Why my spacecraft tumbling when i try to insert it on orbit

[Pawelk198604]

since last update is almost impossible to put almost anything in orbit

The rocket fly well (the first two stages) but when i want to achieve orbit the orbiter start tumbling i lost precocious delta-v and get very angry!

Edited May 19, 2015 by Pawelk198604

[fairytalefox]

It's probably because something is wrong with your rockets.

In order to get more useful answer, you should provide us with more information. Pictures of the rockets would help a lot.

[Pawelk198604]

It's probably because something is wrong with your rockets.

In order to get more useful answer, you should provide us with more information. Pictures of the rockets would help a lot.

[Vanamonde]

Looks like you're using the non-gimballed engine, for one thing. It can't help with steering.

[Indy]

I don't want to be THAT guy, but perhaps putting on some stabilizing fins towards the bottom? Should help with tipping due to air flow.

[Jonboy]

First thing I noticed: you're starting your gravity turn WAY too late. The old ascent strategy of boosting straight up to 10,000m and then pitching over is null and void with the new aero. Start your gravity turn at about 1,000m, or when your velocity is in the 50 to 100 m/s range. Just pitch over 5 or 10 degrees and continue pitching slowly, staying as close as possible to your prograde marker as possible. Do not pitch over too much or you will start to tumble. Aim for 500 to 600 m/s when you hit 45 degrees on the navball. At that point you should be well above 20,000m, where the atmosphere is very thin, and you can safely pitch over father from your prograde marker to pick up horizontal velocity.

Also adding control surfaces near the bottom of your rocket or some reaction wheels near the top can help you stick to that prograde mark. Let us know if that helps.

[Superfluous J]

The center of mass of your rocket is too far backward in the final stage. Try a Terrier in the final stage.

Also, just a couple general tips:

Those radial engines are not pulling their weight. Either you've trust limited them or they're really bad in lower atmosphere (I don't remember now what their Isp curve is). Replace them with something better (solids, perhaps?)

Your gravity turn is all but nonexistent. By the time you're at 10km you should be 45 degrees over and you should do that tilt smoothly.

Also? Thank you for putting up a video. It makes troubleshooting these kinds of issues very easy.

Edited May 17, 2015 by 5thHorseman

[Pawelk198604]

[cybersol]

Spinning out of control essentially comes down to a contest between drag and control. When the drag overcomes your control authority, you go for a spin. You can decrease drag by staying closer to prograde and building a more aerodynamic rocket. You can increase control using engine gimbals, stabalizer wheels, and control surfaces.

Also note that drag increases significantly right around mach 1 (340 m/s). So you should stay pointed as prograde as possible at speeds around 280-400 m/s.

[SRV Ron]

As posted in numerous post, the issue is the new more realistic aerodynamics and parts drag models. There is a range of speed and altitude where drag on the nose increases dramatically. Given that all parts in line are now sheltered from that drag, the rocket can flip over when you hit a critical speed in the lower atmosphere. Fins can help as well as learning all over how to fly in the first 25,000 meters of the Kerbal atmosphere.

[Superfluous J]

Lose the side boosters. They are giving you WAY too much thrust. Just don't use them at all. Compensate by replacing the swivel with a Reliant, and relying on pod torque to do your gravity turn and 4 of the tier-1 fins (the really cheap ones) to keep the rocket straight. Having all your authority in one place (and slowing down!) will eliminate the wiggling.

I can't stress enough to DO YOUR GRAVITY TURN. You are going way to high way too fast and wasting way too much fuel fighting gravity and then adding sideways velocity that you should already have. By the time you're 10km up, you should be at LEAST at the 60 degree mark. By the time your apoapsis is at 50, you should be SIDEWAYS. You did well keeping it straight, and turned well as the air thinned, but early on you need to be more aggressive.

But not too aggressive

EDIT: Sorry I wrote all that after watching only the first launch. The 2nd and 3rd launches were better, but still lose early thrust (and that weight) and turn earlier and more slowly.

[fairytalefox]

So now it doesn't flip, which is good.

From my personal experience:

1. The best payload is symmetric. Try two Goo things instead of one.

2. Your first stage is too small and expensive. It can be combined with the second one, which would save some weight on engines. Also, one larger tank is always better than two smaller ones. Because wobbliness is not a bro.

3. As far as I understand, side-mounted engines are here only for short initial kick up to terminal velocity. It's exactly what SRBs are good at. And fins. SRBs without fins are dangerous.

4. Did you think about KER? Blind engineering isn't the only option these days.

[Pawelk198604]

So now it doesn't flip, which is good.

4. Did you think about KER? Blind engineering isn't the only option these days.

The Kerbal Engineer? I read it need to be unlocked in career mode.

[fairytalefox]

The Kerbal Engineer? I read it need to be unlocked in career mode.

I mean a mod called Kerbal Engineer Redux. dV and TWR readings in the VAB. It contains some unlockable thingies but the core functionality is here from the very beginning.

http://forum.kerbalspaceprogram.com/threads/18230 Here.

Edited May 18, 2015 by fairytalefox

[Pawelk198604]

i found some my previous designs but it not work in new KSP I think i need upgrade spaceport

[kurja]

One thing that could help would be to use fuel tanks that aren't half empty?? Especially on the lower stage launching with less fuel makes no sense whatsoever, you have like twice more thrust than you need anyway.. why are you draining the tanks in vab??

On the last stage you need very little thrust really, you can have more fuel & a small engine there.

