VC-10
Topic Author
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A340 Under Powered?

Thu May 04, 2000 12:01 pm

There have been many references on this forum to the A340 being under powered. Let's look at a few facts.

The principle citeria in the 340 design are a) long range and b) low operating costs.

The results of this are a 6500 Nm range with 295 pax + baggage (27t payload). This has been acheived by:-

1. New technology (high wing efficiency, composite materials etc )

2. A Crz Mach No. of M 0.82 (chosen as result of a survey of prospective purchasers to assess the best compromise of fuel burn & cruise speed)

3. Fuel Burn optimisation which is a result of the previous factors which dictated the choice of engine definition (thrust for T.O. & climb, and optimised specific fuel consumption in cruise).


Twin Vs Quad Engines.

An "all engines operating" twin has a higher thrust than a quad due to the performance requirements in the case of an engine failure during T.O.

e.g.

A340 with CFM56-5C 4 x 31200 lbs = 124 00 lbs thrust

A330 with GE80C2-A1 2 x 67 500 lbs = 135 000 lbs thrust

This overpowering does have benefits in Clb however.
As a result the time to reach cruise flt lvl in a quad is greater. The 340 could have had a greater ROC but at the expense of a greater engine size and a greater fuel consumption in cruise, thus destroying the balanced design of the a/c. Or, to put it another way, the A340 would not do what it was designed to do if the climb gradient times had been a priority

In the cruise phase however, the quad comes in to its own. The long range cruise Mach No. of 0.82 is, as mentioned previously, a result of a compromise between wing definition & efficiency, engine thrust & size, fuel burn etc.

This cruise speed was commonally agreed by the launching airlines as the best compromise in terms of direct operating costs.

M 0.82 does not penalise traffic, few a/c cruise at M.86 (747) whereas most a/c fly around M.80.

Additionally a/c flying at M.86 use most of the time at a lwr alt than the 340 because of their Max Alt is lower limited

When you compare a 747-400 with an A340 the -400 comes out as overpowered.

The drag/lift ratio of the -400 is 30% higher at low speed & 14% higher at cruise speed. An A340 with a -400 charecteristic wing would require 39 000 lb engines to T.O. at MTOW instead of the 31 200 lb engines it has now.

The initial cruise FL of a -400 after a T.O. at MTOW is lower than that of a 340

-400 Opt FL 295

340 Opt FL 325

The cruise M No. are

-400 M .86

340 M .82

The association of both a higher Crz M No. & lower optimum Flt lvl gives the -400 a far higher fuel consumption e.g.

For an A340 pax load of 295 & a -400 load of 402 over a sector of 4000 Nm the fuel burn is:-

-400 79 T

A340 51 T

or put another way the fuel burn per seat of the -400 is 14% higher than the 340. This difference will increase as the range increases.

So in conclusion the A340 is a well tuned a/c, correctly optimised & fulfilling the intial design objectives.



 
ben88
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RE: A340 Under Powered?

Thu May 04, 2000 12:31 pm

Thanks for the informative post. I'm taking my first A340 this summer and i'm very excited about it. From an economical standpoint, the Airbuses seem to be more cost efficient. I am not at all worried about taking an "underpowered" aircraft. I feel very confident that this plane is more than capable.
 
dnalor
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RE: A340 Under Powered?

Thu May 04, 2000 12:59 pm

So you did decide to put all those figures together  
well done

I spose the sales figures and retainment of fleet over time will tell if the A340 has really met all of its objectives for its buyers.

Personally, from what I have witnessed though, I'd rather be on a 744 or 777 with and engine out on take off over the A340, they just look to be struggling when they leave here @ MTOW ie, full runway used and extremely low ROC compared to the Boeing variants listed above.

No denying their economical status or excelent wing design, just a shame that engines of the same physical size arent available with say 20% more power for better field and initial climb performance.
 
VC-10
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RE: A340 Under Powered?

Thu May 04, 2000 1:18 pm

The following gives a comparison of time/distance from brakes release needed to reach 4 different Flt Lvls for both a -400 and an A340-300 taking off @ MTOW

FL ------------ A340-----------400

150 -----------11'/51Nm -------10'/50 Nm

100------------ 8'/29 Nm -------7'/27 Nm

50--------------5'/15 Nm -------4'/16 Nm

15--------------3'/7 Nm---------3'/-

Both a/c have similar T.O. & intial climb charecteristics
 
dnalor
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RE: A340 Under Powered?

