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Why 4 Engines?  
User currently offlineDtswi From Portugal, joined Aug 2001, 126 posts, RR: 0
Posted (12 years 11 months 3 weeks 4 days 8 hours ago) and read 1537 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..?

Thank you for your comments.

29 replies: All unread, showing first 25:
 
User currently offline777kicksass From United Kingdom, joined Sep 2000, 668 posts, RR: 0
Reply 1, posted (12 years 11 months 3 weeks 4 days 8 hours ago) and read 1348 times:

I certainly don't see the point of the a340 having 4 because they actually total less power than the equivalent a330! And, they carry more fuel, thus they are underpowered but thats irrelevant.!

I think nowadays 2 engines are just agood as 4 and should be the way forward for medium-long range, because of the less maintenance and their reliability, so I don't think 2 is less safe than 4.


User currently offlineLowsonboy From United Kingdom, joined Aug 2001, 275 posts, RR: 0
Reply 2, posted (12 years 11 months 3 weeks 4 days 8 hours ago) and read 1333 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.

User currently offlineFritzi From United Arab Emirates, joined Jun 2001, 2762 posts, RR: 2
Reply 3, posted (12 years 11 months 3 weeks 4 days 8 hours ago) and read 1316 times:

Because with four engines you don't have to worry about ETOPS

User currently offlineBA DC-10 From United Kingdom, joined Jul 2001, 145 posts, RR: 0
Reply 4, posted (12 years 11 months 3 weeks 4 days 8 hours ago) and read 1305 times:

Because of ETOPS, some airlines have policies of not flying with 2 engine jets over large stretches of water......

User currently offlineRabenschlag From Germany, joined Oct 2000, 1007 posts, RR: 0
Reply 5, posted (12 years 11 months 3 weeks 4 days 8 hours ago) and read 1299 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.

regards, rabenschlag


User currently offlineGOT From Sweden, joined Dec 2000, 1912 posts, RR: 1
Reply 6, posted (12 years 11 months 3 weeks 4 days 7 hours ago) and read 1260 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.

GOT



Just like birdwatching - without having to be so damned quiet!
User currently offline456 From Netherlands, joined Feb 2001, 328 posts, RR: 1
Reply 7, posted (12 years 11 months 3 weeks 4 days 7 hours ago) and read 1246 times:

If ETOPS is the problem, why not 3 engines? Like a dc/md 10/11 or Tristar...

User currently offlineRabenschlag From Germany, joined Oct 2000, 1007 posts, RR: 0
Reply 8, posted (12 years 11 months 3 weeks 4 days 7 hours ago) and read 1239 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.

regards, rabenschlag.


User currently offlineYoungDon From United States of America, joined May 2001, 407 posts, RR: 0
Reply 9, posted (12 years 11 months 3 weeks 4 days 7 hours ago) and read 1234 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.


User currently offlineBlink182 From Azerbaijan, joined Oct 1999, 5480 posts, RR: 15
Reply 10, posted (12 years 11 months 3 weeks 4 days 3 hours ago) and read 1197 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.
rgds,
blink182



Give me a break, I created this username when I was a kid...
User currently offlineHypermike From United States of America, joined Dec 1999, 1001 posts, RR: 5
Reply 11, posted (12 years 11 months 3 weeks 4 days 3 hours ago) and read 1184 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.


User currently offlineAeroguy From United States of America, joined Aug 2001, 69 posts, RR: 0
Reply 12, posted (12 years 11 months 3 weeks 4 days 2 hours ago) and read 1162 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.

User currently offlineGeebar From , joined Dec 1969, posts, RR:
Reply 13, posted (12 years 11 months 3 weeks 3 days 23 hours ago) and read 1118 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.

ETOPS considerations are vital to this topic.

Regards,
Geebar


User currently offlineDtswi From Portugal, joined Aug 2001, 126 posts, RR: 0
Reply 14, posted (12 years 11 months 2 weeks 5 days 8 hours ago) and read 1064 times:

Thank you all for your very informative comments ...

