flight

Question 1

what are the forces involved in flight

Question 2

what are the principles of how birds generate lift and thrust

Question 3

describe the main factors which determine flights costs in still air

Question 4

outline why flight is important

Answer 4

• 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

Question 5

what is the biggest problem when it comes to flying

Answer 5

GRAVITY

Question 6

what is weight

Answer 6

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

Question 7

what are the four forces which act on birds in flight and which ones oppose each other

Answer 7

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

Question 8

what is parachuting

Answer 8

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

Question 9

what is gliding and how does it work

Answer 9

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

Question 10

who are the two people who can explain the force of lift

Answer 10

1) Daniel Bernoulli
2) Isaac Newton

Question 11

what is the Bernoulli’s principle

Answer 11

as the speed of a moving fluid increases, the pressure within the fluid decreasing

Question 12

how is lift generated in a fixed wing according to Bernoullis principle

Answer 12

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

Question 13

outline the old theory of lift production and why is it wrong

Answer 13

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)

Question 14

what factors need to be considered when calculating lift

Answer 14

• lift coefficient
• air density
• wing area
• velocity

Question 15

outline how lift varies with air density

Answer 15

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

Question 16

how does lift and speed correlate

Answer 16

lift increases with speed^2
= lift must equal the birds weight for it to maintain level flight

Question 17

what is newtons third law and how does it answer ways of getting lift for a bird

Answer 17

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

Question 18

what is the angle of attack and how is lift generated from this

Answer 18

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

Question 19

what happens if the angle of attack is overdone (usually when its more than 20 degrees)

Answer 19

causes turbulence of air behinde the wing so the flow no longer attaches and lift is lost = this is known as a stall

Question 20

how does the role of the alula work in regards to stalling

Answer 20

slots/auxiliary aerofoils on the leading edge of the wing help prevent flow seperation allowing steeper angles of attack and delays stall happening

Question 21

outline how a wing creates lift due to the combination of Bernoulli’s princple and Newton’s third law

Answer 21

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

Question 22

How is thrust generated in the wing compared to lift

Answer 22

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

Question 23

how is lift produced for take off

Answer 23

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)

Question 24

what are the overall costs of flight

Answer 24

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

Question 25

what does the scaling of avilable power explain

Answer 25

why
1- large birds often run to take off
2- large birds dont hover
3- large birds are more likley to soar