Blended Wing Bodies

nuuumannn said:
The fact is, you have no idea as to whether the layout proposed by Airbus in the Maveric is less safe than a conventional one. None at all. There is no evidence out there that proves it either way, so for now, you are surmising based on what you know.
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No novel aircraft configuration has a body of evidence sufficient to prove anything when it first flies, that is a meaningless charge to raise. What it does have is informed assessment of the risks, known as the safety case, and any obvious precautions, which may have been lab-tested - all driven by what the safety experts "surmise based on what they know."

A case in point. The BWB was aired by Boeing around 30 years ago. The FAA responded with various safety concerns, which this discussion is broadly revisiting, and freely stated that it was all a bit hypothetical until Boeing submitted a detailed design. Maveric is in much the same concept-study design phase that Boeing were back then.

So here is another little bit of surmise. The Maveric concept model is, after the current fashion, twin-engined. These may be mounted above the trailing edge but they are positioned wide of the passenger cabin. Is that safe enough in a crash? What about the plane slewing sideways before impact? What about a hot engine smashing into a fuel tank? What about a failure of the blade/blisk containment casing? The RR Trent is designed to contain a broken fan. Some prop airliners had reinforced fuselages just alongside the props. What precautions would a high-rear engine need? Yes the details are largely unknown, but the risks which will motivate those details are clear enough, and some precautions are a lot more practicable than others.

Boeing backed out because of the big problems they faced realising a commercially viable BWB. Will Airbus find a way where they did not? Nothing is certain, but I have my doubts.
 
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bobbymike said:
(CNN) -- Researchers have conducted a successful maiden flight of the Flying-V, a futuristic and fuel efficient airplane that could one day carry passengers in its wings.

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Odd, I get this:

451: Unavailable​
The page you are attempting to access is not available in your country.​

But it's just an ordinary .com domain for nowhere special and I can still access the usual stuff...
... such as this CNN coverage of the flight.

This from Delft Uni is a bit more forthcoming on the technicalities.
And here are some piccies

Wind-tunnel tested, so evidently the aerodynamics are reasonably sound. And Airbus have joined KLM in supporting it.
Nevertheless, the claimed 20% drag reduction for a full-scale airliner flies in the face of all the mid-20th-century research on very sharply-swept wings at subsonic speeds, so we shall have to wait and see.
 
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As for crash-worthiness ... most pusher engines are designed to not penetrate the cabin during impacts of less than 40 Gs. US Navy studies concluded that 40 Gs was about the maximum a properly restrained pilot could survive. Cue long-winded debate.
Secondly, during World War 2, Northrup learned - the hard way - the disadvantages of seating crew in line with propeller discs. After a few P-61 Black Widows landed wheels up and a few navigators died, the FAA banned seating crew in line with prop discs. Fast forward to today, many turbo-props have sacrificial panels bolted on the outside of their fuselages to prevent ice - thrown off propellers - from damaging the cabin pressure vessel.
Thirdly, modern turbo-fans include extra Kevlar belts to contain fan failures.
Fourthly, any modern engineer would be careful to avoid installing passenger seats, fuel tanks, control lines, etc. directly in line with the fan disc. If control lines have to cross a fan disc, they will be routed on the far side of a spar or bulkhead. IOW a broken fan blade will need to penetrate a spar before it can hit a control line. Also consider that modern fly-by-wire systems have three or four different channels to provide redundancy in case of damage.
In conclusion, it is possible to design a BWB so that passengers survive most accidents.
 
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riggerrob said:
In conclusion, it is possible to design a BWB so that passengers survive most accidents.
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You have not discussed high-mounted engines breaking loose and being thrown down on the passenger cabin. This was the chief concern voiced by the FAA. "Most" accidents is not always enough; for example the Boeing 747 Max is safe in "most" conditions of system malfunction.
 
steelpillow said:
riggerrob said:
In conclusion, it is possible to design a BWB so that passengers survive most accidents.
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You have not discussed high-mounted engines breaking loose and being thrown down on the passenger cabin. This was the chief concern voiced by the FAA. "Most" accidents is not always enough; for example the Boeing 747 Max is safe in "most" conditions of system malfunction.
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Unless you have been appointed to the Airworthiness committee, can we work with the self designation system, especially as most of these designs are unlikely to ever kiss the tarmac.

