PoF Flashcards
Units of Distance
1NM = 1852M
1M = 3.28ft
1KM = 1000m
Units of Vertical speed
1m/s to 196.8fpm
Units of Horizontal Speed
M/s = 0.5144 x knots
Approximate Conversion factor -> Halve the number of its to find m/s
Units of Acceleration
Acceleration is the change in velocity
1kg force = 9.81N
Mass x Acceleration = Force
Momentum
Can never be lost -> it’s always in exchange with other masses
Mass(kg) x Velocity(m/s) = Momentum
What is Energy?
Energy is the capacity to do work on something. It is ‘conserved’ meaning it cannot be created or destroyed.
What is kinetic energy?
The energy possessed by a mass in motion.
Kinetic energy can be converted into other sorts of energy.
What happens to the energy when the velocity has doubled?
The energy increases 4x.
What’s the formula for kinetic energy
1/2 x mv^2
What is pressure energy?
It is contained in billions of molecules in a gas.
What is work?
It is energy converted from one to the other.
What is the formula for work?
Force(N) x Distance(m) = Work
What is power? What is the SI unit of power?
Power is the rate of doing work
The SI unit of power is watt(w)
What are the equations of power?
Power = work / time
Or
(Force x Distance) / Time
What is Newtons 1st Law?
A body will remain at rest or in uniform motion unless acted upon by external force e.g throwing a hammer at 5m/s.
What is Newtons 2nd law?
The acceleration of a body in a straight line is proportional to the applied force and inversely proportional to the mass of the body
e.g pushing two balls with the same force but different sizes.
What is Newtons 3rd Law?
To each and every action there is an equal opposite reaction.
e.g when a ball is pushed and hits another ball, the energy is transferred onto the other ball making the ball move along.
What are the implications of newtons laws?
- Thrust force is created with accelerating molecules
- Weight acts downwards.
- In level flight if an aircraft has a weight force of 20,000N the lift force is 20,000N.
What is density proportional and inversely proportional to?
It’s proportional to pressure
It’s inversely proportional to temperature.
What’s dynamic pressure and what is the formula for it?
Pressure in the air that tributes to movement (goes in all direction)
1/2 x p x (v^2)
What are the errors of different airspeed?
Instrument -> Indicated Airspeed -> Position error
Pressure -> Calibrated Airspeed -> Compressibility error
Compressed -> Equivalent Airspeed -> Density error
What’s the equation for True Airspeed (TAS)?
TAS = EAS x sqrt(1.225 (Po) /modified density (P) )
What is the formula for Equivalent Airspeed (EAS)?
TAS = EAS x sqrt ( modified density (P) / 1.225 (Po) )
Which property of air is responsible for frictional forces (stickiness)
Viscocity
Outline the pressure and velocity distribution around an airfoil
- Area of lowest static pressure is around an airfoil
- Higher than ambient pressure at leading and trailing edges stagnation points
- Above the wing the velocity of the air is faster than free stream flow.
- Below the wing the velocity of air is slightly faster or slower than the free stream flow
- The velocity of air is zero at stagnation points
what types of drag does the viscosity of air produce?
Skin Friction Drag - caused directly from friction within boundary layer.
Form Drag - Produced by effect of viscosity on the pressure distribution around the object
Camber describes the distance between?…
The mean camber and the chord line.
What happens to the dynamic pressure when airspeed doubles?
Lift = 1/2 x ρ x V² x S x CL
If airspeed doubles then dynamic pressure will increase by 4.
Lift is proportional to V^2
Remember velocity is squared in the lift equation. so doubling velocity would be 2^2 or (2x2) which equals 4.
What are the effects of wing thickness?
If the thickness is smaller, both the CLMAX and stalling angle (critical angle of attack) decrease. Low speed aerofoils tend to be thicker.
If the thickness is bigger, both the CLMAX and stalling angle (critical angle of attack) increase. High speed aerofoils tend to be thinner.
What is lift proportional to?
IAS^2 x S x C_L
What is parasite/profile drag?
Form Drag, which is the result of the aerodynamic resistance to motion due to the shape of the aircraft.
Skin Friction Drag, which is due to the smoothness.
Interference Drag, which may occur where surfaces with different characteristics meet (e.g. wing and fuselage)
Coefficient of lift is derived from
Camber, AoA & thickness
Bernoulli’s equation
Total Pressure(Pt) - Dynamic Pressure(q) = Static pressure(Ps)
Or
Dynmic pressure + Static pressure = Total Pressure
What are the three AoA protections?
Alpha protection
Alpha floor
Alpha maximum
What is the Force coefficient
F = q S CF
F = 1/2 p v2 S CF
Cf= F/q S
What is the Force coefficient
F = q S CF
F = 1/2 p v2 S CF
Cf= F/q S
What happens in the boundary layer?
All effects of skin friction drag which reduces the airflow as theres is friction obstacles. as the airflow rises amongst the viscous layer it slowly returns to free stream flow
What is the transition point?
When laminar air mixes with turbulent air.
Laminar air can be a few millimetres deep
Turbulent air can be centimetres deep
Whats control buffeting
When turbulent air separates from the upper surface.
As buffet increases AoA increases
What happens to the wings in a stall?
Before:
Lift remains constant
Total drag increases
Centre of pressure moves forward
After:
Lift reduces substantially
Total drag is much greater
Centre of pressure is moved aft
