back to article Concorde? Pffft. NASA wants a Mach 4 passenger jet

The legendary supersonic Concorde jet used to ferry passengers across the Atlantic in just three and a half hours at twice the speed of sound. Impressive, for sure, but NASA now says it's exploring the possibility of doubling that. After completing a survey of business cases for the use of supersonic jets able to travel …

  1. alain williams Silver badge

    This project must not be allowed to happen

    I shudder to think of the emissions per passenger mile that this jet will produce and so make worse our climate change problem.

    Other than ego tripping why would anyone really want to pay what I suspect will be a very high ticket price?

    We can do many meetings these days over the Internet, far better use of most people's time and far kinder to the environment.

    Having said that: I expect to be ignored and NASA will try to build this.

    1. bazza Silver badge

      Re: This project must not be allowed to happen

      Depends. Concorde was exceptionally efficient at 60,000 M2, and so was the SR71 at 90,000 M3. In fact, with aircraft of that sort, the faster they went the more efficient they got, because the ram-compression in their (very carefully managed) adjustable air inlets reduced the amount of power needed to be tapped from the exhaust by the turbine to run the compressor. Thus, the engines can be kept running using far less fuel than on the ground.

      The trouble is getting up to height / speed in the first place. This is a compromise on all jet powered aircraft (turbojet, turbofan), that there is an optimum cruise height / speed for best efficiency, and the further from zero feet / zero knots that is the harder it is to get from runway to cruise. This is true for ordinary airliners. Some time ago, all the airlines started doing quite steep / quick climbs to altitude, because someone worked out that the fuel burned on such a sporty ascent was paid back by spending more of the journey at optimum cruise height. That in turn has had an impact on engine life / design, because by spending more time at a high power setting the engine wears out quicker. Considering that in the light of a new supersonic airliner, it could be that using a solid rocket to get to speed / height fast could pay off. Not that SRBs are particularly clean things...

      But yes, it sounds expensive, fairly pointless, unlikely. The laws of physics haven't changed, nor has the operational experience of Concorde and the SR71. Both needed huge amounts of maintenance, and the SR71 (the wildest, most on-the-edge power plant ever in and aircraft) never solved the inlet un-start problem (Lockheed could only mitigate it), which would be even worse at M4. I suspect that there's some ailing US defence contractor in need of some gratuitous taxpayer funding to produce several lbs of printed paper that 1) says "can't be done" whilst 2) looking like it say "can be done, give us more money".

      1. Justthefacts Silver badge

        Re: This project must not be allowed to happen

        The laws of physics haven’t changed, but airport security has.

        Concorde traded on the idea that reducing a 7 hour flight time to a 3 hour flight time was quite attractive. Including a 1 hour wait on the originating airport, and maybe 45 minutes at the destination with waiting for baggage, that reduces 8 hrs 45 down to 4hrs 45. Half. Now, for transatlantic, you are looking at 3 hours checkin to takeoff. So that’s 10hrs 45 down to 6hrs 45. Only 30% quicker.

        But worse still, the *real* Concorde USP was “London to New York and back, for a meeting, without an overnight stay”. This just no longer works. The difference between 10hrs 45 and 6hrs 45 is basically nothing at all, since all you can do when you get there is go straight to the hotel to sleep. There’s literally nobody you can sell that proposition to, everybody who has loadsamoney will prefer Business (or even First) on a larger slower aircraft.

        1. Anonymous Coward
          Anonymous Coward

          Re: This project must not be allowed to happen

          Or they have their own private jet.

        2. MachDiamond Silver badge

          Re: This project must not be allowed to happen

          "The difference between 10hrs 45 and 6hrs 45 is basically nothing at all, since all you can do when you get there is go straight to the hotel to sleep."

          This demonstrates my concept of going faster by going slower. If you take a longer direct flight and can sleep on the way, the trip takes much less waking time. I also find it better to arrive at a convenient time when shifting time zones rather than going really fast depending on the direction. All the non-flight time it takes these days just getting through to the plane and the interminable layovers since fewer flights are direct just eats up a day. It pushes out the "just drive or take a train" radius. I keep hoping Amtrak will get some money and train advocate management and look at overnight trains more and also schedules that make some smaller station stops happen during daylight. I really don't want to arrive someplace at 2am, but I'm fine leaving really early or late.

        3. imanidiot Silver badge

          Re: This project must not be allowed to happen

          If they were to re-start a Concorde like service, they'd do the same as they did for Concorce -> Have it's own express/vip check in lanes to speed up that process. Concorde also offered the service whereby you could get from your taxi to onboard the plane in 15 minutes iirc. There's absolutely no need for check in times now to be 3 hours except that most airports are too cheap to hire enough personnel to run security efficiently, and part of the self-loading cargo is too stupid to get through the security theater without copious handholding and explanation.

          1. SundogUK Silver badge

            Re: This project must not be allowed to happen

            "...airports are too cheap to hire enough personnel to run security efficiently."

            No, actually it's passengers who are too cheap to allow airports to run security efficiently. If you want to pay peanuts for your flight to Majorca, the airlines can't pay for all those extra security bodies.

            1. jmch Silver badge

              Re: This project must not be allowed to happen

              " most airports are too cheap to hire enough personnel to run security efficiently"

              Indeed, what I often see is 20+ security checkpoint stations at the airport, with typically half or more of them closed, and long queues queuing for the rest.

              "passengers who are too cheap to allow airports to run security efficiently"

              Maybe, but only partly. It used to be that you had 1 security person at the scanner and one at the metal detector, you just put your bag on the belt and walked through the metal detector. Nowadays passengers have to take laptops etc out of their bags, liquids out in small bottles in a separate pouch, belts off, shoes off, body scanner which takes more time than stepping through a metal detector, random swabbing for explosives... not all of that every time, but enough of all that unnecessary security theater stuff that makes each passenger take double the time to get through. And then of course to keep everything moving smoothly, you need more security people to check that everyone is jumping through all the hoops. So you have double the amount of staff to take twice the time to handle the same number of people.

              Many airports relegate the cheap flights to the furthest reaches of the terminal, or another terminal altogether. If how much the airline was willing to pay was a factor to the airport, they could handle the security separately depending on which airline was being used. But in most airports all the security for all the flights pass through a single point.

