# Tag Info

40

Flying wings can be made to have acceptable flying qualities without any artificial assistance. Just look at the Jim Marske glider designs. The principal downfall of flying wings is that stability in pitch is pretty much achieved the same way as with a conventional tail, with a down force balancing out the center of gravity forward of the fulcrum of ...

29

Cargo aircraft (outside the military) almost always started life as passenger aircraft. The ratio of active large cargo aircraft to passenger aircraft is in the single percentages. Therefore, nobody develops a pure cargo aircraft from scratch. That does not mean that no one has tried. Especially for cargo, large flying wings have been proposed which store ...

27

Good question! There's a bit of a misconception: when the elevon moves up, it actually decreases lift. It pushes air up which pushes the wing down. This explains the roll behaviour, but how does decreasing the lift make the plane go up? The key here is that the lift is reduced only at the rear of the plane. In other words, the rear of the plane is pushed ...

21

Directional stability When a swept wing is flying in a sideslip, the windward side behaves like a wing with less effective sweep $\varphi_{eff}$ and the leeward side like one with more effective sweep. Wing sweep causes a flattening of the lift curve slope for two reasons: The effective angle of attack is reduced by the cosine of the sweep angle. Only the ...

16

You basically have the answer right inside of the question (as was mentioned in the comments). In order to make the plane pitch up and down you have the ailerons move up or down in unison (usually called an elevon at that point, again, as noted in comments.) Here's a handy diagram to give you some idea of what we're on about: In the second image the ...

15

Sweepback helps a lot, and the rest is achieved with drag devices near the wingtips. (Source: aerospaceweb.org) Did you notice that the B-2 has split ailerons, and they are partially opened during flight? Their drag pulls the wingtip back, and in combination with sweep the forward wing in yaw will have a longer lever arm, so the same drag produces a bigger ...

12

First of all, the general idea is to avoid reflection of radar energy back to its source. Next, you want to direct the reflected energy into as few directions as possible in order to dazzle any observer with a momentary bright beam, surrounded by as little reflection as possible. That is the reason for the aligned edges and serrated patterns on stealth ...

11

In addition to the other answers, a reason for the lack of flying wings in civil aviation in general is that they need to compete in an environment that has grown alongside conventional, fuselage-and-wings aircraft and is ill-suited for flying wings. This means they need to use the same airports (turning radii, RWY widths), fit into the same parking ...

11

For a start, with what it costs to design and certificate a new aircraft type, if a transport craft can't be reconfigured to carry either passengers or freight it won't make it off the napkin. The conventional transports we have can be switched from cargo to passenger and back, some in just a few hours. For a non-passenger transport to compete, it would ...

9

Theres two different approaches, passive and active stability on all three axis. X axis (roll): In the X axis, flying wings are stabilized the same as any other plane. Passive stability is achieved through a slight upwards dihedral between left and right wing. Active stability is achieved through ailerons near the wing tips which create a controlled ...

8

Twist is closely coupled to the wing's sweep angle, airfoil camber, taper ratio and the desired level of static longitudinal stability. Other factors are the desired spanwise lift distribution and maneuverability. There is no simple, general formula: In the end twist, or, more precisely, local reflex camber, is the consequence of your selection of the ...

8

A somewhat simplified answer. When both elevons go up, they will push the back of the plane down. This makes the nose start to point upwards, or, as we say, the plane pitches up. This increases lift, and so the plane goes up. So the sequence really is: elevons up --> back end pushed down = pitch up --> increased lift --> increasing height. If one elevon ...

7

Flying wings simply don't have much internal space for cargo, so they're a non-starter for cargo planes. You mention the B-2 which will carry 18 tons of bombs. However, bombs are small and heavy: for example, a US Mark 82 bomb is essentially a 130kg (300lb) metal box filled with 90kg (200lb) of explosives. Most airline cargo isn't packed in thick, heavy ...

6

I know, flying wings are cool. But once you have built and flown one, you get a more nuanced view. To find the right configuration, start with a look at your objectives. You want: excellent performance and an observation platform with good stability. Now let's see what a flying wing will do for you. Apologies for the heavy use of technical terms; please ...

6

I would like to discuss the stability argument in a bit more detail. Since it is correct that static longitudinal stability is the main reason why these aircraft are not often developed. However the reasoning given in the other posts is incomplete/not completely correct. First of all, a flying wing indeed has a very small stability margin. This can be ...

