Here's a question totally from out of left field. Is there a possibility of the 777/747 replacement being a trijet? What would be its economic advantages over a four-engined 748 replacement - given the well-worn arguments of structural and maintenance challenges for the No. 2 engine? Considering the slow sales of pax 748 and engine makers' reluctance to develop bigger and evermore powerful engines to put on the next generation planes, would it be easier for them to come up with a comparatively less complicated variant that would satisfy the OEI requirements for a trijet and the high efficiencies and capacities demanded by the airlines? I would imagine a bigger, all-composite fuselage like the 787, or farther out, something like the X-48B that Boeing is testing.

http://www.flightglobal.com/articles...nx-variant-may-yet-power-a350.html

Snecma Tests Future Engine Concept (by Lumberton Apr 27 2007 in Tech Ops)

http://seattletimes.nwsource.com/htm...echnology/2003681476_boeing26.html

http://www.boeing.com/news/releases/2006/q4/061027b_pr.html

[Edited 2007-04-29 16:52:37]

Quoting DEVILFISH (Thread starter): Here's a question totally from out of left field. Is there a possibility of the 777/747 replacement being a trijet?

Interesting idea but small likelihood

Quoting DEVILFISH (Thread starter): What would be its economic advantages over a four-engined 748 replacement - given the well-worn arguments of structural and maintenance challenges for the No. 2 engine?

One less engine=good. However, I think you answered your own question. Triplets are just plain costly. A quad is probably a better idea.

Pity though. I like triplets.

Quoting Starlionblue (Reply 1): Triplets are just plain costly. A quad is probably a better idea. Pity though. I like triplets.

I'm sure the majority of A.net members wish someone would put a new triplet into service, including myself. So, inspired by nothing other than wishful thinking, I wonder if a somewhat near-term (next 5-10 years or so) trijet Y3 design might have just a few advantages that may (or indeed may not) offset the inherent costliness of the type.

Firsly, greater use of composites in a trijet design may close the gap in wieght between it and twin/quad designes.

Secondly, next generation engines (GEnx) are pretty much ready to go in the next year or so, but aren't available in the thrust class necessary for a twin of 777-748 size. Seems to me like developting a 100Klb + NG engine will be very expensive, considering the already high price and and advanced techonolgies used in the GE90, so perhaps development costs saved by installing three existing, highly efficient engines in the 60-80Klb thrust class on a Y3 trijet might offset some of the costs involved in designing and maintaining that #2 engine.

Probably not though, but I wish it were that simple.

Quoting Speedracer1407 (Reply 2): Secondly, next generation engines (GEnx) are pretty much ready to go in the next year

What I've written below are my thoughts as an outsider ...

Looking at the size of the engines currently slung under the wings of the 773ER -- and knowing that they're smaller in diameter than those on the 772LR etc -- I can't imagine there would be any feasible way of plugging one of those into the tail of an aircraft. A lot of the thrust of the current generation engines comes from those fans chewing up enormous amounts of air ... a smaller fan diameter would result in lower thrust.

Furthermore, the sheer weight of modern high-bypass engines would make CG-management a real bear.

It could end up being like the 763-246C, with four engines and an extremely wide body (three - aisle 12 or 13 abreast in economy cabin), on one deck. But instead of it looking like a over size 777( like the 763-246C did) it will look like a oversize 787.

Quoting Brenintw (Reply 3): Looking at the size of the engines currently slung under the wings of the 773ER -- and knowing that they're smaller in diameter than those on the 772LR etc -- I can't imagine there would be any feasible way of plugging one of those into the tail of an aircraft. A lot of the thrust of the current generation engines comes from those fans chewing up enormous amounts of air ... a smaller fan diameter would result in lower thrust. Furthermore, the sheer weight of modern high-bypass engines would make CG-management a real bear.

  
I was going to say almost exactly the same thing; you beat me to it.

Quoting Brenintw (Reply 3): A lot of the thrust of the current generation engines comes from those fans chewing up enormous amounts of air ... a smaller fan diameter would result in lower thrust. Furthermore, the sheer weight of modern high-bypass engines would make CG-management a real bear.

