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[1.2] USI Survivability Pack (Formerly DERP) [v0.6.0]


RoverDude

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  • 2 weeks later...

I put a dozen DERPs on a ship and tried to launch it, and after 30 seconds or so it became unstable and started pitching/yawing uncontrollably, despite having 2 Advanced Inline Stabilizer SAS modules and 3x AV-R8 winglets.. If I try without the DERPs, it flies just fine. I then removed the lifeboat modules, leaving just the propulsion modules, and had the same result. Then I added action groups to decouple them and tried again. Still unstable after 30 seconds or so, but when I decoupled them, the rocket was able to right itself and fly correctly. Even just 4 of the propulsion modules was enough to destabilize the ship.

This was using MechJeb's ascent guidance, and also just using manual control. Whatever I do, it starts out flying fine, but ends up flipping end over end after 30-30 seconds. But as soon as I jettison the DERP propulsion modules, it becomes flyable again.

Any clue what is going wrong? None of my other ships have any problems at all like this.

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I put a dozen DERPs on a ship and tried to launch it, and after 30 seconds or so it became unstable and started pitching/yawing uncontrollably, despite having 2 Advanced Inline Stabilizer SAS modules and 3x AV-R8 winglets.. If I try without the DERPs, it flies just fine. I then removed the lifeboat modules, leaving just the propulsion modules, and had the same result. Then I added action groups to decouple them and tried again. Still unstable after 30 seconds or so, but when I decoupled them, the rocket was able to right itself and fly correctly. Even just 4 of the propulsion modules was enough to destabilize the ship.

This was using MechJeb's ascent guidance, and also just using manual control. Whatever I do, it starts out flying fine, but ends up flipping end over end after 30-30 seconds. But as soon as I jettison the DERP propulsion modules, it becomes flyable again.

Any clue what is going wrong? None of my other ships have any problems at all like this.

Also a picture of the craft and or video of the behaviour would be useful. It does sound like a design issue.

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This was not using FAR.

I did some more experimenting last night. With only 2 DERPs, the rocket would stay stable until it started its gravity turn at ~10km, then it would do one flip, then stabilize and continue to orbit.

So it seems stable early in the flight, then loses stability as the velocity/altitude increases, then eventually regains it (if it gets that far). With 4 or more DERPS, the instability is bad enough that vertical flight is unmaintainable after 30 seconds or so (with MechJeb limiting speed to terminal velocity), but with only 2 DERPs it can hold on while vertical, but when the angle of attack increases at pushover it can't maintain control. The DERPs were mounted near the nose of the rocket.

It kind of seems like the DERPs are making very high drag, which is putting the center of drag in front of the center of gravity. At the start, velocity is low enough that the SAS and engine steering can keep things stable, but after the velocity climbs, the drag increases enough to become dominant and the rocket starts flipping. But if it manages to get high enough so that the atmosphere is thinner, the drag falls to a low enough level that the SAS and engines can again get control. At least that's what it seems like. Decoupling the DERPS also fixes things immediately.

BTW, most of my testing is using MechJEB's ascent autopilot, but I've also tried flying it manually and get similar results.

Tonight I'll try a couple of things. I'll look in the VAB at where the center of lift is and see if it is unexpectedly high (but I'm not sure if the center of lift is the same as the center of drag). Then I'll also try moving the DERPs to a lower location on the rocket and launching to see if that fixes it. I'll also try more/bigger winglets to see if they can overcome the problem.

I'll also post a screenshot of the rocket, but it's a fairly standard design.

  • Top stage is a probe core (I've tried Stayputnik, OKTO, and one other whose name escapes me), an Advanced Inline Stabilizer, a FL-T400 tank with the DERPS mounted near the top, and an LV-909.
  • Then below that is a 1.25m decoupler, then another Advanced Inline Stabilizer, a FL-T400 and a 1.25m quad engine from one of the mods (probably KW or Novapunch - I can't find lists of parts for either of them to get it exactly and I'm at work now), and there are 3 AV-T1 winglets near the bottom of the tank.
  • Then in asparagus fashion around those two central stages I have 3 pairs of liquid boosters with 2xFL-T400 tanks and 1.25m engines.

All the bottom engines are able to gimbal and I've tried it with the gimbals both locked and free. With 2 SAS units, 7 gimballing engines, and 3 steerable winglets, this puppy should be able to keep the pointy end upward, and it has no problem without the DERPs.

I'll also look into making a video, but since I've never tried making a video, there may be a bit of a learning curve. If anyone can point me at a decent tutorial, it would be appreciated.

Without the DERPs it gets to orbit with no problem at all, so I'm pretty sure it's not the rocket design that's the problem. I've launched hundreds with similar designs in the past. I've been playing KSP since version 0.17, so I'm fairly experienced at building rockets that can fly. :)

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I think I've figured it out. I just checked, and the DERP propulsion module has a drag of 1.0, compared to typical drag values of 0.1 to 0.3 for most parts (the lifeboat has a drag of 0.3). I think this explains the behavior I have been seeing. Having 5 times the drag of a typical rocket part will definitely cause problems if it's above the center of mass.

I'm guessing this is to make sure the combined lifeboat plus propulsion module will re-enter with the lifeboat leading. Any reason the lifeboat can't be 0.2 (like most pods), and the propulsion module something a little more reasonable, like 0.4 or so?

Keith

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  • 2 weeks later...

You are providing way too little information. I will expend as much help supporting you as you spend in providing information.

- - - Updated - - -

Start with a screenshot of your gamedata folder. also basic stuff like... KSP version

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  • 2 weeks later...

Hi guys, I encountered a wierd behavior of the floats and was wondering if sb. had the same issue. The airbag are working just fine but the floats not... The radial mouted floats inflate imediately afer selecting them out of the editor toolbox, even if they arent yet attacht to the vessel. They are still attachable but keep the inflatet state. It appears they have no rightclick menue as the airbags have. The inline floats keep retracted but have also no rightclick menue, so are not deployable.

Did I mess up the instalation somehow?

Oh... I derped... never mind ^^

I forgot to move the Firespitter folder...

Edited by Frimi
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Hi everyone, im using Derp for the first time and i noticed that the power supply runs out very very quickly. in the description it said that it has a tiny power slug but i cant find any option to activate that.

do i miss something here? i would really appreciate if someone could explain to me how it works.

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No i use the default settings and never changed anything in any config file.

Is it normal that the charge depletes or am i supposed to activate something manually? Everything else is working perfectly fine.

At first i though maybe i need to unlock/buy something in the tech tree to make it work but i guess thats not the case since i unlocked/bought almost everything in the tech tree.

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  • 3 weeks later...
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