Understanding Parasite And Induced Drag
One of the 4 Forces of an airplane is DRAG. Drag pulls the Aircraft backwards. In order to move forward Thrust has to overcome drag. If you stick your hand out of the window when sitting in a moving car the force pulling your hand backwards is called DRAG.
Drag Equation
Do Not Worry it is easier than it looks like ;)
A pilot should not be able to calculate Drag with help of this formula. However he must understand the variables:
- An increase in velocity will result an increase in Drag. Generally speaking, the faster you fly the greater the Drag
- An increase in Density will result in an increase in Drag that is one of the reasons airplanes fly at a higher altitude to decrease Drag and to increase flight performance.
- Drag Coefficient (CD) is a number that depends on the shape of an object and also increases with angle of attack. An increase in Angle of Attack will increase Lift and Drag
- Increasing the overall Surface Area will increase Drag. Increasing the wing surface area will increase Drag.
There are 2 types of Drag that act on an aircraft in flight: Parasite and Induced Drag. When I started out learning about aerodynamics this seemed a bit confusing. So hopefully by reading this story you'll understand the different types of Drag.
Parasite Drag
Parasite Drag is made out of Interference Drag, Friction Drag, and Form Drag.
- Form Drag: A body that moves through the air displaces air. A body has a certain roughness, thickness,… will more or less increase or decrease Drag as seen in the picture below a streamlined body with low thickness will have small drag. A contaminated wing full of ice may not be able to create enough lift to take off due to the increase in drag.
An airplane has a streamlined body in order to decrease Form drag, and so does a car. A body having less drag is more efficient and can thus move faster through the air.
- Skin Friction Drag is due to the fact that air immediately attached to a body has 0 Flow speed due to friction forces & viscosity. Moving upwards flow speed increases. Surface friction causes heating of the outer skin of a body. The faster and the stronger the friction force → the more the surface is heated up.
Skin Friction and Form Drag → Profile Drag
- Interference Drag is due to aerodynamic interference of different components on a body. This happens for example where the wings are attached to the fuselage (wing struts,…)
Induced Drag
Parasite Drag is all the Drag independent of Lift. Induced Drag is formed due to Lift.
As soon the airplane takes off → induced Drag is created. Induced Drag is the result of pressure equalization between the High Pressure under the wing and the Low Pressure above the wing (more about Lift here).
At the wingtip vortices are created so-called vortex trails. These vortex Trails are especially dangerous for other aircrafts! They create heavy wake turbulences. Planes have crashed before due to the invisible wake turbulences. That’s the reason different types of planes should keep a safe distance from each other, as a heavier and larger plane creates stronger and greater wake turbulences compared to a smaller airplane.
Parasite Drag & Induced Drag effect with Speed
Both Parasite and Induced Drag behave differently when increasing airspeed.
Parasite Drag increases if increasing airspeed
Induced Drag decreases if airspeed is increased.
There is one important speed called the minimum drag speed or also called the best glide speed. That's the airspeed an airplane should fly when suffering from an engine failure
Flying the best glide speed results in the least loss of altitude per distance traveled.
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I hope by having read this story you’ve understood the different types of drag and their importance! Have any Questions? Don’t hesitate to leave a comment in the comments section
HAPPY LANDINGS ;)
