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