bjnorman,

I'll just add a couple things to Jim's comments. When the chord is not constant, the AR is defined as the square of the span, divided by the area of the wing.

Higher aspect ratio wings are more efficient than lower aspect ratio wings specifically in the area of induced drag. Induced drag is the component of drag which is caused by the wing tip vortices ( a slight simplification ). All wings have some induced drag, but high aspect ratio wings have less than low aspect ratio wings. It is useful to keep in mind that induced drag is not always the most important component of drag. It is generally significant during the high-lift parts of a flight, which means flying slowly or turning sharply. Also, increasing aspect ratio may not be favorable for the other components of drag.

The lift curve slope refers to the slope of the curve that you get when you plot the coefficient of lift vs. angle of attack. As Jim points out, higher aspect wings have steeper lift curve slope, which is to say that lift increases faster as you increase the angle of attack. This can be a good thing or a bad thing, depending on the situation.

Higher aspect wings will generally have slower roll rates, which matters if you have aerobatics in mind. One other factor related to aspect ratio is chord length. If you keep the total wing area constant, then a higher aspect ratio wing will have a shorter chord, which means it will operate at a lower Reynold's number, which can be a disadvantage, especially if the plane will fly a slow speeds.

Most of the other implications of aspect ratio that pop into my head are structural in nature.

banktoturn