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PPL 1 > Aerodynamics.2 > Flashcards

Aerodynamics.2 Flashcards

1
Q

Ground effect alters…

A

Wing up wash, downwash, wing tip vortices

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2
Q

Reduction in wing tip vortices due to ground effect alters…

A

Spanwise lift distribution and reduces induced drag from AOA. Lower AOA for same CL

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3
Q

As to thrust, ground effect causes…

A

Less thrust needed for speed due to reduced induced drag. It can also cause change in local pressure at the static source producing lower indication of airspeed and altitude

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4
Q

Percentage of drag reduction based on wing distance to the ground

A

Equal to wing height - 1.4%
1/4 wing height - 23.5%
1/10 wing height - 47.6%

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5
Q

Ground effect during take off…

A
  • require an increase in AOA to maintain the same CL
  • Experience an increase in induced drag and thrust required
  • Experience a decrease in stability and a nose up change
  • Experience a reduction in static source pressure and increase in indicated airspeed
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6
Q

What is a Moment

A

Measure of aircraft’s tendency to rotate about its CG. Equal to the product of the force applied and the distance at which the force is applied. Moment arm is the distance from a reference point to the applied force.

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7
Q

Stability is…

A

Inherent quality of aircraft to correct for conditions that disturb it’s equilibrium

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8
Q

Static stability is…

A

Initial response when disturbed from given pitch, yaw, or bank
Positive, negative, neutral

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9
Q

Dynamic stability is…

A

Aircraft response over time when disturbed from a given pitch, yaw, or bank
Positive, neutral, negative

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10
Q

Maneuverability

A

Quality permitting easily maneuvers and withstand stresses. Governed by weight, inertia, size, location of controls, structural strength, powerplant

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11
Q

Controllability

A

Respond to pilot’s control, flight path and attitude. Regardless of stability characteristics

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12
Q

Longitudinal stability

A

Quality that make aircraft stable about its lateral axis

  • location of wing with respect to CG
  • location of horizontal tail surface with respect to CG
  • Area or size of tail surfaces
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13
Q

Center of lift tendency to change…

A

Its fore and aft positions.with a change in AOA. Tends to move forward with AOA increase, backward with decrease

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14
Q

Typical location of Center of Lift = Center of pressure

A

Behind CG to make aircraft slightly nose heavy. Requires horizontal stabilizer at slight negative AOA to balance

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15
Q

Longitudinal stability in flight…

A

Downwash of wing pushes onto horizontal stabilizer even if level. Decreased speed, decreased pressure on stabilizer, nose dips forward and picks up speed, pushes stabilizer down again

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16
Q

Thrust line for longitudinal stability…

A

Above CG pulling plane slightly down when accelerating

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17
Q

Lateral stability design factors

A

Dihedral (wing tips higher than roots), sweepback, keep effect, weight distribution

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18
Q

Sweepback for longitudinal stability

A

1) Move center of pressure towards rear
2) When yawing, forward wing perpendicular to airflow, airspeed increase, more drag than back wing, pulls wing back, plane back to original path

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19
Q

Dutch roll

A

Lateral/directional oscillation, usually dies out automatically

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20
Q

Spiral instability

A

Strong directional stability as compared to dihedral effect - detail unclear
Can be easily corrected.
Tricky when intense spiral, pulling elevator makes spiral tighter, airspeed faster

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21
Q

Wing planform 3 ratios

A

Aspect - wing span to wing chord
Taper - decrease from root to tip in thickness or chord, decrease drag, increase lift
Sweepback - rearward slant

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22
Q

Changing aspect ratio

A

Increase (increase span and weight) with constant velocity will decrease drag, improve climbing
Decrease causes increase in drag

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23
Q

Turning

A

Vertical component
Horizontal component
Centrifugal force
Total lift

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24
Q

Level turn requires

A

Increase in thrust due to increase in induced drag due to increased angle of bank which causes reduction of lift. Required thrust proportional to angle of bank

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25
Q

Slipping turn

A

Banked too much for the ROT, horizontal lift greater than centrifugal force
Decrease the bank or increasing the ROT

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26
Q

Skidding turn

A

Excess of centrifugal force. ROT too great for angle of bank

Need to reduce ROT, or increase bank

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27
Q

Stabilized climb requires

A

Thrust equal to drag plus percentage of weight. Aircraft uses excess thrust to maintain climb

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28
Q

Wing designed to stall…

A

Wing root first, to keep aileron effective

Wing twist design with root at higher AOA or using stall strips

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29
Q

Unstalling

A

CL is aft CG, nose dips after stall reducing AOA

30
Q

Stall AOA

A

Constant for a particular aircraft independent of airspeed, weight, etc
Between 16-20•

31
Q

Wing icing impacts…

A

Disrupts boundary layer
Increases drag
Reduces lift

32
Q

Propeller: pitch vs blade angle

A

Blade: between chord line and plane of rotation

74-48 = 74in long, 48in effective pitch

33
Q

Propeller thrust

A

Equals mass of air handled multiplied by slipstream velocity minus aircraft velocity. Thrust about 80% of torque, 20% lost in friction and slippage

