Skuzzy,
It's semantics at this point, but the broad approach I was taught dealt with wing design almost like a series of families or categories of wing shapes. Straight unswept without taper would in general behave like *this*, swept would behave like *this*, add taper to the chord and *this* happens, thin the airfoil out towards the tip to address *this* performance drawback which results in *this* other thing... A "delta" wing was merely a roughly triangular shape that would have basic characteristics that were similar and predictable to all "delta" shapes. So you could either pick a generic planform based on the performance characteristics you wanted when you were designing a plane, or if you had an existing design you were trying to test or characterize, you could predict various performance and behavior modes just by looking at the shape and airfoil, and make some assumptions as you started collecting hard data to refine the predictive models, come up with stability augmentation laws, or whatever.
I can look at the planform of any opponent's fighter, and just from looking at the planform view make a good guess as to how I want to fight it, what its good at, and what it sucks at. Without anyone telling me, I can look at a mirage 2000 and know it has one awesome bat-turn that would be deadly at the merge, and it can probably cruise very fast and efficiently with a fairly heavy loadout. But in a sustained turn I can probably out rate it unless I get way too slow as well. The mig-21 has great low speed handling so don't try to win a flat scissors against one, because he can roll faster than I can at low speeds and he can probably get some good AOA to point the nose even when slow, but he'll be bleeding speed fast if he keeps pulling.
Just look at the differences between a spitfire with elliptical wingtips and a cropped-tip spitty. The elliptical planform has very low drag and good handling up to the stall, but the stall almost immediately makes the ailerons useless because of where the flow separation begins on that kind of wing. Crop the tips and you get a completely different (and predictable) set of behaviors in various flight regimes. Adding winglets is another way you can have a very wide variety of wingtip shapes, but they all do things like change the lift distribution across the span and increase loading on the outboard wing, in addition to reducing wingtip vortice drag. The exact shape doesn't matter when considering what ought to happen, you get certain performance changes almost no matter what the actual winglet looks like. The shape DOES matter when you need to know how much things have changed, but only in terms of how much each aero characteristic is changed by the presence or absence of the wingtip device.
And that's because wing shapes can be understood in terms of very broadly defined categories, and you can make a good guess as to how it'll fly in general. Knowing this, you can even predict what happens when the general shape is modified in some way. Like putting swept and cropped wingtips on an F-15 for the area that has the ailerons, you get some behaviors of a delta wing but the wing will have some of the airflow characteristics of a swept wing over just the ailerons and wingtips. They started with a delta wing shape, and modified it to achieve certain behaviors.
Does that make any sense or are we talking in circles still?
