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6 l 2 LIGHT December jth 1944
F MR FY FIREFLYmedia te i l ap se t t ings would resu l t in a
reduct ion in them inirpd m r ad ius of tu rn at full thro t t le
in level f light ,which would g ive the p i lo t an enormous t ac t
i ca l advantage over h i s opponen t , no t on ly in a t t ack bu
t in t ak ingevad ing ac t ion .
As long ago as 1936 the N.A .C.A . inves t iga ted the p ro pert
ies of the aerofoi l f lap and pointed out i ts advant a g e s , bu
t , s t rangely enough , l i t t l e e f fo r t has been madeto
make use of this form of high-l i f t device, mainly, perhaps ,
because o f an er roneous impress ion tha t i t s ins t a l lat ion
must resul t in an increase in weight which wouldlargely offset the
adv an tag e gain ed in incre ased l i f t. Th edes igner c l a ims
tha t i t can be shown tha t in ac tua l fac tan a i rc raf t bu i
l t t o conform wi th cer t a in requ i rementsof take-off l a n d
i n g a n d l oa d - c a r r y in g c a p a c i ty w ill s h o w ^
xa co nsi de rab le sa vi ng in we ight if eq ui pp ed with ae rofc
n Viewed from beneath, the cleanflaps. Co nv ers ely , in a giv en
des ign, th e useful loa d m a y nesting of flaps and undercar-be
very subs tan t i a l ly increased wi thou t de t rac t ing f rom r
i ag e conform with the smoothtt_ i 1 cr J 1 J- , surfac e of the
airc raft as a who le,t he t ake-of f and l and ing qua l i t i es
.
The Fairey Yo ung ma n flaps show n in the three selectableexten
ded positi ons. (Top) Cru ising. (Centre) Take-off.(Bottom) Lan
ding. Cruising selection gives man oeuv rability and slow flying ;
take-off very high lift with smalldrag ; landing, high lift and
high drag so that whe n thethro ttle is cut the mach ine sits down
imme diately.
I t i s also frequent ly argued that the use of high-l i f tf
laps necessari ly involves diff icul t ies in longi tudinal cont ro
l and t r im, and there a re admi t t ed ly some examplesin which t
roub les in th i s d i rec t ion have been exper ienced .Mr . You
ng m an po in t s ou t tha t there i s no reaso n whya machine
equipped with high-l i f t f laps , giving nearlydouble the l i f t
increment of a corresponding spl i t f lap,sho uld prese nt any
diff iculty in long i tudin al con trol andt r im wi thou t
recourse to ad jus tab le o r overs i zed t a i l -p lanes , p rov
ided cer t a in fundamenta l cond i t ions a re fu l f il led . Th
ese cond i t ions m ay be thu s sum m ar i se d .(a) The f lap
should extend at least up to the wing rootand , i f poss ib le ,
under the body in o rder tha t the t a i l -p lan e m ay . der ive
the ful l benef i t f rom the increaseddow n wash p ro duc ed b y
the low er ing o f the f laps.(b ) The e leva to r ba lance shou ld
be ad jus ted to g ivethe cor rec t re l a t ion to make the a i rc
raf t t r im au tomat ic al ly when the f laps are lowered and
raised.
Li f t a n d ra gThe advantage of this form of f lap over the
spl i t f lapit- easi ly appre cia ted b y a .com parison of the
profi le d ragan d lift coefficient of the split and a erofoil
flaps.I t wi l l be seen that whereas the opening of a spl i t f
lapcau ses a rap id incre ase in profile drag , ther e is no ver
yappreciable increase in the profi le drag of the aerofoi lf l ap
up to a po in t beyond tha t a t which the sp l i t f l apstal ls .
Th e aerofoi l flap, more ove r, gives a consid erableinc rem ent
in l if t over the spl i t f lap. Th e imp rov em entin take-off
manoeuvr ing and s low cru i s ing which canbe obtained by the
aerofoi l f lap is not , however, di rect lyrela ted to the m eas
ure d coefficients. Sl ip s t re am playsan impor tan t a l though
a no t eas i ly ca lcu lab le par t , bu ti t goes without saying
that the effect of s l ip s t ream wil lbe s t i l l further to
increase the advantage of the low-dragflap for all the specified
conditions of flight.I t has been s tated that the aerofoi l f lap
presents nodiff icul ty in i ts ins tal lat ion which is , however,
not to saytha t any des ign i s su i t ab le fo r the incorpora t
ion o f h igh-l if t f laps. I t i s alm ost inv ar iab ly nec essa
ry to considertheir appl ic at ion in the ini t ial s tages of
design. In the
f o r m o f f l a p s h o w n , w e . h a v e b y n o j e a n s
r e a c h e d t h el imit of high l i f t , and in t ime^^rfshould
be possibleth rough development to ob ta in a l i f t i ncrement
approachi n g d o u b l e t h e . a mo u n t .In the past , f laps
have f igured almost ent i rely as ana id to l and ing , bu t the
adven t o f the Fi ref ly demonstra bly pro ves tha t f laps, in
add i t ion to take-off and la nding, can also Contribute largely
to the safety and moresucc essful ope ra tio n of airc raft in
flight. //
