flight Flashcards
what are the forces involved in flight
what are the principles of how birds generate lift and thrust
describe the main factors which determine flights costs in still air
outline why flight is important
- contributed to the success of insects, birds and bats
>1000 spp of bat
~10,000 spp of bird
>800,000 spp of insect - allows access to other sources of food
- allows predator avoidance
what is the biggest problem when it comes to flying
GRAVITY
what is weight
the mass of an object will always remain the same
the weight is a force caused by the gravitational attraction of earth
- Force = mass X acceleration (newtons second law)
therefore weight is the force which is influenced by the mass of the object and the speed it moves
what are the four forces which act on birds in flight and which ones oppose each other
1) Thrust = force acting in the direction of travel
opposed by
2) Drag = the force opposing the direction of travel
3) weight = the force caused by the gravitational attraction of earth
opposed by
4) lift = a force that acts perpendicular to the oncoming airflow
what is parachuting
involves maximising drag to minimise the impact speed and requires an airbrake
= to increase drag and reduce speed you need to increase surface area thereby increasing the drag resistance acting on you
what is gliding and how does it work
a different technique which requires the generation of lift but involves no thrust where by spp ascend at a non-vertical angle
- works by angling body to flow and move fowards so air can move over surfaces and generate lifts upwards
who are the two people who can explain the force of lift
1) Daniel Bernoulli
2) Isaac Newton
what is the Bernoulli’s principle
as the speed of a moving fluid increases, the pressure within the fluid decreasing
how is lift generated in a fixed wing according to Bernoullis principle
wings are cambered with a slighlty convex upper surface and a concave under surface
- as the air moves over the wing it is forces to move faster over the top surface than the bottom
- As air speeds up, its pressure goes down
- slower moving air below the wing creates a greater pressure and pushes up
- lift is produced
outline the old theory of lift production and why is it wrong
air moves faster over the top of the wing because it has further to travel = wrong
= flow is accelerated as it hits the curved surface
= when the airflow moves in a circle at a constant spped its velocity is constantly changing due to changing directions
= this constant chnage means the air is accelerating (centripetal acceleration)
what factors need to be considered when calculating lift
- lift coefficient
- air density
- wing area
- velocity
outline how lift varies with air density
according to the lift equation lift is directly proportional to air density so as air density increases the lift force will also increase and vise versa if all other factors remain the same
therefore birds which fly at higher altitudes with less dense air have to work harder to generate lift
how does lift and speed correlate
lift increases with speed^2
= lift must equal the birds weight for it to maintain level flight
what is newtons third law and how does it answer ways of getting lift for a bird
for every action there is an equal and opposite reaction
the rate at which air is deflected down is also the rate at which lift is generated
what is the angle of attack and how is lift generated from this
lift is related to the angle at which air is deflected downward
smaller angles = less air deflected downwards = less lift
larger angles = more air deflected downwards = more lift
what happens if the angle of attack is overdone (usually when its more than 20 degrees)
causes turbulence of air behinde the wing so the flow no longer attaches and lift is lost = this is known as a stall
how does the role of the alula work in regards to stalling
slots/auxiliary aerofoils on the leading edge of the wing help prevent flow seperation allowing steeper angles of attack and delays stall happening
outline how a wing creates lift due to the combination of Bernoulli’s princple and Newton’s third law
faster air, less pressyre causing the wing to go up (method one) as the air hits the wing the air is turned downwards causing the wing to go up (method 2)
= once air is moving over the wing, lift is created
How is thrust generated in the wing compared to lift
Thurst = mainly generated by primary feathers which twist on the down stroke and act like propeller pushing air backwards
lift = mainly generated by the secondary feathers (the inner portion of the wing) which form an air foil
how is lift produced for take off
lift increases as a function of velocity^2
= at low speeds you cant get enough lift to get airborne using Bernoulli effect alone therefore wings need to impart downwards moementum to air (Newton third law)
what are the overall costs of flight
1) induced power= the power needed to impart downward momentum to air decreases with spped because lift increases with speed = when moving slow they need to invest more energy
2)drag increases with speed = in order for an animal to move foward it must produce enough thrust to overcome drag
what does the scaling of avilable power explain
why
1- large birds often run to take off
2- large birds dont hover
3- large birds are more likley to soar
