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Blended Wing Bodies

steelpillow

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There are hybrid wing bodies (HWB) and Blended Wing Bodies (BWB).
Can you provide details of the distinction between HWB and BWB, and who says so - especially who says so with any authority? For example you recently suggested the Airbus MAVERIC is a hybrid, though all the authoritative Airbus statements describe it as blended. On what grounds can you trump the authority of Airbus?
This is a serious query, I am quite prepared to believe that there is a difference, as long as it has some weight of authority behind it. For example one might suggest that the traditional BWB may have a tail, while the more recent HWB is basically a tailless BWB - or whatever.

Saying Flying Wing is like sayin my car is Hot Rod
The term "flying wing" has a well established technical meaning and it does not include either of them, though it does embrace the B-2 - probably as the classic example due to its operational fame. Mind you, the term "hot rod" is pretty well defined too. I guess both phrases also share the property of being widely abused.
 
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djfawcett

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There are hybrid wing bodies (HWB)
A hybrid BWB (HWB) is commonly referred to as a BWB with an epennage (take a look at Lockheed-Skunkworks HWB - below).
1581531557445.png
"Saying Flying Wing is like sayin my car is Hot Rod"
If you say so even though your analogy is wayyyyy out in left field.;)
 
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jsport

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There are hybrid wing bodies (HWB) and Blended Wing Bodies (BWB).
Can you provide details of the distinction between HWB and BWB, and who says so - especially who says so with any authority? For example you recently suggested the Airbus MAVERIC is a hybrid, though all the authoritative Airbus statements describe it as blended. On what grounds can you trump the authority of Airbus?
This is a serious query, I am quite prepared to believe that there is a difference, as long as it has some weight of authority behind it. For example one might suggest that the traditional BWB may have a tail, while the more recent HWB is basically a tailless BWB - or whatever.

Saying Flying Wing is like sayin my car is Hot Rod
The term "flying wing" has a well established technical meaning and it does not include either of them, though it does embrace the B-2 - probably as the classic example due to its operational fame. Mind you, the term "hot rod" is pretty well defined too. I guess both phrases also share the property of being widely abused.
you all are welcome to inaccurate definitions.
 

jsport

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So... opinion is divided then. Jsport says it's not a BWB. The rest of the world says it is. I can live with that.
So much B....
 

steelpillow

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you all are welcome to inaccurate definitions.
Well really, I ask politely for clarification as to what is or is not inaccurate, and I get this. If you do not care who takes you seriously, why bother to post here at all?
 

steelpillow

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A hybrid BWB (HWB) is commonly referred to as a BWB with an epennage
Historical usage is not consistent with that. Early examples such as the Westland Dreadnought, McDonnell XP-67 "Bat" and General Dynamics F-16 have always been described as blended not hybrid, and they had empennages.

Nowadays tailless examples seem to be the norm and web searches for images of hybrid or blended wing bodies return pretty similar sets of images. I have this feeling that only hard evidence can settle the matter.
 
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TomcatViP

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Blended wing fuselage junction is NOT bwb.

BWB have as unique feature an airfoil like airstream around the fuselage resulting in a massive increase of lift (thick section).

Blended wings junction is just a neat way of reducting trim drag mainly.

Flying wings are just what they claim: an all winged aicraft with no tubular fuselage.


All those have different aerodynamics behaviors just like ICE, turbofans and rockets are differents...
 

steelpillow

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The BWB concept has been around for a long time. The engineering mandate for squeezing the payload into a long tube is pretty darn compelling. By comparison the BWB has greater frontal area and its potential benefits such as lighter structure have always failed to compensate. Another problem is the safe location of the engines - you do not want a high, rear-mounted turbofan coming loose in a crash and smashing down onto the passenger cabin, and this was raised by the FAA as a problem with an early Boeing proposal. BWB designs always put them up there in order to maintain its theoretical advantages - but put them where they can be certified safe and the advantages diminish sharply.
In may ways a BWB is just an attempt to make the smallest practicable passenger-carrying flying wing, but the problem of frontal area is so dire that it has to carry thousands of passengers before it gets more efficient than a long tube.
They are very appealing, so let's hope I am wrong.
 

robunos

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BWB have as unique feature an airfoil like airstream around the fuselage resulting in a massive increase of lift (thick section).
Okay, I'll bite . . . so, according to your definition above, this is a BWB aircraft, it has an aerofoil section fuselage . . .

Burnelli RB-2.jpg


cheers,
Robin.
 
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TomcatViP

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Nice one Robin but that one is Not "blended"

Perhaps a definition would be NoB WB which falls apart from the categories discussed above. ;)

Notice that many pre-war European design had airfoil shaped fuselages in order, it was believed, to decrease their drag. As airfoil theory was becoming popular among designer, they found that using a wing profile for the fuselage section will ease decreasing drag.

Saddly as Lift is dependent on the ratio b/w span and chord, it was not and in effect, often the contrary.
 
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robunos

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By your own definition, it has " an airfoil like airstream around the fuselage resulting in a massive increase of lift (thick section). "
QED


cheers,
Robin.
 

