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PBSC > Aerodynamics > Flashcards

Aerodynamics Flashcards

1
Q

-1.(b) Axial Compressors

A

Axial Flow Compressors use rotating, airfoil-based compressors in which air principally flows parallel to the axis of rotation.
(p.91)

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2
Q

-2.(a) Ramjets

A

Ramjets have no compressor and require some other propulsion system to accelerate the vehicle to a speed of 300 MPH, where the ramjet begins to produce thrust.

Intake air has to be sub-sonic for fuel combustion.
(p.87)

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3
Q

-2.(b) Scramjets

A

Scramjets airflow is supersonic throughout the entire engine.

(S for Scramjet = S for Supersonic; SCRAMjet is Super-sonic Combustion RAMjet…)
p.208

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4
Q
    1. How do wings produce lift?

p. 17-20

A

Bernoulli’s principle states that increased velocity (airflow over asymmetrical wing) results in reduced pressure, creating a pressure differential with airflow below the wing (with slower velocity compared to that above). This produces an upward force on the wing.
(High pressure seeking low)
(p.13)

Newton’s 3rd Law states -Every action has an equal and opposite reaction- therefore the downward deflection of the relative wind creates lift upward.

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5
Q

-1.(a) Centrifugal compressors

A

Centrifugal compressors achieves a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller.

(like a washing machine)

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6
Q
    1. Chord line

p. 21

A

“The chord line is the straight line connecting the leading edge and trailing edge.” (review slide)

“The straight line connecting the leading edge, or forward most tip, to the trailing edge is called the cordline and the distance between the leading and trailing edges is referred to as the chord.” (p.21)

Line connecting leading edge to the trailing edge; when measured against the Relative Wind it creates the Angle of Attack; when measured against the horizontal plane determines Pitch.

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7
Q
    1. Center of Gravity

p. 165

A

“Center of Gravity movement is probably the single most important variable in static longitudinal stability.
-All aircraft rotate around their Center of Gravity.” (review slide)

“The center of gravity, CG, is the center of mass of the overall airplane, sometimes described as the point where all of the weight can be considered to be concentrated.” (p.165)

Point about which balance is achieved; aircraft pitches/rolls/yaws about.

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8
Q

-7. Aerodynamic Center of Pressure (p.27)

A

“The Aerodynamic Center is the point at which the pitching moment coefficient for the airfoil does not vary with angle of attack.” (review slide)

“….the point on the airfoil about which the pitching moment does not change, but remains constant will all angles of attack…is located at approximately the quarter-chord position (25 percent of the chord length aft of the leading edge) for most airfoils.” (p.27)

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9
Q

-8. Angle of Attack (p.21)

A

“The angle of attack is always measured between the shoreline and the relative wind.” (p.21)

The angle created by the intersection of the Relative Wind and the Chord Line.

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10
Q

-9. Wing Dihedral (p.173)

A

“Dihedral is the tilting of the wing so that the plane of the wing is at an angle with the horizontal in the lateral direction. Dihedral is one of the most effective means of stabilizing the airplane against sideslipping from a roll.” (p.173)

Upward angle of wing to fuselage in order to provide additional stability.

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11
Q
    1. Wingtip vortices

p. 37-38

A

“Wingtip Vortices modify the air flow around a wing where the air moves from the region of high pressure into the region of low pressure, reducing the wing’s effectiveness to generate lift.” (review slide)

“A flow (of air) around the wingtip from the high-pressure area on the bottom surface to the lower-pressure area on the top” (p.37)

Turbulent air resulting from the high pressure (slower moving air) below an airfoil seeking the low pressure (higher velocity air) above the wing by ‘sneaking’ around the wing tip laterally (perpendicular to direction of travel) instead of flowing smoothly over the wing opposite (parallel) to the direction of travel; spirals inward, moving outward and downward at roughly 400’/min; by definition worst/highest intensity created by heavy, clean slow moving aircraft.

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12
Q

-10. Critical Angle of Attack (p.28)

A

“The Critical Angle of Attack is the angle of attack which produces maximum lift coefficient. Any increase past this point produces a stall.” (review slide)

Point just before stall; maximum production of lift at this point.

