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That is not necessary true. A flying wing can be made completely stable. The biggest issue with flying wings is for passengers experiencing much more up and down movements. Their position is (specially for the most backwards ones) more towards the wingtips. As you can understand a slight correction will move you a few meters up or down. Constantly.

While you are likely technically correct, in terms of passenger experience, pretty much everyone will disagree with this assessment of "stable".

True, but we were specifically discussing aerodynamic stability and how it might affect safety, training, and regulation. The quality of the ride is a separate issue.

Stability in aeronautics is the tendency for an airplane to remain in equilibrium without control inputs. A helicopter is unstable, a Cessna is very stable. Comfort is a different metric. You can have a comfortable helicopter ride even though the aircraft is unstable. Comfort is also subjective, while stability is not.

To be clear: you are being downvoted because your grandparent comment specifically said "aerodynamically unstable". That's why everyone thinks it's so clear in context that your parent comment was referring to the technical, aeronautical meaning of "stable".

Good point! Looking at the wings of a regular airplane it definitely would be a pretty crazy ride sitting out there while the plane is banking.

One of the cited advantages is that the pressurized passenger tubes make the wing structure far more rigid to bending loads, because it has such a deep beam profile compared to a traditional wing. The observation of wing motion really reveals a disadvantage in traditional airplane structures.

The wing planform is passively stable without a tail, so there should be no issues related to certification as suggested upthread.

Source for both is this video from the designer: https://www.jbenad.com/news/2015/2/4/flyingv

Economy Minus!

Just market it as a roller-coaster seat.

He does talk about gusts and stability in the video (around 34min in). Not the greatest communicator, but it does seem like they've put some thought into the concepts.

lots of interesting questions come to mind.

Would the best seats still be in the front?

I think of riding a schoolbus... I know the rearmost seats were bumpier, but were the calmest seats near the center or the front?

where should you put the bathrooms?

Also, should the plane flex or should it be rigid?

The flying wing would be a new "type" and therefore require a new type rating (special training on all the systems and performance) which is not super uncommon for new aircraft. As such it's not a big deal and any quirks would be covered by such training.

The 737 fiasco was almost entirely because they refuse to allow new 737 designs to require a new type rating and therefore force weird aircraft/cockpit designs that would otherwise seem stupid.

Also, commercial aircraft aren't really certified based on how they handle stalls, spins and spirals. Swept wings already handle those situations very badly and therefore systems are designed to prevent the aircraft from entering those parts of its flight envelope.

> […] flying wing aircraft […] are aerodynamically unstable. They can't be flown by humans […]

RC flying wings are regularly flown by humans without any software in between the input and control surfaces.

Really now?

As you might imagine, the scale and operating requirements of _actual_ aircraft introduces complex engineering challenges that aren't present in toys.

There are very specific regulations relating to how transport category aircraft have to behave. One of these is the reason the 737 MAX has the specific MCAS behaviors that are probably responsible for two crashes: causing the aircraft to stall must require continually increasing the pitch-up control input (or something substantially similar), and that wasn't the case at low speed, high thrust, and high angle of attack.

It may be difficult to achieve the required flight characteristics without software augmentation in a flying wing, even if RC hobbyists can usually fly them manually without crashing. The 737 MAX has raised the question of whether it's a good idea to approve transport category aircraft that require help from software to have acceptable flight characteristics.

MCAS wasn't required for the MAX8 to fly it was required for it to maintain the common type rating with the existing 737 fleet. With training the MAX8 would have been fine to fly and pilots would have known to pitch down or decrease throttle when experiencing the engine induced pitching.

MCAS provides for the certification requirement of continually increasing stick forces with increasing pitch, which was otherwise not met at high angles of attack and high thrust settings.

MCAS (or another means to accomplish the same goal) was required for the aircraft to meet certification requirements, regardless of whether it was to share a common type rating with the rest of the 737 fleet (so long as it shared the landing gear with the rest of the 73' line, it was going to have this adverse aerodynamic raw result).

https://www.risingup.com/fars/info/part25-175-FAR.shtml

That regulation seems to be at a static thrust level right?

> 75 percent of maximum continuous power for reciprocating engines or the maximum power or thrust selected by the applicant as an operating limitation for use during climb for turbine engines; and

Wouldn't that give a stable pitch response because the thrust relative to the center of mass is constant? Also if the MCAS is always pushing the plane out of the given AoA (which seems to be what it's logic is, if AoA > x trim down until AoA < x) would that be considered outside the flight envelope anyways? The stick force curve goes screwy for every aircraft in a stall.

It's an aerodynamic issue with the 737 MAX: the engine cowlings themselves produce lift at a high angle of attack, and the engines are mounted farther forward than they are on other 737s.

Airbus and Boeing have been flying fully fly-by-wire airliners for decades. It works just fine.

Those aircraft, as far as I know would meet certification requirements without the software adding control inputs that are opposite to what the pilots command.

And helicopters are aerodynamically unstable as well.

They don't require active stabilization by software, which is the issue here. Specifically, does the plane become unfly-able if your computer crashes.

It is fine if a fighter jet crashes when the electronics fail. Much less so for a passenger yet.

> It is fine if a fighter jet crashes when the electronics fail.

I certainly hope not.