              So sure, what passengers are willing to pay is a factor, and how airports balance passenger throughput with what they can competitively get paid from airlines is a factor. But it's mostly teh security theater rules themselves that are wasting everybody's time.

              1. Great Bu

                Re: This project must not be allowed to happen

                I would prefer the option of a 'no security' flight - if you are willing to take the risk on being exploded without any compensation then you and your like minded risk taker fellow passengers can just get on the plane straight from the parking lot and fly immediately.

                1. John Robson Silver badge

                  Re: This project must not be allowed to happen

                  And those on the ground who are affected by your explody plane?

                  1. Eclectic Man Silver badge
                    FAIL

                    Re: This project must not be allowed to happen

                    Aircrew might be difficult to find, and insurance premiums would be ... exorbitant, plus the problem with 9/11 was not merely that the aircraft were hijacked, but that they were crashed deliberately into occupied buildings, so this is pretty much not something any government would authorise, ever.

                    1. This post has been deleted by its author

                    2. jmch Silver badge

                      Re: This project must not be allowed to happen

                      Completely no-security flights would be a pipe-dream in this day ad age, but surely a sensible outcome can be reached?

                      People who know what they are talking about have said that the no. 1 security measure since 9/11 was securing the cockpit doors. That immediately cuts off the 'plane crashing into a target' scenario, and requires zero extra screening of the passengers. The next security risk is the attacker being able to target multiple passengers or the plane as a whole, meaning explosives or multi-rapid-shot-firearms. Any practical such firearm can be easily screened out with a simple metal detector*. In real life, there aren't any liquids that you can just mix to make a bomb, it's amazing that such fantasies still persist from a 2-decades-old Die Hard movie. Actual proper chemists with degrees and everything have investigated this and concluded that an attacker could either have a highly unstable liquid explosive likely to blow himself** up on the way to the airport, or else need a couple of hours locked in the loo with a portable lab to mix the stable ingredients to form a bomb.

                      More generally speaking, once the threat of the plane exploding mid-air or being used as a missile is ruled out, the risks are no different to that on a bus or plane, or to any mass gathering at a concert or sports event, all of which seem to manage without the 'security' inflicted on airplane travelers.

                      *I know guns can also be 3D printed, but the results so far are just enough to get off a couple of shots, not to bring a plane down. (also AFAIK the ammo still needs some metal component)

                      **other genders exist but the terrorists concerned always seem to be men, probably because women are a bit more sensible

                      1. MachDiamond Silver badge

                        Re: This project must not be allowed to happen

                        "**other genders exist but the terrorists concerned always seem to be men"

                        They are also mainly of a certain ethnicity/faith. Not a judgement, just an observation.

                      2. John Robson Silver badge

                        Re: This project must not be allowed to happen

                        "Actual proper chemists with degrees and everything have investigated this and concluded that an attacker could either have a highly unstable liquid explosive likely to blow himself** up on the way to the airport, or else need a couple of hours locked in the loo with a portable lab to mix the stable ingredients to form a bomb."

                        The idea that they'd be scared of blowing themselves up early when they intend to blow themselves up within a few hours anyway....

                        One could say "there aren't that many people exploding on the way to the airport, so it's unlikely that many are getting through"

              2. Yet Another Anonymous coward Silver badge

                Re: This project must not be allowed to happen

                >No, actually it's passengers who are too cheap to allow airports to run security efficiently.

                The airports need you to spend 3hours waiting and shopping. It's what airports make all their money on - the aeroplanes are an expensive annoyance.

                There have been a few attempts at business-class only UK-USA flights with no luggage, own security line, turn up 15minutes before and walk straight on - but the airports blocked them.

                1. Dave314159ggggdffsdds Silver badge

                  Re: This project must not be allowed to happen

                  Another example of the rule that there is literally nothing that the commentariat here can't turn into a conspiracy theory.

                2. Anonymous Coward
                  Anonymous Coward

                  Re: This project must not be allowed to happen

                  Do you have a link that explains that?

                  I'm pretty sure that when I buy a plane ticket, its price includes an airport tax. And more often than not, that tax is a big fraction of the total price, much more than I ever spent in airport shops. No matter how cunningly they were organized to force me to go through them rather than around-them...

              3. MachDiamond Silver badge

                Re: This project must not be allowed to happen

                "Many airports relegate the cheap flights to the furthest reaches of the terminal, or another terminal altogether."

                The airports aren't doing that directly. Airlines pay for gates, or gate time if they are sharing, and the cheapest gates will be the furthest from the main entrance. The most expensive gates will be right up front.

            2. MachDiamond Silver badge

              Re: This project must not be allowed to happen

              "No, actually it's passengers who are too cheap to allow airports to run security efficiently. If you want to pay peanuts for your flight to Majorca, the airlines can't pay for all those extra security bodies."

              In the US, it's Homemade Security that does the security in most airports rather than the airlines/airport. It's a branch of the government so there is no incentive for them to be quick, schedule enough staff or properly train that staff. I may be wrong, but I think it should be easy enough for the airlines to provide the number of booked passengers/times more than a week in advance and pad the numbers with the average number of last minute flyers they get. That would tell TSA (or equivalent) how much staff they might need. Too much to ask?

              It's like standing in a queue at the bank where they have 10 windows, 3 tellers and 5-6 people working at desks behind the tellers doing... what would they be doing in the age of computers? The DMV has adopted this model as well. DMV has taken it one step further by making sure the staff takes their mandatory breaks only during the busiest times of the day.

        4. werdsmith Silver badge

          Re: This project must not be allowed to happen

          Now, for transatlantic, you are looking at 3 hours checkin to takeoff. So that’s 10hrs 45 down to 6hrs 45. Only 30% quicker.

          VIP passengers and indeed first class passengers don't suffer the queues and waits that cattle class passengers do.

          1. Spherical Cow Silver badge

            Re: This project must not be allowed to happen

            The VIP lane saves time at the check in desk but not at passport control or security. Also, you might board first, but you won't take off sooner.

        5. Xalran

          Re: This project must not be allowed to happen

          Last time took the plane ( it was just before COVD lockdowns ) I only had to be at the airport gate 15 minutes before... which meant reaching the airport ( in my case ORY ) half an hour before and spending about 15 minutes navigating security and corridors to the gate... not 3 hours.

