Drag: Definition, Types, Difference, Equation, Examples

Drag is the force that opposes the motion of an object through a fluid. Drag involves factors including velocity, area, and fluid properties. Drag manifests in various types, each with characteristics and applications. Drag is quantified using equations that incorporate variables. Learn about drag's definition, types, equation, and examples to understand its impact on systems and objects.

Parasite drag and induced drag are two types of drag experienced by aircraft. Parasite drag opposes aircraft motion due to shape and surface irregularities. Induced drag results from lift generation and wingtip vortices. Parasite drag increases with airspeed squared and dominates at faster speeds. Induced drag decreases with increasing airspeed and dominates at slower speeds. Aircraft shape and surface irregularities affect parasite drag. Lift generation and angle of attack influence induced drag.

The drag equation is F = 1/2 ρ v² Cd A. F represents drag force measured in Newton. ρ represents fluid density, which varies with altitude and temperature. v represents velocity, which has a squared relationship to drag force. Cd represents drag coefficient, dependent on object geometry and flow conditions. A represents reference area, the projected frontal area facing fluid flow. Air density at sea level is 1.225 kg/m³ (0.0765 lb/ft³) at 15°C (59°F). Doubling an object's speed quadruples the drag force.

Drag examples include air resistance on skydivers, cars, and aircraft. Water resistance drag affects swimmers and boats. Wind drag impacts structures facing wind forces. Fluid resistance drag occurs in pipes due to fluid movement. Lift-induced drag occurs in aircraft from lift generation. Interference drag occurs where vehicle or aircraft components meet. Hull skin friction drag affects marine vessels due to surface roughness. Parachutes utilize pressure drag to slow descent. Spacecraft encounter atmospheric drag during reentry, affecting descent trajectory and causing intense aerodynamic heating. Drag coefficients for objects range from 0.1 for streamlined shapes to 1.0 for blunt shapes.

What is the definition of drag in an airplane?

Drag in an airplane is a force that opposes the aircraft's motion through air. Drag is generated by interaction between the airplane's body and surrounding fluid. Every part of the aircraft produces drag, necessitating thrust to maintain flight.

Parasite drag results from skin friction, form drag, and pressure drag on the airplane's surfaces. Induced drag is generated by wingtip vortices and relates to lift production. Wave drag occurs at transonic and supersonic speeds due to shock waves.

Airplane configuration and geometry influence drag characteristics. Long, thin wings produce less induced drag than short, wide wings. Smooth surfaces and streamlined shapes minimize skin friction and form drag. Air properties like density and fluid characteristics affect drag magnitude. Higher air density at lower altitudes increases drag on aircraft.

The drag coefficient is a dimensionless parameter measuring aerodynamic efficiency. Lower drag coefficients indicate better efficiency and less drag. The drag equation calculates drag force using parameters like velocity and air density. Drag force increases with the square of airspeed in flight.

Drag opposes the aircraft's motion through air on all components. Wings experience increased drag with higher angles of attack. The fuselage and other surfaces contribute to total drag. Fairings reduce interference drag between aircraft components. Drag management is fundamental for aircraft performance and fuel consumption.

What is induced drag?

Induced drag is a consequence of creating lift when a moving object redirects airflow. Induced drag occurs due to vortex formation at wingtips, resulting from pressure differences above and below the wing. Induced drag increases at lower airspeeds and is reduced by increasing wingspan or using wingtip devices.

Lift force generation correlates with induced drag. Pressure difference between the upper and lower wing surfaces creates lift. Lift angle dependence affects the magnitude of induced drag. Induced drag increases with the square of lift produced.

Wingtip vortices form due to air flowing from high to low pressure areas. Wake formation behind aircraft results from these vortices. Energy loss occurs as air swirls in the vortices. Induced drag performance loss requires power to overcome.

Downwash deflects air downward behind the wing. Velocity changes in surrounding air alter the angle of attack. Impact on effective angle of attack increases induced drag.

Wing geometry influences induced drag. Aspect ratio and the span-to-chord ratio, affects efficiency. Higher aspect ratio wings have lower induced drag. Span efficiency factor measures wing efficiency. Swirl loss quantification helps optimize wing design. Design parameter considerations include lift distribution along the span.

