Stanley flying flying wing

[Spacetraindriver]

As all of you know (I hope) the B-2 is a flying wing. I like it. So I made one. But I have some troubles flying it. When I turn (roll, pitch) it stays in like a drifting position after it (kinda) stalls. Is this how they behave or is it just me? It does even out but still.

Mass: 55.8t
Size:3.7mx42.7mx14.9m

Note: I've added two Big-S flaps.

DARN YOU AUTO CORRECT! Edited November 26, 2015 by Spacetraindriver

[Jovus]

If I'm understanding your description of events, and I remember rightly about how flying wings work, this is pretty accurate to real life.

[Claw]

The lack of tail means that the flight computers actually need to do more work to prevent drift. This sort of functionality doesn't exist inside KSP. (Unless I'm misunderstanding your issue.)

[MaxL_1023]

Flying wings are aerodynamically unstable. Continuous 3-axis control input is required to maintain level flight. The B2 stealth bomber had independently controlled engines which varied their thrust output slightly to act as yaw controllers, in addition to the pitch and roll control you can get through thrust vectoring and control surfaces. Since you are stuck with pitch + roll only ( at least using SAS - a mod or manic mouse clicking could allow differential thrust to some extent, although it would be funny to watch and probably would not work) you end up having difficulty controlling your aircraft.

You might be able to get around this using Vernor engines as RCS thrusters - they point outwards (so near-nose placement gives you decent yaw torque) and they are quite a bit more powerful than standard RCS thrusters. Since you need RCS for spaceflight anyways (if you want the SSTO route) I would recommend using a couple and trying it out. 50+ tons may be pushing it a bit, but you should be able to stay at least somewhat stable with SAS working with your jury-rigged 3-axis control.

In short, you have 3 degrees of freedom with 2 degrees of control, meaning that no matter what you do something is going to mess you up eventually. It would be a nice challenge though - "make it to the island airfield with no vertical lift or control surfaces."

[Spacetraindriver]

Oh ok. Yes you are understanding it correctly. Oh well.
[SIZE=1]

(Heh, I CAN"T CHANGE IT TO ANSWERED!)[/SIZE]

[KerikBalm]

[quote name='MaxL_1023']Flying wings are aerodynamically unstable. Continuous 3-axis control input is required to maintain level flight[/QUOTE]

This is not true.

Were that true, this image from real life would be impossible:

[img]http://www.delta-club-82.com/bible/ailes/laminar-z9_id784p1.jpg[/img]

[img]http://www.icaro2000.com/News/News-gallery/Worlds/Laminar.jpg[/img]


The swept leading edge confers yaw stability, also the tips of the wing are behind the CoM because of the sweep, and are able to give it pitch tability.
Slight dihedral gives it roll stability.

[img]https://upload.wikimedia.org/wikipedia/commons/1/17/Northrop_N-1M_Udvar-Hazy.jpg[/img]

[img]https://upload.wikimedia.org/wikipedia/commons/6/6b/YB49-7_300.jpg[/img]

These were made long before computer controlled flight, although one does have tailplanes to increase yaw stability. (Higher aspect ratio hanggliders with less sweep are a bit harder to fly because they are less yaw stable, and can "snake" at higher speeds, and sideslip much more if you don't coordinate your turn well, sometimes tails are affixed to help either pitch or yaw stability:

[url]http://www.hanggliding.cz/!pictures/aktuality/image/P1180870w.jpg[/url]

[url]http://www.skydogsports.com/hg-1/2013-cloud-9/July-13/IMG_7238.jpg[/url]

These improve stability... but are not neccessary to have a stable flying wing.

Furthermore, you don't need to vary thrust to achieve a yaw torque (you can't yaw a hangglider, they rely on passive yaw stability)
The B-2 for example has a "split rudder"

[img]http://www.richard-seaman.com/Aircraft/AirShows/Edwards2005/B2/B2Landing10oClock2.jpg[/img]
Basically, you deploy an airbrake on the tip of one wing or another.
I think you can use airbrakes to do this in KSP automatically (they do have pitch and yaw settings)

[img]http://i.imgur.com/FzIMFnV.png[/img]

While most hanggliders have no yaw control (not 3 axis control), the "rigid wing" variety (as opposed to "flex wings") need control surfaces as weight shift control is insufficient (a flew wing flexes in such a way when weight is shifted, that there are aerodynamic roll forces as well) for roll.
They use a spoileron system linked to the pilot body position,
[img]http://ozreport.com/pub/gbspoilerons.jpg[/img]

This also creates a yaw torque, which helps stabilize yaw/counteract adverse yaw when turning, and rigid wings can get away with even less wing sweep (as a consequence, their pitch stability often becomes really bad, and they are given a horizontal stabilizer)


There's no reason a flying wing can't be aerodynamically stable

[Van Disaster]

Hanggliders have some inherent pitch & roll stability because the pilot - and thus CoM - is below the wing, of course ( assuming the pilot holds the wing in a steady state ). But yes, the B2 needs yaw brakes as it has no vertical stabs, so if it yaws it won't self recover.

