Space Shuttle Roll Program

[Commodore_32]

Everytime I try to roll a Space Shuttle in liftoff, it just yaws and pitches out of control making me to do a crew bailout.

Yes, the SSME have no roll gimbal

Yes, the elevons are configured correctly.

And, this is bad, because when I use launchpads like the Alpha Mensae Modular Launchpads, I need to flip it over and makes no sense, even the stock Dynawing is pointed heads-down to not roll.

How can I make this happen?

[lemon cup]

Are you using a shuttle mod, such as Benjee’s SOCK, or trying to recreate/kitbash with stock parts? If it’s the former, not much can go wrong other than having an errant control point selected when it should be the cockpit, since the gimbaled SRBs can manhandle the whole stack effortlessly despite small COM imbalances.
If it’s the latter, it could be a whole myriad of small things, especially if using non-gimbaled SRBs, at which point getting the shuttle to launch properly will be a true feat, but it is doable. There’s a ton of variables, pictures of your Shuttle would be helpful to get you on the right track.

[Entropian]

A couple photos would be useful.

[Commodore_32]

39 minutes ago, lemon cup said:

Are you using a shuttle mod, such as Benjee’s SOCK, or trying to recreate/kitbash with stock parts? If it’s the former, not much can go wrong other than having an errant control point selected when it should be the cockpit, since the gimbaled SRBs can manhandle the whole stack effortlessly despite small COM imbalances.
If it’s the latter, it could be a whole myriad of small things, especially if using non-gimbaled SRBs, at which point getting the shuttle to launch properly will be a true feat, but it is doable. There’s a ton of variables, pictures of your Shuttle would be helpful to get you on the right track.

Both stock and mod have the same problem, the gimballed SRB just kinda acts in the pitch program, when there is a yaw the SSME and SRB can not bring it back, making it point to the ground.

 

[lemon cup]

11 hours ago, Commodoregamer118 said:

Both stock and mod have the same problem, the gimballed SRB just kinda acts in the pitch program, when there is a yaw the SSME and SRB can not bring it back, making it point to the ground.

 

So you are using the SOCK and reDirect mods, or something else that provides gimbaled SRBs? What mod, and what is the name of the SRB?

Troubleshooting Shuttle problems can be very frustrating and sometimes leads to dead ends, but they can all be overcome with enough thought and tweaking. But for me to give any really good advice you need to provide more pictures and descriptions.

What mods, are you using MechJeb or KOS, or any other autopilot? Ferram Aerospace or anything else that might affect aerodynamics?

My first thought given the limited information is control point problems. Make absolutely sure your starting control point is the Shuttle’s cockpit. Easiest way to do this is go to the VAB and select the Reroot tool and then click the cockpit. If it is the SOCK shuttle, right click the cockpit and make sure one of the options says “Control Point: Forward”.

Evidence that your control point is correct is when your shuttle is sitting on the pad, the Nav ball is showing you are at full 90 degree pitch, and is solid blue. Any brown means your control point is jacked up somehow.

Again, pictures and descriptions are needed for anything further.

Edited August 24, 2020 by lemon cup
Fix error

[Commodore_32]

On 8/23/2020 at 1:20 PM, lemon cup said:

So you are using the SOCK and reDirect mods, or something else that provides gimbaled SRBs? What mod, and what is the name of the SRB?

SOCK, stock and Cormorant Aeronology

On 8/23/2020 at 1:20 PM, lemon cup said:

What mods, are you using MechJeb or KOS, or any other autopilot? Ferram Aerospace or anything else that might affect aerodynamics?

None.

On 8/23/2020 at 1:20 PM, lemon cup said:

My first thought given the limited information is control point problems. Make absolutely sure your starting control point is the Shuttle’s cockpit. Easiest way to do this is go to the VAB and select the Reroot tool and then click the cockpit. If it is the SOCK shuttle, right click the cockpit and make sure one of the options says “Control Point: Forward”.

Everything is right.

As requested, screenshots:

Test 1:

Spoiler

 

Test 2

Spoiler

(Notice the full control inputs, I was struggling)

 

[Wobbly Av8r]

The space shuttle is a unique arrangement for thrust vectors and changing center of mass throughout flight. While I'm sure there are a number of workable solutions, the one I stumbled upon was to reduce thrust on the shuttle main engines to 50% throughout flight, reduce the amount of fuel in the solids as well as a peculiar arrangement of fuel tanks within the main tank that alter the center of mass in a manageable way as fuel is consumed.

You can download it and take a look if it helps - https://kerbalx.com/Wobbly_Av8r/Space-Shuttle-with-Boosters

If you have MechJeb, in the ascent autopilot window, set Limit thrust to 50% (the solid's are preset to 80%) and set Force Roll Climb 90 turn 180 and a 40% gravity turn profile and set desired altitude about 75,000 m. I suggest enabling the aerodynamic forces overlay (default F12) and observe the amount of control force required to maintain the profile, particularly the shuttle elevators and the relationship to the changing center of mass of the main tank. Adding up to 750 units of ore in the ballast tank of the main tank helps to dampen the rotational movement of the main tank but, of course, reduces overall performance.

A couple of additional actions that will make the flight more 'pleasurable': manually stage the main tank separation after main engine cutoff / coasting phase has been established (but before the circularizing burn) - turning on RCS before doing so dampens rotational forces. Keeping the RCS on for the circularizing burn is essential as well due to the offset thrust of the orbiter's engines, and (finally) you may need to take the controls from MechJeb right near the end of the circularizing burn because MechJeb likes to micro-adjust the burn rather abruptly which can aggravate the very delicate balance of thrust and center of mass of the shuttle!

 

[Edit: Here is a link to original post re: shuttle flipping... ]

 

Edited October 3, 2020 by Wobbly Av8r
Added a link

[Spricigo]

 

On 8/22/2020 at 11:59 PM, Commodore_32 said:

I need to flip it over and makes no sense

 

The big elephant in the room: KSP have plenty of parts to build something that looks like The Shuttle but don't fly like The Shuttle. Different weight distribution, different thrust balance and so on. That is why players come to with "solutions" like severely limit thrust of some engines, adding 'strange' control surfaces, adding ballast and completely change the way it flies.

It's not unheard of KSP shuttles that need a Kranken load of reactionwheels and RCS/Vernors to barely follow that desired flight profile. It may look lite The Shuttle but, at least for me, that makes no sense. Flipping the launchpad to avoid a critical maneuver that is likely to throw  the craft out of the sky? I'd take it in a heartbeat.