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The mach 2.7 capable Boeing 2707 has an interesting design. I'm curious if there has been any studies done that concluded that this aircraft would simply not have worked, given the way it was initially designed, even if sufficient funding existed.

If so, what was the problem with the design? By problems, I don't mean it being financially feasible or sustainable, I mean technical limitations and restrictions imposed by physics. Could this sort of aircraft ever have achieved a sustained mach 2.7, and carry 277 passengers?

I'm personally inclined to believe it might have worked, considering other notable aircraft of the time, such as the military planes; the XB-70, the SR-71, or the civilian Concorde, and Tu-144. The civilian planes mentioned here are somewhat slower, but the military planes are somewhat faster, and puts the 2707 right in the middle.

However, it would be nice to see an actual evaluation of its design, if such a thing exists.

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enter image description here

The three competing supersonic designs are discussed in this videoThe Forgotten American Concordes. Two competing designs from the USA were proposed to the US government, which was going to fund 75% of the development cost: one from Lockheed, and the B2707 from Boeing which was the winning design.

The B2707 was meant to be bigger and faster than Concorde, and this was one of the three issues that eventually saw the project being cancelled:

  1. Concorde flew at Mach 2, heating up the nose to 127 °C and the wing leading edges to 100 °C. The whole plane was considerably longer at cruise than it was on the runway due to heating up from the supersonic flow, but at this speed aluminium could still be used as the main construction material for most of aeroplane. The B2707 would be heating up much more, ruling out aluminium and having to use titanium, skyrocketing the construction price per aeroplane.
  2. The oil crisis of the early 70s raised fuel prices a lot, with unfavourable consequences for the operating costs. It was thought that since the travel time is shorter there could be more daily flights, but:
  3. protests about supersonic booms prohibited supersonic flights over most land, meaning that the only viable market was the US east coast to the European west coast.

If so, what was the problem with the design? By problems, I don't mean it being financially feasible or sustainable, I mean technical limitations and restrictions imposed by physics. Could this sort of aircraft ever have achieved a sustained mach 2.7, and carry 277 passengers?

enter image description hereImage source

It might have, there were military aeroplanes flying at M 2.7 or faster at the time like the XB-70 Valkyrie built out of stainless steel, but the technology was still immature. Passenger transport implies high reliability and long testing times to verify if the safety requirements can be met, and this was a major issue to be crossed out at the time of cancellation.

So the question: "Could this sort of aircraft ever have achieved a sustained mach 2.7" at the required reliability rate was never tested.

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    $\begingroup$ There is also now a US-Asia market, which has unbearably long flights as things are right now, and close to 100% of those flights are over water. This would help Emirates and the middle eastern carriers a great deal less, as most of their flights are mostly over land, where the booms would be not appreciated. That would greatly aid US carriers, for instance Singapore-London would work best as supersonic to SFO, subsonic to Dulles then supersonic to the Irish Sea. $\endgroup$ – Harper Aug 25 at 21:28
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    $\begingroup$ @Harper It sure looks like a different market nowadays, Japan to California for instance. $\endgroup$ – Koyovis Aug 25 at 21:33
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    $\begingroup$ Civilian airlines also have an FAA requirement to descending down to non-pressurized cabin altitude within a set amount of time. This was a huge problem for the concord during design, because it means the aircraft needs to do a much more significant altitude drop in the same period due to their higher cruise altitude. $\endgroup$ – Nelson Aug 26 at 0:44
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    $\begingroup$ @Harper you can't be serious about the Singapore route. gcmap.com/mapui?P=sin-sfo-iad-lhr&MP=polar&DU=mi $\endgroup$ – Douglas Held Aug 26 at 13:27
  • $\begingroup$ @DouglasHeld Holy smoke, that was dumb of me. I blame Mercator! But yes, that is a problem, too many of the world's routes are heavily over land... That's just not an American problem which is why an SST would be so awesome for us... $\endgroup$ – Harper Aug 26 at 16:45
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The 2707 started with a variable sweep, but it was too heavy to be feasible

Here's a mockup of the 2707 with its variable sweep

2707, wings extended

And here's a video of Boeing's mockup

But variable sweep mechanisms add a lot of weight. And, being a civilian airliner, there would likely have to be all sorts of safety backups, adding more weight. As the video notes, the 2707

could cross the Atlantic, but without passengers

And Wikipedia notes this quote

Boeing also faced insurmountable weight problems due to the swing-wing mechanism (a titanium pivot section having been fabricated with a weight of 4,600 pounds and measuring eleven feet long and 2.5 feet thick)[15] and the design could not achieve sufficient range.