Angle of attack affects lift generation and induced drag. Incidence angle determines the amount of lift produced. Relationship to induced drag shows increased drag at higher angles. Stall characteristics limit the maximum usable angle of attack.

What is form drag?

Form drag is a type of drag caused by object interaction with fluid. Form drag arises from pressure differences created around an object due to its shape and size. Separation of the boundary layer from the object's surface creates a low-pressure wake behind it, contributing to form drag.

Pressure drag results from the imbalance of pressure around an object moving through a fluid. Higher pressure at the front and lower pressure at the rear create a net force opposing motion. The shape of an object influences form drag. Objects with larger frontal areas or blunt shapes experience form drag due to increased flow separation and wake turbulence. Streamlined shapes reduce form drag by minimizing boundary layer separation and pressure differentials.

The drag coefficient (C_D) serves as a dimensionless shape factor quantifying an object's drag relative to its size and fluid properties. Lower C_D values indicate more aerodynamic shapes with reduced form drag. Boundary layer separation occurs when the flow detaches from the object's surface at the separation point. Flow instability in the separation region leads to wake formation behind the object. Wake turbulence and vortex formation increase energy dissipation, contributing to the drag force. Recirculation in the separation region creates turbulence and pressure imbalances.

Pressure distribution around an object varies, with higher pressures at the leading edge and lower pressures at the trailing edge. The pressure gradient along the surface affects flow separation and drag magnitude. Form drag relates to the extent of flow separation - greater separation results in higher drag forces. The drag force (F_D) is calculated using the equation F_D = 1/2 ρ v^2 A C_D, where ρ is fluid density, v is velocity, A is cross-sectional area, and C_D is the drag coefficient. Form drag constitutes a portion of parasite drag, alongside skin friction drag and interference drag. Minimizing form drag through streamlined shapes and optimized geometries is fundamental for refining aerodynamic efficiency in vehicles and aircraft.

What is interference drag?

Interference drag is the drag caused by airflow interactions between aircraft components, at junctions where airflows from separate surfaces meet, resulting in turbulence and disrupted flow patterns. Airflow interactions cause turbulence, flow separation, and disrupted patterns. Wing-fuselage junctions and wing-nacelle intersections experience interference drag. Angles between intersecting surfaces increase interference drag severity. Aerodynamic modeling and filleting of junctions reduce interference drag. Computational fluid dynamics analyzes interference drag effects during aircraft design.

Interference drag mechanisms involve intricate airflow interactions between aircraft components. Velocity changes occur as air passes through restricted junction areas, increasing airflow speed and energy consumption. Pressure distribution alterations result from mixing flows, contributing to turbulence and drag. Turbulence generation creates unpredictable flow patterns, disrupting smooth airflow over surfaces.

Constituent geometry and configuration influence interference drag levels. Wing shape impacts airflow behavior at junctions, while optimal junction locations minimize drag. Fuselage body shape and contour affect interference with other components, with smooth contours reducing drag. Junction angles between intersecting surfaces play a part, as sharp angles exacerbate interference drag severity.

Aerodynamic interference manifests through flow interactions between components, disrupting airflow patterns. Pressure overlap effects from surfaces contribute to interference, altering pressure distributions. Airflow distortion patterns emerge as a result, increasing drag and reducing aerodynamic efficiency.

Wing-body junctions present difficulties in managing interference drag. Discontinuities at these junctions force airflow to accelerate through restricted spaces. Junction gaps exacerbate interference effects, creating turbulence. Increased risk of flow separation exists at these areas, leading to severe drag penalties.

Flow separation consequences compound interference drag issues. Boundary layer detachment from surfaces occurs when airflow cannot negotiate turns or adverse pressure gradients. Formation of turbulent wakes behind separated flows increases aircraft drag. Vortex generation and propagation from separated flows create disturbances, disrupting airflow and increasing drag.

What is friction drag?

