[Herra Tohtori]

The European Space Agency's goal is to create a hypersonic passenger plane, one that flies more than five times faster than the speed of sound and six times faster than a standard airliner.

It's not the first time hypersonic flight has been attempted. In 1960, tests took place on the X-15 - half plane, half missile - which carried one pilot and flew for 90 seconds before its rocket fuel burnt out.

Its creators thought it would herald a new era of high-speed civil aviation but more than 50 years later, a hypersonic passenger plane has yet to be tested or even built.

Now a team led by the European Space Agency, known as Lapcat, are working on an aircraft called the A2, which could take up where the X-15 left off.


(...)

The A2 will not be able to fly to New York, the world's busiest business-class route, as the distance is too short for it to reach the necessary altitude.

Mandatory comment:

Awesome.


Discuss.

[Nuke]

is that the one with the sabre derivative engine? its essentially a sabre with a turbine instead of a rocket.

[The E]

Question is if it's actually a viable idea economically. If the Frankfurt/New York route (or Heathrow/NY, or <any major european airport>/<any major east-American airport> route)  can't benefit from this, I believe this to be not as efficient as it can be.

That said, if it can sidestep the issues associated with Concorde (namely, that Concorde could only fly transoceanic routes), then it looks a bit different.

[FreeSpaceFreak]

Sure, it's cool, but economically viable? Doubt it. Especially if they'll need to make detours on the busy Europe-East USA routes. Actually, with noise restrictions, the whole of Europe seems pretty much a no-go. And with tele-conferences and in-flight internet, the amount of people willing to pay a lot for a fast flight is now smaller than ever. And it is gonna cost a lot, that's for sure.

Could make a good mothership for space launches though, if they ever get the technical side of it working of course.

[BloodEagle]

I dislike that article.  It tries to make you think that we haven't already done this.

[TwentyPercentCooler]

Sure, it's cool, but economically viable? Doubt it. Especially if they'll need to make detours on the busy Europe-East USA routes. Actually, with noise restrictions, the whole of Europe seems pretty much a no-go. And with tele-conferences and in-flight internet, the amount of people willing to pay a lot for a fast flight is now smaller than ever. And it is gonna cost a lot, that's for sure.

Could make a good mothership for space launches though, if they ever get the technical side of it working of course.

It really depends on the design. Aircraft flying fast enough actually don't generate large sonic booms, especially because a hypersonic aircraft would want to by flying very high to reduce air resistance. The only times it would need to have restrictions places on it would be during ascent/acceleration and descent/deceleration. From our experiences with the SR-71 and, more recently, the X-43 and X-51, commercial viability really isn't that unlikely. Really, supersonic flight is extremely inefficient, but once you start getting into the hypersonic range, things get a little less obvious. The more people conducting research on hypersonic flight, the better it'll be for everyone, especially since we're going to need a lot of data on the behavior of these kinds of vehicles for orbital spaceplanes.

One of the biggest problems they're gonna have is sinking the absolutely massive amount of heat that skin friction is gonna produce, especially in a way that won't either cause an explosion or cook the passengers anyway in the event of a failure. Cycling the fuel is unlikely to work, unless it's cryogenic...which is enough of a problem in itself.

[Thaeris]

is that the one with the sabre derivative engine? its essentially a sabre with a turbine instead of a rocket.

Yes, it should be. That design, along with the design of the SABRE engine, Skylon, etc., are the proposals of this company:

http://www.reactionengines.co.uk/

[Black Wolf]

Yes, London to New York is a big route, but how long before London-Beijing or New York - Shanghai become more important? Gotta think about the future for projects like this.

[Herra Tohtori]

The article mentioned that to be economically viable, this thing requires a new, cheaper way to produce LH₂.

Efficiency improvements aside, there's no way around the energy requirements. You need a lot of energy to produce lots of hydrogen, regardless of how efficient you can be with it.