GTF could change these equations somewhat. Smaller turbomachinery to drive larger fans...more efficient fan design enabled by more optimally controlable rotational speeds, etc. In theory, it could allow for an upgrade in thrust in roughly the same size/weight package, or the same thurst in a smaller, lighter one...

All of this depends on how well the Y1 engine programs turn out of course, and what kind of operational obstacles they hit with engine design and maintainance...but it's easy to see why Boeing would want to make sure Y3 is behind Y1. They're not going to want to go for a tri/quad if they can help it at all, in any fashion...and that means they need to make some more big breakthroughs in design and materials to get up to 748 sizes in a twin...

Quoting Lemurs (Reply 6): GTF could change these equations somewhat. Smaller turbomachinery to drive larger fans...more efficient fan design enabled by more optimally controlable rotational speeds, etc. In theory, it could allow for an upgrade in thrust in roughly the same size/weight package, or the same thurst in a smaller, lighter one...

But that does not change fan diameter, which would still remain too large to use on the tail.

I would say this would be possible if the MD line in Long Beach was not discontinued when Boeing took over Douglas, and in short, if it really was a "merger." All hopes of a future tri-jet widebody died with McDonnell Douglas.

Boeing on the other hand, has not designed a tri-jet in over 45 years. The 727 narrow-body design will not be brought back and it is highly unlikely Boeing will attempt to engineer their first tri-jet widebody at this point. There is a better chance of us seeing a modernized "L-1011-1000."   

Quoting SEPilot (Reply 7): But that does not change fan diameter, which would still remain too large to use on the tail.

Unless you embeded the engine in the rear empenage of the fuselage aft of the pressure bulkhead. As long as the fan diameter is smaller than the diameter of the fuselage you could make it fit.

Instead of a single S-duct like the 727 and L-1011 you could put Harrier style ducts on to split the size of the intake between the two sides of the aircraft.

Of course, you would have to move the wing further to the rear to compensate for the shift in COG.

Of course the big question remains... WHY?

Hasn't the low sales of the A380 and 747-8 taught us about the direction in aircraft size?

Quoting Speedracer1407 (Reply 2): Firsly, greater use of composites in a trijet design may close the gap in wieght between it and twin/quad designes.

Sure, but wing mounting is still cheaper. Also, wing mounting offsets wing bending moment, allowing a lighter wing.

Quoting Brenintw (Reply 3): Looking at the size of the engines currently slung under the wings of the 773ER -- and knowing that they're smaller in diameter than those on the 772LR etc -- I can't imagine there would be any feasible way of plugging one of those into the tail of an aircraft. A lot of the thrust of the current generation engines comes from those fans chewing up enormous amounts of air ... a smaller fan diameter would result in lower thrust.

And that's one of the things that killed McD. The banjo fitting for the MD-11 was very costly to engineer. Scaling the banjo further for the MD-XX (trijet variant) would have been prohibitibe.

Quoting 747400sp (Reply 4): It could end up being like the 763-246C, with four engines and an extremely wide body (three - aisle 12 or 13 abreast in economy cabin), on one deck

As I recall, you run into structural issues with such a shape. Meaning more weight. Pity. Would be cool.

Quoting MDorBust (Reply 9): Unless you embeded the engine in the rear empenage of the fuselage aft of the pressure bulkhead. As long as the fan diameter is smaller than the diameter of the fuselage you could make it fit. Instead of a single S-duct like the 727 and L-1011 you could put Harrier style ducts on to split the size of the intake between the two sides of the aircraft.

Neat idea. I like it. Doesn't really resolve some of the other problems.


Not trying to be devil's advocate. I really like the trijet concept.

Quoting MDorBust (Reply 9): Unless you embeded the engine in the rear empenage of the fuselage aft of the pressure bulkhead

Wouldn't that make it unbearably noisy for PAX? I think the 727 was acceptable because it was for shortish hops -- imagine sitting at the back of this hypothetical tri-jet for 18/20 hours SIN-EWR. If the noise was anything like I imagine it would be, I would be a total basket-case by the time I got off the plane (probably at some diversion airport because I'd gone starkers).

