How to NOT lose control with asparagus staging?

[nyugnep]

I am trying to launch a satelite using asparagus staging, it is the first time I am not building simple build where i just put few fuel tanks on top of each other and strap a rocket underneath. However, at 6000m ish I lose control, I play around with different builds trying to solve the problem yet i end up with same result. I went on youtube and checked out this video and copy his rocket (only one less fuel tank on each side cause i dont need that much) yet i still run into the same problem. What can i be doing wrong? I spent the last 4 hours trying to get it into orbit. Photo of the aircraft

[Red Iron Crown]

Welcome aboard!

I'd try adding some fins to the bottom of the core stage.

[nyugnep]

11 minutes ago, Red Iron Crown said:

Welcome aboard!

I'd try adding some fins to the bottom of the core stage.

2 Fins: Well I added 2 symetrical fins and as it did help a little bit, i spiraled out of control at 9 km going 300m/s while gradually gravity turning (at that point I was about 30 degrees east) 

4: Fins: Same as above only at 11km

Just thought it would help if i would post my method:

1: Start engines at max

2: Release from launch assist structure

3: Gradually increase velocity to 100m/s (10 m/s per 100m) to 1000 km

4: Start gravity turning by gradually pointing tip to 10 degrees east

5: Follow prograde

6: Gradually increase velocity to 240 m/s by 5km

7: Gradually increase velocity to 320 m/s by 8 km

8: Attempt to maintain control and follow prograde shift

9: Spiral out of control

 

By the way. Thank you very much for helping

 

Edited December 5, 2016 by nyugnep
Added information after another attempt + Formating

[sal_vager]

Hi @nyugnep, welcome to the forums.

Something that caught me out in early career games was failing to account for the new drag model, KSP will simulate blunt front and rear faces and increase the drag these produce.

Your nosecone/decoupler/probe/fueltank combination is actually very draggy, as the partial face of the back of the decoupler and of the tank are causing a lot of drag.

That drag not only slows you down, it will also act like a weathervane and will flip the vessel around.

If you place the probe inside a 1.25m service bay it will avoid having exposed faces and cut the drag, letting the craft fly as intended.

Hope this helps.

[nyugnep]

7 minutes ago, sal_vager said:

Hi @nyugnep, welcome to the forums.

Something that caught me out in early career games was failing to account for the new drag model, KSP will simulate blunt front and rear faces and increase the drag these produce.

Your nosecone/decoupler/probe/fueltank combination is actually very draggy, as the partial face of the back of the decoupler and of the tank are causing a lot of drag.

That drag not only slows you down, it will also act like a weathervane and will flip the vessel around.

If you place the probe inside a 1.25m service bay it will avoid having exposed faces and cut the drag, letting the craft fly as intended.

Hope this helps.

Thank you, I am currently taking a short break so I'll get back to you if I succeeded. So ideally, my airfract should be as tight as possible so that my aircraft get least possible amount of friction with air. Would you propose that I remove nose cone/decoupler completely and just add nose cone to the service bay or should i keep the construction but instead put the probe into the service bay?

Side note: This game is so addicting. I bought it on saturday, spent the whole sunday playing it and as I had no work today classes today I spent whole day playing the game/watching videos. It will ruin my education

Edited December 5, 2016 by nyugnep
Side note:

[sal_vager]

A nosecone/servicebay/fueltank would work fine, the decoupler will only add a tiny bit of mass, but lets you jettison the nosecone in orbit to save on mass while doing any orbital manoeuvres

[nyugnep]

4 minutes ago, sal_vager said:

A nosecone/servicebay/fueltank would work fine, the decoupler will only add a tiny bit of mass, but lets you jettison the nosecone in orbit to save on mass while doing any orbital manoeuvres

I'll test that out. Thanks.

Just out of curiousity. How come the guy in the video [19:45 flight start] doesnt have the same problem?

[Superfluous J]

48 minutes ago, nyugnep said:

I'll test that out. Thanks.

Just out of curiousity. How come the guy in the video [19:45 flight start] doesnt have the same problem?

Not enough information to determine, but one possibility is that he changed the priority of the fuel tanks in the center stack so they emptied bottom-first. This makes rockets inherently more stable as the center of mass shifts upward during flight instead of downward. There's a reason the arrowhead is the heaviest part of the arrow: in atmosphere the heaviest end always wants to be in front.

Note that's just a guess. It's also possible his payload is just heavier than yours so the COM stays far enough forward. it's also possible that he just didn't turn enough to have a problem. If you keep it going straight, even a (moderately) unstable rocket can keep going the way you want it to.

[sal_vager]

It also looks like he was very gentle with his gravity turn, if you can keep prograde enough so your engines gimbal etc can cope with the drag it won't flip out.

Edit:

To show how big a difference having and not having that gap can cause here's my copy of your rocket.

 

There's 63.80 drag on that fuel tank, that's why you're losing control.

Now, here's the new sleeker model.

 

Less drag from the decoupler by about 50%, and a massive reduction in drag from the fuel tank.

The first rocket flipped for me, the second one didn't

[wumpus]

I'd recommend at least trying putting one fuel tank from the center and moving it to the sides.  You will be carrying extra mass [the engines] and the drag, but typically you expect to burn less each stage (there is no exact formula, but twice the fuel in each stage (or equal delta-v per stage) is a good place to start).

Looks like I (and probably a few other returning old hands) have a lot of unlearning to do).  Then again I just took a contract to haul a 2.5m heatshield to 2km/s in the atmosphere with only 1.25m parts available.  Not recommended (the solution was to arrange the boosters around the heatshield and have the drag below the CoM).