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UA857
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Why was the 747-500 cancelled?

Sun Jul 26, 2020 9:59 pm

Back in 1986 when the 747-400 was still under development Boeing studied a ULH 747 called the 747-500 that could be able to fly up to 8,700 nmi (16,000 km), which would allow airlines to fly routes such as LHR-SYD, JFK-SYD, EWR-SIN and LAX-SIN and would have been the 777-8X of its time and could have possibly been bought by airlines such as QF and SQ. Do you guys know why the 745 was cancelled?
 
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TWA772LR
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Re: Why was the 747-500 cancelled?

Sun Jul 26, 2020 10:07 pm

I would go out on a limb and say airlines wanted 747 size with better fuel economy over longer range. Hence the 777 and A340 coming around.
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UA857
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Re: Why was the 747-500 cancelled?

Sun Jul 26, 2020 10:15 pm

TWA772LR wrote:
I would go out on a limb and say airlines wanted 747 size with better fuel economy over longer range. Hence the 777 and A340 coming around.

The 77L and A345 weren't launched until about 2002/2006.
 
bourbon
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Re: Why was the 747-500 cancelled?

Sun Jul 26, 2020 10:19 pm

UA857 wrote:
TWA772LR wrote:
I would go out on a limb and say airlines wanted 747 size with better fuel economy over longer range. Hence the 777 and A340 coming around.

The 77L and A345 weren't launched until about 2002/2006.

The 777-200 and A340 were launched much earlier though...
 
UA857
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Re: Why was the 747-500 cancelled?

Sun Jul 26, 2020 10:22 pm

bourbon wrote:
UA857 wrote:
TWA772LR wrote:
I would go out on a limb and say airlines wanted 747 size with better fuel economy over longer range. Hence the 777 and A340 coming around.

The 77L and A345 weren't launched until about 2002/2006.

The 777-200 and A340 were launched much earlier though...

But they 77E and A343 the same range as the 744.
 
bourbon
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Re: Why was the 747-500 cancelled?

Sun Jul 26, 2020 10:24 pm

UA857 wrote:
bourbon wrote:
UA857 wrote:
The 77L and A345 weren't launched until about 2002/2006.

The 777-200 and A340 were launched much earlier though...

But they 77E and A343 the same range as the 744.

The 77L is a 200


ETOP improvements are what killed the 747. 770-300ER took out the A340-600 and the 747.
 
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Re: Why was the 747-500 cancelled?

Sun Jul 26, 2020 10:34 pm

Couldn't you essentially say the 748 took the place of the 745?

The range of the 748 isn't as great as the proposed range of the 745, but the 745 included a 777-style wing IIRC, new engines, and an enlarged upper-deck, all of which the 748 has.
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UA857
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Re: Why was the 747-500 cancelled?

Sun Jul 26, 2020 11:00 pm

bourbon wrote:
UA857 wrote:
bourbon wrote:
The 777-200 and A340 were launched much earlier though...

But they 77E and A343 the same range as the 744.

The 77L is a 200


ETOP improvements are what killed the 747. 770-300ER took out the A340-600 and the 747.


I'm talking about the late 1980s not the 2000s.
 
blandy62
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Re: Why was the 747-500 cancelled?

Sun Jul 26, 2020 11:07 pm

overall just lack if interrest from the airlines
 
prebennorholm
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Re: Why was the 747-500 cancelled?

Sun Jul 26, 2020 11:23 pm

Interested in the -500, -600 and -700, it's all here: http://www.boeing-747.com/boeing_747_fa ... -700X.html
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LAX772LR
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 12:36 am

The 747-500, 747-600, and 767-400ERX would've all shared an engine that did not come to fruition, and were all subsequently cancelled.
I myself, suspect a more prosaic motive... ~Thranduil
 
UA857
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 3:00 am

blandy62 wrote:
overall just lack if interrest from the airlines

I'm QF and SQ would be interested in the 745.
 
jetwet1
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 6:03 am

UA857 wrote:
blandy62 wrote:
overall just lack if interrest from the airlines

I'm QF and SQ would be interested in the 745.