I think the noise suppression that would be required would be a major hurdle to this idea.

Quoting MDorBust (Reply 9): you could put Harrier style ducts on to split the size of the intake between the two sides of the aircraft

What size would those have to be? I doubt it would be very aerodynamically efficient ...

Quoting Brenintw (Reply 11): I think the 727 was acceptable because it was for shortish hops -- imagine sitting at the back of this hypothetical tri-jet for 18/20 hours SIN-EWR.

I really didn't find 727s that loud, at least from the inside, and I've had to sit waaay in the back a few times in them. Ya, not as quiet as a 73NG or A320, but far from unbearable I'd say. And from what I've heard, DC-10/MD-11s and Tristars weren't all that bad either.

Quoting FLY2HMO (Reply 12): DC-10/MD-11s and Tristars weren't all that bad either.

I've been in both DC-10s and MD-11s -- and yes, they weren't bad. However, all the noise generating machinery is outside of the fuselage, which makes a big difference I would imagine.

I've been in a 727, but honestly don't remember if it was noisy or not (I was 11, and on my first overseas trip -- I had other things to think about, like how much I was going to enjoy Disney World!)

Quoting MDorBust (Reply 9): Unless you embeded the engine in the rear empenage of the fuselage aft of the pressure bulkhead. As long as the fan diameter is smaller than the diameter of the fuselage you could make it fit. Instead of a single S-duct like the 727 and L-1011 you could put Harrier style ducts on to split the size of the intake between the two sides of the aircraft.

MDorBust, I like the way you think!
I've been toying with a similar idea for an MD-80 sized aircraft with twin engines mounted inside the empenage.

Quoting MDorBust (Reply 9): Of course, you would have to move the wing further to the rear to compensate for the shift in COG.

It could work. Ditch the T-tail and go with forward canards for elevation control, plus go with smaller rudders on the outboard ends of the wings...not unlike a larger, jet-engined version of a Beech Starship?

Quoting Brenintw (Reply 11): Wouldn't that make it unbearably noisy for PAX? I think the noise suppression that would be required would be a major hurdle to this idea.

Not necessarily. A few lavs and a galley between the last row of seats and the rear bulkhead would absorb/block a lot of sound.

Quoting TSS (Reply 14): It could work. Ditch the T-tail and go with forward canards for elevation control, plus go with smaller rudders on the outboard ends of the wings...not unlike a larger, jet-engined version of a Beech Starship?

Wouldn't this create possible problems relative to the jetways? (unless the canard is behind the door used for boarding- is that a better idea?)

Quoting Speedracer1407 (Reply 2): next generation engines (GEnx) are pretty much ready to go in the next year or so, but aren't available in the thrust class necessary for a twin of 777-748 size. Seems to me like developting a 100Klb + NG engine will be very expensive, considering the already high price and and advanced techonolgies used in the GE90, so perhaps development costs saved by installing three existing, highly efficient engines

Simplifying like mad, three 90Klb thrust GEnx2 engines should be enough to power a radically lighter 748-sized CFRP airframe. The challenge is finding enough refinements to meet the required 15-20% efficiency increase. This could even increase range and payload. I'm not sure that it would satisfy the OEI criteria.

Quoting Brenintw (Reply 3): I can't imagine there would be any feasible way of plugging one of those into the tail of an aircraft. A lot of the thrust of the current generation engines comes from those fans chewing up enormous amounts of air ..... a smaller fan diameter would result in lower thrust.

McDD already validated the concept two decades ago. A new, bigger #2 engine could straddle the similarly enlarged tail section of the now 22' wide x 250' long fuselage, hopefully with little detrimental effect from the SUD on intake air, given the increased distance to the fan.

Quoting Brenintw (Reply 3): Furthermore, the sheer weight of modern high-bypass engines would make CG-management a real bear.

Don't forget the remaining two engines could be hung on the wings of the proportionately larger airframe.

