Help with understanding how wings work

[Angelo Kerman]

Hi all,

I am trying to create a folding wing for a space probe, something that would fold up like a solar panel for compact storage, and then unfold to generate lift. I'm hoping an expert on wings like @NathanKell or a modder with experience creating wings can answer a few questions, as I've not created a wing in KSP before. Let's say for the sake of argument that the folded wing has lift characteristics equal to the Wing Connector Type C, and the unfolded wing has lift characteristics equal to the Wing Connector Type B. For reference, the Type B wing has the following PartModule:

	MODULE
	{
		name = ModuleLiftingSurface
		useInternalDragModel = True
		deflectionLiftCoeff = 2.0
		dragAtMaxAoA = 0.5
		dragAtMinAoA = 0.0
	}

And the Type C:

	MODULE
	{
		name = ModuleLiftingSurface
		useInternalDragModel = True
		deflectionLiftCoeff = 1
		dragAtMaxAoA = 0.25
		dragAtMinAoA = 0.0
	}

Notice that the Type C, which is half the size of the Type B, has half the lifting capability, which should give you an idea of how I want the folding wing to work.

Questions

1. If I change the ModuleLiftingSurface values at runtime so that the folded wing has parameters equal to the Type C, and the deployed with has parameters equal to the Type B, will KSP honor the changes and change the wing's lift?

2. Do I understand correctly that KSP calculates a wing's lift based upon its drag cube and ModuleLiftingSurface?

Now for the fun part, assuming my answer to question 2 is "yes." From what I can see in a parachute part, there are PartModules that appear to change the drag cube for the parachute. These are ModuleDragModifier modules. Here is an example from the Mk2-R radial chute:

	MODULE
	{
		name = ModuleDragModifier
		dragCubeName = SEMIDEPLOYED
		dragModifier = 1
	}
	MODULE
	{
		name = ModuleDragModifier
		dragCubeName = DEPLOYED
		dragModifier = 58
	}

Questions

3. How is dragModifier applied to the drag cube?

4. How would I go about switching the drag cube for the folding wing? The only thing I can think of is to use semiDeployedDragModifier.enabled = false; deployedDragModifier.enabled = true; How does KSP change the drag cube for parachutes?

So basically the idea of the folding wing is that, assuming that drag cubes play a part in calculating lift, the folded wing would have a small drag cube and lift capability, while the unfolded wing has the fully deployed drag cube and lift capability.

Also, can somebody point me to a post on what the values of a drag cube mean?

Thanks for your help!

[NathanKell]

1. Yes.

2. Wings don't use drag cubes for drag. Note how the dragModel is set to none or override in those wing configs.

3. When PartDatabase.cfg is created, the dragModifier is multiplied into the drag terms of all cube faces.

4. If you use a ModuleAnimateGeneric to handle the animation, it's done for you. If you're writing your own animation module, implement IMultipleDragCubes and set the cube weights yourself. But remember, if you're making a wing, the 'drag' cube is really only relevant for thermo, not drag.

 

For an overview of drag cubes and their terms, see:

 

[Angelo Kerman]

Ohhhhh, so all I need to do for a folding wing is to 1) use ModuleAnimateGeneric to let the game calculate the drag profile, and 2) modify the deflectionLiftCoeff and the dragAtMaxAoA/dragAtMinAoA values? That would make things much easier.

And thanks for the reference on drag cubrs.

Edited March 3, 2016 by Angel-125

[NathanKell]

No, only deflectionLiftCoeff is used these days. You just need to modify it based on the animation state.

[Angelo Kerman]

Thank you, that really clarifies things.

[Angelo Kerman]

@NathanKell another question: can you change the dragModelType at runtime, and the CoLOffset?

[NathanKell]

Yes and yes.

[Angelo Kerman]

Exxxcelent *evil grin*

[Angelo Kerman]

@NathanKellWoot! My prototype deployable wing works!

Here is my prototype wing stowed:

And here it is deployed:

With this test wing I have the deflectionLiftCoeff controlled independently of the animation; now it's just a matter of linking the two together, and of course creating a proper wing..

Thanks again!