drag

The drag is a fluid(Liquid and gas) It is parallel in the speed direction of the flow, and, among power to act on an object I move the inside or was put during a flow, it is an ingredient reverse suitable for it. The ingredient which is perpendicular to the speed direction of the flow is called lift (with the plumb upper part, the lift force) and downforce (the plumb lower part).

I divide drag (-, drag coefficient) into the following ingredients and think. About the induced drag, I regard lift about an occurring object like a three-dimensional wing with the wingtip - a structure (fixed-wing aircraft, a rotor blade airplane) including the wing or a lifting body.

Drag to occur with outbreak of the lift in a three-dimensional wing (an in other words general wing) having a wingtip.
When lift occurs, a vortex (a wingtip whirlpool) to sneak around from the bottom to the top occurs in the wingtip because pressure becomes lower in the wing top surface than the lower part. Downward speed (because it blows down, and the equality style declines in the vicinity of a wing by downwash) downward, the lift to occur for the flow perpendicularly will incline to the down stream direction.) that this whirlpool lasts A parallel ingredient becomes the induced drag in equality style of the lift that declined that this, occurred by a limited part style.
I can hang it to the (I approach a two-dimensional wing) a wing is slimmer that is aspect ratio grows big, and the ratio that a wingtip occupies for the whole wing shrinks, and it blows, and the influence of the lowering shrinks. Therefore, I can reduce induced drag. The pressure drag is small enough as far as I do a streamline, and, as for the large reduction of the frictional resistance, it is difficult to be the missile of the subsonic speed in one. Therefore to reduce induced drag; aspect ratio(AR) It is often that an effort to do を greatly (slim by a wing) is paid. This extreme example is roux tongue Voyager and Helios or a glider and a body such as the human-power aircraft, and there is it to an AR = a little less than 40 thing.