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13
Q

-11. Airfoil classifications (p.33)

A

“Airfoil classifications are based on a percentage of the chord length because they are proportional to the chord.” (review slide)

“…maximum chamber in percent (or hundredths) of chord length; maximum chamber point in tenths of chord; maximum thickness in percent of chord. All characteristics are based on chord length (c) because they are proportional to the chord.” (p.33)

Asymmetrical vs symmetrical

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14
Q

-12. Critical Mach Number (p.193)

A

“The Critical Mach Number is the speed of an aircraft in which airflow over any part of the aircraft or structure under consideration first reaches (but does not exceed) Mach 1.0” (review slide)

“Critical Mach Number: when flow velocities reach supersonic speeds at some location on an airplane, further acceleration will result in the onset of compressibility effects such as shock wave formation & drag increase” (review slide)

“The value of the free airstream Mach number (the forward velocity of the airplane) that causes the flow to just reach Mach one somewhere on the airfoil. “ (p.193)

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15
Q

-13. Propellers limited in speed (p.111)

A

“As the propeller blades travel so fast (tip velocity ) that they approach the speed of sound, shock waves can form. When this happens, drag increases rapidly, and much engine power is lost in overcoming this drag.” (p.111)

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16
Q

-14. Ground Effect (p.80-83)

A

“drag alteration when flying near to the ground; a reduction in the downwash of the wing, and an increase in the effective angle of attack” (p.80-83)

The reduction of wingtip vortices due to the effect of the surface redirecting vortices path; results in increased angle of attack for same pitch, less drag therefor greater lift, reduces power required.

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17
Q

-15.(a) High Bypass Ratio jet engine

A

“By-pass Ratio is the ratio between the mass flow rate of air drawn through a fan which bypasses the engine core to the mass flow rate passing through the engine core which is involved in combustion to produce thrust.

High Bypass Ratio Engines derive the vast majority of thrust from the ducted fan, rather than from combustion gases expanding in a nozzle.” (review slide)

no afterburner…

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18
Q

-15.(b) Low Bypass Ratio jet engine

A

“By-pass Ratio is the ratio between the mass flow rate of air drawn through a fan which bypasses the engine core to the mass flow rate passing through the engine core which is involved in combustion to produce thrust.

Low Bypass Ratio Engines can use afterburners” (review slide)

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19
Q

-15. High and Low bypass ratio jet engines

A

Bypass ratio- ratio between air drawn through a fan which bypasses the engine core to the air which travels through the engine core.

High bypass- majority of thrust derived from ducted fan, as opposed to combustion gases expanding through engine core.

Low bypass- majority of thrust derived from air moving through the engine core, not being ducted around. (After burners)

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21
Q

-16. Induced drag

A

“Induced drag is drag that occurs whenever a moving object redirects the airflow coming at it, and increases in direct proportion to increases in the angle of attack and inversely proportional to the square of the airspeed.” (review slide)

Drag resulting from the production of lift; turbulent air behind the wing caused by separation of laminar flow from the wing; wingtip vortices.

Inversely proportional to the square of the velocity.

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22
Q

-17. Longitudinal Stability of an Airplane

A

“Longitudinal Stability and Control is concerned with an airplane’s pitching motion. (about the y-axis)” (review slide)

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23
Q

-18. Hydrostatic lock

A

“Hydrostatic Lock is when a volume of liquid is greater than the volume of the cylinder at its minimum, which is at the end of the piston’s stroke, and the built-up oil in the cylinder prevents the piston from being able to travel it’s full cycle.” (review slide)

Failure of engine resulting from oil pooling in cylinders (incompressible fluid = part of the engine metal will give way). Radial engines

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24
Q
  1. Wing Camber
A

The shape or degree of curvature of a wing; wing’s upper and lower surfaces relative to its chord line.

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25
Q

-19. Bernoulli’s Equation

A

“Relates the pressure in a fluid to the velocity, so as the velocity changes around the object, the pressure changes as well.” (review slide)

Pressure + 1/2 x density x velocity^2 = constant

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26
Q
  1. Interference drag
A

Drag resulting from the joining of separate aircraft components (i.e. wing/fuselage, or vertical/horizontal stabilizer)

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28
Q
  1. 3 states of stability
A

Positive, Neutral, & Negative

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29
Q
  1. Static stability
A

The initial tendency towards equilibrium of an aircraft after some disturbance is encountered

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30
Q
  1. Dynamic Stability
A

Tendency of an aircraft over time to return to equilibrium after a disturbance

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31
Q

*25. Aerodynamic testing

A

“First attempt at aerodynamic testing is credited to Sir George Cayley, who employed a whirling arm to measure the drag and lift of various airfoils.

Centrifugal forces and the fact that the object is moving in it’s own wake mean that detailed examination of the airflow was difficult.”

Fight & Lab testing (Hot Shot Wind Tunnel & Computational Fluid Dynamics (CFD)

32
Q

*26. Wind Tunnel tests?

A

Types?