Thu May 04, 2000 1:34 pm

Can you tell me where you get all those figures from?
 
VC-10
Topic Author
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RE: A340 Under Powered?

Thu May 04, 2000 1:40 pm

A340 Flt Crew Operating Manual
 
dnalor
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RE: A340 Under Powered?

Thu May 04, 2000 2:28 pm

And the Boeing figures?
 
VC-10
Topic Author
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RE: A340 Under Powered?

Thu May 04, 2000 2:31 pm

Same Place !
 
dnalor
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RE: A340 Under Powered?

Thu May 04, 2000 2:59 pm

hmmm, I'd be interested to see Boeing's own figures.

Kinda like Cessna having Piper performance figures in a Cessna manual.
Doesn't make sense.
 
ben88
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RE: A340 Under Powered?

Thu May 04, 2000 3:14 pm

I think VC-10 means he got the Airbus figures from the A340 manual and the Boeing figures from the 744 manual. Why would the A340 manual have Boeing 744 specs in it? Thanks VC-10......good post
 
dnalor
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RE: A340 Under Powered?

Thu May 04, 2000 3:35 pm

That's not how I read it Ben  
 
VC-10
Topic Author
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RE: A340 Under Powered?

Thu May 04, 2000 4:12 pm

Dnalor is correct.

I did expect your understandable response Dnalor and I cannot counter it. All I can say is there are enough airlines that operate both types to be able to point Airbus in the right direction if they got their figures wrong. Conversly it is highly likely that Airbus got their Boeing figures from an airline that operates both types.

Anyway I'm off to bed now after my nightshift - so thank you & goodnight
 
dnalor
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RE: VC-10

Thu May 04, 2000 5:19 pm

Good point VC-10

Yeah both are very good airliners catering to different needs.

Night, sleep well.
 
sndp
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RE: VC-10

Thu May 04, 2000 6:04 pm

Where did you got these manuals from, VC-10?
thanks
sndp
 
Panman
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RE: A340 Under Powered?

Thu May 04, 2000 9:01 pm

I have to agree with Dnalor in this respect. I would prefer to see Boeing's figures than Airbus' version of Boeing's performance. This is because I have am currently reading a book on the A340 where the author got his figures from Airbus and Airbus claiming not to have certain information on the 747 that can easily be obtained over the net such as fuselage size. I bet if VC10 was to have gotten the Airbus figures from Boeing they would be different to what he has put here.

Then again there are also many cases when what is written is not what is actually achieved. I have no qualms with the A340 don't get me wrong. I am not a member of the immature Airbus vs Boeing fanclub. But the way I see it the A330 is giving the performance it was designed to do and from all reports the A340 isn't.

Just yesterday I was looking at fully loaded 747s, 777s and A340s takeoff from heathrow and there is no way I would say that the A340s were climbing at anywhere near the same rate as the 744's (according to VC10s p
 
richie
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RE: A340 Under Powered?

Thu May 04, 2000 10:18 pm

VC10

where do you get that ailines effectively operate A340 (-200 and 300 Series) at Mach 0.82. Usually the quads and tri jet aircraft have cruising speeds depending on weather and payload requirements of between 0.81 and 0.84 (only unaware people cruise their 747-400 at 0.86, as it deteriorates the engines much too fast). The actual cruise speed is determined by the settings in the Flight Management Computer. The exception is the A340. It usually cruises in the twin speeds (exception of A330/777) of 0.78 to 0.80.

I have talked to pilots who know the A340, the DC10 and the 747, and thir far preferred aircraft is the DC10, followed by the 747. The A340 is underpowered in their view.

Here a little anecdote: one of the former check captain for PanAm did become one of the major presentation pilots for Airbus and for the A340 in the US. An old friend of his, who was becoming the VP of Operations from a start up (finally they centered on the MD11), asked him, what his aircraft could really do. The Airbus pilot had to admit to his long time friend, that even the747-100 (which was a rela slump) was better in climb than the airbus.

