreover, RR's Trent 800's are not THAT much heavier than the CF6's available on A330.

As earlier noted: it's not the weight per se, it's the distribution.

Quoting FlyDreamliner (Reply 5):
Add to that that in fact to carry the outboard engines - the A340 wing had to be upgraded with a bulge like feature on the wing between the inboard and outboard engines.

And while supporting a single hanger could've eliminated the need for that, it still would've called for inner fortification of an already overweight (at EIS) apparatus.


User currently offlineEI321 From Iraq, joined Jul 2009, 0 posts, RR: 0
Reply 6, posted (7 years 8 months 1 week 1 day 4 hours ago) and read 6635 times:

Quoting FlyDreamliner (Reply 5):
Had they gone 2 engines and called it A330-400 and A330-500 instead i'm sure they'd be selling much better right now.

I dont think they really would. It would help, but the 'A340NG's' biggest problem is its weight, not the engines.


User currently offlineScouseflyer From United Kingdom, joined Apr 2006, 3402 posts, RR: 9
Reply 7, posted (7 years 8 months 1 week 1 day 4 hours ago) and read 6554 times:

Quoting FlyDreamliner (Reply 5):
I am nearly certain a GE90-115b wouldn't go under there without really substantial changes to the wing and undercarriage.

and isn't there an exclsivity deal for the GE90 with Boeing?


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2577 posts, RR: 25
Reply 8, posted (7 years 8 months 1 week 1 day 1 hour ago) and read 6298 times:

May I be the first in this thread to pedantically point out that there is no such thing as an "A340NG". Boeing certainly used the NG suffix for the 737-600/700/800/900 and still do. AFAIK, Airbus never did. I know some enthusiasts use the term, I've even seen 777NG used for the -300ER and -200LR, but this is Tech/Ops, so let's keep it factual.

Anyway an A340 with two engines already exists and it is called the A330. Airbus already hang the biggest engines they can off that, and it does not fly as far as an A340. Simply adding two GE90s would not give the A340 a big increase in range. For extra range, as well as more thrust to increase MTOW you need to carry much more fuel, which the airframe can't do. It worked on the 777 because the design had so much growth potential. In contrast, the A340 was designed to be optimal at its orginal size.

The least powerful growth version, the A340-500, has four 53,000 lb engines, that's a total of 212,000 lb thrust. The engine out performance is therefore achieved with 75% of this, which is 159,000 lb. So a twin version with the same engine out performance would need two 159,000 lb thrust engines. That is a little over simplified, but two 115,000 lb engines would certainly not be enough for certification, even though the total takeoff thrust would be higher.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineMandala499 From Indonesia, joined Aug 2001, 6965 posts, RR: 76
Reply 9, posted (7 years 8 months 1 week 12 hours ago) and read 6159 times:

Quote:
Why then didn't Airbus design a two engine version of the A340NG, seeing as they had to redesign the entire wing?

Coz if A340NG is a twin, it'll be called the A330NG!

Obvious isn't it?

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17177 posts, RR: 66
Reply 10, posted (7 years 8 months 1 week 10 hours ago) and read 6104 times:

Quoting Jetlagged (Reply 9):
The least powerful growth version, the A340-500, has four 53,000 lb engines, that's a total of 212,000 lb thrust. The engine out performance is therefore achieved with 75% of this, which is 159,000 lb. So a twin version with the same engine out performance would need two 159,000 lb thrust engines. That is a little over simplified, but two 115,000 lb engines would certainly not be enough for certification, even though the total takeoff thrust would be higher.

Word.



A has ben said above, the outboards relieve wing bending moment and allow a lighter wing. Moving the engines outwards (on a twin version) would have been pretty complicated and expensive.

Sure, Airbus could have made a 777 like twin, but that would have involved a lot of money. Enter the A350XWHBGAHJWEMEBBXXARGH or whatever today's acronym is.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineKukkudrill From Malta, joined Dec 2004, 1123 posts, RR: 4
Reply 11, posted (7 years 8 months 1 week 4 hours ago) and read 5996 times:

Quoting Starlionblue (Reply 12):
Moving the engines outwards (on a twin version) would have been pretty complicated and expensive.

