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Modern Low Speed Airliner

Take a bunch of proven ideas off the shelf ...
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Flying-fuselage designs (eg: Burnelli, BWB, flying-wings) have much more internal room than standard tube-and-wing. For a given size they can carry more passengers. The structure is much more robust - less prone to fatigue and safer in a crash.

A fuel cell plus an electric motor is the most efficient power production method currently available.

Natural Gas is the least polluting, has the highest energy:weight ratio and is the cheapest, of the hydrocarbon fuels. Unlike hydrogen, the delivery infrastructure is well in place. The only issue is storage volume on a vehicle: per unit of energy, natural gas, while lighter, is rather bulky.

Propellers are quieter than jets. Propellers mounted above a wing make them even quieter (from the ground).

Lower speed aircraft do not need long runways. A 400mph aircraft needs less than half the runway as its 600mph brethren.

Add ingredients, blend evenly and...

An electric-motored propeller-driven flying-fuselage design, with internally-mounted fuel-cell and natural gas tanks, is much more energy efficient, produces much less pollution, can use more airports and is safer, all while carrying the same or more amount of passengers and/or cargo.

Initial construction costs would be more if for no other reason than the amount of material required, but the aircraft would be in service longer, not only because of the robustness of design but because the fuel-cell/methane(later hydrogen) paradigm will be around much longer than the jet-engined/heavy-HC one.

The only issues from an operational point of view are travel time (which, thanks to the time added by airport security procedures, isn't much of an issue) and parallel parking.

_____________________________________

[addendum: Due to popular demand in the annotations, towhit:

"higher speed";
"turbofan";
"propfan",

as a special feature for our long-time half-baked readers we're going to add something pretty much totally unrelated to the post. (The post may sound complicated, but it's really just a viable method of shoehorning natural gas and fuel cells into a modern airliner)

Motorjets <link>.

Since electric motors' peak power output can be twice their continuous output, every once-in-awhile you can pop the clutch and light off the supercharged ramjets _in addition to_ the propellers, for JATO, emergency maneuvers, or just to show your tail-lights to that mouthy 757 driver.]

FlyingToaster, Jul 11 2012

BWB http://en.wikipedia...i/Blended_Wing_Body
[FlyingToaster, Jul 11 2012]

Propfan http://en.wikipedia.org/wiki/Propfan
[bs0u0155, Jul 12 2012]

Super motor? http://blog.cafefoundation.org/?p=2067
Ah-dhunno. Maybe. [doctorremulac3, Jul 12 2012]

Fuel cell airplane http://www.boeing.c.../q2/080403a_nr.html
[doctorremulac3, Jul 12 2012]

Motorjet http://en.wikipedia.org/wiki/Motorjet
now now children, this is only to be used in case a propeller falls off or the airfield is too short; not for say increasing the speed by 100kts for recreational purposes. [FlyingToaster, Jul 13 2012, last modified Mar 01 2013]

Facetmobile: FMX4, FMX5, Personal Air Vehicle http://www.wainfan.com/facet.htm
the only homebuilt lifting body(s) around. [FlyingToaster, Jul 13 2012]

except this one http://www.wingco.c...tlantica_design.htm
[FlyingToaster, Jul 13 2012]

Baked http://en.wikipedia.org/wiki/AEREON_26
Flying wing, attempted by Aereon in 1971 [imagin8or, Jul 16 2012]

superconducting motors http://www.azom.com....aspx?ArticleID=949
[bs0u0155, Jul 17 2012]

blown flaps... ahem. http://en.wikipedia.org/wiki/Blown_flap
[bs0u0155, Jul 17 2012]

HawkEye http://www.hawkeyeuav.com/
These guys have done long (hours) duration testing with a fuel cell in place of the batteries to good effect. [neutrinos_shadow, Jul 17 2012]

Talk by Al Bowers - NASA engineer http://www.twitt.org/BWBBowers.html
concerning an 800 passenger double-decker BWB design. [FlyingToaster, Feb 27 2013]

747 vs BWB http://www.twitt.org/Slide5a.jpg
comparison diagram [FlyingToaster, Feb 27 2013]

[link]






       Don't misunderestimate the importance of speed - it was a major factor in deciding the success or failure of aircraft when commercial air travel was getting underway, and only stopped being a factor when all large passenger aircraft became very similar. Concorde is the exception; it had lots of problems, but speed was its only selling point, and made it viable against the odds.   

       But do BWBs have to be slow? My understanding is that a true BWB can combine slow stall-speeds with high cruising speeds. Concorde had some, but not all, of the characteristics of a BWB - its takeoff speed was higher than a normal plane, but lower relative to its cruising speed.
MaxwellBuchanan, Jul 11 2012
  

       Blended-wing aircraft seem to me to be one of those really good concepts that have been hanging around waiting for technology to catch up with them. Diesel engines, for instance, were for nearly a century dirty, noisy, low-rpm, low-hp torque monsters found almost exclusively in big trucks, heavy equipment, ocean vessels, and huge electric generators. Attempts at diesel-powered cars were made from time to time, although they never really caught on. But in the last ten years or so, with the advent of advanced sensors, fast and inexpensive onboard computers, and most importantly electronic variable ignition timing, diesel has finally come into its own.   