This basically brings up the old question of mine - why aren't the governments of the world investing more, significantly more, on research and development of viable fusion reactors.

Or, the inversion: Since this kind of things are seriously considered... does someone know more than general public about the timeframe in which fusion reactors will become available?


The main reason I'm interested in this (and excited by it) is the prospect of expanding this flight regime from experimental/military birds to commercial aviation. The ability to build a consistently safe airframe that you can hurl through atmosphere at hypersonic speeds will develop the technologies required for sub-orbital shuttle transportation, which will again serve as the development step for true, commercial space travel. It's one thing to build an unmanned drone or single person aircraft, and entirely other to build a space plane capable of safely seating a multitude of passengers and their luggage.

Currently there is no need for commercial space travel, since there's literally nowhere to go yet outside the atmosphere. However I hope that orbital installations will eventually be built that will require regular transportation capacity, be it for scientific, commercial, or both purposes. From there, it will be easier to stockpile stuff on orbit, and assemble ships for further missions. Widely accessible and affordable access to low earth orbit is, in my opinion, the single biggest hurdle to overcome in the future of humans as a spacefaring civilization, and anything that can further that goal is good in my eyes.


...weell, developing FTL would be a bigger problem, but since at the moment it seems to involve circumventing a few laws of nature, I'm going to ignore it so far and concentrate on establishing humanity's presence in the larger Solar system.

[Nuke]

we could have had fusion in the 70s if we would have gone the brute force route. icf with particle accelerators.

[FreeSpaceFreak]

It really depends on the design. Aircraft flying fast enough actually don't generate large sonic booms, especially because a hypersonic aircraft would want to by flying very high to reduce air resistance. The only times it would need to have restrictions places on it would be during ascent/acceleration and descent/deceleration.

Indeed it's not the cruise that'll be the problem, but it will have to use airports in the neighbourhood of major cities (if not, where's your time gain?). With an airplane designed for those cruise conditions, you can't even reach a high altitude without enough airspeed; they'd probably have to take a detour over the North Sea or the Atlantic to climb and go supersonic.

From our experiences with the SR-71 and, more recently, the X-43 and X-51, commercial viability really isn't that unlikely. Really, supersonic flight is extremely inefficient, but once you start getting into the hypersonic range, things get a little less obvious.

Air drag scales by velocity squared, regardless of whether you're subsonic, supersonic or hypersonic. I'm not sure how you link the SR-71, X-43 and X-51 to commercial viability? They merely show it can technically be done, when provided with a considerable budget.

The more people conducting research on hypersonic flight, the better it'll be for everyone, especially since we're going to need a lot of data on the behavior of these kinds of vehicles for orbital spaceplanes.

That (and marketing) might be the main reason for ESA to get into this... I can't imagine they'd hope to make this a commercial success where so many others have failed.

One of the biggest problems they're gonna have is sinking the absolutely massive amount of heat that skin friction is gonna produce, especially in a way that won't either cause an explosion or cook the passengers anyway in the event of a failure. Cycling the fuel is unlikely to work, unless it's cryogenic...which is enough of a problem in itself.

It's LH2, it is cryogenic. Which, indeed, poses enough problems in itself. I wonder how much of the hull is fuel tank, and how much is payload compartment

[headdie]

One of the biggest problems they're gonna have is sinking the absolutely massive amount of heat that skin friction is gonna produce, especially in a way that won't either cause an explosion or cook the passengers anyway in the event of a failure. Cycling the fuel is unlikely to work, unless it's cryogenic...which is enough of a problem in itself.

It's LH2, it is cryogenic. Which, indeed, poses enough problems in itself. I wonder how much of the hull is fuel tank, and how much is payload compartment

That would depend on things like how much time the the designers allow the plane to spend at sub cruise speed.

It really depends on the design. Aircraft flying fast enough actually don't generate large sonic booms, especially because a hypersonic aircraft would want to by flying very high to reduce air resistance. The only times it would need to have restrictions places on it would be during ascent/acceleration and descent/deceleration.

