Uncontrollable spinning, Hard to make rocket stable

[nikolay-spb]

Hello pilots,

Please tell me what i do wrong?

In 0.90 i was able to fly rocket perfect into orbit, using gravity maneuver.

In 1.0.x at 10,000 m when i try to do gravity turn to 45deg rocket start to spin with no control...

I tried everything: Controll surface, vector engine and nothing helps, rocket is so unpredictiple and very easy go into spinning.

[Majorjim!]

Do you mean spin or flip?

[klgraham1013]

You have to do a realistic turn now. Start your turn early and don't stray to far from prograde.

[MissStabby]

The new KSP 1.0 aerodynamics model requires you to start turning straight after launch.

I found it was "easiest" to tilt like 10 or 15 degrees over, and then just fire prograde.

If you haven't tipped over fast enough by around 20 km's you can start turning without much risk of spinning.

I noticed trying to turn when just above 300m/s (mach1) a few km's up results almost instantly in tumbling rockets

[Gaarst]

Ascent profile has changed with 1.0 aerodynamics.

Turn 5° a few seconds after launch, and gradually follow prograde marker until ~45° at 10km and ~30° at 25-30km, aerodynamics do not matter anymore >25 km so do whatever you want from then.

Also aim for a TWR of 1.3 to 1.5.

[Depth]

In 1.0.x at 10,000 m when i try to do gravity turn to 45deg rocket start to spin with no control...

Try not going more than 10-15 degrees off your surface prograde marker. Rockets are not supposed to travel sideways.

[Robotengineer]

Ye olde 45°@10km gravity turn is (supposed to be) dead. Try tilting by 5° around the time you reach 100m/s, then slowly bring your prograde marker down. Are you in 1.0 or 1.0.2? I've seen a few posts that the old 45°@10km is feasible again in 1.0.2.

[nikolay-spb]

Do you mean spin or flip?

Well from nose pointing up it go to pointing ground then again sky and hard to stop fliping or spinning

[Commissioner Tadpole]

Give a screenie of your craft, so we can properly help you.

Do you have wings on the tail of your craft? Reaction wheels can only help you so much, and too much of them can be fatal due to excessive torque. Also, keep your rocket pointed prograde at all times. Not pointing prograde is a possible reason to rocket flips.

[nikolay-spb]

Ye olde 45°@10km gravity turn is (supposed to be) dead. Try tilting by 5° around the time you reach 100m/s, then slowly bring your prograde marker down. Are you in 1.0 or 1.0.2? I've seen a few posts that the old 45°@10km is feasible again in 1.0.2.

In 1.0.2 it is better but still not stable as in 0.90.

Im very frustrated becase fins dont do much job. I think in reality so much force (especially on low altitudes) that gives finns and vectoring engine should be enough to keep rocket on the course. But in ksp once it start "stalling" nothing will help you.

Also found that SAS dont help at all! It is even better without SAS on low altitudes.

[Majorjim!]

Well from nose pointing up it go to pointing ground then again sky and hard to stop fliping or spinning

Aside from the others that have posted before me this is my understanding.

Your turn depends on the rockets TWR. I have found that turning straight away after launch is not as efficient as going straight up and then turning around 4500m. Turn very slowly. Aim for 45degrees at around 400-500m/s.

After that slowly turn until you are nearly horizontal at around 45,000m.

That's just a rough guide as you really just need to practice practice practice as every rocket is different. You will be able to naturally adjust your turn based on your speed and acceleration.

[wossname]

Try a gradual gravity turn starting from a few seconds after launch. You may find that turning SAS off might help with controlling the craft (SAS tends to fight against the atmosphere and makes your job harder).

By the time you hit 10,000m altitude, you should be just passing through 45 degrees of turn. The turn should be smooth as possible from start to finish. This is hard to do with a keyboard - I use a joystick to get nice smooth analog control and I find it much easier than keyboard alone.

You can't just "take a right turn at the cloud" to get into orbit any more

And do use the small fins, they will aid your stability without having the SAS turned on.

[EtherDragon]

Please read the Tutorial: "Why Does My FLIPing Rocket Always Flip Over!"

Then, check out this video:

.

These sources should give you an understanding why you have to do certain things to build a stable rocket - or at least, what you need to do to deal with an unstable one.

The basic gist is: (as many have stated) going strait up to 10km and pitching over to 45degrees no longer works as you have realistic aerodynamic forces acting on your rocket (e.g. Nose-Heavy drag and torque causing a loss of control).