       Similarly, all of the world's aviation designers have at one point or another fooled around with 'flying wings', but the advantages of the design never outweighed the drawbacks until high-tech avionics and hypersensitive fly-by-wire systems were developed and, hallelujah, the B-2 bomber was born.   

       All of the things that the Toasted One has pointed out are true: blended wings are efficient, have a high payload-to- mass ratio, and in theory have a greater survivability factor than the traditional tubular fuselage. Unfortunately, despite all that they've gained, they're still waiting:   

       -mass production requires re-tooling of manufacturing facilities as well as estensive reconfiguring the assembly process   

       -gross infrastructure changes will be needed to introduce them to civilian use. New boarding/loading equipment and procedures, new ground traffic control protocol, and in many cases, re-design of taxi lanes and apron arrangements. It's not just changing the shape of the airplane that's the issue; everything else must change to adapt to that shape.   

       -finally, and perhaps most importantly, there is a problem that most Halfbakers will scoff at, but it is very real: public acceptance. People are uncomfortable with change. The public will inherently distrust an airplane that is not shaped like a cigar with wings stuck on. They will ask "Where's the tail? How can it fly in a straight line with no tail?" and many other similarly ridiculous questions.   

       None of these problems are insurmountable, but each of them will cost billions of dollars. As always, it comes down to money.   

       I award my bun in the very dear hope that somebody in the position to make these types of decisions will decide that taking the next great leap forward in commercial aviation is worth the astronomical amount of money and effort it will take to achieve.
Alterother, Jul 11 2012
  

       //do BWBs have to be slow ?//   

       High speed aircraft use jet engines which are much less efficient than electric or ICE, but burning CH4 in a jet engine is just as feasible.   

       As a modern paradigm I don't think speed is an issue. Even for cross-continent flights, there's not that much difference between two hours and three hours, and for a cross-ocean flight bear in mind that, even with the tanks and fuel cell inside, there would still be enough extra room to give much bigger seating (berths perhaps) and a public area (bar/other) while maintaining a similar or better profit per passenger figure.   

       //next great step in aviation// is, as you've surmised, quite a leap. Boeing did a 20' model of a jet BWB for tests... that's about it anytime recent.   

       Burnelli designed his aircraft with flying-fuselages and they were quite successful but he (reportedly) ran into political problems.   

       Sadly I think that the (posted) idea would be difficult to realize in toto in a 1-2 person aircraft: while the NG tanks could be stuffed into the outboard portions of the fuselage, room is still needed for rather bulky and heavy methane-eating fuel cells, and the propeller placement above the wings would be far from optimum in that size.
FlyingToaster, Jul 11 2012
  

       Why not turbofans instead of traditional jet engines? They're a bit bulky up front, but the nacelles taper back in a shape that would naturally conform to the blended wing profile. They're faster than props and more efficient than flow-throughs or ramjets.
Alterother, Jul 11 2012
  

       [pedant] //and most importantly electronic variable ignition timing, diesel has finally come into its own//   

       Uh, you mean variable injection timing, shirley?
Custardguts, Jul 11 2012
  

       Yes, that is what I meant. A slip of the brain, I suppose. Thank you for pointing it out.   

       And don't call me, surely.
Alterother, Jul 12 2012
  

       Given that electric motors are relatively lightweight, and that their plumbing is pretty much non-existant (ie: almost no potential problems), this could be an application suited towards a small flock of tiny propellers rather than 3-4 large ones: that'd lower the thrust line.
FlyingToaster, Jul 12 2012
  

       Since you'd almost definitely have them arrayed as pushers, having small motors with sleek, low-profile casings would also lower the inherent drag and conform to the overall wing structure, yes? But I'm just postulating; all I really know about aircraft design comes from looking at airplanes and reading books that were written for people who don't design aircraft.
Alterother, Jul 12 2012
  

       //rather bulky and heavy methane-eating fuel cells,   

       take the fuel cells out of the bulky and heavy container, glue them to the outer skin (on the outside). Probably on top.
not_morrison_rm, Jul 12 2012
  

       umm... why ?
FlyingToaster, Jul 12 2012
  

       Hmm.. Land transportation has already solved the problem of carrying large loads already. So tow the bulky fuel in a trailer. Small quantities can be held locally for take off and landing. The coupling can be made once airborne.
Ling, Jul 12 2012
  

       I assume you're suggesting something like the military's practice of a light take-off and airborne fueling? Or did I completely misunderstand?
Alterother, Jul 12 2012
  

       I think he's referring to the "Light Aircraft Trailer" post.
FlyingToaster, Jul 12 2012
  

       I'm fairly certain that the work on speed vs fuel efficiency has already been done. Intuitively, I'd say that yes, the slower the more fuel efficient (drag being proportional to velocity squared). What's missing here is whether there are any other factors - I would guess that efficiency for lifting surfaces would drop away at lower speeds ie sheer size of the craft needed to sustain flight at a given low speed would then be high drag, etc. Anyhoo, point is, I'm absolutely confident that the work has been done on this issue and our fraternal aerospace engineering brothers and sisters could speak volumes on the issue without having to resort to "dropped marble" explanations.   

