QXatFAT
Topic Author
Posts: 2310
Joined: Fri Feb 24, 2006 3:51 pm

What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 3:58 pm

I was just wondering what the benifits are for having eather 2,3, & 4 engine jets? Such as, why would Airbus make the A330 with two engines? Is it just for looks? I would wrather fly a B747 based on its 4 engine look then then A330. Is it less cost effective to have the more then 2 engines?
Don't Tread On Me!
 
saturn5
Posts: 308
Joined: Thu Apr 13, 2006 2:49 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:00 pm

Airlines would tell you that it is less expensive to operate 2-engine aircraft if you can. Both because of fuel and actual engine maintanence.
 
superhub
Posts: 398
Joined: Sat Jan 21, 2006 4:17 pm

RE: What Are The Benifits Between 2,3, & 4 Engines

Tue May 23, 2006 4:03 pm

Quoting QXatFAT (Thread starter):
Is it less cost effective to have the more then 2 engines?

Yes. 2 engines burn less fuel.

A B744 has four engines because, correct me if I am wrong, there were no twin-engines with big enough thrust to power such a heavy plane. Same with the A380 nowadays.

As engines become more powerful, you willl see a trend of large airliners with twins. If you look at any B777 engines, it's quite a sight...and they are very powerful stuff.

[Edited 2006-05-23 09:05:28]
 
QXatFAT
Topic Author
Posts: 2310
Joined: Fri Feb 24, 2006 3:51 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:10 pm

Quoting Superhub (Reply 2):
A B744 has four engines because, correct me if I am wrong, there were no twin-engines with big enough thrust to power such a heavy plane. Same with the A380 nowadays

Now if you look at the engine sizes, the A380 has quite a huge engine size. I would say more close to the 777 as the 747 has much smaller engines. Could the 747 run off of two 777 engines?
Don't Tread On Me!
 
saturn5
Posts: 308
Joined: Thu Apr 13, 2006 2:49 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:12 pm

Quoting QXatFAT (Reply 3):
Could the 747 run off of two 777 engines?

No.
 
superhub
Posts: 398
Joined: Sat Jan 21, 2006 4:17 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:16 pm

Quoting QXatFAT (Reply 3):
Could the 747 run off of two 777 engines?

There was a thread about it a while ago....but I forgot what was said in there. My guess is no though, otherwise Boeing might have proposed it for the 748.
 
QFA380
Posts: 2013
Joined: Fri Jul 22, 2005 4:38 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:17 pm

Quoting Saturn5 (Reply 1):
actual engine maintanence.

Wouldn't this still be the same as a bigger engine is harder to do mx on or is it easier? Also are different engines eg Engine 2 and 3 different from 1 and 4. having a look at the A380 landing in LHR, it seems that 1 and 4 dont have reversers? If so would the ones without reversers be easier to do mx on?
 
saturn5
Posts: 308
Joined: Thu Apr 13, 2006 2:49 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:22 pm

Quoting QFA380 (Reply 6):
Wouldn't this still be the same as a bigger engine is harder to do mx on or is it easier?

No, because a mx on an engine which has twice the power is not twice as expensive, maybe it is only 20-30% more expensive (don't know precise data), so airline save money having fewer engines.
 
superhub
Posts: 398
Joined: Sat Jan 21, 2006 4:17 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:22 pm

Quoting QFA380 (Reply 6):
having a look at the A380 landing in LHR, it seems that 1 and 4 dont have reversers? If so would the ones without reversers be easier to do mx on?

They all have reversers, but the pilots probably didn't deploy the ones on 1 and 4.

This is sometimes done on the 747 too. And probably done because deploying reversers on two engines is good enough (eg. because the runway is long enough, because the ramp would be closer if the plane exits further down the runway)
 
NAV20
Posts: 8453
Joined: Thu Nov 27, 2003 3:25 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:23 pm

QXatFAT, it's a matter of balancing the size and weight of the aeroplane, the power of the engines, and the performance required.

How big and fast you can make a given design is governed by the power of the available engines, more than any other single factor. At the beginning, jet engines generated so little power (only around 5,000 pounds of thrust) that any jet airliner needed four of them (Comet, 707). Later three-engined or twin-engined types became feasible, provided that the aircraft were small (Trident, 727, 737), but four engines were still needed for larger long-distance types (747, VC10). Four engines were also needed for reliability on long over-ocean trips.

Engines have now improved in terms both of power and reliability. Even so, though, the 777 (say up to 350 passengers in comfort) remains about the twin-engine limit at current available engine power. Anything bigger than that (A380, 748) still requires four at the moment.

[Edited 2006-05-23 09:30:08]
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
brendows
Posts: 801
Joined: Thu Apr 27, 2006 4:55 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:30 pm

Quoting Superhub (Reply 8):
They all have reversers, but the pilots probably didn't deploy the ones on 1 and 4.