          Now this is valid for most EU Internal flights, and s definitely not valid when you fly wth some specifc companies where there's multple layers of security checks on top of the airport provided ones ( El Al for example )

          I can't imagine any company not offering a special fast lane through security along with supersonic flights, since the ticket price would be high enough to provide that kind of service ( and the people paying for supersonic flight expect that kind of service )

          1. MachDiamond Silver badge

            Re: This project must not be allowed to happen

            "I only had to be at the airport gate 15 minutes before... which meant reaching the airport ( in my case ORY ) half an hour before and spending about 15 minutes navigating security and corridors to the gate... not 3 hours."

            That might be true, but if there is any construction at the airport, which seems to be continuous, parking is full where you wanted to park and must now visit a lot further away. Just as you park up you will see the shuttle bus headed away so you have to wait 10-15 minutes for the next one to make its loop. I would guess you have no luggage, even carry-on and your boarding pass doesn't have the code "SSSS" meaning a trip to the back room and a bit of groping prior to departure.

            If you always pay the added fees for fully refundable tickets, go ahead and risk missing your flight by showing up at the last minute. Just make sure you aren't booking the last flight of the day or need to arrive at the destination before the next possible flight will get you there.

            1. Xalran

              Re: This project must not be allowed to happen

              *That might be true, but if there is any construction at the airport, which seems to be continuous, parking is full where you wanted to park and must now visit a lot further away. Just as you park up you will see the shuttle bus headed away so you have to wait 10-15 minutes for the next one to make its loop.*

              I'm not dumb enough to go to the airport with a car... that I don't own anyway. For ORY, from home, I have two options, both are about 20 minuteish... and reliable enough ( bus line, a bus ever 10 minutes, RER + Orlyval, one train every 5 to 7 minutes ) and soon I'll add a direct subway ( which will reduce the trip to 12 minutes )

              There's always construction works, but they are a non issue.

              * I would guess you have no luggage, even carry-on and your boarding pass doesn't have the code "SSSS" meaning a trip to the back room and a bit of groping prior to departure. *

              Just a carry on backpack... and the SSSS code doesn't exist here, so no back room groping. At worst you're tagged for a shoe & hand brush to check if you handled drugs or explosive, and it takes a minute for the result. ( which occurs while your putting back in your bag and pockets all the things you removed from there for the security check so no delay )

              As I said, this is only valid for flight inside the EU ( + Norway and Switzerland ), for flights across the Pond it's another matter... ( and CDG is much further away )

      2. imanidiot Silver badge

        Re: This project must not be allowed to happen

        Unstarts in Concorde where apparently basically impossible, because the design of the inlet ramps themselves and the computers controlling the inlet ramps being far more sophisticated than those of the SR71/A-12. Engine Surge was however possible and apparently quite spectacular and potentially destructive on Concorde.

        (As always, PPrUNE has an appropriate thread filled with nuggets of wisdom from those who flew her: https://www.pprune.org/tech-log/426900-concorde-engine-intake-thrust-5.html#post5944556)

        1. adam 40
          Happy

          Re: This project must not be allowed to happen

          Computers :-)

          Well, electronics.

          1. imanidiot Silver badge

            Re: This project must not be allowed to happen

            Computers, some of them completely analog.

    2. Anonymous Coward
      Anonymous Coward

      Wrong approach

      Try - "this project should not have public funds wasted on it". It should be privately funded, just as development of regular passenger aircraft are funded with the end goal of making a profit. (Not just operating profit, but also recovering development costs many times over).

      Supersonic large capacity passenger jets will never recover development costs(*). Finally, the result of following common sense economics would be the same - the project wouldn't happen.

      (* Maybe one small enough to carry Jeff Bezos and a dozen hangers on and bodyguards - that's possibly profitable for a production run of 100, all pre-paid orders, 10~100 million a jet - but should be privately developed.)

      1. M.V. Lipvig Silver badge

        Re: Wrong approach

        Actually, civilian flights would be a side benefit, not the actual goal regardless of what they say. A Mach 4 passenger plane is also a Mach 4 troop transport that can have a full company of men anywhere in the world in a couple of hours, 4 hours at the outside. NASA and the US military have worked closely together since 1958. It's no accident that astronauts almost always have military rank, while those who don't are always referred to as civiilian astronauts.

    3. MachDiamond Silver badge

      Re: This project must not be allowed to happen

      "I expect to be ignored and NASA will try to build this."

      NASA's mandate is science more than engineering and product development. The question they might be trying to answer is IF a hypersonic transport CAN be built large enough for passengers with enough range. So, it's a bit more engineering than typical, but maybe there will be technology spinoffs that apply to other aircraft.

      I agree that supersonic flight is not that useful these days. A flight on Concorde was on my bucket list years ago, but I didn't have any business case for paying the premium and could afford the time to take a standard sub-sonic flight if I had to. Even Concorde had limitations that really held it back. If you wanted to go from Los Angeles to Sydney direct and had the $12,000 to pay for business class, maybe a supersonic flight would be worth the few more $$ it would take to shave off a bunch of time if one could make that hop but Concorde couldn't. If was just going NYC to LHR, I don't see enough of a time savings to be worth a price increase. I'd prefer to bump up a class. The Concorde wasn't all that fancy due to the size of the airframe.

      1. Yet Another Anonymous coward Silver badge

        Re: This project must not be allowed to happen

        This project will be funded, but remember it is being funded NOT to build a SST

        Boeing are in serious trouble. They announced they aren't even going to think about designing a new airplane for the next decade. All their engineers left, to keep their pensions in the MD takeover, Boeing had planned to buy Embraer to get a bunch of young cheap Brazilian engineers, when that fell through they opened a design center in Moscow to get all those cheap Russian engineers !

        If US GovtNASA don't do something soon, Boeing are going to be reduced to half a dozen near-retirees doing 100 year updates on B52s and the next generation of US airliners are going to have to be bought from China - or worse - Airbus

        Grumman are getting in on it because they lost out to Lockheed-Martin on the F35 and the US Govt is smart enough not to be reliant on a single seller of shiny new fighter jets

        1. david bates

          Re: This project must not be allowed to happen

          Boeing have already demonstrated their inability to build an SST, so thats OK.

