On a constant-chord wing the distribution of lift coefficient has the same shape as the distribution of gross lift. (Note that this is a local 2-dimensional lift coefficient as opposed to the full-wing 3D lift coefficient that is computed using total wing lift and wing area.) The local lift coefficient is the local lift per running distance divided by the local wing chord and the dynamic pressure of the airflow. We now turn our attention to the distribution of local lift coefficient over the wing. Up until now, we have been looking at the distribution of absolute lift across the span. While this is a subject very dear to my heart, today’s discussion is for more “conventional” wing aspect ratios. Low aspect ratio wings behave differently. Note that this is true only for wings with aspect rations higher than about 2.5. The range of taper ratios for good tapered wings runs from approximately 0.5 to not smaller than between 0.2 and 0.25. Also, as we will see soon, highly tapered wings tend to stall from the tips inboard, which can produce very unpleasant stall characteristics. If the wing is tapered too much, it becomes excessively root loaded and its span efficiency deteriorates. While pure structural considerations may suggest a wing with a pointed tip or very high taper (small tip chord i.e., small taper ratio), there are limits to this. The situation is not that simple, however.
Accordingly, tapered wings will have a higher span efficiency and lower induced drag at the same span and total lift.Īll of these factors infer that tapered wings should be the obvious choice for a designer. In terms of aerodynamic efficiency, we also saw that properly tapered wings have a span loading that is closer to elliptical than a constant-chord wing. Both of these factors reduce the structural weight of the wing. Last month we saw how tapering the wing moves the centroid of the wing load inboard, reducing bending moment at the root and also how taper makes the spar deeper at the root. In the last few months, we have explored how planform and taper affect both the distribution of total lift across the span and the weight of the wing structure.
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