A few points from me:

Passengers at the extreme edge, spilling their drinks, surely the passengers will be in the middle, and cargo in the edges?

As to an engine landing on the pax, and also the issue of the body/airflow, surely moving the engines a little outboard, maybe 2 engines, and as above, cargo in the area in front of them, would help.
 
@Fluff, I find your points oblique. The only one which makes any sense in the present context is moving the engines outboard. I look forward to your analysis of the all-engines-out-on-one-side flight condition.
 
steelpillow said:
@Fluff, I find your points oblique. The only one which makes any sense in the present context is moving the engines outboard. I look forward to your analysis of the all-engines-out-on-one-side flight condition.
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Clearly your understanding of 'little' needs some calibration.

You mean one engine out, on one side, again, seems to work fine on a 757 etc.

There, if that's all the airworthiness questions, lets move on.

Biggest hurdle to PAX flights, as apposed to cargo flights, imho, is the 'grandfather' 'rights' which is why we still fly in what was basically designed in the 60's, with a few modern dingledangles added on. The person that designs and certifies a whole new aircraft, is going to torn apart when we get that 'Comet' moment when 2 crash in the same 3 month period.

And then the second hurdle, is that mostly, the cargo bods dont buy new. So unless you can convince Fedex to invest, its not going to start with Cargo.
 
Fluff said:
steelpillow said:
The only one which makes any sense in the present context is moving the engines outboard. I look forward to your analysis of the all-engines-out-on-one-side flight condition.
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Clearly your understanding of 'little' needs some calibration.

You mean one engine out, on one side, again, seems to work fine on a 757 etc.
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May I suggest that your analysis needs to be a little more in-depth.
The 757 has a rudder with a long moment arm. That gives it high control authority. A BWB in the engine-out condition does not have that luxury. Precisely why I suggested you analyse the condition. Let me give you the general idea.

Say 40 M span, twin engines at 50%.
Conventional rudder; moment arm ca. 25 M in all conditions, thrust asymmetry 10 M. Rudder sideforce ca 40% single-engine thrust. Don't know the span of the 757 but very practicable.
BWB with drag rudders mean 90% span. One side out, drag rudder moment arm on the working side ca. 8 M. This has to counteract the drag of the whole of the rest of the airframe on the far side of the working engine, which has a mean moment arm from the engine ca. 15 M. So the drag rudder must exert twice the drag of the rest of the airframe - all to be overcome by one engine's worth of thrust! Even if sufficient emergency thrust is available to keep airspeed above the stall, the rudder force is 67% of emergency thrust and range is utterly knackered. Not so very practicable, especially on the trans-oceanic routes which are the main market.

Seriously, it is a well-known problem with all tailless multi-engine proposals; they have to keep the engines well inboard.

And sadly, flinging personal insults at either me or the rest of the world will not improve your numbers.
 
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What ever considerations, the final word is compliance to FAR 25 and CS 25. They deal with subjects such as zones free of essentials in the case of blade separation and the 90 sec rule for evacuation, among other things i.e. engine transgress into the cabin. No manufacturer as far as I know (AFAIK for the young ones;)) have adressed this in a concise way.
 
How did all the old mostly 3 engined birds cope, they had an engine inset into the fin, and the 2 on the side, if rear engine seperation was a risk, we should have banned all rear engined aircraft by now?

I mean its only a risk in some accidents anyway - most accidents your not going to care.....
 
steelpillow said:
Fluff said:
steelpillow said:
The only one which makes any sense in the present context is moving the engines outboard. I look forward to your analysis of the all-engines-out-on-one-side flight condition.
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Clearly your understanding of 'little' needs some calibration.

You mean one engine out, on one side, again, seems to work fine on a 757 etc.
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May I suggest that your analysis needs to be a little more in-depth.
The 757 has a rudder with a long moment arm. That gives it high control authority. A BWB in the engine-out condition does not have that luxury. Precisely why I suggested you analyse the condition. Let me give you the general idea.

