Rocket tipping over

[jtommi]

Hi,

I'm pretty new here (and in KSP) and have a problem.

I'm trying to launch my first space station.

But my rocket tips over each time I try the gravity turn at about 10.000m.

The tanks above the lander can are all empty.

I added the huge delta wings but it didn't help.

If I remove everything above the lander can it works, obviously.

Do you have any ideas?

Edited June 29, 2015 by jtommi
Change to answered

[Gaarst]

Do not do your gravity turn at 10km

Start turning a few degrees at ~50 m/s depending on your TWR, and gradually follow prograde marker until 45° at 10km and 15° at 30km. Then atmosphere is thin enough and you can basically do what you want.

This has been the easiest ascent profile since 1.0 aero.

Welcome to the forums BTW

EDIT: V V - Kaos is right, a TWR of 2 at launch is a bit high, try going down to 1.5-1.7 TWR ASL (click atmospheric on your KER display)

Edited June 28, 2015 by Gaarst

[Kaos]

Flying slower can also help.

[BasKing]

Do these fins have control surfaces?

Or do you have any inline reaction wheel(s)? Some pods have reaction wheels in them, but the lander can has not.

(and put 4 nosecones on it to reduce drag)

[BasKing]

Perhaps hide the top in a protective shell to reduce drag on it.

[jtommi]

Thanks for the tips.

@Gaarst : Unfortunately that didn't work. It turns fine and at about 10.000m it get's out of control (SAS on)

@Kaos : I reduced thrust gradually, ddidn't help either

@BasKing : How would I do that?

[BlueCanary]

Like BasKing said, try putting drag reducing parts on, particularly either a fairing or a nosecone (which would be detachable because of the docking port) on top and on top of the boosters. Even if it doesn't stop tipping, it will make your rocket more efficient.

More control surfaces down low could help make it more stable by moving the aerodynamic center back, and would give more control authority to avoid flipping.

EDIT: Just saw your reply, to add a fairing you would put one of the 1.25m aerodynamic fairing parts inbetween, say, the lander can and the tank below it. This will let you create a fairing around it. It's probably be easier though to just put a nose cone on top of the docking port at the top.

[BasKing]

Research 'flight control' (its in tier 4) for both the winglets with control surfaces, and the small inline reaction wheel (reaction wheels require electricity while functioning btw)

You need to research 'aerodynamics' (tier 5) for the protective shell nosecone. Just play around with it, it is very selfexplanatory.

[BlueCanary]

Maybe try lowering those fuel lines to the bottom of the rocket too. I don't know how much of a difference that would make though.

[Mad Rocket Scientist]

Try replacing the four outer "Reliant" engines with "Swivel" engines, those have gimbals, so it should be easier to maintain stability.

[rofltehcat]

You normally want the front of the rocket to be as heavy as possible (think of an arrow: the arrow head is the heaviest part and the fins are the part creating the most drag). Is there a reason why you are launching the station empty?

You could also move the fuel from the center fuel tank to the space station's fuel tank and transfer it back into the lower tank before the asparagus fuel pods run out. But it also depends on how hard you are trying to turn when you initiate the gravity turn.

[ExaltedDuck]

Flipping in the low atmosphere is often a sign of you center of mass falling behind your center of drag. I'd add nose cones to every leading edge and set the fuel lines to pump from the top to the bottom. Extra fins down low on the booster might help too. Also, it almost looks like those axial docking ports are not placed symmetrically. If that's the case, they could pull the nose toward the side they're on.

[Snark]

Add nosecones to those boosters! Big flat surfaces on the front of things = bad.

Another alternative to using a fairing to reduce drag on the front would be to add a disposable nosecone so that the front end of your ship isn't so blunt/flat. Like this:

1. Put a 1.25m stack decoupler on the top of the ship, on top of that docking port. Important: Flip it upside down before attaching, otherwise it will remain stuck to the docking port after decoupling.

2. Put a nosecone on top of the decoupler, the pointier the better.

3. Move the decoupler to the top of your staging order (i.e. so that it happens last). Go to "Action Groups", pick some reasonable unused one (I like to use "Abort" for this), and then choose that decoupler as the action for that action group.

Now you have a more aerodynamic rocket. When you get high enough in the atmosphere that drag's not an issue anymore (say, 30 km), you can ditch the nosecone by activating that decoupler (e.g. by hitting "backspace" if you assigned it to the "Abort" action group).

Another suggestion: You're flipping because your center of mass is behind your center of drag. You can make the rocket more stable by moving the center of mass forward. You mentioned that the fuel tanks above the lander-can are empty. That's bad: they're big, draggy, and not very massive. Here's the suggestion:

1. Fill up that 4-ton tank that's on top of the lander can.

2. To make up for the added mass, empty the tank that's at the bottom (i.e. the one that has those fins attached). This will make your rocket a lot more stable.

3. Launch.

4. By the time you get to the point where you actually need the fuel in that tank you emptied, you should be above most of the atmosphere. So when you've dropped your last radial boosters, transfer the fuel out of that tank in the front and into the tank down below.

(This plan will only work once "resource transfer" is enabled in your career, which happens when you upgrade your science facility the first time.)

[Kryxal]

I'd be tempted to lose the engines on the first asparagus stacks that you'll be dropping ... your launch TWR is entirely too high. Alternatively, replace the center LV-30 with an LV-909 and have it kick in when you drop the first pair (and this will give you better delta-v besides!)

[jtommi]

All your suggestions brought me to pay attention to more things and finally to get it up there.

Straight up till 25.000m, then full thrust and turning.

Thanks a lot for your help. I'm going to check out the aerodynamics parts.

@Snark : I only read your reply after succeding, but tried them just for practice. I think filling up the top tank did it, no flipping at 10000m, BUT the whole construction was very wobbly (which might be due to the docking port between the station and the bottom tanks). I suppose it works like a shuttlecock, the mass first against the wind.

- - - Updated - - -

I thought that it would be better to reduce the weight, since it was my first time. Apparently I was wrong.

[Snark]

@Snark : I only read your reply after succeding, but tried them just for practice. I think filling up the top tank did it, no flipping at 10000m, BUT the whole construction was very wobbly (which might be due to the docking port between the station and the bottom tanks).

Wait, there's a docking port between the station and the bottom tanks? Couldn't tell that from the initial screenshot.

Yeah, any time you have a docking port as part of a stack, it's super bendy. For little things (like slapping a nosecone on the front end) this doesn't matter, but if there's significant mass on both sides of the connection, the docking port will flex a lot. The typical solution to this is to add struts; for example, you could add struts from your radial boosters to the station above to hold it steady.

I suppose it works like a shuttlecock, the mass first against the wind.

Yes, exactly this! "Put the center of mass in front of the center of drag."

It's just like playing badminton (or archery, or darts), with the addition of several tons of high explosive. Same principle, bigger scale.

[RidiculousRichard]

It's just like playing badminton (or archery, or darts), with the addition of several tons of high explosive. Same principle, bigger scale.

Many times the entertainment!

[Snark]

Many times the entertainment!

Well, naturally, that goes without saying. Everything is more entertaining with explosions.

, for example.