2-2 Lift Production and Drag

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  1. EXPLAIN the aerodynamic relationship of the four primary forces of equilibrium flight
    • Weight - the force of the Earth's gravity acting on the mass of the aircraft.
    • It is always pointed to the center of the Earth.
    • Lift - the force that primarily acts against weight. A component of the aerodynamic force.
    • Thrust - the force produced by a jet engine or engine/propeller combination.
    • Drag - the force that primarily acts against thrust and retards aircraft motion.
  2. DESCRIBE how the four primary aerodynamic forces affect each other
    • Weight and Lift oppose each other.
    • Thrust and Drag oppose each other.
  3. STATE the pressure distribution around an airfoil, given changes in angle of attack and camber
    • Pressure acts normal (perpendicular) to the body.
    • Positive Camber - pressure over the top is less than under at 0 AOA.
    • Semetric - pressure over the top is equal to under at 0 AOA
    • Negative Camber - pressure over the top is less than under at 0 AOA.
    • Changes in AOA - different AOA can cause the pressure over and under the airfoil to change.
  4. DEFINE the lift component of aerodynamic force
    • Lift (L) is the component of the aerodynamic force acting perpendicular to the relative wind.
    • Lift is mainly due to an imbalance of pressure distributions over the top and bottom surface.
  5. DESCRIBE how factors in the lift equation affect lift production, given density, velocity, surface area, and coefficient of lift
    chart?chf=bg,s,00000000&cht=tx&chl=L%3DqSC_L%3D%5Cfrac%7B1%7D%7B2%7DpV%5E2SC_L&chs=358x64

    • L=Lift
    • q=dynamic pressure
    • S=Surface area
    • CL=Coefficient Lift
    • p=density
    • V=Velocity
  6. LIST the factors affecting coefficient of lift that the pilot can directly control
    • The shape of the airfoil
    • the Angle of Attack (AOA)
  7. DEFINE parasite drag and its components: form, friction, and interference drag
    • Parasite Drag - drag that is not associated with the production of lift.
    • Form Drag - aka pressure drag or profile drag, is caused by airflow separations from a surface and the low pressure wake that is created by that separation. It is primarily dependent upon the shape of the object.
    • Friction Drag - Drag arising from friction forces at the surface of an aircraft, due to the viscosity of the air.
    • Interference Drag - Generated by the missing of streamlines between components. For example, the air flowing around the fuselage mixing with air flowing around an external fuel tank.
  8. DESCRIBE the measures that can be taken to reduce each of the components of parasite drag
    Form Drag - the fuselage and other surfaces exposed to the airstream are streamlined (shaped like a teardrop). This reduces the size of the high static pressure area near the leading edge stagnation point and reduces the size of the low static pressure wake. Because of the decreased pressure differential, form drag is decreased.

    Friction Drag - can be reduced by smoothing the exposed surfaces of the airplane through painting, cleaning, waxing, or polishing. Also, using flush rivets on the leading edges helps.

    Interference drag - proper fairing and filleting, which allows the streamlines to meet gradually rather than abruptly.
  9. STATE the effects of upwash and downwash on an infinite wing
    • Upwash - high pressure air under the wing attempts to equalize with the low pressure air above the wing. This results in some air flowing over the wing that should have flowed under the wing.
    • Upwash increases lift because it increases the average angle of attack on the wing.

    • Downwash - Some of the air on top of the wing attempts to equalize with air under the wing by flowing under the trailing dge.
    • Downwash decreses lift by reducing the average angle of attack on the wing.
  10. STATE the effects of upwash and downwash on a finite wing
    • Some of the air in the leading edge stagnation point flows spanwise to the wingtips instead of chordwise over the upper surface of the wing.
    • Once it reaches the wingtips, it flows around the wingtips and up to the upper surface to combine with the chordwise flow that has already produced lift and adds to the downwash.
    • Downwash approximately doubles by this process. Wingtip vortices also result.
  11. DEFINE induced drag
    • that portion of total drag associated with the production of lift.
    • It is the parallel component of total lift since it acts in the same direction as drag and tends to retard the forward motion of the airplane.
  12. STATE the cause of induced drag on a finite wing
    Image Upload 1Downwash causes the average relative wind to have a downward slant compared to the free airstream relative wind.
  13. DESCRIBE factors affecting induced drag, given the induced drag equation, and changes in lift, weight, density velocity, and wingspan
    chart?chf=bg,s,00000000&cht=tx&chl=D_I%3D%5Cfrac%7BkL%5E2%7D%7B%5Crho%20V%5E2b%5E2%7D%3D%5Cfrac%7BkW%5E2%7D%7B%5Crho%20V%5E2b%5E2%7D&chs=294x82

