how to avoid cyan aerodynamic lines?

[Gooru]

I´ve build a bunch of planes the last few days and all sufferd from the cyan lines that show up in the aerodynamics overlay.

These lines appear on non-lift-parts of the plane for no reason and seem to pull it in random directions, mostly left or right, till the plane starts to spin.

I don´t know what force these lines represent or shall represent, as there is no reason, why my prograde flying plane would be pulled by a super strong sideway force.

What is this?

How can i avoid it to happen?

Edited October 16, 2015 by Gooru

[Warzouz]

It's body lifting.

Nothing to worry about except that if they show up, that mean you're not in the way the plane is designed to be. That's not a cause of flipping, but more a consequence.

[Gooru]

The plane isn´t flipping, its spinning.

It flies straight prograde.

Then these cyan lines show up (sideway bodylift as you say?) , and the yaw-control tries to compensate till the lines get too strong.

Then it starts to spin.

[The Aziz]

Post a picture of your plane. Maybe from sph with CoM and CoL visible.

[Warzouz]

I have those lines on my space plane. They show up when I pitch too hard, as long as increased drag. I think your spinning problem is not related to those lines, but maybe both are related to the real cause. Planes are usually spinning because of lack of control surfaces or badly wing propositioning (CoL wrongly in front of CoM).

You should post a picture from the SPH with CoM and CoL displayed. (ninja'd)

[Gooru]

It´s really nothing special.

[Streetwind]

Assemble it again from scratch, save it as a different craft. See if it behaves the same.

[Gooru]

As i stated im my opening post this is not a problem of this special craft.

I´ve got this problem with every single plane i build.

On some planes the "cyan sideforce" isn´t strong enough to overcome yaw-control.

These planes fly stable but with the nose tilted to one side.

One plane flies stable with the nose 4° right from prograde and a strong sideforce.

[Racescort666]

Try adding a small amount of dihedral to the wings and see if that helps improve stability. When you start to yaw, it'll change the angle of attack of the main wing and start to roll and bank rather than just yawing out of control.

[Claw]

The cyan lines aren't the cause of the problem, that's a result of what is happening. The lines are showing you the forces that are going on while flying. In this case, something is causing yaw instability, which causes the craft to start to yaw until the body lift and drag forces are enough to overcome the craft's yaw authority, causing it to spin out.

Flat and wide designs like you have there often suffer from not enough directional stability. That's usually because the plane is simply not very long, which means drag forces on the front and back have very little margin with regard to their distance from the CoM (lever arm). Also, the tails are usually much less effective because of how much closer they are to the CoM.

It helps if you can shift some drag back (like moving the FL-T800s back, and the wings a little forward). Or add another vertical fin as far back on the central tank as possible. Or use the all moving tails (instead of the ones with the small tabs).

The other thing that might be happening is that the engines might be suffering from asymetric rollback. The game has a quirk with intake air generation that can cause one of the engines to starve of air, depending on the flight profile. To help avoid that, place one intake, then one engine, then the other intake, and then the second engine. (Symmetry off.)

Perhaps that will help some.

Cheers,

-Claw

[Stoney3K]

There's also a bug that happens with parts added in symmetry which causes one side to generate body lift while the other side doesn't, or one side is excessively draggy while the other side behaves normally.

[Gooru]

There's also a bug that happens with parts added in symmetry which causes one side to generate body lift while the other side doesn't, or one side is excessively draggy while the other side behaves normally.

I think this is whats happening.

When flying with about 300m/s the right tank shows a cyan line upwards while the left tank shows nothing.

The Tanks produce a different cyan-drag.

Is there a way to avoid this bug?

Edited October 16, 2015 by Gooru

[ajburges]

I think this is whats happening.

When flying with about 300m/s the left right tank shows a cyan line upwards while the left tank shows nothing.

The Tanks produce a different cyan-drag.

Is there a way to avoid this bug?