          1. Yet Another Anonymous coward Silver badge

            Re: This project must not be allowed to happen

            >Boeing have already demonstrated their inability to build an SST, so thats OK.

            Interesting conundrum.

            We could give the money to CMOT Dibbler Aviation, but since he has no record of failing to build an SST - it's just possible that he will successfully build one.

            So we have to give the handout to Boeing because they are the only ones with a proven ability to not produce a passenger plane.

          2. MachDiamond Silver badge

            Re: This project must not be allowed to happen

            "Boeing have already demonstrated their inability to build an SST"

            If I remember the story correctly, they didn't see a good business case for building one after they had done some preliminary designs and showed them to the airlines. The price would have been crazy if they were getting the impression that one airline might buy as many as 10 over the next decade. It was better to spend the time and money on other aircraft that lots of airlines would place regular orders for.

        2. imanidiot Silver badge

          Re: This project must not be allowed to happen

          Boeing is already dead. It's run by managers who don't understand how skill transfer works, how engineering legacy gets transferred from old to new engineers and how "technical debt" works. Not all knowledge in a company is documented and known. A lot of it is experience buried somewhere in the bony domes of the companies graybeards. Once Boeing management decided that engineers weren't important, the company was doomed. The whole 737-MAX saga is evidence of that. 787 isn't an undivided succes either. As is the whole Starliner stupidity on the space side of things.

          1. Yet Another Anonymous coward Silver badge

            Re: This project must not be allowed to happen

            >Boeing is already dead.

            Fortunately in centralised planned economies, strategic state assets can't be allowed to fail and will continue to be funded for the good of the people.

  2. bazza Silver badge

    Is a Mach 4 Airliner Possible?

    Hmmmmm.

    Above 40,000ft, or thereabouts, a human cannot survive even if breathing pure oxygen. The pressure they're breathing has to be higher (equivalent to a lower altitude) for enough oxygen to enter the bloodstream for survival.

    This is why U2 / SR71 pilots wear / wore full pressure suits, in case of cabin depressurisation (and ejection). Pilots of jets like Typhoon can wear partial pressure suits, that can squeeze them around the chest to stop them exploding when breathing air at > ambient pressure in the event of depressurisation. On the odd occassion aircraft like the EE Lightning got up to U2 heights, they were effectively taking a chance that they'd not get a cabin depressurisation when up that high.

    So hang on a mo. What did Concorde do about depressurisation? No special clothing was required, pilots and passengers just wore ordinary garb?

    The answer is that, for Concorde, its cabin pressursation blowers and air con could keep the pressure inside high enough to be able to breath and survive, even if two whole windows had blown out at 60,000ft / Mach 2. Had that actually have happened, it would have been extremely noisy inside and very uncomfortable, but the occupants would survive long enough on oxygen masks for the aircraft to descend to a more accommodating altitude.

    For a Mach 4 airliner, I can't see that flying below 90,000ft. To avoid a pressure suit it'd require a similar spec to Concorde's, but with at least another 30,000ft drop in pressure. That might not be so very different - there's barely any air at 60,000ft as it is. So perhaps that aspect of a Mach 4 airliner - ordinary cloting - is possible.

    1. karlkarl Silver badge

      Re: Is a Mach 4 Airliner Possible?

      > So perhaps that aspect of a Mach 4 airliner - ordinary cloting - is possible.

      What about TikTokers? Will they still be able to do their weird little dances between the isles?

      1. bazza Silver badge

        Re: Is a Mach 4 Airliner Possible?

        This sounds like a modern popular cultural phenomenon of which I have hitherto been entirely ignorant. Is my already tenuous belief in the sanity of humanity best served by 1) not Googling it to see it, and 2) spending more (or less?) on airline tickets so as to be in a class less likely blighted by such shifts in self-loading-freight?

    2. DS999 Silver badge

      Re: Is a Mach 4 Airliner Possible?

      This is no different from regular airliners which also pressurized. The only difference is in the degree of pressurization, but the difference between one atmosphere and zero atmospheres is really not all that great. No one worries (well maybe some do now after the Titanic thing) about those small subs that take tourists down to 50 ft which is a much larger pressure change. If windows are shown to a weak spot there's an easy fix - no windows on those planes. If necessary they could install OLED "windows" that show the outside view from cameras along the outside of the plane and few would care they aren't "real" windows.

      The big issues will remain noise and efficiency. The number of routes that could possibly benefit are a lot smaller if it is too loud to travel over populated areas, and airlines won't buy it if it requires so much fuel per passenger that they are taking a huge risk that there won't be enough rich people willing to fly it often enough that they make a profit. Then you have the risks of economic downturns, greater pressure from world governments against less efficient means of travel, or a black swan like finding that emissions at 90k ft are far worse in some important way than emissions at 35k ft.

      1. bazza Silver badge

        Re: Is a Mach 4 Airliner Possible?

        There's not much difference in the degree of pressurisation, but there is a massive difference in air flow. On a regular airliner, it has to be able to maintain pressurisation whilst dribbling air out the exhaust vent at a slow rate, and if it fails the passengers survive because the oxygen from the masks is sufficient to keep them alive. On Concorde, it has to be able to maintain partial pressurisation whilst there's two windows blown out - a huge rate of air flow - because oxygen alone would not keep the passengers alive at 60,000ft air pressure. Without that partial pressurisation they would asphyxiate, even on 100% pure oxygen.

        What's also not good is that the boiling point of water at 60,000ft is only 24C, so bodily fluids (such as is found lining lungs, blood, etc) start to boil if not kept at a higher pressure. At 40,000ft, boiling point is 54C, so no blood boiling there.

        1. DS999 Silver badge

          Re: Is a Mach 4 Airliner Possible?

          But why design for "two windows blown out" when windows are not a necessary component of a commercial airliner? Especially not one with a specialty market for rich people, who will want lie flat seats for a nap, showers so they can arrive fresh at their destination, and big screen TVs to entertain them during their three hour flight from LA to Tokyo?

          1. bazza Silver badge

            Re: Is a Mach 4 Airliner Possible?

            I dunno, you'd have to travel back in time and find out why. My guess is that they wanted passengers to have a view. Having decided, two popped windows is what they went with.

            1. DS999 Silver badge

              Re: Is a Mach 4 Airliner Possible?

