5.2 The aerofoil

decrease pressure

5.2.1 An introduction to flight dynamics IfywlooL&abird~intbe~t@oiw,aaatanWwiPg,yauwiU s e c t h a t i t b m a d i n ~ . A ~ b i r d w i n g & i s ~ i n Fqpe5.2a W h m p i r h d i n a n a i r b w , the a i r tba t~dver tbe topof thtwing&movasWthanWtrav~be2aa,1sr~meofthe ~ ~ 0 f t b t W i n g . T b e M ~ i a ~ ~ a d i f I s P e n c e i t i ~ a t g w r e b e t w e m l t h e u p g e r a d l o w e r ~ . k , w m i a a ~ ~ ~ a c r o s s t b e w i n & w i t h t b e h i * ~ ~ , ~ ~ ~ 5 . Z a , b ) . T b e h r p r t k ~ a r e a w a ~ ~ a i t f l a a s r , ~ ~ t b ~ Y ~ h a v e r e r d p b W t ~ ~ o f h y ~ ~ l i f t a s a ~ h m o r e s througharster,inMw~2.3.3.Iatbe~h,Wwas~geaeratbdif~ m a n ~ d ~ a a d i f h @ w ~ s m a l l . S i m i l a r l y , k a n ~ , l i f t i s ~ ~ h ~ ~ o f a & q b o f ~ ( ~ - S 0 t o + 1 5 ° ) . A t ~ m g l m a f ~ t b e I i f t d ~ .

W h j r d o e s t k f i f t ~ a t l a r g c ~ o f i n c l d e n c e ?

-61 l i n * i y r r W d - JB-=

h y o u h a v e r C p d i a ~ 2 . 3 . 1 , f o r t b e h y d r o f o i I a t d ~ s o f ~ khoverraWdblaarinPr@gure5.3a,b).hthea@eofinci~ i a m P s e s ~ ~ 5 . 3 b , c ) t h t ~ w ~ u p a e d B p i l l s o f f ~ u p p e r s u r f ~ o f the itemfoil as turbulence. The velwity of the flow and the pressure g d k n t xmm tbe atemfoil is mbmtial ly redud, h d h g to a loss of lift. At P h e p o i n t w b o r e t b t l i f t i s s o ~ ~ i t ~ ~ t m ~ t h t p v i ~ d force, the wing starts to fall and is mid to have stalled The optimum anglt of incidence for m is around 15'.

fast air flow

d o i l (wing) C

F@m 53 (aHc) The M - t of h b d e n t a i r f i o w ~ m m f d a s t h angle of lacidence U. (d) All the a u g l e o f ~ o f t h e ~ e ~ f o i l km=h lift (L) - dra% (Dl ~ P , . T b c ~ o f t h t n s o w s f m L d D ~ * ~ t a d t o f ~ fmxa.

*c 9 J

low asps d o

-5.5 % o b i r d ~ W h a v e & ~ a ~ e p b o c ~ ~ r p t i o s T b e t w o ~ ~ ~ ~ ~ ~ t t k c ~ ~ ~ l r t - . N O t e ~ t b e w is a -t & from wing-tip to IAy, mM *-tip to wing-lip. (a) A shrwater ( & @ k ~ l r P i n g ; I b ) r p h a m t ( P A s s h c d c A k i r s ) ~

~ a r e s o m ~ ~ b e t w ~ ~ r a t i o a n d t b e ~ f e o f ~ t . I n ~ , b i F a g t h a t ~ o r u s t h i ~ @ f l i g b t h a v e w i a g s ~ h i ~ ~ ratios. Birds cslpableofarapid talra-offorofsoaringonthmdj gtnerallyhvt W i n g S w i t f i l o w ~ ~ S o m a - f o a t b e s E ~ ~ ~ l ~ w i l l b e c o m e ~ t w f i e a w e ~ m a r h g d g I i d m g i n ~ o n 5 . 4 .