Quoting SEPilot (Reply 7): But that does not change fan diameter, which would still remain too large to use on the tail.

Considering the 115Klb thrust of the 773ER engine, a smaller diameter fan must be feasible for one rated at 90 Klb. A 10' o.d. engine wouldn't be too big on the tail of a 748 sized plane.

Quoting TrijetsRMissed (Reply 8): All hopes of a future tri-jet widebody died with McDonnell Douglas. Boeing on the other hand, has not designed a tri-jet in over 45 years. The 727 narrow-body design will not be brought back and it is highly unlikely Boeing will attempt to engineer their first tri-jet widebody at this point.

The knowledge gained from those did not die with them. If anything, the vast advances in technology now give designers the leeway to choose the most efficient ways to tackle typical problems. And speaking of chances, this is just a hypothetical exercise.

Quoting Starlionblue (Reply 10): And that's one of the things that killed McD. The banjo fitting for the MD-11 was very costly to engineer. Scaling the banjo further for the MD-XX (trijet variant) would have been prohibitibe.

It's not like all the lessons learned there were lost. An interesting challenge would be providing enough directional control without resorting to very large or twin tails, due to the big engine reducing available rudder area. And as already mentioned, the beefing up of the tail section wuld be similarly challenging. IMO, Boeing wouldn't shirk from the cost if they could see a big demand for such an aircraft.

Quoting MDorBust (Reply 9): Of course the big question remains... WHY? Hasn't the low sales of the A380 and 747-8 taught us about the direction in aircraft size?

The answer may lie within this.....

Quoting Lemurs (Reply 6): They're not going to want to go for a tri/quad if they can help it at all, in any fashion...and that means they need to make some more big breakthroughs in design and materials to get up to 748 sizes in a twin...

Pending which, they'd have to placate the market's clamour for greater capacities with piecemeal iterations of their current product line, until it's no longer practicable.

Quoting TSS (Reply 14): not unlike a larger, jet-engined version of a Beech Starship?

Essentially, the one in the last link at the thread's start. Having three of which on top, tells me Boeing couldn't be bothered about MX issues on the No. 2 engine on a conventional trijet. (Although their clients likely would.) All of these of course, from my uneducated layman's view.

Quoting GAIsweetGAI (Reply 15): Wouldn't this create possible problems relative to the jetways? (unless the canard is behind the door used for boarding- is that a better idea?)

It would indeed. Moving the canards rearward solves that problem but lessens their effectiveness, thus creating another problem.

Quoting TSS (Reply 14): I've been toying with a similar idea for an MD-80 sized aircraft with twin engines mounted inside the empenage.

Whoa there. Now you're putting both engines next to each other AND in the empennage? The Sioux City victims are here. They'd like a word.  

Quoting DEVILFISH (Reply 16): Pending which, they'd have to placate the market's clamour for greater capacities with piecemeal iterations of their current product line, until it's no longer practicable.

What clamor for greater capacities? With precisely one model of large to very large aircraft selling better than week-old flapjacks (i.e. the 777-300) I don't see any great demand for bigger airplanes at this time. What there is a great clamor for is greater efficiency, and that is in every aspect. I suspect that the airlines will be happy to wait for new VLA's until there are engines big enough to make them as twins. I also believe that Boeing, at least, will not launch a new program unless they can improve the economics at least 15% over what it is replacing.

Quoting SEPilot (Reply 19): What clamor for greater capacities?

I think you answered your own question.....

Quoting SEPilot (Reply 19): I suspect that the airlines will be happy to wait for new VLA's until there are engines big enough to make them as twins.

So there is that demand - however, they can't help but wait until their requirements could be more efficiently met. I didn't find it necessary to qualify further what you quoted as I had already made the point twice earlier.....

Quoting DEVILFISH (Thread starter): and the high efficiencies and capacities demanded by the airlines

Quoting DEVILFISH (Reply 16): The challenge is finding enough refinements to meet the required 15-20% efficiency increase.

Quoting Starlionblue (Reply 18): Whoa there. Now you're putting both engines next to each other AND in the empennage?

