Aerodynamics Bob Tait Flashcards
What sort of drag is required to achieved maximum range?
Minimum drag
What will an increase to drag do to range?
Reduce range
What is required to achieve maximum endurance?
Minimum power, lowest rpm, minimum fuel flow
To have the same amount dynamic pressure available in thinner air, what must the aircraft do with regards to its TAS?
Fly at higher TAS
What has more effect on kinetic energy, speed or mass?
Speed
What does the ASI measure?
Measures total pressure and static pressure then it assumes the difference between the two is dynamic
If a mass of air has decreased, what must happen to the velocity of air to maintain asme dynamic pressure?
Increase
What is lift and where does it act?
Resultant of all aerodynamic forces Acts at right angles to direction of motion through centre of pressure
What is drag and where does it act?
Resultant of all aerodynamic forces which act to oppose motion of aircraft. Acts through single point and opposite to direction of motion
What is thrust and where does it act?
Resultant of all forces produced by prop. Acts to produce motion through single direction in direction of motion
Where does weight act?
Centre of gravity
Where does total reaction act?
Centre of pressure
What is the centre of gravity?
Point where weight are evenly distributed
What is centre of pressure?
Point where pressures are even distributed
What is the chord line?
Straight line joining the leading edge to trailing edge
What is the mean chamber line?
Line drawn from leading edge to trailing edge so that it always remains central from top and bottom surface to aerofoil
What is maximum chamber?
Point where greatest separation occurs between chord line and mean camber line
What is the boundary layer?
Shallow layer which is profoundly affected by friction with surface. At point of maximum thickness, laminar flow gives way to turbulent flow
What is the transition point?
Point of maximum thickness where laminar flow gives way to turbulent flow.
What does the energy absorbed by the turbulent flow do to an aerofoil?
Creates extra drag
As air flows over cambered top surface, what happens to its speed and the pressure on the surface?
Speed is forced to increase Decrease in pressure exerted on the surface
What will an aerofoil with point of maximum thickness well back along the chord exhibit?
More extensive laminar flow Less drag
What is the angle of attack?
Angle between chord line and relative airflow
What happens to lift an drag as angle of attack increase?
Lift increase and drag increases
What is lift coefficient?
Measure of how much of the energy available is being converted to lift
Where does air flow across the top surface reach its maximum speed?
Point of maximum thickness
As angle of attack increases, what happens to minimum pressure region on top surface?
Moves forward and becomes lower
What happens to centre of pressure with increasing angle of attack?
Moves forward until stall angle of attack (then moves rearward
What is a stall?
Where any increase in angle of attack produces net loss of lift.
What will the lift coefficient be for a symmetrical aerofoil be when angle of attack is 0?
0
What is the difference in stalls for symmetrical aerofoil compared to laminar flow aerofoil?
More abrupt in symmetrical aerofoil
What is parasite drag?
Form drag and friction generated as air passes over surface
When does parasite drag increase?
As speed increases
At a constant speed, the angle which produces the lease drag produces what sort of lift?
Little lift
At a constant speed, the angle which produces max amount lift produces what sort of drag?
Lots of drag
Where does the best lift/drag ratio occur?
Between angle which produces least drag and max amount of lift (normally about 4 degrees)
At what speed will ratio of lift to drag be at its best when an aerofoil is operate at it’s best lift/drag ratio?
Any speed
What is weathercocking?
Tendency of aircraft to yaw into wind
In what sort of aircraft is weathercocking more pronounced?
Tailwheel aircraft
If the wind is from the front right, what should you do with the control column on the ground?
Pull column back (elevator up) Turn column towards the wind (right aileron up)
If the wind is from behind and left, what should you do with the control column on the ground?
Push column forward (elevator down) Turn column away from wind (right aileron up_
With a clockwise rotating prop as seen from the cockpit, which way will the slipstream effect push a plane?
Pushes tail to the right and yaws nose to the left
When is slipstream effect strongest?
Full power at low speeds
How can pilots fix slipstream effect?
Full right rudder
What are some designer features that can assist with the slipstream effect?
