Flight Mechanics Flashcards
What are the properties of gliding flight/wings?
- High aspect ratio wings
- -> Reduces lift at wingtip (pressure gradient)
- -> Thus, reduces induced drag
- Maximize lift, minimize drag
- Good for flying at max Cl:Cd velocity (max range)
What are the properties of soaring flight/wings?
- High aspect ratio wings
- Compromise: aspect ratio is lowered
- -> Allows lower wing loading, slower speed
- Advantage is to fly slow, take advantage of updrafts
- Allows tighter turning
- Robust/strong structure for take off and landing on land
- Slotted wingtips help to reduce induced drag to mitigate lower aspect ratio
- Good for minimum sink speed
What are the properties of rapid take off flight/wings?
- Elliptical wings
- Low aspect ratio but large lift
- Shorter wings are more mechanically robust
- -> good for resisting forces seen in aerodynamic maneurvers
- -> easier to flap
What are the properties of high speed flight/wings?
- Short tapered wings
- Center of mass and center of lift closer to body
- -> reduces inertia
- -> can be rapidly flapped to increase thrust
Elliptical wings are for ___________ flight
Rapid take off
Pointed wings are for __________ flight
Low speed
Concave wings are for ___________ flight
Gliding?
Convex wings are for ____________ flight
Soaring
Swept back wings are for _________ flight
high speed (supersonic)
Forward wings are for ________ and __________ flight
Maneurverability and Low speed (landing)
Why is high lift and high drag useful for landing?
Slows you down while still supporting your weight
What are the procedures for take off?
- Take off into the wind
- Increase forward velocity (eg: dive off high place(small), jump into air, run forward(big))
- Increase angle of attack and camber
What are the procedures for landing?
- Land into the wind
- Increase angle of attack and camber
- Lower landing gear
- Swoop up wherever possible (approach perch from below)
- Stall
- Touch down
What is the Alula and what does it do?
The alula is the first digit of the hand or the thumb of a bird.
- -> Delays boundary layer separation which allows a higher angle of attack for slow flight
- -> aids in take off and landing
What are covert feathers and what do they do?
Covert feathers are feathers on the top of the wing which can be raised or lowered.
- -> delay boundary layer separation from spreading to the leading edge which allows an increase in the angle of attack
- -> Prevent trailing edge eddies
What is gliding?
The exchange of gravitational energy for horizontal velocity to power flight
The lift:drag ratio is equivalent to the __________:___________ Ratio
Horizontal velocity:Sink speed Ratio
What is soaring?
When you extract energy from atmospheric structure rather than rely solely on gravity and descent
What is slope soaring?
Birds take advantage of ascending air on the upwind side of a hill.
- -> glide normally but the updraft compensates for descent speed and horizontal wind compensates for forward motion
- Bird remains in position relative to the ground, rides the wind
What is thermal soaring?
A bird circles a thermal updraft in order to gain height.
- -> As long as the birds sink speed while in a turn radius of r is less than the thermal updraft Vclimb, the bird will rise
- -> the smaller the diameter of the thermal, the tighter the turn, the larger the sink speed and therefore, makes it harder to extract energy
- -> More useful for birds with broader, slotted wings than high aspect ratio winged birds (gliders)
What is sea anchor soaring?
Bird faces into the wind, spreads wings to generate lift and thrust, but keeps feet in the water to create drag
–> bird moves slowly backwards ensuring constant wind
What is dynamic soaring?
Soaring that takes advantage of variations in wind speed. (eg: flys up into shear wind and down away from shear wind when flying along the coast/ocean)
How do birds measure pressure differences and thus airflow? (along water)
Their beaks resemble pitot-static tubes (manometer sort of thing)
Why is formation flying useful?
Make use of an otherwise unwanted drag (induced drag)
–> birds behind another bird can capture/use the induced drag vortexes of the bird in front of them to create lift
Why would one evolve flight? (5)
- Help escape from predators
- Help catch flying or speedy prey
- Help move from place to place (leaping/gliding)
- Free hind legs for use as weapons
- Gain access to new food sources/unoccupied niche
Why would birds have a lower mortality rate than land mammals?
Ability of fliers to move in three dimensions
–> increases probability of escape
How did wing structures evolve?
- Flate planes originally used for one purpose provided drag to slow descent when jumping, possibly away from predators –> evolve to wings
What are the properties of parachutes?
- Slow descent –> increase dispersal
- Small size is favorable
- Reynolds # is low, viscous forces dominate and drag is high
- -> Lowers descent velocity and increases distance traveled
- Favors bristles or hairy fringes
- -> Bugs should look like dandelion seeds
What would cause someone to evolve wings?
- Sexual selection
- Bounded ignorance
- Solar collectors
- High oxygen
What is the arboreal origin of flight?
Wings evolved from gliding ancestors who began to flap their gliding structures in order to produce thrust
What is the cursorial origin of flight?
Wings evolved because bipedal animals were leaping into the air; large wings assisted leaping
What is the wing assisted incline hypothesis?
Feathers are used as spoilers to increase traction
–> improves escape performance –> leads to flapping which leads to flight
What is the jesus christ hypothesis?
Ancestors ran over water to escape from predators and travel between islands
- -> thrust and weight support were provided by the feet slapping
- -> wings took over some of weight support, with every step toward increase lift providing a fitness advantage
