CoL and CoM issues with mk3

[max_42]

I cannot get the CoL in line with CoM. Does it mattter? this craft will not glide to save its life, it flips and spins uncontrollably The game is 100% stock and the cargo bay is empty

 

http://imgur.com/G3DZfXs

Edited January 12, 2016 by max_42

[Thiagobs]

There's too much weight in the back, move those monoprop tanks and place them between the cockpit and cargo bay.

Also, I don' t know what you're trying to build, but it looks like you have too much monoprop... two tanks are a bit overkill in my opinion... maybe perhaps you confused them with the Rocket Fuel tank?

[Snark]

So, here's the thing:  CoL is not what's important here.  Turn it off and stop looking at it.

Your craft has two problems.

The first is that it's aerodynamically unstable.  For a craft to be stable, the CoM needs to be in front of the center of drag.  That's the center of drag, not the center of lift.  Look at your craft:  the CoM is all the way at the back end!  The center of drag is almost certainly way out in front of it; it's no wonder it has stability problems.

Unfortunately, there's no handy visualization for center of drag, the way there is for CoM or CoL.  You just have to eyeball and estimate.

What you need to do is move the center of mass of that craft way far forward.

The second problem you have is that your ship has no effective control surfaces.  The effectiveness of a control surface is directly proportional to its distance from the center of mass:  when it's far away from the CoM, it has more lever arm to work with.  When a control surface is right at the center of mass, it has zero effectiveness.  Now look at your ship, look where the center of mass is, and look at all of your control surfaces:  they're all right there next to it.  You might as well not even have them.

So the recipe to success, here, is to move the CoM way far forward.  That will make the craft more stable, and will also give the control surfaces more of a lever arm to work with.

Now, earlier I said to turn off the CoL and ignore it.  That was actually a bit of an overstatement-- it's not irrelevant, it's just not relevant to stability.  If your CoL is too far behind your center of mass, then your shuttle is going to want to nose-down a lot and you won't be able to fly it like a plane.  The easiest way to deal with that is to add some canards up front.

So, to sum up:

• Move the CoM way far forward, to get it in front of the center of drag
• Add some canards up front (or move the wings farther forward), so the CoL isn't too far behind your newly-forward-moved CoM.

[Vegetal]

As Snark said, the problem is drag. Empty Mk3 cargo bays are well known for this issue, as they are mostly an empty shell - no weight, and lots of drag.

Your shuttle may fly straight if you keep it perfectly on prograde, but as soon as you try to maneuver it, the bay's sides will be exposed to the flow and the monster drag will kick in, turning your nose around.

[max_42]

Thank you very  much for the insight. I will try again!!