A380 - combined threads
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Well, the A330/A340 were developed as the one programme - they are essentially 2 and 4 engined derivatives of the same aircraft.
I do believe that ETOPS restrictions were a lot tighter when the A340 was being developed, but with these being relaxed, there are now many more routes open to 2 holers that only 3 and 4 holers could previously operate.
There is also the 'safety net' of having more engines to rely on should things go wrong, and less problems due to assymmetrical thrust. This has to be balanced by increased maintenance costs with having more engines. Indeed, 2 engine ETOPS aircraft have greater engine reliability records than 4 engine aircraft.
Still, many airlines, like Virgin, Cathay, and Lufthansa are happily flying the A340, and the -500 and -600 series are a definite improvement over the hairdryer powered -200s and -300s.
I don't think Airbus have suffered too much in sales, as the A340 has been a good seller, and the A330 a very good seller.
I do believe that ETOPS restrictions were a lot tighter when the A340 was being developed, but with these being relaxed, there are now many more routes open to 2 holers that only 3 and 4 holers could previously operate.
There is also the 'safety net' of having more engines to rely on should things go wrong, and less problems due to assymmetrical thrust. This has to be balanced by increased maintenance costs with having more engines. Indeed, 2 engine ETOPS aircraft have greater engine reliability records than 4 engine aircraft.
Still, many airlines, like Virgin, Cathay, and Lufthansa are happily flying the A340, and the -500 and -600 series are a definite improvement over the hairdryer powered -200s and -300s.
I don't think Airbus have suffered too much in sales, as the A340 has been a good seller, and the A330 a very good seller.
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There is also the 'safety net' of having more engines to rely on should things go wrong, and less problems due to assymmetrical thrust. This has to be balanced by increased maintenance costs with having more engines. Indeed, 2 engine ETOPS aircraft have greater engine reliability records than 4 engine aircraft.
Still, many airlines, like Virgin, Cathay, and Lufthansa are happily flying the A340, and the -500 and -600 series are a definite improvement over the hairdryer powered -200s and -300s.
But i just wondered - it seemed like Airbus was bucking the trend a little in putting them out.
One reason for using 4 engines for long haul is that the wing structure can actually be lighter as the downward bending weight of the outboard engines can help to counteract the weight of fuel in the centre tanks.
So when the A330 and A340 were designed together the A340 was a long range aircraft and the A330 was a medium range aircraft. The 340 carried much more fuel than the 330 so the wing bending relief of the outboard engines offset the weight of the extra fuel.
The early 330s and 340s had identical wings, just on the 330 there were no engines mounted on the outboard attachment points. Proved very useful for the A330 tanker cos this is where they mounted the refueling pods - the wing structure could take them without any redesign.
Since the early days differences between the 330 and ater 340 models has increased dramatically.
So when the A330 and A340 were designed together the A340 was a long range aircraft and the A330 was a medium range aircraft. The 340 carried much more fuel than the 330 so the wing bending relief of the outboard engines offset the weight of the extra fuel.
The early 330s and 340s had identical wings, just on the 330 there were no engines mounted on the outboard attachment points. Proved very useful for the A330 tanker cos this is where they mounted the refueling pods - the wing structure could take them without any redesign.
Since the early days differences between the 330 and ater 340 models has increased dramatically.
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Okay, but what is in it for the airline in terms of selling points ?
Why would they prefer the A340 to the 777 (genuine and not rhetorical question).
To put it another way. Of the various large carrier airlines in the US flying both trans-atlantic and trans-pacific, the majority of every fleet seems to comprise of twins with a scattering of 747s.
What was Airbuses thinking behind bringing out a 4 engined jet in this market? I'm not claiming there isn't any, i'm just wondering what it was.
Why would they prefer the A340 to the 777 (genuine and not rhetorical question).
To put it another way. Of the various large carrier airlines in the US flying both trans-atlantic and trans-pacific, the majority of every fleet seems to comprise of twins with a scattering of 747s.
What was Airbuses thinking behind bringing out a 4 engined jet in this market? I'm not claiming there isn't any, i'm just wondering what it was.
"What was Airbuses thinking behind bringing out a 4 engined jet in this market?"
Basically, as I said, they could produce a new medium range airliner, the A330, and a long range airliner, the A340, simultaneously and with about 90% commonality between the two - hence greatly reducing the development costs of both types.
"Okay, but what is in it for the airline in terms of selling points ?"
What about Virgin's "4 engines for long haul" slogan. Don't know if it had much impact on their pax but they thought it was a selling point.