And you would be wrong, Boeing shopped the idea to airlines and heard crickets.Boeing offered the plane in 96, by 97 it was killed.
 
VSMUT
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 6:50 am

As history has shown, most airlines wanted the 747 for it's range, not size. If you wanted a long range jet in the late 80s, a 747-400 or an MD-11 was the only game in town, and we all know that the MD-11 didn't exactly live up to its promises. When the A340-300 and 777-200ER started offering similar range with a cheaper, more right-sized airframe, 747 sales started to slow and eventually died out completely. In that light, a 747-500 would have achieved little success, too much plane to achieve the same job.

I recall that the proposed wing was also a point on contention. The highly-swept wing of the 747 has been a problem for the type in newer years, as it is designed for cruising at higher speeds than what is efficient for modern turbofans to run at. The solution was to offer a brand new wing with less sweep. A completely new wing was going to make the aircraft uncertifiable as a grandfathered design, meaning it would have to go through the full certification as a new type with all the costs involved.

The diagram below shows the proposed 747-700X which went even farther, with a widened fuselage, but the wings would have been the same they wanted to use for the 747-500X and -600X.

Image

LAX772LR wrote:
The 747-500, 747-600, and 767-400ERX would've all shared an engine that did not come to fruition, and were all subsequently cancelled.


Which engine was that?
 
DIJKKIJK
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 7:14 am

UA857 wrote:
Back in 1986 when the 747-400 was still under development Boeing studied a ULH 747 called the 747-500 that could be able to fly up to 8,700 nmi (16,000 km), which would allow airlines to fly routes such as LHR-SYD, JFK-SYD, EWR-SIN and LAX-SIN and would have been the 777-8X of its time and could have possibly been bought by airlines such as QF and SQ. Do you guys know why the 745 was cancelled?



There was an ULR version of the 747 developed . It was called the 747SP. It did not sell very well. :biggrin:

ULR has been and will always be a niche thing. The 77L also has not sold well, despite it being twin engined and more fuel efficient than the 747.
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GSOtoIND
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 7:42 am

VSMUT wrote:

LAX772LR wrote:
The 747-500, 747-600, and 767-400ERX would've all shared an engine that did not come to fruition, and were all subsequently cancelled.


Which engine was that?

A Trent derivative. I believe it was to be designated the Trent 600.
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maude
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 7:54 am

DIJKKIJK wrote:
There was an ULR version of the 747 developed . It was called the 747SP. It did not sell very well. :biggrin:


The 747-300 could pretty much match the SP, but with more passengers. The -400 easily surpassed it. The SP was a product of its era...the Stone Age.
 
TheWorm123
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 9:47 am

prebennorholm wrote:
Interested in the -500, -600 and -700, it's all here: http://www.boeing-747.com/boeing_747_fa ... -700X.html

That 747-700 sounds like a tail strike waiting to happen
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aemoreira1981
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 1:27 pm

The idea of ULH was not being considered yet and such would have sold pretty poorly. It would also have been hard to find that many passengers willing to fill the plane and pay a premium for ULH, and airlines would not have wanted to carry around the unneeded weight.
 
UA748i
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 2:52 pm

The 747Xs models are what eventually led up the the 747-8.

I feel like the -500 would have been a long range version, while the -600, your heavy routes.

But my goodness, the -500 with winglets like that would have been SEXY

Image

Image
 
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 3:18 pm

UA857 wrote:
blandy62 wrote:
overall just lack if interrest from the airlines

I'm QF and SQ would be interested in the 745.


You need to recognize that QF + SQ don't make a market for a new long-haul type. They just don't buy enough. Try to identify carriers and routes to support 500+ aircraft. You can't. ULR was, and is, a niche. Add up all the 345s and 77Ls (and 380s, which didn't match the mooted 747-500 in range) that have been sold. Three types across both manufacturers across ~fifteen years and you still don't see even 400.
 
