Large Tri-Jet extinction?

The change in SFC from the JT8D to the CFM56 was a healthy 25% and more, the engine only weighted a little bit more and had better thrust/weight ratio.
The GTF isn’t so much better than the CFM56-5C.

Not to mention the GTF is still very much a developmental engine, whereas CFM 56’s routinely run more than 20,000 hours on the wing.

I confess I don’t understand all this talk about the GTF as if it were a real, up and running, in full scale production, engine.

And the A340-500/600 Trent 500 engines are in any case too big to be replaced by GTF-s. A340-300, on the other hand, is small enough to be propelled by GTF. And its competitors are B777-200ER and A330-300.

DC-8 reengining was quite worthwhile, even though new built DC-10s were competing against them. However, the production line had been shut down too thoroughly to build new DC-8-70s. Would the A340-300 fleet be worth reengining?

The change in SFC from the JT8D to the CFM56 was a healthy 25% and more, the engine only weighted a little bit more and had better thrust/weight ratio.
The GTF isn’t so much better than the CFM56-5C.

The re-engined DC-8 wasn’t competing against DC-10, most of them were converted freighters. Remember: at that time used jet airframes with some cargo hold and the option to put on an engine like the CFM56 didn’t exist that much.

As for the A340-500/600 with GTF: The problem is twofold (attention: here comes good information for free on the public internet!).

1. The competitor, B777-200LR/300ER uses the GE90-115, which is a very efficient engine and more advanced than the CFM56-5B/C. The claimed increase in SFC would therefore be less. Additionally, a better SFC does not directly translate into better fuel burn when a complete aircraft os looked at mission-wise.
2. The A340-600 suffers not only from its engine but also from its higher OEW and some other disadvantages. Re-equipping with GTF would only increase the OEW. It remains doubtful if the A340-5/6 could beat the B777-2/3 with any useful margin.

And the A340-500/600 Trent 500 engines are in any case too big to be replaced by GTF-s. A340-300, on the other hand, is small enough to be propelled by GTF. And its competitors are B777-200ER and A330-300.

DC-8 reengining was quite worthwhile, even though new built DC-10s were competing against them. However, the production line had been shut down too thoroughly to build new DC-8-70s. Would the A340-300 fleet be worth reengining?

What are you smoking?

You’re not the first person to think that when viewing one of his replies. :rolleyes:

Paul

Have a look at CFM56.

2xCFM56 is pretty efficient, on Boeing 737. But even Boeing Business Jet cannot match the range and efficiency of 4xCFM56 on A340-300.

Therefore, it makes sense that 4xGTF reengined A340 would accomplish tasks which are quite impractical with 2xGTF CS100ER.

What are you smoking?
Comparing a 737 BBJ to an A340?!?!

Try comparing the 777 to the A340 like for like. They are one anothers competitor. I think you’ll find the 777 trounces the A340 at nearly every turn for efficiency. There is no reason to think a GTF 777 would not continue that trend versus a GTF A340.

Indeed. See
http://www.flightglobal.com/articles/2009/03/24/324078/gtf-versus-open-rotor-which-is-best.html

240 cm diametre engine – compared to 170 cm of the best existing A320 engines. Which means reengining the A320 looks impractical. Whereas A340-500/600 already has 240 cm diametre engine, and so does A330, so the free space should be right there under A340-300 wing.

A re-designed pylon could take some of the missing 50cm, basically as done on the B737Classic. Of course, that is heavy and clumsy, but would work somehow.

As for the A340-500/600 with GTF: The problem is twofold (attention: here comes good information for free on the public internet!).

The A340-5/6 will be replaced by A350-9/10 in near future, so these aircraft are dead, although they are sound designs.

Have a look at CFM56.

2xCFM56 is pretty efficient, on Boeing 737. But even Boeing Business Jet cannot match the range and efficiency of 4xCFM56 on A340-300.

Therefore, it makes sense that 4xGTF reengined A340 would accomplish tasks which are quite impractical with 2xGTF CS100ER.

