Why is my Rocket tipping over?

[SultanSaidi]

Hey there

so i have currently the problem that always when i start my rocket at around 1200m or 120m/s my rocket tips complety over without reason

i checked it mutipel times the center of mass is right in the middel the center of thrust is as cloose to the center of mass as it can be and when i launch

my rocket is strait until around 1200 where it just flipps completly randomly even when i pre direkt my rocket to 5° right it flips it to the left without real reason

i have the Ferram_Aerospace mod installed but nothing else that would change the game physiks

is it because i m too slow or to fast? still to top heavy?maybe an atmospheric change?or something else i couldnt think off?

Im getting slowly really furious because i cant figure that one out

Edited May 26, 2015 by SultanSaidi

[Guest Darth Gerbil]

Put fins at the bottom.

[MrDude]

How Many Fuel Tanks arraigned in what stages? Is it a monster single stage?

Rockets should stay mostly nose heavy for stability. The larger mass tends to lead the way unless there are other forces (like Darth Gerbils Fins creating drag preventing a flip).

The fuel flow logic pulls fuel towards the engine and thus empties the furthest tanks first (since if you remove fuel from beside the engine, and there is fuel further out that can flow toward the sucking engine then the emptiness starts at the furthest point away).

Put those aspects together and your center of gravity will shift rear ward unless A) you add more stages thus trap that fuel mass forward until you shorten the ship. or you use the right click dialogue on the fuel tanks to click the little play buttons to cut access to the 2 fuel types. You will have to manually turn this back on (especially if you use MechJeb's Autostaging!) but you can then drain the rearward tank first. C) add fins (especially if this occurs while the atmosphere is Thick - but if this happens again at 50K or something then you need to think weight shifting or torque control systems and the associated batteries -but beware the shake caused by multiple torque systems spread out being out of sync).

Its probably not that your heavier side is being pulled down unless your going REALLY slow (Vertical speed gauge at top at or above 100 is my standard) or your speed at the bottom is... well bellow a few hundred by that altitude.

1200 does seem a little low for this to happen - mines happened around 6-12Km.

If this doesnt fix it please describe the layout of your ship.

[SultanSaidi]

So i tried different types of Rocket layouts multipel staging over height distributed and multipel staging over more or less the same height but dropping over time the empty tanks. i usually have a lot of starting stages with solid fuel boosters to get my speed up and overcome the starting inertia. i start with all my possibel engines on the same time and throttel them so i get an steady acceleration over time

and side note its still completly at the start of carrer mode i have i think unlocked all 45 science stuff. i got further some other runs but i like to restart with knowledge i got and refine my carrier

it could be i missred one 0 and it was at 6-12 km

what i dont understand is why should a rocket be top heavy for stability? if the center of thrust is far away wouldnt then every little change make it tillt?(like balancing an pencil on your finger)

i ll try to make some screenshots of my different designs

[Motokid600]

Read this.

http://forum.kerbalspaceprogram.com/threads/117876-Why-Does-My-FLIPing-Rocket-Always-Flip-Over!-%28Easy-Picture-Explanation%29

It is like balancing a pencil, but only for the first 30 seconds or so. Try balancing that pencil when it's moving super sonic. With no weight up top it'll want to rip around backwards.

Also it's good practice to build rockets so they stage higher up around 25-30km. Radial boosters is fine they can be dumped whenever. But when it comes to serial staging that will make your craft shorter you must make it so the first stage does more work. Once your above 30km it's easy. The air is thin.

Another hint is to simply wait. This had been working great for me. The problem is in the early careers your limited to small rockets. Small rockets are harder then big rockets because they are far more susceptible to the air and lack a heavy payload. So what I've been doing is if I can't get my rocket to stage really high up I wait. Let the first stage burn out then just hold prograde and wait until 25-30km before separating and continuing on. Really works well.

Edited May 25, 2015 by Motokid600

[SultanSaidi]

mmm oke i understand that but i kinda followed that already naturally with my rockets so i dont understand what is wrong with them then take a look please

this one is how i build them normaly http://images.akamai.steamusercontent.com/ugc/711912327654707228/0298254A71D2465F407A63A86949C7621BD75C83/

the next two where i just experimented around and they all failed the same from tipping over at around 12km

http://images.akamai.steamusercontent.com/ugc/711912327654707618/38974A6AE5B724D4D7E8D0E6D82B8B6BF51FE55C/

http://images.akamai.steamusercontent.com/ugc/711912327654707921/E840D67AE1913DD7C7D3E858F85D4D39C9530282/

any idears maybe? and thank you guys you helped already very much

[Fengist]

any idears maybe? and thank you guys you helped already very much

There's lots of things that could be wrong. Pinpointing just one would be a bit difficult without the actual .craft file. But I'll take a stab at it.

Stability increases as the distance between the center of mass and the center of thrust increases. A perfect rocket would have the center of thrust all the way at the bottom and the center of mass all the way at the top.

Winglets and control surfaces increase stability in that they counteract aerodynamic pressures exerted on the opposite end of the rocket.

Your rocket is a big lever with the COM being the fulcrum. Your job is to keep the top of the rocket from being pushed in the wrong direction by aerodynamics by controlling the direction of thrust coming out the bottom. The more difficult you make it for that lever to be pushed the wrong way, the more stability your rocket will have.

Nextly, SRB's. While they have their use, their main purpose is to get you off the pad and moving so that your control surfaces can take over. They have no ability to direct your rocket other than forward. The longer you burn them, the more magnified errors in flight become.

My advice:

1. Rely less on SRB's and more on engines with gimballed nozzles.

2. Keep your COT as low as possible. In two images, you have SRB's half way up the rocket. Bad physics.

3. Until you get some more experimentation under your belt, use winglets, canards are better. Two of your rockets have no winglets.

4. Reaction Wheels - Adds another control factor to your rockets. Get them as soon as you can.

5. Drag. With version 1.0+ This has become a new huge reality. Do this as a test. Send up just your SRB with a cockpit on top. Let it fly straight up, and check it's max altitude. Next, strap 4 of your parachutes on it and launch again. Again, check the altitude. I think you'll be stunned at the results.

6. This is just my preference and may make no difference. Have your stability enhancers detach in the same stage as your engine ignition. If you fire off the engines without detaching, you'll soon see your rocket start to wobble. That wobble gets translated into your launch direction. Anything you can do to keep pointed the right way, do it. Even better, only use stability enhancers when you absolutely need to. I always put my rockets on the pad without them and only add them if absolutely necessary. Rocket engines and SRB's, unlike jet engines, have no spool-up time. Their thrust is almost instantly translated from your trust setting.

Hope this helps.

[SultanSaidi]

Ah yeah i figured it out my problem was that i put my center of mass and center of thrust too close together because i didnt wanted a too high mass shift while destaging because of that i builded my rockets always a bit more wrong but now i think my wrong physiks thinking got correct thank you all for your help yaall

[mrclucks]

I know you've found the problem but I'll input my .02 for launches

1 make it somewhat aerodynamic

2. Fins at the bottom, generally four is all that's needed

3. As few 'directional' factors as possible I'd gimbaled engines and SAS

4. Keep away from mach effects. I go as fast as possible but lower thrust if I see mach effects