Shuttle won't fly straight.

[Frozen_Heart]

FrozenHeart,

Minor detail, but I was able to launch the stack with just the 2 SRBs. I hear that if you clip the 14 boosters together like in your setup and turn the centers way down you can get the cool STS delayed seperation, but you don't actually need bigger SRBs to make it work.

Best,

-Slashy

I just like the larger SRBs due it being more accurate to the real shuttle. Almost all of its thrust came from them while in KSP its the opposite on most shuttles.

[Vegetal]

Interesting that you have this problem with mk3 cargo bays, because I feel it on some space plane designs too. It seems they generate a lot of drag when sideways, so you have to consider their position too along with the CoL.

Now, if other people don't feel this effect, something might be off in my install too...

[Frozen_Heart]

Interesting that you have this problem with mk3 cargo bays, because I feel it on some space plane designs too. It seems they generate a lot of drag when sideways, so you have to consider their position too along with the CoL.

Now, if other people don't feel this effect, something might be off in my install too...

I've narrowed it down to the Mk-3 cargo bay which is doing it. Though if it is a glitch then my only option is to simply not use Mk-3.

[Kobymaru]

I've narrowed it down to the Mk-3 cargo bay which is doing it. Though if it is a glitch then my only option is to simply not use Mk-3.

[Frozen_Heart]

I had a problem as well, with my spaceplane which also had a Mk-3 cargo bay. It would start flipping out as soon as I went supersonic and the AoA was above 10°. Could you elaborate what exactly "doing it" is and how you found it out?

Doing it is only flying backwards/sideways, even when I move the CoL behind the CoM. I turned on the setting to show aero forces and as soon as I deviate from prograde a massive arrow comes from the cargo bay. Its essentially creating a lot of lift but only when angled, so when going straight it will lawn dart, and while not straight it flies backwards. Worst of both worlds.

[Val]

I turned on the setting to show aero forces and as soon as I deviate from prograde a massive arrow comes from the cargo bay. Its essentially creating a lot of lift but only when angled

I saw the same forces, huge cyan bar from Mk3 cargo bay, from both my own replica and the craft you provided, but both were still very stable.

[Frozen_Heart]

I saw the same forces, huge cyan bar from Mk3 cargo bay, from both my own replica and the craft you provided, but it was still very stable.

Really not sure what to do now. Replaced the physics file, tested every variation of CoL/M, rebuilt from scratch.

I've tested it launching 4.5 tons of cargo to orbit now. I reckon it could do 10 if I tweak the launch vehicle a bit. Its just coming down that's the problem.

[worir4]

Not sure if this helps but you can clip canards or more wings into the fuselage. Then it wont effect the look.

[Frozen_Heart]

Not sure if this helps but you can clip canards or more wings into the fuselage. Then it wont effect the look.

I don't like clipping wings, fuel tanks, or engine bells into each other much. I happily clip parts that could go together in real life such as structural parts.

[sal_vager]

Would you consider fitting a pair of rudders so they are partly clipping? This will double your yaw stability, bring the CoM back a bit further and allow you to use the rudders as a Shuttle style airbrake.

Edit:

I noticed there's a very long red line in your pic of the aero forces, can you fit stuff to the front internal node of the cargobay or will it not connect?

Edited September 17, 2015 by sal_vager

[Frozen_Heart]

Would you consider fitting a pair of rudders so they are partly clipping? This will double your yaw stability, bring the CoM back a bit further and allow you to use the rudders as a Shuttle style airbrake.

Edit:

I noticed there's a very long red line in your pic of the aero forces, can you fit stuff to the front internal node of the cargobay or will it not connect?

http://i.imgur.com/ahz7gN2.jpg

As I mentioned I'm not a fan of clipping control surfaces together. I've put a pair of airbrakes either side of the tail which helps a bit.

I can put things either side of the cargo bay without difficulty. I've managed to get 9 tons of payload to a 500km orbit. Did 5 or 6 flips on the way up as the launcher wasn't balanced as well.

I have extended the lower wing area underneath the engines like in your shuttle. I'm hoping that will help.

Edited September 17, 2015 by Frozen_Heart

[GoSlash27]

Frozen Heart,

You might want to try replacing the single cargo bay with 2 half-size bays; see if the weird aero behavior disappears.

Also, if you give the wings a little incidence it will both both improve the low speed handling and move the CoL further back. The body flap should be enough to compensate for that and give you a more stable orbiter.

sal_vager,

That is a beautiful shuttle! I need to steal a couple of those design concepts!

