What Is Induced Drag In Aviation
Tsunami Air • • Reading time: 8 min
Induced drag is a type of drag that occurs as a byproduct of lift generation on aircraft wings. Induced drag results from the airflow patterns created around a three-dimensional airfoil as it produces lift. The force of induced drag relates to the wing shape, aircraft speed, and amount of lift being generated. Induced drag plays a part in aircraft performance and efficiency. Understand how induced drag impacts aerodynamics, flight characteristics, and fuel consumption of aircraft designs.
Air flows from high-pressure areas to low-pressure areas around wings, creating wingtip vortices. Wingtip vortices contribute to drag and represent energy lost to air instead of motion. Lift pressure difference creates wingtip vortices between wing surfaces, causing a downwash wake behind the wing. Aerofoil design impacts induced drag through its shape and camber. Wings with higher aspect ratios produce reduced induced drag, as aspect ratio inversely correlates with induced drag.
The dimensional induced drag equation is expressed as Di = L^2 / (0.5 * ρ0 * VE^2 * π * b^2). L represents lift, ρ0 represents air density, VE represents airspeed, and b represents wingspan. Induced drag coefficient is calculated as CD,i = CL^2 / (π * AR * e). CL represents lift coefficient, AR represents aspect ratio, and e represents Oswald efficiency factor. Aspect ratio is calculated as wingspan squared divided by wing area. Higher aspect ratios result in more efficient wings and reduced induced drag. Efficiency factor ranges from 0.7 to 0.95, with higher values indicating better overall wing performance and lower induced drag. Sea level air density is 1.225 kg/m³ (0.0765 lb/ft³). Speeds reduce induced drag for a given lift.
What is induced drag in aviation?
Induced drag in aviation is a consequence of lift production. Air flows from high-pressure areas below wings to low-pressure areas above, creating wingtip vortices. These vortices contribute to drag, representing energy lost to air instead of motion.
Airflow and pressure dynamics influence induced drag formation. Lift pressure difference between the upper and lower surfaces of the wing creates wingtip vortices. Wingtip vortices trail behind the wing, causing a downwash wake and deflecting airflow. Downwash flow disturbance increases the angle of attack, contributing to induced drag.
Aerofoil shape and camber influence lift efficiency and vortex strength. Angle of attack affects lift magnitude and induced drag intensity. Higher angles of attack increase pressure difference and wingtip vortex strength. Aspect ratio, the ratio of wingspan to chord length, inversely correlates with induced drag. Wings with greater aspect ratios produce less induced drag due to wingtip vortices.
Prandtl Lifting-Line Theory approximates wings as lifting lines to estimate induced drag. The induced drag force equation is Di = L^2 / (0.5 * ρ0 * VE^2 * π * b^2), where L is lift, ρ0 is air density, VE is airspeed, and b is wingspan. Induced drag coefficient is expressed as CD,i = CL^2 / (π * AR * e), where CL is lift coefficient, AR is aspect ratio, and e is Oswald efficiency factor.
Induced drag represents an unavoidable aerodynamic penalty associated with lift generation. Lift production relates to induced drag magnitude. Efficient wing design and operations minimize but cannot eliminate induced drag. Induced drag is a constituent of total aircraft drag, affecting overall aerodynamic performance. Understanding induced drag enables optimization of aircraft design and flight efficiency.
What are the types of induced drag?
The two types of induced drag are given below.
- Lift-induced drag: Results from the tilting of the lift vector rearward due to downwash behind the wings.
- Vortex drag: Caused by the formation of wingtip vortices, which create rotational airflows and disturb the surrounding air.
The types of induced drag include lift-induced drag and vortex drag, which result from lift generation and wingtip vortices. Angles of attack increase both types of induced drag. Wing design plays a part in managing induced drag, with higher aspect ratio wings reducing its effects. Induced drag dominates over parasite drag at low speeds, during takeoff and landing phases.
What is the difference between induced drag and parasite drag?
The difference between induced drag and parasite drag is explained in the table below.
