Impossible...

[Huitoan]

Hi, i've been playing KSP since May 2014 more or less, and in the beta version I could escape from Kerbin easily. Now I'm playing the full version and I can't escape from Kerbin... And I don't know why. When I launch my spacecraft, at 10-15 km it starts to move uncontrollable and I can't do anything. I have SAS activated... etc... What can I do?

[Montag]

Atmospheric drag is the likely issue. Add some fins to the bottom of the rocket. When you start the gravity turn, keep your heading relatively close to pro-grade. This will keep the drag forces closer to the direction of acceleration - reducing the likely hood of tip over.

[OhioBob]

Try fins to help stabilize it while in the atmosphere. Also keep the angle of attack as small as possible. I find that setting SAS to 'prograde hold' during the brief period when it is most unstable helps to keep it from flipping out of control.

[sardia]

Go slower, and add fuel to compensate.

[SpeedDaemon]

As OhioBob said, fins at the bottom are pretty much required. Also, minimize drag at the top - if you have a bunch of little bits hanging off of the top of the rocket, put a fairing around it.

In the new version, the old common tactic of going straight up, and then doing a "gravity turn" to 45 degrees no longer works. Once you have an aerodynamically clean rocket, launching can be almost hands-off: once you get a few tens of m/s of momentum, turn SAS off and nudge it a few degrees east - it will pretty much fly itself to orbit.

[RCgothic]

In the Vehicle Assembly Building make sure every atmospheric stage is aerodynamically stable. Click the toggles to the right of the symmetry selector to bring up the centre of mass (yellow) and centre of lift (blue) balls. The centre of mass must be ahead of the centre of lift at all times. It's possible to pilot an unstable ship to orbit, but it requires a lot of control authority and a very cautious flight profile. Be aware that the centre of mass will move backwards as the top tanks in a stage drain whilst the bottom tanks stay full.

Move the centre of lift by putting fins on the back of the rocket or taking draggy bits off of the front. Move the centre of mass by putting heavy things up top.

When you launch a rocket, never deviate more than 5deg from prograde. Start turning pretty much straight off the pad and aim for 45' by 10km. By 35km you should be burning pretty much at the horizon or just above. Gradual change is the order of the day.

[Friend Bear]

Id love if you post a picture of the ship. We suggest things but for all we know it is this exceedingly tall rocket with far too many parts.

If you want a mod that helps but does not autopilot (and therefore, ruin the game), look at EngineerRedux. Gives per stage weight, thrust to weight ratio readings, and delta v.

Far be it for me to tell you how to build the rocket; I'd rather you figure it out on your own. But this lets us point you in the right direction per rocket rather than giving you general knowledge without realizing that knowledge's applicability.

[Superfluous J]

Agreed that we really need to see the rocket to help, but keep several things in mind while climbing through the atmosphere:

Things like to fly with the heaviest parts in front. Look at arrows flying, hammers being thrown, and the like. As your rocket burns fuel, it starts at the top and burns down, which can make a rocket that starts top-heavy (which is good) become bottom-heavy (which is bad). The obvious solution here is to break your ascent into stages, so you're keeping more fuel up front.

Turning violently is a no-no in 1.0 and on. Do NOT burn up to 10km and then crank it over 45 degrees. Instead, tip over almost immediately (Get up to say 50-100m/s first) and then slowly tilt over so you're about 45 degrees at 10km, You may need to be tilted more or less than that, but until you've got the system down 45 is a good target.

Fins help push the margins in your favor, but they won't fix a bad design flown poorly. And don't put them too high up without having other ones lower to compensate.

Going very fast in the lower atmosphere means you're shoving a LOT of air out of the way, quickly. This will make anything hard to control. This is not a problem in itself, but it WILL exacerbate any other issues with your rocket. Slowing down will compensate for bad flying and design, but if you have a good rocket and fly it true, you can pretty much go as fast as you want.

[Friend Bear]

Agreed that we really need to see the rocket to help, but keep several things in mind while climbing through the atmosphere:

Things like to fly with the heaviest parts in front. Look at arrows flying, hammers being thrown, and the like. As your rocket burns fuel, it starts at the top and burns down, which can make a rocket that starts top-heavy (which is good) become bottom-heavy (which is bad). The obvious solution here is to break your ascent into stages, so you're keeping more fuel up front.