Basically, as I said, they could produce a new medium range airliner, the A330, and a long range airliner, the A340, simultaneously and with about 90% commonality between the two - hence greatly reducing the development costs of both types.
"Okay, but what is in it for the airline in terms of selling points ?"
What about Virgin's "4 engines for long haul" slogan. Don't know if it had much impact on their pax but they thought it was a selling point.
Groundloop
Hope this doesn't sound picky but I thought that the "wing bending" that needed relief was generated by the lift forces on the wing. In flight this creates an upward stress at the wing/fuselage join which can be "relieved" by filling the wing with fuel. That either one or two engines are also fitted there is added relief not an "offset"
so the wing bending relief of the outboard engines offset the weight of the extra fuel.
ETOPS,
True the wing bending is caused by aerodynamic forces but the A340 wing bends up more than the 330 because it generates more lift because the 340 is a heavier aircraft because of its higher fuel load.
Therefore as the outer wings bend up more, hanging engines off them bends 'em back down again.
True the wing bending is caused by aerodynamic forces but the A340 wing bends up more than the 330 because it generates more lift because the 340 is a heavier aircraft because of its higher fuel load.
Therefore as the outer wings bend up more, hanging engines off them bends 'em back down again.
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Just to be picky, really picky.. the wing bending moment is not just caused by lift.. its caused by the fuselage being pulled down by gravity whilst the wing is maintained by a pretty uniformly distributed lift force.
If you think of the wing with no engines as a simple cantilever, like a pencil held between two fingers it moves up and down quite a lot as you apply load to one end....then try to stop it moving and you soon see how it snaps.
However add a weight at the mid point and the movement is reduced and the force needed to restrain it is reduced, hence the tendency to snap is also reduced...add another weight further out and its going to move even less.....and less force is needed to restrain it is reduced and so even likely to snap. So for an equal strucutral strength you can reduce the dead weight of structure by hanging engines off it..
That's the thought behind the use of engines spread across the wing and also the thought behind having fule in the wings spread across the majority of the span.
My guess for the A340/A330 divergence is that for an equal strucutral weight the A340 can carry a higher fuel load.. hence longer range. As the A330 is not destined for such long sectors the additional fuel is not needed and hence the 4 engines are not helpful.
Detailed examination of the 767/ 777 dry weights versus fully loaded weights may reveal an increased efficency in the A340 solution.
If you think of the wing with no engines as a simple cantilever, like a pencil held between two fingers it moves up and down quite a lot as you apply load to one end....then try to stop it moving and you soon see how it snaps.
However add a weight at the mid point and the movement is reduced and the force needed to restrain it is reduced, hence the tendency to snap is also reduced...add another weight further out and its going to move even less.....and less force is needed to restrain it is reduced and so even likely to snap. So for an equal strucutral strength you can reduce the dead weight of structure by hanging engines off it..
That's the thought behind the use of engines spread across the wing and also the thought behind having fule in the wings spread across the majority of the span.
My guess for the A340/A330 divergence is that for an equal strucutral weight the A340 can carry a higher fuel load.. hence longer range. As the A330 is not destined for such long sectors the additional fuel is not needed and hence the 4 engines are not helpful.
Detailed examination of the 767/ 777 dry weights versus fully loaded weights may reveal an increased efficency in the A340 solution.
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Any dates for the Hawarden visit? My hour building is coming to an end, but I'm sure I can find a few more hours to grab an aircraft and get up there for the day.
A great place to watch the A380 land would be from downwind 1000ft!!
Cheers.
A great place to watch the A380 land would be from downwind 1000ft!!
Cheers.
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Fly long haul over the north pole and suddenly 4 engines makes A LOT of sense!
It seemed a while ago like twins ruled the world in a way, they seemed to be partially responsible for the death of the trijets. Just wondered why Airbus was able to buck the trend.
Does the A340 have a lower operating cost than the 777 ?
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While the wing bending moment relief provided by the outboard engines is real and quantifiable feature, it is only one factor in integrating an airplane. Other Twin vs Quad issues come into play.
The latest versions of the 777-300ER and A340-600 have almost the same payload - range. Comparing airplane weights and fuel volume should give you an idea of the relative efficiency. You can draw your own conclusions.
773ER A346
Operating Empty Weight (tonne) 166.8 181.9
Max Takeoff Weight (tonne) 351.5 380.0
Fuel Volume (USG) 47,890 51,379
The latest versions of the 777-300ER and A340-600 have almost the same payload - range. Comparing airplane weights and fuel volume should give you an idea of the relative efficiency. You can draw your own conclusions.
