Unstable mk3 shuttle

[MysticTURBO]

Hello all, 

after following the build up and launch of falcon heavy it has got me pumped to build a mk3 shuttle. I had a go last night using the mk3 mod but have a few issues I can’t seem to figure out. Could some kind soul help me out.

 

- during launch with the correct fuel tanks etc the shuttle is unstable during corrections. As I try to roll shortly after takeoff it just pulls the shuttle way out of alignment and I end up with a terrible trajectory.

- I haven’t made it to an orbit with it yet but when testing for landing I can’t keep the nose up, it just drops on me.i

- also I’m having trouble with decouplers. One is not enough and various parts just flap about.  What’s the best part to use to keep it rigid.

 

i have mainly used the mod parts including engines etc.

i don’t run any other mods currently as I don’t really understand ckan and what mods I can use with 1.3

 

thanks in advance for your help.

 

MT

[Val]

Moved to from Tech Support.

[Flavio hc16]

some images would be very helpful

[MysticTURBO]

I will grab some after work. What sort of images would be helpful? 

[Flavio hc16]

1 hour ago, MysticTURBO said:

I will grab some after work. What sort of images would be helpful? 

images of the craft from one side, then one from top-to-bottom and then one from the front ( one per axis), Also if you have Ker(mechjeb installed it would be helpful to see those data about twr and deltaV.

Or you could give us the craft file

[Geonovast]

4 hours ago, MysticTURBO said:

also I’m having trouble with decouplers. One is not enough and various parts just flap about.  What’s the best part to use to keep it rigid.

You can only use one decoupler to connect two pieces together.  To make it more rigid, you need to use struts.  Not knowing this was a killer for me right when I got the game.  I'd try to use three decouplers to attach a booster, and it would just flop around on one.

You can either enable advanced tweakables in your game settings and use the autostrut feature, or you can strut manually.  I prefer to strut my own stuff.

Just a couple struts at the top and bottom will make everything so much better.

Try to place your coupler in line with or just ahead of the CoM of the boosters for the boosters, and the tank for ejecting the main fuel tank.

 

[Spricigo]

7 hours ago, MysticTURBO said:

I don’t run any other mods currently as I don’t really understand ckan and what mods I can use with 1.3

 

[Snark]

7 hours ago, MysticTURBO said:

the mk3 mod

Aside from giving us some screenshots... can you explain what you mean by "mk3 mod"?  You've got a mod installed?  Which mod, specifically?  Got a link?  (I ask because Mk3 spaceplane parts are part of the stock game, no mod involved, so just want to make sure there's no confusion there so we're not all talking at cross-purposes.)

7 hours ago, MysticTURBO said:

As I try to roll shortly after takeoff it just pulls the shuttle way out of alignment and I end up with a terrible trajectory.

A couple of things.  First, any particular reason why you're doing a roll?  I could understand doing a pitch, but why is a roll necessary?  Reason I ask:  any time you're having trouble with any sort of vessel in KSP that's unstable during launch, it's really helpful to absolutely minimize any unnecessary maneuvering, particularly around multiple axes-- best if all you ever do is just pitch.  So, if there's any chance that you're following an odd flight path or doing unnecessary maneuvers, that could exacerbate any other stability problems you might be having.

My personal guess as to the worst problem is that comment about pulling the shuttle out of alignment, and about things flapping around, and trying to use multiple decouplers.  As @Geonovast points out, it's physically impossible in KSP to use multiple decouplers, due to the "tree" nature of how ships are modeled.  You need to use struts to stabilize the ship, as he suggests.

If you have even a little bit of "flex" between the shuttle and the booster assembly, that's going to hork you, because the shuttle likely has enough aerodynamic wing area that even slight misalignments can cause hilarity to ensue.  I don't know if you might have some other problems as well, but that right there is probably enough to mess up your launch even if everything else were perfect.  So, I'd suggest solving that before looking at anything else.

[MysticTURBO]

1 hour ago, Snark said:

Aside from giving us some screenshots... can you explain what you mean by "mk3 mod"?  You've got a mod installed?  Which mod, specifically?  Got a link?  (I ask because Mk3 spaceplane parts are part of the stock game, no mod involved, so just want to make sure there's no confusion there so we're not all talking at cross-purposes.)

A couple of things.  First, any particular reason why you're doing a roll?  I could understand doing a pitch, but why is a roll necessary?  Reason I ask:  any time you're having trouble with any sort of vessel in KSP that's unstable during launch, it's really helpful to absolutely minimize any unnecessary maneuvering, particularly around multiple axes-- best if all you ever do is just pitch.  So, if there's any chance that you're following an odd flight path or doing unnecessary maneuvers, that could exacerbate any other stability problems you might be having.

My personal guess as to the worst problem is that comment about pulling the shuttle out of alignment, and about things flapping around, and trying to use multiple decouplers.  As @Geonovast points out, it's physically impossible in KSP to use multiple decouplers, due to the "tree" nature of how ships are modeled.  You need to use struts to stabilize the ship, as he suggests.

If you have even a little bit of "flex" between the shuttle and the booster assembly, that's going to hork you, because the shuttle likely has enough aerodynamic wing area that even slight misalignments can cause hilarity to ensue.  I don't know if you might have some other problems as well, but that right there is probably enough to mess up your launch even if everything else were perfect.  So, I'd suggest solving that before looking at anything else.

