Stayputnik seems useless without SAS

[NecessaryWeevil]

In the current version, unmanned rockets seem impossible; they're just uncontrollable. In frustration, I constructed a very simple rocket: a Stayputnik core on top of two FL-T400 fuel tanks, four batteries arranged radially just below the core, a Swivel engine and six Delta Deluxe winglets for control. Yet the rocket flips over at about 14,000 meters.

The same rocket, replacing the Stayputnik with a Mk1 command pod, has no such issues.

What's the point of a Stayputnik?

[ghpstage]

This isn't a SAS thing, its a mass thing. Or more specifically, centre of mass.

Once the centre of mass moves behind the aerodynamic centre, the rocket will do everything in its power to flip over. Testing your rocket design suggests that fuel burn is likely to be causing this to happen at around 11,000-14,000m, depending on your ascent profile.

During the tests I found that it is possible to make your craft very stable, you just have to mount those fins at the very lowest point on the lower tank.

The reason this happens to Stayputnik and not the command pod is due to Stayputnik being 1/16th of the mass of the pod.

[Rocketology]

I recreated the rocket you described above and had no issues:
http://imgur.com/gallery/rYDrUm4/new

Are you running any mods? If not, the general rule on rockets is weight as for up as possible and all drag (i.e. fins) at the bottom.
I did several launches, going straight up, only hitting space bar to launch, it went to 350,000 meters. Doing a slight gravity turn, I nearly put it into a stable orbit.

[NecessaryWeevil]

*blink* weight as far UP as possible? Wouldn't that make it MORE likely to tip? Also I'm pretty sure I DID mount the fins as low as possible.

I'll go back into the game and double check.

So confused now.

EDIT: Turns out the fins could have been lower. Moving as absolutely low as possible managed to make it stable enough to reach a suborbital trajectory, though it still felt like a near thing. Thanks for pointing that out. Still confused about this CoM thing, though. I thought the point was to get it as low as possible. I'll look up 'aerodynamic centre'.

[Empiro]

Yes, counterinuitively, mass in the front, drag in the back makes the rocket more stable. You can try pumping fuel from the rear tanks to the front ones (just make sure to set things up before you launch).

Note that anything attached radially and not in a fairing induces quite a bit of drag (e.g. batteries). If you have them, putting stuff in a fairing makes everything much easier.

Also, if your TWR is high (like it is for your craft), then you'll want to throttle back or add more fuel so that you're not going to fast in the low atmosphere.

Finally, turn on fine control mode and try your best to keep the nose close to the prograde marker. If you start having trouble keeping control, reduce thrust a bit.

[NecessaryWeevil]

Thanks, I'm in career mode and so low on the tech tree (was trying to accomplish a Mun flyby) so I don't yet have access to fairings or fuel lines. But I'll keep this in mind. I did have the throttle low-ish I think.

[Ottomic]

Probes without SAS are stupid as hell, I do agree.

Get SETI. It's balanced around probes first. Parts, contracts, tree, everything.

[Oxytropis]

You should try to spin stabilize at launch, and make sure your upper stages have vectoring engines. instead of putting your fins on like | | | | put them on with a slight tilt / / / / the rocket will spin and stabalize it self. just give it a slight bump at launch in the direction you want it to go and let gravity do the rest.

[NecessaryWeevil]

OOooh cool. I'll try that.

[Bubba Fett]

The spin thing might work if you were only trying to go in a straight line, but how would you do your gravity turn?
Wouldn't you get a severe wobble as soon as you touch one of the pitch or yaw controls?

[Oxytropis]

https://youtu.be/VUZC60JvFYs

use a decoupler for a little nudge at start. you have no control, the rocket has to fly itself until the final stage. you might not even need the spin, I've been playing modded version where I needed it to keep it stable.

the launch decoupler force was set at 30% for this rocket.