It’s fine in the sense that a fighter jet can glide for quite a while and even land without engines. If that’s not possible, the pilot can steer it to crash in a remote area and the pilot can escape.

A modern fighter jet is not a good glider. An F-16 can't fly without the computer. Have you tried to sit in the cockpit? The sticks don't even move, they are pressure sensitive only. You are right about the ejection, that's how the pilots survive a computer malfunction, with a complete hull loss as consequence.

But it is. Militaries like to play the "protect our troops at all costs" card when it helps them, but ultimately they make decisions based on a nonzero amount of acceptable deaths.

Or alternately phrased - low performance is also a safety risk in the military context. Increasing accident death rate in exchange for reducing the enemy-action death rate can be a good tradeoff.

> RC flying wings are regularly flown by humans without any software in between the input and control surfaces.

Technically this is definitely not true. Any modern RC wing will use software to do elevon mixing and get elevator/aileron input into the actual mechanical surfaces. It's possible to do this mechanically but software is so much simpler it's a no brainer to just have a servo per surface and do everything else in software.

It may be true in the spirit of this discussion in the sense that most RC wings just do fixed software mappings between inputs and outputs instead of having an on-board computer taking into account attitude/airspeed/etc and adjusting the inputs based on this. That's what's actually needed for aerodynamically unstable aircraft and RC wings generally don't need that, although similar kinds of hardware do exist in the RC world and are used sometimes.

I mean, you could just as easily do the mixing on the TX side rather than the RX side. In that case, there is not software between the RX-servos and the control surfaces. I think that counts as 'no software between the input and control surfaces'.

The relevant question is whether there is an IMU providing feedback without which the plane would not fly.

It's my impression that "everybody" puts a flight controller between the servos and the receiver these days, either a sophisticated one running something like ArduPilot [1] or at least a cheap, dedicated flight stabilizer like (random pick) [2].

[1] http://ardupilot.org/copter/docs/common-choosing-a-flight-co...

[2] https://hobbyking.com/en_us/quanum-gyro.html

Maybe there is region differances here. Here in Sweden most RC-Wings, actually all, I have seen have been self made and do not use any active controller.

What kind of observations do you have to support your statement?

Ps. Most of them I have seen, and built, has been to play a game where you put a string on your tail and try to cut each others with the propeller. They were airodynamic stable.

This depends a lot on the cost of the model. For a powered model costing hundreds, or thousands of dollars, this is a wise addition because it protects the motor in the event of something going wrong (usually the control link dying)

However in RC gliders (slope especially) it's not necessary - the plane is made of foam and will bounce off any obstacle with minor damage, and they don't fly at long range. It's quite uncommon in this type of flying.

I've flown flying wing gliders that didn't have a flight controller - they work just fine. They're very aerobatic, though, which is less than ideal for carrying passengers.

The main issue I can see with this flying configuration is that the Centre of Gravity is extremely sensitive. You have quite a lot of leeway with a conventional airframe, but with a flying wing the CoG has to be spot-on or it becomes uncontrollable.

>However in RC gliders (slope especially) it's not necessary - the plane is made of foam and will bounce off any obstacle with minor damage, and they don't fly at long range. It's quite uncommon in this type of flying.

If your reference is simple foam planes this is true. But in high-performance applications like F3F people will run on-board accelerometer based control units that stabilize flight.

The whole discussion is a bit silly though. The standard for toys is clearly not the same as for a passenger carrying commercial airliner, even if sometimes they are very expensive toys...

Oh sure. Those F3B/F3Fs sure fall under the expensive category! I would probably add one for anything not foam.

> "everybody" puts a flight controller between the servos and the receiver these days

This was the point I was trying to address. It's definitely commonplace, but not essential, and the plane is aerodynamically stable without one.

A static mixer does not qualify as a stability augmentation system. SAS uses feedbacks from the state of the vehicle to change the plant dynamics.

I can see why this might seem like the case with present time flying wing aircrafts. But most of the initial design and theory for the flying wing design (such as the Horten Brothers) was actually done on a glider which is passively stable. Most, if not all, military fighting aircraft (like the F and B series) are purposely designed to be dynamically unstable since this allows much faster control and reaction time at the expense of special computer and ASICs to maintain aircraft stability.

I don't think things like the Northrop YB-35 had much in the way of computer control. Never heard about flying wing aircraft being intrinsically unstable. Maybe the designs you've heard about were (things like fighter jets are designed to be unstable)

One could argue that as a result of the B737-MAX fiasco, no matter how small your change, you are likely to be required to go the full recertification route. This being the case, why not go big? You have to recertify anyway.

Disclaimer: I am not an aviation expert, and don't know what I'm talking about.

That would be absolutely insane. Aircraft development would halt.

If you can really save 20% on fuel for the same load though, that would be worth quite a bit of engineering and retraining.

you don't know what you're talking about at all. Every single point is incorrect.

This video (shot from a chase car) of a B2 landing demonstrates the challenges with an configuration closer to a flying wing than an airliner: https://www.youtube.com/watch?v=ih57FiOeZXU

Uh.. that's a U2, not a B2. The U2 is not a flying wing, and the two are really not even comparable.

That's a U-2, not a B-2. How is it closer to a flying wing than an airliner?