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 3:29 pm

VSMUT wrote:
LAX772LR wrote:
The 747-500, 747-600, and 767-400ERX would've all shared an engine that did not come to fruition, and were all subsequently cancelled.
Which engine was that?

GSOtoIND wrote:
A Trent derivative. I believe it was to be designated the Trent 600.

Because we are talking about undeveloped variants, the waters are somewhat murky here.

Assuming you are correct, I believe the Trent derivative would have applied to the 747-500X, -600X, and quite possibly the 767-400ERX.

But none of those above are the same as the 747-500 we are discussing! :shakehead:

The original proposal for the -500 required GE to develop... (wait for it)... a rather large unducted fan (UDF). :o


I know, I know. It's barely believable today, but I guess in 1986 they had other ideas.

Please don't blame me, blame the Financial Times. And before you ask; I have no idea where they got their info from, although there are quotes attributed to Messrs Sutter and Bavaria :white:

{see Financial Times, January 20, 1986 }
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einsteinboricua
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 3:53 pm

UA857 wrote:
Back in 1986 when the 747-400 was still under development Boeing studied a ULH 747 called the 747-500 that could be able to fly up to 8,700 nmi (16,000 km), which would allow airlines to fly routes such as LHR-SYD, JFK-SYD, EWR-SIN and LAX-SIN and would have been the 777-8X of its time and could have possibly been bought by airlines such as QF and SQ. Do you guys know why the 745 was cancelled?

It probably would have suffered from the same issues the A380 suffers from today: too big an airplane for many airlines, and only enough for certain high premium, high demand routes. And this is before oil spiked for the first Gulf War.

The 744 was a good replacement for many airlines already operating the 747 on intercontinental or high capacity routes. But given that twin and trijets were slowly encroaching the need for quads, the economics wouldn't have been justified. An airline might have bought a 747 and flown a daily round trip across the Atlantic but not sold all the seats (just needed a jet to fly the route while getting around ETOPS); with ETOPS relaxed in 1985, airlines could now fly smaller equipment (767 or A300/A310) and sell all the seats or fly two daily round trips. With ETOPS expanded yet again in 1988, the need for a high capacity quad jet simply vanished.
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B-HOP
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 5:14 pm

747-500X and 600X was designed at the time when A3XX were still in the drawing board. It has many advanced feature include 777 wing, Fly By Wire etc, several briefing to operators were made, SQ/TG/MH/CX/BA/QF were interested but only TG signed, Asian economy started to slow in 1996, with debt being particular an issue, the price tag were simply too high, as they already had several things in hand. There were various attempts to improve 747-400, 747-400X, using 747-400F's wing, ultimate led to 747-400ER, there was plans to lengthen the jet to seat another 70, with a slight reduction in range, there were test to have blended winglet on 747 (done on a leased 747-200F, promising, with 6% reduction in fuel consumption), but Asian economy were simply too poor to make substantial order. Came 2000, A380 were launched with launch order from QF and SQ, MH and TG order came a bit later, 747X Stretch was also defined, with overhead gallery and blended winglet, MTOW at 473,000kg and hybrid FBW on spoilers, KE was very closed to getting the Freighter verison in summer 2001, then 911 came, the current -8 came from proposal to re-engine 747-400 to meet LHR QC2 requirement based on then 787 engine with slight increase in seat numbers, 787 were still a concept, with wish list being drawn up.
Both Asian Financial Crisis and 911 means airlines both US, EU and Asia looks for aircraft more flexible, with great cargo capacity and lower cost, that is where 77W and now 35K gain its ground, VLA simply have no place bar a few global city pairs SYD, LAX, SIN,HKG,FRA,LHR,CDG. I would think with airport running out of space to build new runway, global warming and peak oil, VLA would come back on trunk route, maybe with a small upper deck for first class, but front that can be opened replacing modern 747, build by a global consortium (not just A and or B), that is just my two cents.

