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Making a real flying wing [FAR]


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Hello, I've been building a real flying wing for about two months and tried various designs. I even tried real concepts which really flew, like Ho-229, B-2 Spirit, RQ-170, X-47B....

I'm using FAR and procedural part mods in my modpack, because I like a bit more realistic performance it can give. I'm really good at making planes and even Fly-by-wire planes, naturally unstable. Still I'Ve been building flying wing for two months and still no results. The wing was very bad at first. Nowadays its pretty stable except turning. I'm using drag rudders and spoilers and double side flaps for turning. I put spoilers of wing size and still it can't compensate the sideslip it sometimes get. Any ideas how to build it better?

Here is example of my last flying wing. Pretty stable except turning with too high AoA. This one has old photo with smaller drag rudders(I added one more to the wingtips).

Thanks for any reply! Any idea would help me!

v0Sjdps.jpg

TL,DR: My question is how to make flying wing stable even in turning at transsonic and supersonic speeds. My wing is unstable even when it have drag rudders big as the main wing....

 

Ave! Toonu

Edited by Toonu
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Personally, I don't use FAR. However, since it models aerodynamics more accurately than stock, you should be able to draw from RL planes and apply it to your craft.

Here's a possible solution (source):

Quote

[...] Z Axis (yaw) Similar to pitch, the passive and active yaw control on conventional planes is done with a stabilizer fin with a rudder at the tail.

In true flying wings this is not present (Some don't even have winglets) But the high wing sweep (usually the wings of a flying wings meet at roughly 90° angle at the tip) causes a higher drag force at the forward facing wing if the craft yaws to one side, which enacts the required corrective force. Active control is achieved by causing additional drag through some sort of braking flaps near the wing tips (the actual implementations vary - split elevons - separate break flaps - ...) [...]

It's hard to see in the image you provided but it looks like your craft has the shape of a triangle. According to the design proposed above, it should rather be V-shaped. A quick check in stock KSP: works like a charm :D

c6oqFQq.png

edit: maybe the airbrakes on my wingtips make the difference

Edited by Chemp
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Yeah, the tip airbrakes make a difference. Mount them so they extend left and right, and in their right-click menu activate yaw control (and tune authority limit to taste).  This is the only stock way I know to get active yaw drag control to work with the stock control scheme. Getting the split-aileron drag brakes to activate momentarily on control inputs is going to take a mod (not sure what - something like ModActions?)

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Yeah guys, I already had drag rudders and split ailerons. I know how to make flying wing after so long time but the problem is still present. Turning and supersonic...

I think if I add more drag rudders it will have really wing sized drag rudder :D 

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Are there supersonic flying wings? If I recall, the drag profile becomes very Important supersonic. Also having wingtips outside the shock cone created by the nose causes some horrible effects, which is why supersonic tends towards stubby wings that extend down the fuselage a long way. I'm not sure the typical flying wing geometry has enough sweep to keep the whole thing inside the cone.

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No,there aren't any supersonic flying wings nowadays. Except Boeing are developing its F/A-XX program for 6th-generation fighter jet which in concept arts is flying wing fighter, meant to be supersonic. Thanks for the answer with 90 degrees nose, I will try it. And you suggest have less longer wings? 

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FAR  models the shock cone produced by the crafts nose at supersonic speeds. The angle of the cone depends on how fast you go, faster flight having a narrower cone. Anything that protruds from the cone (like wing tips) will creat a shock cone of its own. When those new cones intersect with the original cone, you get a lot of turbulence/drag and heat. So for very high speeds, short wings are needed to stay inside the cone. To keep the required surface area, that means wings that are wider front to back. A supersonic flying wing would probably look more like a long narrow arrow head rather than the broad triangles of current subsonic ones.

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Thanks for all replies! The biggest thing that helped was Making it more sweep, with 90 degrees nose. The wing is now pretty stable event when turning at mach 1 (cause I couldnt get more from that engine so low :D) still it turn and slow down cause drag rudder. But that  isnt problem, its maybe better than turn a lot wider curve. Yeah, supersonic is whole new level. I can see that now... But thank you anyway for making transsonic wing working now guys!

Curent craft:

eWH8zkU.jpg

fKCHihX.jpg

This is my first wing of my recon fleet. Now I will focus on heavy scout using two vectoring engines with small storage. Then maybe wing bomber (see you B2, B21! :D)

And maybe even supersonic like Boeing F/A-XX 6th gen program :D

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8 hours ago, Red Iron Crown said:

The drag rudders aren't far enough behind the center of mass to be effective by the look of it. Try a more swept wing, or add some massive part to the nose, or both, and see if that helps.

That helps when they are behind CoM? I thought it is just air flow around wing stopped at back wingtip (if FAR models it...) I will try to move them. I'm just not sure what it can help with. More control?

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Think of the drag as the end of a lever attached to COM. The force applied to the end of the lever is in the retrograde direction.

Suppose you have drag in front of COM, if the craft is flying with its nose pointed a few degrees above prograde, which isnt uncommon. When that drag is activated, the force on the lever will move the nose further away from prograde, the further away it gets, the stronger the force.

Now if the drag is just behind COM, it has the opposite effect in the same situation. It forces the nose closer to prograde. The further away it is when you start, the greater the force.

If your drag is level with COM, but off to one side instead, it will start with inducing a yaw towards the drag. But because its level, it will start with maximum force which will reduce the more the craft yaws from prograde. Thats cool, it can make for a craft thats quick to respond, but it also makes for a craft that cant make small yaw corrections. The further behind COM your drag is, and the closer to centre line, the more subtle its effect will be, making small corrections with small surface movements much easier. If you need a large correction, make a large control surface movement.

One other thing, thats related. FAR also models shadowing, so if you have a drag rudder above the wing mirrored with one below the wont generate equal drag in all situations. A nose up orientation can cause the upper surface to be shadowed at some speeds, which means when you try to yaw the bottom surface creates more drag which pitches the craft as well as inducing yaw. So be aware of that effect as well.

Tldr;

the further behind COM a drag control surface is, the more sublte of movements it can induce.

Forward of com often ends up with a runaway effect, behind COM self corrects towards stability

Watch out for control surfaces loosing their effectivness if they are shielded from airflow at certain speeds and attitudes.

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