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POF > High Speed Flight > Flashcards

High Speed Flight Flashcards

1
Q

Local Speed Of Sound

A

LLS = 39 x square root (K)

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2
Q

Mach Number calculation

A

Mach number = TAS/LSS

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3
Q

What is Mcrit

A

Fastest speed at which there is no supersonic flow

Or

Slowest speed at which there is no supersonic flow

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4
Q

First signs of a shockwave

A

Appear on the upper surface just after Mcrit half way back

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5
Q

What does transonic mean

A

Some Mach numbers lower than 1, but some Mach numbers above 1

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6
Q

Flying faster in transonic speed does what to shockwaves

A

Shockwaves intensify and move backwards a shockwave can also then form on the bottom on the aerofoil leading more drag

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7
Q

Wave drag

A

As shockwave intensify more separation aft of shockwave

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8
Q

Airflow in front of shockwave properties

Static pressure
Velocity
Temperature
LSS
Density
Total pressure

A

Static Pressure - Less
Velocity - Higher
Temp - Lower
LSS - Lower
Density - Lower
Total pressure - higher

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9
Q

Airflow properties behind a shock wave

Pressure
Temperature
LSS
Density
Total pressure

A

Pressure - higher
Temperature - higher
LSS - Higher
Density - higher
Total pressure - lower

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10
Q

What changes Mcrit

A

Factors which influence the acceleration of airflow over the upper surface

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11
Q

Factors influencing Mcrit

A

Forward CG - Lower
Thicker wing - lower
Increased Mass - lower
Turning - lower

Anything that is producing additional lift on upper surface to increase the airflow

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12
Q

Mach Drag Diversion

A

Mach number at which CD rapidly rises due to flow seperation

Mach buffet

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13
Q

High Mach number will do what to lift and drag

A

Reduces lift and increases drag in supersonic flight

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14
Q

Advantage of flying close to Mcrit

A

Increase in cruise speed for not so much drag

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15
Q

Increasing Mcrit - Sweepback Wings + consequences

A

Speed of airflow at 90 degrees to leading edge is going to be slower than in relation to airplane

Mcrit greater for sweep angle

  • reduction in clmax higher stall speed
  • increased t/o l/d distances
  • poor stall characteristics
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16
Q

Practical design for supercritical wing

A

Flat Top

Negative Camber on lower surface

Extreme positive camber at trailing edge

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17
Q

Mach Buffet is

A

Produced by the turbulent flow behind a strong shock wave

Can lead to structural fatigue

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18
Q

Vortex generators and Mach buffet

A

Used to reattach airflow behind normal shockwave located inboard and further back

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19
Q

CP movement in transonic flight

A

Due to rearward movement overall L/W couple gets bigger so more nose down

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20
Q

Mach Trimmer

A

To improve stick force stability in transonic flight due to L/W couple movement at Mcrit

Mno is limited if inoperative

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21
Q

Why can we fly at a higher TAS/Mach at altitude

A

Reduces temp and density therefore allows a greater TAS and a greater MACH as LSS is reduced and TAS increases

22
Q

Chicken Tika Masala

A

CAS

True Airspeed

Mach

23
Q

Inversion effect on CAS/TAS/MACH

A

As temperature is getting warmer Mach number decreases

C M T

24
Q

Isothermal layer on CAS TAS MACH

A

TAS and Mach will stay the same

25
Q

Climb Schedule

A

Switching between TAS and Mach from low altitude to high altitude

26
Q

What speed limits you in a climb

A

Mach number above climb schedule

CAS is decreasing at constant Mach

AOA increase to maintain lift reducing stall margin

27
Q

What happens to climb angle in the climb up

A

Climb angle decreases as less thrust

28
Q

Speed of sound is affected by

A

Temperature of the air

29
Q

Critical Mach number is when there is evidence of

A

Local sonic flow

30
Q

Dutch Roll and shockwaves

A

Shockwaves have different intensity’s on each wing therefore Dutch roll gets worst

Yaw damper must be operative

31
Q

Why do we need a Mach trimmer

A

To adjust incidence of horizontal stabiliser to counter aft movement in cp due give us a positive stick force stability

32
Q

Mach Tuck is

A

Shock induced separation near wing roots which decreases downwash on tailplane

Nose down pitching moment

33
Q

High speed buffet

A

Constant MACH speed CAS decreases (low speed stall)

Altitude decrease Mach buffet margin to high speed buffet

Reduction in lift and increase in drag

34
Q

Aerodynamic ceiling

A

Altitude at which high speed stall and low speed stall coincident

35
Q

Factors on the low/high buffet margin

A

Mass
Load Factor
Altitude

Anything that requires more lift from the wing

36
Q

Aircraft in climb at constant Mach what happens to pitch angle/CL and climb angle

A

Climb angle decrease
Pitch angle decreases

CL increases

37
Q

Constant Mach in a descent on:

AOA
CL
CAS
Pitch Angle
Descent Angle

A

AOA decrease
CL decrease
CAS increases
Pitch angle decreases
Descent angle increases

38
Q

Buffet Onset Boundary Chart

A

Shows us variables for altitude/weight/load factor on the low and high speed buffer margin

Mach numbers at which low speed and Mach buffet occur at different mass and altitudes

39
Q

Supercritical Wing

A

Allows for no noticeable shockwaves when flying just above MCRIT

40
Q

Flying from warm to cold air mass will do what to Mach speed

A

Mach Speed will remain constant

TAS will decrease as density will decrease
LSS will rise due to temperature decrease

41
Q

Advantages of flying near mcrit

A

Flying just past MNO gives a CL increase for a slight CD increase up until the mdrag divergence point

42
Q

What happens to stall speed with altitude when compressibility is concerned

A

Stall speed is constant with altitude and then increases due to compressibility

43
Q

What happens to the aerodynamic centre in the trans/supersonic speed region

A

CP moves from 25% to 50% chord

44
Q

Deflection of a aileron upwards when the wing is generating a shock wave will

A

Move the shock wave slightly forward in front of the upward deflected aileron

Decrease in camber reduces the aft movement of the shockwave- moving slightly forward as increase in Mcrit

45
Q

Exceeding MCRIT without a Mach trimmer the stick force stability will

A

Reduce as the nose will want to move down due to reduction in tailplane effectiveness

46
Q

Mach Trim

A

Used to trim ac at high Mach numbers - prevents instability and tuck under

Does one of the following to counteract the pitch down:
- adjusting stabiliser
- adjusting elevator
- trim tank

+ stick force gradient maintained
+ longitudinal stability increases
+ tuck under avoided

47
Q

Compared to a conventional airfoil the supercritical wing has the advantage of

A

Larger leading edge radius/flatter upper surface/both positive and negative camber and enables thick wing to be used for the same cruise Mach number

48
Q

Moving the aileron downwards does what to shock wave

A

Increased camber therefore shockwave will move rearward

49
Q

What happens to controls surfaces (ailerons) effectiveness in subsonic flight

A

Shock wave separates the wing into two parts so aileron only affects the back part therefore less effective

Aileron deflection only partly affects the pressure distribution around the wing

50
Q

How does swept back wings allow for a higher mcrit value

A

Increases the effective chord

POF (25 decks)

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