What's wrong with RCS on my SSTO?

[El wonso]

So I have this nice SSTO spaceplane with 2 RCS block and 2 linear ones.

Is it normal that:

1. rolling barely uses RCS so it I have to use gyros (it's extremly slow otherwise)?
   
2. throttle controls both engines and RCS (NOT in docking mode)?
   

pls help

[Jas0n]

Pictures would be nice, so that we know where your rcs blocks are.

[Renegrade]

Not sure what's going on with #2 (unless you're using the OMS engine), but to get your craft rolling nicely, you have to have RCS quads around it's center of mass.

KSP's RCS controller is kinda basic and doesn't know how to use RCS quads at the end of the craft for rolling properly - it scales their output way down.

Example craft:

(front) A--------------B---------------C (rear)

Assuming that B is at the center of mass for the craft, that's the best place for roll-control RCS. A and C won't have much roll control authority (they will have good pitch and yaw authority though).

They'll work even better if they're far away from the central axis (while still around the CoM):

                       d
                       |
                       |
(front) A--------------B---------------C (rear)
                       |
                       |
                       d

(quads at d, so long as the pair/ring are around the CoM,

But this may or may not be practical with a given design.

[Starman4308]

#2 is strange: throttle is only supposed to fire your RCS if you have no other engines. #1, though, is mostly likely just insufficient RCS port placement. They're not a magic wand: you need at least a ring of 4 to get all possible translations and rotations, because they can only thrust in the direction of one of the nozzles. If #2 can't be resolved otherwise, you might try posting a thread in the support forum (taking a good look at this thread first).

[peachoftree]

I think mechjeb adds rcs to throttle if you have the rcs balancer enabled, that would also explain your roll problem because it sees that you do not need rcs to preform a roll maneuver

[Wanderfound]

We need screenshots to diagnose properly.

However, for balancing spaceplane RCS (and many other spaceplane building tricks), the RCS Build Aid mod is invaluable.

[El wonso]

KSP's RCS controller is kinda basic and doesn't know how to use RCS quads at the end of the craft for rolling properly - it scales their output way down.

Oh... Well, since I cannot set specific thrusters to control roll only I will have to rely on reaction wheels.

#2 is strange: throttle is only supposed to fire your RCS if you have no other engines.

Huh, didn't know that. So that imaginary issue is solved.

btw Can I turn it off? I would prefer not to have my RCS controlled by throttle no matter if any engine is active.

here are pics if anyone is interested:

Javascript is disabled. View full album

[Wanderfound]

Oh... Well, since I cannot set specific thrusters to control roll only I will have to rely on reaction wheels.

Huh, didn't know that. So that imaginary issue is solved.

btw Can I turn it off? I would prefer not to have my RCS controlled by throttle no matter if any engine is active.

here are pics if anyone is interested:

http://imgur.com/a/8me2L

You turn it off by toggling off RCS with the R key or by throttling down when your main engines are deactivated. And you shouldn't be using RCS in atmosphere; it's not strong enough to overcome aerodynamic forces, so you're mostly just wasting RCS fuel. Also, any force on a spaceplane is effectively a lever on to the CoM; the closer the thruster is to CoM in regards to the relevant axis, the less rotation authority it has. Your blocks are very close to the longitudinal axis, hence the lack of roll authority.

If you want RCS control from four 4-way RCS blocks, you need them all placed bang on top of CoM. Either one on each flank plus one each on top and below, or all four placed at 45°. If you don't want them on top of CoM (or if you want more rotation authority, rather than just translation), you need to use eight blocks, placed in two sets of four balanced either side of CoM. Like so:

In atmosphere, you control roll with your aerodynamic surfaces. In vacuum, the cockpit torque (possibly aided by an optional SAS unit) is plenty strong enough to control rotation; RCS is primarily for translation during docking.

Again, however, I highly recommend the RCS Build Aid mod. As well as helping to place your thrusters, it will tell you exactly how much power they have (in terms of both torque and thrust) in any direction you choose.

Edited November 18, 2014 by Wanderfound

[El wonso]

You turn it off by toggling off RCS with the R key or by throttling down when your main engines are deactivated

I was asking if I could completly disable this feature, when in space I often disable my engines so I won't throttle up by accident.

And you shouldn't be using RCS in atmosphere; it's not strong enough to overcome aerodynamic forces, so you're mostly just wasting RCS fuel.

Well, I've been playing KSP since 0.8.5 (I think) so I know basic stuff. I just not playing that much lately since recents updates were not very interesting to me.

Also, any force on a spaceplane is effectively a lever on to the CoM; the closer the thruster is to CoM in regards to the relevant axis, the less rotation authority it has. Your blocks are very close to the longitudinal axis, hence the lack of roll authority.

I get that, but I think it's just stupid. RCS barely works when rolling.

If you want RCS control from four 4-way RCS blocks, you need them all placed bang on top of CoM. Either one on each flank plus one each on top and below, or all four placed at 45°. If you don't want them on top of CoM (or if you want more rotation authority, rather than just translation), you need to use eight blocks, placed in two sets of four balanced either side of CoM. Like so:

The problem is my CoM moves back and forth, that's why I put 2 sets of blocks in the front and two on the back.

Also I need both translation and rotation (see next paragraph).

Also I consider the looks important so I prefer 2 x (block + linear) than 4 x block.

In atmosphere, you control roll with your aerodynamic surfaces. In vacuum, the cockpit torque (possibly aided by an optional SAS unit) is plenty strong enough to control rotation; RCS is primarily for translation during docking.

The cockpit is too powerful imo so I usualy disable it and rely on RCS and externall reaction wheels.

[BudgetHedgehog]

I was asking if I could completly disable this feature, when in space I often disable my engines so I won't throttle up by accident.

Did you see this? I suspect it's the reason why.

I think mechjeb adds rcs to throttle if you have the rcs balancer enabled, that would also explain your roll problem because it sees that you do not need rcs to preform a roll maneuver

EDIT: Now I think about it, with regards to #1, your RCS quads aren't situated that far from the roll axis - that would explain why they're not doing much, it's because they don't have the torque. EDIT 2: Ah, I see that has been covered. I think I'm talking nonsense anyway..

Edited November 18, 2014 by ObsessedWithKSP

[El wonso]

RCS Balancer Enabled is disabled.

[Redshift OTF]

You have a fair amount of fuel tanks on the wings. That would make it harder to roll. Perhaps place the RCS thrusters on the outside fuel tanks?

[El wonso]

The things is that rcs barely uses any fuel when rolling. It's (or should be) strong enough.

[Redshift OTF]

So it doesn't roll quickly enough and it doesn't use enough RCS mono-propellant? Is pitch and yaw working correctly? I must admit I use SAS for roll, pitch and yaw and leave RCS for translation controls but I can understand you disabling SAS for realism.

[El wonso]

exactly

both pitch and yaw work fine