       The option of LTA freight haulage has also been explored, elsewhere on the HB if I recall. I still think it's not such a bad idea.
Custardguts, Jul 12 2012
  

       //speed vs. fuel efficiency//   

       Certainly there are some passengers for whom time-in-the-air is an issue: the Concorde proved that.   

       But let's look at more normal air travel...   

       For a relatively short air-commute, say Toronto to Montreal (400 miles'ish) it'll be an hour in the air on the low-speed flight, and 40 minutes on the high speed jet. But it still takes .75 hours on each end for destination travel and you have to be there an hour ahead of time for airport reasons.   

       So the times are 3:15 vs. 3:35.   

       A longer haul, say a third of the way 'cross the 'States, Chicago to New York, 714 miles is going to be 4:15 for the low-speed flight and 3:40 for the high speed. And the low-speed flight will be more comfortable.   

       (umm [Cg] it's not a dirigible, nor dirigible-like in any fashion except it's using a gas that's lighter than air for fuel... except the gas will be pressurized so there's still no LTA elements. The main reason the design uses a lifting-fuseleage is so big pressure tanks can be fitted inside without compromising passenger-capacity compared to a more traditional design.)
FlyingToaster, Jul 12 2012
  

       Pretty sure you're adding weight to this system by not just burning your natural gas in an internal combustion engine. You're replacing that one element with two, the electric motor and the fuel cells. Adding power transfer mechanisms, no matter how efficient they are, takes away from your bottom line.   

       I'm also pretty sure that electric motors weigh more per hp than internal combustion engines. Just doing a quick search I'm seeing a 7.5 hp electric motor weighs 144 lbs and the same hp gas engine weighs 53 lbs. And that's without the fuel cells or batteries.   

       Additionally, I know you can burn natural gas in a fuel cell, but hydrogen being the preferred fuel, I assume you're sacrificing some efficiency there as well.
doctorremulac3, Jul 12 2012
  

       //a 7.5 hp electric motor weighs 144 lbs//   

       Sure you weren't looking at a gas or diesel genset ? those are designed to operate continuously for hundreds of hours at a time, and there's no need to design them for light-weightedness. EM's are always lighter than their equivalent ICE's.   

       The nift of the idea lies in using the overly large interior volume of a BWB to make up for the extra storage space that natural-gas requires (and that I assume a fuel-cell requires). Natural gas instead of hydrogen simply because it's available now. Hydrogen later of course when they overcome the supply issues.   

       I haven't been able to find anything useful about SOFC power:weight, and from the looks of things so far there's been no work done on making them vehicle-friendly (because of the long warmup time required: a non-issue in an airliner that's shuttling back and forth all day long), but the Honda FCX's PEM fuel cell has a power to weight ratio of 1KW/Kg... slightly better than an aircraft engine of the same power output.
FlyingToaster, Jul 12 2012
  

       //Sure you weren't looking at a gas or diesel genset ?//   

       Yes, but it was hardly a scientific analysis. I just found the first electric and gas motors with similar horse power and looked at their shipping weight.   

       I'm also making the assumption that if electric motors were a better way to make airplanes fly we'd be using them instead of the internal combustion engines, both jet and piston, that we use now. I understand that you've taken out the battery weight by replacing them with fuel cells but I still believe electric motors are heavier per hp, something that counts with an airplane.   

       Certainly open to being shown otherwise though.
doctorremulac3, Jul 12 2012
  

       I found a site that shows a 13kg, 50kW (67HP) electric motor (5HP/kg)   

       In contrast, a 50HP ICE for ultralight aircraft weighs about 40kg (1.2HP/kg)   

       I couldn't find a 50HP jet engine, but a 14HP model jet engine weighs about 3kg (5HP/kg)   

       A full-size jet engine like a Rolls Royce RB211 produces something like 30,000HP and weighs about 4,000kg (7HP/kg).   

       Electric motors have become incredibly power- dense in the last few years. What also surprised me was the weight-efficiency of small jet engines compared to big ones. I'm not sure how power/weight scales for an electric motor, but I would expect bigger motors to be better.
MaxwellBuchanan, Jul 12 2012
  

       Most electric motors seem to fall into the 1hp/lb range whereas gasoline engines are in the 2hp/lb range (not counting turbo/supercharged because we want continuous power not "for about half a minute then it blows up"). I was reading about a prototype permanent magnet motor a couple weeks ago which weighed 1lb and produced 5 horsepower (or something like that; maybe it was 2lbs and 10hp or half a pound and...) at over 90% efficiency.   

       Electric motors are being tested in small experimental aircraft all the time, moreso as both they and batteries become even lighter.   

       On the other hand I've been drooling... err, I mean looking, at a 3cyl diesel Deutz genset that produces 30kW... it weighs over 700 lbs. It's designed to be operated continuously 24/7 for almost 3 weeks at a time (I have no clue what you're supposed to do before you turn it back on again). Of course the bulk of the weight is the diesel, though the generator bit probably weighs much more than it would have to if it only had to be in continuous operation for 8-10 hours at a time.   

       I am going to guess that one large fuel-cell running some electric motors will weigh more than its equivalent power's worth of standard airplane ICE engines.   