[Snark]

Another point that frequently gets overlooked:

Fairings Are Your Friend

A pretty common scenario is that you have an ungainly, non-aerodynamic orbiter perched atop a sleek, streamlined booster section. Upper stages tend to have all sorts of draggy bits poking out (batteries, solar panels, radially attached paraphernalia of various sorts).

This is a BIG contributor to the rocket-flipping problem.

Draggy thing in front of streamlined thing = bad.

Fortunately, there's a good solution to this problem. Just put a fairing around the ugly draggy top stage; you can pop it (and save the mass) once you're above 25km and drag's not an issue.

Works wonders. You still have to be careful not to point too far from prograde, as other posters have already pointed out ("straight up and crank to 45 degrees at 10km" is dead as the dodo), but the fairing mitigates a lot of the problem.

Edited May 4, 2015 by Snark

[nikolay-spb]

Thank very much for video, it really helped. But still i think that if you put fins far from center of the gravity, in low height they should do the job and bring back up rocket, but i am not very good @ calculations so will take as it is

[EtherDragon]

Thank very much for video, it really helped. But still i think that if you put fins far from center of the gravity, in low height they should do the job and bring back up rocket, but i am not very good @ calculations so will take as it is

You are absolutely correct - tail-fins are on most rockets for a reason, they make them way more stable on the way up.

[Zeratul_r]

Thank very much for video, it really helped. But still i think that if you put fins far from center of the gravity, in low height they should do the job and bring back up rocket, but i am not very good @ calculations so will take as it is

I think that if there are so many large fins far from the centre of gravity that they can reliably bring back the rocket that started to fall, they would also make it almost impossible to do gravity turn (or any turn for that matter below 15-20 km). It would be like trying to make tilting doll lower its head and don't go back. In my experience (which is not very large to tell the truth) some fins can help but they are not always a best solution. After I've learnt to keep level indicator point inside the prograde market, don't go too fast (not faster than the terminal velocity, although I don't know how to determine it for different rockets) and put things like goo canisters, batteries and protruding antennas inside the service module, my rate of catastrophic failures decreased significantly.

- - - Updated - - -

You are absolutely correct - tail-fins are on most rockets for a reason, they make them way more stable on the way up.

As far as I know many modern rockets don't have tail-fins. For example: US Antares and Falcon 9, Russian Soyuz 2 and Angara, based on the photos neither of them have tail-fins.

[Garius]

If you put fins as far down on your rocket as possible, it will want to stay prograde. The only steering (including SAS, turn it off if you use fins) required is the start of the gravity turn and then once you are in high atmosphere.

Incidentally, the old "go up to 10k, turn to 45, burn until apo is high enough" is not a gravity turn, the name simply got applied as it shares some very general features. A gravity turn has your engines firing prograde 100% of the time after the initial tilt of a few degrees. Whenever you aren't flying straight up or down, gravity will cause your prograde to move downwards. Thus gravity alone literally turns your velocity vector, the engines can then apply all of their thrust prograde with no steering losses while still following a good ascent profile. The shape of the profile can be tweaked by adjusting thrust, going faster will cause you to turn downwards more slowly, and vice versa. I aim for horizontal between 35 and 40 at which point I end my gravity turn and start steering again.

With fins, the atmosphere will happily keep you pointing prograde, without, you'll need to ensure you have enough control between reaction wheels and gimbaling to stay prograde. The closer to prograde you stay the easier it is, as the torque from atmosphere increases the more you are off of prograde. Also the faster you go the more torque. But really, just use fins so that the torque keeps you pointing forward.

[Jeez]

Also aim for a TWR of 1.3 to 1.5.

Interesting!

[nikolay-spb]

As far as I know many modern rockets don't have tail-fins. For example: US Antares and Falcon 9, Russian Soyuz 2 and Angara, based on the photos neither of them have tail-fins.

That is because they have alot of thrust vectoring, they simply dont need fins.

For example Russian Proton-M has 7 engines with thrust vectoring and 6 helper thrust vectoring engines on first stage, so fins are absolutelly unnecessary.

But rockets which dont have thrust vectoring like SAMs etc havõ large fins to change directions, and fins do pretty god job at altitudes 0-20km.

So having fins dont mean that it will go prograde all time, if fins are in neutral position it will, but if they move force will move rocket respectively.

Example of usage -