With rudders on the outboard ends of the wings and forward canards for pitch control, why not? There would be few if any hydraulic lines that far rearward in the fuselage.

Quoting TSS (Reply 21): With rudders on the outboard ends of the wings and forward canards for pitch control, why not? There would be few if any hydraulic lines that far rearward in the fuselage.

The fact that all commercial airliners since the earliest days have had essentially the same layout is not an accident. Different layouts (canards, flying wings, etc.) have advantages but they also have very real disadvantages. The canard layout has been widely touted as being "stall-proof" and when correctly loaded it is; but the downside is a very restricted CG range compared to a conventional layout. I do not believe that the airlines would accept this; they have enough problems with CG as it is. Putting rudders at the ends of the wings has structural (i.e. weight) penalties. The flying wing (read BWB) concept is actually the one that holds the most promise for the future; the primary problem is passenger acceptance of having no windows. When first introduced it was not practical because stalls were pretty much unrecoverable, but with FBW technology that is not such a factor. If Y3 turns out to be a BWB there is the possibility that it could be a trijet; but I don't think it is likely as Boeing does not believe that the public is ready for it. But if an airliner bigger than the A380 ever is built my bet is that it will be a BWB. Of course one big disadvantage to the BWB is that it is one size; different size variations are impossible.

Quoting SEPilot (Reply 22): Of course one big disadvantage to the BWB is that it is one size; different size variations are impossible.

I guess that depends on the level of blend. A pure flying wing is tricky to resize. But if you make it a semi-blend with a partly distinct fuse, changing the fuse length becomes possible.

This may sound really dumb, but I have an excuse, I'm no aeronautical engineer...

Would it be possible to have a large centerline engine used primarily for cruise and two smaller wing mounted augmenter engines for take off, landing and redundancy in case of the "main" engines failure? The smaller bypass engines could be in clam shelled housings to reduce drag when not need during cruise?

I realize it's a bit goofy and may be too complex, but who's to say that all three engines have to be the same thrust rating and capable of operating throughout the full continuum of flight?

Just another hair-brained thought....

Quoting Okelleynyc (Reply 24): Would it be possible to have a large centerline engine used primarily for cruise and two smaller wing mounted augmenter engines for take off, landing and redundancy in case of the "main" engines failure? The smaller bypass engines could be in clam shelled housings to reduce drag when not need during cruise?

Neat idea. You've solved the windmilling problem of an idle turbofan by putting it in a clam. However you haven't removed the complex and heavy centerline mount.

As for aircraft with an extra engine different from the rest behind an intake with doors, dare I mention the infamous fourth engine on the Trident 3B?


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Photo © Michel Gilliand


[Edited 2007-05-05 05:17:11]

[Edited 2007-05-05 05:17:56]

I always assumed that trijets are inefficient (only the center one though) given the possibility of dual engines.

Quoting CoolGuy (Reply 26): I always assumed that trijets are inefficient (only the center one though) given the possibility of dual engines.

Weeeeeellll... When the aircraft is too large for a twin, a triplet is a good option unless you count engine placement. If the third engine could be slung under one wing and magically still give centerline thrust, that would be a great option.

The issues with triplets are related to center engine placement. That's why modern quads skip straight to four despite the possibility of powering them with 3x very large engine.

[Edited 2007-05-06 20:36:26]

Quoting Starlionblue (Reply 25): I mention the infamous fourth engine on the Trident 3B?

OK, either I'm blind, or stupid (or both) -- but I'm not sure where the 4th engine is on that -- and why was it "infamous"? Enquiring minds want to know  

Bren

Quoting CoolGuy (Reply 26): I always assumed that trijets are inefficient (only the center one though) given the possibility of dual engines.

All three engines are the same, just the No.2 is shaped differently for obvious reasons. For example, an MD-11 may have three PW4462's, 62,000lb of thrust each.

