dtswi
Posts: 81
Joined: Wed Aug 29, 2001 10:34 am

Why 4 Engines?

Tue Sep 04, 2001 12:10 am

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.
 
777kicksass
Posts: 648
Joined: Thu Sep 07, 2000 9:52 pm

RE: Why 4 Engines?

Tue Sep 04, 2001 12:41 am

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.
 
Lowsonboy
Posts: 269
Joined: Thu Aug 16, 2001 10:37 pm

RE: Why 4 Engines?

Tue Sep 04, 2001 12:44 am

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.
 
fritzi
Posts: 2598
Joined: Sat Jun 30, 2001 2:34 am

RE: Why 4 Engines?

Tue Sep 04, 2001 12:44 am

Because with four engines you don't have to worry about ETOPS
 
BA DC-10
Posts: 140
Joined: Sun Jul 15, 2001 8:40 pm

RE: Why 4 Engines?

Tue Sep 04, 2001 12:51 am

Because of ETOPS, some airlines have policies of not flying with 2 engine jets over large stretches of water......
 
rabenschlag
Posts: 1011
Joined: Fri Oct 20, 2000 10:28 pm

RE: Why 4 Engines?

Tue Sep 04, 2001 12:53 am

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
 
GOT
Posts: 1843
Joined: Sun Dec 31, 2000 6:44 am

RE: Why 4 Engines?

Tue Sep 04, 2001 1:26 am

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!
 
456
Posts: 315
Joined: Mon Feb 26, 2001 4:20 am

RE: Why 4 Engines?

Tue Sep 04, 2001 1:45 am

If ETOPS is the problem, why not 3 engines? Like a dc/md 10/11 or Tristar...
 
rabenschlag
Posts: 1011
Joined: Fri Oct 20, 2000 10:28 pm

456

Tue Sep 04, 2001 1:51 am

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.
 
YoungDon
Posts: 495
Joined: Thu May 31, 2001 9:33 am

RE: Why 4 Engines?

Tue Sep 04, 2001 1:55 am

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
Posts: 5272
Joined: Mon Oct 18, 1999 3:09 am

RE: Why 4 Engines?

Tue Sep 04, 2001 5:11 am

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...
 
HyperMike
Posts: 968
Joined: Sun Dec 05, 1999 7:03 am

RE: Why 4 Engines?

Tue Sep 04, 2001 5:25 am

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
Posts: 66
Joined: Wed Aug 15, 2001 1:33 am

RE: Why 4 Engines?

Tue Sep 04, 2001 6:22 am

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.
 
Guest

RE: Why 4 Engines?

Tue Sep 04, 2001 9:04 am

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
 
dtswi
Posts: 81
Joined: Wed Aug 29, 2001 10:34 am

RE: Why 4 Engines?

Mon Sep 10, 2001 12:56 am

Thank you all for your very informative comments ...

Geebar, Aeroguy and Rabenschlag, I learned something !

Best regards,

Daniel T.

 
advancedkid
Posts: 740
Joined: Wed Jun 14, 2000 1:27 pm

RE: Why 4 Engines?

Mon Sep 10, 2001 1:49 am

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
 
BA
Posts: 10133
Joined: Fri May 19, 2000 11:06 am

RE: Why 4 Engines?

Mon Sep 10, 2001 1:53 am

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
 
srbmod
Posts: 15446
Joined: Tue Mar 20, 2001 1:32 pm

RE: Why 4 Engines?

Mon Sep 10, 2001 2:35 pm

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.
 
eddgge
Posts: 121
Joined: Thu Jul 26, 2001 2:21 pm

RE: Why 4 Engines?

Mon Sep 10, 2001 7:07 pm

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

Best regards,
Gustaf
 
SQ325
Posts: 1274
Joined: Wed Jul 18, 2001 7:54 pm

RE: Why 4 Engines?

Mon Sep 10, 2001 7:11 pm

TAM flys Frankfurt Sao Paolo with a A330
Varig Takes a B767 to Carbita!
 
SailorOrion
Posts: 1959
Joined: Tue Feb 06, 2001 5:56 pm

RE: Aeroguy

Mon Sep 10, 2001 7:21 pm

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
 
cfalk
Posts: 10221
Joined: Mon Dec 04, 2000 6:38 pm

RE: Why 4 Engines?

Mon Sep 10, 2001 7:44 pm

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
The only thing you should feel when shooting a terrorist: Recoil.
 
jwenting
Posts: 9973
Joined: Mon Apr 23, 2001 10:12 pm

RE: Why 4 Engines?

Mon Sep 10, 2001 8:11 pm

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
 
eddgge
Posts: 121
Joined: Thu Jul 26, 2001 2:21 pm

RE: Why 4 Engines?

Mon Sep 10, 2001 8:20 pm

Thanx Jwenting!
 
Superfly
Posts: 37735
Joined: Thu May 11, 2000 8:01 am

RE: Why 4 Engines?

Tue Sep 11, 2001 12:48 am

If for no other reason.
Four engines look better!

LONG LIVE THE QUADS! ! ! ! ! !


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Bring back the Concorde
 
Guest

RE: Why 4 Engines?

Tue Sep 11, 2001 1:05 am

United doesn't fly the 757 across the pond. The longest flights the 757 flies on for United are between California & Hawaii.
 
dtswi
Posts: 81
Joined: Wed Aug 29, 2001 10:34 am

RE: Why 4 Engines?

Tue Sep 11, 2001 10:59 am

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...

What do you all think ?

Daniel T.
 
RC Pilot
Posts: 139
Joined: Sun Jul 22, 2001 11:21 am

RE: Why 4 Engines?

Tue Sep 11, 2001 11:19 am

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 care less actually but i do like the quads better.
 
lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

RE: Why 4 Engines?

Tue Sep 11, 2001 8:40 pm

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 engines -- think of the drag.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
V1-Rotate
Posts: 53
Joined: Sun Feb 11, 2001 11:12 am

RE: Why 4 Engines?

Fri Sep 14, 2001 4:25 pm

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 can on four!!
I for one have no problems with twin engined a/c.Think about it!