       But I'm also going to guess that the increased various efficiencies and relative simplicity more than makes up for it.
FlyingToaster, Jul 12 2012
  

       What about propfan mounted in a pusher configuration? 35% less fuel use over standard turbofans.
bs0u0155, Jul 12 2012
  

       Ok, here's what Wikipedia (for whatever it's worth) says about power to weight ratios from best to worst:   

       ICEs:   

       Space Shuttle turbopump: 93 hp/lb   

       Turbofan jet engine: 6.10 hp/lb   

       BMW gas "Otto" engine: 6.10 hp/lb   

       Mazda Wankel engine: 0.92 hp/lb   

       Container ship Diesel engine: 0.02 hp/lb   

       EMs:   

       ElectriFly GPMG4805 Brushless DC: 3.45 hp/lb   

       Toyota Brushless Prius motor: 0.84 hp/lb   

       Panasonic AC servo motor: 0.19 hp/lb   

       But I also put up a link for some motor that's supposedly 6.5 hp/lb so depends on who you believe I guess. I'm just parroting stuff I find on the web so take it for what it's worth and do your own research.   

       Bottom line: FT, you can probably get all the numbers to see if your fuel cell plane would work with "off the shelf" numbers you glean from the web. If you can take that motor in the link I put up and power it with gas powered fuel cells and show a bottom line power to weight ratio that works then badda-bing-badda -boom. You've got an airplane concept.   

       I'm leaning towards no but hey, prove me wrong. Got a bun or bone in a holding pattern depending on what you come up with.
doctorremulac3, Jul 12 2012
  

       //6.5hp/lb// That's that one's peak power which can only held for a short amount of time.   

       Since there's not currently a SOFC (hydrocarbon fuel cell) of a proper power/design-weight (the ones that have the power are designed for stationary operations), it's all pretty theoretical at that point.   

       Wikipedia claims that Honda's fuel cell has a p:w of about 1:1 (kW:kg) which, since it's a 100kW fuel cell means it only weighs about 100kg; that could be a bit of statistics shiftiness but not by much. Honda spent over a decade designing a hydrogen fuel-cell specifically for a passenger automobile. I doubt that at any point they doubted it could be done.   

       Either way I think I could probably get decent electric motors almost right off the shelf.   

       ----   

       OKAY LISSEN UP YOU GAS GUZZLERS, YOU KNOW WHO YOU ARE.   

       post addendumed.
FlyingToaster, Jul 12 2012
  

       [FT] - I was just taking [NotationToby]'s example to the extreme and pointing out that the ultra-low speed/drag case would need to be LTA rather than aerodynamic lift.
Custardguts, Jul 12 2012
  

       oh okay, I didn't actually understand [NT]'s anno. I'm not sure if a BWB (or the other designs I mentioned) have any superpowers in the very-low speed range, maybe stall-resistance.   

       Either way, for illustration purposes, I just figgered on a comparable speed to a standard airliner with the same cruising speed.   

       The "less than half the runway length" bit in the post was just a guess based on KE of an airplane with wings designed to hold it up at 600 mph vs. wings designed to hold it up at 400mph. Now that I think about it that doesn't make any sense whatsoever. But according to the Internet...   

       A Lockheed Consteallation requires 4,600 feet.
A 747 requires 10,000 feet.
  

       Close enough: no harm no foul.
FlyingToaster, Jul 12 2012
  

       The fuel cell thing needs some pretty good numbers to be worth while since at some point you need to figure in the weight of the fuel.   

       If you're going with hydrogen, (you're not, but if you were) just the containment vessel alone is a problem. Hydrogen leaks really easily and needs special containment that doesn't come without weight penalties.   

       That being said, it has been done. (link)
doctorremulac3, Jul 12 2012
  

       //weight of the fuel// umm... you mean the weight of natural-gas versus the weight of jet-fuel ? NG packs waaaaay more bang for the buck. Hydrogen even more but the post isn't about hydrogen.   

       re: fuel-cell airplane link: cool, but it really isn't that much of a difference between that and a battery powered airplane and they only flew it for 20 minutes.   

       At which point, since I still see that bun floating around, may I point out that the exercise of the post was not to say "why not put a fuel cell into an airplane and see if it works for 20 minutes" which is pretty much a given, but   

       "use a design(s) which have enough internal space to hold, as well as passengers, tanks of a gaseous fuel (which regular airliners can't), because NG produces a much smaller carbon footprint and (unlike hydrogen for the near to mid future) already has infrastructure in place and, as long as there's all that room, also use a fuel cell (which I'm assuming is going to be bulky) to generate electricity which can be fed to electric motors outside at a much greater efficiency than ICE engines or jets of any kind, and might as well use propellers since modern passengers won't mind, based on the machine being more ecologically friendly, (theoretically) cheaper to fly in, we've already done the Concorde for speed, a few minutes more in the air doesn't matter especially given modern time-spent-in-the-airport requirements",   

       which I, granted a little egotistically, also think of as a "given"; one that hasn't been done yet. But it's feasible.   

       ie: it's a good idea, and if you're only here today for the laughs, read the addendum though that could be done as well.   