Oh, maximum fraud. The reason why Airbus didn’t really jump on the GTF bandwaggon is that it doesn’t yield much advantage. As I said elsewhere, the problem with single aisle aircraft is not that they are aerodynamically inefficient or have thirsty engines, but that they are normally extremely oversized for the missions they fly.
Ask an EasyJet pilot how often he performs MTOW take-offs or makes take-offs without FLEX-regime thrust reduction (considering that his CFM56-5B are already castrated by default), you’ll see that using an A319 for a trip from London to Paris is a total efficiency disaster.

But then you have a quad again.
How would it perform against a similarly equipped twin?

My bet the twin would win out.

Have a look at CFM56.

2xCFM56 is pretty efficient, on Boeing 737. But even Boeing Business Jet cannot match the range and efficiency of 4xCFM56 on A340-300.

Therefore, it makes sense that 4xGTF reengined A340 would accomplish tasks which are quite impractical with 2xGTF CS100ER.

But then you have a quad again.
How would it perform against a similarly equipped twin?

My bet the twin would win out.

I recently read that P&W does not completely rule out a large thrust GTF. But the question is how the benefit compared to latest technology turbofans really is.
Would be interesting to know if a A340-300 with GTF could compete with new twins.

Indeed. See
http://www.flightglobal.com/articles/2009/03/24/324078/gtf-versus-open-rotor-which-is-best.html

240 cm diametre engine – compared to 170 cm of the best existing A320 engines. Which means reengining the A320 looks impractical. Whereas A340-500/600 already has 240 cm diametre engine, and so does A330, so the free space should be right there under A340-300 wing.

Yes. And now that Pratt and Whitney geared turbofan is available for small thrusts, like 10 500 kgf Cseries, but widebody twin sized GTF is ruled out, would this require development of a GTF trijet to make better use of GTF?

I recently read that P&W does not completely rule out a large thrust GTF. But the question is how the benefit compared to latest technology turbofans really is.
Would be interesting to know if a A340-300 with GTF could compete with new twins.

would this require development of a GTF trijet to make better use of GTF?

Why would a new type of engine require the design and development of an entirely new aircraft? :confused:

Paul

All widebody designs of the late 60ies and early 70ies basically were build to take advantage of the new generation high bypass turbofans (which could be traced back to the CX-HLS competition of the USAF).
The B737-3/4/5 were launched when a new low thrust turbofan was available (which based on the F101 of the B-1B, so again, a military spin-off).

Which also led to DC-8-70…

One is sometimes astonished how much the development of new aircraft is hinged to engines.

Yes. And now that Pratt and Whitney geared turbofan is available for small thrusts, like 10 500 kgf Cseries, but widebody twin sized GTF is ruled out, would this require development of a GTF trijet to make better use of GTF?

I think the whole debate about whether a new Three-holer will ever be built is moot.
The DC-10 and Tristar were built to overcome restrictions placed upon twin engined aircraft at the time.
The high position of the No.2 engine has always made it maintenance intensive, hard to get to and difficult to remove and replace.

Today a twin engined jet can easily compete with a quad on a broad range of missions.
Short of twin engined jets suddenly being restricted again, I don’t thing there is a need for a 3 holer commercial airliner any more.

But they might have built a small quad DC-10 or Tristar, like A340 or Il-86. For some reason, three engines seemed better.

But what engine for a quad DC-10?
At that time, there were the PW JT9D, the CF6-50 (TF39 with reduced bypass) and the RB211 on the horizon. All were basically suited to power the B747-100.

A four engine DC-10-30 would have needed an engine in the thrust class of
555klbs * .23 * 1/4 = 32klbs.
That kind of engine didn’t exist at that time.

All widebody designs of the late 60ies and early 70ies basically were build to take advantage of the new generation high bypass turbofans (which could be traced back to the CX-HLS competition of the USAF).
The B737-3/4/5 were launched when a new low thrust turbofan was available (which based on the F101 of the B-1B, so again, a military spin-off).

One is sometimes astonished how much the development of new aircraft is hinged to engines.

