Explain the environmental contributions to flapping flight – how do geese fly in a v shaped formation
There is a region of up wash generated by the wingtip vortices and are a potential source of upward moving air to be used by the birds. Intensity of the vortex increases during the power stroke
How is soaring different from gliding?
- soaring involves a local wind coming from below the animal because it is at an angle the drag force is compensated such that the resultant lift+drag force= weight
- gliding requires a loss of altitude whereas soaring does not ( soaring = gliding with an updraft)
- if the vertical component of the wind is greater than the glider’s sink speed then it can gain altitude
What are 3 sources of wind in the environment?
- hills and cliffs
- rising thermal
- dust devils
What are the 4 different sub types of soaring
- slope soaring
- thermal soaring
- sea-anchor soaring
- dynamic soaring
What is slope soaring
- hillside forces the wind to move upwards
2. have an updraft created that an animal can use
Describe the structure of a thermal vortex
- sun heats the ground and warms up the air
- a bubble of warm air rises up from the ground
- as it cools it expands
- a donut shaped vortex ring is formed (vortex grows in size)
Describe thermal column soaring
- glider gains altitude by circling through a thermal allows spiral ascension.
- bird needs to fly in a circle by banking its wings to some angle to the horizontal
- increasing the angle of bank to circle within a thermal increases the rate of descent
- increasing the angle to turn a smaller radius reduces the vertical component of lift. thus lift force must be increased by increasing sink rate to increase air speed
- for a glider to not sink the rate of sink due to banking must be smaller than the updraft velocity
What limits the size of the thermal that a gliding animal can use
the vertical updraft of the thermal ( because if you bank at a high angle - the greater the banking angle the less vertical force you have to compensate the weight )
How does the small thermal affect banking angle
small thermal means you need to turn under a tighter radius which means the banking angle increases
How does wing loading affect the minimum turning radius
high wing loading implies a greater lift force is needed, so high flight speeds are needed to produce high lift and so larger turning radiuses are needed
Describe sea anchor soaring
- birds can glide above the surface of the water
- to maintain the airflow over their wings without being blown backwards, their feet are used as sea-anchors and are dragged through the water, the drag through the water resists the aerodynamic drag induced by the wind moving past its body
- when sea-anchor drag = wing drag the body is suspended
What is dynamic soaring
- flight pattern that uses velocity gradients of the wind above the ocean
- bird turns into the wind to increase the altitude (potential energy increases and the kinetic energy decreases
- turn 180 degrees travel down towards the water to increase the kinetic energy and decrease the altitude
What affects the radius which a bird can turn in a wind thermal
the wing loading
What other factors are needed for soaring ability
need to have high maneuverability
What are the advantages of winglets
reduce induced drag, even though you have a low aspect ratio you can reduce vorticity – can function like long thin high aspect ratio wings
Where do thermals normally occur
occur over land so birds avoid straying into water