Best,

-Slashy

[gavman420SSJ]

Well, I'd try adding air brakes to the rudder. The real Shuttle had its barn doors open during re-entry. You can't do the split control surface thing that the real Shuttle did, but you can add the normal air brakes. And yes, Big-S is not big-s enough. If you look at pictures, you'll see that the real Shuttle had proportionately larger wings. However I recall Scott Manley saying in one of his videos that such big wings weren't actually necessary and there was some other reason for adding them so that might be somewhat irrelevant. Whü knuws...

i don't think the shuttle had its "barn doors" open until it hit the runway. but i would be interested to see if i'm wrong

[Frozen_Heart]

You might want to try replacing the single cargo bay with 2 half-size bays; see if the weird aero behaviour disappears.

Didn't work either. I think all the Mk-3 parts create a lot of lift at an angle, but none when straight on which is causing this. The tail airbrakes and the body wing section have both helped a bit but I can't think of anything else which would improve it from there. I can now at least re-enter on an empty tank. Burning off excess fuel is a pain. We need a fuel dump part.

[match]

Just a thought, but with the CoM so far back, won't any body lift generated by the nose be exaggerated? Once any AoA is introduced the craft will lose stability and naturally attempt to align behind the CoM. Might have a battle between control and its natural tendency.

[Val]

Just a thought, but with the CoM so far back, won't any body lift generated by the nose be exaggerated? Once any AoA is introduced the craft will lose stability and naturally attempt to align behind the CoM. Might have a battle between control and its natural tendency.

I believe there's a lot of merit to this assessment.

The CoL indicator does not factor in drag/body lift for non-wing parts. I believe what is happening to your shuttle, Frozen Heart, is that the CoL the SPH is showing you a deceiving CoL. If you move both your (D)CoM and CoL forward by the same amount, so they don't move relatively to each other only, the shuttle will become stable.

Could you as an experiment, add canards and a dummy weight, to test that hypothesis?

[Frozen_Heart]

I believe there's a lot of merit to this assessment.

The CoL indicator does not factor in drag/body lift for non-wing parts. I believe what is happening to your shuttle, Frozen Heart, is that the CoL the SPH is showing you a deceiving CoL. If you move both your (D)CoM and CoL forward by the same amount, so they don't move relatively to each other only, the shuttle will become stable.

Could you as an experiment, add canards and a dummy weight, to test that hypothesis?

I'll have a go doing that. Will add something in the front cargo bay which allows docking which should move the CoM forwards. Takes up a bit of room but I can't take an orange tank up anyway so no loss. Will try the canards but want to find a better solution as they weren't there on the real thing.

[Gaarst]

Having the same problem here. :/

Displaying aero forces shows that the cargo bay creates massive amounts of lift (cyan arrow) whenever the angle of attack is non-zero. Even after tweaking the CoL/CoM, the cargo bay screws things up and ruin my shuttles (several designs suffer the same problems, each using Mk3 bays).

As the cargo bay is at the front of the craft (usually), and also in front of the CoM, this immense lift created completely changes the lift vector: because this lift is so huge, the CoL moves in front of the CoM and therefore the shuttle flies backwards; trying to correct this by any pitch/yaw movement is pointless because of this lift appearing as soon at the cargo bay is exposed to airflow.

I know that body lift is simulated in KSP, but this cargo bay should never give a lift vector several times greater than the one generated by the Big-S wings (it is just ridiculous when seen with aero forces overlay).

Does anyone have a solution ? Or can we agree that this is a bug, so that it can get fixed (quickly is better) ?

Right now, none of my crafts with Mk3 bays (I have only 2 but, still, it is annoying ) are flyable...

[GoSlash27]

Having the same problem here. :/

Displaying aero forces shows that the cargo bay creates massive amounts of lift (cyan arrow) whenever the angle of attack is non-zero. Even after tweaking the CoL/CoM, the cargo bay screws things up and ruin my shuttles (several designs suffer the same problems, each using Mk3 bays).

As the cargo bay is at the front of the craft (usually), and also in front of the CoM, this immense lift created completely changes the lift vector: because this lift is so huge, the CoL moves in front of the CoM and therefore the shuttle flies backwards; trying to correct this by any pitch/yaw movement is pointless because of this lift appearing as soon at the cargo bay is exposed to airflow.

I know that body lift is simulated in KSP, but this cargo bay should never give a lift vector several times greater than the one generated by the Big-S wings (it is just ridiculous when seen with aero forces overlay).

Does anyone have a solution ? Or can we agree that this is a bug, so that it can get fixed (quickly is better) ?