Turning violently is a no-no in 1.0 and on. Do NOT burn up to 10km and then crank it over 45 degrees. Instead, tip over almost immediately (Get up to say 50-100m/s first) and then slowly tilt over so you're about 45 degrees at 10km, You may need to be tilted more or less than that, but until you've got the system down 45 is a good target.

Fins help push the margins in your favor, but they won't fix a bad design flown poorly. And don't put them too high up without having other ones lower to compensate.

Going very fast in the lower atmosphere means you're shoving a LOT of air out of the way, quickly. This will make anything hard to control. This is not a problem in itself, but it WILL exacerbate any other issues with your rocket. Slowing down will compensate for bad flying and design, but if you have a good rocket and fly it true, you can pretty much go as fast as you want.

Following this, I have also had the reverse happen for taller rockets with awkward COM.

When I ran into this problem and the design wasn't absolutely horrible, I upgraded my engines and went a bit faster. The problem occurred between 75 and 250 m/s; where my rocket would uncontrollably turn down, catch the air, and face downward without being able to recover. I fixed it by making the rocket faster to cut through that heavier atmosphere faster.

Not the most certain fix but it works assuming your rocket is going really slow.

[GoSlash27]

#1 cause of this is poor aerodynamics. You really need to streamline your rockets these days to keep them stable in the transsonic region.

If that's not enough to keep it pointed in the right direction, add some fins in the back.

Best,

-Slashy

[Snark]

+1 to previous posters' advice. A couple more things to bear in mind:

- Keep the front of your rocket streamlined. Drag on the front of rocket = bad, drag on the back = not so bad. The front end should be smooth, pointy, and not have radially-attached stuff sticking out. If you need to put up something very draggy and awkward-shaped, consider putting a fairing around it.

- Really, really don't go too fast too low. (This is different from pre-1.0, which had very different aero rules.) Aerodynamic drag spikes upward dramatically when you pass Mach 1, which is a bit over 300 m/s at sea level and gets faster at higher elevations. A good rule of thumb, keep it under 300 m/s until you get up to 10 km altitude, then floor it. Going too fast too low is bad for two reasons: First, the extra drag means you're wasting a lot of fuel. Second, the dramatically increased aero forces mean that if your rocket has any tendency towards instability, it will get drastically magnified.

The simplest, easiest thing to do is to add fins to the bottom of the rocket, as far down as possible. If that doesn't work, use bigger fins. If you can use steerable fins (like the AV-R8 Winglet), that's best of all-- they'll use SAS to help keep you on track.

[Mastikator]

As the ship burns fuel it uses the top fuel first, this moves the center of mass back. Things that fly through air always want to have their center of mass in front of the center of lift/drag.

A simple trick to combat this is to disable the upper fuel tanks until the lower ones are out, the center of mass will move up instead of down and the rocket will become more stable.

[Warzouz]

Also, smaller rocket are harder to fly because the flip faster : you may not have time to compensate.

[xtoro]

Tall rockets with steerable fins on the bottom are my first design, but when that doesn't work, I add another set of 4 steerable fins to the top of the main lifting stage and that usually sorts it out. Also, keeping your speeds lower for longer also help minimize getting flipped around by aerodynamic cross forces.

[Snark]

As the ship burns fuel it uses the top fuel first, this moves the center of mass back. Things that fly through air always want to have their center of mass in front of the center of lift/drag.

A simple trick to combat this is to disable the upper fuel tanks until the lower ones are out, the center of mass will move up instead of down and the rocket will become more stable.

This is true-- however, it's only relevant when you have multiple tanks stacked in-line one on top of the other (as tends to happen early in career mode, when the taller tanks haven't been unlocked yet). Reason:

- Decouplers are not fuel-crossfeed-capable. Therefore, if you have a rocket with a top stage, then a decoupler, then a bottom stage: the bottom-stage engine won't (can't!) drain any fuel from the top stage, and will drain fuel from the bottom tank only. (Which actually helps stability, since that will move the CoM upward.)

- If you have a single tall tank, it doesn't drain the "top of the tank first"-- KSP has no concept of mass distribution within a fuel tank, it just lowers the overall mass of the tank while leaving the tank's CoM in the same place.

Therefore, the moral of the story:

- Try to avoid stacks of in-line tanks if you can. It's better to have one tall tank than several small tanks stacked one atop another.

- If you have to have a stack of tanks, be aware of this drain-from-the-top-down issue, and deal with it (for example, as Mastikator suggests).