Quoting Brenintw (Reply 28): OK, either I'm blind, or stupid (or both) -- but I'm not sure where the 4th engine is on that

The three main engines on the Trident (RR Spey 512s – 10,050-11,960lbs thrust, depending on the model) were mounted similarly to those on a 727. On the Trident 3B, a fourth booster engine was added (RR RB162, 5250lbs) in a pod above the center engine.

The booster’s exhaust is obvious in this picture (the upper one with the silver ring in the solid blue area of the tail), and at the front of the pod you can see the doors which opened to let in air when the booster engine was running.


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Photo © John Farrington - FlightLineImages

Quoting Starlionblue (Reply 23): guess that depends on the level of blend. A pure flying wing is tricky to resize. But if you make it a semi-blend with a partly distinct fuse, changing the fuse length becomes possible.

But what would be the point? Weight would be pretty close to the same, structure would be the same, and trip costs would be pretty much the same. You might as well put the same number of seats in.

Quoting Brenintw (Reply 28): OK, either I'm blind, or stupid (or both) -- but I'm not sure where the 4th engine is on that -- and why was it "infamous"

It's "infamous" in the same way h VFW-614 engine placement is "dreaded".  Just in my own mind in other words. Both are fugly and inelegant solutions in my highly subjective opinion. These factors also add to their charm.

The Trident also had that wacky off center nose gear .


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Photo © Ray Pettit

Quoting SEPilot (Reply 31): Quoting Starlionblue (Reply 23): guess that depends on the level of blend. A pure flying wing is tricky to resize. But if you make it a semi-blend with a partly distinct fuse, changing the fuse length becomes possible. But what would be the point? Weight would be pretty close to the same, structure would be the same, and trip costs would be pretty much the same. You might as well put the same number of seats in.

Agreed. I was just skyballing.

Quoting Starlionblue (Reply 32): The Trident also had that wacky off center nose gear .

And the 4 side-by-side main gear wheels... British design at it's best lol!

Well, still better than this...


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Photo © Andy Marks-ManxAirPix

Quoting MrFord (Reply 33): Well, still better than this...

Oddly, I've always found the Victor breathtaking despite being really weird.

The next to last pic on this page http://www.thunder-and-lightnings.co.uk/victor/history.html shows the art applied after a Victor ran out of taxiway at Offutt AFB. It also tells the tale of the kill marking applied after a Victor taxied into an incorrectly parked vehicle. The whole site is marvelous btw.

[Edited 2007-05-07 23:08:41]

Quoting Starlionblue (Reply 32): The Trident also had that wacky off center nose gear

It would fit right in with a squadron of (some marks of) Canberras.

View Large View Medium Photo © Dirk Jan de Ridder - MilAvia Press

View Large View Medium Photo © Daniel Butcher - UK Airshow Review

Quoting MrFord (Reply 33): Well, still better than this...

Wow, that one looks straight out of a Hollywood special effects department on LSD!
  

Quoting SEPilot (Reply 36): Wow, that one looks straight out of a Hollywood special effects department on LSD!

Viciously cool looking up close and personal. And it has the same gorgeous fin/stab as the VC-10.

Quoting Starlionblue (Reply 34): Oddly, I've always found the Victor breathtaking despite being really weird. The next to last pic on this page http://www.thunder-and-lightnings.co.uk/victor/history.html shows the art applied after a Victor ran out of taxiway at Offutt AFB. It also tells the tale of the kill marking applied after a Victor taxied into an incorrectly parked vehicle. The whole site is marvelous btw.

You have to give them, they really tried to 'think outside the box' hehe!

Nice site there, thanks! I've read somewhere before about the Falkland Islands mission, that was an impressive feat!
I was always under the impression that those Vulcan were powered by some derivate of the Avon engine, not the Conway... you learn something each day  

P.S: That tail do look similar to the VC.10 one, but after someone smashed the top   The VC.10, that was a beautiful jet...

Quoting MrFord (Reply 38): Nice site there, thanks! I've read somewhere before about the Falkland Islands mission, that was an impressive feat! I was always under the impression that those Vulcan were powered by some derivate of the Avon engine, not the Conway... you learn something each day

Mostly I find all the references to how the government slowly killed the UK aviation industry fascinating and disturbing. Those guys seemed to change their minds at every turn, creating an impossibly uncertain environment.