              What I mean is in a Mach 4 airliner they don't have to make the same decision they did 50 years ago. When Concorde was designed windows were required for a view, because it would have been impractical to fit a CRT tube there instead. Today there are other options - if windows are compromising passenger safety we have the technology to eliminate them today without the weight/size penalty of a CRT tube, at a much higher quality of 'picture', and with no cost impact on the overall aircraft.

              1. Julz

                Re: Is a Mach 4 Airliner Possible?

                While your at it removing windows turn the seats 180 so in the event of 'landing' on water your forced into the seat back and not doubled up over the lap belt.

                1. DS999 Silver badge

                  Re: Is a Mach 4 Airliner Possible?

                  The aerodynamics required to travel Mach 4 might make survivable water landings impossible.

                  Plus some people get sick sitting backwards from the direction of travel, at least in cars. I suppose they could turn off their "window", but they'd see other people's windows. Nobody paying thousands of dollars for luxury air travel wants the smell of puke as the price of avoiding the tiny tiny inconvenience of having to put their head between their leads in a 1 in a million chance they need to attempt a water landing.

        2. SnailFerrous

          Re: Is a Mach 4 Airliner Possible?

          Not only do bodily fluids boil, but 24C boiling water at 60,000ft makes a lousy cup of tea.

    3. werdsmith Silver badge

      Re: Is a Mach 4 Airliner Possible?

      Virgin Galactic say hold my beer.

      I guess the risk is mitigated by how little time is spent in the danger zone.

      1. Richard 12 Silver badge

        Re: Is a Mach 4 Airliner Possible?

        Virgin Galactic are selling a thrill ride, not transport. I guess the risk is part of the thrill.

        The entire experience from takeoff to landing is about 90 minutes, most of which is spent dangling from the carrier aircraft fairly low in the atmosphere.

        It spends less than ten minutes at altitude, which is perhaps survivable if a window failed partway through. A passenger jet couldn't descend that fast, so...

        That said, SpaceShipTwo is entirely manually flown, so if the pilots pass out it will never feather or unfeather, creating a noticeable dent in the desert in either case.

        1. MachDiamond Silver badge

          Re: Is a Mach 4 Airliner Possible?

          "It spends less than ten minutes at altitude, which is perhaps survivable if a window failed partway through."

          Pete Siebold survived the breakup of the first SS2. He wasn't entirely unscathed, but alive. Mike didn't fare so well.

  3. Winkypop Silver badge
    Flame

    Heat

    Concorde was affected by heat created by the air rushing across control surfaces. This problem was engineered out. The internal expansion joints were quite wide. M4 sounds so much harder for a large passenger jet.

    Would I fly it? Definitely.

    1. Zolko Silver badge

      Re: Heat

      The Concorde's skin temperature was 110°C at Mach 2 cruise speed. The SR-71's skin temperature was about 250°C at Mach 3. So the main problem for a Mach 4 aircraft would indeed be heat and it's probably not solvable for a commercial aircraft. NASA cannot ignore this simple fact, which means that this project covers something else (where is the black helicopter icon ?)

      1. Antony Shepherd

        Re: Heat

        The SR-71 had expansion gaps so large to allow for metal expansion that sitting on the runway it would be constantly leaking fuel until it got up to speed.

        1. MachDiamond Silver badge

          Re: Heat

          "The SR-71 had expansion gaps so large to allow for metal expansion that sitting on the runway it would be constantly leaking fuel until it got up to speed."

          It would also be topped up via mid-air refueling which isn't an option for passenger flights.

          1. Yet Another Anonymous coward Silver badge

            Re: Heat

            >It would also be topped up via mid-air refueling which isn't an option for passenger flights.

            Not with that attitude !

            Also the SR71 leaked fuel not just because of the expansion joints, but because it didn't have fuel tanks. The special fuel it needed dissolved the rubber tank lining material of the day so it had to run with a wet wing

            1. MachDiamond Silver badge

              Re: Heat

              "Not with that attitude !"

              They didn't top up at 70,000', but after climbing out of the airport and warming up the fuselage. Depending on the mission, they might also re-tank after coming back down to where it was possible.

              1. Eclectic Man Silver badge

                Re: Heat

                Confused.

                If the SR71's pair of Pratt 7 Whitney JT58d* engines needed fuel that that ate through the rubber fuel tank linings, how did the fuel tanker aircraft carry it for refuelling after take-off? They would have needed some sort of sealing for the refuelling mechanism as the joints had to be flexible.

                * (if I have remembered the description from the 'Observers' Book of Aircraft' 1972 edition correctly)

                1. Yet Another Anonymous coward Silver badge

                  Re: Heat

                  Large metal cylinder tanks in the fuselage of the KC, because it couldn't mix it with its own JP4. I suspect most of the hoses and fittings would be stainless. Any gaskets or seals could be more easily replaced than the entire corroded lining of a built-in wing tank in the SR71

    2. Fruit and Nutcase Silver badge
      Black Helicopters

      Re: Heat

      SR-71 - loose fitting panels to allow for heat expansion...

      https://nodum.org/was-sr-71-blackbird-leaking-fuel/

    3. MachDiamond Silver badge

      Re: Heat

      Heat can be an issue, but fuel use is a real biggy. It's hard to go back to customers that booked and paid for their tickets a month ago and ask them for more money due to an increase in fuel costs. Using bog standard Jet-A is also going to be a limitation unless the aircraft only flies between limited destinations and the required fuel isn't substantially more money to produce.

  4. JimmyPage
    Happy

    The internal expansion joints were quite wide

    So much so that the last pilot of Concorde famously left his cap jammed between the instruments ...

    1. werdsmith Silver badge

      Re: The internal expansion joints were quite wide

      Somebody ripped that capped out of its eternal resting place (leaving some of the material still in the gap), a thief in Seattle.

      The torn piece was returned anonymously but couldn't be put back in place very easily.

  5. steelpillow Silver badge
    Boffin

    Civilian spend on, uh...

    This kind of hypersonic passenger plane is half way between Concorde and SpaceShip Three. Very high altitudes are necessary for the air to be thin enough to obtain these speeds, so the flight path will likely be semi-ballistic. The payback is that, despite the humunguous fuel burn, flight time is so short that seat-mile costs and pollution can actually fall; you don't have to spend several hours holding the thing up in the air. And if SpaceShip Three can go even higher while meeting safety standards, I don't see why this thing can't.