[KerikBalm]

Yes, having the pilot below the wing could help if they are rigidely attached... but there is only a single attachment point going directly to the wing with a non rigid connection... the attachment of the mass to the glider cannot exert any torque under normal conditions - if you hung a sack of potatoes from the wing, you'd get no stabilizing effect from having the potato mass below the wing.
If the nose goes up, the control bar moves forward relative to me, I don't move with it unless I choose to exert a force to pull my mass "forward" as well and bring the nose down.
That mass (the pilot) can only exert torque through the control bar (which does have a more or less rigid connection to the wing through the wires that hold it in position.

You aren't flying with the pilot rigidly attached to the control bar.
While that would help pitch and roll stability, it is not needed, and the gliders are stable with no pilot at all.
The pilot does not hold the glider in a steady state... the pilot flies with a "finger-light touch" on the bar most of the time.
Most of the pitch stability comes from a twist in the wings so that the wingtips are at a different pitch than the nose. This can be adjusted, and the less twist... the better they glide... many pilots flying the gliders in competitions tune the twist to very low levels, and have gliders that have little passive pitch stability and require fast reactions from the pilot... competitions actually have quite a few pilots tumbling their gliders (which normally requires a parachute deployment)
In contrast.. a paraglider has massive roll and pitch stability from hanging from their wing from many lines, not a single one like a hangglider

And... that still does nothing to address yaw stability.... even in paragliders


The B2 is yaw stable without the yaw breaks... because it has a swept leading edge.
As it yaws relative to its direction of flight, one wing will present more frontal area than the other, resulting in a stabilizing torque...
Of course a thin low drag "blade" wing won't present nearly as much torque as the flat surface of a vertical stabilizer.
It is *less* yaw stable, but it is still yaw stable. It just means more "gentle" and less "aggressive" maneuvers are needed if you're going to rely on passive stability.
Which is not typically a restriction that the military likes to have.
Again, I'll point to the flying wings from te 30's, 40's, and 50's, in particular that yellow one above...
They were perfectly safe when flown within their limits. Its true that many eventually crashed and they were largely abandoned... but thats what happens with experimental craft and test pilots... they were flown beyond their safe limits.

Much like a plane in KSP can be pitch stable enough... but if you pitch up too hard/fast... it will flip (this is particularly likelyto happen if your CoL is just barely behind the CoM)... The flying wings are stable, they are just *less* stable and a pilot that isn't aware of their limits or pushes their limits will eventually go beyond them.

Hang gliders are quite yaw stable because of the relatively high angle of attack and low wing loading (a consequence of slow speed flight). So when one wing starts presenting more frontal area than the other... there's actually quite a torque that gets exerted. Edited November 25, 2015 by KerikBalm

[A_name]

Try slapping some AIRBRAKES on the edge of the wings, they'll give you some yaw control.

You can also try to put on some vertical stabilizers and then use the offset gizmo to hide them inside the fuselage (this used to work in 1.0.4, it will probably work in 1.0.5 but I'm not sure.)

[Van Disaster]

@Kerikbalm: if you *did* hang your potatos from your glider & launched it, would it self-correct phugoid pitch oscillations? you could design a wing that was ( quite ) pitch stable in all sorts of unstable wind conditions, but would that be a usable craft? ( I'd imagine it's glide ratio wouldn't be special... )

The other thing about yawing swept wings is that the straighter wing generates more lift. I'd also debate the B2 is yaw stable given where the fuselage is, but that is pure guesswork.

[KerikBalm]

Yes, the less sweep, the more efficient.

[url]https://www.youtube.com/watch?v=ke7oZMRlBPE[/url]

[url]https://www.youtube.com/watch?v=CiDZfo7gmKI&t=20s[/url]

They aren't sacks of potatoes... but they might as well be...

If you do nothing... depends on how the glider is trimmed, if its trimed to fly near stall, it may keep entering a shallow dive then minor stall, then shallow dive, then minor stall.
If its trimmed a little faster, the oscillations get smaller each time and go away.

I'm sure the B2 has some yaw stability... but given the wingloadings and the mass... its probably not sufficient for practical flight modes. Edited November 25, 2015 by KerikBalm

[Spacetraindriver]

Oh, OK. I'll add it right now (Airbrakes). Is this good (Pre Airbrake) as in swept wing?

[IMG]http://i.imgur.com/YIeSPD7.png[/IMG]

You can also see the drift.



After Airbrakes:

It still did that thing, but the brakes stabilized it, is that what it is for? The turn is not all that bad, just when I try to roll back it does the stall stuff. I guess this is answered.


I'm pretty sure! I just saw a vid of one flying and it dipped down a bit, but once those split flaps came out, it stabilized! Edited November 26, 2015 by Spacetraindriver

[Van Disaster]

If you're really into building replicas you might want to check out one of the procedural wing mods. I started a B2 thing just out of idle curiosity a while ago, didn't quite get it right, but it came out ok:

[url=https://flic.kr/p/z6u1vv][img]https://farm6.staticflickr.com/5726/21721820671_6d16f1c51b_c.jpg[/img][/url]

If you're trying to set up aero stuff make sure you turn reaction wheels off while you're doing it, or they might try and hold the craft in some other attitude.