Please produce a picture of this behavior. Asymmetrical body lift display can either be a graphical bug or actual lack of lift.

If your plane is pulling port or starboard it could be a few things:

1) incorrect manuvering: yaw is to control slipstream not turn.

2) excessive yaw authority: see above

3) CoP too far ahead: you need a larger/additional verical stabilizer (or more yaw authority and a fly-by-wire system we don't have)

[cantab]

I would try a single tailfin further back.

[Claw]

The cyan line mismatch is a bug with the aero overlay.

There is a bug with mismatched drag, but that is usually associated with cargo bays being used on the sides. Another problem is if your cargo bay is actually the root part (that can cause problems on revert). You can verify it isn't asymmetric drag by turning on the right-click drag info in the Debug F12 menu. Then ALT+Right-Click on some parts and check the drag cube numbers to make sure symmetric parts match.

Cheers,

~Claw

[Gooru]

So,m i activated "Physics > Aero > Display Aero Data in Action Menus" and checked the Drag value for the Tanks, the Intakes, and the RAPIERS.

As far as i can tell there are small differences between the symetric Tanks, up to 2% of the total value.

The drag-vector are also different.

left drag-vector is (0.0,1.0,-0.1)

right drag-vector is (0.0,1.0,0.1)

Edited October 16, 2015 by Gooru

[Stoney3K]

So,m i activated "Physics > Aero > Display Aero Data in Action Menus" and checked the Drag value for the Tanks, the Intakes, and the RAPIERS.

As far as i can tall there are small differences between the symetric Tanks, up to 2% of the total value.

The drag-vector are also different.

left drag-vector is (0.0,1.0,-0.1)

right drag-vector is (0.0,1.0,0.1)

That is well within limits. The latter number that is different is the direction along the plane's "up" axis which could introduce a *tiny* roll moment, but that should be more than enough for any control surfaces to compensate.

My guess is that you have SAS enabled and all of your HUGE elevons are contributing to movement on all axes, which would cause a positive feedback loop and the plane wobbling around all over the place. You have too much control authority for a plane this small (a pair of Elevon 2's would be more than enough).

Try assigning only the outer elevons to control roll, both the outer and inner elevons to control pitch, and the vertical fins to only control yaw.

Also check if the plane flies well by hand if you disable SAS and enable fine control (CAPS LOCK) so your control inputs are small.

Edited October 16, 2015 by Stoney3K

[Gooru]

That is well within limits. The latter number that is different is the direction along the plane's "up" axis which could introduce a *tiny* roll moment, but that should be more than enough for any control surfaces to compensate.

My guess is that you have SAS enabled and all of your HUGE elevons are contributing to movement on all axes, which would cause a positive feedback loop and the plane wobbling around all over the place. You have too much control authority for a plane this small (a pair of Elevon 2's would be more than enough).

Try assigning only the outer elevons to control roll, both the outer and inner elevons to control yaw, and the vertical fins to only control yaw.

Also check if the plane flies well by hand if you disable SAS and enable fine control (CAPS LOCK) so your control inputs are small.

The vertical fin is yaw only, the elevons are for pitch and the inner elevons are for roll in my current setup.

if i use the outer elevons for roll the roll gets a little wobbly.

But i can fly the plane fine even without fine control enanbled.

_________________________________

[edit]

Replaced the 4 big evelons with a pair of evelon 2´s and now it wobbles

[Stoney3K]

Replaced the 4 big evelons with a pair of evelon 2´s and now it wobbles

If it's stable when you fly it by hand it's definitely control fighting through the SAS. Try disabling the cockpit torque wheel. And the tail fins may not have enough yaw authority because of the tiny flaps, the bigger fins are beter in that respect.

As a final measure to improve stability, add a slight amount of dihedral angle (wings and tail fins in a more "V"-like orientation as opposed to flat) which will stabilize your aircraft.

Think of the lift vectors as a set of strings that are hoisting your aircraft into the sky. If those strings are pointing towards each other, it's a more stable arrangement than the strings being parallel.

