What is Parasite Drag? | How Does it work?

Parasite Drag: How it Works on Aircraft?

In the aerodynamics of flight, some forces act on the aircraft. These forces are thrust, lift, weight, and drag. You have to understand how these forces work and know how to control them using power and flight controls.

When an aircraft is in flight, drag is the force that resists the movement of a plane through the air. In general, drag is the resistance of an airplane’s movements through the air. The drag force principle isn’t discussed much in terms of aircraft performance and aerodynamics. Total drag is generated from different types of drag and has two major types. In today’s blog, we are going to discuss parasite drag. So, what is parasite drag, and how does it affect your aircraft? Let’s take a thorough look.

What is Parasite Drag?

Parasite drag, also called profile drag, is a categorization of aerodynamic drag caused by the aircraft’s shape, material, and type of construction. It acts on any object when the object is moving through a fluid. For example, a plane with a rough surface creates more parasite drag than a smooth surface. 

This type of drag combines form drag and skin friction drag, affecting all objects regardless of whether they can generate lift. The parasite drag includes all kinds of drag except lift-induced, as it is unrelated to the lift and can take the form of skin friction drag, form drag, or interference drag.

Types of Parasite Drag

There are three basic types of parasite drag: Skin Friction Drag:

Skin friction drag is one of the types of drag force caused by the rough spots on the surface of an airplane. When an aircraft moves in the flight, the rough spots of the plane cause drag by disrupting the smooth airflow over the plane’s surface. For example, Olympic swimmers wear swim caps to reduce the drag caused by their hair and allow them to move swiftly through the water. When you reduce this drag, the aircraft performs better and saves more fuel. Structural sources that cause this drag are rivets and ridges which reinforce the flight controls. Also, if the debris builds in the airframe then it can also cause the skin friction drag. Form Drag: Form or pressure drag is caused simply by an object’s general shape and how it interacts with the relative wind. In the case of aircraft, the form drag is the result of the overall shape of the plane and how that shape interacts with the airflow. Some shapes of airplanes are more aerodynamic than others, and the cleaner the plane moves through the air, the less drag it will create. You have to reduce the cross-sectional area of a wing, and using an aerodynamically designed airfoil can reduce the form drag.

For instance, have you ever put your hand out the car window tilted it flat and vertically into the wind? You may notice that it takes little effort to stick it outside when your hand is horizontal, like an airfoil. However, when you open your hand to the wind, your hand tends to fly backward, and it requires more force to hold its position.  Interference Drag: Interference drag is caused by vortices forming when two surfaces meet at a sharp angle on an airplane. It is created by the acceleration of air into the vortex, which causes drag on the plane. Furthermore, the low-pressure area formed behind the aircraft also contributes to this drag. It can also be created by closely spaced parallel surfaces like the wings of a biplane or triplane, the facing surfaces of an external load, and the fuselage or wing. To reduce the interference drag, remove sharp angles by adding fairings, which smooth out any sharp angles on the plane by forming fillets. Like other types of parasite drag, the interference drag also follows the drag equation and increases with the square of the velocity. Other Drag Forms in Aviation: Here is the list of other drag forms that are important to know.

Wave Drag: The wave drag occurs when the shock waves form near the surface of an airplane during the transonic and supersonic flights. 

Lift-Induced Drag: Lift-induced drag is a byproduct of lift. When higher-pressure air from under the wings flows up and over the top of the wing, it creates lift-induced drag. Wings with a lower aspect ratio create more lift-induced drag than wings with a high aspect ratio.

How to Calculate Parasite Drag?

To calculate the parasite drag, follow the below instructions:

To measure parasite drag, you need computational fluid dynamics, wind tunnel testing, and flight data. You have to combine all of this information to optimize aircraft design. to reduce drag and improve performance.

Then, you need a zero-lift drag coefficient, an essential aerodynamic parameter that indicates the amount of drag experienced by an aircraft when it’s generating zero lift. For instance, the P-51 Mustang has a zero-lift drag coefficient value of 0.0163.

You must use the following equation to calculate the parasite drag DP = ½ ρ V2 C,0 A. This equation uses ρ = air density, V = velocity (airspeed), C,0 = zero-lift drag coefficient, and A = surface area.

Factors Influencing Parasite Drag in Aircraft

The parasite drag is directly proportional to many variables like air density, airspeed, and surface area. For instance, the parasite drag increases with the square of the airspeed. Other factors include flight conditions, shape, configuration, and contamination. 

• Flight Conditions: These include air temperature, humidity, and altitude, which affect air density and, consequently, the amount of parasite drag experienced by an airplane.  

• Shape: The shape of the aircraft or component influences the form drag, which is why airplane manufacturers streamline most components to reduce drag. 

• Configuration: The configuration refers to the position of the airplane landing gear and flaps. Extending either of them will increase the area exposed to the airflow and, as a result, increase form drag.

Contamination: The contamination can increase surface roughness, which increases skin friction drag. There are many contaminants, including dirt, snow, and mud.

Conclusion

In conclusion, parasite drag is a type of aerodynamic drag. It is a crucial factor contributing to the total drag experienced by an airplane. Pilots must know all the components of parasite drag to reduce them. Parasite drag is vital in flight operations, aircraft performance, and fuel efficiency.