Dtswi From Portugal, joined Aug 2001, 126 posts, RR: 0 Posted (14 years 8 months 4 weeks 13 hours ago) and read 1757 times:
Can anyone explain to me why manufacturers would still make 4 engines-a/c, whereas 2 more porwerful ones would be enough ?
(for ex. could the A330 potentially replace the A340 entirely with larger engines reaching longer range)
I can see a need for 4 eng. on very large a/c such as A380 or B747, but not really for A342 or 343..?
Lowsonboy From United Kingdom, joined Aug 2001, 275 posts, RR: 0
Reply 2, posted (14 years 8 months 4 weeks 12 hours ago) and read 1553 times:
One reason is that 4 engined planes aren't restricted by ETOPS. This puts a limit on how far twin-jets can be from an airport at any time (I'm not sure how long but I think it is an hour's flying time - can someone confirm this?) in case one of the engines fails.
Rabenschlag From Germany, joined Oct 2000, 1080 posts, RR: 0
Reply 5, posted (14 years 8 months 4 weeks 12 hours ago) and read 1519 times:
ETOPS isnt such a big topic. if you look at maps displaying ETOPS blindspots (http://gc.kls2.com/) youll only see serous problems on some pacific routes. so one only can repeat your question. i would like to add one more question:
why does the pioneer of large twins (airbus started the trend in the sixties when they launched the A300 and A310) nowadays insist on quads for long-haul AC's?
i think boeing perfectly grabbed up the vision that was behind the A300/310 and used it to develop successful planes like the 767 and the 777. its somewhat sad that the inventor gave up pursuing his best idea.
GOT From Sweden, joined Dec 2000, 1912 posts, RR: 1
Reply 6, posted (14 years 8 months 4 weeks 12 hours ago) and read 1480 times:
Airbus haven't give up the twin idea. The A380 is too heavy too be a twin, the A318 is developed as a twin. But in the case of A330/A340, it was not so accepted to fly ETOPS routes and Airbus thought that people might prefer to fly in a quad, rather then a twin. Nowadays people fly in a twin, but there are still people that don't like to fly in a twin for long distances.
Just like birdwatching - without having to be so damned quiet!
Rabenschlag From Germany, joined Oct 2000, 1080 posts, RR: 0
Reply 8, posted (14 years 8 months 4 weeks 11 hours ago) and read 1459 times:
why no trijets? because the no. 2 engine causes even more trouble in maintainance than four engines under the wings. note that its not fuel efficiency that makes twins cheaper, but its lower maintainance costs. an A343 should be as fuel efficient as a 777 when operating under good conditions.
YoungDon From United States of America, joined May 2001, 500 posts, RR: 0
Reply 9, posted (14 years 8 months 4 weeks 11 hours ago) and read 1454 times:
Well really, neither the A300 or the A310 are catered toward ultra long-range ops that a quad would be suited for. They both only have a bit more than transatlantic range, while the A340 has transpacific range, which has a few ETOPS holes. I do not understand why AI hasn't made a very long range A330-300 though. (Using the extra fuel tanks of the A340.)
As for three engines, I bet an all new large, long-range trijet with better fuel efficiency than the 772ER would be viable since it would have at least the efficiency of the 343 but would not be constricted by ETOPS like the 777 is.
Blink182 From United States of America, joined Oct 1999, 5499 posts, RR: 14
Reply 10, posted (14 years 8 months 4 weeks 8 hours ago) and read 1417 times:
I don't know about you all, but I would feel more comfortable flying LAX-SYD in a 747 or A340 vs. a 777. I think 4 engines makes flying a little more at ease with people who are afraid of flying.
Give me a break, I created this username when I was a kid...
Hypermike From United States of America, joined Dec 1999, 1001 posts, RR: 5
Reply 11, posted (14 years 8 months 4 weeks 8 hours ago) and read 1404 times:
Its the mind of the passenger that is key to what blink182 said. You'd think that the four-engine plane is more reliable, but from what Boeing has stated, the 777 has a better dispatch rate. In a 747, you have twice the number of things that can go wrong than in a 777.
Sure, if the engine itself fails, you can continue on two or three engines. But most times, its a different type of problem that causes dispatch failures.