Rudder trim Offsetting the fin so it produces right yaw Biasing the rudder Offsetting the engine thrust line
What does the torque reaction attempt to do?
Attempts to roll the plane in the opposite direction as the prop
With a clockwise spinning prop (as seen from the cockpit), what would happen to a plane if it was in effect of the torque reaction?
Roll to the left. Presses left wheel harder on surface than right wheel, causing left yaw
What is the gyroscopic effect?
When tail is lifted, top of the disk moves forward. Prop responds by attempting to push right hand side of prop disk forward, a yaw to the left
When is the gyroscopic effect going to occur?
Only when change is occurring and its strength depends upon the rate at which change is made
Describe how in a tailwheel aircraft the gyroscopic effect takes place?
As it begins its take off run, prop disk is inclined to the relative airflow. Down going blade makes more thrust than up going blade and thrust line is displaced towards right hand side.
Is there gyroscopic effect in nose wheel aircraft?
Little to none
What is ground looping?
In a tailwheel aircraft, if swung to either side (but mainly left) and allowed to continue unchecked an unstable condition combo of forces prevents it from stopping even with full rudder.
What are the advantages of tailwheel aircraft?
Weight and drag saved Less prone to damage on bad strips and better prop clearance Less rolling friction
What can excessive forward pressure at high ground run speed do for a nosewheel aircraft do?
Wheel barrow (mainwheels leave the ground and running on nosewheel only)
What are some factors that can reduce thrust?
Part throttle Reduction in density Use of carby heat Carby ice Incorrect mixture Fouled spark plugs
What are some factors that increase resisting force?
Too much flap Too much back pressure during take off run Removed doors/windows Soft wet surface/long grass Up hill slope High take off weight
An aircraft is taking off on a day where the density is low, what will its take off speed be in comparison to one taking off with a density that is high?
Will need to accelerate to a higher TAS to compensate for reduction in density
What does low density do to engine performance?
Reduction in engine power Less efficient prop Drastic reduction in performance, TODR and climb gradient
How is skin friction caused?
Air sticking to surface as it passes aircraft
How can parasite drag be reduced?
Changing shape or form of shape (streamlining) Reducing speed
What happens to parasite drag as speed is increased?
Increases (twice the speed = four times the drag)
What is induced drag?
Modification to airflow as it interacts with any lift producing surface
What is the most effective for reducing induced drag?
Keeping wing tip as small as possible. A long thin wing will produce less induced drag
What does vortexes cause to other aeroplanes?
Strong rolling moment
What are two factors which decide how much air spills across the wing tip and hence the development of vorticies?
Magnitude of pressure between top and bottom surface of wing. Time available for air to complete the journey
At what weight, speed and flap setting is wing tip vortexes high?
Heavier, slower speeds and with flaps up
What sort of wing tip vortices will there be with high aspect ratio wings?
Low wing tip vortices
What does washout do to wing tip vortices?
Reduces them
What is the difference in stalling angle between high and low aspect wings?
Low aspect wings have higher stalling angle
Which has the greater lift coefficient, high or low aspect wings?
High aspect wings
If two wings were the exact same except for the aspect ratio, which would produce greater lift for same angle of attack?
Higher aspect ratio wings (long thin). Lower aspect ratio wing would have to travel at higher IAS if it wanted same AoA
Which produces less wing tip vortices, high or low aspect wings?
High aspect wings
What are the disadvantages of high aspect wings?
Long and thin Can take less load
What direction rotation will the vortex be from the left and right wing?
Left wing clockwise Right wing anticlockwise
What rate do vortices sink and stabilise?
400-500 feet per min and stabilise about 900-1000 feet below
When do wing tip vortices being to spread laterally outwards and at what speed?
About 200 feet above ground 3-4 knots
In stable conditions how long can wing tip vortices persist for?
3 mins
Once wing tip vortices stabilise below an aircraft, what area of the sky do they occupy?
Equal to two wingspans horizontally and one wing span vertically
What do aircraft need to do to avoid wing tip vortices?
Remain above aircraft level OR more than 1000 feet below
If vertical separation is not possible, where should aircraft remain to avoid wing tip vortices?
Up wind of generating aircraft
Where should you plan to land if landing behind a large heavy aircraft?
