Why does my Mk2 Airplane keep flipping around? [resolved]

[Ninjadude501Alt]

The issue has been resolved! Thanks for the help

 

So, I've played around with Mk2 planes a few times, and each time I do, it always seems to be unstable and want to flip around at the slightest over-turn. Why is this?

Here are two photos of the plane that I was using just now: 

Spoiler

https://gyazo.com/4c924fb37e1a8f2daa8859ef32603ff8

https://gyazo.com/3e71166b2d4ae727eb376bf17aee8fd6

 

 

 

Also note that often when I flip around, it really isn't in situations where you'd think that you would flip around. I'd just be lightly tapping W/S to re-adjust my trajectory and WHAM! I'm in an uncontrollable spin-dive.

Edited October 18, 2016 by Ninjadude501Alt
Resolved

[Capt. Hunt]

Well, it's not a very stable design, I can see that right away.  Add a horizontal stabilizer to the back and that should help a little.

[Plusck]

The easy, standard answer is simply "because CoL is in front of CoM".

Of course it's a canard design so you might think that CoL should be further forward, but it doesn't really (IMHO) work like that.

As soon as you deviate off prograde, air over the canard is going to push it further off prograde. If the canard isn't fast enough to reverse direction immediately, the craft can do nothing but pitch or dive into a tumble. In KSP this is even worse because engines push the centre of gravity more towards the rear than is generally the case in real life, so canards have a long lever arm with which to exert that drag-and-lift-induced torque.

So basically (IMHO), if you want to use canards, you really need to add another set of elevons right at the back to prevent loss of control, which somewhat defeats the purpose of having the canards in the first place...

[Clipperride]

Also, as you're probably aware, caps lock can also help.  You get a finer level of control once it is toggled on. 

[TheEpicSquared]

Move your center of lift behind the center of mass and you should be fine.

[Snark]

A few things.

First, as folks have said, you want to have CoL behind CoM:

10 hours ago, Plusck said:

The easy, standard answer is simply "because CoL is in front of CoM".

 

6 hours ago, TheEpicSquared said:

Move your center of lift behind the center of mass and you should be fine.

...However, it's important to note that simply having CoL behind CoM does not necessarily mean you're aerodynamically stable.  Lots of people in KSP think that, but it's not the case.   It's possible to have CoL behind CoM and still be really unstable.  People get bitten by that all the time-- especially folks who try to build a KSP replica of the US space shuttle.  (Just do a forum search for "unstable shuttle" and you'll find lots of discussions about the problem.)  The reason for this is that a craft that has its CoM towards the back is likely to be unstable, regardless of where its CoL is.

So, some ways to improve your stability:

• Move your CoM farther forward.
• Make sure that you've turned off control authority on your vertical stabilizer for everything except yaw.  If you haven't, then it's not helping you as much as it can, because it ends up fighting itself (its efforts to add yaw stability directly counteract its efforts to add roll stability).
• Turn off the canards' control authority for everything except pitch.  Any time the canards deviate from 0 degrees, they're adding drag to the front of the plane, which tends to make it want to flip.  But the only time that their deviation actually helps your stability is for pitch control.  So you want to make sure that the only time they deviate from 0 degrees is when they're actively trying to help your pitch.
• As others have suggested, add a horizontal stabilizer at the back of the plane, as far behind the CoM as you can make it.
• Be aware that those ailerons that you have on the wings are doing essentially zero work to help your stability.  They may help you for roll authority, but they don't add anything to pitch stability at all.  That's because they're right smack dab on your CoM, so they have no lever arm to work with.  Control surfaces only work to help your pitch if they're far in front of or far behind your CoM (and "behind" is better than "in front of", which is why you need a stabilizer at the back).

 

[Ninjadude501Alt]

6 hours ago, Snark said:

A few things.

First, as folks have said, you want to have CoL behind CoM:

 

...However, it's important to note that simply having CoL behind CoM does not necessarily mean you're aerodynamically stable.  Lots of people in KSP think that, but it's not the case.   It's possible to have CoL behind CoM and still be really unstable.  People get bitten by that all the time-- especially folks who try to build a KSP replica of the US space shuttle.  (Just do a forum search for "unstable shuttle" and you'll find lots of discussions about the problem.)  The reason for this is that a craft that has its CoM towards the back is likely to be unstable, regardless of where its CoL is.

So, some ways to improve your stability:

Quote

• Make sure that you've turned off control authority on your vertical stabilizer for everything except yaw.  If you haven't, then it's not helping you as much as it can, because it ends up fighting itself (its efforts to add yaw stability directly counteract its efforts to add roll stability).
• Turn off the canards' control authority for everything except pitch.  Any time the canards deviate from 0 degrees, they're adding drag to the front of the plane, which tends to make it want to flip.  But the only time that their deviation actually helps your stability is for pitch control.  So you want to make sure that the only time they deviate from 0 degrees is when they're actively trying to help your pitch.

Already done.

Quote

• Be aware that those ailerons that you have on the wings are doing essentially zero work to help your stability.  They may help you for roll authority, but they don't add anything to pitch stability at all.  That's because they're right smack dab on your CoM, so they have no lever arm to work with.  Control surfaces only work to help your pitch if they're far in front of or far behind your CoM (and "behind" is better than "in front of", which is why you need a stabilizer at the back).

Yep, they're only set to help with roll.

Quote

• As others have suggested, add a horizontal stabilizer at the back of the plane, as far behind the CoM as you can make it.

By horizontal stabilizer, do you simply mean another wing segment? Or a wing segment with ailerons on it? Or canards? Etc. I'll be trying a wing segment with ailerons on it while I await your response.

Quote

• Move your CoM farther forward.

Will be done, and I'll edit this section with the results (for moving my CoL as well).

Results at the bottom

14 hours ago, Clipperride said:

Also, as you're probably aware, caps lock can also help.  You get a finer level of control once it is toggled on. 

Actually, I was entirely unaware of that. Thanks for the tip!

 

EDIT: OVERALL RESULTS:

Holy crud!

I did everything that was suggested (CoM further foward, CoL behind CoM, add rear stabilizers, etc.) and took it out for a flight. I couldn't get it to flip around, and I tried as hard as I could! Thanks so much for the help!

Edited October 18, 2016 by Ninjadude501Alt
results

[Clipperride]

Glad to hear things are looking up (up and away!)