Airbus files for patent of a flying triangle

a reply to: Thill

I would say that they are a little late in the game of triangle building. If it is to be jet powered, the concept will, ahem, never get off the ground.

Another major advantage of Blended Body aircraft is noise reduction.

Higher Lift to Drag ratio = Less power required = Less fuel required = Less noise created.

Increased lift also allows for lower stall speeds, lower landing and takeoff speeds and therefore a safer aircraft.

There are so many advantages it makes ya wonder why we still fly conventionally configured aircraft.

With this solution from Airbus to the problem of form weakness in an irregular shaped pressure vessel we get another step closer to fulfilling the dreams of Jack Northrop.

The one remaining problem could be converting assembly lines, supply chain conveyances and airports to accommodate it's monolithic form.

While this concept is an improvement over some of the previous BWB efforts like Boeing's, it will still suffer from one major drawback and that is passenger comfort. Sticking a bunch of people in an enclosed doughnut with apparently no windows will result in sick bag and motion sickness tablet manufacturers stock going through the roof. A lot of people will not react well to being in a seat that is on the outer rows and sideways or even backwards to the direction of flight. Add in a bank or roll and I guarantee you vomit will start orbiting around the cabin! It wont be as bad as designs with seats out in the wings but it will still not be as good as traditional tube fuselage designs. There is also another issue that hasn't rally been touched on and that is crashworthiness and the fact some passengers will be in seats that face the wrong way in an emergency. People on some of the side facing rows run a far greater risk of head, neck and chest trauma or even a broken neck if the aircraft comes down hard.

Until or if they can solve these problems I don't see BWB's being used for passenger travel, however they would be great for cargo where the efficiency gains make a compelling argument. It will just require interest and enough orders to build a business case.

LEE.

a reply to: Psynic

Psynic wrote:

“Yes I realize that the passengers board through the centre of the ring shaped pressure vessel, but that is not the purpose of the ring…”

This is not an “either/or” situation; it is a “both/and” situation. The toroidal shape of the passenger compartment provides BOTH a structurally efficient pressure vessel as you suggest AND an efficient means of ingress and egress for the passengers as Zaphod points out. You and Zaphod are not actually in disagreement.

You also wrote:

“…Blended wings are all about high lift to drag ratios, which translates into fuel efficiency. Something like 50% more efficient. ..”

Not exactly. About 10 years ago, I was leading a small NASA project to build a special purpose UAV for research purposes. The configuration we were looking at called for a 60 degree delta fuselage with conventional outer wing panels. This was right about the time that the Boeing Phantom Works was spending a lot of internal resources on their blended-wing-body (BWB) aircraft concept—they had all the computer analysis tools and specialist engineers spooled up to go. When they heard about my project, they offered to donate an aerodynamic design because the configuration I was working on was quite close to what they were already working with and they were eager to gain some acceptance for their work. So they did the design, gave me the outer mold line data files and my team built a 2+ meter wingspan UAV and tested it.

Aerodynamically, the L/D ratio was very comparable to a conventional wing-and-tube type of construction; I don’t remember the exact numbers, but they were not noticeably different. Why is that? It has long been known that the mathematically ideal span-wise lift distribution is elliptical. You can’t do better than that. One way to achieve that lift distribution is by keeping the airfoil section constant along the span and making the planform of the wing be an ellipse. This is what was done with the Spitfire, for example.

Another way to achieve an elliptical lift distribution is to vary the airfoil characteristics along the span such that all the pieces of the wing are doing the same amount of lifting work that would be done by an elliptical wing of the same span. This would involve, for example, using different airfoil sections at different locations, and operating them at different angles of attack. This is what the BWB design accomplishes. Even though the planform of the aircraft is not an ellipse, the lift distribution is elliptical, and that’s what counts as far as the aerodynamic lift-to-drag ratio is concerned. The wings of conventional wing-and-tube aircraft are also designed this way and approach an elliptical lift distribution as well. Since both designs approach an ideal lift distribution, and have similar aspect ratios, they both approach the same L/D.

The theoretical advantage of the BWB is a more efficient (i.e., lighter) structure for the same amount of internal volume (i.e., a lower empty weight). A lower empty weight means that a smaller amount of lift is required for a given payload weight. Given a fixed L/D ratio and a fixed payload weight, less thrust is required for forward flight and therefore less fuel burn. This is where the supposed 50% improvement in fuel efficiency comes from.

This theoretical improvement in structural efficiency comes from the short stubby design. A short stubby design reduces the total external skin area (the “wetted area”) and reduces the skin thickness required to achieve a given strength or stiffness requirement. This advantage is greatest when most or all of the internal volume of the aircraft is unpressurized—as in a cargo lifter or aerial refueler.

When you start adding large amounts of pressurized internal volume to carry passengers, the added weight of the pressure vessel itself starts to overpower the weight savings you get from a short stubby external shell. It has long been known that the most efficient way to design a pressure vessel is with predominantly circular cross-sections. The most efficient is a sphere, but spheres have lousy drag characteristics. The next best is a long thin cylinder. A cylinder can be almost as light as a sphere and has much lower drag; that’s why it has become the most common design solution. For some reason, the BWB design approach being studied 10 years ago envisioned an internal pressurized volume that did not use a circular cross section pressure vessel. The NASA publication, NASA SP-2005-4539 [history.nasa.gov...] discusses this problem:

“Finally, of all the disciplinary design challenges facing the BWB concept, perhaps none is as important as the design of a highly noncircular pressurized cabin. The structural weight advantage of circular fuselage shapes for airplanes has been exploited since the earliest days of pressurized structures….”

I would surmise that this Airbus patent represents an effort to solve this problem by utilizing a circular cross section cabin (a toroid) that fills the skin of a BWB design pretty efficiently.

a reply to: 1947boomer

What about two tubes at an angle, merging at the nose?

a reply to: mbkennel

I think that this too would suffer the same effects as Zaph mentioned earlier. People seated at the ends of the tubes would feel much greater disorienting forces as the aircraft banked on way or the other. Would make for quit a ride but maybe not the most relaxing one.