       Bun please :-)
FlyingToaster, Jul 12 2012
  

       // public acceptance   

       I think the solution here would be to initially offer the flying wing as a luxury mode of travel, similar to travel by dirigible, supersonic jet liner, or spacecraft.
Cuit_au_Four, Jul 12 2012
  

       //Bun please :-)//   

       Can't argue with a smily face. [+]
doctorremulac3, Jul 12 2012
  

       The B2 Spirit does about 0.95Mach, so it's not exactly slow. Loadout is comparable to a 747. Not sure what takeoff and rollout length is required.   

       I feel reasonably certain the unit cost would come down markedly if the design was commercialised.
UnaBubba, Jul 12 2012
  

       I don't think tha the initial R&D costs would be *quite* into the ballpark of almost-one-off military hardware: if nothing else the investment would be spread out over many different models both concurrent and sequential, in the same manner that the A380 contains elements that were refined on the Comet.
FlyingToaster, Jul 13 2012
  

       That's right. There are only 20 B-2 bombers in existence. Not a big pool over which to spread your R&D investment.
UnaBubba, Jul 13 2012
  

       Well, the problem with this idea isn't that it couldn't be done, but that it couldn't be done in a small mass-produced aircraft to start off with. A small airliner would be the first rendition and those aren't cheap:   

       A couple of Hydrogen tanks could be tossed into the Facetmobile <link> and plumbed into the existing ICE engine easily enough. But the weight of a fuel-cell+motor might be too much for its design.. The slightly larger FMX-5 (languishing on the drawing board) or BW's PAV maybe, but it'd probably have to lose a few passengers. (I could be wrong about that: see [doc]s link).   

       But those are Hydrogen fuelled PEM FCs, and H2 won't have an in-place infrastructure for the forseeable future.   

       Natural Gas' infrastructure, on the other hand, is well-embedded. The fuel-cell that *can* handle natural gas (and propane) is a SOFC type, and those run at 900 degrees C. You wouldn't want to be sitting near one of those in a small aircraft no matter how much heat shielding was on it.   

       So now we look at slightly larger aircraft: ones with enough legroom in the design such that any non-fatal crash doesn't include molten pieces of whatever flying around changing the verdict: something equivalent in generic size and capacity to a small business jet.   

       So a big company could probably start designing and producing them in business-jet size, right ? Well technically they could, and for a fraction of the cost of a really big liner, except for two things:   

       1) Without enough height to stand up in (like all small business jets) and no side-windows, the passengers might feel a bit cramped, possibly even claustrophobic: the opposite of the whole business-jet paradigm. This *might* be overcome with more creative design than I can think of, off the top of my head, but even if that's overcome...   

       2) Airports aren't going to start piping in natural-gas until the big boys are using it. Simple economics.   

       So, except for the odd rich-guy one-off and *maybe* a few company-owned demonstrators from the big aircraft manufacturers, so much for business-sized aircraft.   

       Ah, but now let's move one notch further up the line to "regional transport", aka small airliner; at this point the production viability level changes drastically.   

       Not only is the interior big enough to swing a small to medium-sized cat (and there may even be a few pairs of side-windows up at the front), but the minute Boeing/Airbus/ McDonnell-Douglas/etc. announces production of a small natural-gas airliner, every major airport and their feeders will be equipped with new gas pumps/equipment in about the same amount of time it takes their local gas companies to install a line for free. Again, simple economics.   

       So, long story short, the sweet spot for current'ish viability of a mass-produced aircraft of this type is a small to medium sized airliner.   

       [Alterother] small and medium-sized BWB airliners could probably use large-airliners' boarding and parking spots without problems.   

       On a very slightly related note, since a BWB doesn't have a usage-limiting circular cross-section and is quite structurally strong, it could be thinner cross-sectionwise: ie: have only one deck, baggage/cargo stored in the middle section or in the nooks and crannies where the cross-section gets too thin to put a seat. While this means pressurization has to be looked at, electric motors don't need to be at 30-40,000 feet to be efficient, unlike jet engines.   

       [CuitAuFour] 'Luxliner' sounds like a good name. Between that and the miniature golf course in first-class, there shouldn't be any problems getting passengers.
FlyingToaster, Jul 13 2012
  

       I might be wrong but isn't the development cost of traditional jet liners already so huge that there are effectively only 2 huge companies that can afford to do it? Even Boeing/Airbus are effectively government subsidized for aircraft development. This is all with tube+wings aircraft which haven't really changed since the 1950's. So, your blended wing liner is going to bring a whole bunch of developmental issues to the party; the design isn't suitable for modular construction. This is serious, because Airbus at least, is a consortium dependent upon spreading component construction around Europe before assembling them like a massive kit. This is for both technical and political reasons, which you would have to abolish, and then build a HUGE assembly building and combine nearly all of the expertise in modern aircraft construction in one place.   

       Secondly, safety and maintenance are going to be a nightmare. If you have an engine problem, like on that Quantas A380 a couple of years back, then you're in much more serious trouble with a blended wing than with the engines hanging out on their own. Equally, replacing engines and general access for maintenance is going to be tougher.   