TomcatViP

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A blended wing body (BWB), Blended body or Hybrid Wing Body (HWB) is a fixed-wing aircraft having no clear dividing line between the wings and the main body of the craft.[1] The aircraft has distinct wing and body structures, which are smoothly blended together with no clear dividing line.[2] This contrasts with a flying wing, which has no distinct fuselage. A BWB design may or may not be tailless.
 

DWG

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Another problem is the safe location of the engines - you do not want a high, rear-mounted turbofan coming loose in a crash and smashing down onto the passenger cabin,
A related safety issue is where do you put the hatches for emergency scenarios. There's less fuselage length per passenger, so the hatches will need to be closer together, increasing the chance of multiple exits being blocked, plus you'll likely need both lengthwise and crosswise movement to get to the hatches, as opposed to the current follow the aisle straight to the exit.

And of course there's the sheer practical issue of how do we dock this thing to a terminal....
 

nuuumannn

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An addition to the practicalities of these designs, in response, Steelpillow, let's face it, if you were in a scenario where the engines might crash into the fuselage full of passengers, you are probably gonna die from what caused it, so it's a moot point. Aviation is hazardous to our health at any rate - the average passenger jet operates in an environment where, if we were outside, we'd die from oxygen starvation, that is if we didn't freeze to death beforehand. As an aircraft engineer I am confronted with things that have the potential to kill me, every day. From carcinogenic solvents to a hydraulic system pressurised to 3,000psi, undercarriage doors that snap shut, being sucked into an engine...The list goes on.

And of course there's the sheer practical issue of how do we dock this thing to a terminal....
As for the practicalities of the thing, these are worthy concerns and if the design was to get the go ahead for production, they'd have to be examined in depth. The 90 second evacuation rule would surely have to remain however. As for docking, the industry would find a way. Look at the A380 and the lengths airports went to to accommodate it, i.e. double deck air bridges, yet the type is on its way out already. What's to be done with the massive amounts of effort put into modifying terminals once it has gone from airline fleets? Anyway, back to scheduled programming.
 

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Rhinocrates

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There is also the problem that passengers seated well away from the axis will suddenly find themselves on a rollercoaster ride if the aircraft hits turbulence. The inevitable injuries and spilled drinks would lead to floods of lawsuits against the operators. I think it makes sense for cargo that can be tied down, but passenger-carrying BWBs or dual-fuselage designs would be impossible to sell.
 

nuuumannn

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The inevitable injuries and spilled drinks would lead to floods of lawsuits against the operators.
It happens now, all the time, we just don't always hear about it. You know that surplus of cash that airlines talk about when they say they made a profit this financial quarter? It goes into things like that. If there is incentive, the design will get the green light, but it won't happen if the airlines don't want it. Airlines are notoriously conservative in aircraft selection, particularly when it comes to trends. Pax don't want jazzy, they want safe, they want normal. Something that looks like a flounder might not live up to pax expectations as to what a airliner looks like and so we'll be stuck with 707 copies for ever.
 

DWG

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let's face it, if you were in a scenario where the engines might crash into the fuselage full of passengers, you are probably gonna die from what caused it, so it's a moot point.
Engines regularly separate in non-fatal crashes, and aircraft breaking their backs are equally common, cf last week's crash in Istanbul. The problem with a BWB with engines over the rear fuselage in a crash is whether the engine breaks free, or the aircraft breaks its back, you then have a large, high-inertia lump of engine that wants to keep moving forward, while the fuselage in front is decelerating.

An uncontained blade loss, or worse, disc loss, is also more problematic in an over-fuselage engined BWB than a conventional layout - there's a much wide range of exit angles from the engine that take the debris through the fuselage.
 

steelpillow

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Steelpillow, let's face it, if you were in a scenario where the engines might crash into the fuselage full of passengers, you are probably gonna die from what caused it, so it's a moot point.
I agree with you that some of the potential hazards may be being over-emphasised here, for example roof and floor hatches with built-in ladders have been proposed. But I report only a concern expressed by the official US regulator. Crash survivability is a major regulatory area and we are far less likely to die in a major landing or takeoff incident than our forebears.
I also think the engine mounting issue is not a showstopper. BWB designers move them back from the front to clean up the wing airflow and make the wing more efficient, then claim it is a virtue of the BWB. That claim is unjustified. A generation of conventional airliners - Caravelle, Trident, VC 10, I forget the US models - did the same in the 1960s and the disadvantages showed: engines now less efficient in the disturbed wing wake, structural weight penalties. The idea was dropped and, as had happened long ago with pusher vs. tractor propellers, the marginally less efficient wing was restored in preference to less efficient engines. BWB can be no different. In fact it is worse: with engines high and at the back, as a stall approaches the engine airflow will begin to break up, leading to the risk of compressor surge and major loss of power, just at the point the plane is most desperate for increased thrust. The BWB will thus draw itself into a superstall state in which it pancakes near-vertically and controls are ineffective. Such as superstall was first experienced on the Dunne D.7 tailless swept monoplane ca. 1911, when Dunne deliberately pushed the machine beyond its stability limits when about 60ft. up. It "pancaked down, bursting like a shell all around me", he wrote afterwards. It happened again later when he cut his engine too soon before landing and pulled back on the elevators to try and gain extra distance. 40 years later the superstall was rediscovered by the Gloster Javelin, with the loss of too many RAF pilots. So both high-tailed and tailless demonstrably suffer from the same vulnerability. The later Trident had its T-tail raised further above the wing wake, and the prototype used to investigate the stall condition had a short-duration rocket pack mounted vertically in the tail should it enter a superstall. Of course, as with conventional fuselages, that high T-tail eats into the claimed efficiencies of the BWB wing. So any practical design is likely to have engines in the conventional forward under-wing position - negating also the shorter, lighter undercarriages assumed by the BWB proponents, while the sharp sweepback will necessitate long and heavy attachment pylons. It can probably be done, but I am not convinced that it would be worth it.
 