Geebar, Aeroguy and Rabenschlag, I learned something !

Best regards,

Daniel T.



User currently offlineAdvancedkid From United States of America, joined Jun 2000, 762 posts, RR: 2
Reply 15, posted (12 years 11 months 2 weeks 5 days 7 hours ago) and read 1046 times:

Hi there,
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
around.
They simply don't go ahead
with a program and then ask
the engine makers to taylor
cut an engine for that new
aircraft.
I hope that helps.
Kindest regards.
Advanced


User currently offlineBA From United States of America, joined May 2000, 11153 posts, RR: 59
Reply 16, posted (12 years 11 months 2 weeks 5 days 7 hours ago) and read 1042 times:

We will probably see a long-ranged A330 one day. However, it probably wouldn't replace the A340, because of ETOPS like everyones been saying.

Regards.



"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran
User currently offlineSrbmod From , joined Dec 1969, posts, RR:
Reply 17, posted (12 years 11 months 2 weeks 4 days 18 hours ago) and read 996 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.

User currently offlineEddgge From Sweden, joined Jul 2001, 123 posts, RR: 4
Reply 18, posted (12 years 11 months 2 weeks 4 days 13 hours ago) and read 973 times:

Interresting question! Is their any companys who fly transocean with a twin jet, like the 777 or A330?

Best regards,
Gustaf


User currently offlineSQ325 From Germany, joined Jul 2001, 1451 posts, RR: 7
Reply 19, posted (12 years 11 months 2 weeks 4 days 13 hours ago) and read 973 times:

TAM flys Frankfurt Sao Paolo with a A330
Varig Takes a B767 to Carbita!


User currently offlineSailorOrion From Germany, joined Feb 2001, 2058 posts, RR: 6
Reply 20, posted (12 years 11 months 2 weeks 4 days 13 hours ago) and read 971 times:

The A340 -500 and -600 series will have completly new wings, so the wing structure cannot really be compared to the -200 and -300 series.

btw, you made the way in my respected user's list.

SailoOrion


User currently offlineCfalk From , joined Dec 1969, posts, RR:
Reply 21, posted (12 years 11 months 2 weeks 4 days 13 hours ago) and read 969 times:

Gustaf,

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.

Charles


User currently offlineJwenting From Netherlands, joined Apr 2001, 10213 posts, RR: 18
Reply 22, posted (12 years 11 months 2 weeks 4 days 12 hours ago) and read 962 times:

Gustaf,
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)




I wish I were flying
User currently offlineEddgge From Sweden, joined Jul 2001, 123 posts, RR: 4
Reply 23, posted (12 years 11 months 2 weeks 4 days 12 hours ago) and read 960 times:

Thanx Jwenting!

User currently onlineSuperfly From Thailand, joined May 2000, 39831 posts, RR: 74
Reply 24, posted (12 years 11 months 2 weeks 4 days 8 hours ago) and read 921 times:

If for no other reason.
Four engines look better!

LONG LIVE THE QUADS! ! ! ! ! !


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Bring back the Concorde
25 KonaB777 : United doesn't fly the 757 across the pond. The longest flights the 757 flies on for United are between California & Hawaii.
26 Dtswi : I can see for my part the A340-200 and-300 being potentially replaced by the A330 longer range, with A340 remaining for the -500 and -600 series... Wh
27 RC Pilot : the aircraft makers can yapp all they want about 2 engines being safer than four but most passengers would feel mor comfortable in a quad. I could car
28 Lehpron : Everyone pretty much answered your question. As for me, I think subsonics should have two, supersonic should have four and hypersonics could have 5/6
29 V1-rotate : Let's think of mantainence,on turnaround times which can be very short,the ground engineers can spend TWICE as much time on two powerplants as they ca
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