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FlyingHonu001
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 5:34 pm

einsteinboricua wrote:
UA857 wrote:
Back in 1986 when the 747-400 was still under development Boeing studied a ULH 747 called the 747-500 that could be able to fly up to 8,700 nmi (16,000 km), which would allow airlines to fly routes such as LHR-SYD, JFK-SYD, EWR-SIN and LAX-SIN and would have been the 777-8X of its time and could have possibly been bought by airlines such as QF and SQ. Do you guys know why the 745 was cancelled?

It probably would have suffered from the same issues the A380 suffers from today: too big an airplane for many airlines, and only enough for certain high premium, high demand routes. And this is before oil spiked for the first Gulf War.

The 744 was a good replacement for many airlines already operating the 747 on intercontinental or high capacity routes. But given that twin and trijets were slowly encroaching the need for quads, the economics wouldn't have been justified. An airline might have bought a 747 and flown a daily round trip across the Atlantic but not sold all the seats (just needed a jet to fly the route while getting around ETOPS); with ETOPS relaxed in 1985, airlines could now fly smaller equipment (767 or A300/A310) and sell all the seats or fly two daily round trips. With ETOPS expanded yet again in 1988, the need for a high capacity quad jet simply vanished.


Boeing's R&D might also have been overconfident in the success of the 747 series at the time. Imo they didnt taken into account the changing need for fuel efficiency which become more and more prevalent among airlines with twin engine widebodies.
 
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 9:16 pm

VSMUT wrote:
As history has shown, most airlines wanted the 747 for it's range, not size. If you wanted a long range jet in the late 80s, a 747-400 or an MD-11 was the only game in town, and we all know that the MD-11 didn't exactly live up to its promises. When the A340-300 and 777-200ER started offering similar range with a cheaper, more right-sized airframe, 747 sales started to slow and eventually died out completely. In that light, a 747-500 would have achieved little success, too much plane to achieve the same job.

I recall that the proposed wing was also a point on contention. The highly-swept wing of the 747 has been a problem for the type in newer years, as it is designed for cruising at higher speeds than what is efficient for modern turbofans to run at. The solution was to offer a brand new wing with less sweep. A completely new wing was going to make the aircraft uncertifiable as a grandfathered design, meaning it would have to go through the full certification as a new type with all the costs involved.

The diagram below shows the proposed 747-700X which went even farther, with a widened fuselage, but the wings would have been the same they wanted to use for the 747-500X and -600X.

Image

If the design couldn't be grandfathered, surely all the seats in the Nose (and upstairs) wouldn't be allowed? Would that amount of 'wasted' space have made financial sense, or did that rule come in later?
 
prebennorholm
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Re: Why was the 747-500 cancelled?

Mon Jul 27, 2020 11:43 pm

VSMUT wrote:
LAX772LR wrote:
The 747-500, 747-600, and 767-400ERX would've all shared an engine that did not come to fruition, and were all subsequently cancelled.


Which engine was that?

There were actually three different engines projects aimed at various 747X and 764ERX projects.
- First Trent 600 (which did in fact run test in 1990)
- Second Trent 600 (around 2000)
- Engine Alliance GP 7100 (around 1990 ?)

The first T600 was originally named RB 211-524L and was pretty much a 211-524H with increased fan diameter (94 in up from 86 in) and four LPT stages instead of three. It was tested at Derby in 1990. With slightly further increased fan it became the T700 a couple of years later.

The later second T600 was never made. It was more like a scaled down T800. Including five LPT stages.

Little is known about how far GE and PW went with the GP 7100 project. We can guess that some of the thoughts went into the GP 7270 on the A380. But I think that it remains mostly guesswork.
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CowAnon
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Re: Why was the 747-500 cancelled?