5

Yeah you could start with X-plane, which claims that it can figure out the flight characteristics from geometry parameters. It is based on laminar flow theory and on classic aeroplane shapes and configurations, but it is a start. They have something called Plane Maker which could serve your application. FlightGear is a similar program, open source so you ...

4

It's all about CG range and how much abuse the design can take. Take a look at the C-130 Hercules. It has a huge Hstab to cope with a wide range of CG. Really a bi-plane. So is the Chinook helicopter. Holding the table up with 4 legs (6 with a canard). So, what do we do to get to a viable flying wing? Sweep back offers improvement in pitch stability as ...

4

Net wing loading (weight per unit lifting area) can't be zero in level flight. Lift must equal weight, else the aircraft will accelerate in the direction of the net force. The loading distribution on the Helios is designed to reduce flexing moment along the span, which is an entirely different thing. As you note, that optimization wasn't perfect, although ...

3

A downward deflected elevon creates an upward force, an upward deflected elevon creates a downward force. This pair of forces thus produce a rolling moment, making the aircraft start to roll.

3

Flying wings use differential thrust for yaw control instead of vertical stabilizers and rudders. Some also have small outboard rudders or spoilers for this purpose.

3

OK, I found one, from a friend's suggestion about hang gliders. The late 1970's UFM Easy Riser, initially a go-kart engine strapped to a foot-launched hang glider, the "first ultralight." But this is even more Octave Chanutesque than the 1912 Dunne! Are there any, shall we say, nonprimitive models? If not, why?

3

The term "3 point landing" is derived from old taildragger (3rd wheel in back) designs. In reality a 3 pointer is not desirable, as the wheel, front or back, being away from the center of gravity, can produce a nasty pitch if it bounces. At landing speeds this can be uncontrollable. The term "3 pointer" does imply good landing speed management, as the ...

2

As for flying wings, longitudinal control (let alone stability) depends on being able to being able to move the center of lift backwards and forwards. That would be hard to do with a straight flying wing which doesn't have a separate tailplane or carnard -- all the lift is generated at the same (longitudinal) position. On the other hand, if your flying wing ...

2

It will not primarily affect roll but it will affect yaw. And if your wing have any yaw-roll coupling (and swept wings certainly do) the yaw will cause your wing to roll a bit but generally not much and generally not completely controllable by you. Here' one flying wing with no moving control surfaces: Note that without ...

2

First thing first: I think you mean yaw not roll. See Yaw definition If you actually mean roll, then the answer is no. If you mean yaw; then the answer is yes. However it is impractical for two reasons: 1) Engines, especially jets but also propellers have a latency when speeding up and down. This will make it impractical, and might create pilote induced ...

2

The reason an elevator can cause pitch up/down is by providing a force, pushing down/up, on a point aft of the Center of Gravity (CG). A canard provides pitch up/down by pushing the nose up/down (forward of CG). An elevator provides pitch up/down by pushing the tail down/up (note that pushing the tail DOWN pushes the nose UP). Are your elevons (...

2

The first certified stable aeroplane flew in 1910 at (and without) the hands of J W Dunne. It was also the first tailless swept plane to fly, sort of a biplane flying wing except that everything was piled in between the wings so not a true flying wing. Contemporaries Handley Page and Igo Etrich were obliged to add tails to their more bird-like attempts. ...

2

It is arguable that these planes are not true flying wings because things like the pilot and engine sit or dangle outside the wing airfoil. Besides Dunne's D.1, D.3, D.4, D.5, D.8 and D.10 of varying success, W Starling Burgess in the US built 19 Burgess-Dunne tailless biplanes, many of them waterplanes, e.g. the 1916 AH-7. The 1930 Smith B2 Arrowhead was a ...

2

Probably not. Spins usually start from a stall, not a side slip, and yaw stability generally improves spin resistance and recovery. For model flying wings, removing the tip fins usually makes spins far more likely and much harder to recover from. The usual explanation is that the end plate effect delays the stall at the wing tip.

2

One reason for spin issues with tailless designs is that a spin is a stalled condition, and there's no secondary surface that can be forced out of the stall (or prevented from stalling entirely) as is the case with canards and conventional layouts. Standard spin recovery in most conventional aircraft is to apply forward stick and use rudder to stop the spin ...

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