You certainly didn't want to be a non-pilot crew member on a V Bomber.
Crew escape [on the Valiant], in common with the other two V-bombers, was a mixed affair. The two pilots had ejection seats (the canopy being blown off before ejection) but the rear crew had to bale out via the crew hatch on the port side of the nose. This was however substantially easier than on the Vulcan (no nose gear to hit) and the Victor (the Valiant crew door being much lower than the engine intakes). Unusually, the casualty of this crash was the co-pilot, Squadron Leader Brian Foster (an RAF officer attached to Vickers for Valiant testing) - his ejector seat struck the tailfin.

Quoting MrFord (Reply 38): I was always under the impression that those Vulcan were powered by some derivate of the Avon engine, not the Conway...

I just know it was the Olympus. No idea it was a Conway derivative. It later went on to power the TSR.2 (and what a cool plane that was! http://www.thunder-and-lightnings.co.uk/tsr2/history.html) until that was canned, and finally ended up in Concorde.

And now we're very OT.

[Edited 2007-05-08 03:37:13]

[Edited 2007-05-08 03:37:34]

[Edited 2007-05-08 03:41:52]

Quoting Starlionblue (Reply 39): I just know it was the Olympus. No idea it was a Conway derivative.

Quote: With the much higher thrust Sapphire 9 engines cancelled in the usual lunatic manner of the Air Ministry's dealings throughout the 1950s and 1960s, Rolls-Royce Conways were instead earmarked for the Victor B.2

But then I don't know much of the history of the Conway or the Sapphire, for that matter... Just that I saw that, I may be wrong hehe!

But you're right, it's impressive how they were able to kill almost their entire aerospace industry, one by one, with those requirements, changes and cancellations... as reliable as a division on an early Pentium... but then, we're totally off-course  

Quoting MrFord (Reply 40): But you're right, it's impressive how they were able to kill almost their entire aerospace industry, one by one, with those requirements, changes and cancellations... as reliable as a division on an early Pentium... but then, we're totally off-course

And despite that all that, the UK still had kick-ass aircraft that allowed it to project force in the South Atlantic in the 1980s. Can't keep good designers down.


10001 POSTS ON A.NUT!!!

Quoting Starlionblue (Reply 41): 10001 POSTS ON A.NUT!!!

That should give you access to Elite status on you frequent flyer account with that !   Congrats, you're now officially addict !

Quoting Okelleynyc (Reply 24): This may sound really dumb, but I have an excuse, I'm no aeronautical engineer... Would it be possible to have a large centerline engine used primarily for cruise and two smaller wing mounted augmenter engines for take off, landing and redundancy in case of the "main" engines failure? The smaller bypass engines could be in clam shelled housings to reduce drag when not need during cruise?

I've never heard this seriously proposed - however Boeing did propose a "thrusting APU" for the 777. This engine would fulfill all the normal functions of the APU, but it would provide significant thrust. It would have been a version of a fighter jet engine, and would be used only on takeoff. It would allow for a greater payload on takeoff . This is because the limiting factor for MTOW on a big twin is often engine-out performance. It turns out that the engine makers were able to get enough performance out of the 777's engines to make the "Thrusting APU" unnecessary. No airline believed it to be worth the added complexity and maintenance burden.

That's the only serious proposal I've heard for putting two different engine types on an airliner at the same time.

Maybe a thrusting APU + composite construction could allow a twin engined A380-800 sized aircraft with engines not much larger than those of the longer range 777 versions. If that were possible, it could be used on Y3. But that is just guesswork......

Quoting Cloudy (Reply 43): That's the only serious proposal I've heard for putting two different engine types on an airliner at the same time.

Well, there was the aforementioned Trident.  


Incidentally, there have been several military jets with dual propulsion, both in service and proposed.
- Yak-38 Forger.
- XF-91 Thunderceptor.
- SR.53
- SR.177
- B-36.