Space Shuttle Tipping

[Gamer217]

I'm trying to build a Shuttle replica (NASA style) and I can't seem to get it to fly straight. Whenever I try to fly it it tips forward immediately. Here is the Shuttle in question:

Any help is appreciated.

Edited March 13, 2015 by Gamer217

[Tex]

My first impression is your use of mainsails. Those things have tremendous power, probably more than you need right there.

However, we're going to need a picture of it in flight to really judge what's going on, if you can please provide.

[Mr. Scruffy]

Try attaching a shuttle to each side of the lifter and see if that works.

EDIT: Just noticed our avatars, OP. I have the one you use on my comp as well...

[Leszek]

You should use the Klockheed Martin SSME mod for that. No need for the SAS or verniers to help if you do that. Also your ET goes way too far down, way too far, both in KSP and in real life the ET ends well above where you have yours ending. This greatly helps because you keep the CoM out far enough the engines don't need to gimble as much to track it. In your pic that top tank is going to drain fast and then the engines will not be able to track the CoM and it is all over folks. (The Klockheed Martin SSME mod also comes with ET parts that will look better and allow you more flexibility in how you make your ET.

http://forum.kerbalspaceprogram.com/threads/55985-0-90-Space-Shuttle-Engines-%28Dec-27%29

[karamazovnew]

Of course it does. As you can see from the Green arrow heading from the CoG, you need to readjust your engines. But that's not the whole story. The Shuttle is a very complex thing. At launch, engines start at the proper thrust so that the booster induced rotation is canceled. As you burn fuel from the center tank (and boosters), the COG slowly moves towards the shuttle, the boosters tend to push it more nose up, so the engines must be throttled up to stop that from happening. As the boosters loose thrust (not in KSP), there is a point where the booster influence on the shuttle's acceleration becomes zero. At that moment, the boosters are released and the Shuttle throttle is just perfect to keep it steady. As the fuel continues to burn, the engines are throttled back more and more to prevent a nose-dive. So here's how I did it in Kerbal:

- First tweak the bottom 2 shuttle engines so that the shuttle is perfectly stable with center tank at about 1/4 full at full thrust. In orbit, only use these 2 engines at low thrust, so that the SAS can hold them in place. That means a veeery slight rotation on those 2 engines, much less than in your pictures. And no need for those 2 side engines. Low center of gravity is the key here, for example use fuel in the wings, and place them under your shuttle, not like you have them.

- Then add the 3'rd top engine and retweak everything for about 50% thrust on launch.

- As you go higher and higher, you should reach full thrust on shuttle engines as the SRB's are about to cut out.

- When they do cut out, stop engines or you'll spin out of control. Release boosters and restart engines slowly. Once you reach a happy attitude, leave throttle like that and just reduce the max thrust on the top engine. When tank is 1/4 full, you'll probably be at thrust zero on the top engine so shut it down. Continue to reduce throttle on the 2 remaining engines until tank dropoff.

Not easy, action groups are the key to do this (for example, releasing srb and shutting down all engines with action group 1, instead of staging) Good luck.

Edited March 12, 2015 by karamazovnew

[Rusty6899]

you should be able to control your pitch with your throttle level. More thrust will tip it forward, less to tip backwards.

The real problem comes when you release your SRBs, as you will no longer be able to control your thrust vector with the throttle and you will lose control as your COM changes. One way to remedy this is to constantly alter your thrust limiter on the central Mainsail, but it's a bit of a hassle.

I think there is a mod that has shuttle engines with better gimbal ranges etc, but I haven't used it yet, so don't know how strongly to recommend it. Also can't remember what it's called ðŸ˜Â.

Personally I found making a mk2 shuttle fairly challenging but doable, but I couldn't get a mk3 one to work, so maybe trying a mk2 one first would be a good idea.

[mythbusters844]

This might be stupid, but try putting it on launch clamps. Maybe the "sticky launchpad" bug happens and the engines cause the entire thing to pivot forward.

[PlonioFludrasco]

At low altitude, you also have to consider lift from wings. Given the direction of the green arrow, you are starting with very high AoA, meaning lot of lift. Since in this configuration your center of lift is very far from CoM, that lift causes a big momentum you should correct for.

Sidenote: you can also add some fins on the side opposite of the orbiter, to offset CoL to a better position. Because this is a replica, I guess you don't want those fins to be visible at all. If you like, you can clip them inside the ET or inside each SRB for a better look.

Edited March 12, 2015 by PlonioFludrasco

[Gamer217]

Ok thanks for all the info, I'm going to try the SSME mod since the mainsails don't have the gimbal range of the actual Shuttle SSMEs.

Edited March 12, 2015 by Gamer217

[Skorpychan]

Shuttles do that in KSP. Try the Saturn-Shuttle approach, which was basically sticking the Shuttle atop a whacking great Saturn-V first stage.

[Gamer217]

The SSMEs did the trick with control, now just need to find the right fuel amount (SRBs are only partially filled) and find a good flight path, max Q is a pain.

[Leszek]

Glad it worked out for you. They make it much more easy.

Play with it as you like, I personally have the SRB's set to full and only throttle them down a bit with the main engines to keep 1.25 TWR at launch. I drain the fuel from my overly large ET, bottom part first to get the DV I need. Just the way I do it.

[zekes]

My first impression is your use of mainsails. Those things have tremendous power, probably more than you need right there.

However, we're going to need a picture of it in flight to really judge what's going on, if you can please provide.

UwotM8?

JK for that sized shuttle those are probably too big.

[Alshain]

If you still want to go with stock parts, you should check out this video.