Wrong. The A380 does NOT have reversers on engine 1 and 4.

Quoting QXatFAT (Reply 3):
Could the 747 run off of two 777 engines?

Such an aircraft would need large modifications to the wings, and it would need an engine producing about 180+klb of thrust. In other words, no, a 747 could not use two 777 engines.

Quoting QXatFAT (Reply 3):
Now if you look at the engine sizes, the A380 has quite a huge engine size. I would say more close to the 777 as the 747 has much smaller engines.

True, the engines on the A380 (Trent 900 and GP2700) are actually a bit larger than some of the engines for the 777. (The fan on the Trent 900 is 5cm larger than the fan on the Trent 800m and the fan on the GP2700 is about 10cm larger than the fan on the PW40XX.) The engines on the 747 (excluding the 748) are puny in comparison Big grin
 
zarniwoop
Posts: 255
Joined: Wed Apr 27, 2005 11:43 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:33 pm

Quoting Superhub (Reply 8):
They all have reversers, but the pilots probably didn't deploy the ones on 1 and 4.

Only engines 2 & 3 have reversers on the 380
 
superhub
Posts: 398
Joined: Sat Jan 21, 2006 4:17 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:36 pm

Quoting Brendows (Reply 10):
Wrong. The A380 does NOT have reversers on engine 1 and 4.



Quoting Zarniwoop (Reply 11):
Only engines 2 & 3 have reversers on the 380

Sorry, I BSed. I deserve to be shot.

Apologies for the mistake.
 
scoliodon
Posts: 212
Joined: Mon Oct 31, 2005 4:15 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 4:59 pm

Quoting QXatFAT (Thread starter):
why would Airbus make the A330 with two engines? Is it just for looks? I would wrather fly a B747 based on its 4 engine look then then A330.

It's definitely not for the looks. I'd say Airbus made the A330 such that it could fly a particular payload for particular ranges on two engines, to suit various customers. And the same airbus made the A340 with 4 engines to suit the relevant payloads and ranges.

And I think the A330 is a beautiful aircraft, to boot  Smile
JFK-LGA-EWR-DTW-IND-PHX-CLE-SFO-LAS-SEA-ORD-MCO-MIA-DFW-ATL-CDG-FRA-BOM-MAA-DEL-TRZ-DXB-CLT-CVG-DEN-MSP
 
aa777sjc
Posts: 46
Joined: Fri Mar 24, 2006 6:19 am

RE: What Are The Benifits Between 2,3, & 4 Engines

Tue May 23, 2006 5:17 pm

Quoting Brendows (Reply 10):
Such an aircraft would need large modifications to the wings, and it would need an engine producing about 180+klb of thrust. In other words, no, a 747 could not use two 777 engines.

According to the AC Data pages,

741 has 46,500 lbs X 4 thrust ~180K of thrust
773ER has 115,000 lbs X 2 thrust ~230K of thrust

So thrust wise it may be possible. There are still issues with engine ground clearance and wing strength (by the time the wings are reinforced enough to hold the engines, they may weigh alot more and 230K might not be enough thrust to get it in the air.) Also, you may be able to get in the air, but if the 2 777 engines weigh alot more than the 4 741 engines, you've lost alot of your lifting capacity.

I bet it is possible, but as someone pointed out, they didn't try it on the 748 so they don't think it's worth the effort.
 
brendows
Posts: 801
Joined: Thu Apr 27, 2006 4:55 pm

RE: What Are The Benifits Between 2,3, & 4 Engines

Tue May 23, 2006 5:24 pm

Quoting AA777SJC (Reply 14):

741 has 46,500 lbs X 4 thrust ~180K of thrust
773ER has 115,000 lbs X 2 thrust ~230K of thrust

You have to think of an engine-out situation. With one engine out, the 741 would still have almost 140klbs of thrust left, compared to only 115klbs for the 77W. In other words, the GE90-115B doesn't deliver enough thrust to perform a safe takeoff with a 74X.
 
zarniwoop
Posts: 255
Joined: Wed Apr 27, 2005 11:43 pm

RE: What Are The Benifits Between 2,3, & 4 Engines?

Tue May 23, 2006 6:00 pm

Like Brendows said, a twin jet will have more total thrust than a 4 engine plane of the same size to cope with the engine fail on take off situation.

You should do a search in the tech/ops forum to get details on the specifics, there have been some detailed discussions on 2 v 4 engines, here are some:

A330 & A340 Climb Rates
Fuel Burn Delta A340-500 Vs. 777-200LR
Is It Possible To Make A Twin Engined B 747?
77W-A346 Weight Difference