    The powerplant is likely to be a variable-cycle beast of some kind and, whether it's an airbreathing rocket/bypass-ramjet like SABRE or a turbo/ramjet like the SR-71, will feature Reaction Engines' revolutionary pre-cooler.

    The real problem will be thermal management. The SR-71 leaked fuel like a sieve until it warmed up and the gaps closed, SpaceShip Three uses a rocket but lacks the extended burn time. The cruise time of the SR-71 meant that fuel had to be circulated round the undercarriage bays to keep the tyres from melting. It used its fuselage-full of fuel tanks as a huge heatsink. By contrast a hypersonic passenger jet has to cool the whole fuselage - while having twice the heat to get rid of unless it flies so far up that it struggles for air. At least the sonic boom will be no real problem up there.

    I can't help wondering if this is all just a way to screw funding for black project hypersonic research out of the civilian budget.

    1. MachDiamond Silver badge

      Re: Civilian spend on, uh...

      "And if SpaceShip Three can go even higher while meeting safety standards, I don't see why this thing can't."

      Do you mean "SpaceShip 2" rather than "3"? Virgin Galactic is so far in the hole that I'd be surprised if they could raise money for a whole new craft. Their biggest issue has been that they didn't have the rocket engine done and dusted before the airframe was built so they were constrained to the initial size estimate for the motor. They still have some structural issues which is why there can be long intervals between flights. White Knight 2 is the bigger issue. It's rather old now and has had to have major restoration work done a couple of times to take care of cracks. For there to be a real SpaceShip 3, they still need to find a way to make a stable hybrid motor at the size they need first. It turned out that they don't scale as well as some thought. In the mean time, I have no doubt that lots of work will be done on tail number 3 of SpaceShip to make it better due to lessons learned from numbers 1 and 2.

      1. steelpillow Silver badge

        Re: Civilian spend on, uh...

        The first SpaceShip Three has been rolled out, so my comments are valid for both - technically assuming it gets its CofA I suppose, but let's be charitable there. I chose 3/III/Three because it is a production design, whereas 2 is essentially experimental and takes a handful of fare-paying passengers only to try and get Three up and running.

    2. david bates

      Re: Civilian spend on, uh...

      "Reaction Engines' revolutionary pre-cooler."

      It seems to have gone quiet on that front in the last few years, which suggests to me its being used in a black project. Skylon was always a red herring when the real market was always going to be military.

      1. werdsmith Silver badge

        Re: Civilian spend on, uh...

        Turns out it has uses beyond aero propulsion.

        1. John Brown (no body) Silver badge
          Joke

          Re: Civilian spend on, uh...

          Do tell?

          Are Birdseye funding research into freezing fishfingers faster? :-)

          1. John Robson Silver badge

            Re: Civilian spend on, uh...

            No because LN2 is already plenty fast enough.

            They do however now point out that peas frozen in the field are fresher than never frozen peas - and the speed of the freeze is important for those who don't like mushy peas.

            1. Eclectic Man Silver badge

              Re: Civilian spend on, uh...

              "peas frozen in the field are fresher than never frozen peas"

              Not if you literally grow your own in your back garden and pick what you want just before dinner, as my father used to.

              1. MachDiamond Silver badge

                Re: Civilian spend on, uh...

                "Not if you literally grow your own in your back garden and pick what you want just before dinner, as my father used to."

                They're super sweet when you do that, but I find it cheaper to buy frozen peas and grow berries and stuff that's often expensive. I run numbers on the cost to grow my own foods and something like tomatoes are too much to not buy instead. I'm estimating time to keep up with the garden as well. Tomatoes need looking after if you don't want to use pesticides. I have no idea how those caterpillars go from nothing to huge overnight.

      2. steelpillow Silver badge

        Re: Civilian spend on, uh...

        "It seems to have gone quiet on that front"

        Not really, I recently saw a public announcement of a cash injection to get the pre-cooler into a new generation of military jets. Reaction Engines have realised that it is wise to learn to walk before you try to run.

        1. bazza Silver badge

          Re: Civilian spend on, uh...

          I was quite impressed to find out that they'd used the hot exhaust from a jet engine as input air for their pre-cooler testing. In the heat exchange design engineering community, that probably counted as "showing off (aka deeply impressive)".

    3. John Brown (no body) Silver badge

      Re: Civilian spend on, uh...

      "I can't help wondering if this is all just a way to screw funding for black project hypersonic research out of the civilian budget."

      That was my first thought on reading the headline. The US seem to be behind the curve when it comes to hypersonic missiles, both Russia and China claiming to have productions models in service while the US appear to have cancelled the only thing close to working.

      With this is a starting point, and if NASA genuinely are looking at commercial hypersonic passenger flight, one wonders if they are so far behind the curve that one of SpaceXs originally stated goals of fast point to point passenger flights with Starship[*] may come sooner :-)

      [*] Not really, I doubt that will come to pass in my lifetime, if ever, not least because of the limited take-off and landing sites around the world, however, there's still Reaction Engines to keep in mind :-)

      1. MachDiamond Silver badge

        Re: Civilian spend on, uh...

        A big question is if a hypersonic missile is worthwhile. I'm sort of hoping a field trial isn't forthcoming to put theories to the test.

        The question of point to point rocket travel hasn't changed in 100 years. It's not feasible and not an improvement over regular airline flights that even when they are behind schedule are going to be much faster and safer on average. What problem would a rocket solve? Speed?, that's disproven given the operating requirements. Cost?, luxury first class on a premium airline is cheaper. You can get up and use the loo in-flight as well. Destinations become a big issue as well. The sound of big rockets means they have to be far away from population centers. Rockets also have a much less safe accident record than aircraft as well.

        I'll take the train, thank you very much.

  6. StrangerHereMyself Silver badge

    Energy

    The biggest problem IMHO is that the energy usage rises exponentially with speed and that this aircraft would therefore be economically unsustainable. Per seat prices would quadruple or more. That would translate into $3000 air fares for a NYC - LDN trip and well into the 5 figures for a ticket to Australia (if it's even feasible to fly such distances at that speed).

    Just because it's technically feasible doesn't mean it will become a reality. Only if they solve the sonic boom problem will these flights become somewhat economically viable, since land routes are shorter and therefore cheaper.

