Airbus Wins Patent For 'Concorde 2' Hypersonic Passenger Jet
Funny article, as in very poor reporting. I don't think a ramjet will work outside the atmosphere. But then again 18mi is only 95k, so don't see the reason why they would use a 'conventional rocket booster'.
I saw stuff like this in Boeing PD 25 years ago. I was also wondering how well a ramjet would work with little or no air to compress...unless it was going umpteen thousand MPH. What the heck do I know, anyway, that stuff is too far out for me.
Probably just a red herring to throw people off from what they are really doing... A patent like that is cheap to file, their patent staff could whip it up in a day to two and throw it over the wall. Think of it as way to reduce boredom in the workplace... Boeing will now spend close to 4 man years at a cost of over a million dollars to figure out the concept is worthless... Besides, by the time Airbus got the plane to market the patent would have long expired.. Lest you think I jest, look at how long it took them to bring the A400 to market, and there wasn't any new technology in that plane. There are going to have to be some very serious inventions made to pull this one off and I can tell you from experience that "It's very hard to invent something on a rigid schedule"!!! Countless dollars have been spent looking at trying to come up with a high Mach airliner.. Remember the "Orient Express" that was in Av Leak about 20 years ago... yea, we have a lot of them flying around too.. When you run the numbers objectively going faster than an aluminum airplane can go (around Mach 2+ a bit), the cost, and weight go though the roof and the payload shrinks down to a small crew, and the faster you go the smaller the payload gets (think SR-71 and B-70)... Oh yea, and we've got new materials that we can make this out of right.. Well, not really, when you get that hot there aren't any new materials other that titanium aluminide that work up there and that stuff is hell to work with.. The guys doing the Concorde and the SST were no dummies. They figured out pretty quickly that there was no pony in the high Mach pile and they went as fast as they could with what they had, and today it isn't much different....
It's not the fiber that is limited, rather the matrix. Regular epoxy resins are only good up to 180degF after which properties start falling fast. Then there are bismalimide and polyimides resins which have operating temps up to 450-600degF. But they can have other issues too (e.g. heat cycling induced micro-cracking).
Engineers have been trying to push the strength to weight ratio of materials in the temperature range where aluminum goes to taffy for an awfully long time. As noted above it isn't the carbon fiber that is the issue, it's the matrix that holds it together that goes soft and both the compressive and interlaminar shear strength goes down the toilet... Titanium is a wonderful material, but it weighs 70% more than aluminum. Think about that for a minute. Make the airframe weight of an airplane like the Concorde 70% heavier and look at what happens to the payload.. It doesn't take a rocket scientist (or an airframe designer) to realize that if you want to go faster you need a breakthrough in fuselage materials. GE has had some success with making low pressure turbine blades out of titanium aluminide. This is a hybrid material that has better high temperature properties than aluminum but is lighter than titanium, but the material is extremely brittle and doesn't lend itself into being made into thin sheets, never mind trying to join a material like that with any conventional joining process. Gas turbines have temperatures inside from -65 F (inlet temps at altitude) all the way to 3000+ degrees in the combustor. The internal temperatures rise up from the inlet thru to their peak at the combustion primary zone, and then drop down to 400 or so depending on the bypass ratio. The turbine industry has been at the forefront of developing high temp materials since if you can substitute a material that is more capable, you can take out some cooling and there is a big gain in performance from that. Other than the aforementioned TiAL, we're pretty much using the same materials that we've used for the last 30 years. The real gains haven't come in material capability, but the ability to use finite element analysis to more accurately predict the stress in parts and make them lighter by taking material out of low stress areas. The other issue is keeping the payload cool. When you get to Mach numbers like the SR-71 flew at, the air at the INLET of the engine is over 900 degrees F, and that's the same temperature that is on the skin of the airplane behind the shock.. With the SR-71 they cooled lots of stuff with fuel, things like the tailpipe actuators and other stuff. But when you look at trying to keep an entire cabin cool and pressurized for a hour or two, starting with air that is 900 F is no picnic. It takes a ton of energy to try to do that. I've just raised to of the more obvious issues and there are tons of other issues too, propulsion being a key, and maybe it could be done, but to do it and make it economically viable is beyond the state of the art at the present time.
