ksp 1.2 my rocket keeps flipping [need rocket design help]

[Rampagerslife]

so, long story short i made a rocket to hold some resources i need on my lunar base. however when i launch it, it quickly starts to spin out of control. i checked with rcs build aid and it is a problem with the engine setup. 

i have no idea what mods you need to even load the damn ship so im just sending my GameData and the save file so its easier. [you'll need winrar to extract the files]

https://mega.nz/#!m9sQ0AQC!F4x67rMEIQ5ktRTIGrb2iEQlKSavOqJIBlJJL-cTwlA 

 

i need someone to help me cause i know bugger all about rocket science [i did use fuel cheat but you can make a functional launcher if you want] [and i would prefer if you could send me the craft file :3]

Edited September 3, 2017 by Rampagerslife

[Vanamonde]

How about a screenshot of your ship? Often that is enough to diagnose a problem, and will save people the trouble of downloading and unpacking your save. 

Welcome to the forum, by the way.

[Rampagerslife]

how do put in a picture?

Edited September 3, 2017 by Rampagerslife

[Spricigo]

3 hours ago, Rampagerslife said:

I have no idea what mods you need to even load the damn ship so im just sending my GameData and the save file so its easier. 

Consider it by the potential helper's perspective. It's a lot of trouble for something that may be solved by a quick look at a screenshot.

The whole file can even be unusable if the wannabe helper happens to not have access to KSP at the time he is looking at this thread. (Like me.)

3 hours ago, Rampagerslife said:

checked with rcs build aid and it is a problem with the engine setup. 

If so, enable the CoT indicator and make sure you have the thrust aligned with CoM. You may need to move engines around to get a balanced configuration alternatively your payload may be the offender. 

3 hours ago, Rampagerslife said:

...need someone to help me cause i know bugger all...

If you don't know something,  you can learn it. And people that know can teach.

There is a lot of good guides around. And lots of people willing to give advice. Ask and we will try to point you in the right direction. 

[Vanamonde]

2 hours ago, Rampagerslife said:

how do put in a picture?

The F1 key (on Windows PCs) places a screenshot in your KSP folder. You can then upload it to an image sharing site, such as Imgur.com (free accounts), then copy the link they provide into your post here on this forum. 

[Rampagerslife]

the important specs about my ship are this:

mass: 26.7 tons

propulsion: i forgot the name but its one of the karbonite engines [and i use fuel cheat]

https://imgur.com/fldFjpx   https://imgur.com/WF06u7m

Edited September 3, 2017 by Rampagerslife

[Vanamonde]

Is that the whole craft you are launching? You have a reaction wheel part and steering fins to help with attitude control, but that blunt nose and exposed surfaces will generate a lot of drag, which will try to yank the ship to the sides. I'd suggest putting a fairing around the whole payload, or at least add a nose cone (which you could eject later). 

[Rampagerslife]

xD lol somehow i had not thought of that

[linuxgurugamer]

And move the fins further down if you can

[Snark]

Also, for an explanation of why it doesn't stay stable:  Because you've built a rocket that wants to be pointed the other way around, and you haven't given it anything to steer with.

Note where your CoM is.  It's back near the back of the ship.  That's bad, because ships going through atmosphere really really want to have their CoM in the front.  So your ship wants to be pointed engine-end forwards.  Adding a nosecone might help a little, but I suspect not much; with a CoM in the back, there's not much you can do.

Compounding the problem is that you haven't given the ship any way to steer itself.  Yes, you've got some AV-R8 winglets on there, but you've put them in a location where they can't actually provide any stability or steering authority.  Why?  Again, look at the screenshot.  Look at where the CoM is, and then look at where those winglets are.  They're only very slightly below the CoM.  That means they're of very little use even as passive fins, and they have very little control authority because they just don't have a lever arm to work with.

So, my advice to you would be to do the following:

• Put a nosecone on.  It's not enough to solve the problem, but it will make your ship fly a lot more efficiently through air.  Note that you don't need a decoupler or anything-- you can attach the nosecone straight to that big docking port.  The docking port has a "decouple node" option on its menu in flight that will allow you to ditch the cone once you're out of atmosphere.
• If there's anything you can do to move heavy components higher on the rocket, do so.  For example, put that probe core up top-- it's a full half-ton in a very vertically-compact package, so it's nice and dense; it'll help you a bit for that to be on the front end.
• Move the control fins down-- waaaaaay down, as far down as you can manage.  The farther down you can put them, the more they will help you.  You want them way behind the CoM.

 

[Spricigo]

 

Incidentaly something that may help to make your rocket more stable is ading fuel tanks. Not because those have some kind of special effect on stability, but just because your rocket will be longer and your winglets can have a longer lever arm. Also, depending on the weight of all those parts, it may help to make the CoM move up.

It can even be made in a rocket functional enough to not require infinite fuel to reach the moon if you decide to try. You have a lot of power in this engine (TWR 10+), what you need is, lets put it in a kerbal way, MOAAR FUEL.

 

[Rampagerslife]

2 hours ago, Spricigo said:

 Also, depending on the weight of all those parts, it may help to make the CoM move up.

 

Unfortunately, karbonite is VERY heavy (i had to have the tank half full for some reason to do with weight (i actually forget the original reason but its necessary))

[John Cochran]

Snark pretty much answered the question. In general, while you're in atmosphere, your center of mass MUST be in front of your center of lift. And with the default way that fuel flows in earlier versions of KSP, this is a problem. With the original "Fuel is taken from tanks furthest away from the engines." This would cause the tanks towards the top to empty first ... Which causes your center of mass to shift to the rear ... which would result in a rocket that's marginally stable upon launch to start out fine and then start flipping end over end later in the flight. Thankfully, that's no longer the default behavior. But if you want your rocket to be as stable as possible, change the fuel priorities so that the rearmost tanks in a stack of tanks are emptied first. Have your center of lift well behind your center of mass. And aerodynamic control surfaces near your center of mass are worthless. 

[Palaceviking]

On 03/09/2017 at 10:46 PM, Snark said:

  Because you've built a rocket that wants to be pointed the other way around,

Edited September 26, 2017 by Palaceviking

[Palaceviking]

Just put this on your clipboard @Snark 

[Spricigo]

15 minutes ago, Palaceviking said:

Just put this on your clipboard @Snark 

He would end with a lot of those little notes pretty soon.

 

I have a link in my signature explaining the issue of aerodynamic unstable rockets...and still is so common to people ask: why the flipping rocket flips?