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DRAG AND STALLS
Terms in this set (17)
DEFINE parasite drag and its components: form, friction, and interference drag
Parasite drag is drag not associated with the production of lift and is composed of two basic types:
1.) Form: Form drag is produced by laminar airflow separation from a surface creating a low pressure wake behind the object.
2.) Friction Drag: friction drag is friction of air moving across the aircraft. No material is perfectly smooth, and differences in the smoothness of the aircraft exterior can cause resistance to smooth airflow.
Describe induced drag.
Induced drag is created as a result of the wing developing lift. Induced drag is inherent whenever a wing is producing lift and, in fact, affects the vertical lift component counteracting weight. This is why induced drag is the portion of total drag associated with the production of lift. As the air curls upwards around a wingtip, the combines with the wing's downwash to form a fast spinning trailing vortex.
Describe the factors affecting induced drag, given the induced drag equation, and changes in lift, weight, density velocity, and wingspan.
The Di equation assumes equilibrium of flight, so as weight increases, induced drag will increase because more lift will be needed to balance weight. Reduction in airspeed will mean higher induced drag.
List prevention methods of induced drag.
1.) Increasing density (lower altitude)
2.) Increasing velocity (reducing AOA)
3.) Increasing wingspan (swing wing).
Define Total Drag
Total drag is the sum of parasite and induced drag. Dt = Di + Dp
Describe the effects of changes in velocity on total drag.
Total drag is induced drag added with parasite drag. Parasite drag increases with airspeed, and induced drag decreases with airspeed. At a certain airspeed, induced drag and parasite drag become equal, and with increased airspeed beyond that, total drag increases sharply. Reducing air below that point will reduce total drag.
Explain the importance of L/Dmax
-L/Dmax AOA is located at the bottom of the total drag curve, so it produces the minimum total drag.
-Any movement away from the L/Dmax will increase drag.
-L/Dmax AOA is the most efficient AOA. (but not the engine)
-At L/Dmax, induced drag and parasite drag and equal.
-L/Dmax AOA produces the greatest ratio of lift to drag.
Define the boundary layer.
The boundary layer is that layer of airflow over a surface that demonstrates local airflow retardation due to viscosity.
Describe the difference types of flow within the boundary layer.
Laminar flow: the air of the boundary layer moves smoothly in streamlines. It produces very little friction, but it easily separated from the surface.
Turbulent flow: the streamlines break up and the flow is organized and irregular. It produces higher friction, but doesn't separate as easily.
Describe boundary layer separation in regards to adverse pressure gradient.
As the air flows from the point of max thickness to the trailing edge (moving low to high static pressure). This pressure gradient is highest in high lift conditions. If the boundary layer does not have sufficient kinetic energy to overcome this pressure gradient, the boundary layer will stagnate. This will cause the boundary layer to separate from the airfoil, and airflow along the surface will reverse (because of the pressure gradient). If this separation advances to the leading edge, the airfoil will stall.
Define a stall.
a condition of flight in which an increase in AOA results in a decrease in coefficient of lift.
Explain the difference between true and indicated stall speed.
True stall speed is the actual airspeed that the aircraft will stall at; indicated stall speed is the true stall speed input into the TAS equation to determine what speed on the instruments the aircraft will stall at.
Explain the effects of gross weight, altitude, and flaps given the stall speed equation.
As airplane weight decreases, stall speed decreases because the amount of lift required to maintain level flight decreases. An increase in altitude will increase the stall speed (less dense air produces less lift).
Explain the difference between speeds with respect to power and power off stalls.
Power on stalls will have a lower stall speed compared to power off stalls, because at higher AOAs some portion of the aircraft's weight is being supported by thrust, and in propeller aircraft, the wind behind the prop is accelerated over the wing, increasing lift there.
Describe the factors necessary for an airplane to spin.
1.) The aircraft must be stalled.
2.) Yaw must be present.
Describe the relationship between the wings during a spin.
The introduction of yaw creates an AOA difference between the left and right wings. the down going (inside) wing senses a different relative wind than the up-going (outside) wing. The inside wing experiences a higher AOA, which means its stalled more than the outside wing.
Describe the actions necessary to recover from a spin.
Reduce the AOA to recover from a stall and use opposite rudder to correct the yaw input.
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