As well as creating a problem of directional stability when flying on one engine?



Make the most of the available light ... a lesson of photography that applies to life
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17177 posts, RR: 66
Reply 12, posted (7 years 8 months 6 days 11 hours ago) and read 5808 times:

Quoting Kukkudrill (Reply 14):
Quoting Starlionblue (Reply 12):
Moving the engines outwards (on a twin version) would have been pretty complicated and expensive.

As well as creating a problem of directional stability when flying on one engine?

Indeed. At the very least the rudder would have to be increased in size, increasing drag and maybe requiring strengthening of the rear fuse.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineConcordeBoy From , joined Dec 1969, posts, RR:
Reply 13, posted (7 years 8 months 6 days 4 hours ago) and read 5745 times:

Quoting Scouseflyer (Reply 7):
and isn't there an exclsivity deal for the GE90 with Boeing?

Boeing is obligated to GE (on 700K.lbs+ Triple7s), not the other way around.

Quoting Jetlagged (Reply 8):
The engine out performance is therefore achieved with 75% of this, which is 159,000 lb. So a twin version with the same engine out performance would need two 159,000 lb thrust engines.

...even taking the A345's higher weight relative to its competition; why would a(ny such) twinjet attempt to conform to a 75% OEI thrust percentage??


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17177 posts, RR: 66
Reply 14, posted (7 years 8 months 6 days 2 hours ago) and read 5726 times:

Quoting ConcordeBoy (Reply 13):
...even taking the A345's higher weight relative to its competition; why would a(ny such) twinjet attempt to conform to a 75% OEI thrust percentage??

Because that is the eqivalent. That is:
- Quad needs to continue take-off with 75% thrust,
- Twin needs to continue take-off with 50% thrust.
It thus follows that for "the same" aircraft one engine on the twin (50%) needs to be as strong as 3 on the quad(75%) . A twin needs 50% more power in total than a quad.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineConcordeBoy From , joined Dec 1969, posts, RR:
Reply 15, posted (7 years 8 months 6 days ago) and read 5718 times:

Quoting Starlionblue (Reply 14):
Because that is the eqivalent.

No it isn't. If it was, then quads would have no advantage over twins in hot/high.

Quoting Starlionblue (Reply 14):
A twin needs 50% more power in total than a quad.

...the numbers don't support anywhere near that assessment.

OEI THRUST differential: 36%
773ER = 115,300
A346HGW = 180,000

POWER/WEIGHT differential: 4%
773ER = 29.75
A346HGW = 28.65


User currently offlineSpeedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Reply 16, posted (7 years 8 months 5 days 23 hours ago) and read 5705 times:

Quoting Starlionblue (Reply 14):
Because that is the eqivalent. That is:
- Quad needs to continue take-off with 75% thrust,
- Twin needs to continue take-off with 50% thrust.
It thus follows that for "the same" aircraft one engine on the twin (50%) needs to be as strong as 3 on the quad(75%) . A twin needs 50% more power in total than a quad.

As concordeboy notes, the numbers don't add up, and I think the reason for this is that twin engine planes have lower engine-out minimum climb gradient requirements. Betwen liftoff and gear retraction, a twin must maintain an unspecified positive climb, whereas a quad must maintain .5% climb gradient. After gear retraction and before 400ft AGL, a twin must maintain 2.4% climb gradient, and a quad 3%. Above 400, and at "final takeoff speed" (According to FAR, but I don't really know what this means), a twin must maintain 1.2%, and a quad 1.7%.

Perhaps his accounds for the discrepency in available power with one engine inoperative between twins and quads.

http://www.airweb.faa.gov/Regulatory...41A8A86256C8C005BB2B0?OpenDocument



Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17177 posts, RR: 66
Reply 17, posted (7 years 8 months 5 days 13 hours ago) and read 5640 times:

Quoting Speedracer1407 (Reply 16):
As concordeboy notes, the numbers don't add up, and I think the reason for this is that twin engine planes have lower engine-out minimum climb gradient requirements. Betwen liftoff and gear retraction, a twin must maintain an unspecified positive climb, whereas a quad must maintain .5% climb gradient. After gear retraction and before 400ft AGL, a twin must maintain 2.4% climb gradient, and a quad 3%. Above 400, and at "final takeoff speed" (According to FAR, but I don't really know what this means), a twin must maintain 1.2%, and a quad 1.7%.