Never believe what the sales book says, look at the real world. Please understand me right, I am very much a friend for airbusses, and one of my most preferred aircraft (short behind the Douglas Tris) is the A330-200, but that does not change the actual performance of the A340. I've sat in evaluation meetings, and one of the most important issues was the effetive performance of the A340-600 and -500 compared to the -200/-300. They (the Airbus sales guys) admitted that their product initially is underpowered. Still does the job, but you don't want to experience an engine failure on a hot and high day.
 
flyf15
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RE: A340 Under Powered?

Thu May 04, 2000 10:47 pm

Relating back to the original post.. Why is this? The MD-11 is approximately the same size as the A340-300, but it has up to 150% the power of the A340 (MD-11 has 186000lbs of thrust) and a higher cruise speed, yet it still has about the same range as the A340-300? Does it carry more fuel or is it efficient as the A340-300 during flight?
 
WorldTraveller
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Richie

Thu May 04, 2000 10:50 pm

Airbus did a lot of tests with the A340 in hot and high environments.

In Quito, Ecuador, the did take-off's with only two engines running (both on one side), and absolutely no problems surfaced.

The 747 classics and the DC-10 may have better climb rates, but do you know how much fuel they burn until they reach cruising altitude?? A LOT!

I think the A340's slower climb rate was never a reason not to order this plane!

Regards
 
dnalor
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RE: Flyf15 & Richie

Thu May 04, 2000 11:10 pm

Richie first of all thanks for your ealier post and relevent comments.

How heavy was the A340 that took off with two engines on one side out???? I thought double Assymetric training and testing was a big no no especially since the RAAF lost a 707 and 5 crew that way.

Flyf15 150%????? I cant get that on my calculator, wanna recheck the maths on that one mate???  
 
cricri
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RE: A340 Under Powered?

Fri May 05, 2000 12:02 am

There is a little joke among the A340 tech crews saying that thank god the earth is curved for a t/o with this plane...  
 
VC-10
Topic Author
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RE: A340 Under Powered?

Fri May 05, 2000 6:33 am

Sndp
The manuals are in my office.

Panman.
I find it difficult to believe AI can't get such basic 747 info. I would question the how good the book is.

How do you know the 777's, 747 & A340's were all operating at or close to MTOW ?

Richie
All the info came from FCOM Bulletin, not a sales brochure.

Flyf15
I have no idea what the fuel capacity of the MD-11 is.

Finally I have no particular views on the subject, I just thought I would throw into the debate the figures I have at my disposal

 
Panman
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RE: A340 Under Powered?

Fri May 05, 2000 9:30 am

VC10, a good way to tell if an aircraft is heavily loaded if you are not sure is to look at two things.

1. The length of the takeoff roll and
2. How much the wings are flexed (bent) during initial rotation).

You will never get a lightly laden aircraft with the wings flexed to a high degree on rotation. The bend in the wings is showing how much lift is being generated in order to lift the aircraft off the ground. Now obviously with these aicraft mentioned (747, 777, A340) they are no anorexics even when empty but you can still notice the difference in how much the wings are flexed between an empty 747/777/A340 and a heavy one. Case in point there was one BA 777 followed by an AA 777 and you could tell the AA one was carrying more than the BA 777 it took up more runway and the wings were bent upwards more.

So even though I don't have the figures with me, I was making an educated guess.

As to the book, I agree with you, I doubted myself when I read it that Airbus couldn't get the figures for the 747 fuselage size (yet they quoted the 777). So it was as I was saying constructive figures from Airbus. The book in question was the Airliner Tech Series, Airbus Industrie, Airbus A340, written by Scott E Germain who himself is an A320 pilot. Page 99.

Page99
 
flyf15
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RE: 150%

Fri May 05, 2000 11:09 am

A340 with CFM56-5C4 4x31200 lbs = 124800lbs thrust
MD-11 with PW4462 3x62000 lbs = 186000lbs thrust

186000/124800 = 1.49 (approx 150%)

 
VC-10
Topic Author
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RE: A340 Under Powered?

Fri May 05, 2000 11:24 am

I make that 50% more power
 
flyf15
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RE: A340 Under Powered?

Fri May 05, 2000 11:49 am

"but it has up to 150% the power"

50% more or 150% of... same thing, sorry they got confused.
 
dnalor
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RE: A340 Under Powered?

