Four Engines Good Two Engines BETTER.

[Rollerboy]

Hi All

Just wondering about the industry take on the four vs two engine debate.

With fuel getting ever more expensive and likely to remain at the current levels for long into the fuel hedged dates, and the possibility of United grounding 4 B747 all be it the older ones. Does this not spell the demise of four engines on most routes?

The only wide body 4 engined aircraft to be newely designed on the past 15? years has been the A380 which I grant will fill a gap in the market. Is there any room for more?

Engines have grown larger and more reliable allowing increasing loads and ETOPs capability. This has allowed twins to slot into previously 3 and 4 engined routes and it seems to have worked. Also, as aviation grows more expensive and inflation bites less pax will travel making ever larger aircraft redundant on most routes.

The Tprop market is now exclusively twin over four engines, I realise these are different operations eg regional short distances that allowed a swift change from four to two. However the world seems to be getting alot smaller so surely the shift will occur to jet aircraft. Some may say with the Boeing 787 and Airbus 350 it already has.

any takers?

Roller

[Rainboe]

Tried flying 550 people on 2 engines lately?

A stretched A380 with 600 or 650 people (at least) will be better than 2 twins. It will have a capability of extreme long range high capacity travel. Don't write it off too early.

[Rollerboy]

I realise that there is a case for large 4 engined aircraft on some routes. Most notably the very high dinsity routes, but surely even these routes will eventually see a cut in pax due the world wide crunch.

Being a UK regional pilot I have no idea of these super high density asian routes so can't comment but would be interested to know. Has anyone seen pax figures for singapore A380 routes? I do realise that the super high density models have not entered service yet.

Any other takers?

[Re-Heat]

It depends entirely on the cargo loads you require on particular routes as well. For some routes as a result, a 744 will always beat a 777 due to cargo capacity, while other routes cannot justify a 744.

[Rollerboy]

Good point Re-Heat I had not thought about cargo capacity. I take it that cargo is a big revenue earner on intercontinental routes. However if the boing point to point concept is accepted smaller aircraft will serve more direct routes thus splitting the freight load. Might this effect the 4 engine models?

Will there ever be a super eco 4 engined model? Or are the next super eco models likely to be twin engined narrow bodied aircraft.

Roller

[Tediek]

When looking at the new B777F compared with the B744F, the max payload has a 9ton difference on the normal 744F model. What is the economical difference to operatie the 777 or 747? Two engines vs 4, the higher operating costs vs payload "restrictions"?

I am not talking about the prize tag difference but purely to operate the beast.

[Rollerboy]

Interesting stuff maybe in pure freighter terms the B777F might have the rush on B744F if those stats are correct. I can't see 9t making that much difference.

How about the pax airliner world? must be some 4 engine pilots knocking about on here.

[Torquelink]

In a nutshell, and as a bit of a generalisation, if it can be done with two engines it will always be better, from a commercial viewpoint, than three of four: A340-300 vs 777-200ER, A340-500 vs 777-200LR, A340-600 vs 777-300ER and 747-400F vs 777F hence the 747-8F which has a significant payload advantage over the 777F. Until there are, presumably, engines of 150,000lb thrust and a wing high enough to sling them under, the A380 will be a quad! There may be other operational / safety considerations, but on the basis of operating economics, it's game over.

[Rollerboy]

Thanks for your input Torquelink interesting to note you are an aircraft lessor. Still I wonder if how the economics add up A340 vs B777 in terms of fuel usage and engr bills.

Any feelings?

[airfoilmod]

The GE 90 has the record thus far at 126,800 lbs thrust. 150k is not far away. I can't envision 660 pax needing to go 7000nm on a regular basis, scheduled. I think the 380 is a beauty, but thus far, I think it doesn't "pencil out". I hope it does.

Airfoil

[SNS3Guppy]

Just wondering about the industry take on the four vs two engine debate.



What debate?

It has nothing to do with four being better than two, or visa versa. Extra power equals extra performance, which means more lifted revenue, etc. Some airframes achieve this with additional powerplants, some don't. But a debate?

The Tprop market is now exclusively twin over four engines,


Perhaps you're not familiar with the C-130? Still doing a fine job today.

[Torquelink]

Roller,

In our experience, and we have no A vs B axe to grind, model for model the Boeing twins show lower fuel burn and engineering costs, including engines, than the Airbus quads. The other major cost issue is that of ownership - Airbus aircraft realised purchase prices are generally lower than for the Boeing equivalents but, other than the twin A330, depreciation costs are higher.

AirFoil / Fingers

Hadn't really dawned on me that we're only 25,000lb away from 150,000lb engines! But, even if feasible, the fan diameter would be enormous - among other things transporting spare QECs would be an interesting challenge?

[World of Tweed]

I think this debate is a little too general.

One cannot say with certainty whether a Twin or Quad is going to be 'better' on any particular route without asking several pertinent questions.

Are routes intended more profitable in PAX or Cargo?
If so what are the yields from each? Where is your projected growth?
Can the proposed aircraft(s) lift both in sufficient/equivelant quantities?
Route structure of the airline?
Are you simply satisfying a nieche with a quad on one route whilst it is over-kill on the rest of your network?
What is the Fleet integration cost/Approval cost for a traditional Quad operator switching to ETOPS?


For example Virgin Atlantic came within a millimeter or should I say mil. of ordering a fleet of 777-300ERs/772LR in 2004. Shortly before announcing their top-up order for the 340-600 in fact.

On the face of it the 777 was a much stronger candidate. Some of the intended routes were the Beach routes from LGW and LHR > US. But a significant section of the routes were east bound where both pax and cargo capacity is key.

