NIFE Aerodynamics 2-2-1 Flashcards
Total drag eqn (Not EO)
Dt = Dp + Di
Define Parasite drag and its components
Drag that does not aid flight. Has two basic elements: Form drag and Friction drag. Dp = qf
Form drag
Disruption of the streamline flow and the resistance of skin friction.
Caused by laminar airflow separation from a surface creating a low pressure wake behind an object.
The pressure differential between the front and rear creates suction that retards forward motion.
Friction drag
Rough surfaces increase the thickness of the boundary layer and create greater skin friction.
Describe induced drag
Created as a result of the wing developing lift. Whenever the wing is producing lift, wingtip vortices are produced.
The lower the airspeed, the greater AOA required to produce lift equal to the airplane’s weight and consequentially, the greater the induced drag.
Describe factors affecting induced drag, given the induced drag equation, and changes in lift, weight, density, velocity, and wingspan
Di = kW2/pV2b2
+ Lift increases > induced drag increases
+ Weight increase > Induced drag increases
+ Density increase > Induced drag decreases
+ Velocity increase > Induced drag decreases
+ Wingspan increase > Induced drag decreases
List prevention methods of Induced drag
- Wingtip Devices: Helps inhibit airflow around the wingtip
2. Ground effect: Reduces full rotation cycles of wingtip vortices
Define total drag
Sum of induced drag and parasite drag
Describe the effects of changes in velocity on total drag
Parasite drag increases as the square of airspeed, and induced drag varies inversely as the square of the airspeed. As speed decreases to near stall speed, the total drag increases due to the sharp rise in induced drag. As speed reaches terminal velocity, the total drag increases due to parasite drag.
Explain the importance of L/D max
- Used to determine the efficiency of an airfoil
- High L/D indicates a more efficient airfoil.
- L/Dmax AOA is at the bottom of the total drag curve
- L/Dmax AOA is the most efficient AOA AKA MAX RANGE
- Any movement away from L/Dmax will increase drag
Define the boundary layer
The layer of airflow over a surface that demonstrates local airflow retardation due to viscosity. Usually 1mm thick at the leading edge of an airfoil and grows as it moves aft.
List the different types of flow within the boundary layer
- Laminar flow
- Turbulent flow
Describe laminar flow
Air that moves smoothly along in streamlines. Laminar boundary layers produce little friction but can easily separate from the surface.
Describe turbulent flow
Streamlines break up and the flow is disorganized and irregular. A turbulent boundary layer produces more friction drag than a laminar boundary layer but is harder to separate from the surface
Describe boundary layer separation in regards to adverse pressure gradient
The boundary layer requires high kinetic pressure to adhere to a surface. As the static pressure increases as air flow aft from the point of max thickness, kinetic pressure decreases. If the boundary layer does not have sufficient energy to overcome the adverse pressure gradient then it will stagnate and separate.