Say 40 M span, twin engines at 50%.
Conventional rudder; moment arm ca. 25 M in all conditions, thrust asymmetry 10 M. Rudder sideforce ca 40% single-engine thrust. Don't know the span of the 757 but very practicable.
BWB with drag rudders mean 90% span. One side out, drag rudder moment arm on the working side ca. 8 M. This has to counteract the drag of the whole of the rest of the airframe on the far side of the working engine, which has a mean moment arm from the engine ca. 15 M. So the drag rudder must exert twice the drag of the rest of the airframe - all to be overcome by one engine's worth of thrust! Even if sufficient emergency thrust is available to keep airspeed above the stall, the rudder force is 67% of emergency thrust and range is utterly knackered. Not so very practicable, especially on the trans-oceanic routes which are the main market.

Seriously, it is a well-known problem with all tailless multi-engine proposals; they have to keep the engines well inboard.

And sadly, flinging personal insults at either me or the rest of the world will not improve your numbers.
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I'd be expecting the aircraft designer to be covering the control influence issues, thats his job.

I'm not sure where a personal insult was sent - perhaps your a little sensitive?

I suggested moving them a little out, to align with freight, now you feel they need to be well inboard? We both seem a little imprecise? And I didnt state tailless, you did.

Another suggestion, as this is clearly going to take a few years, is that these will end up as electric powered, so this seems to favour a large number of relatively small engines, so one out isnt going to be such an ordeal.
 
If rear-mounted engines are bolted to 40 G pylons, wrapped in Kevlar and multiple control routings,the risk of engines hitting passengers can be minimized.

As for docking and loading passengers????
How difficult is it to assign two sets of air-bridges to each BWB airliner? ... one air bridge to each leading edge tube ...
Or you could dock at a 45 degree angle to the boarding lounge so that one leading edge almost touches the windows while the other leading edge tube is served by conventional air-bridges.

Roof and belly escape hatches can serve as emergency exits during the worst survivable crashes.
 
From this report.
 

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From this report.
 

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FXXII said:
…. , the final word is compliance to FAR 25 and CS 25. They deal with subjects such as …. engine transgress into the cabin. No manufacturer as far as I know (AFAIK for the young ones;)) have adressed this in a concise way.
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I addressed your concern in 2 previous replies.

Republic invented a solution circa 1944 when the installed 40G engine mounts on their RC-3 Seabee light flying boat. Engine mounts prevent the engine from moving forward - into the passenger cabin - during crash decelerations of less than 40Gs.
US Navy testing concluded that properly-restrained pilots could survive crash decelerations of up to 40Gs. Try to picture hitting the fantail while trying to land on a aircraft carrier. Those USN and USAF sled tests were done during the 1950s and produced the seatbelts that are now standard on motor vehicles.

Lake Amphibian has an engine pylon of similar strength. Several Lakes have landed HARD, wheels-up on land and the engine stayed in its proper place on top of the pylon.

Wing-mounted engine pylons are designed to the opposite standard. Wing-mounted engine pylons are designed to fail early, before wing strength is compromised. The design goal is to be able to wreck an engine on take-off and still be able to fly long enough to land back on a runway. Try to picture an airline engine hitting a truck just as the airliner lifts off. The engine and pylon are supposed to break off and fall free, but leave the wing intact.

Landing gear are designed to similar criteria so that they will break off before damaging the fuselage or wings.

I am tired of reading your repeated scared concerns about problems that engineers developed solutions to 80 years ago (Seabee example).
 
Arjen said:
Image from AW:
View attachment 626268
Flugrevue has an article about the Maveric demonstrator with more images:
www.flugrevue.de

Blended-Wing-Body-Konzept: Airbus enthüllt Maveric

Auf der Singapore Airshow hat Airbus erstmals sein neues Blended-Wing-Body-Konzept Maveric für Verkehrsflugzeuge der Zukunft gezeigt. Es soll 20 Prozent Kraftstoffeinsparung bringen.
www.flugrevue.de www.flugrevue.de
Span 3.2m - first flight June 2019, France - flight testing in progress
View attachment 626269
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Pretty engine pylons/fins, but I question why Airbus wanted to build ring frames as complex and expensive as the ring frames/fin spars on DC-10.
A much simpler solution would be to build straight spars and hang engines off the sides of the spars.
Since fins are already offset from the center line, the asymmetry would make little difference, but would reduce construction cost and weight.
 
robunos said:
Okay, I'll bite . . . so, according to your definition above, this is a BWB aircraft, it has an aerofoil section fuselage . . .