       I can actually see a blended wing being more likely in a military environment as a transporter, for several reasons; they're a bit more forgiving with the occasional crash, they're willing to pay over the odds for a relatively small advantage, they're more adaptable with regard to infrastructure.
bs0u0155, Jul 13 2012
  

       //the military// seems to have settled on heavy HC's for general-purpose fuel: using heavy HC's would require adding a reformer before the fuel cell (of course then you could dump damn near anything into the tank).   

       //maintenance// Huh ? all the power innards are at the centerline of the aircraft (fuel, fuel-cells) accessible by opening a full-sized hatch, and the electric-motors are on pylons on top of the wings: just stand on the non-slip sections conveniently placed by each engine pylon. There's no plumbing running to the motors either: just an electric main-power cable, two digital wires for control and sensors, and a pair for electronics power. And for anything else I can't see anything being more difficult than on a regular-plan aircraft.   

       //modular construction// not a problem: just because the flying-fuselage bit is really wide doesn't mean it can't be made in sections just like anything else, just that those sections will be open to the air until they're all connected. There are support pillars inside; it's not just a big completely open space, and even if it was, you'd just build part of the roof as one section and part of the floor as another.   

       Perhaps I mispoke the company names: the only BWB drawing in Wikipedia is of a jet designed to hold 800 people or so, whereas the very first ones of these would most likely be small regional airliner-sized, replacing turboprop aircraft, having a passenger capacity of 50-80 people: big enough to stand upright in and common enough and thirsty enough that airports would start offering natural gas as a fueling choice, but not so big that the airport would have to make any changes to the buildings because of the odd shape. So rather than Boeing or MD's usual sized offerings, think BAE, Sud, Bombardier, etc. as being either the developers or the aircraft being replaced.   

       Until the idea catches on that is.
FlyingToaster, Jul 13 2012
  

       // has the highest weight:energy ratio and is the cheapest, of the hydrocarbon fuels. Unlike hydrogen, the delivery infrastructure is well in place. The only issue is storage volume. //   

       // settled on heavy HC's for general-purpose fuel: //   

       Energy density; CH4 just doesn't deliver. Too much H, not enough C. LNG needs high pressure and refrigeration; the critical point is 191K. You can carry JP-1 round in a bucket ...   

       Actually, you can carry AVGAS round in a bucket, too. Sometimes more than once.
8th of 7, Jul 13 2012
  

       ... your 2 quotes aren't exactly related to each other: I'm not saying the military should go for NG use in field equipment or anything else that absolutely has to be painted green or spends its time away from a supply chain, nor am I promoting this design (or BWBs in general) for combat assignment: the body and landing gear track is too wide, the cargobay while voluminous has too small weight-loading per square foot to carry seriously heavy equipment, and it's not a STOL.   

       Now if the usage was troop and supply/cargo transport between airports/airfields: on that they'd save a bundle in the long or even medium run.   

       You *could* build a field-ready military BWB of course: reformer, higher ceiling, bracing for oversized and weight-concentrated cargo, high-wing, thinner fuselage and narrower landing-gear track, propellers on top of the wing at the front for STOL performance.   

       But you'd probably want to build the "on-road" version first to get a better picture of low-speed handling of BWB's in general.
FlyingToaster, Jul 14 2012
  

       This does seem to be echoing a lot of the DIY Vulcan bomber project.   

       The easiest way to get a lightweight fuel tank for a fuel cell is to store hydrogen in a mylar sausage shape, the mylar can take about 10 bar (from memory) and at that it's not that heavy. It might even be neutral air buoyancy at a guess.   

       The bit about taking the fuel cells out of the fuel cell cell cradle and sticking them on a convenient outer surface is that, having looked at one, they cradle just seem to be about 200kg of ironmongery, as most of the big arrays are for trucks, or static power-plants, not for flying machine.   

       The fuel cell wallah I talked to gave a provisional ok, so long as it wasn't too high lack of oxygen, and humidity. Apparently they need some humidity to function, so I thought put them on top of the craft, then the water created would provide a lot of humidity, in fact it might need to be channeled away, possibly through a waterwheel, the crank fitted with a wooden gnome that seems to be turning the wheel.   

       Although, strictly speaking the gnome is not absolutely necessary.
not_morrison_rm, Jul 15 2012
  

       ah, so to summarize, you didn't actually read the idea then ? :-)   

       This idea is for a 400 mph airliner: putting the fuel cell (probably half the size of a small shipping container) on the outside of the aircraft would tend to mitigate the aerodynamic advantages of putting the gaseous-fuel tanks inside same: the idea that inspired this post in the first place.   

       Though, now that you mention it, the Vulcan wing-roots almost blend into the fuselage at the front because of the intakes.
FlyingToaster, Jul 15 2012
  

       //Natural Gas ... has the highest weight:energy ratio//   

       I suggest you review that statement.   

       ..   

       How much more efficient are we talking here, approximately?
That is, how much more efficient is a BWB to fly a given distance, and how much more efficient is natural gas than current methods?
Loris, Jul 16 2012
  

       haw! sorted, thanks.   