Beyond point of touchdown
Where should you plan to take off from when you are behind a heavy aircraft?
Before its lift off point
What will a 3-4 knot cross wind do to wing tip vortices?
Cause upwind vortex to persist in vicinity of runway
If a heavy aircraft carries out a missed approach, how long may its wing tip vortices be present?
Entire length of runway
Will there be vortices if a heavy aircraft takes off before a runway incursion?
Yes
What is the effect of lowering flaps for wing tip vortices?
Vortices not as pronounced
What will you get if you fly at S2?
Maximum range in nil wind
Least gallons per nautical mile
Best lift/drag ratio
Best gliding range in nil wind
What does the amount of thrust being generated depend on?
- Mass of air being accelerated (density)
- Velocity change imparted to that air by prop disk
What will full throttle at low speed and high speed mean for thrust?
Low speed = high thrust
High speed = low thrust
If full power is applied, when is the thrust highest?
When forward speed is lowest
What happens during take off as forward speed increases to thrust and drag as you apply full throttle?
Thrust decreases and drag increases until they are equal
What happens if you fly at speed S1, S2 and S3?
S1 = Max surplus thrust, max angle of climb
S2 = Minimum thrust for level flight, speed at which total drag is minimum
S3 = Max speed possible for level flight
What is S1, S2 and S3?
S1 = Maximum possible speed for level flight
S2 = Max surplus power and max rate of climb
S3 = Max endurance speed, minimum power and minimum fuel in level flight
What happens when you fly below S3?
You are in the region of revese command.
Flying below S3 requires more power, not to increase speed but to prevent continuous drop in speed
How is parasite drag increased?
- Flap/undercarriage extension
- Increase of AoA
- Increase in speed
How is induced drag increased?
- Decrease in speed
- Increase in gross weight
What does minimum drag get you? And how do you achieve it?
- Provides maximum range in still air
- Best lift/drag in level flight
- Best glide range in still air
- Requires minimum thrust in level flight
What does minimum thrust give you in level flight?
Minimum drag
What does maximum surplus thrust determine?
Max angle of climb
What does minimum power determine?
Maximum endurance in flight
What does max surplus power determine?
Max rate of climb
What will need to be done if speed is reduced and you want to maintain level flight?
Increase angle of attack
If speed is increase and level flight is to be maintained, what will need to be done?
Decrease in angle of attack
As weight is reduced in flight and power is kept constant, what needs to be done to maintain level flight?
Decrease angle of attack
Is range and endurance affected by wind?
Range is but endurance is not
What speed should you fly at to achieve max range in a headwind?
A speed faster than minimum drag speed
What speed should you fly at if flying with a tailwind to achieve max range?
Slower than minimum drag speed
What affect does weight have on max range?
Increase in weight has no effect provided pilot flies at best lift/drag in nil wind
What speed should you fly at to achieve best endurance?
Minimum power at any weight in any wind
Which speed is higher, max range or max endurance?
Max range
What is a higher speed, minimum drag or minimum power?
Minimum drag
What do slats do?
- Delay stall
- Operate at higher angle of attack
- increase max coefficient of lift of wing
What are wing fences?
Improve wing performane and allow slower approach speeds
What do vortex generators do?
- Lower lift off and stall speed
- Improved controlability
- Improved slow speed characteristics
- Almost no effect on total drag or cruise speed
What is a stall strip?
- Strip attached to the leading edge to encourage separation of airflow and promote stall
- Ensures stall commences near wing root and progresses in ‘orderly fashion’ towards tip
How is a climb possible?
Surplus thrust remaining after drag has been accounted for
How do you achieve max rate of climb?
Climb at IAS with max continuous power, this provides max surplus power
As height increases, what happens to power required, power available, surplus power/max rate of climb for level flight?
- Power required increases
- Power available decreases
- Surplus power/max rate of climb reduces
What is the absolute ceiling?
Height where power required increases, power available decreases until no surplus power left
As weight increases in level flight, what happens to power available and power required?
- Power available remains the same
- Power required increases at particular speed due to increased drag at higher speed
How do you achieve max angle of climb?