Indeed it's not the cruise that'll be the problem, but it will have to use airports in the neighbourhood of major cities (if not, where's your time gain?). With an airplane designed for those cruise conditions, you can't even reach a high altitude without enough airspeed; they'd probably have to take a detour over the North Sea or the Atlantic to climb and go supersonic.

UK-US routes already fly up to Scotland and across because believe it or not due to the curvature of the Earth this is shorted than flying strait across the Atlantic at London's latitude, it would only be a slight tweak of the international flight paths to take them up the north sea for the hypersonic planes to do their climb.  if there is an issue it would be damage to the North Sea oil platforms.

All in all the plane would have to be used long haul to make the best use of it's speed, but the speed increase and the, I presume, reduced Sonic Boom once cruising would make it more viable than concord with a decent passenger capacity.

[Nuke]

Air drag scales by velocity squared, regardless of whether you're subsonic, supersonic or hypersonic. I'm not sure how you link the SR-71, X-43 and X-51 to commercial viability? They merely show it can technically be done, when provided with a considerable budget.

its more complicated than that. the equation for drag looks something like this:

F = 0.5*D*V^2*A*Cd

where force is F air density is D, velocity is V, A is the cross section of the aircraft (as appears perpendicular to velocity vector), and cd is your coefficient of drag. making a low drag aircraft involves reducing cross sections, using laminar flow airfoils. you can kinda optimize for better Cd through experimentation in the wind tunnel and computer models, identify areas of high Cd in you design and redesign those areas and retest.

but here is where it gets complicated. when you pass into supersonic, a cone shaped shock front forms. when this happens local air velocities on parts of the aircraft within those cones, like wings and most of the fuselage, are for the most part sub sonic, and the above equation applies with the local sub-sonic air velocity. thats why supersonic aircraft have pointed protrusions (pointed fuselages and shock cones) at the front to reduce the amount of cross section exposed to supersonic airflow. the sr-71 needed to be refueled immediately after take off, but once it got supersonic, the engines became far more efficient, and overall drag is actually somewhat reduced during supersonic flight. im not sure what happens when you go hypersonic though.

[TwentyPercentCooler]

Air drag scales by velocity squared, regardless of whether you're subsonic, supersonic or hypersonic. I'm not sure how you link the SR-71, X-43 and X-51 to commercial viability? They merely show it can technically be done, when provided with a considerable budget.

its more complicated than that. the equation for drag looks something like this:

F = 0.5*D*V^2*A*Cd

where force is F air density is D, velocity is V, A is the cross section of the aircraft (as appears perpendicular to velocity vector), and cd is your coefficient of drag. making a low drag aircraft involves reducing cross sections, using laminar flow airfoils. you can kinda optimize for better Cd through experimentation in the wind tunnel and computer models, identify areas of high Cd in you design and redesign those areas and retest.

but here is where it gets complicated. when you pass into supersonic, a cone shaped shock front forms. when this happens local air velocities on parts of the aircraft within those cones, like wings and most of the fuselage, are for the most part sub sonic, and the above equation applies with the local sub-sonic air velocity. thats why supersonic aircraft have pointed protrusions (pointed fuselages and shock cones) at the front to reduce the amount of cross section exposed to supersonic airflow. the sr-71 needed to be refueled immediately after take off, but once it got supersonic, the engines became far more efficient, and overall drag is actually somewhat reduced during supersonic flight. im not sure what happens when you go hypersonic though.

