Spaceplane help.

[Thordan Ssoa]

I have been trying to create a spaceplane recently, and every time I launch I get off the runway and my plane immediately flips itself upside down. Even with sas enabled and holding the w key from the moment it starts to pull up until it crashes, it rotates until it is facing the way it came and reduces it's speed to nothing before landing in the ocean. Any ideas as to what might cause this?

[Aphox]

It sounds like your center of mass is too far back or behind your center of lift.

Use the center of mass, lift, and thrust visual cues in the SPH to see where all of those are. You want your center of lift slightly behind your center of mass, and make sure your center of thrust isn't pointing down or anything.

The center of lift cue has a line coming out of each of the 4 sides; I usually have the one facing the center of mass barely touching the back of the mass ball. Makes my planes very stable.

That's an example of a plane I have that is probably the most stable I've ever built. It's not pretty or crazy looking and awesome, but it's by far the most stable plane I have, even compared to the stock models that came with .17.

Play with your parts a bit, it doesn't have to be spot-on. Use control surfaces in the right spots and play with part rotation and see what you can come up with.

The closer your center of lift and mass are together, the more maneuverable the plane is, but the more unstable it becomes (uncontrollable flipping and doing exactly what you don't want it to).

If you get these in the right spot you don't even need SAS or ASAS/flight computer.

[Thordan Ssoa]

Well, I've been doing a lot of playing around, and now i can take off fine. However, the plane pulls upwards. Hard. This problem gets worse the higher my altitude/speed, and right around the time I clear 13km it flips around, with any attempts to regain control leading to and uncontrollable tumble. Is this just a problem of location of center of mass/lift yet? Or am I doing something else wrong?

[Aphox]

Well, I've been doing a lot of playing around, and now i can take off fine. However, the plane pulls upwards. Hard. This problem gets worse the higher my altitude/speed, and right around the time I clear 13km it flips around, with any attempts to regain control leading to and uncontrollable tumble. Is this just a problem of location of center of mass/lift yet? Or am I doing something else wrong?

I'm not cool enough to know exactly how these things are supposed to line up, but I've experienced the problem you're having. I have a few designs that work fine below 10Km and get very unstable higher up, but no idea how to fix them. Hopefully someone who knows this stuff a little better passes by the thread. That design I posted a screenshot of is great under 10K, but if I put a turbo jet engine on it and climb above that, it becomes very wobbly.

[EndlessWaves]

Is it altitude, time or speed that triggers it? If it's altitude then it may be that your axis of thrust isn't in line with your centre of mass and with the stabilising drag of the wings reduced your thrust that's pushing at the bottom of the plane causes it to rotate upwards.

[Thordan Ssoa]

Time. I'm betting it's time. I'm shootin in the dark a bit here, but I think it might be that as my fuel tanks empty, the center of mass moves towards the back. Eventually, it moves behind my center of lift, which is where my flipping problem came from before. In theory, this should be a simple fix. However, if anyone who knows better comes along, please do say something.