Chapter 5: Flight

Question 1

Lift

Answer 1

• upward force produced by airflow over the wings
• movement going upwards

Question 2

Thrust

Answer 2

• movement of wings carrying the bird forward, forward thrust is the forward component of lift
• created by rotating the wing forward during the downstroke

Question 3

Drag

Answer 3

• frictional force of air molecules moving over its surface (wings in this case)
• movement that pulls wings/bird backwards

Question 4

Gravity

Answer 4

• force that pulls the mass of an object toward earth
• movement of the bird downward

Question 5

Which part of the wing is the primary generator of lift?

Answer 5

• lift is created perpendicular to the flow of air over the wing
• air flow over the secondaries primarily helps with lift
• producing lift since air flows faster over the upper surface than the lower surface

Question 6

Bernoulli effect

Answer 6

• air can be decomposed into static pressure pushing against a surface and the dynamic pressure moving along the surface
• When air moves faster over the top surface than over the bottom over a cambered wing, the static pressure pushing on the upper surface of the wing will be lower than the static pressure pushing on the bottom surface of the wing
• top: faster, low pressure/ bottom: slower, high pressure
• the difference in static pressure creates a net upward force

Question 7

How does Newton’s 3rd Law relate to lift?

Answer 7

• Lift is also produced by the wing as the asymmetrically curved shape of the airfoil deflects the airstream downward (Newton’s 3rd Law)

Question 8

How do wingtip vortices generate lift?

Answer 8

• When the air flowing more rapidly over the wing meets the air flowing more slowly under the wing at the wing’s trailing edge, the airflow begins to shear or twist against itself, creating rotating vortices of air on the edges and tips of the wings
• A downward wash of air immediately behind the wing and an upwash of air just beyond the wing tips
• formation flying takes advantages of wingtip vortices to generate lift (rotating air pushes off on other wings in V-formation)

Question 9

Angle of Attack

Answer 9

-The orientation of the wing to a current of air - affects the generation of lift

• slight increases of angle can generate more lift with less drag, but at steep angles, lift can be reduced drastically with severe turbulence occuring on the wings, creates stalling

Question 10

What does the Alula do in regards to lift?

Answer 10

• present on primary coverts
• it reduces turbulence/stalling
• it allows for steep angle attacks, can generate greater lift, without reducing lift due to turbulence/ circular airfoils

Question 11

What muscle generates the downstroke?

Answer 11

The downstroke is powered by the contraction of the large pectoralis muscles, which work to pull the humerus bone down as the supracoracoideus muscle stretches

Question 12

What muscle generates the upstroke?

Answer 12

During the upstroke, the supracoracoideus contracts, enabling its tendon to pull the humerus up while the pectoralis muscles stretch

Question 14

Which part of the wing generates thrust?

Answer 14

• the primaries (outer wing)
• Birds produce forward thrust in flapping flight by rotating the angle of attack downward during the downstroke

Question 15

How do birds produce a net positive thrust during forward flapping flight?

Answer 15

• Their wings flex to decrease the angle of attack, reduce camber, and reduce the flapping velocity
• birds fold wings in more to avoid cancelling out forward and backward movement

Question 16

What is profile drag?

Answer 16

• Comes from air colliding with and moving past the bird

Question 17

What is induced drag?

Answer 17

• Comes from accelerating air to produce lift, thrust

Question 18

Why is the curve describing flight power and velocity J-shaped?

Answer 18

• because of many forces at work here!
• From the sum of induced power (which decreases with speed) and profile power (which increases with speed)
• birds have to find balance of distance, speed, drag, etc.

Question 19

Describe the velocity of Minimum Power

Answer 19

• in terms of flight speed relative to power and distance
• the flight speed required to fly with the minimum energy cost per unit time

Question 20

Describe the velocity of Maximum Range ( VMR)

Answer 20

• in terms of flight speed relative to power and distance
  – the speed required to fly with the minimum energy cost per unit distance

Question 21

Power curves

Answer 21

• which measure the mechanical output of the flight muscles, vary across bird groups, owing to differences in morphology, flight style, and kinematics
• Virtually all birds lack the mass‐specific power to hover at low velocities for long periods. However, hummingbirds have an exceptional aerobic capacity to sustain high mass‐specific power.

Question 22

Name two major types of flight

Answer 22

• powered and nonpowered