       No idea about BWB efficiency: some articles go on and on (without numbers), and you can't tell how much poetic license is being used. But it seems to me that they'd certainly be more efficient in any "per volume" metric, which is pretty much the one you need to use for transporting squishy whiny cargo and/or for carrying voluminous fuel.   

       Wainfan's Facetmobile lifting body, from what I as an armchair pilot can tell, doesn't get particulary dazzling gas mileage for a one-person small aircraft. But the faceted design and use of a lossy-2stroke may have contributed to that.   

       Burnelli's aircraft (wing bodies?) seem to have flown quite well and saw regular use: certainly not hangar queens. As far as safety is concerned there's a 1935 video of an early design crashing at 130mph, tumbling a few times... and the crew literally walking away from it.   

       Boeing's X48 is a tiny model which I haven't read too much up on since I'm miffed they managed to get an 'X' designation for it.   

       At this point I wish we were all rich and could afford 'guest posters' from various fields to get some hard figures.   

       Fuel efficiencies in MJ/kg:
LL100: 44, Diesel: 46.2, NG: 55
  

       The only CO2 table I could find seemed to contradict itself. The figure bandied about in the press is "33% less".
FlyingToaster, Jul 16 2012
  

       [imagin8or]   

       I was actually just reading the WP page (Aereon26) you <linked> to about an hour ago. It's not a flying-wing, but it is a lifting body... and has a pusher above-wing engine. It wasn't just an "attempt" though, they conducted flight tests. Neat, thanks.   

       But, what are you calling "baked" on ?
FlyingToaster, Jul 16 2012
  

       I may be a bit late on your motor discoution but I see on big difference here is that plane motors are made to run in cold enviroments. Electric motors can trim a lot of weight if your not having over heating issues. Since the windings will not be overly hot they can be smaller and with out the need for thermal mass you can drop the big heavy steel housings for a mostly open composit. It's not uncommon to drasticly over work a motor as long as you can keep the windings cool you'll be fine that's how you get some of the amazing peek power out puts it could maintain it if you keep the windigs from melting.
dev45, Jul 16 2012
  

       ^ could use 7-8 little engines and props instead of 2-3 big ones: that'd make the propellers' centreline lower. I'd like to drop the Facetmobile guy a line seeing if he couldn't put a hydrogen fuel-cell into the Facetmobile when they fix it... but I think it'd still be overweight: they've got a 2stroke engine on there now.
FlyingToaster, Jul 17 2012
  

       So electric motors can be made smaller, lighter more efficient and so on by using superconducting magnets <link>. Normally, you wouldn't want the huge pain in the a** that cryogenics represent. However, considering superconductors are available that work at the sort of temperatures that liquid natural gas is at.... it becomes tempting.   

       In addition, a: design using ducted fans would a: look cooler b: provide an opportunity for gaining bleed air from the rotor tips (bleed air could be used for blown flaps <link>) c: the evaporated natural gas that was recently used to cool the motors could be injected into a combustion chamber further down the duct to create a kind of coolant-derived afterburner.   

       Also, the aircraft should be sat on the apron, having baggage loaded etc with a huge flame coming out of the top as the excess LNG is burnt off.... everyone loves huge flames.
bs0u0155, Jul 17 2012
  

       So true.   

       Remember that LNG is only very cold for a short time, and only because it is kept under, and released at, great pressure. I'm not sure it could be counted upon as both coolant and fuel source.
Alterother, Jul 17 2012
  

       well, considering you've got a limited time frame (4-6hrs) for storage, and you need very little of it to remain at the destination it's not a big a problem as it first appears. Then, unlike in those LNG transport ships, you're not mooching about in a big thick conductive ocean in big thick conductive sea level air. Instead, the outside air at 40,000ft is around 20% of sea level pressure and conveniently at about -45C so the temperature gradient you're dealing with is 120C rather than 190. Also can't we blend a little propane in or something? there's actually a little wiggle room on the superconductors, 10-15C or so. a 100C gradient's pretty easy to look after. Use aerogel or whatever.I think the problems of a flying LNG aircraft are smaller than we think.
bs0u0155, Jul 17 2012
  

       Your math is convincing, but icing will be a practical concern, especially if you blend in propane. In my almost exclusively hands-on experience with thermodynamics, nothing frosts regulators and clogs gas lines with ice like fecking propane.
Alterother, Jul 17 2012
  

       wait, the problem was cooling a minute ago.... I'm sure the fuel cells will produce all the spare heat you need, and remember, the electrical system's pretty robust in this aircraft, so a little careful heating here and there's child's play.
bs0u0155, Jul 17 2012
  

       <mutters something about halfbakers and attention span> What problem ? the CNG is inside the aircraft. LNG, while probably a better idea in some respects eventually, isn't something your standard local gas company can just toss a feeder line into the airport for. In fact most of the post is devoted to smugging about that the internal space of a flying fuselage allows for big compressed gas tanks.   

       If you were going to go for LNG you might as well use a normal design and allow 1.5x as much volume for fuel (plus whatever for the insulation + cooling system)   

       H2(compressed) - 4.5 MJ/l
NG(compressed) - 9 MJ/l
NG(liquid) - 22 MJ/l
Jet-A - 33 MJ/l
FlyingToaster, Jul 17 2012
  

       but.... superconducting motors!
bs0u0155, Jul 17 2012
  

       k but I'm not putting it in the post: I already put "supercharged ramjet" in there.   