Tue Jul 28, 2020 12:09 am

SheikhDjibouti wrote:
VSMUT wrote:
LAX772LR wrote:
The 747-500, 747-600, and 767-400ERX would've all shared an engine that did not come to fruition, and were all subsequently cancelled.
Which engine was that?

GSOtoIND wrote:
A Trent derivative. I believe it was to be designated the Trent 600.

Because we are talking about undeveloped variants, the waters are somewhat murky here.

Assuming you are correct, I believe the Trent derivative would have applied to the 747-500X, -600X, and quite possibly the 767-400ERX.

But none of those above are the same as the 747-500 we are discussing! :shakehead:

The original proposal for the -500 required GE to develop... (wait for it)... a rather large unducted fan (UDF). :o


I know, I know. It's barely believable today, but I guess in 1986 they had other ideas.

Please don't blame me, blame the Financial Times. And before you ask; I have no idea where they got their info from, although there are quotes attributed to Messrs Sutter and Bavaria :white:

{see Financial Times, January 20, 1986 }

The 747-500 engines weren't unducted, but they did have UDF technology - the contrarotating fans had a shroud. The engines were like the Kuznetsov NK-93, except without gearing.

The airports were not thrilled with this concept, though that may not have been the showstopper. The death of the UDF and subsequent low-key failures of other ducted ultra-high bypass engines were probably the killer.

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airzona11
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Re: Why was the 747-500 cancelled?

Tue Jul 28, 2020 4:33 am

UA748i wrote:
The 747Xs models are what eventually led up the the 747-8.

I feel like the -500 would have been a long range version, while the -600, your heavy routes.

But my goodness, the -500 with winglets like that would have been SEXY

Image

Image


What a lineup in that Boeing house livery too. Thanks for sharing. Remember those days.
 
Max Q
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Re: Why was the 747-500 cancelled?

Tue Jul 28, 2020 5:29 am

VSMUT wrote:
As history has shown, most airlines wanted the 747 for it's range, not size. If you wanted a long range jet in the late 80s, a 747-400 or an MD-11 was the only game in town, and we all know that the MD-11 didn't exactly live up to its promises. When the A340-300 and 777-200ER started offering similar range with a cheaper, more right-sized airframe, 747 sales started to slow and eventually died out completely. In that light, a 747-500 would have achieved little success, too much plane to achieve the same job.

I recall that the proposed wing was also a point on contention. The highly-swept wing of the 747 has been a problem for the type in newer years, as it is designed for cruising at higher speeds than what is efficient for modern turbofans to run at. The solution was to offer a brand new wing with less sweep. A completely new wing was going to make the aircraft uncertifiable as a grandfathered design, meaning it would have to go through the full certification as a new type with all the costs involved.

The diagram below shows the proposed 747-700X which went even farther, with a widened fuselage, but the wings would have been the same they wanted to use for the 747-500X and -600X.

Image

LAX772LR wrote:
The 747-500, 747-600, and 767-400ERX would've all shared an engine that did not come to fruition, and were all subsequently cancelled.


Which engine was that?




‘Too fast for modern turbofans to run on’ ?


That makes no sense, the 787 and A350 both cruise around .85, basically the same as the 747 using the most modern turbofans available and of course so does the 747-8
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744SPX
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Re: Why was the 747-500 cancelled?

Tue Jul 28, 2020 5:38 am

Recall around the same time (1985/6) Boeing also proposed the 747ASB (Advanced Short Body) which was basically a 747SP with all the 744 improvements: engines, wing, wing-to-body fairing, cockpit, interior, lighter aluminum alloys, etc.

250 pax in high comfort at 8000+ nmi with lower fuel burn than the original SP but with all the performance of the original (possibly better) in terms of cruise speed, cruise altitude and excellent hot/high capability
 
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CALTECH
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Re: Why was the 747-500 cancelled?