It's a PR stunt to make Airbus seem relevant while the sales for the A380 TANK. It's got one big supporter: Emerates. http://www.nytimes.com/2014/08/10/business/oversize-expectations-for-the-airbus-a380.html?_r=0 Airbus has struggled to sell the planes. Orders have been slow, and not a single buyer has been found in the United States, South America, Africa or India. Only one airline in China has ordered it, and its only customer in Japan has canceled. Even existing customers are paring down orders. The A380 has a list price of $400 million, but the pressure has forced Airbus to cut prices as much as 50 percent, according to industry analysts. So far, Airbus has received 318 orders and delivered 138 planes to just 11 airlines — a disappointing tally given forecasts that the plane would be a flagship aircraft for carriers worldwide. Only one airline — Emirates — has made the A380 a central element of its global strategy, ordering 140 as it built a major travel hub in Dubai. But Emirates is unique. No one else has bet on the plane with quite the same confidence.
I have always considered the A380 a white elephant (literally,now) and a vehicle with limited utility. Can you picture it being put on a scheduled routine where it has to launch whether it's full or not.Yeah, that's a simplistic example but it's more of a cruise ship type of thing and fits a very narrow niche...like Emirates or any other ultra wealthy uniquely limited operation. Consider all the airports that can't handle or support it. Then when you do get to the big terminal facility that can handle it, it isn't really where you wanted to go so you have to take the train or another airplane to get there. This is from my perspective since I'm not in Dubai or near any other A380 terminal and I'm not going to the middle East, what would I do? If I'm going to London from SEA I couldn't leave from here in an A380 like I could in a 777. I would have to go to San Francisco on something and then get on an A380. Okay, I'm open to pot shots.
Density of Ti is only 60% greater than aluminum, BUT it is typically 100% stronger. Thus strength-to-weight of Ti is better than Al. Steel is 3 times more dense than aluminum, BUT it can be more than 3 times as strong. Just using those simplistic parameters Al is not anything special. There are many other design parameters which make Aluminum a better choice. Ti is also very expensive. Most of the Ti raw material used in the US comes from other countries. There was a recent article regarding the B787 and its extensive use of Ti (in large part due to compatibility with composite materials, e.g. corrosion). They were saying how the cost of the Ti parts is huge compared to Al and were looking at ways to redesign with aluminum.
All true, the strength to weight ratio of Ti is much better than aluminum, that's why we use it in rotating disks and blade assemblies. The strength to stiffness of most metals is about the same, that is aluminum is 1/3 the density and about 1/3 the stiffness of steel, and Ti is right between them with very close to the same stiffness to mass ratio. That's important because the stiffness (material modulus) is the key material parameter that is used in bucking calculations. While the strength to weight of Ti is better, many areas of the skin of an aircraft aren't sized for stress, they are sized for bucking and that limits how thin you can make a part. That is, while you could conceivably thin the skin down by more than half and still have a fuselage capable of meeting the internal pressure loading requirements, if the skin was that thin it may well have a problem with bucking, and that would require more internal stiffeners and other things that can increase the weight. Bucking of structures is a big deal in aircraft and for that reason you don't get to take as much advantage of the higher strength to weight ratio as much as the simple strength to weight ratio would appear. And Ti, while a lot stronger than aluminum at room temp falls off in material strength pretty quickly as the temperature rises. At 600F (Mach 3 speeds) typical TI is only 60% of it's room temperature strength, so there goes much of that strength advantage. That is, while you are going faster, and running with hotter skins, you didn't get to make the airplane any lighter going to Ti, you just made it a lot more expensive. While a lot of materials (like nickel and steel) stay strong as the temperature increases and then go "over the hill" and fall off pretty quickly, Ti falls off in the mid temp range and then flattens out for a bit then goes down again as you approach 1,000F. I was perhaps a bit simplistic in my previous post, but just trying to say that going to Ti isn't a panacea either. In a military airplane (like the SR-71) you do what you have to do and eat the cost, but as you noted, in the real world you have to viable on the economics side and that is the rub.
All good, many facets to design and material selection as you have explained. Are you with 'Allison'? Engine structure and components are markedly different than typical airframe. Dynamic loading is often primary. Once saw a new fan case manufacturing concept, that statically was as good or better than what is was intended to replace, fall apart about 10 minutes after engine start (due to vibratory/acoustic loading).