    1. adam 40
      Thumb Up

      Re: Energy

      First class is more than $3000, so I can see it would be a billy baaargin!

      1. StrangerHereMyself Silver badge

        Re: Energy

        I'm talking about $3000 for a cattle-class seat. A first class-seat will cost you the price of a luxury car.

    2. MachDiamond Silver badge

      Re: Energy

      "That would translate into $3000 air fares for a NYC - LDN trip"

      Out of curiosity, I looked up the cost of Los Angeles (LAX) to Heathrow (LHR) and business class was in the realm of $4,000 with baggage since it should be a huge flag if somebody is making that trip with no bags. I would expect a supersonic flight (or perhaps just NY to London supersonic) would cost closer to 3x that much or more. A 747 used about 4x less fuel and could carry more passengers on a flight than Concorde. Concorde used around 2 tons of fuel just to get from the gate to the end of the runway. Those hydrocarbons just keep getting more expensive so become something airlines pay close attention to.

  7. martinusher Silver badge

    The real problem with Concorde.....

    .....was that it wasn't an American product.

    Relatively few of us around now followed the development and politics surrounding this plane and also predecessor aircraft like the TSR2. It took a lot of political horsetrading for it to just get the two transatlantic routes it used. The reasons given at the time for the US not liking -- banning -- it were ecological (coming from the US at the time that was a bit rich) and the sonic boom (which wasn't anything like as dramatic as people keep saying -- it certainly wasn't anything like as loud as the Space Shuttle coming into Edwards AFB)(yes, I've experienced both). I contend that the fundamental problem with Concorde is that it outperformed most, if not all, US military jets. The SR71 is often quoted as faster/higher and so on but this wasn't a practical plane -- it leaked like a sieve on the ground and you had to change fuel load mid-air after taking off for the fuel needed for the supersonic/high altitude flight (while the Concorde's fluid problems were limited to chilling the chapagne -- supersonic or not that plane worked like a regular plane and could use exactly the same systems and procedures as any other civilian plane).

    Yes, Concorde was inefficient. Yes it was really noisy. But its a 1960s design and planes from that era were inefficient and really noisy by modern standards. The fact is that nobody's been able to build anything like it since.

    (If you don't believe the way that knocking works then you probably missed out on the PR campaign to get the A380 withdrawn and scrapped.....it was a big thing in the US prior to the 737-Max fiasco.)

    1. Yet Another Anonymous coward Silver badge

      Re: The real problem with Concorde.....

      >.....was that it wasn't an American product.

      Worse, it was French.

      After all the costs of the refit following the crash in France, Concorde was just getting back on its feet when 9/11 happened

      The attacks killed a lot of Concorde's regular customers and disincentivized a bunch of others from air travel.

      Then when we decided on Operation Dodgy Dossier, the "Cheese Eating Surrender Monkeys" failed to see the intelligence in having a war with a country that had bugger-all to do with the attacks.

      As a result even when BA Concordes returned to service, Air France were operating at 20%-25% capacity Paris-NY

      1. Xalran

        Re: The real problem with Concorde.....

        It was not just French... IIt was a cooperation between France and UK ( imagine Frogs and Rosbeefs cooperating to snub Rednecks )

      2. Potemkine! Silver badge

        Re: The real problem with Concorde.....

        No, it wasn't French only, hence its name of Concorde. Initially it was designed by Sud-Aviation and British Aircraft Corporation. At that time, the computer used for calculation and simulation was a CDC 3600, a monster at that time There were huge discussion between France and UK about how to write "Concorde". UK graciously accepted to add a "e", like in "Excellence, England, Europe and Entente".

        The US did whatever possible to kill Concorde, to protect its Aerospace industry who was lagging berhing. For instance, Kennedy himself put a lot of pressure on PanAm when he learned PanAm was ordering 6 Concorde.

        1. Yet Another Anonymous coward Silver badge

          Re: The real problem with Concorde.....

          Yes everyone knows it was Anglo-French. But the problem from the American point of view was that the French one went to France, the problem from the French point of view was that no Americans wanted to go to France, no French wanted to fly to America and the flagship of French technical prowess was being beaten by Le Rosbif

    2. Neil Barnes Silver badge

      Re: The real problem with Concorde.....

      Yes, Concorde was inefficient. Yes it was really noisy. But its a 1960s design and planes from that era were inefficient and really noisy by modern standards. The fact is that nobody's been able to build anything like it since.

      That, and that there's something really cool about a commercial passenger jet that could outdrag virtually all the jet fighters out there at the time _and_ keep it up for three hours...

      (favourite cartoon from the time: two engineers looking at the droop-nose and commenting 'why yes, Caruthers, it *is* eating ants!')

      1. PerlyKing
        Go

        Re: The real problem with Concorde.....

        It could outdrag virtually all the jet fighters. I'll give you the three hours thing ;-)

        1. Yet Another Anonymous coward Silver badge

          Re: The real problem with Concorde.....

          In fact to even take the only photo of it in supersonic flight the RAF had to strip a Tornado down to the minimum weight, give it a head start and red-line the engines, while the Concorde had to throttle back to Mach 1.5

          1. Eclectic Man Silver badge

            Re: The real problem with Concorde.....

            On paper Concorde was faster (Mach 2) than the original USAF F-16 (Mach 1.95).

            The Olympus engines were supposed to be used in the UK's TSR-2, but the Wilson government scrapped it, even though it was technically very capable, though I don't know its design top speed.

        2. MachDiamond Silver badge

          Re: The real problem with Concorde.....

          "It could outdrag virtually all the jet fighters. I'll give you the three hours thing ;-)"

          In the real world, any jet fighter would need to get a go order far enough in advance to make a fuel optimum intercept. Some fighters can go faster, but not long enough to do anything useful. Even firing a missile might amount to nothing.

    3. david bates

      Re: The real problem with Concorde.....

      It always amazes me that even now there are about 8 supercruise capable aircraft according to Wiki, and Concorde could supercruise faster than any of them.

      1. adam 40

        Re: The real problem with Concorde.....

        They think that theoretically, with a few optimisations, Mach 2.3 would be possible in bursts.

        Not too long or the fuel would overheat.