[Gooru]

If it's stable when you fly it by hand it's definitely control fighting through the SAS. Try disabling the cockpit torque wheel. And the tail fins may not have enough yaw authority because of the tiny flaps, the bigger fins are beter in that respect.

As a final measure to improve stability, add a slight amount of dihedral angle (wings and tail fins in a more "V"-like orientation as opposed to flat) which will stabilize your aircraft.

Think of the lift vectors as a set of strings that are hoisting your aircraft into the sky. If those strings are pointing towards each other, it's a more stable arrangement than the strings being parallel.

Dectivated the torgue wheels.

According to the description, the Delta-Delux Winglet has the highest leift-rating.

Wings are dehidral already.

The craft is wobbly like hell now. The last two advices made it worse.

[Stoney3K]

You haven't answered any questions which provide information about the possible cause of the problem (there is no "one size fits all" recipe for spaceplanes/SSTOs).

In *what* phases of the flight is the aircraft unstable? Low altitude, high altitude, low speed, high speed, supersonic? Is SAS engaged or is it off and are you touching the controls? Have you set any trim?

[Gooru]

The unstabability starts from the start of and gets bigger the more the plane accelerates. It is designed to reach orbit, but hasn´t to be a SSTO. I don´t mind if i have to drop tanks.

It can get supersonic up to 400m/s before the *sideforce/unstabability* gets overwhelming.

Without SAS and Trim it is noseheavy. I moved the tanks/wings forward to counter and it helped, but it´s still noseheavy a little.

Without the torque wheels it is very wobbly.

If SAS is off i have to use the controls to avoid dropping.

[Stoney3K]

Going 400m/s at sea level isn't good for any plane, supersonic is fine in the higher atmosphere but it is dangerous to fly supersonic at sea level.

When you're flying at Mach 1.3 even the tiniest deviation from prograde will cause drag which gets amplified by the SAS (over)compensating.

Nose-heaviness is best countered by moving your CoM back (it is very far forward) or adding canards. That also allows you to camber the wing so you can stay on prograde while accelerating beyond Mach 1.5. The simplest thing you can do is just add another FL-T200 tank in front of the RAPIERs so you have some wiggle room to move the wings back and forth.

CoM and CoL should be quite close with the CoL slightly behind. The arrow touching the surface of the CoM ball should be good.

[Val]

The craft is wobbly like hell now. The last two advices made it worse.

The unstabability starts from the start of and gets bigger the more the plane accelerates. It is designed to reach orbit, but hasn´t to be a SSTO. I don´t mind if i have to drop tanks.

It can get supersonic up to 400m/s before the *sideforce/unstabability* gets overwhelming.

Without SAS and Trim it is noseheavy. I moved the tanks/wings forward to counter and it helped, but it´s still noseheavy a little.

Without the torque wheels it is very wobbly.

If SAS is off i have to use the controls to avoid dropping.

If it's still the plane you pictured on the first page we're discussing, then it's 99% certain that the problem is your vertical stabilizers not being far enough back. I wouldn't change anything else.

If you google delta winged craft, you'll notice pretty much all of the pure-delta's like yours, have a most of the vertical fin behind the trailing edge of the wing.

I think you'll see much improvement if you do the same.

Cantab is right.

I would try a single tailfin further back.

If you really don't want to move the fins for aesthetic reasons...

According to the description, the Delta-Delux Winglet has the highest lift-rating.

Yes, but they don't have much control authority in my experience.

Try using the Tail Fin or AV-R8 Winglet instead.

[Generalstarwars333]

Dectivated the torgue wheels.

According to the description, the Delta-Delux Winglet has the highest leift-rating.

Wings are dehidral already.

The craft is wobbly like hell now. The last two advices made it worse.

THe description says that although they make more lift, their small flaps don't offer much control. Lift rating means how much lift they provide, not how much control. tail fins for the win. always.