Fri May 05, 2000 5:05 pm

I would have called that 50% more too

but I see what you mean now Flyf15
 
richie
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RE: A340 Under Powered?

Fri May 05, 2000 10:18 pm

VC10
that is very nice, but I recently talked to some ATC guys, and their biggest worry is, that A340s never make the projected climb and trouble the whole planning in the levels. The A340 is a slow climber, as it is specifically designed for being very economical.

World Traveller
That is part of aircrat certification, and it cetainly is possible to make the required engine fail take-offs. But we don't know the gross weight of the aircraft during the demos, and we don't know the exact power setting used (it may have been one that requires you to exchange the engines after the incident. If Airbus ould not have demonstrated these capabilities, there would be no A340 flying, as they would have failed certification.

Let's stop the hickhack and agree on following:

The A340 is a very bad climber and slow, but that's what makes it so efficient. And efficiency is what the bean counters in airlines are interested in (I used to be one of those, so I know).
 
Guest

RE: A340 Under Powered?

Sat May 06, 2000 2:31 am

VC-10, very informative post. With the demise of the DC-8 and 707, it is good to see a smaller 4 engine comercial aircraft for spotting. Sure it's a little slow but it was designed for economical, long range cruising. Again, thanks for the post.
 
ZRH
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A 340-500/600?

Mon May 08, 2000 4:08 am

Will the A340-500/600 be better powered?
 
Panman
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RE: A340 Under Powered?

Mon May 08, 2000 5:01 am

Yes they will be using Trent 500s which are about twice as powerful as the CFM56.

Don't have the exact figures.

PANMAn
 
Ruscoe
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RE: A340 Under Powered?

Fri May 12, 2000 12:39 pm

If the A342 & A343 are not underpowered why are the A345 & A346 going to have a signifigantly higher thrust to weight ratio?
Ruscoe
 
Panman
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RE: A340 Under Powered?

Fri May 12, 2000 2:25 pm

Because they won't be using CFM56s (i.e. engines designed for the Boeing 737) which are only capable of producing around 30000 lbs.thrust. The Trent 500s produce something like 50000 lbs.thrust.

paNMan
 
turbulence
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RE: A340 Under Powered?

Sat May 13, 2000 2:08 am

It has been said so macuh about this subject!!!

As World Traveller says, I do not think the ROC is a sales argument. Something which is much more important than the rate of climbing is taht the a/c is going to keep flying, for the longest time possible, with the least expenses possible.

In reference to Michael Schumacher, a journalist said once: “The best champion is the one who wins as slowly as possible”. Actually, he was the first with 20 laps to go, 35 seconds ahead, and at the end, his advantage was only 5 seconds. Does it mean that in 10 more laps he would have lost his race? Or that he managed to keep the first place taking good care of his engine, which could have been burnt if kept continuously used 100%?

As for my cent of info, here, and comparing Airbus' on board computers to the above experience in F-1, I have read, not too long ago, (SabenaPilot, where are you?) that modern airbusses (actually all of them except the older 300s/310s), are designed for being economic, and equipped with some kind of calculator reviewing continuously the optimum thrust/economy ratio. The result of such a continuous check from the computer results in some kind of “standard COR” (meaning that an empty A340 won't climb faster that an MTOW one), because the thrust is something like “the-less-possible”. As a result of it, too, 100% throttle does not necessarily mean 100% thrust.

From my own experience, it makes sense since I have jumpseat taken off in a B737-400 and in a last generation A300-600R. This could be a logical explanation: although the throttles of both airplanes were “full-forward”, while the revs. of the 734 where ABOVE 100% (something close to 105%), in the AB6 they never reached to 85%. Then, at cruise level, both were flying 80-82%. I must confess that it happened before I had read anything of it all, and I didn't give any importance to it since they were so different A/Cs. But now I believe it.

Best turbulences
 
Guest

RE: A340 Under Powered?

