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Problem with plane (getting slower all the time)


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For the Circumnavigation Challenge I have build a simple plane that is aerodynamical stable, as long as I don't touch any button. I acitvate the J33, it lifts off without assistance and stabilizes itself in an height between 9500 and 12000 m (it will oszillate between these two borders without me ever pressing any button).

The problems start about 1 to 2 hours in flight with maximum physics warp. The plane will get slower and slower (fuel and intake air are both redundant available and the engine is put on 100%) till the plane stalls and crashes between 3 and 4 hours in flight.

I have no idea, why this happens. Could anyone give me a hint what is going wrong?

Here a picture in SPH and in flight:

5oNt7Oj.jpg

Jh71qkX.jpg

Edited by Heimdall5008
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The question is, is your Jet engine losing power this whole time? The basic jet loses power the higher it goes and the faster it goes. So there is a max speed that engine will go.

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The only thing I can think of is the plane climbs too high at one point, loses power and the nose tilts downward. And if your not at your pc to pick it back up when that happens you'll return to find it crashed.

You should probably consider mechjeb or other automation means to keep the plane at a specified altitude.

Isn't there a way to trim control surfaces so they always pitch up? I had always thought it was alt+pitch, but it doesn't seem to do anything for me what so ever.

Edited by Motokid600
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This was also my first assumption, but according to the flight log I never got higher than just below 12.000 meters. And at this hieght I still have enough air intake as you can see in the screenshot.

I did a second attempt while I was at the PC, during this time the plane got also slower while it was loosing height.

Could this maybe be an artifact from physics awrp or so?

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Hello,

the answer is simply: Changing atmosphere properties during time of day and latitude. Hotter and thinner air makes your engine lose power and vice versa. For example, flying at the poles at night will help increase thrust.

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Hello,

the answer is simply: Changing atmosphere properties during time of day and latitude. Hotter and thinner air makes your engine lose power and vice versa. For example, flying at the poles at night will help increase thrust.

Thanks :)

But this is really extreme, about 150 m/s difference is really a lot for difference between night and day... o.O

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Hello,

the answer is simply: Changing atmosphere properties during time of day and latitude. Hotter and thinner air makes your engine lose power and vice versa. For example, flying at the poles at night will help increase thrust.

Really? KSP simulates that now?

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Really? KSP simulates that now?

Yes, it was in one of the recent updates (either the 1.0 or the ones that immediately followed it). There was a post about it somewhere on the forums.

Thanks :)

But this is really extreme, about 150 m/s difference is really a lot for difference between night and day... o.O

Read the rest of the thread. My guess is that time warp is the culprit. I've noticed that using it can cause odd problems. Almost always if I encounter a problem while under physics warp I've found that simply canceling the warp fixes it. My advice would be to try that and get back to us on if it fixed the problem.

Another troubleshooting step you could do is install Kerbal Engineer and do the flight with the Vessel info window open. The problem may reveal itself in one of the readouts.

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As suspected the time warp was the problem.

Cancelling the timewarp everey 5 minutes real time and engaging it again solved the issue. Not what I would have liked but to be expected with four times greater time steps in a physics simulation...

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