No need now.
The trijet was to overcome the ETOPS “No twins” attitude. Now that twins can cross the pond, and the engines are getting safer and safer…..and more economical, I doubt if we see a trijet again. 3 engines is 50% more maintenance costs than a twin, too.
You could build a twin engined design to lift the A380, but the wings would need to be considerably higher off the floor (Probably top mounted), which would mean a fuse mounted undercart.
It would also mean a dihedral wing, which is not as economic as the anhedral, and doesn’t lend itself to winglets or other aerodynamic improvement ideas.

3x GE90-115B would yield round-about 155t reference thrust.
With 560t MTOW that would result in a thrust/weight ratio of .27ish.
So, very roughly, should work thrust-wise.

Currently the A380 has up to ~135t reference thrust, or a thrust weight ratio of .23ish.

Conclusion: if you can avoid three engines, do it! The reason in the late 1960ies was that two engines were considered insufficient for long range flight and that no suitable engines existed for a twin DC-10 or L1011. Today the only reason remains the availability of suitable engines.

But they might have built a small quad DC-10 or Tristar, like A340 or Il-86. For some reason, three engines seemed better.

Both Douglas and Lockheed planned to build widebody twins by deleting the tail engine (neither accomplished that). How much fuselage and wing commonality were they going to keep?

I think wing commonality would be basically 100%, as the wing doesn’t care if there is an engine in the tail. What would be different is the fuselage between wing and tail (due to completely different loads and system layout), the vertical tail and the overall systems map.
Think: three engines, each running a generator and hydraulic pump, that gonna change the system arrangement tremendously. It is not necessarily much heavier, but the changes reduce commonality to basically the wing and the forward fuselage, maybe the horizontal tail (while even that gonna need different size due to changed lever arm).

Conclusion: if you can avoid three engines, do it! The reason in the late 1960ies was that two engines were considered insufficient for long range flight and that no suitable engines existed for a twin DC-10 or L1011. Today the only reason remains the availability of suitable engines.

The original idea to build a twin and a quad from the same basic airframe denied a tri-jet configuration. The differences in CG, VTP arrangement and fuselage strength would have meant that both airframes would have been entirely different.

Both Douglas and Lockheed planned to build widebody twins by deleting the tail engine (neither accomplished that). How much fuselage and wing commonality were they going to keep?

But the engine of choice was the Superfan, which could not be built. CFM56 was emergency replacement, and an unsatisfactory one. Let´s see if Pratt and Whitney GTF works.

What was wrong about, say, 3X Trent 600?

The original idea to build a twin and a quad from the same basic airframe denied a tri-jet configuration. The differences in CG, VTP arrangement and fuselage strength would have meant that both airframes would have been entirely different.
The CFM56-5C surely was no tailor-made solution, but I think it provided a useful solution due to the ambiguous availability of spare parts. The -5C bares very strong resemblance to the -5A and -5B, and also to the -7.

McDonnell-Douglas seriously tried to buy A330/A340 wings for their MD-11 stretch. This fell through; but Airbus also might have done something similar themselves.

I think a tri-jet is always a compromise to fit an aircraft into a mission with a certain engine in mind. The DC-10 and L1011 profited from sharing the same engine as the B747, A300 and later B767. It is interesting to see that all widebodies were basically built around 3 engine families of similar thrust capability:
P&W: JT9D/PW4000
GE: CF6-50/80
RR: RB211
That changed with arrival of the A330 and B777.

Why has the A340 4 engines?

The A340 has a design mission and was then consequently adapted to the available engine. The engine of choice was the CFM56, I guess because of its wide spread use.

But the engine of choice was the Superfan, which could not be built. CFM56 was emergency replacement, and an unsatisfactory one. Let´s see if Pratt and Whitney GTF works.

The only other option would have been an extremely derated PW2000 for 4-engine config or the same engine at max thrust rating in a tri-jet.

What was wrong about, say, 3X Trent 600?

McDonnell-Douglas seriously tried to buy A330/A340 wings for their MD-11 stretch. This fell through; but Airbus also might have done something similar themselves.