    • DI = Induced Drag
    • K
    • L = lift
    • p = density
    • V = Velocity
    • b = wingspan

    • Induced drag is reduced by increasing density, velocity, or wingspan.
    • In level flight where lift is constant, induced drag varies inversely with velocity and directly with Angle of Attack (AOA).
    • Induced drag can also be reduced by installing devices that impede the spanwise airflow around the wingtip.
  14. STATE when a plane will enter ground effect
    when the plane is within one wingspan of the ground.
  15. STATE the effects of ground effect on lift, effective lift, and induced drag
    • Lift - increases
    • effective lift - increases
    • induced drag - decreases
    • In Ground Effect, downwash at the trailing edge of the wing is unable to flow downward. The decrease in downwash allows the total lift vector to rotate forward, increasing effective lift and decreasing induced drag.
  16. DESCRIBE effects of angle of attack changes on coefficient of lift and coefficient of drag
    • Lift - AOA is the most important factor in the coefficient of lift, and the easiest for the pilot to change.
    • As AOA increases, the coefficient of lift initially increases until it gets to CLmax. Any increase in AOA after CLmax will cause a decrease in the coefficient of lift.Image Upload 2

    • Drag - at low AOA, the coefficient of drag is low and nearly constant.
    • As AOA increases, The coefficient of drag rapidly increases.Image Upload 3
  17. EXPLAIN the lift to drag ratio, using the lift and drag equations
    • The lift to drag ratio is used to determine the efficiency of an airfoil. a high L/D indicates a more efficient airfoil.
    • chart?chf=bg,s,00000000&cht=tx&chl=L%3D%5Cfrac%7B1%7D%7B2%7D%5Crho%20V%5E2SC_L&chs=224x64
    • chart?chf=bg,s,00000000&cht=tx&chl=D%3D%5Cfrac%7B1%7D%7B2%7D%5Crho%20V%5E2SC_D&chs=234x64
    • p=density
    • V=Velocity
    • S=surface area
    • C=coefficient of L or D

    Since both equations are the same exception for using the corresponding coefficient, the Lift to Drag ratio is equal to CL divided by CD.
  18. EXPLAIN the importance of L/D MAX
    • L/D MAX is when the airfoil is most efficient.
    • L/D MAX AOA produces the minimum total drag.
    • At L/D MAX AOA, parasite drag and induced drag are equal. Velocities below L/D MAX, the airplane is affected primarily by induced drag, velocities above - parasite drag.
    • L/D MAX AOA produces the greatest ratio of lift to drag. It does not indicate the maximum amount of lift that can be produced, nor does it correspond to the airplane's max speed.
    • L/D MAX AOA is the most efficient angle of attack. Note that L/D is the efficiency of the wing, not the engine.
    • An increase in weight or altitude will increase L/D Max airspeed, but not affect L/D MAX or L/D MAX AOA.
    • A change in configuration (landing gear, flaps, etc.) may have a large effect on L/D MAX.
  19. DEFINE total drag
    Total drag = Parasite drag + Induced Drag
  20. DESCRIBE the effects of changes in velocity on total drag
    • Image Upload 4
    • At lower velocity, Induced drag is high while Parasite drag is low.
    • As velocity increases, Induced drag decreases while Parasite drag increases.
    • Since Total drag is the sum of the two drags, Total drag will start high, decreasing until the L/D MAX is achieved, then increase.
  21. DEFINE thrust components: thrust required and thrust available
    • Thrust Required - the amount of thrust that is required to overcome drag.
    • Thrust Available - the amount of thrust that the airplane's engines actually produce at a given throttle setting, velocity, and density.
  22. DEFINE power components: power required and power available
    • Power Required - the amount of power that is required to produce thrust required.
    • Power Available - the amount of power that the airplane's engines actually produce at a given throttle setting, velocity, and density.
  23. DESCRIBE the effects of throttle setting, velocity, and density, on thrust available and power available
    • Throttle Setting - the most important factor in thrust available. Maximum engine output occurs at full throttle. As throttle decreases, thrust available decreases.
    • Velocity - for propellers, air can only be accelerated to a max velocity. As the velocity of the incoming air increases, the air is accelerated less through the propeller, and thrust available decreases.
    • For turbojets, the ram effect overcomes the decreased acceleration. Thrust available is approximated by a straight line.
    • Density - As the density of the air decreases, thrust available decreases.
  24. DEFINE thrust horsepower and components: shaft horsepower and propeller efficiency
    • Thrust Horsepower - the output from the propeller
    • Shaft Horsepower - the output from the engine
    • Propeller Efficiency - the ability of the propeller to convert SHP into THP
    • chart?chf=bg,s,00000000&cht=tx&chl=PE%3D%5Cfrac%7BTHP%7D%7BSHP%7D&chs=182x68
  25. STATE the maximum rated shaft horsepower in the T-6B
    The PT6A-68 engine is flat rated at 1100 SHP
  26. EXPLAIN how propeller efficiency affects thrust horsepower
    • The higher the Propeller Efficiency, the better the engine can translate shaft horsepower into thrust horsepower.
    • Friction in the reduction gearbox and drag o the propeller reduces efficiency
  27. DESCRIBE power required in terms of thrust required
    Power required is the amount of power that is required to produce thrust required.
  28. STATE the location of L/D MAX on the thrust required and power required curves
    • Thrust Required
    • It is at the bottom of the curve (similar to the L/D MAX on the Total Drag Curve) since Thrust required would be need to be the same.
    • Image Upload 5
    • Power Required
    • To find L/D MAX on the Power Required curve, draw a horizontal line tangent to the bottom of the curve. Apply the Power required equation [PR=(TR*V)/325] to the line. The result is a line from the origin that is tangent to the power curve at L/D MAX.
    • Unlike the Thrust available curve, L/D MAX is not at the bottom of the PR curve, but is to the right of the bottom of the curve.
    • Image Upload 6
  29. DESCRIBE how thrust required and power required vary with velocity
    • Image Upload 7
    • Thrust Required
    • Flight at greater velocities requires a reduction in AOA (to maintain constant lift) and an increase in thrust (to match the increase in parasite drag).
    • Flight at lower velocity requires an increase in AOA and an increase in thrust (to match the increase in induced drag).
    • Image Upload 8
  30. DEFINE excess thrust and excess power
    Excess Thrust - occurs if thrust available is greater than thrust required at a particular velocity.

