SAS Changed in 0.23?

[icebalm]

So I just realized new KSP was out (yay!) and saw the rapier engine. I love building spaceplanes so I took my latest SSTO plane out, took off the rocket engines and put on rapiers to see how it would fare. I got barreling down the runway, lifted off, set my attitude to 45 degrees, hit T, let go of the up arrow and... wtf... the SAS indicator turns into a couple of arrows and my attitude drifts down to my prograde marker. Uhm.. What's going on? Who broke SAS and what do I have to do to get it to keep my attitude stable? (in before "you need meds and a therapist":confused:)

[chrisb2e9]

I haven't played much, but i have had a few moments in space where it seems like Sas has not worked like it should.

[Daddy Cecil]

I believe the two arrows were introduced in the .22 reaction wheel "improvement"

[Madrias]

Am I the only one who wants the 0.21 SAS back? It did a great job of keeping a plane flying straight.

[AlamoVampire]

ive not used SAS yet in .23 as I let mechjeb handle the work on my missions lol

[Markus Reese]

Hiya, first question are you using a joystick or other analog input? My guess is yes. Here is why:

They added an improvement to the SAS where it locks heading, but any command input overrides the SAS until released at which point, that is your new heading. helps with springyness and makes for finer flight adjustments.

When you get the two arrows, that means that the SAS is receiving a command input. Pretty much a guarantee that a joystick or other analog control device is sending a signal, no matter how small. Set a slight deadzone for your control input. A new install has deadzone by default, but older updates will have your old settings still.

[Klingon Admiral]

If your SAS is working all the time and your plane is pitching down torwards the prograde marker, then your plane simply does not have enough pitch control. Stick a control surface (or two, or four) on the plane and it will fly perfectly.

[federicoaa]

The two arrows actually means the SAS cannot control the ship, and can be either because you are pressing wasdqe or your ship is spinning out of control, and the SAS torque is not enough to counteract the spin.

[Superfluous J]

Am I the only one who wants the 0.21 SAS back? It did a great job of keeping a plane flying straight.

I don't. Magical heading control isn't fun. I want my rocket to fly the direction I aim it because I built it correctly.

[Col_Jessep]

I don't. Magical heading control isn't fun. I want my rocket to fly the direction I aim it because I built it correctly.

Agree 100%.

[ComradeGoat]

In 0.23, SAS doesn't do a good job of holding pitch if your centre of lift is a long way from your centre of mass, and you aren't festooned with control surfaces, it seems. I've had a few flights where I've had to hold down S to climb away to orbit because SAS refuses to hold the angle of attack.

[ComradeGoat]

If your SAS is working all the time and your plane is pitching down torwards the prograde marker, then your plane simply does not have enough pitch control. Stick a control surface (or two, or four) on the plane and it will fly perfectly.

I've seen the same issue the OP has. This happens when there *is* sufficient command authority to maintain heading, but SAS simply doesn't try to use it.

[CaptRobau]

If your center of lift is a long way from your center of mass, you've basically built a lawn dart. And lawn darts tend to pitch down after a while. SAS shouldn't be able to hold your pitch in this case, as it's not a substitute for bad design. Move your wings closer to the center of mass to make it fly better.

[Javster]

Apart from the yellow arrows, I have not noticed any change in SAS since 0.19.

[Wjolcz]

Maybe you have Caps lock turned on? The ASAS works in damping mode when in precise controls, and the roll, yaw and pitch controls turn green.

[TMS]

Basically, SAS doesn't use the authority it has available to it.

For the most part, that's fine, but shifting COMs in long-range aeroplanes make it somewhat irritating.

It does seem to have got worse in .23.

[icebalm]

Hiya, first question are you using a joystick or other analog input? My guess is yes. Here is why:

They added an improvement to the SAS where it locks heading, but any command input overrides the SAS until released at which point, that is your new heading. helps with springyness and makes for finer flight adjustments.

