What's The Difference in Wings?

[Red Iron Crown]

What about the earlier talk about wing aspect ratio? Does that mean it doesn't matter? Because I have a feeling that the fat wings aren't nearly as good as a bunch of S strake wings clipped together. Is it just my imagination or are there other differences that are more important?

Aspect ratio is irrelevant in stock KSP aero. Wings behave like low aspect ratio wings at high speeds and high aspect ratio wings at low speeds. It's a rather large simplification but probably appropriate for a game that is (nominally at least) focused on spaceflight.

[Claw]

Wait... there's only a generic set of curves in there. Are these values all multiplied by the wing's lift rating to generate the final values?

Yeah, sorry. The lif equation I mentioned is the one that Nich posted. KSP looks up Cl and Cd values, then uses the standard lift equation (rearranged) to calculate lift.

I'll be interested in seeing a graph if you make one. Because lift isn't actually a V^2 lift model, due to the Cl(Mach) curves. So you might have to make a curve for Cl(Alpha) and keep Mach constant, then do the same for Cl(Mach). Or create an indes od Cl(Alpha) curves at different Mach values.

What about the earlier talk about wing aspect ratio? Does that mean it doesn't matter?

As RIC said, the actual wing shape doesn't matter for lift generation. KSP uses a simplified model which does one basic thing: makes planes built and flown in usual situations fly like you would expect.

So if you build a long wing glider and fly it around slow, it flies like a glider. If you build a supersonic jet, it flies like a supersonic jet when zipping around at high speeds.

This system is quite simple and works well for most cases that (as RIC said) rely on notional flight for a game focused on space. The pitfall to this system is that you can get "unrealistic" behavior in the sense that it's possible to build a fighter looking plane with enough lift that it still glides pertty well at low speeds. Or build a glider that you can get up to Mach 2 with enough thrust.

There are also other things that come into play, like Moments of Inertia and other physics bits that affect how some big wings might make a plane respond vs. a differently shaped wing of similar lift rating. Such as long wings at high speeds are also vulnerable to wing twisting and roll reversal. So, in that sense, wing shape still matters.

Cheers,

-Claw

Edited September 2, 2015 by Claw

[Nich]

I was simply going to do a 3D CL/CD vs alpha vs mach graph. I suspect alpha(CL/CDmax) will not change much with mach but if it does I was going to use my gut to pick an optimal AOI for my SSTOs. I still have not looked at the files but is sounds like there is only 1 set of tables for all wings so at the end of the day wing selection is purely ascetic and stability. Then all you need is enough lift and thrust to get off the runway.

[GoSlash27]

Yeah, sorry. The lif equation I mentioned is the one that Nich posted. KSP looks up Cl and Cd values, then uses the standard lift equation (rearranged) to calculate lift.

I'll be interested in seeing a graph if you make one. Because lift isn't actually a V^2 lift model, due to the Cl(Mach) curves. So you might have to make a curve for Cl(Alpha) and keep Mach constant, then do the same for Cl(Mach). Or create an indes od Cl(Alpha) curves at different Mach values.

Claw,

Okay, so if KSP uses the curves in the physics cfg to generate the lift and drag, then what value are the results applied to? The stock lift and drag coefficients in the part config files, or just the lift rating?

If both values are used, then it would definitely matter which wing parts are being used.

Thanks,

-Slashy

[sardia]

WhyWhy do fat wings feel like they perform worse than strakes?

[Claw]

The stock lift and drag coefficients in the part config files, or just the lift rating?

The drag numbers in the part.cfg file is meaningless in the new aero. Also, we might need to take this elsewhere, so we don't hijack the thread.

WhyWhy do fat wings feel like they perform worse than strakes?

I think what would help us answer your question is if you can show some pictures or, even better, provide craft files and a description of what exactly feels different. Or at least be a little more specific about which FAT and what measure of performance you are using. That would allow us to answer your specific question without diving into the wrong technical details.

Cheers,

-Claw