Max surplus thrust
What effect does a headwind have on max angle of climb?
- Reduced horizontal distance covered
- Angle of climb increased
What effect does a tailwind have on max angle of climb?
- Increased horizontal distance covered
- Angle of climb reduced
When is ground effect noticeable?
One wingspan from the ground approx
What will a conventional aircraft experience upon entering ground effect?
- Nose down pitch
- Increase in longitudinal stability
- IAS and altimeter indications decrease
- Floating sensation
- Decrease in induced drag
On take off, what will a conventional aircraft experience upon leaving ground effect?
- Induced drag increases
- Nose up pitch
- Decrease in longitudinal stability
What does ground effect do with regards to best lift/drag ratio?
Increases it for any given angle of attack
In nil wind, what effect does weight have on glide range?
None, providing we fly at best lift/drag speed
Two aircraft, one heavy and one light are gliding at best lift/drag ratio in a headwind, which will reach the ground first and which will travel further?
Heavier reach ground first and travel further distance over ground
A sudden decrease in headwind will result in what with regards to IAS, lift, rate of descent and angle of descent?
- IAS decrease
- Reduction in lift
- Rate of descent increase
- Angle of descent increase
What will a sudden increase in headwind do to IAS and lift?
- Increase in IAS
- Increase in lift
What will a sudden increase in tailwind do to IAS and lift?
- Decrease in IAS
- Decrease in lift
What will a sudden decrease in tailwind do to IAS and lift?
- Increase in IAS
- Increase in lift
If you double the speed at the same bank, what will you do to the radius of the turn?
Quadruple the radius
If you fly faster with the same angle of bank, what do you need to do to remain level?
Decrease AoA
In a 60 degrees turn, what is the load and stall speed?
Load = 2
Stall speed = 1.5
If the TAS increases and the angle of bank is kept constant, what happens to the radius of turn?
Increases
If bank increases and TAS is kept constant what happens to radius and rate of turn?
Radius decreases
Rate increases
If two aircraft, one heavy and one light, carry out a turn at same angle of bank, same TAS, what will their radius of turn be?
The same
What is a rate 1, 2, 3 and 4 turn?
Rate 1 = 3 degrees/sec (360 in 2 mins)
Rate 2 = 4 degrees/sec (360 in 1 min 30)
Rate 3 = 6 degrees/sec (360 in 1 min)
Rate 4 = 12 degrees/sec (360 in 30s)
What is the formula for finding angle of bank required for rate one turn?
TAS / 10 + 7
eg if TAS was 120, for rate 1 turn, 120/10 = 12, 12 + 7 = 19
Therefore 19 degrees AoB for rate 1 turn
What happens to rate and radius of turn if TAS increases?
Rate will decrease
Radius will increase
What is the tendency of the aircraft during a climbing turn and why?
- Over bank during turn
- Outside wing must cover greater distance than inside wing, and must travel faster. Extra speed = extra lift
In a clockwise turning prop, the combination of high power and low airspeed during a climbing turn produces what sort of tendency?
Yaw to the left
What does an increase in weight do to angle and rate of climb?
Reduces both rate and angle of climb
What does a reduced density do to angle and rate of climb?
Reduces both rate and angle of climb
During a turn, what must the horizontal and vertical component do?
- Hozizontal component of lift generated by wings must provide centriputal force
- Vertical component must be equal to weight
The faster you fly, what must you do to stay on minimum radius path?
Have a greater angle of bank
How is the max rate of turn achieved?
When aircraft flies as quickly as possible around minimum radius path
When is the limit achieved for max rate of turn?
When aircraft is at stalling angle at speed which produces limit load factor
What sort of wing loading are prone to stalling at stalling angle regardless of airspeed?
High wing loading (small wing area compared to weight)
What happen to stall speed as weight is increased?
Stall speed is increased
What happens to the stall speed if load is increased?
Stall speed is increased
What happens to the stall speed with an increase in power?
Stall speed decreases
What happens to the stall speed with flaps extended?
Stall speed decreases
What may ice and/or damage to the wings do to stall speed and stall angle?
