Week 2 p 1 Flashcards
What forces act on a moving car?
Fgrade (mgsin0), Fdrag, and Froll resist movement.
Fpropulsion moves forward.
Flift and Fnormal act perpendicular to road surface,
Fweight acts down.
What is the net force acting on a car?
Fnet = Fpropulsion - Fdrag - Froll - Fgrade = ma
What are the work and power formulae for a car?
Work = force x distance = Fpropulsion x distance
Power = force x distance/time = Fpropulsion * velocity
What are the forces acting on a plane in flight?
Drag, (1/2 Cd p Vair^2 S), weight, (mg), lift, (1/2 Cl p Vair^2 S), thrust (Ft)
What components of drag contribute to a plane in flight?
CD0 - parasitic form drag - caused when lift = 0 and solid object moves through fluid, is a function of shape and Reynolds number
Lift-induced drag CL- Occurs as the result of the creation of
lift on a three-dimensional lifting body, such as the wing of an airplane
When is aviation drag optimum?
When parasitic form drag (increases with velocity) meets with lift-induced drag (proportional to 1/v^2) at the minimum level.
How does a heavier aircraft require greater thrust?
A heavier aircraft requires more lift, which leads to more induced drag, which in turn requires greater thrust
What is S and what is AR?
S = wing area (cross-sectional area of the top of the wings)
AR = aspect ratio = wing span (b)^2 / S
What is level flight?
When drag and thrust forces are equal
What is the drag force expression and how does it relate to power in level flight?
πΉπ· = πΆπ· * 1/2 *ππair^2 * S
Where CD= CD0 + CL
Power in level flight= FD*Vair
In takeoff what gets the plane moving?
Whatβs the efficiency of the aircraft?
Thrust provides force to accelerate aircraft - combustion of jet fuel provides energy to provide thrust
Efficiency = FT * Vair / m-dot-f * hf
Why has energy efficiency improved for flights?
Tech
* Thermal efficiency (overall pressure ratio)
* Propulsive efficiency (bypass ratio)
* Reducing weight of aircraft using composite materials (reduced lift-induced drag)
* Improved aerodynamics that reduce parasitic drag (e.g. wingtips, 3-6% reduction in
fuel use)
Operations
* Routing, load factors, better maintenance
Why is energy per passenger km important for flights?
kWh/passenger km reduces when planes are filled
What energy transfers are involved in vehicles?
A petrol (stored chemical energy) car has an internal combustion engine that converts this energy into heat, kinetic and sound energy
An electric car relies on electricity that has (typically) been produced in a
power plant (combustion), stored in a battery, and then fed to an electric
motor that converts electrical energy into kinetic energy
What are typical inputs for combustion?
In: fuel (C(alpha)H(beta)) + air (N2 and O2) -> high temperatures as heat energy made + CO2 + water + products from incomplete combustion (left over fuel, CO, black carbon) + contaminants in fuel (lead and sulfur) + NOx if temps high
What is hf and how does it link to combustion?
Combustion of a fuel releases energy, the heat of combustion, βπ. (a.k.a. lower heating value, lower calorific value) units [MJ/kg]
Why is the amount of CO2 released a property of fuel?
The amount of CO2 released through combustion is a property of the fuel, as the combustion energy is released by splitting C-H bonds
How can you calculate CO2 intensity?
CO2 intensity = no. of CO2 molecules released in reaction * molecular weight [g/mol] / no of fuel molecules required * molecular weight of fuel = kg of CO2 released per kg of fuel used