    Excess power - occurs  if power available is greater than power required at a particular velocity.
  31. DESCRIBE the effects of excess thrust and excess power
    Excess Thrust - Causes a climb, acceleration, or both

    Excess Power - Causes a climb, acceleration, or both
  32. DESCRIBE the effects of changes in weight on thrust and power components: thrust required, power required, excess thrust, and excess power
    • Thrust Required
    • An increase in weight requires an increase in lift. In order to increase lift at a constant AOA, velocity must increase.
    • A higher velocity and more lift increases both parasite and induced drag, therefore total drag increases.
    • The net result is the TR curve shifts up and to the right.
    • Image Upload 9
    • Power Required
    • An increase in weight requires an increase in velocity and a corresponding increase in thrust required at a specific AOA.
    • Since PR is a function of thrust required and velocity, an increase in weight will result in an increase in power required.
    • The PR curve moves up and to the right.
    • Image Upload 10

    Weight changes have no effect on thrust available or power available. Weight increases cause TR and PR to increase while TA and PA remain constant.

    • Therefore:
    • Excess Thrust
    • Decreases at every AOA and velocity.

    • Excess Power
    • Decreases at every AOA and velocity
  33. DESCRIBE the effects of changes in altitude on thrust and power components: thrust required, power required, thrust available, power available, excess thrust, and excess power
    • Thrust Required
    • Aircraft will weigh the same no matter the altitude.
    • At higher altitude, density decreases.
    • Velocity must increase to maintain the same amount of lift.
    • As altitude increases, the TR curve shifts to the right.
    • Image Upload 11

    • Power Required
    • Since PR is the product of TR and velocity, the PR curve will shift to the right as altitude increases and the TR curve shifts to the right.
    • Because the same thrust is multiplied by a higher velocity, the PR curve will move up as well.
    • Image Upload 12
    • Maximum engine output decreases with a reduction in air density. Thus, both TA and PA decrease at higher altitudes.

    • Thrust excess will decrease with an increase in altitude due to the decrease in thrust available.
    • Power excess will decrease with an increase in altitude because power available decreases and power required increases
  34. DESCRIBE the effects of changes in configuration on thrust and power components: thrust required, power required, excess thrust, and excess power
    • Lowering the landing gear has no effect on the lift produced by the wing, so no change in velocity is required to maintain lift.
    • It does, however, dramatically increase parasite drag.
    • Thrust Required
    • More thrust and power are required to maintain altitude for and given AOA and velocity, so the TR curve shifts up.
    • Image Upload 13
    • Power Required
    • More power is required to maintain altitude when landing gear is deployed.
    • The PR curve shifts up.
    • Image Upload 14

    • Excess Thrust
    • TA is not affected. Excess Thrust will decrease since TR increases.