Yep. It's not anywhere near as simple as saying air resistance increases with velocity. Hypersonic craft do have to travel at high altitudes (100,000+ ft) to mitigate the effects of air resistance, but, when you get into the hypersonic range, you have to deal with effects like molecular dissociation of gas particles and ionization effects, not to mention that almost all aircraft designs don't have uniform airflow in the first place. It's a very interesting area of study and it's something we still don't understand very well, despite having several aircraft and projects that have traveled in the hypersonic range. The X-15 pilots, especially, had some absolutely enormous brass ones. They were basically strapped to a manned missile with no real landing gear and minimal control surface cross-sections, so that they could reach speeds at which the aerodynamic effects were almost completely unknown at the time. Amazing. 

Of course, the U.S. government and NASA are still pretty far ahead of the game in designing hypersonic aircraft. The extent to which their funding has been cut for these studies is CRIMINAL. Out of curiosity, is anyone else here remotely interested in whether or not the Aurora exists? I'm not a conspiracy nut or anything, but it's fun to think about.

And, as Nuke mentioned, I brought up the SR-71 because it actually got more fuel efficient at higher speeds because of its engine design (essentially, they ceased to be turbojets and instead became ramjets at high speeds). In fact, its top speed was actually limited by the behaviour of the supersonic airflow through the engine inlets and by heat buildup rather than by more traditional thrust:weight ratios. Experiences with the SR-71 and other projects like the X-15 showed us that hypersonic aircraft design is very, very different than supersonic aircraft design.

http://www.grc.nasa.gov/WWW/BGH/index.html is a pretty good summary of why it's different, but needless to say, everything we learn about hypersonic travel from the X-43 and the X-51 can certainly be applied to other projects that intend to produce hypersonic aircraft, whether they be airliners or reusable spaceplanes.

[Mongoose]

The other fun thing about the SR-71 is that it apparently leaked fuel like a sieve on the ground and during take-off, since many of its surfaces and fittings were designed to expand from the high temperatures generated by its top speeds.  I got to see one at the Air & Space Museum annex at Dulles Airport (fantastic place), and the info card there mentioned that they had flown that particular aircraft from California to DC in right around two hours.

[TwentyPercentCooler]

The other fun thing about the SR-71 is that it apparently leaked fuel like a sieve on the ground and during take-off, since many of its surfaces and fittings were designed to expand from the high temperatures generated by its top speeds.  I got to see one at the Air & Space Museum annex at Dulles Airport (fantastic place), and the info card there mentioned that they had flown that particular aircraft from California to DC in right around two hours.

I bet the ground crews were relieved that JP-7 was pretty hard to ignite, otherwise that would have been a heck of a fire hazard. I've seen the Blackbird, too, it's an absolutely incredible aircraft, even today. The engine design especially was way ahead of its time. Supposedly, newer materials used for the shock cones and inlets would have set an upper speed limit of around mach 6 for engine operation; I'm curious as to how fast the Blackbird could have gone with the benefits of new materials.

[Nuke]

Of course, the U.S. government and NASA are still pretty far ahead of the game in designing hypersonic aircraft. The extent to which their funding has been cut for these studies is CRIMINAL. Out of curiosity, is anyone else here remotely interested in whether or not the Aurora exists? I'm not a conspiracy nut or anything, but it's fun to think about.

i saw a ufo once when i was 5, some years later i saw the same ship at an airshow, it was an f-117. the skunk works is still in buisness, so rest assured they are designing and producing things now that will be classified for decades to come. they probably have 20 or 30 year old projects still classified. and i wouldn't doubt that most ufo reports are of these vehicles.

[TwentyPercentCooler]

Of course, the U.S. government and NASA are still pretty far ahead of the game in designing hypersonic aircraft. The extent to which their funding has been cut for these studies is CRIMINAL. Out of curiosity, is anyone else here remotely interested in whether or not the Aurora exists? I'm not a conspiracy nut or anything, but it's fun to think about.

i saw a ufo once when i was 5, some years later i saw the same ship at an airshow, it was an f-117. the skunk works is still in buisness, so rest assured they are designing and producing things now that will be classified for decades to come. they probably have 20 or 30 year old projects still classified. and i wouldn't doubt that most ufo reports are of these vehicles.