C

Summary of - xtion 5.2 A n d d c a a ~ l i f b ~ a w s w i a g ~ ~ m & m f o i l . T l m e ~ ~ m ~ t h e ~ o f l i f f : t b e a r e a o f t b e * t 8 e s p e e d o f t h e a i r f l o w i n g o w r i t a a d t B e a n g l e o f ~ a f t b t w i a g t o ~ ~ o f s i r ~ ~ T h e a r t a o f t h e ~ i s ~ t e t b e s i a e o f t B e ~ d l a r g t r ~ ~ ~ ~ w i n g s . ~ e m , t b e ~ ~ ( m p s s & t b E ~ d i ~ ~ ~ W ~ r e s t o f the wings)isg&inhgesbirds.'Ik *oftbe wingsofabirdrekchits l i f e s t y l e . W ~ c a a h s h o a o r l o n g , ~ o r ~ , b u t t t S e ~ c a n b e -h- . , ~pptio(thtfatiO0fthtwimgspatltDtht Chad).

5.3 The fsrces acting en a bird in flight

lift

rter 5 Princip

~ ~ l i f t a s a n u p w a r d f o ~ c e i s n o t s ~ c t l y ~ s i n c t i t ~ ~ ~ ~ m that thebird i s f ly ingpara l l e l trohgnrund.I tmaywel l~be ,w~more~ ~ t i o n o f l i h i s : t h a t p w t o f t h c f a r c t ~ o n ~ w i n g w h i c b i s ~ t o t h e Man of the air flow. &s in the samc dimdon as tbe air flow ( F i i 5.2b). Both lift and drag inmast with the speed of air flow, roughly accarding to h e square law--tbat is, lift and drag arc p q m t i d to ?he quare of the sped of air flow which is compamble to tk situation of a fish in water (Section 2.3.1). Soth alm depend u#m the size of the bird and the density of the air.

T h e f m ~ & @ i n F ~ 5 . 6 h a s h ~ n t s . T h e f i ~ k w t t b e b o d y ~ ~ d r o g , D , , w h i c h i s d e p e n d t n t u p o a t h e s h P p e a n d s i z e o f ~ b o d y . T b e Q a g ~ r e g ~ f m m t b t a i r f l o w o v g t h e w i n g s i s ~ ~ ~ ~ a n d i t i s ~ d b y t h e s t n r c t u r e o f t b e w i n g s . T b e t h i r d c o m p o a e n t i s . ~ drag, Di, w M is armcktd wih the beating af the wings to gen#abe lift Di, unhrce D, and D,, does not inmeme with the square of the speed, but is greatest at slow speeds close to stalling (Pipre 5.7). We shall retm~ to the phenomenon of induced drag in Section 5.7 in cuxmdon with wake analysis d vortex tbewy.

Most birds develop lift and h t on the downstroke of the wing, flexing the wing on the upstroke to minimize D,. However, this is not the case far all birds. For example, the ltestrel ( F a h t innmch) generates lift on the upstrake also, which c u n t n i to supporting its weight, but reduces tk man thmt Analysis of the fight of biPds in w i n d ~ h h a s s h o w n t h a t i n s m p l l b i r d s t h e u p s ~ ' ~ ' s ~ y has little or no d y n a m i c effect h the pigeon, for example, the wing lip is moved close to the body on the upstroke and only a small @on of each wing is in tlae air flow.Thisactionreducesdrag,but~notgeneratethrustorlift.

~ h a t i s t h e ~ ~ ~ ~ ~ d ~ h f w t b e v e l o c i t y o f the bird?

I f t h e ~ t r o k e d o e s m t ~ l i f t o r t h r u s t , t b e b i r d ~ ~ ~ ~ ~ However, birds ldapted for gliding may keep th wings exteadd during tbe qMmh m fast flight, generating lift A bid that glidea m d l y has thimr wings with a high d o , factors that wjll give lower drag. For birds with a wing that produecs high drag, generally the smaller b a d and tborse with a low aspect ratio, the Optimum strategy is to have a passive upstroke.

