Theory of Flight Flashcards
What is the air density in an ISA?
1.225 kg / m^3
What is the standard pressure in an ISA?
1013.2 hPa
1 Pascal = ? ft at low level
30 ft
What occurs with temperature at the Tropopause?
It remains constant.
What is the average Tropopause height over the UK?
36 090 ft
What is the rate of temperature decrease in the troposphere?
1.98 C per 1000 ft (lapse rate)
What occurs with density as height is increased?
It reduces.
What factors affect density?
Pressure, temperature, altitude, water vapour
How is density affected by temperature?
Density decreases with temperature.
What is Newton’s First Law?
A body remains in a state of rest or in a uniform motion in a straight line unless acted upon by an external force.
What is momentum?
The property a moving object has due to its mass and velocity.
What is Newton’s Second Law?
The rate of change in momentum is proportional to the applied force and change in momentum takes place in the direction of the applied force.
What is Newton’s Third Law?
Every action is opposed by an equal and opposite reaction.
What one word summarises Newton’s First Law?
Inertia
What one word summarises Newton’s Second Law?
Force
What one word summarises Newton’s Third Law?
Action/Reaction
A gas in steady motion has what properties?
Potential Energy Heat Energy Pressure Energy Kinetic Energy
Total Pressure = ? + ?
Static Pressure + Dynamic Pressure = Total Pressure
Write Bernoulli’s Theorem
Total Pressure = P + (1/2 x ρ x V^2)
In Bernoulli’s what is ρ?
Density
What happens to pressure with an increase in speed?
Pressure decreases.
What are the four forces acting on an aircraft in flight?
Weight
Lift
Thrust
Drag
What is an Aerofoil?
An aerofoil is a surface designed to gain lift from the airflow that moves over it.
What is the Chord Line?
A straight line drawn from the leading edge to the trailing edge.
What is the Chord?
The Chord is the physically distance between the leading and trailing edge.
What is Camber?
The curvature of the aerofoil above and below the chord line.
What is the Mean Camber Line?
A line, equidistant between the upper and lower surfaces of an aerofoil section.
What types of camber are there?
Positive and Negative Camber, providing upwards and downwards force.
What is Angle of Incidence?
The angle at which the aerofoil is attached to the fuselage.
It is defined as the angle between the chord line and the longitudinal fuselage datum.
What is Relative Air Flow?
Direction of the airflow remote from the aircraft and unaffected by its presence.
What is the Angle of Attack?
The angle between the chord line and the relative air flow.
What is Laminar Flow?
The point where the airflow is smooth with no disruption.
What is the Transition Point?
The point on the aerofoil where the boundary layer becomes turbulent and thickens.
What is Wingspan?
The maximum lateral dimension of a wing.
What is Wing Area?
The planform area of the wing.
What is Wing Aspect Ratio?
Aspect Ratio = Span / Mean Chord
What is the Mean Chord?
The average length of the chord is known as the mean aerodynamic chord (MAC).
What shape would a high aspect ratio wing be?
Thin Narrow Wing.
What shape would a low aspect ratio wing be?
Short and Stubby.
What are the three types of steady streamline flow?
Classical Linear Flow
Controlled Separated Flow
Unsteady Flow
Describe Linear Flow
Low AoA
Streamlines follow the contour of the aerofoil
No separation of the flow from the surface
What is the Boundary Layer?
The layer of airflow close to the aerofoil surface. In this layer the velocity of flow is reduced from the free stream flow by the action of viscosity.
What is the Transition Point?
Where laminar flow transitions to turbulent flow.
What is the equation for lift?
L = .5 * Cl * r * V^2 * A
The lift equation states that lift is equal to the lift coefficient (Cl) times the density of the air (r) times half of thesquare of the velocity (V) times the wing area (A).
What is Drag?
Drag is the resistance to the aircraft’s movement in flight.
What is relative air flow?
The direction of the airflow remote from the aerofoil and unaffected by its presence.
What is CL?
The Coefficient of Lift
What is α?
Angle of Attack
What is Rho (ρ) ?
Density
What is CD?
Coefficient of Drag
What is P?
Pressure.
What direction is lift in relation to RAF?
Lift is perpendicular to the Relative Air Flow.
What is the Critical Angle for the Prefect?
15-16°
How does Camber affect the critical angle?
If camber is increased the stalling/critical angle is reduced
What variables are used to calculate the Coefficient of Lift?
Camber
Aspect Ratio
Alpha
Surface condition
What types of drag are there?
Zero Lift Drag (ZLD)
Lift Dependent Drag (LDD) or ‘induced’
What is drag?
Drag is the resistance to the aircraft’s movement in flight. Total drag is the sum of the aerodynamic forces which act parallel and opposite to the direction of flight.
ZLD comprises?
Surface Friction Drag
Form Drag
Interference Drag
Zero Lift Drag occurs when an aircraft is flying at a zero lift angle of attack. All drag forces act parallel and opposite to the direction of flight.
What causes interference drag?
Interference drag is created by the result of flow interference at the wing/fuselage, wing/nacelle, external fuel and weapons.
This can be reduced with internal storage, aerodynamic shapes.
What is form drag?
Form drag is created by the separation of the airflow from the surface. This forms eddies which disrupt the streamline flow.
What is Form Drag?
Form drag or pressure drag arises because of the shape of the object. The general size and shape of the body are the most important factors in form drag; bodies with a larger presented cross-section will have a higher drag than thinner bodies; sleek (“streamlined”) objects have lower form drag.
What factors affect vortex formation?
Wing Planform
Aspect Ratio
Lift and Weight
Speed
AoA
What methods can be use to reduce induced drag?
Winglets
Tip Tanks
Taper
High Aspect Ratio
Washout
Change of the aerofoil section
What is V IMD?
Indicated Minimum Drag Speed
The best Lift/Drag Ratio
Describe the relationship between ZLD and LDD
Zero Lift Drag (ZLD) is dominant at high speed and increases as speed increases.
Lift Dependent Drag (LDD) is predominant at low speeds and decreases as speed increases.
Total drag is the sum total of all the drag forces.
What is the purpose of the Lift/Drag Ratio?
Lift/Drag ratio allows the performance of and aerofoil at a given AoA and airspeed to be determined.
At what AoA is the Lift/Drag Ratio greatest?
4 degrees
The angle of attack at which we obtain the best lift/drag ratio is called the Most Efficient Angle of Attack.
(For the Prefect in the example)
What is the further effect of Ailerons?
Yaw
What is the further effect of elevator?
Height gain or loss/speed interchange
What is the further/secondary effect of rudder?
Roll