Yeah, I don't really believe that UFOs are extraterrestrial craft, for reasons that belong in another discussion. It's a much more likely and much simpler explanation that the government just has a bunch of stuff flying around that we civvies can't identify, like they've been doing since...oh, I dunno, forever? Hell, places like the Skunk Works and the agencies probably love the alien conspiracy kooks. They're rolling around laughing at the multiple levels of crazy while they don't even have to bother denying that they're working on secret projects. "Uh...yeah, it was aliens, good theory! We'll look into it.  "

[Nuke]

i remember the whole 90s ufo craze. so many people sucking up and parroting american propaganda without even knowing it

[FreeSpaceFreak]

UK-US routes already fly up to Scotland and across because believe it or not due to the curvature of the Earth this is shorted than flying strait across the Atlantic at London's latitude, it would only be a slight tweak of the international flight paths to take them up the north sea for the hypersonic planes to do their climb.  if there is an issue it would be damage to the North Sea oil platforms.

Well, the shortest route London-NYC is over Ireland, not Scotland (link) - flying that much more up north might have more to do with ETOPS restrictions (diversion airports along the way) than actual economy. But you're right, it's being done already, so a detour may not be that big an issue.

its more complicated than that. the equation for drag looks something like this:

F = 0.5*D*V^2*A*Cd

where force is F air density is D, velocity is V, A is the cross section of the aircraft (as appears perpendicular to velocity vector), and cd is your coefficient of drag. making a low drag aircraft involves reducing cross sections, using laminar flow airfoils. you can kinda optimize for better Cd through experimentation in the wind tunnel and computer models, identify areas of high Cd in you design and redesign those areas and retest.

but here is where it gets complicated. when you pass into supersonic, a cone shaped shock front forms. when this happens local air velocities on parts of the aircraft within those cones, like wings and most of the fuselage, are for the most part sub sonic, and the above equation applies with the local sub-sonic air velocity. thats why supersonic aircraft have pointed protrusions (pointed fuselages and shock cones) at the front to reduce the amount of cross section exposed to supersonic airflow. the sr-71 needed to be refueled immediately after take off, but once it got supersonic, the engines became far more efficient, and overall drag is actually somewhat reduced during supersonic flight. im not sure what happens when you go hypersonic though.

When you go hypersonic, the cone becomes sharper (sin(beta) = 1/M, where beta is the angle between axis and side of the cone). At M = 5, beta is around 11.5deg. Behind a shockwave that sharp, and with that inflow velocity, you still have supersonic flow (it's only normal shocks that always lead to subsonic flow, which you don't want on an airplane, since it causes excessive drag). More interesting is that the shockwave will pretty much lie flat on the airplane surface (look at the picture in the article, the nose cone angle seems about 10 deg) and start interacting with the boundary layer. Which is complicated and a pretty much unknown realm for now. But really, I doubt that it'll lead to large efficiency increases over lower airspeeds; the equation you mentioned is correct, and V^2 is still in there

I brought up the SR-71 because it actually got more fuel efficient at higher speeds because of its engine design (essentially, they ceased to be turbojets and instead became ramjets at high speeds). In fact, its top speed was actually limited by the behaviour of the supersonic airflow through the engine inlets and by heat buildup rather than by more traditional thrust:weight ratios. Experiences with the SR-71 and other projects like the X-15 showed us that hypersonic aircraft design is very, very different than supersonic aircraft design.

Fuel efficiency is one thing, actual fuel flow is another - I doubt the SR-71 could have done a certain distance with less fuel than a subsonic aircraft, even if it could have flown at optimum speed. And then there's weight (even just the cooling system) and noise (high-speed engines tend to be noisy at take-off) issues, and maintenance of course (flying at higher altitudes means more fatigue on the hull, for one). I'd be surprised if supersonic aircraft will ever be more economical than the subsonic airliners we have now, however cool they may be.