Sudden performance change of SSTO.

[Spunge_bub12]

Just built a large SSTO with 6 Turbojets, 4 Rapiers, and 4 Aerospikes weighing in at around 132t fully loaded. It managed to escape Kerbin atmosphere on multiple tests with very few Issues. in atmosphere at around 2km above sea level it could easily cruise at 700+m/s with the turbojets thrust capping out somewhere around 250-300. I saved my game and left my computer for an hour to go run some errands and when I got back the SSTO's engine performance for some reason changed drastically. At 2000m above sea level the engines can't even achieve a thrust above 190 and the SSTO struggles to get past 300m/s. I have made no changes to the craft prior to its successful test flights and the weight in the editor has remained unchanged. Is this some sort of bug?

[Serenity]

Did you leave your game open while you were gone?Does the same thing happen when you restart?Kerbal perfomance tends to degrade very fast, maybe it calculates too slow to be correct.

Other than that, i have no idea  .

Edited June 16, 2019 by Boyster

[Spunge_bub12]

6 minutes ago, Boyster said:

Kerbal perfomance tends to degrade very fast, maybe it calculates too slow to be correct.

See, thats what I figured but sadly no, it doesn't seem like restarting or leaving ksp running fixes the problem. This is getting very frustrating. it also looks like some other planes that I have built using the Turbojets cant break above 350m/s even though they where capable of doing so in the past. this is a very strange bug indeed, perhaps something to do with the drag coefficient being changed?

[Serenity]

When you re saying past do you mean current version of the game or you made/test them in older versions?

Edited June 16, 2019 by Boyster

[bewing]

Did you have any DLC robotics parts in this craft? Is it a pure stock craft? If so, could you post it on KerbalX or pastebin or some other file sharing service?

Edited June 16, 2019 by bewing

[Spunge_bub12]

9 minutes ago, Boyster said:

When you re saying past do you mean current version of the game or you made/test them in older versions?

1.7.1 the change happened the same day after restarting my game through the EXE directly and not the launcher.

7 minutes ago, bewing said:

Did you have any DLC robotics parts in this craft? Is it a pure stock craft? If so, could you post it on KerbalX or pastebin or some other file sharing service?

No. The only mods I am using is Mechjeb and tweak scale and the only scaled parts being some light fixtures on the wings. 

[linuxgurugamer]

Any chance this is a steam install and it did an update to 1.7.2?

[Spunge_bub12]

Just now, linuxgurugamer said:

Any chance this is a steam install and it did an update to 1.7.2?

Nope. never owned a copy of KSP from steam.

[4x4cheesecake]

Something similar happened to me some time ago after installing missing history, which messed up the part database a little bit. No idea if this can also happen in a running game and without adding an additional mod but I guess it's worth a try: Delete the "PartDatabase.cfg" from your game directory so it will be recreated on the next game launch. This helped me with my issue

[Spunge_bub12]

37 minutes ago, 4x4cheesecake said:

Something similar happened to me some time ago after installing missing history, which messed up the part database a little bit. No idea if this can also happen in a running game and without adding an additional mod but I guess it's worth a try: Delete the "PartDatabase.cfg" from your game directory so it will be recreated on the next game launch. This helped me with my issue

Nope this didn't seem to do anything.

I'm doing some tests and just built a fail plane that only weighs 40t and has 10 turbojets. It cant break 350m/s either.

[4x4cheesecake]

2 minutes ago, Spunge_bub12 said:

Nope this didn't seem to do anything.

aw

Well, then I'll second the suggesting to post a craft file so we can figure out a) if this is an issue with your local install or b) something that happened to your craft.

[Spunge_bub12]

12 minutes ago, 4x4cheesecake said:

aw

Well, then I'll second the suggesting to post a craft file so we can figure out a) if this is an issue with your local install or b) something that happened to your craft.

will do when I get home tonight.

[Aegolius13]

Did you use a different ascent profile this time?  Rapiers generate much more thrust after they hit ~450 m/s, so it's pretty common to get stuck behind transonic drag if you try to go too fast, too low.  The usual fix for this is to climb subsonic to a few km, and then level off or gently dive until you hit the sweet spot.  Not sure which engine you're referring to as "turbojets," but if Whiplash or Panther it seems like you'd be getting enough low-end thrust.  However, it's hard to know if this is applicable without seeing the craft. 

And apologies if you're already familiar with this stuff; just taking a stab based on info provided.

[mystifeid]

Limiting Q in Mechjeb Utilities?

[Spunge_bub12]

9 hours ago, mystifeid said:

Limiting Q in Mechjeb Utilities?

Um. Not sure what that is, and how would I change that?

[mystifeid]

14 minutes ago, Spunge_bub12 said:

Um. Not sure what that is, and how would I change that?

Just a wild guess and given this statement, probably wrong.

Q is the dynamic pressure on the craft. You mentioned you were using Mechjeb - if so, open the Utilities module and make sure the Limit Q option is not checked (it's the very first option). By default this option is set to 20 kPa and at lower altitudes would result in your craft being throttled back to around the speeds you described.

[Lazarus MonkeyMan]

On 6/17/2019 at 6:04 AM, mystifeid said:

Q is the dynamic pressure on the craft. You mentioned you were using Mechjeb - if so, open the Utilities module and make sure the Limit Q option is not checked (it's the very first option). By default this option is set to 20 kPa and at lower altitudes would result in your craft being throttled back to around the speeds you described.

Had that same issue, and turning off Q definitely helped.  I mean, I still suck as SSTOs, but now it's my fault instead of the game.   

[Socraticat]

I had this issue on console. Someone suggested that it could be my cargo bay, if that was the root part. Haven't tested it yet. Seems plausible.