Sat May 13, 2000 4:00 am

I flew on an A340 three months after it was introduced in service by (launch customer?) Lufthansa. The plane was D-AIBA, now wearing the Star alliance colors. I flew from FRA to MIA. Naturally, at one point during the flight I ended up on the flight deck. I did ask the captain a few (!) questions, and the engine power was discussed. The Captain admitted that the plane is actually deliberately underpowered, for economical reasons. But this has it's downside. He did not seem concerned about what would happen if he lost an engine on T/O. The plane is fullly capable of handling that on the remaining three. But in normal operations the plane climbs so slowly that a controller only clears an A340 a few thousand feet at a time, less than he would normally do other planes. This may cause an A340 to get stuck at lower final levels for the flight, which will result in excessive fuel consumption, as was the case on my flight. Do not worry, we had 108 tons of fuel on board ! Quite enough for the crossing ! We also spoke about winglets, and when I asked the Captain what is the advantage of the winglets, he replied that the plane simply looks better !
I have flown many types of planes, from 707 to 747-400 (no 777 yet) and the 340 rates with my favorites - no doubt.
 
Panman
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RE: A340 Under Powered?

Sat May 13, 2000 4:30 am

"We also spoke about winglets, and when I asked the Captain what is the advantage of the winglets, he replied that the plane simply looks better ! "

That's pilots for you, if you ask me we should dispense with them altogether computers do most of the flying from around 400ft after takeoff anyway. Basic theory of flight and all he could say is the plane looks better?

pANMAn
 
Guest

RE: A340 Under Powered?

Sat May 13, 2000 4:54 am

Panman, would you fly in aircraft with no pilots? I agree that some pilots are a detriment in the cockpit for serveral reasons, including being incapable of flying, but worse still, their attitude. And thank God for the autopilot. Most would not be capable of handflying the machine for too long.
But who would have landed the AC 767 that ran out of fuel? Or that incredible Sioux City feat?
 
FDXmech
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RE: Turbulence

Sat May 13, 2000 11:14 am

The onboard computers I take it you are referring to are the flight management computers (FMC). The specific function I think you are talking about, "thrust/economy calculator" would be the "CI" or cost index entry.

The cost index is a ratio of the cost of flying time, to the cost of fuel. The lower the CI, the slower the speed for better fuel savings. The higher the CI, the greater the speed which saves time and and time related expenses (crew pay, etc).

Values from "0" - "999" are entered for CI. "0" being the most economical mode with maximum endurance time.

The FMC and CI are standard AI, Boeing and Mcdd.
You're only as good as your last departure.
 
Guest

RE: A340 Under Powered?

Fri Jun 09, 2000 7:51 am

Airbus, because the development of the IAE Superfan version of the V2500 was dropped they had to go for the CFM56. I think this was a mistake to put an engine meant for the 737 & A320 on the A340-200/300 models. I think the best engine should have been the P&W 2000 engine used on the 757 the Air Force's C-17 Globemaster III and Russian IL-96M.
 
prebennorholm
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RE: A340 Under Powered?

Fri Jun 09, 2000 7:05 pm

Please keep in mind that the name CFM-56 refers to an "engine family". Those on the A340 are roughly 50% more powerful than an avarage CFM-56 on 737 or 320.
Comparing a CFM-56 on a 737-300 with one on an A340 is like comparing a JT8D-1 on a 727-100 with a JT8D-209 on a MD80.
what we should look at it the total combined max engine trust to max take-off-weight ratio. The A340 ratio compares well to other four engined airliners. The only difference is that the A340 has the worlds most sophisticated economy management computers, and they are used.
Twins need to act more sporty since they must leave a wider margin to be able to fight an engine flameout during take-off. They need to have more power, and they also need to use it to be safe. They must be prepared to recover from the worst thinkable situation with only 50% power, while a four engined must be able to do the same with 75% power.
Always keep your number of landings equal to your number of take-offs
 
dnalor
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RE: Prebennorholm

Sun Jun 11, 2000 12:17 pm

 
dash8
Posts: 389
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Planes, Wings And FMC's

Sun Jun 18, 2000 12:11 pm

This subject isn't all that complex.
All modern jetliners have FMC's with CI, optimum flight altitude/cruise speed calculations.
All are designed to be the most economical in their class.
The A340 can only be compared to the 777. And not the 747-400.
As for twins needing more total thrust to fight a failed engine. Don't beleive it. Are you then telling me that a
heavy A340 won't fly on two engines?
One thing is fore sure. The A340 is underpowered in climb. The MD-11 is overpowered in......everything.
All have the best wing for their time.
All are great jetliners.
It all boiles down to that elusive number that no one will ever get their hands on.
SEAT-PER-MILE-COST......

