Wing Plugin [Beginings...Concept...]

[drewmacrae]

The present system to generate an atmospheric flight model in KSP is the best I\'ve seen made available to the public. It allows for arbitrary design of craft and then arbitrary destruction of the assembled components while maintaining a reasonably credible flight model. Designing planes is a frustrating process, and I think it\'s great that this realism affects KSP. There have been claims that the difficulty in designing large planes is due to innacuracies in the winglet model used to compute lift and drag. I don\'t think that\'s the case, but the current model does encourage the sorts of things we saw when people were trying to fly for the first time, and this is partly a result of the winglet model. I\'m not a fan of telling people how to do their jobs, but I\'m of the opinion that Squad should focus on features that require intimate knowledge of the KSP code base, and ones that are impossible with mods; I don\'t feel this is one of them and it seems this could be developed externally in a mod, so I\'m going to take a crack at it. I have a tendency to move slowly on some projects or to put them down entirely so I think opening up this process for comment might be beneficial to the community. If someone wants to pick this up at any point and do the next step, I\'ll be grateful for the help. I\'ll post a link to a Google code project once I have built up some source code. All I know about aerodynamics I\'ve learned from RC planes, model rockets, simulators and from the internet. I don\'t consider myself an expert, but I feel I have a lot of the knowledge needed to produce a wing plugin and that it will be an interesting problem.

I asked a friend for help, regarding a problem of wings flying sideways through the air especially if there was information available at sub/trans/and supersonic regimes. He was the one who originally showed me KSP last August, and has more formal aerospace training than I do. I thoguht he might know which terms to punch into Google at the very least. He informed me that a sideways version of AOA is called sideslip, and that there\'s not much information characterizing wings behavior in side-slip because the aircraft tend to be characterized as a whole instead. He sent me one paper he felt might be helpful.

http://openae.org/files/resources/datcom/Datcom_handbook_1978_edition/Section_5_Slideslip.pdf

If that qualifies as not much information I\'d hate to be researching something where there is a lot.

I find I can\'t understand that resource on it\'s own, and no amount of math is going to get me there, so here\'s the equivalent of a decoder ring for all the funny looking letters: http://lahso.megginson.com/2005/07/18/the-alpha-beta-of-flying/

The first referenced paper in the long one looks helpful: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930082233_1993082233.pdf I\'ve been told that these old NACA publications are worthwhile. In fact it\'s nice because as they develop the theory here along with some early swept wing development they\'re introducing terms for the first time which means they see fit to define them. This is a great collection of data, and it looks like it\'s almost ready for implementation. It\'s coverage of swept wings doesn\'t quite isolate winged pairs.

Wing plugin scope

0.1 release:

The C7 swept wing and small control surface will each have their lift and drag model overridden with a subsonic model for lift and drag at a variety of AoA and sideslip conditions based on interpolation of some data set, likely from the above NACA paper. The model will assume the wing is moving trhough the air in a symmetric but otherwise independant pair through the air so as not to require simulation of the wakes of other parts. This will enable craft to generate more lift at smaller AoAs and then to simulate stalls with reduced lift and increased drag at higher AoAs, so we get to see our planes fly with 5 degree AoAs instead of 55 degrees.

I imagine constructing 0.1 in the following manner

[list type=decimal]

[li]plugin will be an extension of the winglet, parts will be changed to 'wings' and 'control wings'[/li]

[li]Removing the current forces by setting drag and lift to zero[/li]

[li]Checking that I can insert craft relative lift by applying it in the vessel.up direction[/li]

[li]printing AoA and sideslip for the wing when arbitrarily attached to a plane[/li]

[li]use nearest interpolation to lookup lift and drag as a function of sideslip and aoa[/li]

[li]develop interpolation methods to better compute lift and drag as a function of aoa and sideslip[/li]

Future releases may have the following features in no particular order:

• 
  [li]Stall horns[/li]
  [li]Stick pusher stall prevention[/li]
  [li]Improved drag models for other types of parts (nosecones, aeroshells, everything else)[/li]
  [li]Trans/supersonic models[/li]
  [li]Atmospheric heating effects[/li]
  [li]Stochastic Raycast based wake effects[/li]
  [li]Exhaust aware wake effects[/li]
  

Open questions

• 
  [li]How do I determine velocity relative to the air?[/li]
  

and plenty more to follow I\'m sure...

[Romfarer]

Since there is no wind in KSP, velocity relative to the air is equal to the velocity relative to the rotating frame.

Vector3d rotatingFrameVelocity = nonRotatingFrameVelocity - vessel.mainBody.getRFrmVel(position); 

This is taken from the following ksp wiki page: http://kspwiki.nexisonline.net/wiki/Module_code_examples

[Taverius]

A simple simulation of ground effect, so we can ekranoplanes, would be awesome

[Emilio]

Are you still working on this ? It looks cool

[Mr_Orion]

I\'d like to note that Iskierka has already made a semi-finished wing module long before this (though it\'s not been publicly released, apparently the thick atmosphere makes aeroplanes feel like feathers with realistic wings), but also I hear that Mu has been working on some official wings that should be eventually implemented.

[DrPoo]

Holy moly, talk about verbosity!

Im very interested in this plugin. Theres something really wrong with vanilla wings and i cant tquite put a finger on what.

Ill try this when i can. Good night.

[White Owl]

I\'d like to note that Iskierka has already made a semi-finished wing module long before this (though it\'s not been publicly released, apparently the thick atmosphere makes aeroplanes feel like feathers with realistic wings), but also I hear that Mu has been working on some official wings that should be eventually implemented.

Yeah, I believe many modders have been holding back from tackling the wing behavior precisely because we were told a lot of the work was already done. Sometime. Somewhere...

[semininja]

A week or two ago, I made a suggestion about how the drag model could be improved. Having reflected on that suggestion, I think that with the right values in the .cfg file, that drag model would create a lift effect without any need for a specific \'wing\' case, because of the way the drag forces are applied.

[Emilio]

Wich values ? If you can create lift from drag it would interess me for my plugin.

[semininja]

In my suggestion, the way drag forces are applied causes \'deflection lift\' of sorts as a side effect.