When you get the two arrows, that means that the SAS is receiving a command input. Pretty much a guarantee that a joystick or other analog control device is sending a signal, no matter how small. Set a slight deadzone for your control input. A new install has deadzone by default, but older updates will have your old settings still.

I'm not using any kind of joystick, just keyboard and mouse with stock input controls. I hold S to pitch up to 45 degrees, turn SAS on, let go of S, and it pitches down with the two arrow orange icon where SAS is until it hits prograde, then switches to SAS again. Frustrating....

[icebalm]

If your SAS is working all the time and your plane is pitching down torwards the prograde marker, then your plane simply does not have enough pitch control. Stick a control surface (or two, or four) on the plane and it will fly perfectly.

Well if I can hold the S key to pitch it up manually wouldn't that suggest that I have enough control?

[AlexanderB]

Basically, SAS doesn't use the authority it has available to it.

Which was the "fix" for wobble, wobble that was caused by over-use of the availible control authority.

It does seem to have got worse in .23.

it was already worse in 0.22, but in 0.23, the aerodynamic surface controls seem to have become more sluggish, as if fine control is permanently turned on, making the effect on things with aerodynamic stabilisation (over pure pod torque or thrust vectoring) even worse, yes.

[SRF Industries]

Just got through registering here on the forums for this reason alone... SAS is broken in .23, pure and simple. I've been building perfectly balanced aircraft, from VTOL's to high speed low atmo jets, from air ships to space worthy rocket planes and all the way up until .22 my aircraft that were tested and retested were ALWAYS stable from low speed to high speed... since about ver .16.

Now, any of my craft get over roughly 175m/s and they're still nice and stable WITHOUT SAS on, but turn that baby on and all hell breaks loose. They start shuddering like they did (with SAS) back pre-.21 or .22, can't remember which. SAS will hold them steady thru take off, picking up speed, etc. But reach that roughly 175m/s mark, leave SAS on and they're uncontrollable, flipping out of control, nose diving, shaking themselves apart, etc. Turn SAS off and they're flying smooth as silk like they used to but it's difficult to fly aircraft without the assistance of a properly operating SAS system... it just is. This happens on ALL my aircraft, none are exempt.

[boomerdog2000]

Which was the "fix" for wobble, wobble that was caused by over-use of the availible control authority.

it was already worse in 0.22, but in 0.23, the aerodynamic surface controls seem to have become more sluggish, as if fine control is permanently turned on, making the effect on things with aerodynamic stabilisation (over pure pod torque or thrust vectoring) even worse, yes.

They act sluggish for the same reason the SAS uses less of the available torque at first, to reduce the wobble, but this wobble resulted from the flapping of control surfaces jumping from 100% to -100% instead of having any points in the middle.

[dazhat]

Could you show us a picture of the craft.

[icebalm]

Could you show us a picture of the craft.

I'll do you one better, a video demonstration of the issue!

http://www.twitch.tv/icebalm/b/489926975

[T_S_Kimball]

Thanks, that video clarifies an unusual behavior I could not put my finger on.

So, basically, the problem boils down to:

In 0.22: SAS sets the 'base' orientation from whatever it was when turned on, and will only change when told to. Prograde/Retrograde/etc will follow it.

With 0.23, this 'base' orientation has changed to the current Prograde (does this also happen with Retrograde?) and will shift to that unless actively 'nudged' to where you want it.

It's hard to tell, but from what I've seen this really only gets bad in an atmosphere, and is not as big a hindrance once in space. I've been able to compensate (manually for planes, and Mechjeb for rockets), but seems an interesting oddity. Perhaps related to a change in Unity itself?

[megaprime13]

It seems that your craft has the center of lift too far back.

Either that, or you dont have enough power to change the prograde in the atmosphere.

EDIT: if you had to hold S and your nose doesn't go up very much, then your design could be bad. Show us a picture in teh hangar with the C.O.Gravity, C.O.Lift and C.O.Thrust please

Edited December 24, 2013 by megaprime13