  • Pressure Measurements/distributions (paints/belts)
  • Pressure-Sensitive Belts (distributions)
  • Static Pressure Taps (holes drilled)
  • Laser Doppler Velocimetry (laser beams)
  • Surface Flow Visualization (oil or tufts)
  • Surface Oil Flow
  • Particle Trace Methods (smoke & lasers)
  • China Clay (oil/dye)
33
Q

*27. Mach Number

A

“The Mach Number is the ratio of the true airspeed to the speed of sound at flight conditions.” (review slide)

34
Q
  1. x, y, & z axis
A 
x = roll; longitudinal (nose-to-tail)
y = pitch; lateral (wingtip-to-wingtip)
z = yaw; vertical (top-to-bottom)
35
Q
  1. Static & Dynamic Stability
A 
Static = initial tendency, short time period
Dynamic = tendency over time
36
Q
  1. Types of drag
A

Form (skin & profile), Induced, Parasite, Interference

37
Q
  1. Angle of Attack and Stall Angle vs Gross Weight
A

Angle of attack vs. Stall Angle does not change. Addition or reduction of weight at fixed airspeed will result in greater power requirement/airspeed to climb or descend

38
Q
  1. Load Factors and Stall Speed
A

Load factor is resulting weight “felt” by aircraft/components as a result of inertia/centrifugal force (“G-forces”)

Stall speed is the speed at which the airfoil produces insufficient lift to maintain flight ( stops producing lift?)

As load factor increases the stall speed increases

39
Q

*33. Bernoulli’s Principle with Compressibility

Final

A

“Bernoulli’s Principle with Compressibility has opposite effects as compared with subsonic.

  • Converging : Pressure goes up as velocity goes down.
  • Diverging: Pressure goes down and velocity goes up.” (review slide)

Bernoulli’s principle states that pressure is inversely related to velocity. As air is compressed it inherently becomes more dense, increasing pressure thereby decreasing velocity. (explanation of jet engine compressibility effects?)

40
Q

*34. Sears-Haack body

A

“shown to be a perfect cross-sectional shape for any given internal volume.” (review slide)

41
Q

*35. Supercritical Wings

A

“Supercritical airfoils are characterized by their flattened upper surface, highly cambered aft section, and greater leading edge radius compared with traditional airfoil shapes.”

  • Flat upper
  • High camber aft
  • Greater leading edge radius

Shockwave minimized and created as far aft as possible reducing drag…

Strong nose down tendency

42
Q

*36. Mach Critical Drag Number

A

The point at which wave drag increases significantly/steeply

43
Q
  1. Freise Ailerons
A

Compensate for adverse yaw. Rigged so that down-going aileron deflects less than up-going.

44
Q
  1. Aircraft Slip
A

Operation of rudder and ailerons in opposite directions; used to rapidly decrease altitude by increasing drag

?When, in a turn, the nose of the aircraft is more inward facing than the rate of turn calls for; falling towards the center of the turn?

45
Q
  1. Elevon
A

Delta wing configuration combining elevator with aileron control surfaces.

46
Q
  1. Flaps:
    - Slotted
    - Split
    - Fowler
    - Krueger
A

Slotted- gap between flap and wing forces high pressure air over the flap to keep airflow attached to the flap

Split- rear, lower surface of airfoil hinges downwards while upper surface stays immobile. Acts like spoiler; high drag, little lift

Fowler- split flap that slides backwards then down. First increases chord, then camber.

Kreuger- hinged flap that folds out from underneath the wing’s leading edge.

47
Q
  1. Spoilers
A

Plates on the top surface of a wing which can be extended upward into the airflow to destroy all lift.

?Disrupt laminar flow thus creating drag and reducing lift of wing/airfoil?

48
Q

*42. Drag Coefficient

A

Describes how much of the dynamic pressure force gets converted into drag.

(How draggy the wing is) Characteristics of wing such as shape of the body surface roughness and other factors which determines how much of the dynamic pressure force it gets converted into drag

Ratio of the Drag force to the force produced by the dynamic pressure times the area
?

49
Q

*43. Area rule

A

“The area rule says that drag at high speeds is a function of an airplane’s total cross-sectional area (the thickness of the fuselage).” (review slide)

50
Q
  1. Boundary Layer
A

Quarter inch to half-inch layer of air where the velocity is changing from zero to that of the free stream

?The airflow immediately adjacent to the fuselage/airfoil (approx 1/4-1/2”) whose velocity ranges from zero (molecules in contact with aircraft skin) to the actual airspeed of the aircraft, where the Laminar Flow begins?

51
Q
  1. Winglets
A

Increase the effective aspect ratio of the wing without increasing the wingspan. Reduces vortex interference

?Extensions to the end of an airfoil which minimize the wingtip vortices, decreasing drag and wake turbulence thus increasing efficiency?

52
Q
  1. Frank Whittle
A

Frank Whittle was the first person to patent the jet engine in 1928. (Salinas)

Turbojets were developed during the 1930s by Sir Frank Whittle of England. Whittle actually completed the first turbojet and ran it on a test stand in 1937 (textbook)

53
Q
  1. de Havilland Comet
A

The D have a land, it was the first commercial jet aircraft introduced in 1949 which unfortunately suffered from fatigue problems in the fuselage structure. Several disasters with this airplane set back commercial jet development for several years.