The redesigned 2707 went with a delta wing like the Concorde, but by then other cost factors caused the US government and Boeing to cancel the project

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  • $\begingroup$ Note the larger tail, the placement of the engines, the canard. Should have been the 2737. $\endgroup$ – Robert DiGiovanni Aug 25 at 0:52
  • $\begingroup$ The wings could be folded for storage like the Handley Page type W, would not have to swing in the air (keep it subsonic). $\endgroup$ – Robert DiGiovanni Aug 25 at 1:20
  • $\begingroup$ Was the redesign with a delta wing also slanted for mach 2.7? $\endgroup$ – AlphaCentauri Aug 25 at 1:50
  • $\begingroup$ @AlphaCentauri I can't find anything that says the new design was any different in speed from the old $\endgroup$ – Machavity Aug 25 at 3:10
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    $\begingroup$ Even after all these years, I can recognize a KSP render when I see one :) $\endgroup$ – AEhere Aug 26 at 13:50
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It certainly would have worked, as there weren't really any technical obstacles, only financial.

The real issue is, was it possible to build it and put it into service with un-subsidized ticket prices that would fill seats AND make it possible to make a profit on its operation?

It's important to note that the Concorde was only feasible because British and French government direct operating subsidies made it possible to charge only astronomical prices for tickets, vs down-a-black-hole prices that would have been required without subsidies (even with subsidies, traveling on Concorde was about as expensive as traveling to Europe on a Clipper flying boat in the late 30s. The British and French governments were basically subsidizing, or giving away money to, rich folks for national pride reasons).

Even allowing for the fact that Boeing benefits from de-facto subsidies in the form of military development contracts for designs with ultimate civilian use, and assuming such had been available for the 2707 (a military related development program to get it off the ground that is), the direct operating costs would have made it unfeasible in a non-subsidized airline environment (if the KC135/707 wasn't able to make money in 1958 at the airline operating level, it wouldn't have worked either).

Bottom line: the operating numbers simply didn't work out, except as a "national pride" sort of project, like Concorde, and outside of military applications, that sort of thing doesn't happen very often in the US.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

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    $\begingroup$ Sounds like a lengthy personal opinion. Developing any airliner costs a lot of money. Supersonic travel was economically competitive with the turbojets of the time, before high bypass turbofans were developed. $\endgroup$ – Koyovis Aug 24 at 22:33
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    $\begingroup$ Why would you want to be just another person who says something on the internet? $\endgroup$ – Koyovis Aug 25 at 2:40
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    $\begingroup$ Can you speak as to how a privatised British Airways made Concorde profitable in the 1980s, without any subsidies and while paying the British government a profit share? $\endgroup$ – Moo Aug 25 at 5:34
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    $\begingroup$ you're quite wrong saying the problems were purely financial. The design was (in part because of the requirements for it) overly ambitious and dependent on technology that was immature at best, non-existent at the time at worst. The work towards building the aircraft did help the aircraft industry a lot for the future, but it's highly unlikely it would have yielded a functional aircraft meeting the design specs, certainly within the time constraints put forward by congress. $\endgroup$ – jwenting Aug 26 at 4:04
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    $\begingroup$ @magallanes do you have any supporting evidence that British Airways has unpaid loans related to Concorde? There's a lot of crap surrounding Concorde, a lot of it false. $\endgroup$ – Moo Aug 26 at 7:19
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I know the airplane was re-designed during development due to weight and complexity issues associated with the swing wing design. Variable geometry was the rage in the sixties and Boeing felt that, from initial studies of the problem, that is could make use of the swing wing design for improved low speed flight. It turned out that even with a titanium wing box, the airplane was just too heavy to carry the proposed passenger load. A delta wing configuration was selected in later iterations of the 2707 design. This, combined with the unprofitably, environmental issues, heat control, drove the company to cancel the nearest thing America ever got to an SST.

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