AsyouwillreadinSection5.7, t h e d i f f e r m c e s b e t w e G a t h e w i n g ~ o f different s p e c k ofbirdhaveameqmws forth rtir mmmm@ aPolaad -birds.

5324 Iamk 4 Animal Perfmrrnance

Summary of Section 5.3

5.4 Soaring and gliding .,

b t h w i n g i o a d a ; a g d ~ r a t i o ~ ~ @ ~ T h e ~ o f a g l i d e ~ m t b e w i n g ~ w ~ a l s r g e b i r d t r * v d s ~ ~ a d c l l p e r & d ~ a t a ~ a n g l e . T h e a n & i s p f i o ~ o n ~ ~ p e c C r r t i o d t l a e w i n g . A M w i t h r ~ ~ - r a t i o ~ b t b e ~ (Dhdea sp.), can glide at a ddhwer angle d m a vuhm (e.g. Gypsjulvus), whkhbPsalow~mqmct&io.

Tbe rate 3 which a bird is the-- qss& Measuremwts of ~ s p a a d a t ~ a i r s p d s h a v e ~ t b a t t f t e r e a r e d i f f e a w a c e s b e t w s e r r ~ k . ~ ~ h a s a m i n i m u m s i a L i n g @ d ~ t r n d t r 2 m ~ - ~ -facapigeoaphefigrrreis25m~~.Byaomparison,anaircraftbuiltb ~ c a n h a v e a s i & n g s p c a d o f d e a d e r tmrl.

A h i @ + p c t - m t i o w i n g w o d d b e ~ w i t h g m i ~ a b i l i t y a n d b a slow nlnlrmpspd, s u t k ~ w d d b a v e r higher aspectratio wing than the pigeoa.

5.4.1 Forces acting on a gliding bird 1 . ~ s t i m 5 . 3 ~ m ~ ~ ~ ~ . c t i . l l m . ~ & i t * . I ~ . O b v i d y t h e f - ~ m a ~ b i r d . = ~ , k r t t b s ~ i s W ~ . F i g u m 5 . 8 h a g h h g b h d ~ i s ~ r r t a a ~ . T b e ~ p P t h i a i e c l i n e d t o ~ ~ m ~ t h e ~ t h r U s t i s ~ b y t h c & a g - ~ i s a v g t i c a l r m d t x n t f o n x t h s t ~ t b c w e i j # a d t b t W d e s c e ~ a t a ~ ~ v e l o c i t y a n d ~ Y ~ ~ p Y w a a ~ r e ~ i t w a ? 3 ~ ~ t 8 t i i f t w a d d ~ ~ ~ L L - ~ m ~ - a r i t f i a w v + i t y .

, Why W M l M t k f ~ ~ ~ a r d v c k i t y ~ ?

Chapter 5 Principles rf Flight

5.4.2 Soaring on thermals

S324 Bask 4 Animal Ptrfermanct

r n n r ~ o c h . p . * ~ ~ ~ l ; r ' ~ 5 . 4 ) , r n . t b e a m r l ~ p r o r i d e a n o t g r i S i e ~ . ~ ~ ~ ~ I 1 ' ~ ~ 0 ~ 1 ~ ( ~ ~ U u ) o v s r t k ~ p l a i n s b a v e s b o w n t h a t l a r g e ~ c a n b e ~ ~ y b y ~ o n a t h e r m a l a n d t b e n g l i d h g t o t l a e w x t . T B t ~ P s r t o e ~ a t ~ e d g e oftheplaiaandh travel to their ~ ~ m m d ~ ~ B f A l p m m o ] f i h t W t t b e S e r e p g e t i . Colin ~ o f B r i g b o l U n i v a & y ~ t k v u l t l l r e s i n a m o t o r i z e d g l i d e r a a d d i ~ ~ c m e ~ ~ t r o ~ 7 5 k m h d y % ~ e n t i r e l y b y ~ ~ ~ . ' I b e ~ e a n ~ v e l t o ~ ~ o a ~ , t h u s risigghthelevcloftbeiacliff~befcwetrtrvnIagfromfaading.