    • Excess Power
    • PA is not affected. Excess Power will decrease since PR increases.
  35. DESCRIBE the aerodynamic effects of raising or lowering the flaps
    • Lowering the flaps increases the coefficient of lift, allowing the aircraft to fly at a lower velocity to produce enough lift to offset weight.
    • However, it is offset by induced drag, causing thrust required to increase.
    • The net effect of lowering the flaps is to shift both the TR an PR curves up and to the left.
    • More thrust and power are required to maintain altitude for any given velocity.
  36. DESCRIBE the aerodynamic effects of raising and lowering the landing gear
    • Lowering the landing gear does not affect the lift produced by the wing.
    • However, parasite drag is increased, causing TR and PR to increase.
  37. EXPLAIN the aerodynamic effects of each primary flight control on the aircraft
    • Elevators
    • Attached to the trailing edge of the horizontal stabilizer.
    • Controls the pitching movement around the lateral axis.
    • Moving the stick forward causes the elevator to move down and the nose to pitch down.

    • Ailerons
    • Attached to the outboard trailing edges of the wings and produce a rolling movement.
    • Moving the stick left causes the left airleron to move up, causing negative camber, and the right to move down, increasing camber.
    • The result is a roll to the left.

    • Rudder
    • Attached to the trailing edge of the vertical stabilizer.
    • Produces yawing moment.
    • Stepping on the right rudder moves the rudder to the right, creating an airfoil positively cambered and creating lift, causing the tail to "fly" left and yawing the nose to the right.
  38. DESCRIBE how the trim tab system holds an airplane in trimmed flight
    • Trim tabs are attached to the trailing edge of each control surface and have two functions.
    • Trimming reduces the force required to hold control surfaces in a position necessary to maintain a desired flight altitude.
  39. DEFINE aerodynamic balancing and mass balancing
    • Aerodynamic Balance
    • the feature of a control surface that reduces the magnitude of the aerodynamic moment around the hinge line.
    • Used to keep control pressures associated with higher velocities within reasonable limits.

    • Mass Balance
    • the feature of a control surface that reduces the magnitude of the inertial and gravitational moments around the hinge line.
    • Placing weights inside the control surface in the are forward of the hingeline
  40. STATE the methods for aerodynamic and mass balancing employed on the T-6B
    • For aerodynamic balancing, the T-6B uses shielded horns on the elevator and rudder.
    • -Shielded Horns - the part of a control surface of longer chord than the rest of the surface, lying forward of the hinge line and partially shielded by the surface to which it is attached.

    For mass balancing, weights are placed inside the control surface in the area forward of the hinge line.
  41. STATE the characteristics of the three basic types of control systems
    • Conventional
    • the forces applied to the stick and rudder pedals are transferred directly to the control surfaces via pus-pull tubes, pulleys, cables, and levers.
    • External forces that move the control surfaces cause the stick and rudder to move in the cockpit.

    • Power-boosted
    • Have mechanical linkages with hydraulic, pneumatic, or electrical boosters to assist the pilot in moving the controls, similar to power steering in cars.
    • Has some reversibility.
    • Pilot receives some control feel through the cockpit controls.
    • Pilot can still control the plan if the boost system fails.

    • Full-power
    • aka fly-by-wire
    • Pilot has no direct connection with the control surfaces.
    • Controls are connected to hydraulic valves or electrical switches which control the movement of the control surfaces.
    • System is not reversible and require artificial means to produce control feel.
  42. STATE how trim tabs can be used to generate artificial feel on a control surface
    • They are added to the trailing edge of the control surfaces to help the pilot maneuver easier or generate feedback.
    • For instance, a Servo trim tab moves in the opposite direction as the aileron, helping the pilot to deflect the control surface and making the maneuver easier.
    • Anti-servo trim tabs moves in the same direction as the rudder, but at a faster rate. The more the pedal is pressed, the greater the resistance that the pilot will feel.
    • Neutral trim tabs on the elevator maintains a constant angle to the elevator when the control surface is deflected. Bobweights and 2 downsprings are used to provide the pilot with some artificial feel. The downsprings increase the force required to pull the stick aft at low airspeeds when required control pressures are extremely light. The bobweight increases the force required to pull the stick aft during maneuvering flight.
  43. DESCRIBE the purpose of bobweights and downsprings
    • Used on the elevators
    • Bobweights and 2 downsprings are used to provide the pilot with some artificial feel.
    • The downsprings increase the force required to pull the stick aft at low airspeeds when required control pressures are extremely light.
    • The bobweight increases the force required to pull the stick aft during maneuvering flight.
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2-2 Lift Production and Drag
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