Tue Jul 28, 2020 3:41 pm

UA857 wrote:
Back in 1986 when the 747-400 was still under development Boeing studied a ULH 747 called the 747-500 that could be able to fly up to 8,700 nmi (16,000 km), which would allow airlines to fly routes such as LHR-SYD, JFK-SYD, EWR-SIN and LAX-SIN and would have been the 777-8X of its time and could have possibly been bought by airlines such as QF and SQ. Do you guys know why the 745 was cancelled?


Didn't get a lot of interest from airlines so they never made it off the drawing board. Boeing was not able to attract enough interest to launch the aircraft.

The engine design was the GP7176 Engine for the Boeing 747-500X/-600X. No problem with the engine, the engine was not the reason it was cancelled. The engine used on the A380 also is of the GP7000/GP7200 family,
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VSMUT
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Re: Why was the 747-500 cancelled?

Wed Jul 29, 2020 9:02 am

Max Q wrote:
That makes no sense, the 787 and A350 both cruise around .85, basically the same as the 747 using the most modern turbofans available and of course so does the 747-8


The 747 is a lot faster than mach .85. It will easily cruise at up to mach .92. That most 747s cruise at the same speed as a 787 is because *drumroll* that's where the engines are most efficient.
 
Some1Somewhere
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Re: Why was the 747-500 cancelled?

Wed Jul 29, 2020 9:15 am

A few years later, of course, Qantas got their 747-400ERs. More fuel and more strength for more MTOW and range.

The market for an actually larger aircraft just wasn't there.
 
b747400erf
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Re: Why was the 747-500 cancelled?

Wed Jul 29, 2020 9:36 am

VSMUT wrote:
Max Q wrote:
That makes no sense, the 787 and A350 both cruise around .85, basically the same as the 747 using the most modern turbofans available and of course so does the 747-8


The 747 is a lot faster than mach .85. It will easily cruise at up to mach .92. That most 747s cruise at the same speed as a 787 is because *drumroll* that's where the engines are most efficient.


That makes zero sense. The person you replied to talked about the regular cruise speed of modern turbofan engines and the 747 regularly flys at the same speed. The fastest I have seen in normal operations is .86
 
VSMUT
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Re: Why was the 747-500 cancelled?

Wed Jul 29, 2020 2:36 pm

b747400erf wrote:
That makes zero sense. The person you replied to talked about the regular cruise speed of modern turbofan engines and the 747 regularly flys at the same speed. The fastest I have seen in normal operations is .86


You don't see 747s flying faster, because that means they have to burn more fuel than what it's worth. But the wing is still optimized for higher speeds than the engines are optimized. The 747s wing is swept back more than most aircraft, at 37.5 degrees. Had it been optimised for the same speeds as most modern airliners, you would have found a wing sweep of around 30-32 degrees, as the 777, 787, A350, A330/340 and 767 all have. It is also why Boeing proposed a completely new wing for the 747-500X/600X/700X.
 
Armadillo1
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Re: Why was the 747-500 cancelled?

Mon Aug 03, 2020 9:00 pm

the answer lies in A380 history. Boeing estimated VLA niche several times smaller than Airbus. reality was in between, but close to Boeing.
 
b747400erf
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Re: Why was the 747-500 cancelled?

Tue Aug 04, 2020 9:33 pm

VSMUT wrote:
b747400erf wrote:
That makes zero sense. The person you replied to talked about the regular cruise speed of modern turbofan engines and the 747 regularly flys at the same speed. The fastest I have seen in normal operations is .86


You don't see 747s flying faster, because that means they have to burn more fuel than what it's worth. But the wing is still optimized for higher speeds than the engines are optimized. The 747s wing is swept back more than most aircraft, at 37.5 degrees. Had it been optimised for the same speeds as most modern airliners, you would have found a wing sweep of around 30-32 degrees, as the 777, 787, A350, A330/340 and 767 all have. It is also why Boeing proposed a completely new wing for the 747-500X/600X/700X.