34
Q

Propeller slip

A

Difference between geometric pitch of propeller and effective pitch
Geometric pitch based on no slippage

35
Q

Twisted propeller

A

Outer part travels faster, different AOA
Twisted to change blade angle in proportion to differences in speed of rotation along length of prop, keeping thrust equal

36
Q

Constant speed prop

A

Take off: low blade angle, AOA small, smaller mass of air, engine at high rpm
After liftoff, higher pitch, keep AOA small efficient, increase mass of air per revolution
After climb, reduce power, increase blade angle

37
Q

Torque 4 elements

A

From engine and prop
Corkscrewing of slipstream
Gyroscopic prop action
Asymmetric loading of prop

38
Q

Torque reaction

A 
Reaction to action of prop spin, cause roll tendency, left yawing on ground
Counter with wing or engine offset
Depends on
Size and hp of engine
Size and rpm of prop
Size of plane
Ground surface condition
39
Q

Corkscrew effect

A

Rotating slipstream, sideward force on tail, yawing to the left, rolling to the right

40
Q

Gyroscopic action

A

Precession is resulting action of a spinning rotor when a deflection force is applied. Resulting force takes effect 90• Ahead of and in direction of rotation

41
Q

Asymmetric loading, P factor

A

High AOA flying, Prop down more bite/speed/lift than prop up causing left yawing around vertical axis (helicopter Example)

42
Q

Load factor important for two reasons

A

Overload aircraft structure

Increase stall speed

43
Q

Different load factors

A

Gust load factor
Maneuvering load factor
Load limit factor
Ultimate load

44
Q

Load factor in steep turns

A

Exponential increase after 45•
60• = 2G
80• = 5.76G

45
Q

Stalling speed increases…

A

In proportion to square root of load factor
50knots regular stalling speed
100knots at 4G

46
Q

Design maneuvering speed VA

A

Move single flight control one time full deflection for one axis of rotation only in smooth air without risk of damage
Entered in AFM/POH

47
Q

Vg Diagram

A

Velocity vs load factor
Each aircraft has its own
Lines of maximum lift capability - stalls above that line
Intersection of positive limit load factor and line if max positive lift capability - minimum airspeed for limit load

48
Q

ROT formula

A

= (1,091 x tangent of bank angle)/knots

49
Q

Radius of turn formula

A

R = v2 / (11.26 x tangent of bank angle)
Or
R = (speed fps x 360/ROT)/Pi/2

50
Q

CG position influences…

A

Lift and AOA and force on the tail

51
Q

Forward CG stalls at…

A

Higher speeds due to increased wing loading

52
Q

Aft CG aircraft cruises…

A

Faster because of reduced drag due to smaller AOA, less downward deflection of stabilizer

53
Q

CG moved rearward…

A

Less stabile due to decrease in AOA, wing contribution to stabilize decreases until neutral stability, then unstable

54
Q

CG moved forward…

A

Increases need for greater elevator pressure, may not be able to opposes nose-down pitching

55
Q

Aircraft speed regimes

A

Subsonic - below 0.75 M
Transonic - 0.75-1.20
Supersonic - 1.20-5.00
Hypersonic - above 5

56
Q

Critical Mach number

A

Speed at which some part of airflow reached M 1.0

57
Q

Drag divergence

A

5-10% above Mach Crit compressibility starts causing drag rise impacting buffet, trim, stability, control effectiveness

58
Q

Max operating speed limit

A 
Vmo = lower altitudes, structural loads and flutter
Mmo = higher altitudes, compressibility, flutter
59
Q

KIAS, KCAS, KTAS calculation?

A

??

60
Q

Boundary layers

A

Laminar
Turbulent
Separation

61
Q

Shock wave or compression wave

A

Boundary between undisturbed air and region of compressed air

62
Q

Supersonic airstream passing through normal shock wave

A

Airstream is slowed to subsonic
Airflow behind shockwave does not change
Static pressure and density of airstream behind wave is greatly increased
Energy of airstream greatly reduced

63
Q

Wave drag

A

Shock wave causes drag due to dense high pressure region behind wave
Drag from airflow separation

64
Q

Mach tuck

A

CP move aft, diving moment is produced, if it moves forward, a nose-up movement
Reason for T tail

65
Q

Sweepback for Mach

A

Delays onset of compressibility effects

Increase in critical Mach number, force divergence mach number

66
Q

Force divergence Mach number

A

Number producing a sharp change in coefficient of drag

Exceed critical Mach number by 5-10%

67
Q

Sweepback disadvantages

A

Stalls at wing tips rather than roots
Boundary layer flows spanwise
Causes CL to move forward causing nose to rise
Aggravated by T tail

68
Q

Stick pusher and stick shaker

A

Push stick forward to prevent stall

Shaker at 5-7% above stall speed

69
Q

Mach buffet occurs…

A

High altitudes
Heavy weights
G loading

70
Q

Variable incidence horizontal stabilizer

A

For jet needing large pitch trim changes

Larger than elevator, leaving elevator with full range of motion

PPL 1 (15 decks)

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