Making a Shuttle- Aligning COM/COT

[Zucal]

I'm building my first space shuttle (standard orbiter style) and I'm having trouble aligning the center of mass with the center of thrust. Every time it flies, it just pitches over immediately. RCS Build Aid hasn't been much of a help either. How do?

Thanks!

[Hcube]

(The picture links are not working on my mobile so im gonna say general stuff)

If they are properly aligned, there is no reason for the craft to flip over at launch. At first just use the CoT and CoM in the VAB to have them roughly aligned, launch it, see the way it flips, change SLIGHTLY the orientation of the engines and repeat until it flies right !

That's pretty much the only way you build a shuttle.

The real problem is : even if it launches right, it has to stay so at SRB separation, and this is very hard IMO.

Tip : If it is somehow stable but you need more control, spam Vernor engines (the LFO RCS ports) on the top of the external tank, and on the bottom of the shuttle.

Tip 2 : the further away the engines are from the center of mass, the more efficient the gimbal will be.

Hope this helps

EDIT : Seeing how the SRBs were thrashed in 1.0 and drag augmented in 1.0.2, good luck building a Mk3 shuttle that can get to orbit ! The huge SRBs now burnout pretty damn fast

Edited May 3, 2015 by Hcube

[Raptor9]

I haven't tried to make a shuttle in the latest version, but here's a few more tips:

1: Piggybacking on what Hcube said about placing the engines further back from the center-of-mass, you're shuttle and boosters might be mounted too high on the fuel tank. If you reference real shuttle pics, you'll see that the shuttle's aft end hangs further back from the external fuel tank. This might help with the gimbal authority of the shuttle engines, and it also helps the angled thrust of the three engines get in line with the center-of-mass when the tank is placed further in front of the shuttle.

2: Especially when making planes/spaceplanes, but also when making craft of asymmetry, you need to make sure all you're force vectors are aligned throughout various levels of fuel capacity. As fuel is drained from each fuel cell, either evenly or sequentially, the CoM will shift, and like Hcube pointed out, getting rid of the boosters will cause a HUGE shift in not just the Center-of-Thrust but the CoM as well.

3: Don't forget what effect the lift-producing parts of the shuttle will have on your flight; as well as if the aero control surfaces should be active during ascent. If they are, they may not have the intended effect compared to the gliding descent profile.

EDIT: This definitely goes to show how the STS was one of the most complicated and impressive engineering feats in aerospace history.

Edited May 3, 2015 by Raptor9

[ratchet freak]

The shuttles main engines are above where the should be, either move the CoM up or the shuttle down.

You can also throttle down the main engines until some fuel has been burned and you jettisoned the boosters.