This second time you repeat the comment of the person you replied to, the engines preform optimally at the mach speeds they cruise at an airplane is more then a wing
 
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Re: Why was the 747-500 cancelled?

Wed Aug 05, 2020 12:49 am

The economics of ULR change as fuel efficiency improves, and the practical economic maximum range increases. The first real ULR plane was the 747SP, and it sold poorly, because it simply used too much fuel and carried too few passengers. Then the 744 came out, and exceeded the range of the 747SP. That was the longest range plane until the A345 came along. The 745 would in essence have been an SP version of the 744, and there just was not enough interest in it for the same reason that the SP didn’t sell. The A345 was also a poor seller. Then the 77W came along and was able to profitably fly 8,000 nm routes, which had been previously unviable. But the 77L, which offered considerably more range, was a sales flop. But now the A350 is able to profitably fly routes that previously only the A345 and 77L could fly, but not profitably. The moral of the story is that shortening a plane and stuffing more fuel in it is not a recipe for sales success. And while the 745 would have offered better engines, they were not enough better to make a difference.
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Re: Why was the 747-500 cancelled?

Wed Aug 05, 2020 1:51 pm

VSMUT wrote:
Max Q wrote:
That makes no sense, the 787 and A350 both cruise around .85, basically the same as the 747 using the most modern turbofans available and of course so does the 747-8


The 747 is a lot faster than mach .85. It will easily cruise at up to mach .92. That most 747s cruise at the same speed as a 787 is because *drumroll* that's where the engines are most efficient.


The 747, powered with PW JT9D series engines was designed for M0.86.
Initially the 747 was operated (with very low fuel prices) with a fixed mach of 0.86 (Long Range Cruise), only slightly faster if neccessary for important operational circumstances (closure of destination, etc. ),
I never operated any 747 with a flightplan exceeding M0.87. Flying faster than M0.86, even at the 747, will increase the fuel flow exponentially, due increased drag.

I saw M0.92 only during sudden wind direction and/or speed changes and than you had to be fast to lower your engine power to avoid an overspeed warning.

With rising fuel costs we cruised at CRZ ECON, a function of aircraft weight/ altitude/ and wind, presented initially in graphs and calculated by the F/E.
But Remember: initial the 747's had only a ATS for approach and (auto) land and it was not easy to operate at speeds below M0,83, because of reduced speed stability (wrong side of the curve)

Later a Performance Management System was installed and via a Full Flight Regime Auto throttle System (FFRATS) the exact calculated Mach number was established.
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Re: Why was the 747-500 cancelled?

Wed Aug 05, 2020 2:25 pm

Thanks for this bit of information....didn't know all this

747classic wrote:
VSMUT wrote:
Max Q wrote:
That makes no sense, the 787 and A350 both cruise around .85, basically the same as the 747 using the most modern turbofans available and of course so does the 747-8


The 747 is a lot faster than mach .85. It will easily cruise at up to mach .92. That most 747s cruise at the same speed as a 787 is because *drumroll* that's where the engines are most efficient.


The 747, powered with PW JT9D series engines was designed for M0.86.
Initially the 747 was operated (with very low fuel prices) with a fixed mach of 0.86 (Long Range Cruise), only slightly faster if neccessary for important operational circumstances (closure of destination, etc. ),
I never operated any 747 with a flightplan exceeding M0.87. Flying faster than M0.86, even at the 747, will increase the fuel flow exponentially, due increased drag.

I saw M0.92 only during sudden wind direction and/or speed changes and than you had to be fast to lower your engine power to avoid an overspeed warning.

With rising fuel costs we cruised at CRZ ECON, a function of aircraft weight/ altitude/ and wind, presented initially in graphs and calculated by the F/E.
But Remember: initial the 747's had only a ATS for approach and (auto) land and it was not easy to operate at speeds below M0,83, because of reduced speed stability (wrong side of the curve)

Later a Performance Management System was installed and via a Full Flight Regime Auto throttle System (FFRATS) the exact calculated Mach number was established.

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