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PPL 1 > Aerodynamics.2 > Flashcards

Aerodynamics.2 Flashcards

(70 cards)

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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
Slipping turn
Banked too much for the ROT, horizontal lift greater than centrifugal force Decrease the bank or increasing the ROT
26
Skidding turn
Excess of centrifugal force. ROT too great for angle of bank | Need to reduce ROT, or increase bank
27
Stabilized climb requires
Thrust equal to drag plus percentage of weight. Aircraft uses excess thrust to maintain climb
28
Wing designed to stall...
Wing root first, to keep aileron effective | Wing twist design with root at higher AOA or using stall strips
29
Unstalling
CL is aft CG, nose dips after stall reducing AOA
30
Stall AOA
Constant for a particular aircraft independent of airspeed, weight, etc Between 16-20•
31
Wing icing impacts...
Disrupts boundary layer Increases drag Reduces lift
32
Propeller: pitch vs blade angle
Blade: between chord line and plane of rotation | 74-48 = 74in long, 48in effective pitch
33
Propeller thrust
Equals mass of air handled multiplied by slipstream velocity minus aircraft velocity. Thrust about 80% of torque, 20% lost in friction and slippage
34
Propeller slip
Difference between geometric pitch of propeller and effective pitch Geometric pitch based on no slippage
35
Twisted propeller
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
Constant speed prop
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
Torque 4 elements
From engine and prop Corkscrewing of slipstream Gyroscopic prop action Asymmetric loading of prop
38
Torque reaction
``` 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
Corkscrew effect
Rotating slipstream, sideward force on tail, yawing to the left, rolling to the right
40
Gyroscopic action
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
Asymmetric loading, P factor
High AOA flying, Prop down more bite/speed/lift than prop up causing left yawing around vertical axis (helicopter Example)
42
Load factor important for two reasons
Overload aircraft structure | Increase stall speed
43
Different load factors
Gust load factor Maneuvering load factor Load limit factor Ultimate load
44
Load factor in steep turns
Exponential increase after 45• 60• = 2G 80• = 5.76G
45
Stalling speed increases...
In proportion to square root of load factor 50knots regular stalling speed 100knots at 4G
46
Design maneuvering speed VA
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
Vg Diagram
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
ROT formula
= (1,091 x tangent of bank angle)/knots
49
Radius of turn formula
R = v2 / (11.26 x tangent of bank angle) Or R = (speed fps x 360/ROT)/Pi/2
50
CG position influences...
Lift and AOA and force on the tail
51
Forward CG stalls at...
Higher speeds due to increased wing loading
52
Aft CG aircraft cruises...
Faster because of reduced drag due to smaller AOA, less downward deflection of stabilizer
53
CG moved rearward...
Less stabile due to decrease in AOA, wing contribution to stabilize decreases until neutral stability, then unstable
54
CG moved forward...
Increases need for greater elevator pressure, may not be able to opposes nose-down pitching
55
Aircraft speed regimes
Subsonic - below 0.75 M Transonic - 0.75-1.20 Supersonic - 1.20-5.00 Hypersonic - above 5
56
Critical Mach number
Speed at which some part of airflow reached M 1.0
57
Drag divergence
5-10% above Mach Crit compressibility starts causing drag rise impacting buffet, trim, stability, control effectiveness
58
Max operating speed limit
``` Vmo = lower altitudes, structural loads and flutter Mmo = higher altitudes, compressibility, flutter ```
59
KIAS, KCAS, KTAS calculation?
??
60
Boundary layers
Laminar Turbulent Separation
61
Shock wave or compression wave
Boundary between undisturbed air and region of compressed air
62
Supersonic airstream passing through normal shock wave
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
Wave drag
Shock wave causes drag due to dense high pressure region behind wave Drag from airflow separation
64
Mach tuck
CP move aft, diving moment is produced, if it moves forward, a nose-up movement Reason for T tail
65
Sweepback for Mach
Delays onset of compressibility effects | Increase in critical Mach number, force divergence mach number
66
Force divergence Mach number
Number producing a sharp change in coefficient of drag | Exceed critical Mach number by 5-10%
67
Sweepback disadvantages
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
Stick pusher and stick shaker
Push stick forward to prevent stall | Shaker at 5-7% above stall speed
69
Mach buffet occurs...
High altitudes Heavy weights G loading
70
Variable incidence horizontal stabilizer
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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