Spaceplane spins uncontrollably

[thevegimobil]

During re entry or high speed drop tests my spaceplane that is similar to the shuttle ends up spinning wildly out of control... It ends up spinning with the left wing facing the ground and rotating around its axis... It's impossible to get out of... I was wondering what the problem was? Here is a photo...[ATTACH=CONFIG]33818[/ATTACH]

[draeath]

In the VAB near the bottom left you see some buttons. See where the center of mass is. It should be along the centerline axis, and as close to the center (between nose and tail) as possible. Lift vector (if any) should be in the same place as the center of mass and pointing out the back (eg "up" if you were sitting in the cockpit). Center of thrust (not sure it's name, but it's the only one remaining after Mass and Lift) should be behind the center of mass, and on the same centerline axis.

[thevegimobil]

Yes but with all the wings the centre of lift is on the nose in the picture... No matter how many wings I add its still there

[pwnedbyscope]

you need more weight it the rear, lower its center of gravity, or shift it back, bigger engine would do the trick most likely

[sal_vager]

Okay two things, first, the limited coding of the wings means that if they are on sideways they do not work at all, your rearmost wings are adding weight with no lift whatsoever.

Secondly, for stability you'll want your CG in front of your center of lift, you'll have to guess where the CG will move to after you have used up most or all of your fuel.

With the CG and CL in the same place you'll have a nice, highly maneuverable craft, twitchy is the word, with the CG in the back like you have you'll have a hell of a time keeping her straight.

[EndlessWaves]

Okay two things, first, the limited coding of the wings means that if they are on sideways they do not work at all, your rearmost wings are adding weight with no lift whatsoever.

That's incorrect, wings placed in that orientation definitely do function and generate lift (or did in 0.16, it's possible something has changed in 0.17).

[thevegimobil]

No I have changed the design... They do generate lift but in the wrong direction I think.... Anyway now my launch vehicle spins when I add Srb's ...it's fine when I have just one main engine but add srbs and it spins...???

[sal_vager]

Yeah I didn't look properly, they are on backwards, not sideways, so they will work.

Your lift will still be very far forwards though, you can change this a bit by angling your wings with Shift+WASD and QE, but it'd be better to add more wings at the back.

[thevegimobil]

Don't worry I redid the design and its brilliant... I'm just having trouble building a launch vehicle....when I add srbs it spins on launch... Without srbs it's fine.... Hmm

[EndlessWaves]

Probably the SRBs waggling side to side (especially if you're using the longer ones), try a ring of struts between the top or bottom of them.

[thevegimobil]

Nah it's not that... It was weird.... I've gone for the shuttle design external tank now... Just a case of balancing it with unused fuel tanks...

[draeath]

Are you hitting terminal velocity? I've found if you hit that and keep pushing, things like wings begin to act like airbrakes...

[Fendleton]

Also make sure that center of thrust is directly below the center of gravity. Anything else is a recipe for an uncontrolled spin and a breakup. Fuel tank balance is one solution, but you can also vector the engines themselves. Or just have boosters on the upper AND lower wing surfaces, if your craft is already symmetrical. It's not as pretty or as elegant as a perfectly-balanced shuttle-style spaceplane....but it's a lot easier to get working.

Edited September 28, 2012 by Fendleton