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nuuumannn

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An uncontained blade loss, or worse, disc loss, is also more problematic in an over-fuselage engined BWB than a conventional layout - there's a much wide range of exit angles from the engine that take the debris through the fuselage.
Maybe. Would it be enough to not build the design? Probably not, after all, in thousands of turboprops around the world the propeller disc is less than three feet from the fuselage full of passengers, yet the rear engine placed above the fuselage is supposed to be unsafe enough to warrant not building it? How about the current conventional engine layout where, while the pylons are not as close to the fuselage, they are mere feet away from fuel tanks. By the way, I've seen the result of a prop throwing a blade at the fuselage - it leaves a mighty great hole. Lucky the aeroplane was on the ground and no one was hurt, but in the air would have been catastrophic.

And yes, pax have survived from these incidents you describe, but in terms of the incidents, that's remarkable and almost could be called miraculous, because in reality it could have gone either way, so that in itself does nothing to prove that an over the fuselage engine layout might be less safe.

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.

The idea was dropped and, as had happened long ago with pusher vs. tractor propellers, the marginally less efficient wing was restored in preference to less efficient engines. BWB can be no different. In fact it is worse: with engines high and at the back, as a stall approaches the engine airflow will begin to break up, leading to the risk of compressor surge and major loss of power, just at the point the plane is most desperate for increased thrust. The BWB will thus draw itself into a superstall state in which it pancakes near-vertically and controls are ineffective.
Again, steelpillow, the jury is out. The most that has been tested is a scale model. No full scale rendition that has been subjected to the rigors of operational use. Just wind tunnel models, a few manufacturers mock-ups and a flying model or two. The basic concept is a long way off becoming reality and we can only hope that such things will be investigated before any metal is cut (or composite is formed). It still remains to be seen what impact such a design might have on the industry. Airlines are forever looking to find even more ways of saving money and making a profit. Its fate will, as it has been with almost every jet airliner since the Comet, be determined by this.
 

steelpillow

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The most that has been tested is a scale model. No full scale rendition that has been subjected to the rigors of operational use. Just wind tunnel models, a few manufacturers mock-ups and a flying model or two. The basic concept is a long way off becoming reality.
The Westland Dreadnought Postal Monolane was a tailed BWB which flew briefly back in 1923, almost a hundred years ago. Although it was nominally a freighter, its windows show that it could accommodate eight passengers. For an airliner concept that has been investigated many times since then, there has to be a reason it is still as far from reality as ever. As I said, It can probably be done, but I am not convinced that it would be worth it.
 
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DWG

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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.
Wow, aggressive much?

Like all safety cases (which I have occasionally worked on, though they were never my main thing), it comes down to probabilities. What is the likelihood of a blade or blisk off hitting the fuselage or tankage? That depends on the percentage of exit trajectories that intersect the fuselage or wing, with the predominant trajectories roughly perpendicular to the engine axis, with some forward component as they bounce around and out of the cowl. If an engine is mounted over a BWB fuselage, the percentage of trajectories which intersect the fuselage is likely to be somewhere between 33% and 50%. (And note that I was talking about BWBs in general, not just Maveric). For conventional layouts it's closer to 10%.
 

trose213

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This startup, Natilus, is working on a 737 sized cargo hauling UAV



 

trose213

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IMOHO the massive cargo door on the LE will be quite a design challenge, even before any certification attempt.

I don't know how representative that is because they haven't revealed anything in a while and they wasted a lot of time on their sea drone, when the FAA changed the rules.

 

steelpillow

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The Nautilus is great but off-topic as it is not a BWB by any stretch of the imagination. Please could y'all create a new topic for it elsewhere?
 

steelpillow

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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.
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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steelpillow

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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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riggerrob

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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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steelpillow

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In conclusion, it is possible to design a BWB so that passengers survive most accidents.
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.
 

Fluff

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In conclusion, it is possible to design a BWB so that passengers survive most accidents.
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.
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.
 

steelpillow

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@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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@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.
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.
 

steelpillow

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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.
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.
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.
 

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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.....
 
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