How do I stop a space shuttle from flipping?

[Neil Kermstrong]

I'm trying to build a space shuttle and the design looks cool, but when I launch it the shuttle flips instantly, and when I place an engine in its external tank it lasts longer but still flips

[HebaruSan]

You have to tilt the engines so the overall thrust vector (main engines plus side boosters) goes through the center of mass. That's why they didn't point straight backwards.

[Aniruddh]

Make sure you align the center of mass (yellow-black marker) with center of thrust (pink-black marker) on the space-shuttle, and make sure they are aligned even when the fuel tank is empty. You can move the center of thrust by moving the engines to different positions using the offset tool (or rotate them), and you can move the center of mass by changing where you place fuel tanks/SRBs. This is tricky as when tanks are drained from, the center of mass will shift, so just go for a compromise (maybe balance them when all tanks are half full).

To make it easier, use the KS-25 vector engines, they have large gimbal range this will allow the engine to automatically change the thrust vector so it is aligned with the center of mass.

Edited September 18, 2020 by Aniruddh

[Neil Kermstrong]

6 minutes ago, HebaruSan said:

You have to tilt the engines so the overall thrust vector (main engines plus side boosters) goes through the center of mass. That's why they didn't point straight backwards.

 

5 minutes ago, Aniruddh said:

Make sure you align the center of mass (yellow-black marker) with center of thrust (pink-black marker) on the space-shuttle, and make sure they are aligned even when the fuel tank is empty. You can move the center of thrust by moving the engines to different positions using the offset tool (or rotate them), and you can move the center of mass by changing where you place fuel tanks/SRBs. This is tricky as when tanks are drained from, the center of mass will shift, so just go for a compromise (maybe balance them when all tanks are half full).

To make it easier, use the KS-25 vector engines, they have large gimbal range this will allow the engine to automatically change the thrust vector so it is aligned with the center of mass.

I just noticed I had forgot to place lifting surfaces on the wings, gimbal wasn't enough to fix the shuttle's direction

Now I placed 2 big elevons in each wings and it's way better

Thanks for the tips though, I have never felt so embarrassed

[Spricigo]

5 hours ago, Neil Kermstrong said:

I'm trying to build a space shuttle and the design looks cool, but when I launch it the shuttle flips instantly

Mind you, making "a shuttle" that looks less like "The Shuttle" is often a easier way to solve the issue.  Putting more of the weight up front and making it more symmetrical improves stability more than a bit of control surfaces, reaction wheels and RCS usually can.

[Neil Kermstrong]

39 minutes ago, Spricigo said:

Mind you, making "a shuttle" that looks less like "The Shuttle" is often a easier way to solve the issue.  Putting more of the weight up front and making it more symmetrical improves stability more than a bit of control surfaces, reaction wheels and RCS usually can.

Damn, did you spy my game or something? I was doing exactly what you said, and by the way now I noticed it is also flipping in the re-entry and won't glide.

guess I should do what you said

[Spricigo]

1 hour ago, Neil Kermstrong said:

Damn, did you spy my game or something?

I will neither confirm nor deny that. 

 

 

Don't worry, you are not the first to come there with a flipping spaceplane.

 And I'm sure you will not be the last either.

[Grogs]

If you're not intent on making it look just like the real shuttle, you could do something like in this thread and put some wings on the top of the external tank. That would give you a lot more pitch control while still low in the atmosphere when the tank is pulling the center of gravity way over.

 

[Wobbly Av8r]

From the "A picture is worth a thousand words", a .craft file has gotta be worth at least a few lines of explanation....

https://kerbalx.com/crafts/64413

Check it out in the VAB and you'll see some things that needed to be done to keep the fuel balanced and if you set it up with MechJeb like I have in the image below, it'll give you a pretty nice hands off flight.

As the SRB's separate you'll see that the Orbiter is at max control deflection to counteract the SRB's, but is then brought back into full control as the SRB's burn out. Turn on RCS after the Orbiter completes its burn and awaits the circularization burn, also manually stage the main tank after turning on the RCS (it helps with the rapid change of CG). Limiting the throttle to 50% helps to allow the reaction wheels to stabilize things since the thrust vector relative to the CG is not quite aligned.

Re-entry only requires that you keep the nose up around 45 degrees and wings level as you descend from 45km down to 25km and then slowly lower the nose to "Lawn Dart" position around 20 km and land it.

Edited September 19, 2020 by Wobbly Av8r

[Echo__3]

This is how I like to make shuttles.