Aeroguy From United States of America, joined Aug 2001, 69 posts, RR: 0
Reply 12, posted (14 years 8 months 4 weeks 7 hours ago) and read 1382 times:
You might also keep in mind span loading and structural considerations of 4 engines vs. 2. According to Airbus, the A330/A340 have virtually identical wings and there is only about 2% difference in structural content between the two aircraft. The 2 extra engines on the A340 greatly reduce the wing bending moment compared to the A330. This allows the A340 to fly a lot heavier than the A330 with the same wing. (At least that's true for the older A340s, I don't know if Airbus has beefed up the wing structure of the -500 and -600 considerably or not.) I believe that 4 engines are also more helpful in damping out flutter than 2 as well.
Geebar From , joined Dec 1969, posts, RR:
Reply 13, posted (14 years 8 months 4 weeks 4 hours ago) and read 1338 times:
Getting back to Dtswi's original question >>why manufacturers would still make 4 engines-a/c, whereas 2 more porwerful ones would be enough ?
(for ex. could the A330 potentially replace the A340 entirely with larger engines reaching longer range<<
Even if two engines are capable or producing as much as or more thrust than that is produced by the four on the A340, this doesnt mean that this kind of conversion can take place.
Speaking from the Ausralian Reg's, Civil Aviation Order (CAO 20.7.1B) states that these type of aircraft must be able to sustain the loss of thrust from one engine during the most critical phase of the take-off, just after V1. If a twin producing the same amount of thrust as a quad were to lose an engine just after V1 it has lost half of its total thrust whereas on a quad, an engine failure at this point would see it only having lost a quarter of the aircraft's total thrust. Would this twin having half the thrust still be able to climb out as required? It certainly cant match the quad with three-quarters of its thrust.
The four engines allow the heavier weights and therefore more payload to be taken as the loss of one engine is not so critical as is the case in a twin. This is also a reason we see twins climbing much better than quad's with all engines operating, the required exceess thrust needed to combat the loss of an engine.
Advancedkid From United States of America, joined Jun 2000, 762 posts, RR: 2
Reply 15, posted (14 years 8 months 3 weeks 1 day 11 hours ago) and read 1266 times:
One more forgotten aspect.
Before aircraft manufacturers
persue designing and building
a new airframe, they must be
full aware of the availability
of the engine (of the size and
thrust) they are designing it
They simply don't go ahead
with a program and then ask
the engine makers to taylor
cut an engine for that new
I hope that helps.
Srbmod From , joined Dec 1969, posts, RR:
Reply 17, posted (14 years 8 months 3 weeks 22 hours ago) and read 1216 times:
Four engine jets are a still manufactured for several reasons. First off, as it has been noted, ETOPS and range; secondly, some airlines have policies on the number of engines on transoceanic aircraft (like Virgin Atlantic); lastly, tradition. Since transoceanic flights became commonplace, many of the aircraft used for these routes have been four engined (DC-7, the Connie, the Comet, the Stratocruiser, DC-8, 747, Concorde, VC-10), with the exceptions being the DC-10/MD-11 and L-1011. Twinengine transoceanic flights have only become commonplace in the last 20 years with improvements in powerplants, allowing airlines to operate using ETOPS. And you could add to the fact that with a four (or three) engined aircraft, you still have 3 (or 2) engines still working if you lose and engine, as opposed to one, so the chances of making a diversion airport with 2 or three engines as opposed to one are greater; in fact, one could in theory still make your final destination with one engine out on a three or four engined aircraft.
Cfalk From , joined Dec 1969, posts, RR:
Reply 21, posted (14 years 8 months 3 weeks 17 hours ago) and read 1189 times:
Long over-water flights using twinjets has been common for the past 15-20 years, starting with the A310 and 767 on the Atlantic routes. Twinjets now fly virtually every route in the world, except for some gaps in the Pacific, South Atlantic, where alternative landing sites are far apart. Recent extensions of ETOPS to the 207-minute and even 240-minute standards may even eventually eliminate those gaps.
Jwenting From Netherlands, joined Apr 2001, 10213 posts, RR: 17
Reply 22, posted (14 years 8 months 3 weeks 17 hours ago) and read 1182 times:
AMS as an example:
The following airlines use twins to the Americas (maybe more, these I know of):
- Martinair 767
- United 777 and 757
- Delta 767
- US Airways 767
- Air Holland 757
- Air Transat A310 A330
- Canada 3000 A330
- KLM ?? (think they use some 767s to the Carib, not sure)