Why does this craft backflip in Space?

[cloud167]

Hello,

I am building a SSTO and I am having a lot of issues of when I get to space the craft just back flipping of control when I apply thrust only once I get it to space. 100km is the orbit I am trying to establish with the craft.

It flies just fine in Kerban atmosphere.

The drymass and wetmass are aligned and I use TAC balancer to keep it like so in flight.

I don't think it is a mass shift issue, however if you say its that its that.

Some things that are needed to know. I modified the thrust output of B9s SaberM and SaberS to be able to push the craft.

For the life of me I can't figure out how to get rid of the Red Torque arrow.

Below are some pictures

[iM

]

Edited September 7, 2014 by cloud167

[Wanderfound]

Looks like you CoT is slightly below your CoM. You've got a massive amount of torque generated by this.

Rearrange mass and/or engines until the torque figure displayed by RCS Build Aid reduces to sensible levels. These figures update live in the SPH as you build. Grab any heavy part from the parts list and move it around the surface of the craft while watching the torque figure change.

Alternately, grab this mod: http://forum.kerbalspaceprogram.com/threads/77710

[cloud167]

thanks a bunch i was trying to find a gimbal trim mod

[CattyNebulart]

The B9 engines allow you to trim them to compensate for such, just experiment a bit till you find the right trim and then set a hotkey to switch trim when needed.

[Taki117]

Alternatively, if you don't mind the drop in TWR, you can just use the center SABRE engine which appears to be more inline with the CoM.

[cloud167]

The B9 engines allow you to trim them to compensate for such, just experiment a bit till you find the right trim and then set a hotkey to switch trim when needed.

Was looking for that option it used to be present now it is missing maybe i should try a re install of b9

[Hodo]

Oh and you may want to get FAR, because last I checked B9 does not support stock with its parts.

[Murph]

Oh and you may want to get FAR, because last I checked B9 does not support stock with its parts.

The B9 parts work just fine with stock aero. They just don't provide support if you hit a bug in stock aero.

[cloud167]

I am running NEAR right now. To my understanding that my problem isn't solved by removing Near/FAR, since the issues I am having are only happening in space where no atmospheric conditions are present.

[Murph]

I am running NEAR right now. To my understanding that my problem isn't solved by removing Near/FAR, since the issues I am having are only happening in space where no atmospheric conditions are present.

It's probably worth experimenting to conclusively rule out a problem coming from NEAR, if the behaviour is quite similar to an aerodynamic loss of control (hard to know from your description). It's possible that you're getting some negative interaction between mods (not B9 & NEAR, they should be fine together, but something else), which is somehow causing NEAR to not properly disengage outside the atmosphere. Just a possibility to consider, if there's no other explanation forthcoming.

[Hodo]

I am running NEAR right now. To my understanding that my problem isn't solved by removing Near/FAR, since the issues I am having are only happening in space where no atmospheric conditions are present.

I pretty sure I know what the problem is.

It looks like from your pictures your fuel tanks may drain from differently, top to bottom then you would like. Your CoM is then moving up putting your CoT below your CoM, and causing your pitch issues in zero atmosphere. This isn't noticed as much in atmosphere because your wings and control surfaces are able to counter that force with increased control input.

You have a couple of options confirm this and fix it.

-Download TAC Fuel Balancer, it lets you balance out the fuel tanks so your CoM stays pretty much in place. Or download PYB auto balance, does the samething just newer.

-Check the fuel flow of your tanks, and see if you can get them to drain all of the tanks evenly or feed to a centralized tank to keep your CoM pretty close to where you started.

- redesign the whole thing and start over with a single wing design, bi-plane wings are bad. Ask Ferram if you want more information on that, he is far more tactful then I would be talking about it.

[cloud167]

I pretty sure I know what the problem is.

It looks like from your pictures your fuel tanks may drain from differently, top to bottom then you would like. Your CoM is then moving up putting your CoT below your CoM, and causing your pitch issues in zero atmosphere. This isn't noticed as much in atmosphere because your wings and control surfaces are able to counter that force with increased control input.

You have a couple of options confirm this and fix it.

-Download TAC Fuel Balancer, it lets you balance out the fuel tanks so your CoM stays pretty much in place. Or download PYB auto balance, does the samething just newer.

-Check the fuel flow of your tanks, and see if you can get them to drain all of the tanks evenly or feed to a centralized tank to keep your CoM pretty close to where you started.

- redesign the whole thing and start over with a single wing design, bi-plane wings are bad. Ask Ferram if you want more information on that, he is far more tactful then I would be talking about it.

I do use TAC balancer.