Friction drag is a force opposing object motion through fluid. Friction drag results from fluid layers rubbing against object surfaces. Friction drag increases with velocity and surface area. Surface roughness and fluid viscosity influence friction drag magnitude. Smoothing surfaces reduces friction drag effects.

Skin friction drag is an element of friction drag. Skin friction drag arises from direct fluid-surface interactions in the boundary layer. Surface texture and roughness influence skin friction drag magnitude. Smoother surfaces result in lower skin friction drag. Shear force magnitude and distribution affect friction drag. Higher shear forces lead to increased friction drag on the object's surface.

Viscosity creates resistance to fluid motion, increasing friction drag. Higher fluid density results in greater dynamic pressure and friction drag. Rougher surfaces promote turbulence and increase shear stresses. Boundary layer formation is influenced by surface texture, affecting friction drag.

Boundary layer thickness and velocity gradient impact friction drag magnitude. Thicker boundary layers with steeper velocity gradients result in higher friction drag. Flow regimes affect friction drag characteristics. Laminar flow exhibits orderly fluid motion with lower shear stresses. Laminar flow produces less friction drag compared to turbulent flow. Turbulent flow demonstrates chaotic fluid behavior with considerable mixing. Turbulent flow generates increased shear stresses and increased friction drag. Reynolds number serves as a dimensionless indicator of flow regime. Reynolds numbers indicate turbulent flow conditions, leading to friction drag.

The friction drag coefficient relates wall shear stress to freestream dynamic pressure. Turbulent flat plate friction drag coefficient is estimated using Reynolds number. The frictional force equation incorporates fluid density, velocity, drag coefficient, and surface area. These calculations provide quantitative assessments of friction drag for objects and flow conditions.

What is wave drag?

Wave drag occurs when an object moves through a fluid at transonic or supersonic speeds, resulting in the formation of shock waves. Shock waves form when airflow accelerates to sonic speed, around Mach 1. Pressure jumps across shock waves contribute to aircraft drag in transonic and supersonic flight regimes. Supersonic flight involves velocities exceeding the speed of sound, above Mach 1.0. Critical Mach number, 0.8 for many aircraft, marks the onset of wave drag increase. Oblique shockwaves form at the leading and trailing edges of aircraft in supersonic flight. Airfoil geometry affects wave drag, with thickness and curvature directly influencing shock wave formation. Swept wings and supercritical airfoils have been developed to mitigate wave drag while maintaining lift at lower speeds.


Transonic flight occurs at speeds around Mach 0.8 to 1.2. Airflow reaches supersonic speeds on parts of the aircraft in this regime. Critical Mach number marks the onset of considerable wave drag increase, around Mach 0.8 for most aircraft. Drag divergence phenomenon occurs as the aircraft approaches and exceeds this threshold. Mach number, the ratio of object velocity to speed of sound, determines the onset and severity of wave drag.

Airfoil geometry plays an important part in wave drag formation. Airfoil curvature and thickness influence shock wave formation. Reducing curvature and thickness helps minimize wave drag, but must be balanced with lift generation needs. Swept wings make the wing appear thinner to the airflow, reducing shock wave formation. Supercritical airfoils minimize wave drag while maintaining lift. Area rule shapes the fuselage to match the Sears-Haack body, assuring smooth cross-sectional area transition and reducing wave drag.

What is parasite drag?

Parasite drag is the resistance to aircraft motion through air that includes form drag, skin friction drag, and interference drag, opposing movement without relation to lift generation. Form drag arises from aircraft shape disrupting airflow, depending on frontal area and pressure distribution. Skin friction drag results from air viscosity and surface roughness, influenced by boundary layer configuration. Interference drag occurs at junctions of aircraft components, causing flow interference and increased turbulence. Parasite drag increases with the square of airflow velocity. Induced drag decreases with increasing speed. Streamlining aircraft geometry reduces airflow effects and optimizes aerodynamic performance.

Parasite drag consists of three components: form drag, skin friction drag, and interference drag. Form drag depends on the aircraft's shape and frontal area, creating resistance as it moves through the air. Skin friction drag arises from air molecules interacting with the aircraft's surface, influenced by surface roughness and viscosity effects. Interference drag occurs at junctions between aircraft components, causing turbulence and flow disruption.