View attachment 626394


cheers,
Robin.
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Most of Vincent Burnelli’s lifting fuselages were not “blended.”

They looked great judging by the numbers generated by 2D airflow calculations. Sadly, they failed to account for the 3D airflow around fuselage edges at steeper angles of attack. At steep angles of attack, those sharp corners generate massive wing tip vortices that generate massive amounts of lift, but also massive amounts of drag. IOW they generate more drag than lift.
OTOH rounded fuselages only generate gradual increases in lift and drag as angles of attack increase.
 
Fluff said:
Another suggestion, as this is clearly going to take a few years, is that these will end up as electric powered, so this seems to favour a large number of relatively small engines, so one out isnt going to be such an ordeal.
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You still have whatever is generating or holding the electricity to deal with.

Batteries need to hold about 50% of the energy equivalent of the fuel in the dino-burner version of the jet you're dealing with. That's going to require a two order of magnitude increase in energy density even over Lithium batteries for a long flight. And those batteries will be SOLID, not fluid. Or you're running a big electrical generator off something massive and routing power to all those little props.

In either case, you have big heavy items, whether engines, generators, or batteries, that will want to break loose and go smashing forward in a crash.


======
Now, as to the viability of electrically powered flight:

Short hops, on the order of Seattle-Vancouver/Victoria BC, are presently viable on pure electric converted Beavers and Otters. 160km. The recharge time takes about as long as the postflight, pilot's break, and preflight; completing before passenger load.

So a flight from London to Paris (300-350km) is viable with some delay between flights. Say, one hour between flights of that particular plane.

Hawaiian Airlines might be the business case for electric commercial flight on the short hops between islands.
 
Scott Kenny said:
…. In either case, you have big heavy items, whether engines, generators, or batteries, that will want to break loose and go smashing forward in a crash. …
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As I explained in 2 earlier posts - engineers solved that problem 80 years ago with 40G engine mounts on Republic’s RC-3 Seabee.
Will you please stop beating a dead horse.
 
Scott Kenny said:
No offense, but you're assuming that the 22yo "engineers" designing these things bother to read what the old timers did.
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"Those that fail to learn from history are doomed to repeat it." Despite historical as well as contemporary information being more readily and universally available than any time before, this Winston Churchill quote is sadly more pertinent than ever in pretty much every aspect of global society. Instead, "ignorance is bliss" seems to be the ruling motto these days. My apologies for editorializing, but thankfully I've seen better days.
 
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Sounds nerdy, but when I started studying engineering, I almost immediately went to the library to borrow Harry Ricardo's "High speed internal combustion engine" (the 1954 edition). There are and allway will be at least some engineers who have a passion for their job.
 
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riggerrob said:
Pretty engine pylons/fins, but I question why Airbus wanted to build ring frames as complex and expensive as the ring frames/fin spars on DC-10.
A much simpler solution would be to build straight spars and hang engines off the sides of the spars.
Since fins are already offset from the center line, the asymmetry would make little difference, but would reduce construction cost and weight.
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As you pointed out, the engine need to stay fixed even at 40 g and here, the streight direct fixing of the engines to the fuselage is the better solution. The ring frames will likely be necessary in every case to hold the engines in position. From an aerodynamic stand point, the solution will surly also be better than using additional fixing elements in the airstream which adds drag. Also, the interference drag of the integrated solution will surly be better.
 
riggerrob said:
Pretty engine pylons/fins, but I question why Airbus wanted to build ring frames as complex and expensive as the ring frames/fin spars on DC-10.
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Anybody consider putting engine/pylon/fins stop a pass-through direct to the wingbox/landing gear?

Keep the strength in a central location with lighter forms radiating out from it?
 
You mean to integrate the engines in the fat inner wing section? Quite a good idea, despite it would need long injector/ ejectors and might be of safety concerns. Otherwise, it could be a very efficient solution.
 
Nicknick said:
You mean to integrate the engines in the fat inner wing section? Quite a good idea, despite it would need long injector/ ejectors and might be of safety concerns. Otherwise, it could be a very efficient solution.
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Greatly complicates maintenance.

Engines in a pod are easy to access, easy to change, and easy to upgrade with bigger engines if needed. Engines buried in the airframe are a pain to access and replace, and an absolute nightmare to upgrade.
 

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