 

 

 

I was trying to do it like in real life, they launch, roll 90 and then slowly fall onto its back before rolling again to jettison the main fuel tank.

The mod i'm using is the add-ons for the mk3 sorry, so the OMS system, heat tiled wings and body, tail flap, boosters etc.

I'm just jumping on now i will get a picture as best i can. then figure out how to get it on here haha

 

MT

[MysticTURBO]

 

 

I can get any other images you require.

Thanks

[Geonovast]

How does the shuttle fly by itself?  The CoL looks way, way too far back from the CoM.  So unless you have a payload in the bay in you SPH picture, I don't think it's going to fly well.

Have you done any atmospheric flight testing of the shuttle?

[MysticTURBO]

5 minutes ago, Geonovast said:

How does the shuttle fly by itself?  The CoL looks way, way too far back from the CoM.  So unless you have a payload in the bay in you SPH picture, I don't think it's going to fly well.

Have you done any atmospheric flight testing of the shuttle?

sorry CoL? i assume CoM is centre of mass, i have no payload only the airlock for payload area.

[Geonovast]

4 minutes ago, MysticTURBO said:

sorry CoL? i assume CoM is centre of mass, i have no payload only the airlock for payload area.

Center Of Lift, it's the blue arrow.  With it so far behind the CoM, it's going to want to flip really, really bad.

When I get home, I can give you a similar picture of the shuttle I showed before.  It took quite a bit of tweaking to get it glidable.

In KSP, it's very necessary to build backwards.  You need to change your focus to strictly the shuttle first.  Get it so it can re-enter, fly/glide, and land.  Then work on strapping it to a rocket.  If you don't, you might find that after hours of tweaking to get the shuttle up, it can't come down.  Then you need to change the shuttle.  And once you've changed the shuttle... then comes the lifter tweaking again.

Launch your shuttle to the runway, then use the F12 menu (Alt+F12 on Windows) to cheat it into orbit, and bring it down.  That way you can test it over and over without worrying about launching it up first.

[foamyesque]

38 minutes ago, Geonovast said:

Center Of Lift, it's the blue arrow.  With it so far behind the CoM, it's going to want to flip really, really bad.

 

What? No, that's the opposite of true. If there's a problem it's going to be lawn-darting from excessive aerodynamic stability, not flipping.

[Geonovast]

7 minutes ago, foamyesque said:

What? No, that's the opposite of true. If there's a problem it's going to be lawn-darting from excessive aerodynamic stability, not flipping.

You're thinking of drag for a rocket, not lift for a plane.  Take the thing for a flight and see how it handles.

Edited February 7, 2018 by Geonovast
Thought I was quoting OP.

[MysticTURBO]

1 minute ago, Geonovast said:

You're thinking of drag for a rocket, not lift for a plane.  Take the thing for a flight and see how it handles.

it handles like excrements

 

[foamyesque]

30 minutes ago, Geonovast said:

You're thinking of drag for a rocket, not lift for a plane.  Take the thing for a flight and see how it handles.

 

I've built more planes in KSP than I really care to think about, including various shuttle replicas. I promise you I'm right, and to prove it, I mocked up a replica (I don't have his mod parts, but for proving this point it is irrelevant):

 

 

You may note the complete lack of flipping happening.

Edited February 7, 2018 by foamyesque

[Geonovast]

7 minutes ago, foamyesque said:

I mocked up a replica (I don't have his mod parts, but for proving this point it is irrelevant):

Your CoM and CoL are significantly close than his, and your screenshots are only showing re-entry at roughly mach 3.5.  That's not the same as gliding down to land.

 

@MysticTURBO can you link the exact mod you're using and post the craft file from the SPH so I can see if my concerns are valid?

Edited February 7, 2018 by Geonovast

[MysticTURBO]

8 minutes ago, Geonovast said:

Your CoM and CoL are significantly close than his, and your screenshots are only showing re-entry at roughly mach 3.5.  That's not the same as gliding down to land.

i have improved it a little

8 minutes ago, Geonovast said:

Your CoM and CoL are significantly close than his, and your screenshots are only showing re-entry at roughly mach 3.5.  That's not the same as gliding down to land.

 

@MysticTURBO can you link the exact mod you're using and post the craft file from the SPH so I can see if my concerns are valid?

how do i upload craft file to here

 

mod is shuttle lifting body through CKAN

Edited February 7, 2018 by MysticTURBO

[Geonovast]

4 minutes ago, MysticTURBO said:

how do i upload craft file to here

You can't, but you can at https://kerbalx.com or use a regular file sharing service like Google Drive.

[MysticTURBO]

3 minutes ago, Geonovast said:

You can't, but you can at https://kerbalx.com or use a regular file sharing service like Google Drive.

i have uploaded it to that site, how do i get it to you?

 

[Geonovast]

Just post the link for it.

[MysticTURBO]

5 minutes ago, Geonovast said:

Just post the link for it.

https://kerbalx.com/MysticTURBO/Space-shuttle

 

[Geonovast]

3 minutes ago, MysticTURBO said:

https://kerbalx.com/MysticTURBO/Space-shuttle

 

Diggin' the picture for it.  I'll play with it when I get home.

[MysticTURBO]

Just now, Geonovast said:

Diggin' the picture for it.  I'll play with it when I get home.

i didnt give it a picture. no idea where crashy came from lol