Spaceplane Keeps Flipping Over Mid-Takeoff

[Shiloh8686]

Hi, could you please help me with this problem? Why does it happen and how can I fix it? Also, before you tell me that my center of mass and center of lift need to be at the same spot, they already are. Here's a screenshot to prove it:

Here's what happens:

How do I fix this? Any help would be much appreciated, thanks.

[Moon Goddess]

First you may need to upload those images to the internet we can't see images that are on your C drive. (You want to say thank you for that, it would be VERY BAD if we could.)

[Pursuedtank]

I can't actially see the screenshots. You'll have to upload then to an image hosting site like imgur and then copy the BB code to your post. I can't help much without seeing pictures. Is the center of thrust off line with the center of mass? If so that might be the reason why.

[Zephram Kerman]

As you get going along the runway, "pull up" (hold S). This takes weight away from the nose wheel and helps you go straight. Going really fast (>60 m/s) with three wheels on the ground tends to be unstable.

[Lanfranc]

Little hard to see without pictures, but generally the centres of mass and lift should not actually be in the same spot – it's better if the CoL is slightly behind the CoM.

[Deadweasel]

Is it just me, or does it seem like more and more people are just posting things and walking away without even glancing at what their post actually looks like after the fact? :/

[HarvesteR]

One thing I've found can cause losing control during a takeoff run is to have a misaligned wheelbase. That can happen if your landing gears aren't all parallel to each other (and aligned in the general direction you want to go towards). If it's a minor misalignment, it can cause some wobbling, but if it's significant, the wheels will get dragged slightly sideways and the skidding could tear your craft apart.

Try to reattach your gear with angle snap turned on (or off), or move them somewhere else. If they're converging or diverging, they'll likely be unstable. You want to make sure they are parallel, as much as possible.

Cheers

[Cykyrios]

It would seem wheels in general don't like stability, and prefer going wild when they can

As an example, this contraption turned sharply to the right without any input other than S (was trying to take off, after all):

(this is with "standard" rover wheels (the yellow ones))

And in this video, the landing gear literally rips the rover apart:

(but granted, going almost 300 m/s isn't exactly the best idea)

These videos are from 0.19 and 0.18, IIRC, but the wheels physics shouldn't have changed much since then.

[arq]

Since this is happening on the ground, I'm going to agree with many of the others here and suggest that it has to do with your wheels being ever-so-slightly misaligned.

If this happens in the air, though (and typically only at high-speed), it sometimes has to do with having a forward center-of-drag. If your CoD is forward of the CoM, it will make your plane unstable flying forward (but stable backward - lucky you!) and it will try to flip around. The solution in this case is to move your wings backward to keep the drag towards the back.

[M5000]

Hi there, OP. I've moved your thread to the help section, where it's likely to get more users that can help.

But as a general rule, if what you're describing is happening, you probably have way too much lift on the front. Or drag. If it's in the air, it has to be one of those two if your CoM and CoL are in line.

I've built many-a-plane with canards, especially on short ones, and they flip over every time.

[Guest]

Hi there, OP. I've moved your thread to the help section, where it's likely to get more users that can help.

But as a general rule, if what you're describing is happening, you probably have way too much lift on the front. Or drag. If it's in the air, it has to be one of those two if your CoM and CoL are in line.

I've built many-a-plane with canards, especially on short ones, and they flip over every time.

I second the canards. I quit putting canards of any kind up front. My planes don't flip anymore.

[Sma]

I've been working on developing an SSTO Spaceplane my self and ran into problems where over a certain speed on the runway it'd take (or try to take) an almost 90 degree left turn. As I suspected upon closer look it was because of the positions of the rear wheels. They were tilted one way by just a few degrees (from using shift while rotating). Fixed it by rotating the wheels to they were straight up and down, which I thought they were originally.

The other problem I'm having is in taking off. Sometimes I can get it right, but lately the problem has been I get off the ground and angle my nose up roughly 20 degrees, then I try to go up to 45 and it flips upside down. CoL is just behind CoM. I'm trying to fine tune the position of the wings, canards etc. With out the canards it doesn't get off the ground until it gets to the end of the runway.

I might have gotten it fixed last night, I don't remember now (it was late). Even when it doesn't do that it tends to wobble +/- 10 degrees from where I want it until it finally settles in place. I've tried with a single asas, a single sas, 1 of each and multiple sas together. I think it's just a matter of getting the wings and canards just right, along with getting the position of the CoM in just the right spot in relation to the wings. It's pretty close right now. Maybe I'm just being too picky in wanting to get it so it's controllable by 1 degree. My "dream" is to get the plane so it can sit at 1m/s climb rate.

Sorry, didn't mean to "hijack" the thread.

I second the canards. I quit putting canards of any kind up front. My planes don't flip anymore.

Sounds like the problem I've had from time to time, though with out them I can't get off the ground until the end of the runway. Well except if I move my wheels closer to the CoM, and then it pitches up too fast and breaks off the engines.

It's a fine art, this spaceplane business.

Here is a screen shot from my steam album of an earlier version I was working on, had two front landing gear. Read this helped sometimes in going down the runway. New version has one, and spaces the two turbojets out from the center hull. Also the new version I added a bunch of the radial mount xenon tanks just a head of the wings to bring the CoM a little further forward.

Edited August 7, 2013 by Sma
Added screenshot

[Stephen Locksley]

Some of my aircraft would start to flip ,but their elevators, which are for the pitch, can prevent it.

[jimmymcgoochie]

35 minutes ago, Stephen Locksley said:

Some of my aircraft would start to flip ,but their elevators, which are for the pitch, can prevent it.

Did you even look at the date stamps on this thread before posting? This thread was posted nearly SEVEN YEARS AGO!

It's generally considered bad forum etiquette to revive threads that old, so check the dates on the posts first before replying in future.

[Vanamonde]

What he means to say, @Stephen Locksley, is that it was kind to offer a fellow KSP player your feedback. Thank you for being a helpful forum member.

That being said, KSP's aerodynamics have changed quite a bit since this thread was created, so the content of this thread is no longer relevant. 

[Starhawk]

Hi @Stephen Locksley.  Thanks for being helpful to another forum member.

That is exactly the sort of spirit and attitude that keeps the KSP Forums a great and friendly place to visit!

Happy landings, @Stephen Locksley!