They had issues with the 340-600 since introduction in 2002 with its air-systems, fuel and warranty issues. And recently the Trents on the wing are being changed at 4 times their advertised rates due to a fault in the oil system regularly producing smoke/fumes in the cabin. The 346 is a troubled machine it would seem.

Despite all that... The triple lost.

Why.... ?

Cargo.... Simply put the 340-600 would always be able to yield more from cargo revenue than the 777 would like for like. This was particularly key on the eastern deployments intended for the incremental aircraft. In addition the opportunity cost of aligning maintenance procedures to qualify for ETOPS, creating a new fleet within the airline and assymilating a highly customised product into the boeing cabin were additional factors.

So this is the case where actually the scope of a Twin vs Quad argument goes beyond the number of engines it has.

Perhaps this thread was more intended to incite the 'Moral/Root' issues surrounding the principle of operation of twins at almost 5hours (as is now proposed) distance from an alternate?

If so perhaps heed this:

EU-OPS introduced a 'reduced' margin on the nomination of Suitable En-route Alternates.

Now instead of the traditional "take one approach below available" (i.e. a VOR instead of a ILS and apply the non-precision minima to the forecast to see if you can use it) it now states that you only need to add an increment to the minima for the approach intended. For an ILS that is +200FT on DH and +800m vis.

What you now end up with is a regularly occuring situation in my airline where we are applying stricter (traditional 'one approach below' expected) criteria to our 3%Contingency En-route Alternates (normally a land locked location where we are no longer etops anyway) than we are to our ETOPS alternates (KEF, SNN, YQX etc).

It is somewhat contradictory and has the potential to lead you to being able and willing to fly to your ETOPS diversion for 5hours happy as a pig in **** but then find that actually you can't get in!

The whole point of applying such restrictive criteria to the ETOPS alternates was as is their nature they are pretty much your only options. EU-OPS /FAA has now deemed that not to be the case.

Rant over.

[Rollerboy]

SNS3Guppy

I take your point maybe debate was the wrong word all I am asking is what peoples feelings are between the 2 vs 4 engine types. As I have said I realise there is a market for 4 engines but I for one feel it's getting smaller. Which wide bodies will be the first to be grounded due higher fuel costs, higher ticket costs and lower pax numbers. Only time will tell but United are grounding 4 wides all B747.

As for the C130/L-100 it is still doing a fine job but not against the Dash/ATR within the civilian market.

Torquelink thanks for your input. Very interesting initial costs and depreciation must be taken into account interesting to see your info on the A330. Wonder what usage is compared A330 vs A340. I have no axe to grind just interested.

Cheers

Roller

[Rollerboy]

World of Tweed thanks for your answer very interesting I was wondering how far ETOPs can be pushed. 5 Hour limits seem a little excessive if not dangerous. However as engines become ever reliable and money hits hard who knows how far the industry will push.

I do wonder if Virgin Atlantic are getting the most out of there A340s in terms of cargo. Any ideas?

Roller

[airfoilmod]

The fan might not be so big as you imagine. Without enhancing the core, the Disc only needs an additional 30cm in diameter.

I'd like to suggest dual fan/single core to you. Three holes per side/six total but four large and two "small". "Y" driven cold fans w/central core on each wing. Better ground clearance, good fuel specifics, and a whole new set of specs and considerations. It's in the Tunnel.

Airfoil

[411A]

"Must be a few 4-engine folks here"
Yep, I'm one, three engine also.

All civil jet transports, in command, for over thirty years.

The future?
Two engines, make NO mistake, for pax ops.
And, why not?
Seems to work OK, provided that ETOPS regulations are not relaxed..slim chance of that, in our combined lifetimes.

I remember it well.
Thirty years ago, this week, the DFO of SQ, Capt SK (Charlie) Chan asked me personally what I thought about two engine ops, Singapore-Maldives.
I replied, OK...except have a look at the proposed aircraft specs...large underslung engines, fan disc departs enroute, travels under the fuselage and impacts the opposite engine...not good.
It can happen, make no mistake.
I reply..."you need more information, send a fax to the senior 411A', ...who was, among other assignments, the senior engineering project manager on the DC6/DC7/DC8 programs at Douglas.

Message received, and the advice was..."forget about it".
Thus, the B707 was pressed into service.
Things are totally different now.
Two engines, generally OK.

[Old Aero Guy]

It depends entirely on the cargo loads you require on particular routes as well. For some routes as a result, a 744 will always beat a 777 due to cargo capacity, while other routes cannot justify a 744. (Reply 4)

A fine argument, except that a 773ER has more cargo capacity/capability than a 744. Ask AF, SQ or AC.

[World of Tweed]

411A,

ETOPS regulations have already been relaxed - look up EU-OPS 1.297

No longer do you cover yourself with bolts holes across the pond we now just expect not to use them!

[Torquelink]

2 x fan, 1 x core - interesting concept for obtaining significant bypass ratio improvement although I would have thought installation might be a bit problematic assuming there is a rigid transmission from a gearbox mounted on the core to each fan - presumably it would have to be either buried in the wing Comet style or mounted at the rear: core in rear fuselage, fans either side? Imagine that transmission weight and complexity/reliability would be an issue too although I guess the GTF is addressing gearbox issues right now. What about having the core drive a generator and powering the fans with electric motors? - you could then mount the individual components whereever weight, structure and aerodynamic considerations dictated was optimum. (Upon reflection I seem to remember reading something about this concept not that long ago).

[rubik101]

Put the engine on top of the wing and have a fan as big as you like!
The wing also provides an excellent platform for maintainence etc.
Incidentally, if you need lots more wing span/lift, why not the bend the winglets around until they reach the top of the fuselage?
I think it should be called a Bi-plane.