Project Sign Progress Report, 1948

MARCH
S,
19
48
281 THE AEROPLANf
ewi
ng
, tru
ctu
res
as
well
as
for
the pos\lbility
of
housing every·
thing
w11hm
a wing.
Hence 1hc
1e
a re very real design reasons
for
the preference
of disc wings, quite a p
an
from
the ea~cd accommoda11on
ofshor
t-s
pan ae
roplanes.
So
me R ernurkable R
esu
l
ts
Zimmerma
nn
establ.shed
that the optimum
a~pcct
rauo
"'"~
fo
und
bet,..een
the
values o f 0.75
and
1.5. l he,c
value,
include both
,quare
an
d
ctrcubr
wmg
,hapes.
F
or
a g1Hn
wing sccu on (Clark
Y)
the
latter
gave the h1gh~t hft coefficient.
1.
85
at
45 degrees incid
en
ce,
compared
"uh
a value
of
t.:!4
at
14
degr
ee,
mc1dencc for
an
aspect ratio o f six.
Funhcr
more. an important result
"'•'\
evidence that
at
~,n
a,pect
ra110
of
unity
hquare
or
elhpllcal
....
,ng,),
and
:11
an
a,pec
t
rauo
of
0.9
("
mg "11h faired ups),
no
tendcnc)'
111
autorotauon could be found. A
circular
" mg (:1,ix-ct
raw,
...
/
-
-- of
1.27) ind c.llcd
the
po\\1hili1y
of
~1urnrntation
(1.e
.,
,rinningl
at
incidence\ below that
of
maximum l
if1.
1 he 1nm1biht)'
of
,pinning
before the actual
,tall
is reached is. indeed,
e,tra
·
ordinary. All these
rcwh,
r.:fer to
te,t•
"ith
the
( lar~ ,Fig
.
_14.-A
Russian •
puabola'
glider
of
1924. aerofoil section.
Less establi,hed
"a
s the
contenuon
th:11
d1..c
wing would
11ive
improved
la11:ral
and
longuudmal ,1.1h1htv
at
l
ow
incidence,
extensive wind-tunnel investigation
and
the
publbh
ed reports 1
hi,
..ecm,
,11II
10
be a moot point
of
the Flyin!l Saucer.
\till
form
the
ba,is
of
prc~ent development. In places. In Fig. 16, Fig. 17. and Fig.
18
some charactcri,tic result,
,,fthe re,ults confirm, qual1tat1vel)', the experiments made
'.!O
year~
before. But,
as
mentioned earlier, these experiments
had
been
praet1C111ly
forgotten.
Zimmermann's target has been the development
of
a really 7fool-proof aeroplane for
amateur
pilots. It is no
uroved that small variations in
the
aspect ratio made
pr
ofound 't
differences
and
that
the shape of the wing tips also
had
a great
0-,
influence.
...
~.
~
At
the same time
he
confirmed
that the
induced
drag
of
circular
or
square wings is
by no mean
s
as
proh1b111ve
as
the
simple theory
of
the " horseshoe " vo rtex line would indicate.
He also proved that it was simply the induced
drag du
e
to
thepredominant in
fl
uence
of
the
marginal vortices which brou~ht
••
about
the
behaviour
at
high incidence~: the idea th
at
the
provision
of
oblique slots might help in this connection proved,
h owever, abortive.
An advantaae which Z1mmermann's research brought to
liaht was
that
disc wings gave less profile
drag
at
small
CIA°',
IIC,,O,.
incidences (high-speed flight). because
of
the
reduction of
the
-1....
___
_...
_
.,,.
JO'
-:
relative thickness
of
the
aer
ofoil sections. 1 h is drag
reduction
has indeed become one
of
the rr.ain rea
so
ns
for di.c
wings
being
adop
t
ed for aer
oplanes
capable of
flying
at
~
reed
s
atwhich the compressibility of the
air
needs
to
be co
nsid
ere
d . Fl&, 16
.-
N .A.C.A.
te
sts by C. H. Zimmermann which prove
the extraordinuy
sull1ng qual1t1es
of
disc wines,
Fo r supersonic flight disc wings seem,
at
P.rcscnt, to be a
necessity. Alternatively,
for
a given aerofoil thickness ratio,
!he height avail
_a
ble f
<?
r st,:ucture
_a
nd stora1te
(J?O
wer plant
_sl
Zimmem1ann·~ _wind-tunnel experiments
of
1932
are
given. It
1s
greatest within a disc wmg; this ma.,es
for
light and sutr
1~
seen from F,,.
18
that the difference between the mc1deoce
of
ma,umum hft and the gliding angle
at
m:i
1t1mum
hft
("ma
'<
•a ma'<) rem:im'I fairly independent o f aspect ratt,,,
and
of
the o rder
of
9 to
13
degree,. 1
h1~
would me:in th
.11
the attitude
of the . disc-type aeroplane, when flattening out,w
ou
ld n
ot
greatly d iffer from that
of
convcnuonal aeroplane,
In particular, there
"'ould
be no need
10
provide
h1g_h
under·
cama;ies
for
disc
aeroplane,
a .. their gliding path
1s
steer
Thi,
1s
an important di
ff
erence
from "''"IJS
w11h
lead1ng-cd~~
,lots.
. In P
!'3C
tice, however: the landing
of
disc-wing aeroplane,
~•vcs rise to undercarriage problem,. As the induced
dra~mcrcascs rapidly
"ith
the reduction of !tying ~recd, when the
aeropla ne
fl
attens o ut prior to touchina·d
o"
n, the
ihdt
nti angle
.iecpens abruptly.
Th
is
1s
particularly true of ta1llc..s
de"gn,
.
and the result
•~
. a strong tendency to pancake 10 the ground
a, so~n as the
p1lo_t fl
:\ltcn, out. Thu~
to
avoid the nccc\,il)
of
litt1!)2 _undercamal\cs able to sta nd the strain
of
abnormally
high sink mg ~pecds,
1t
has been found practical to land
"Jtll
powe r on.
For a ta11le~s a
eroplane " ith an aspect ratio
of
three,
M. B. Morgan found that. without
flaps, the
tr
immed l\liding
angle at
160 m.p.h. was th ree degree
,:
it increased to 17 degree,
at 126 m.p.h .. while the \tailing speed was I IS m.p.h. Thi,pronounced , teepcning of the g)idintt anttle makes a mer~er
hct""ce~. the aeroplane and the helicopter an attrac11ve
, propos111on.
. Another occulia_rity o f . !he di~ wing cstahlished b~Fie, 15.
-A
' puabola ' aircraft by B. I. TschennowskyNND 927545. Zimmermann wns us scns
111v11
y to the , hape of the wing•ur,,