Well, sure. I was talking about "the same" within quotation marks. I AM aware that quads and twins are more different than that.  Wink



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineKaddyuk From Wallis and Futuna, joined Nov 2001, 4126 posts, RR: 25
Reply 18, posted (7 years 8 months 5 days 7 hours ago) and read 5585 times:

Quoting CygnusChicago (Thread starter):
Why then didn't Airbus design a two engine version of the A340NG, seeing as they had to redesign the entire wing?

Because customers who didnt have ETOPS and didn't want ETOPS demanded a four engine aircraft...

Virgin, Lufthansa, South African... Not ETOPS carriers (or certainly weren't when they had their original A340's delivered).

Just because the more economical solution exists doesnt mean that the airlines will choose it. The B777 is a VERY expensive airframe and when you consider more than just the economical performance. It makes alot of sense...



Whoever said "laughter is the best medicine" never had Gonorrhea
User currently offlineConcordeBoy From , joined Dec 1969, posts, RR:
Reply 19, posted (7 years 8 months 5 days 6 hours ago) and read 5572 times:

Quoting Kaddyuk (Reply 18):
Because customers who didnt have ETOPS and didn't want ETOPS demanded a four engine aircraft.

...name some.

Quoting Kaddyuk (Reply 18):
Virgin, Lufthansa, South African... Not ETOPS carriers (or certainly weren't when they had their original A340's delivered).

Neither is true in the case of LH.


User currently offlineKaddyuk From Wallis and Futuna, joined Nov 2001, 4126 posts, RR: 25
Reply 20, posted (7 years 8 months 5 days 2 hours ago) and read 5523 times:

Quoting ConcordeBoy (Reply 19):
Neither is true in the case of LH.

In the case of LH they already operated the A340 and it would have made sense to continue with the same type of airframe rather than start a whole new line...

Quoting ConcordeBoy (Reply 19):
...name some.

Virgin Atlantic Airways...

South African Airways are another carrier who operated a four engine long haul fleet...

Airbus built the A340-500 and -600 Because there was a market demand for it They wouldn't have built the aircraft if they didnt think it wouldn't sell...

Can you explain to me why would airbus build an aircraft they weren't sure would sell?



Whoever said "laughter is the best medicine" never had Gonorrhea
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17177 posts, RR: 66
Reply 21, posted (7 years 8 months 5 days ago) and read 5504 times:

Quoting CygnusChicago (Thread starter):
Why then didn't Airbus design a two engine version of the A340NG, seeing as they had to redesign the entire wing?

To answer the question again, because they didn't really redesign the entire wing. They created a tapered root insert (a wedge shaped piece) and expanded the existing wing around it. This is not redesigning the entire wing. Making a whole new wing optimized for, say, a GE-90, would have been much more work.

The 345/6 is evolutionary, not a new aircraft. It is still based on the old. And so Airbus can offer it much cheaper than the 777. While the 777 may be superior in some ways, being the cheaper aircraft offsets some of the advantages of the 777.

Also, there are the usual suspects:
- Commonality of maintenance, operations and engines.
- Delivery availability.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineConcordeBoy From , joined Dec 1969, posts, RR:
Reply 22, posted (7 years 8 months 5 days ago) and read 5497 times:

Quoting Kaddyuk (Reply 20):
In the case of LH they already operated the A340 and it would have made sense to continue with the same type of airframe rather than start a whole new line.

As true as that may be, it does nothing to redeem your earlier (false) statement that LH was not an ETOPS certified airline at that time.

Quoting Kaddyuk (Reply 20):
Virgin Atlantic Airways.
South African Airways are another carrier who operated a four engine long haul fleet...