Aircraft geometry and configuration impact parasite drag. Streamlined designs minimize form drag by reducing frontal area and optimizing pressure distribution. Arrangement of aircraft parts affects interference drag, with specific positioning reducing negative interactions. Drag increases with the square of airspeed, leading to increased resistance at faster velocities. Turbulence and flow separation exacerbate drag in areas with adverse pressure gradients.

Boundary layer behavior influences skin friction drag. Thicker boundary layers and earlier transition points from laminar to turbulent flow increase drag. Separation due to adverse pressure gradients contributes to parasite drag. The drag coefficient serves as a non-dimensional measure of aerodynamic efficiency, with lower values indicating better performance. Reynolds number characterizes flow regimes and allows for scaling comparisons between different aircraft sizes.

Surface optimization techniques reduce skin friction drag. Smooth textures and minimal irregularities decrease air molecule interactions with the aircraft surface. Streamlining strategies focus on design optimization to minimize form drag. Teardrop shapes experience less drag than blunt objects, guiding aircraft designers in creating geometries. Retractable landing gear reduces form drag during cruise flight by 25-30%.

What is the difference between parasite drag and induced drag?

The difference between parasite drag and induced drag is that parasite drag opposes aircraft motion through air due to aircraft shape and surface irregularities, while induced drag results from lift generation and wingtip vortices. Parasite drag increases with the square of airspeed, becoming dominant at faster speeds. Induced drag decreases with increasing airspeed, dominating at low speeds. Aircraft shape and surface irregularities affect parasite drag, while lift generation and angle of attack influence induced drag. Aerodynamicists categorize drag into different types of drag, including form drag, skin friction drag, and interference drag for parasite drag. Wing aspect ratio impacts both lift and drag, with higher aspect ratios reducing induced drag but increasing parasite drag due to larger surface area.

Skin friction drag results from air molecules interacting with the aircraft surface. Form drag arises from the shape of the aircraft disrupting airflow. Surface roughness contributes to parasite drag through scale irregularities on the aircraft exterior.

Lift dependency means induced drag increases as lift production rises. Vortex formation occurs at wing tips due to pressure differences between upper and lower surfaces. Wingtip vortices create a downwash effect, reducing the effective angle of attack and generating induced drag.

Lift magnitude and coefficient affect induced drag, with higher lift values increasing induced drag. Total aerodynamic resistance force combines parasite and induced drag effects on the aircraft. Drag coefficient serves as an efficiency indicator, with lower values representing better aerodynamic performance.

Wing geometry and planform shape affect both parasite and induced drag. Angle of attack influences lift generation and drag production, with higher angles increasing both lift and induced drag. Wing aspect ratio, the span-to-chord ratio, affects aerodynamic efficiency. Aspect ratios reduce induced drag but increase parasite drag due to larger surface area.

What is the difference between drag and friction?

The difference between drag and friction is their nature and conditions affecting their occurrence. Friction opposes motion between contacting surfaces, while drag resists objects moving through fluids. Friction depends on surface properties and normal force, whereas drag relates to object speed, shape, and fluid density.

The difference between drag and friction is outlined in the table below.

Drag encompasses types of fluid resistance. Pressure drag results from differences in fluid pressure around an object. Form drag arises from the shape of an object moving through a fluid. Skin friction drag occurs due to friction between the fluid and the object's surface. Friction involves contact resistance between solid surfaces. The coefficient of friction determines the strength of frictional forces. Static friction prevents objects from starting to move. Kinetic friction acts on objects in motion.

Fluid density and viscosity influence drag forces. Higher fluid density increases drag on objects moving through it. Relative speed between the object and fluid affects drag magnitude. Flow velocity determines the strength of drag forces experienced. Normal force impacts friction between surfaces. Greater normal force leads to stronger frictional resistance. Surface roughness enhances friction by increasing contact area between surfaces. Irregular surface textures promote increased friction coefficients.