Stall speed may be higher and stall occur at lower angle of attack
What happens to the stall speed if centre of gravity is moved aft?
Stall speed decreases
What are two design features that assist with satisfactory progression of stall?
- Washout
- Stall strips
Which wing stalls first in a spin and why?
- Down going wing
- Has a larger angle of attack
If after a small displacement in pitch and the nose moves back towards the level attitude, is the aircraft dynamically or statically stable?
Statically stable
After being displaced, decreasing oscillations are a feature of what sort of stability?
Positive dynamic stability
If after a small displacement in pitch nose moves back towards level however the restoring force is too strong and the nose overshoots. Each oscillation diverges further from the level attitude, what is this said to be?
Dynamic instability
For an aircraft in level flight to cover the greatest distane per litre of fuel consumed, it must be flown at speed which produces?
a) Least amount of drag
b) greatest amount of lift
c) lowest possible drag coefficient
d) lowest possible fuel flow
a) Least amount of drag
Indicated airspeed is proportional to?
a) Angle of attack being used
b) density of free airstream
c) kinetic energy of free airstream
d) true outside air temp
c) kinetic energy of free airstream
For an aircraft to achieve maximum range in level flight in nil wind conditions, it must be flown at a speed which requires?
a) maximum thrust
b) minimum thrust
c) maximum power
d) minimum power
b) minimum thrust
As angle of attack of aerofoil is increased beyond stalling angle at constant IAS, magnitude of lift force of lift:
a) less lift more drag
b) more lift less drag
c) more lift more drag
d) less lift less drag
a) less lift more drag
Laminar flow in the boundary layer tends to persist:
a) across most of the upper surface
b) across most of the lower surface
c) while ever aerofoil section is thickening
d) to separation point
c) while ever aerofoil section is thickening
A laminar flow aerofoil has the point of maximum thickness:
a) well forward and produces less parasite drag
b) near 50% of chord and produces less induced drag
c) well forward and produces less induced drag
d) near 50% of chord and produces less parasite drag
d) near 50% of chord and produces less parasite drag
As angle of attack of a cambered aerofoil is increased in flight towards the stalling, the effect on the total reaction is?
a) point on the chord through which total reaction acts moves aft
b) point on chord through which total reaction acts reamains stationary
c) total reaction increases up to best lift/drag ratio angle, then moves aft
d) magnitude of total reaction continues to increase up to stalling angle
d) magnitude of total reaction continues to increase up to stalling angle
B)
The value of minimum drag coefficient of a particular aerofoil is a factor in determining
a) Max range of plane
b) minimum speed in level flight
c) stalling speed of plane
d) maximum speed in level flight
d) maximum speed in level flight
C
Compared to a nosewheel aircraft, tailwheel aircraft are more prone to weathercocking in a crosswind on the ground because?
a) there is a greater keel surface area behind mainwheels
b) the small tailwheel makes steering more difficult
c) there is a smaller keel surface area behind the main wheels
d) the high nose attitude reduces forward visibility
a) there is a greater keel surface area behind mainwheels
When taxiing in a strong quartering tailwind from the right, the control column should be held?
a) back and to the left
b) forward and to the left
c) back and to right
d) forward and to right
d) forward and to right
The designer can eliminate torque effect during cruise by?
a) offsetting engine thrust to the left
b) biasing the rudder to the right
c) offsetting engine thrust to the right
d) setting one wing slightly higher angle of incidence than the other
D
A
P factor or asymmetric blade effect is present whenever the prop is advancing:
a) at right angles to the direction of the relative airflow with most thrust generated on down going prop
b) inclined to direction of relative airflow with most thrust generated on down going prop
c) at right angles to the direction of the relative airflow with most thrust generated on up going prop
d) Inclined to direction of relative airflow with most thrust generated on up going prop
B
The least amount of total drag in level flight is produced when aircraft is flown:
a) slowest possible speed
b) speed which produces best lift/drag
c) speed which produces minimum lift
d) speed which produces minimum drag coefficient
B
The greatest amount of induced drag would be prouced by applying
a) high angle of attack at high speed
b) high angle of attack at low speed
c) low angle of attack at low speed
d) low angle of attack at high speed
A