Again, your statement of (rather obvious) past fleet compositions, has no bearing on the fact that you've failed to present a shred of evidence that these airlines "demanded a four engine aircraft" for fleet succession-- particularly in the case of VS, whom if you'll recall, was the loudest voice in support of Boeing's (twinjet) Sonic Cruiser; at around the timeframe in question.

Quoting Kaddyuk (Reply 20):
Airbus built the A340-500 and -600 Because there was a market demand for it They wouldn't have built the aircraft if they didnt think it wouldn't sell.

That covers pretty much every aircraft ever built.

Quoting Kaddyuk (Reply 20):
Can you explain to me why would airbus build an aircraft they weren't sure would sell?

Dunno, ask this fella:

View Large View Medium
Click here for bigger photo!

Photo © Florian Eggenschwiler
View Large View Medium
Click here for bigger photo!

Photo © Erik Frikke



User currently offlineConcordeBoy From , joined Dec 1969, posts, RR:
Reply 23, posted (7 years 8 months 5 days ago) and read 5496 times:

Quoting Starlionblue (Reply 21):
being the cheaper aircraft offsets some of the advantages of the 777.

initially it did... but even that began to fall out of the A340's favor.


User currently offlineTrex8 From United States of America, joined Nov 2002, 4871 posts, RR: 14
Reply 24, posted (7 years 8 months 4 days 23 hours ago) and read 5489 times:
Support Airliners.net - become a First Class Member!

Quoting ConcordeBoy (Reply 19):
Quoting Kaddyuk (Reply 18):Because customers who didnt have ETOPS and didn't want ETOPS demanded a four engine aircraft.
...name some.

CI didn't have etops , didn't want to be delayed with transpac services getting etops and thats why they chose the A343 rather than the 772ER.


25 Kaddyuk : Ouch... Okay I'll alter that statement to reflect Lufthansa's position. "Even though LH had ETOPS capability, they still chose the quad jet over a Tw
26 ConcordeBoy : I'm curious as to why (based on your presentation here) that you assume this to be the ultimate element of (or even of primary consideration in) the
27 Kaddyuk : The fact that their choice was a quad is just an observation... You must draw your own conclusions as to why, if a twin jet is that much better than
28 ConcordeBoy : I just listed the typical factors for such in the prior post.... Though interesting to note that while plenty of former A340 operators, and even some
29 Kaddyuk : You'll have to forgive me, i assume that "B-Market 777's" are the -3ER and -2LR versions... This is true... the next gen 777's out perform their quad
30 BuyantUkhaa : Can we please leave the A vs. B threads in "Civil" Aviation? Thanks very much! This forum has arguably the highest quality of all, let's keep it that
31 ConcordeBoy : 772LR is a C-market aircraft 772ER and 773ER are B-market
32 Jetlagged : It's also another twins versus quads argument. There are at least two others on the go here at the moment. Seems some people just don't like four eng
34 Boston92 : I agree, it would be a different airplane.
Top Of Page
Forum Index

Reply To This Topic A340NG - Why Does It Have 4 Engines?
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Why Does Ksea Have Class D Airspace posted Thu Jun 16 2005 04:13:05 by Qxeguy
Why Does 777 Have Glass "backup" ADI posted Tue Aug 26 2003 19:34:57 by Jhooper
Why Does Airbus Not Have C/n Numbers? posted Sun Jan 2 2005 15:29:23 by DeltaWings
Why Does The Nose Go Up? posted Fri Mar 23 2007 20:40:35 by Xbraniffone
Why Does The AN124 Need Six Flying Crew? posted Tue Mar 20 2007 13:30:02 by EI321
Why No Wing-mounted Engines Small Jets posted Wed Feb 21 2007 20:08:02 by Redcordes
How Long And How Much Does It Take To Paint A Plan posted Thu Jan 25 2007 06:12:38 by FL370
Why (OH) CRJ Have Flaps Down All The Time? posted Sat Jan 20 2007 21:37:04 by KLM672
What Is 'DIAL A FLAP' And How Does It Work? posted Tue Jan 9 2007 12:51:50 by Strathpeffer
Why Does Vyse (blue Line) Decrease With Altitude? posted Sun Dec 31 2006 20:51:28 by Dreampilot

Sponsor Message:
Printer friendly format