Induced Drag | Parasite Drag |
Results from lift generation and wingtip vortices, typically around 10-20% of total drag at low speeds. | Arises from aircraft-air interaction independent of lift production, including form, skin friction, and interference drag. |
Varies inversely with airspeed, becoming significant at velocities below 150 knots. | Increases with the square of airspeed (m/s), dominating at speeds above 250-300 knots. |
Wing aspect ratio plays a role, with ratios above 7-9 reducing effects by up to 20% and improving lift efficiency. | Aircraft shape and surface characteristics determine magnitude; streamlined shapes with fineness ratios of 3-4 reduce drag by reducing cross-sectional area. |
Depends on lift generation; higher lift coefficients (e.g., Cl > 1.5) increase drag. | Comprises form drag, skin friction drag, and interference drag, totaling about 50-70% of total drag at high speeds. |
Vortex induction intensifies at slower speeds (e.g., below 100 knots) and higher angles of attack (e.g., α > 10°). | Surface roughness increases skin friction drag by disrupting the boundary layer, adding up to 10% more drag. |
Higher lift coefficients (e.g., Cl > 2.0) result in increased drag due to stronger wingtip vortices. | Becomes the primary factor above 250-300 knots for most aircraft, contributing significantly to total drag. |
Wingtip vortex intensity increases with lift production, especially during takeoff and landing. | Affects aircraft performance by increasing fuel consumption and reducing range at high speeds. |
Wing design balances structural considerations with aerodynamic efficiency to minimize drag. | Optimized through materials and coatings that reduce surface roughness and friction. |
The difference between induced drag and parasite drag is that induced drag results from lift generation and wingtip vortices, while parasite drag arises from aircraft-air interaction independent of lift production. Induced drag varies inversely with airspeed, becoming substantial at lower velocities. Parasite drag increases with the square of airspeed, dominating at increased speeds. Wing aspect ratio influences induced drag formation, with higher ratios reducing its effects. Aircraft shape and surface characteristics determine parasite drag magnitude. Flight efficiency requires balancing induced and parasite drag contributions.
Induced drag depends on lift generation. Higher lift coefficients result in increased induced drag. Vortex induction intensifies at slower speeds and higher angles of attack. Angles of attack above 15-20 degrees cause airflow separation and stalling. Wing aspect ratios above 7-9 reduce induced drag effects.
Parasite drag comprises form drag, skin friction drag, and interference drag. Surface roughness increases skin friction drag by disrupting the boundary layer. Streamlined shapes with fineness ratios of 3-4 minimize form drag through pressure distribution. Parasite drag increases with the square of airspeed, becoming the primary factor above 250-300 knots for most aircraft.
Lift acts perpendicular to the wind direction. Lift coefficients range from 0.2-1.5 for subsonic aircraft. Wingtip vortex intensity increases with lift production. Vortex circulation strength affects induced drag magnitude.
Wing aspect ratio is defined by the span-to-chord ratio. Aspect ratios above 12-15 minimize wingtip vortex circulation. Longer, narrower wings reduce induced drag than shorter, wider wings. Wing design balances structural considerations with aerodynamic efficiency.
What is the equation for induced drag coefficient?
The equation for induced drag coefficient (C_{di}) is C_{di} = C_L^2 / (π × AR × e). C_L represents lift coefficient, AR denotes aspect ratio, and e is efficiency factor. This equation shows the coefficient's direct proportionality to lift squared and inverse relationship with aspect ratio and efficiency. Induced drag decreases with increasing aspect ratio. Long, slender wings reduce induced drag.
Lift coefficient (C_L) quantifies the lift force generated by a wing. C_L relates to the magnitude of lift produced. Aspect ratio (AR) measures the wing's slenderness as wingspan squared divided by wing area. Efficiency factor (e) accounts for non-ideal wing effects and ranges from 0.7 to 0.95. A higher efficiency factor indicates better overall wing performance and lower induced drag.
High-aspect-ratio wings produce lower induced drag coefficients. An elliptical wing planform with an aspect ratio of 8 yields an induced drag coefficient of 0.318. A high-aspect-ratio wing with an aspect ratio of 20 reduces the coefficient to 0.212. A delta wing with a 45° sweep angle generates a low induced drag coefficient of 0.159. A low-aspect-ratio wing with an aspect ratio of 2 results in a higher coefficient of 1.592.
A rectangular wing planform with an aspect ratio of 6 produces an induced drag coefficient of 0.785. A tapered wing with a taper ratio of 0.4 yields a coefficient of 0.637. A swept wing with a 30° sweep angle creates a coefficient of 0.509. Configurations offer unique induced drag characteristics. A wing equipped with winglets 1.2 times the chord height reduces the coefficient to 0.424. A biplane configuration with wing spans increases the coefficient to 1.273. A canard configuration with the canard area at 15% of the wing area results in a coefficient of 0.955.
Pi (π) appears in the equation as a mathematical constant with a value of 3.14159. Air density (ρ) affects induced drag, with sea level density around 1.225 kg/m³ (0.0765 lb/ft³). Velocity (v) influences induced drag calculations, with higher speeds reducing induced drag for a given lift. Wing area (S) factors into drag coefficient calculations and affects the lift and drag forces produced.