Right now, none of my crafts with Mk3 bays (I have only 2 but, still, it is annoying ) are flyable...

Gaarst,

I think Frozen Heart has hit upon the answer. Those of us with working STS shuttles don't have a problem with body lift forcing us backwards. In my case I think it's the docking/ payload adapter attached to the rear of the crew cabin. This forces the CoM forward, which makes it much more stable.

Also in accurate shuttles there's never fuel in the rear tank, just in the clip- on OMS tanks. Once the external tank is jettisoned the SSMEs should have no fuel source. Neglecting this can cause serious imbalance issues.

Best,

-Slashy

[Gaarst]

Gaarst,

I think Frozen Heart has hit upon the answer. Those of us with working STS shuttles don't have a problem with body lift forcing us backwards. In my case I think it's the docking/ payload adapter attached to the rear of the crew cabin. This forces the CoM forward, which makes it much more stable.

Also in accurate shuttles there's never fuel in the rear tank, just in the clip- on OMS tanks. Once the external tank is jettisoned the SSMEs should have no fuel source. Neglecting this can cause serious imbalance issues.

Best,

-Slashy

I'm not sure I got your point with the "docking/payload adapter" thing (though I already have reaction wheels and docking port Sr. behind the crew cabin adding a little mass); but I indeed do not have any fuel storage for the SSMEs in the orbiter itself (only a little for the OMS), also, the CoM/CoL balance for the orbiter gliding is made with dry CoM.

[GoSlash27]

I'm not sure I got your point with the "docking/payload adapter" thing (though I already have reaction wheels and docking port Sr. behind the crew cabin adding a little mass); but I indeed do not have any fuel storage for the SSMEs in the orbiter itself (only a little for the OMS), also, the CoM/CoL balance for the orbiter gliding is made with dry CoM.

Gaarst,

The docking/ payload adapter is something every shuttle needs IMO.

Aside from giving you the ability to dock and release a payload, it moves the CoM forward. This allows you to build your shuttle with the CoM and CoL closer to the pressure center.

The other 2 points clearly don't apply to you, so you can disregard them.

Best,

-Slashy

[Gaarst]

Gaarst,

The docking/ payload adapter is something every shuttle needs IMO.

-snip-

Aside from giving you the ability to dock and release a payload, it moves the CoM forward. This allows you to build your shuttle with the CoM and CoL closer to the pressure center.

The other 2 points clearly don't apply to you, so you can disregard them.

Best,

-Slashy

OK, I get what you mean now. Thing is, an adapter, and docking port and panels are not that massive compared to the overall shuttle, so I doubt it will help that much in moving the CoM. Thank you for the advice anyway, I will try it asap.

[Frozen_Heart]

I don't actually use the main engines in orbit, just the OMS engines, despite them using the same fuel.

They docking adaptor is already coming in handy for station building, though I now need to leave a bit of fuel in or its too front heavy. I think the new shuttle engines in 1.1 will counter that though as they are quite a bit heavier than the skippers from the screenshot I saw.

[GoSlash27]

I don't actually use the main engines in orbit, just the OMS engines, despite them using the same fuel.

Frozen Heart,

I'm sure you don't use them; you wouldn't be able to because their alignment would spin the orbiter. My point is that tank should ideally have no fuel. Variations in piloting and mission profile mean that it will wind up with varying fuel levels once orbit is achieved. The fuel will be left in a tank far from the CoM with no way to counterbalance it and nowhere to shift it to.

That's why the rear tank is left empty and the OMS engines have their own dedicated supply. Extra fuel is carried in the external tank and any unneeded fuel is jettisoned with it.

They docking adaptor is already coming in handy for station building, though I now need to leave a bit of fuel in or its too front heavy. I think the new shuttle engines in 1.1 will counter that though as they are quite a bit heavier than the skippers from the screenshot I saw.

I'd recommend rearranging the fuel allocation as above and then adjusting the wings to rebalance it. I wouldn't count on any of the engine stats in the preview.

Best,

-Slashy

Edited September 19, 2015 by GoSlash27

[Frozen_Heart]

Thanks for the help guys. The shuttle is now in a workable state and seems to be pretty reliable. Only thing I need to be careful of now is turning too fast which removes the wings.

~I'd recommend rearranging the fuel allocation as above and then adjusting the wings to rebalance it. I wouldn't count on any of the engine stats in the preview.

Best,

-Slash

I'll probably start doing that pretty soon. Where could I store the fuel so the thud engines could use it but the main ones couldn't? And the only place I can put their fuel is either in the cargo bay or at the back where it already is.