Some parts of engines are indeed very different from airframes in that the rotating stuff is under very high stress, but some of the static stuff is sized more for pressure loads and deflections, and when you get out into the larger cases they get sized and designed to stay round and keep things square in the engine. As the parts get big and weight becomes a bigger issue, we get into bucking and with every part there are always LCF issues, even more so with the rotating parts. It was once remarked to a friend who was looking for a job in another discipline that "if you can design turbine engines, you can design anything"... The reason the interviewer said that to my friend is that he understood that gas turbines inherently have the capability to fail any part in them from any way that it can possibly fail. Dynamic stress from vibration, aerodynamic flutter, stress rupture, creep, low cycle fatigue, high cycle fatigue, burst from pressure or speed, bucking, erosion, dissimilar metal corrosion, thermal growth to where parts interfere, are all present in GT engines, and I'm sure there are others that I haven't mentioned off hand. Add to that the relentless need for weight reduction and it never ceases to amaze me that these engines are as reliable as they are. Was with Allison once upon a time... Good place to be from... Turbine engines is a small community, most of us have made the rounds of the "big 3" at one time or another. now I'm doing consulting and have a company that is designing engines for "special" applications.
I really appreciate these posts regarding gas turbines because they have been very informative and gives us all an insight into just how difficult it is to design one. For a brief time I was a mechanic in the experimental gas turbine division of Boeing (1951-52) working on the Boeing 502. I recall that the burner cans were made of Inconel and the turbine blades were made of Stellite. There was no problem of anything coming apart probably because of the small size of the engine. The centrifugal compressor was 11.00" in diameter and rotated at a constant speed of 40,000rpm, a split stage design. We had a glass window mounted just aft the tail pipe and we could watch the turbine blades at engine start and before the airflow built up, the blades turned almost white hot for a brief moment. It was a fascinating job, especially when an engineer at the rpm controls got confused and opened up the test rig instead of shutting it down. The explosion in the test cell was a real blast...literally.
Smaller engines don't run any slower (relatively) because they run to the same blade tip speed to do the same work (pressure ratio). That is, if you cut the engine size in half, you'll spin it twice as fast (and make 1/4 the power since the area is equal to the power). The stress is the same in a scaled part if it's run to the scaled speed. In the gas turbine world we do a lot of scaling of engines, up and down and other than Reynolds number effects, it actually works really well. The TF-30 was basically a half scale JT-8D. The blade vibration scales along with everything else, so the vibratory characteristics don't change. Efficiency can go up or down a bit when you get to the point where leading edges don't scale any more, but it is amazing how much you can scale and get away with. Remember that very tiny 5 stage compressor that was in the earl Williams version of Eclipse? That shows you how far you can't go... They got eaten alive by Reynolds number effects because the blades were so small and the performance went in the toilet at high altitude.. Oh well, live and learn...... The biggest thing that doesn't scale is the combustor length. That is because you need a certain amount of time in the combustor and if the speed it same, the length doesn't get any shorter, but in a lot of configurations that screws up shaft length and then the shaft critical speeds don't scale, so you end up needing a bigger shaft and then it all goes down the drain... I was once on a sailboat and was talking to another engineer and he asked what kind of loading did engine guys use for limits... I told him that we had a nickel alloy disk on an engine that was loaded to over 170,000 psi of stress at the bore and it was running at over 1,000 degrees F and it was spinning at over 45krpm.. The look on his face... priceless..... With all the energy in the disks failures of any of the rotating parts are bound to be spectacular. When I first came into the field I was doing failure analysis on the F100 engine during the "build em and bust em" days.. We had to figure out what let loose first from mountains of boxes of torn up parts.. Pretty much did figure it out, but that was a real challenge... When they had some data or a camera running on it, it was a lot easier.. Most spectacular failure I can think of was when we a titanium fire in an F100 at the NASA tunnel.. The engine was outside the envelope at high Mach on the deck and an obsolete titanium disk spacer that shouldn't have been in the engine let go... NASA had to supply pressure from a pump house that had a good distance of high pressure plumbing and that kept it burning even after the engine shut down... Everything was torched from the front to the back and the engine was hanging by its front and rear mount and it was broken in the middle and hanging down and you could see what was left of the rotor through the cracked and broken cases... Probably the most amazing failure was the containment testing for loss of a fan blade of the TF30 (ok, the parts were rigged to fail) but when it all stopped (and it contained the failure) there was this engine case with all the parts, and other than the inside of a couple of disks that were sitting on the pile in the engine, nothing was as big as a two inches square. It took all those pieces and shredded them in about a revolution and a half.....