5.4.3 Slope soaring

Chapter 5 Principles m f Flight

Summary of % d e n 5.4 L a r p s e ~ ~ ~ g C - e - e ~ b y ~ ~ l b P ~ ~ . W t r b * i n h p i t i o n , a b i r d p i f i - h . s p r 3 d m & i g s ~ ~ b y t f R w i n g B o a d i n g d * ~ ~ ~ * Z a r e l i p r p w h e r e t h e r e a m - a r ~ Q t m s i r ~ , ~ m ~ ~ ~ 4 y ~ ~ t k ~ a i r . T b e W w i U ~ ~ ~ ~ a i r i s r i s i n g f a s t e r t h a n t h e b u d ' s ~ ~ m d l l i c ~ g m d a k g e o c e a n w a v e s w i l l ~ I l i r ~ d ~ ~ u s e t h i s t o ~ a s t r a O e g y called slope soaring.

Structure of the bird wing Birds first in the fmd recard during tht ZllnsaiE p i m i 1 6 2 0 8 million ago, evolving b m tbe -m gmq of-. Thebirdwingevolvedfromtbefront~dm~ ' " "' withhfrmt l i m b o f k @ p d s ~ a s ~ d ~ . ' I h t s c ~ ~ ~ when a wing is cumpad with a kPlaen arm ( F i i 5,12). Swne of tbe W m directly mmpmbk, but from tbe wrist to tk lip of th limb l h r c k w immediate similarity. The birds wdved from q t h wbich had a peatadactyl

5324 B4.k 4 Animal Perfmrm

O v e r b o t b ~ o f t h e w i n g ~ ~ t h c c o n t r w r f ~ w h i & g i v e t b e W i n g i ~ ~ ~ . T h t c o n t o p r ~ h a v e b e e n ~ ~ ~ ~ ~ illustrddin Pigwe 5.12. They a M oeQ the skin-,dwcwm hwings,mmfeathers,mthcwfesthers,donothahh.

Thefmt d i g i t & a d groupof fe s tbgswhichtog~famtbt~rr ~ ~ ( ~ b l e c m t b e ~ i n P & t e 5 . 1 ) . T h t ~ h a s a ~ ~ o f m o v e m e n t . I t m ~ m i m d i a t o ~ P i T ~ o y e l c t k ~ t O ~ m a s t h e ~ ~ o s b l l . T b e b m i n m ~ ~ t b e ~ ~ o b * i r o v a t b e ~ I x g i m t o ~ u p a t l a i r s p d d m p s o e O h e m g l e o f ~ ~ a i r f l m ~ ~ t , l i f t d a c l i a e s d t h e w & a ~ W b s n a M ~ t b e a l u l n i n t o t h e ~ t b # l t i s a o ~ i n t h e v e h i @ o f t l x a i r t r a v e ~ ~ t k ~ p p ~ t b e p l p l n s D d t b e m a i n w i n g . ~ hmase gcnem?m extra lift d tbe pmmm of the ahla idp m*inbain f l o w , s o ~ ~ s o f i a e i d w c e c a n b e ~ k f m ~ d ~ lift is pmblxd

b

W Wbenmightywseeabirdithh-rPisadWtbe-ovah wing?

rttr 5 Principles ef Flight

v a n -

5324 Book 4 Animal Pcrferm,

-+ A~~~~~ ufabirdabowiaghowthethin ~ J 1 ~ ~ b y ~ a i b o t # T b e ~ * ~ t b h W . ~ p r e 6 u e d a r i t h air.

Summary of Section 5.5

Chapter 5 Principles of Flight

5.6 Flapping flight

c S Anirn

~ i ~ r b o u t h ~ t i o n o f t h e ~ ~ r ~ ~ t e o ~ p o i a t o f articulationoftbe wing?

W i s - t e r - ~ v c ~ t t b e ~ b m s ~ ~ t h a t ~ t b e w i n g b e i n g below the point of d c u W h ?

