1. Lecture 28: Swimming & Flying

2. direction of biofoil motion direction of biofoil motion
How to fly or swim with a biofoil
1) Lift-based propulsion
direction of biofoil motion
direction of
average force
1) Drag-based propulsion
direction of biofoil motion
direction of
average force

3. Gliding Flight q q a Fvertical lift
Therefore, glide angle is minimal at maximal CL/CD.
Fvertical
lift q
wing tip path
drag q
glide angle a mg
Speed of descent along glide path is determined
by weight

4. Gliding Flight Aspect ratio = span/chord
High aspect ratio wings have largest
lift-to-drag ratio.
Span, R
Chord, c
High aspect ratio reduces
‘induced drag’ – a loss in efficiency due to tip effects.

5. Extended primaries also reduce induced drag.

6. Forward Flight wing tip path lift lift drag drag wing tip path
downstroke
wing tip path
lift
drag
upstroke
wing tip path
upstroke
downstroke
sign of circulation does not change

7. Hovering Flight FV upstroke FV FH lift drag drag lift FH downstroke

8. Hovering Flight upstroke downstroke drag Note that
sign of circulation does change
drag

9. Thunniform swimming lateral Undulation of biofoil FL lift
drag
lift FT
tail tip path FT FL
lift

10. Thunniform swimming lateral Undulation of biofoil tail tip path lift
Note that
sign of circulation does change
tail tip path
lift

13. Penguiniform swimmingFL
drag
lift FT
tail tip path FT FL
lift

14. But these are gross simplifications.
Four basic types of fish swimming
thunniform
carangiform
anguilliform
ostracoderm
But these are gross simplifications.

15. Energetics of Flight Pind Ptotal
Two main costs associated with flight:
1) Induced Power= power required to push air downward
R = wing length F = angle swept by wing U = flight speed
2) Parasite Power= power required to overcome drag on body
Flight speed, U
Power
Pind
Ptotal
‘U-shaped’ power curve
Flight cost minimum at intermediate speed