Induced drag is the drag produced as a byproduct of generating lift with a finite-span wing. Air flowing from the high-pressure lower surface around the wingtip to the low-pressure upper surface creates trailing vortices. These vortices tilt the local lift vector rearward, producing a component in the drag direction.
The induced drag coefficient is:
C_Di = C_L² / (π × AR × e)
where C_L is the lift coefficient, AR is aspect ratio, and e is the Oswald efficiency factor (0.7–0.95, depending on planform shape). This equation reveals the two levers for reducing induced drag:
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Increase aspect ratio. Doubling AR halves induced drag at the same C_L. This is why long-endurance UAVs (MQ-9 Reaper, ScanEagle) use high-AR wings despite the structural cost.
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Reduce lift coefficient. Fly faster or use a larger wing area. Since C_L appears squared, a small reduction in C_L substantially reduces induced drag — but requires more wing loading analysis to avoid other penalties.
At low speeds and high lift coefficients, induced drag dominates total drag. At high speeds and low lift coefficients, parasitic drag dominates. The crossover speed is the speed for maximum lift-to-drag ratio.
For delta-winged drones with AR 1.5–2.5, induced drag is the dominant drag component throughout the flight envelope, making the delta inherently less efficient than a conventional wing — a trade-off accepted in expendable designs for structural and manufacturing reasons.
Related terms
- Parasitic Drag — the other major drag component, independent of lift
- Aspect Ratio — the geometric parameter that controls induced drag magnitude
- Lift-to-Drag Ratio — the efficiency metric that induced drag directly affects