F h m * r b r t p u k w w ~ t b c p w r s b ' o t c i a ~ f l i s a t , which a w s c l ~ b W y t o b t 8 t ~ ~ r b t ~ o r t k ~ ?

T h e ~ o ~ ~ a B ~ d t B c ~ ~ l a i a b a p m r b c c s n u ~ ~ a f i m o r t k j e i a t ~ t b e ~ d d ~ . I f y o u ~ a ~ ~ ~ . 1 6 u d ~ ~ - ~ ~ - ~ t u ~ H i t l W M @ t h e p i n t i a to* tbemidlipe. IkhwmIBe t w o p h i s a u - r l u p s d b s a t , ~ f u r d a , w ~ i s ~ l y m o r e ~ t o y a a s t 8 t wisbbonc. It appears that tbis bone aud its joint can store energy, like a spring, dperhapsxttoprwi&an~gfonxtotbeinwardfacegencmted when the supmwmoideus musck mntmt. I n f d o n about the role of the furcula camcs h m ~ o ~ c analysis of stadhgs in Qht. Traces from the 6lm made in tbis study arc shows in Fqpm 5.17. During the downstroke the furcula Figure 5.18) h d s laterally, spinging back during the upstroke.

During the wingbeat cycle, Pbe sternum alsb moves as the musck attached to it cuntract. On the do-, & sternum mom upwards and backwards, dropping q a h and moving focward during the upstroke. A corrlequatce of these b e movemnts is that tfre rib cage changes shape, altering f k size of dw thoracic cavity. So, there is a link b e e n the wiq- cycle and the respiratory cyck, tbough ttse d e of the d b u t i m maBe by tbe flight muscle contriwtiom to on is not yet horn.

Chapter 5 Principles ef F l i~ht

*- (a)

Summary- mf W o n 5.6

k 4 Anim

5.7 The wake Inm2.3.2youdabart&&d-in&lidsttlatbrr~c ~ o n ~ w P L e I c f t b y ~ m o v i n g ~ t h e w a t e t . ~ h a v e ~ b e a a ~ o f ~ o f t b e ~ d ~ ~ a s t b e w a k c i s ~ a ~ - l i v s d p b s s r u m e r m a , p o d m # w l y ~ s u c t r ~ b n v e n o t b e e a e s s y . ~ ~ w O I 1 C b d m i h i s p z O M c m a t t h e S e v e r t z w ~ i n M o F m w i a t b t l a t e 1 9 7 a s ~ ~ t h a t & : ~ t r a i a a d ~ f t y b a t w e e a twopchpiWakw~slptdAsabirdfaewbea#loankpgcbas, beblewd&*the&.TbeMaeph*dtBaM'BwPlrt.% ~ ~ ~ b e c r v r r i e d o u t t b e ~ i a d k h m s a D d u s e d s u t hhedhm~dttbeetbt&@dtkbitdd~a&dhsh~. ' I k B O ~ a t r i g b C ~ ~ a g e h o t h e a ~ t b c ~ a b e ~ S o d n e o f KokshaysQ's pbtop#w are shown in Fqgue 5-19.

'a-

Figwe 5.19 Four photographs taken by Nikolai KoWysky of a chafhch flying through an abnosphe of wood dust in a darkend room. Tbe flashes wert triggered as the bird flew though an inhmd k tm (a) The effect of a single downstroke. (b) The wake resulting from a series of three dowmlrokes. Tbe wake sen h m the front (c) and anduhmusly from the side (dl. A vortex ring is visible in the wakeof the bird in photograph (dl.

k.

I b t

Chapter 5 Principles of Flight

/-

of- 0s-

k 4 Animal ferfrrm

I n ~ ~ t a s F ~ 5 . 1 9 ~ & a ~ x i s f o l r a s d m t h s ~ o f t#t wing. Fqure 5.21a shows M, as the wings move down, two vortcx shtats farm, ane f- IS& wing. Tbe bets roll up to forrrm r hdf-rbg ( F i p 5.2tb) d h , a s t b c d a w n s t r o k e i s c o m p W h m r s e x t W a s a ~ r i n g ( P i i 5.2112). The wings are limed during the ups&ok, have W e h m a c t h w i t b t t r e & d p r o d u c e ~ ~ : d t B a t i t ~ t B e ~ t b s l t d y tbe pmer (!Stdm 5.3).