Viscosity measures a fluid's resistance to flow. Dynamic viscosity quantifies the friction of a fluid. Fluid thickness correlates with viscosity values. The Reynolds number is a dimensionless parameter in fluid mechanics. Reynolds number values determine flow regimes as laminar or turbulent. Lower Reynolds numbers indicate laminar flow, while higher values suggest turbulent flow.

What is the aerodynamic drag equation?

The aerodynamic drag equation is F = 1/2 ρ v² Cd A, where F is drag force, ρ is fluid density, v is velocity, Cd is drag coefficient, and A is reference area. This equation calculates drag force on objects moving through fluids like air.

The drag force (F) represents the resistance experienced by an object moving through a fluid. Drag force is measured in Newton and opposes the object's motion. Fluid density (ρ) varies with altitude and temperature, impacting drag force calculations. Air density at sea level is 1.225 kg/m³ (0.0765 lb/ft³) at 15°C, decreasing with increasing altitude.

Velocity (v) has a squared relationship to drag force in the equation. Doubling an object's speed quadruples the drag force, making velocity fundamental in speed applications. The drag coefficient (Cd) depends on object geometry and flow conditions. Streamlined shapes have lower drag coefficients than blunt objects. A sphere has a drag coefficient of 0.47, while a plate perpendicular to flow has a coefficient around 1.28.

Reference area (A) is the projected frontal area facing fluid flow. Aircraft use wing area as a reference area, while cars use the frontal area. The choice of reference area affects drag coefficient values and must be specified when reporting results. Dynamic pressure (1/2 ρv²) represents the fluid pressure resulting from motion. Dynamic pressure equals the kinetic energy per unit volume of the fluid and influences drag force calculations.

Engineers apply the aerodynamic drag equation to optimize designs in aerospace, automotive, and sports equipment industries. Wind tunnel experiments determine drag coefficient values for object shapes and orientations. Minimizing drag coefficients and optimizing object shapes reduce drag forces, refining performance and efficiency in world applications.

What is the relationship between lift and drag?

The relationship between lift and drag involves aerodynamic forces acting on aircraft. Lift is directed perpendicular to the flight path, keeping planes airborne. Drag opposes motion along the flight path. Aircraft shape, size, and speed influence both forces. Understanding this relationship optimizes aircraft performance.

Aircraft shape, angle of attack, air density, and velocity all influence lift and drag. Lift and drag coefficients are dimensionless parameters characterizing aerodynamic performance. Coefficients vary with angle of attack and flow regime. Lift generation occurs through pressure differences created by airfoil shape. Wings generate lift by causing faster airflow over the surface.

Induced drag results from lift generation and increases with the square of lift coefficient. Vortices form at wingtips due to pressure differences, contributing to induced drag. Airfoil geometry influences the lift and drag relationship. Camber and shape influence lift generation and drag reduction. Angle of attack affects aerodynamic forces. Increasing angle of attack raises both lift and induced drag up to the stall point.

Lift-to-drag ratio (L/D) serves as a performance metric. Higher L/D ratios indicate better aerodynamic efficiency. Typical commercial airliners achieve L/D ratios of 15-20, while gliders exceed 50. L/D ratio impacts aircraft range, endurance, and fuel efficiency. Balancing aerodynamic forces is vital for flight performance. Level flight requires lift to equal weight and thrust to match drag. Aircraft designers aim to maximize L/D ratio across flight regimes. Optimizing the lift-drag relationship involves trade-offs between lift generation and drag minimization.

What is ram drag?

Ram drag is a type of drag in gas turbine engines that occurs when stream air enters the inlet. Ram drag represents the difference between gross and net thrust, resulting in a loss of thrust due to energy required to accelerate air.

Ram drag coefficient relates to the efficiency of air capture and compression in the engine inlet. Lower coefficients indicate better inlet design and reduced drag. The ram drag force is influenced by pressure and velocity changes during air intake. Airflow deceleration and compression lead to energy losses, contributing to ram drag.

Turbojet engines have a simpler intake system compared to turbofans. All air entering a turbojet is compressed and used for combustion. Turbojet performance is influenced by compression ratio and inlet design. Turbofan engines include a fan at the front that accelerates a portion of air around the core engine. Bypass ratio in turbofans affects engine performance and efficiency. Bypass ratios boost propulsive efficiency at subsonic speeds but increase drag at supersonic speeds due to larger frontal area.