[Cebi]

I see some flaws on your test 3 rocket. You have 4 liquid boosters which have low fuel fraction. You are using 4x RT-30 for barely 10 sec. That is wastefull. Also try to do proper gravity turn. You dont need boosters at all. Make first stage with RT-30 that has enough trust to lift of the pad, then second stage with RT-45 and you are good to go for orbit.

Also you are fliping becouse that engine under your pod weights more then your capsule. You need more tanks on last stage or you need to use lighter engine. RT-45 is ok for last stage if you dont have LV-909.

@Kurja: He reached limit of how much rocket can weight. He did not upgrade buildings. That is why he is draining fuel out of tanks. Better solution is to drop those 4 engines with small tanks and add more fuel per engine.

Edited May 18, 2015 by Cebi

[kurja]

Ah I missed that... browsing on a phone. Sorry.

[fairytalefox]

Did you read the posts above? Okay, let me retell it one more time.

Unlike previous versions of the game, there's no "one ring to rule 'em all" type of engine anymore. Different engines are situated for different cases.

There are SRBs: great thrust, crappy Isp, uncontrollable after firing up and heavy as hell. They are good for initial stages.

There are "intermediate" engines like LV-T30 and LV-T45. Still heavy, but good thrust and kinda not bad Isp both in atmosphere and in vacuum. They are good for gravity turn stages.

There are "space" engines like LV-909. Isp at sea level sucks but in vacuum is great. Vacuum thrust kinda exists, atmospheric thrust kinda doesn't. Feather weight, which is good for lowering dry mass of the last stage, which is great for dV. They are good for orbital maneuvers, such as circularization.

This ship consists of 15 parts, all of these you already have unlocked, weights less than 13 tonnes, costs less than 6k funds and is capable to reach highly elliptic orbit (while being piloted by me; I terribly suck at piloting) to do both high orbit and low orbit science.

[KerikBalm]

Yea.... 4x LV-T30/s45s with each only being fed by one FL-T200 tank.... wayy too much engine mass for to little fuel mass.

Don't have a half drained FL-T200 tank, use a FL-T100 tank.

You have the LV-909, use it on your upper stage... sticking a LV-T30 there is.... ......

Sometimes, I actually do the math to determine the optimum proportions for 3 stages if I do a 3 stage design.

Having too little fuel in a stage can actually hurt your dV, and youd be better off without the stage.

Don't add a LV-T45 2nd stage just to feed it with on FL-T400 tank.

Every ton of engine is a ton not used for fuel tanks + weight used for a decoupler.

Think carefully about when you split things into stages.

Suppose I have 3 stages:

Top: Command pod + FL-T200 + LV-909

Middle: FL-T400+ LV-T45

Bottom: FL-T400+LV=T45

That 2nd stage is *stupid*

If I instead did:

Top: Command pod + FL-T200 + LV-909

Bottom: 2x FL-T400+ LV-T45

I would remove 1.5 tons of mass in the form of a 2nd engine, and simply carry another 0.25 tons of empty tank for half the duration of the bottom stage.... which doesn't affect much considering the "dry mass" already includes the top stage (3 tons) + the LV-T45 (1.5 tons) + another FL-T400 tank (0.25 tons).

The design does much better by consolidating the bottom and middle stage into 1.

Likewise, you have too many stages with too little fuel per stage.

[Pawelk198604]

thank you all :-)

Thanks to all these new aerodynamics

I feel like newbie again

But i made it

[fairytalefox]

Gratz

Can you mark the thread as answered now? http://forum.kerbalspaceprogram.com/threads/85063-How-to-change-Unanswered-to-Answered

[wilt57]

I didn't watch all your videos, but your ascent profile was much better on that last video. Keep trying to stay within the prograde marker until around 15-25k or so. Try to time it so that your prograde marker is around 45 degrees in the 10-15k range. These are all general though, different TWRs will warrant different ascent profiles.

It's your game and I don't want you to play with rockets you don't enjoy building or flying, but you are still bringing too much engine at launch, at least at the beginning of your last video, which was a far as I watched. I aim for an off-the-pad TWR of 1.2 using atmo thrust. This way you shouldn't have to lower your throttle so much. By the time your thrust increases with altitude and fuel burn-off, you should be able to maintain a decent TWR without going too fast. Not only are you spending funds on rather expensive-ish engines, you are burning excess fuel to accelerate their mass. Reaching terminal velocity ASAP isn't as big a deal as many players make it out to be.

[n0xiety]

I must say you are doing a great job with manual control in that last video yet i must recommend using mechjeb even if you don't like it and try the default ascent guidence which is now working perfectly for 1.02 . This will help you get a better grasp of the perfect gravity turn. Truth is if your rocket controlls can take it, starting the gravity turn right after you takeoff while you are at 200 meters is the best. Check this video out and you will notice the dV gains:

Edited May 19, 2015 by n0xiety

[EtherDragon]

I'll add another bit of advice to what wilt57 said, reaching terminal velocity isn't the end-all-be-all of launch efficiency any more.

In your launch profile you have to do a lot of manual flying to push your rocket in the direction you want to go, which tends to pull you off the prograde marker. Any time you are not flying prograde you lose efficiency to atmospheric drag and risk losing control from uneven forces acting on the length of your rocket.

Instead try this:

1. Blast off!

2. Almost immediately (before 100m/s velocity) kick your rocket over to 5 degrees off of vertical.

3. THROTTLE BACK, and go slower. You should be able to let your rocket more or less naturally tip over*. Aim to be at 45 degrees by 20km (much like you already did.

3a. Note: if you used tail-fins, the gravity turn would literally be automatic without any SAS needed.

Here are two videos for your consideration:

*Note: It's called a Gravity Turn because Gravity does the turning) with just a little bit of control input.