       So... won't the fact that it's a motor running on magnetic fields tend to unsuper the superconductor ?
FlyingToaster, Jul 17 2012
  

       There's an idea... put the superconducting electric motors inside the compressed LNG tanks. They'll become more efficient as the gas pressure falls and the temperature drops... until the fuel:air mix will sustain a massive explosion... hmm, time to dust off the drawing board again.
UnaBubba, Jul 17 2012
  

       Electric motors are desirable in cars because there is less gearing and a lot of stop-start which can be recovered. At constant speed, ICEs are quite efficient.   

       I'm sure the only reason BWB aircraft are not around is due to cost. Creating the A380 nearly killed Airbus and their task was just to add a deck. The 787 is just made of different materials and that has taken years too.   

       If a normal plane crashes, there is no stigma attached to that particular model number, but if a unique aircraft crashes, like Concorde, its entire existence is called into question.
marklar, Jul 17 2012
  

       Well, they've also sorta painted themselves into a corner.   

       A jet airliner has to be built to withstand cabin pressurization @ 40,000 feet since that's where jets operate efficiently. Cylinders are (relatively) easy to pressurize, though the Comet engineers might feel otherwise. But BWB's haven't got any nice neat circle cross-sections.   

       So the aircraft would have to be designed either for the relatively low-altitude operation of the pre-jet era, or built as overlapping, side-by-side cylinders to enable interior pressurization.   

       The only real obstacle IMHO is that, if you don't mind the cynicism, as soon as one company goes through the trouble of building a BWB, then the next company to do so doesn't have near as much R & D to do.
FlyingToaster, Jul 17 2012
  

       There is a market need for a short-haul airliner, where speed is not as important as the trans-oceanic or transcontinental routes. When trips are less than 600 miles, the wait time for security is often longer than the actual trip time; a short-haul airliner could be competitive even with a cruising speed of under 300 mph. A BWB with fanjets might replace the aging B737 fleet.
whlanteigne, Feb 25 2013
  

       Its a new market for people who want to get there slowly. Advertise slow motion, and get everybody walking and talking slower.   

       I know it can be done, because when I was a kid we all used to chase each other real slowly while saying: "Steeeeve Austin, a man barely alive..."
pashute, Feb 26 2013
  

       Don't forget that expanding gasses absorb heat as well. If you keep the CNG at ultra-high pressures until you reach the motor jacket, expand it there, then supply it to the fuel cell, that will cool the motor.   

       My concern, is my belief that a BWB aircraft has a longer wingspan to get the same sort of cabin space as a conventional design. I haven't been able to confirm this. If true, that would present significant problems with trying to implement this sort of design for commercial use.   

       Shorter runways would be possible, but they would have to be more widely spaced. Likewise, gate spacing is defined by (and defines) the sort of aircraft they can handle, and this would be a real problem.   

       If I'm wrong, then never mind.
MechE, Feb 26 2013
  

       well, a B2 and early generations of 747 have roughly the same max takeoff weight, the 747's wingspan is 3-4ft more though. So it doesn't necessarily hold up. The A380 has nearly an 80m wingspan, so, for some airports at least, there's nearly 20m of wiggle room with a BWB aircraft in the sort of weight class of a 747.
bs0u0155, Feb 26 2013
  

       also, a BWB designed for a slower cruising speed, in the 400-ish mph range will have a correspondingly slower take-off and landing speed (as mentioned above). Now, traditional aircraft try and mitigate their landing speed issues with lots and lots of that flap-and-spoiler jiggery pokery. Now, not so much jiggery pokery will be required, meaning the wing will not be the mess of jackscrews and hydraulics (actually, nearly everything will be electric, what with the beefy on-board supply). This means it'll be much easier to have the last few feet of the wing as a folding section, like carrier aircraft.
bs0u0155, Feb 26 2013
  

       It's not so much take off weight as space. The B2 has a very thin profile, and very little of it is even as tall as a seated person. Obviously a commercial aircraft of the same plan would have to have a much wider cabin area than the B2s cockpit, and much wider and shorter than a conventional aircraft of the same seating capacity. My understanding is that doing this results in the overall wingspan increasing.
MechE, Feb 26 2013
  

       it's OK, we've got 20m of wiggle room and folding wing tips, we're all good.
bs0u0155, Feb 26 2013
  

       Typical "Compressed Natural Gas" is stored at around 3000 to 4000 psi, necessitating very strong (and thus, heavy) fuel containers.   

       I recommend instead using an Adsorbed Natural Gas container, which reduces the pressure required to 500 psi or less, and either keeps the fuel density the same or even increases it.   

       Not only does this pressure reduction allow the fuel pressure vessel to be lighter, but it allows refueling directly from the existing natural gas pipelines, without additional compression.
goldbb, Feb 27 2013
  

       Newly linked are, a talk by a NASA engineer on a very large passenger BWB design, and a diagram contrasting the sizes of a BWB of 800 passengers vs a 747 of 421 passengers.
FlyingToaster, Feb 27 2013
  
      
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