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POF > Drag > Flashcards

Drag Flashcards

1
Q

Profile Drag

A

Combination of Skin Drag and Form Drag

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2
Q

Skin Drag

A

Surface roughness of the surface of aerofoil skin
Traps and slows air molecules in boundary layer
Direct result from friction in boundary layer

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3
Q

Form Drag

A

Pressure differences
Static pressure to rear is lower so creates force rearward

Air speed
Frontal Area
Shape/Streamline
Surface

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4
Q

Boundary Layer

A

All skin friction occurs within
Molecules at surface at a stand still
Layers above slowed down until outside boundary lower
Greater viscous air = greater shearing force

Laminar/Turbulent flow within

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5
Q

Laminar Boundary Layer

A

Few mm deep
Shallow velocity gradient
Not much friction/less heat/less energy loss

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6
Q

Turbulent Boundary Layer

A

Thick measured in cm - more mass = more turbulent = more skin friction than laminar
Flow in all directions
High energy exchange between layers
Steep velocity gradient
Greater K resist separation compared to laminar

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7
Q

Transition Point

A

Point of change from laminar to turbulent flow
Laminar flow when viscous force more dominant
Turbulent flow when high inertial forces dominant

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8
Q

Factors determining transition point

A

Speed:
- High speed = greater laminar flow - transition point further back
- Low speed - Greater turbulent flow - transition point closer to LE

Surface Roughness:
- More friction reduce flow of energy laminar to turbulent earlier

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9
Q

Adverse Pressure Gradient

A

High static pressure moves from lower surface to upper surface of wing
Causes separation at boundary layer
Reduction in surface area therefore drop in lift force

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10
Q

VMD Means

A

Minimum drag speed best lift/drag ratio
Induced = parasite
Thrust equal drag to maintain stable constant speed in lvl flight

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11
Q

Speed Stability

A

Natural tendency to return to original speed

Drop in say speed would result in a reduction drag force so natural acceleration back up to the set speed

Speeds greater than VMD

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12
Q

Speed Unstable

A

Back of drag curve - natural tendency to diverge
Speed increases drag increases
Danger of stalling

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13
Q

Speed Netural

A

No tendency to return or diverge
Located around VMD

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14
Q

Effect of Alt on Drag Curve

A

IAS no difference (density not taken into account)
TAS whole drag curve moves right as altitude increase

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15
Q

Effect of weight on the drag curve

A

Increase in weight moves drag curve up and right
Higher induced drag for mass (induced drag curve moves up and right)

Faster VMD/stall speed increases

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16
Q

Effect on configuration on drag curve (flaps/landing gear etc)

A

Increase parasite drag
Induced drag constant
Total drag curve moves up and left

Slower VMD

17
Q

Parasite drag + CL

A

No variation as CL increases parasite drag is the same

18
Q

Induced drag with CL

A

Coefficient of induced drag varies with the square of coefficient of lift

CDI = CL2/Aspect ratio

19
Q

Drag Polar Curve

A

Total Drag (Induced + Parasite) against coefficient of list

Cl/Dmax occurs at Vmd

More efficient wing steeper cl for cd
Flaps move up and to the right (increase parasite and increase in clmax)

20
Q

Factors impacting induced drag

A

Speed - Slower more (Double speed quarter of drag)
Mass - Heavier more drag (More Cl/More induced AOA)
Manoeuvre - More cl more di
Aspect ratio - High aspect less vortices/less AOA so less induced drag

CDI = Cl2/AR

21
Q

Interference Drag

A

Occurs in 3D flow
Around structural joints (Wings and fuselage)
Use of filets to smooth joints and reduce

FILLET OF FISH

22
Q

Value of induced drag in S+L varies with

A

1/V2

23
Q

Effects of fitting tip tanks on induced drag and parasite drag

A

Parasite drag will increase as surface area has increased more friction

Induced drag will decrease as tanks prevent flow around the tip of wing to decrease the vortices

24
Q

How do CDI vary with speed

A

If speed drops by a half (1/4) therefore CDI will be 1/16

25
Q

VMD in jet and prop

A

Jet = 1.6VS
Prop = 1.3VS

26
Q

Aerofoil polar is a graph showing relation between

A

Lift coefficient and drag coefficient

27
Q

Increasing altitude on vmd as a TAS

A

Density reduced therefore TAs increase meaning higher Vmd as more drag from skin friction

28
Q

Polar Drag Curve - Point A on the graph

A

At the bottom below the tangent line
Best rate of climb speed Vy
Best range (jet)

29
Q

Polar Drag Curve - Point B - Tangent line

A

VMD -
Best prop range speed
Best glide range speed
Best L/D ratio
Best endurance (jet)
Best angle of climb (VX)

30
Q

Polar Drag Curve - Just past the tangent line (between VMD and VS) - VMP

A

Best rate of climb Vy
Value for minimum sink rate

POF (25 decks)

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