?First and only British manufactured passenger airliner; square windows developed fatigue stress? cracks at the corners in the fuselage resulting in multiple crashes leading to the British abandoning commercial passenger aircraft design/manufacture?

54
Q
  1. Ram Recovery
A

Increases the mass of the air in front of the compressor, reducing the load on the compressor & leaving more of the internal work produced available for thrust

?The process by which forward airspeed forces air into a jet engine at a sufficient rate to overcome the point at which the engine can draw air under it’s own power/design limitations at rest?

55
Q
  1. Describe the first 4-stroke engine.
A

Internal combustion engines were developed in the mid-1800s and the four stroke cycle engine diversion used an aircraft engines is credited to a German name Nicholas auto in 1876.

Chuck Taylor i.e. Charles Manley (the Wright brothers guy) designed an engine that had no fuel pump no carburetor no spark plugs and no throttle.

?Designed by for the Wright Brothers first airplane. Had no carburetor, no fuel pump, no throttle, no spark plugs, no radiator?

56
Q
  1. Horsepower
A

Measure of how much work is accomplished in a given period of time as defined by James Watt. One horsepower equals 33,000 foot pounds per minute

?Dude (insert name here) in mining observed horses pulling loads out of shafts

57
Q
  1. Brake Horsepower
A

Power delivered to the shaft

?Horsepower measured at the ground/to the wheels vs. originating from the engine. Takes into account losses in power resulting from friction of drivetrain and other components in-line?
Jeff this is false. What you’re describing is shaft horsepower. Brake horsepower is what the engine creates; shaft horsepower would be equivalent to horsepower at the wheels

58
Q

*52. Supercritical Wings

A

“Supercritical airfoils are characterized by their flattened upper surface, highly cambered aft section, and greater leading edge radius compared with traditional airfoil shapes.”

  • Flat upper
  • High camber aft
  • Greater leading edge radius

Shockwave minimized and created as far aft as possible reducing drag…

Strong nose down tendency

59
Q

*53. Ideal Fluids

A
  • Zero viscosity

- no resistance to movement

60
Q

*54. Compressibility Effects

A
  • Density increases

- Large increases in drag occur

61
Q

*55. Wave drag

A

Wave Drag is due to the unstable formation of shock waves which transforms a considerable part of the available propulsive energy into heat, and to the induced separation of the flow from the airplane surfaces.

-shockwaves = heat & induced separation of airflow

62
Q

*56. Inventor of the wind tunnel.

A

Francis Herbert Wenham (1871)

63
Q

*57. Testing “Aerodynamic Forces”

A

Flight Testing
Lab Testing
-Hot Shot Wind Tunnel
-Computational Fluid Dynamics (CFD)

63
Q
  1. Hot Shot Wind Tunnel
A
  • speeds up to Mach 27
  • running time of less than 1 second
  • ballistic missiles
  • space vehicles re-entry
  • plasma physics or heat transfer at high temperatures
64
Q

*59. Computational Fluid Dynamics

A

fluid mechanics using numerical methods and algorithms to solve and analyze problems of fluid flows

64
Q

*60. Laser Doppler Velocimetry

A

Uses a laser that sits outside the tunnel and splits a laser beam into two parallel beams that are sent into the tunnel and focused on a small test area near the model

64
Q

*61. Best endurance speed

A

Consumes the least amount of FUEL per TIME

Speed at which an aircraft can remain airborne the LONGEST TIME on a given amount of fuel.

66
Q

*62. Best range speed

A

Consumes the least amount of FUEL per DISTANCE

The speed at which an aircraft can fly the FARTHEST DISTANCE on a fixed amount of fuel.

67
Q

*63. Cruise-optimum Speed

A

Consumes the least amount of FUEL per unit of VELOCITY

?The speed at which an aircraft is most fuel efficient; can fly the FASTEST for the LONGEST time; best balance between speed and time?

69
Q
  1. Load Factor
A

A load factor is the maneuver force in a particular direction divided by the weight of the aircraft. In the vertical direction the load factor is the lift divided by the weight.

?The amount of “G-Force” resulting from any flight maneuver; most relevant to aircraft loading potentially resulting in in-flight structural failure or in the case of acrobatic-rated aircraft, pilot loss of consciousness due to blood flow restriction to the brain?

70
Q

Flaps: slotted

A

Slotted- gap between flap and wing forces high pressure air over the flap to keep airflow attached to the flap

72
Q

Flap: split

A

Split- rear, lower surface of airfoil hinges downwards while upper surface stays immobile. Acts like spoiler; high drag, little lift

72
Q

Flap: Fowler

A

Fowler- split flap that slides backwards then down. First increases chord, then camber.

72
Q

Flap: Kreuger

A

Kreuger- hinged flap that folds out from underneath the wing’s leading edge.

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