T b e s i g n B m m o f t t s e v o r t e x f o a t h e ~ I s ~ ~ i t ~ C B t h e d m o f @ a i r t o t b e b i r d ~ g ~ i t , ~ m d ~ O f t b e ~ ~ b y ~ c a n + 1 d d m b k i n f d o f l ~ a e t o d y a r m i c E o r # s , ~ e m e q @ a i , w i n g ~ r e d o t b e r ~ o f ~ F o r ~ k , H ~ 5 . 2 2 ~ ~ ~ v o t t e x r i n g i s t i l t 6 d fFom the h k n t a l . Tbe rraglt of tilt is related to tb ~ - t u - w e i & t ratio of tk bird.JeremyRPynrr*atBristdUni~,hasbeearintbef~ofthiswork. ~ h e p u b ~ a ~ d m o d e l o f v o a e x f " inthesameyear t h a t N * K o h d l a y s k y ~ ~ b ~ o f t h e ~ h S ~ p t t y , ~ y R a y ~ e r a w & a d w i t h ~ t o p h m g q h m e ~ k f t bya~of~ofMaad,nithCtareteZarssatBM,thewaLtleft bybets.t~eW~buWles~amixkofkhmndair,suchtbatttrey were mukdy buoyant. As the animal flew tttrougb tb clad of buwles, a h e . w ~ o f ~ w a s b i g g e d i n ~ . A p r r i r o f ~ ~ s t e r w , ~ w h i c h s Q o w d ~ m v i n g ~ a s a s u k d & t s , t t s e d i s t a H c e b t t w e e n e s r c b ~ o f a b u b b l e o n t h e f l I m ~ t h e t i m e b e t w e e n t w 0 ~ l v a d t 8 e ~ t h a t t h E b u b b l c ~ t r a ~ i n t h s t ~

Chapter 5 Principlts *f Flight

5324 Book 4 Animal Performance

5.8 Conclusion - tbqWdhtbderdapDsat&avirt ioahprwadada ~ h m c d f a t b s a d y d & g h t i n ~ T b t p i m w y ~ b e t w s m o n ~ d a b i a d , i n t e r m s o X t b e ~ ~ s a c t i a g m t b e m , b t b r r t t k ~ o f m ~ p v x k l i f t d i l ~ i t s ~ h m e a g i a e , w b t 2 t a 8 i n a & d t b ~ p r o v i d e ~ f i f t a d ~ ~ B i r o l s ~ ~ ~ b r r t ~ t h e ~ 1 D a y ~ t h t s t e ~ b e c a g g e l i g h t e t , t b t ~ b e c a m ~ y ~ t b a . ~ ~ r c p b c e d b y featbg's rrtd tBc m d a involved in forclimb movement dm@ -. ~ s h p o f t b e w i n g s h r r ~ ~ ~ i s a p ~ t o a ~ l m d e o f W s u c b a s ~ ~ g ( r f s P t 8 1 p p i n 8 ~ A ~ o f t h e ~ a f a w i n g i s t h e ~ r r t i o , k r a t i o g P t b e ~ a p n b o h m e a n c h o r d .

Chapter 5 Principles of Flighr

Objectives for Chapter 5

Questions for Chapter 5

(a) Aspect ratio d c a ~ & ~ tbe m of a wing.

(b) A b i r d f l y i n g s l o w l y w e v l d ~ t h t + a f ~ o f b ~ t o inaease lift.

(c) ~ ~ a e d ~ B r o g ~ f r o m t h c ~ ~ d t b e w i n g s i n birds.

5324 l o o k 4 Animal Pedarmance