    4. phuzz Silver badge

      Re: The real problem with Concorde.....

      the fundamental problem with Concorde is that it outperformed most, if not all, US military jets

      It's not just the speed, it's the range too. Concorde could supercruise at mach two across the entire Atlantic. An F-22 can go faster, but not for as long.

      I've heard that the average Concorde pilot clocked up more supersonic hours in one year, than every USAF pilot put together.

      1. MJI Silver badge

        Re: The real problem with Concorde.....

        The whole Concorde fleet holds more supersonic hours than all other aircraft together.

    5. Marty McFly Silver badge
      FAIL

      Re: The real problem with Concorde.....

      >you had to change fuel load mid-air after taking off for the fuel needed for the supersonic/high altitude flight

      Uhh... No. The SR-71 used the same JP-7 on the ground, launching, and at super-sonic speed. Yes, the special KC-135Q tankers had to manage multiple fuels types as they burned JP-4.

      1. Yet Another Anonymous coward Silver badge

        Re: The real problem with Concorde.....

        Perhaps the confusion is that the SR71 took off with almost empty fuel load. It's a very heavy aircraft with the low speed aerodynamics of a brick so had a very high take-off speed. In case of an 'oops' you want the minimum fuel load and mass.

        That means you then start flying with tanks full of highly flammable fuel vapour (not good). It had a N2 purge system but with limited capacity, so you want to get the tanks full of nice cold JP7 as soon as possible. This is fine since you are probably going to be doing multiple refuelling to get to the picnic spot to take the photos.

    6. Eclectic Man Silver badge

      Re: The real problem with Concorde.....

      Reading the accumulated posts in response to yours, martinusher, I am even more impressed with the Concorde aircraft than I was before. Even though it could not carry a full load of passengers on the London - New York route, for which it was in theory designed, it seems to have been a genuine technological masterpiece of its day.

      Makes me feel rather nostalgic, even though I never flew in it.

      I did hear a radio program that it was the subject of considerable attempts by Russian agents to obtain technical information. To the extent that one 'operation' was to scrape rubber off the tarmac where it had landed to be analysed. MI5 got there first and ensured that the 'sample' had the consistency of chewing gum. The other problem the Russians had with their rival, the Tupolev Tu144, was the absence of any long routes to fly over sea, so the sonic boom was a bit of a problem.

      1. MachDiamond Silver badge

        Re: The real problem with Concorde.....

        "The other problem the Russians had with their rival, the Tupolev Tu144, was the absence of any long routes to fly over sea, so the sonic boom was a bit of a problem."

        The USSR didn't head the complaints of the peasants so flying over land (USSR held territory) and making noise doing it wasn't a big deal.

      2. druck Silver badge

        Re: The real problem with Concorde.....

        Most of Russia is empty if they even cared about anyone on the ground, but more of a problem was the noise level inside the Tu-144 of 90-95db which is about the same as on the outside of most aircraft.

      3. Xalran

        Re: The real problem with Concorde.....

        The main problem of the Soviet Concordsky was that the spy didn't manage to get the exact values used for the wings.... they only managed to steal "work in progress" values which led to a double angled wing on the TU-144 while the Concorde has a double curved one. This forced the TU-144 to have canard wings in front... because the Soviets wanted to have, and show their supersonic before the West.

    7. MachDiamond Silver badge

      Re: The real problem with Concorde.....

      "The fact is that nobody's been able to build anything like it since."

      There isn't a business case for an aircraft like that which is what killed the Concorde. It's even worse now as we can have high-res video conferences with people on the other side of the planet using our phones. Maybe there would be a case for a supersonic cargo aircraft so a company that's waiting for parts that are anchored off the coast of a major port can get enough in a hurry to keep a production line from needing to be shut down. I wouldn't be surprised if an auto assembly line being shut down for lack of parts might cost as much as $1mn/hour in lost revenue. Years ago I dated a women that worked at GM and the cost was $125k/hour for a line to be shut down. Spending $20k to hire a private jet to ferry in components was something that didn't even need to be approved from higher up (justified later, sure).

  8. xyz Silver badge
    Trollface

    Mind you mach 4....

    Will still be faster than Teams loading.

  9. MJI Silver badge

    Wrong companies

    Try Airbus, they actually suceeded (sort of), well their predecessors did.

  10. CowHorseFrog Silver badge

    Morons....

    Wasting their life flyihg thousands of mile just to give a powerpoint presentation...dont they have anythign better to do ?

  11. ecofeco Silver badge

    Again?

    Does this mean the flying car is finally coming as well?

    /s

    1. MachDiamond Silver badge

      Re: Again?

      "Does this mean the flying car is finally coming as well?"

      I've never worried about flying cars being a thing. A ratty old Cessna 150 is still a chuck of money to buy, keep certified and fly. A brand new modern flying car that has been compromised in all sorts of way to be able to perform both modes isn't going to be cheap to buy or operate. That C150 is going to be a bargain in comparison and you'd still need an airport/strip at either end in both cases. The 'copters are an even worse case for private transportation. I was working with a guy on an interesting STOL hybrid aircraft for firefighting but he passed away before we ever got to building hardware. That sort of niche application seems like a much more feasible application and investment.

    2. Alan Brown Silver badge

      Re: Again?

      Look at all the scrapes and dings on cars in the average supermarket car park

      Would you trust the average driver (or their car) to be airborne?

  12. Alan Brown Silver badge

    Major issue in sight

    Forgetting all the issues with engines and efficiency, these proposals invariably run into 2 major issues which grounded the Boeing 2707

    1: Going much faster than Mach2 requires specialist and very expensive metallurgy due to friction heating.

    Stainless steel is doable on Rockets because the heat impulse is short lived (launch and reentry are minutes, not hours)

    2: At these speeds, sonic booms are a major problem even if the aircraft is at 60-100,00 feet

    XB70 proved this in the 1960s and SR71 operations underscored it - people can put up with a couple of light booms a day but not the kinds of repetition associated with commercial operations

    NOISE is a major major issue and it's _already_ limiting speeds on terrestrial high speed trains - Shanghai maglev had to be slowed down most of the day (it only hits max speed on runs for a 2 hour afternoon window on weekdays. slowing down further after dark) and the much-vaunted Japanese maglev Shinkansen is likiely to face similar protests before commercial operation, despite being routed away from occupied areas as much as possible.

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