Air inlet geometry helps in minimizing ram drag. Efficient inlet designs aim to recover as much dynamic pressure as possible while decelerating airflow. Inlet area and flow deceleration are vital factors in inlet design. The intake diffuser's function is to decelerate airflow while recovering as much pressure as possible. Diffuser geometry and efficiency impact ram drag. Designed diffusers minimize pressure losses and reduce drag force associated with ram drag.

Compressibility effects become important at Mach numbers above 0.8. Pressure waves and density variations occur as air approaches the speed of sound. Shock waves form as aircraft approaches or exceeds Mach 1, leading to increased drag. Shock wave strength and pressure jump contribute to ram drag by increasing drag force magnitude.

Ram drag force acts opposite to the direction of motion, contributing to drag. The magnitude of ram drag is influenced by dynamic pressure and efficiency of the intake diffuser. Ram drag results in performance reduction by decreasing net thrust available for propulsion. Thrust loss occurs at higher speeds where inlet conditions become critical.

Pressure is proportional to air density and the square of velocity, given by Pd = 1/2ρv^2. Velocity and air density are factors in determining dynamic pressure. Dynamic pressure plays a part in determining ram drag force, influencing pressure distribution around the inlet.

What are examples of drag?

Examples of drag include air resistance on skydivers, cars, and aircraft; water resistance on swimmers and boats; wind force on structures; and fluid resistance in pipes. Drag opposes motion through fluids, affecting activities and systems.

Examples of drag are provided in the list below.

• Air resistance drag: Experienced by skydivers, cars, and aircraft when moving through air.
• Water resistance drag: Experienced by swimmers and boats moving through water.
• Wind drag: Experienced by structures facing wind forces.
• Fluid resistance drag: Experienced in pipes due to fluid movement.
• Lift-induced drag: Occurs in aircraft from the generation of lift.
• Parasite drag: Includes form drag, skin friction drag, and interference drag on aircraft.
• Wave drag: Experienced at supersonic speeds by aircraft, causing shockwaves.
• Profile drag: Combination of form and skin friction drag on airfoils.
• Form drag: Encountered by vehicles and is dependent on shape.
• Interference drag: Occurs in vehicles and aircraft where components meet.
• Hull skin friction drag: Experienced by marine vessels due to surface roughness.
• Viscous drag: Experienced by marine vessels due to water viscosity.
• Pressure drag: Utilized by parachutes to slow descent.
• Re-entry atmospheric drag: Experienced by spacecraft during descent.

Aircraft experience different types of drag during flight. Lift-induced drag results from the generation of lift, increasing at low speeds due to higher angles of attack. Parasite drag includes form drag from aircraft shape, skin friction drag from surface roughness, and interference drag at unit junctions. Wave drag occurs at supersonic speeds, causing shockwaves. Profile drag combines form and skin friction drag on airfoils.

Vehicles encounter form drag dependent on their shape. Streamlined cars experience less form drag than blunt shapes. Interference drag occurs where components like bumpers and hoods meet. Marine vessels face hull skin friction drag from surface roughness and viscous drag from water viscosity.

Parachutes utilize form drag to slow descent. The canopy creates a pressure differential, resulting in pressure drag. Gliders experience parasite drag from their shape and surface, lift-induced drag from wing lift and vortex formation.

Parasite drag encompasses non-lifting drag and surface drag. Skin friction drag relates to viscous friction and surface roughness. Form drag results from pressure differentials and shape. Interference drag occurs at junctions and part interactions. Lift-induced drag involves vortex formation and circulation. Wave drag is associated with shock waves and compressibility effects. Base drag results from wake formation and pressure loss behind objects.

Spacecraft encounter atmospheric drag during reentry, affecting descent trajectory. Re-entry drag causes intense aerodynamic heating. Air density at sea level is 1.21 kg/m³ (0.075 lb/ft³). An 85-kg (187 lbs) skydiver reaches a terminal velocity of 44 m/s (144 ft/s) due to drag forces.