773ER A346
Operating Empty Weight (tonne) 166.8 181.9
Max Takeoff Weight (tonne) 351.5 380.0
Fuel Volume (USG) 47,890 51,379
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Another reason to have four (or more than two-three can help as well) is in high MORA areas. The most extreme case I am aware of is near PURPA where the min alt is FL280, just adjacent to K2. I don't believe that a twin can take a commercial payload and sustain FL280 on one engine. We are lucky to fly the route quite frequently and pass over the mountains just after sunrise on the way to Japan, it is quite odd to watch all these majestic peaks rushing past at 450 kts, five thousand feet away, as an aside, we are all waiting for one of our picky training captains (note the small caps) to require us to come back to 250 knots over PURPA!)
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Sorry, PURPA ? I didn't get the 250knots reference either.
Very envious of your opportunity to see what must be one of the best views in the world - and view it whilst sitting in air conditioning and sipping a cup of tea!
--
Very envious of your opportunity to see what must be one of the best views in the world - and view it whilst sitting in air conditioning and sipping a cup of tea!
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Sorry about that! PURPA is the waypoint on the Pakistan/Indian/Chinese border and the only way we can do the Japan/Korea northern route out of Dubai. The reference to the 250 knots is due to the general speed restriction below 10,000 feet AGL required by ATC and our company, it was slightly sarcastic as IAS at our typical cruising levels is below that anyway, we just have to put up with a lot of anally retentive nifnaf sometimes, but the price we pay!
Sims Fly Virtually
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Mr. Ree
Yes, I'm one of the "old f@rts" that feels "more comfortable with 4 donkeys"
Always happier if there's 4 on the wings, give me a chance of 6 and I'm with you!
Remember the "good old days" of the SVC-10 which could climb out at a pretty normal rate with "2 on the same side out"
Looking forward to the 380 and hoping that my favorite carrier (GF) will buy them (?- your FFP is asking a question here
)
Yes, I'm one of the "old f@rts" that feels "more comfortable with 4 donkeys"
Always happier if there's 4 on the wings, give me a chance of 6 and I'm with you!
Remember the "good old days" of the SVC-10 which could climb out at a pretty normal rate with "2 on the same side out"
Looking forward to the 380 and hoping that my favorite carrier (GF) will buy them (?- your FFP is asking a question here
)
Look at the aircraft flying between Hong Kong and Europe, they are all 4 jets. The route takes you over North West China with MORAS above one engine stab height in a twin.
A 747-400s fuel burn is about 10t anhour, the 340-300 about 6t. For long lean routes there is no competition.
A 747-400s fuel burn is about 10t anhour, the 340-300 about 6t. For long lean routes there is no competition.
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Both the A330 and the A343 burn approx 6T/hr.
Obviously losing an engine an engine on the A330 loses you 50% of your thrust, whilst of the A343 you only lose 25%.
At 230T an A330 will drift down to approx FL200.
At 230T a A343 will drift down to approx FL290.
(*At LRC)
The A343 can carry 33T more fuel than the A330 too. (ie: an extra 5hrs)
Figs quoted abv are rules of thumb only; more accurate info is in the FCOM. The MTOW of a heavy weight A330 is 233T, whilst a A343 is 275T.
Lastly, many routes that are now ETOPS, werent ETOPS 15yrs ago. The enroute airports werent suitable, didnt have navaids or were communist. (The polar route is one.....plus USSR, Eastern Europe China, Iran were hardly our friends).
There is less of a requirement for 'light' 4-engined aircraft nowadays...but as Dan explains above, it is still there.
Obviously losing an engine an engine on the A330 loses you 50% of your thrust, whilst of the A343 you only lose 25%.
At 230T an A330 will drift down to approx FL200.
At 230T a A343 will drift down to approx FL290.
(*At LRC)
The A343 can carry 33T more fuel than the A330 too. (ie: an extra 5hrs)
Figs quoted abv are rules of thumb only; more accurate info is in the FCOM. The MTOW of a heavy weight A330 is 233T, whilst a A343 is 275T.
Lastly, many routes that are now ETOPS, werent ETOPS 15yrs ago. The enroute airports werent suitable, didnt have navaids or were communist. (The polar route is one.....plus USSR, Eastern Europe China, Iran were hardly our friends).
There is less of a requirement for 'light' 4-engined aircraft nowadays...but as Dan explains above, it is still there.