That's all you need to see which one is better,......unfortunately.


Regards,

Xander
 
777X
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RE: A340 Under Powered?

Mon Jun 19, 2000 12:57 am

An A340 might continue to fly w/ 2 engines, but it could never climb out - that's what everyone's talking about

AFAIK for certification, 4 holers need to be able to take off with 3 engines running, and 2 holers need to be able to take off with 1 engine running

I don't think that an A340 would be able to maintain level flight with two out

 
prebennorholm
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RE: A340 Under Powered?

Mon Jun 19, 2000 8:42 am

A340-300 with CFM56-5C4 at MTOW is 4.21lbs per pound of thrust.
Airliners have a lift to drag ratio (L/D) in the low 20'es meaning that it needs 1/20 or 1/25 of its weight as trust to keep level flight. (Except the Concorde which has a subsonic L/D around only 9).
With two engines out the A340 will still have a thrust to weight ratio at 2 * 4.21 = 8.42 or far better than the L/D.
With two engines out, but windmilling freely, and a fairly symmetrical power, then it will have absolutely no problem to keep level flight. But only at low altititude. At sea level it could do it on two engines at half power.
To lift off with gear and flaps extended, that's an entirely different thing. It would only be possible at very leight weight. With most of the fuel burned or dumped it will easily make a missed landing on two engines too, even with gear and flaps extended. With half payload and half fuel on board an A340 would have much the same take-off power to weight ratio as a 777 or A330 at MTOW.
But why do we talk about two engines out? In case that could happen, then all twins - from the 777, 330 and down - had to be grounded.
Always keep your number of landings equal to your number of take-offs
 
Guest

RE: A340 Under Powered?

Thu Jun 22, 2000 3:08 am

I was in Rolls Royce's website where I read that yesterday 20 Jun 2000, marked the first flight of the new RR Trent 500 that will be used on the A340-500/600. It was mounted on an A340-300, on an engine pylon where a CFM56 engine was. Everything went flawlessly on this first flight with the engine to be certified I believe in December this year.
 
Guest

RE: 150%

Fri Jun 23, 2000 3:46 am

Airbus A340-300 CFM56, 34,000X4=136,000
Boeing 777-200ER RR Trent 895, 98,000X2=196,000
 
VC-10
Topic Author
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RE: A340 Under Powered?

Fri Jun 23, 2000 5:37 am

A340-600 RR Trent 500, 56,000 x 4 = 224,000
 
Guest

VC-10

Fri Jun 23, 2000 8:26 pm

I hope in the future I have the opportunity to fly on one of Virgin Atlantic's A340-600s. I my book I rank Rolls Royce #1 with the best quality reliable engines with P&W #2. I think Airbus should have a re-engine program where they replace the underpowered CFM56s on the A340-200/300 with a version of the RR RB211 that is used on the 757.
 
BigGiraffe
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RE: A340 Under Powered?

Sat Jun 24, 2000 12:14 am

"Underpowered" is a term from the early days of jet airliners when engine development was young and they could not provide as much thrust as ideally required. That doesn't even apply to today. There is no reason they couldn't have put a 60,000 lb-class engine on the A340 if that had been a requirement. But it wasn't, and had they done it just so the aircraft performed like a hotrod, then the aircraft would have been uneconomical to operate. So if the designers had required a stronger engine for the A340, don't you think they would have used one?
 
Guest

BigGiraffe

Sat Jun 24, 2000 2:09 am

In an earlier reply, I stated that the A340 was originally to be powered by a new Superfan version of the IAE V2500. Because of technical risks the Superfan project was dropped and Airbus had no option but to put a version of the CFM56. Was wondering why they didn't put a version of the RR RB211 or P&W 2000 engine used on the 757 on the A340 instead?
 
dnalor
Posts: 346
Joined: Fri Mar 10, 2000 7:58 pm

RE: A340 Under Powered?

Sat Jun 24, 2000 10:12 am

I would have thought the RB211 would have too large a diameter for ground clearance on a A340?

is this subject gonna die*L*

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