Looks like I dumbed my post down a little too much.
I'm a commercially rated pilot, so I try not to over do it on messageboards.
Per "relative wind," yes, you are always flying within a small angle of it in most normal situations. Unless you're doing Sean Tucker style aerobatics, the angle between your flight path and your direction of travel is within a few degrees.
The opposite is true. The airplanes ground track is the sum of its propulsion through the "relative wind", and the force and direction of the wind as measured against the ground. In this sense, the pilot is ALWAYS under the influence of wind, regardless of its direction. That is, the airplane has a 360 in 360 chance of being affected by the wind, unless the wind velocity is zero -- the same as a hot air balloon.
Again, dumbed that statement down a little too much. I didn't say that it wasn't affected by the wind, rather that the only time you're generally safe the assume the wind is coming mostly as a headwind, is on take off and landing. I've been flying for 15 years, and I've only done a few quartering tailwind landings.
Don't get me wrong, I'm not saying that an airplane either A. doesn't have to have airspeed to fly, B. it's not at a small angle to the relative wind, or C. it isn't affected by the wind.
Also, the 1/360 comment means if winds are 210@40, the only heading you can fly to point the nose directly into the wind is 210 (and if you slow flight dirty, you'll hang out in the same spot...I love doing that in the late afternoon when the winds near the coast are up).
I also would have an issue with a yaw string on my windscreen in a car. I'd always want to fight the urge to coordinate the airpla...I mean car.
Wait...thinking that one through, if you're on the freeway, and not sliding the Leaf, you'd be pointed into the relative wind coordinated, so you'd just have a piece of yarn on your windscreen telling you that you're coordinated, unless you had a massive crosswind (which is possible, but not terribly common).