It is to be expected that the advantageous properties, hitherto discovered in many slotted wing sections, depend very largely on the contour of the slot and the structural details of the wing. It is therefore of interest, aside from measurements on wings of constant cross-section along the span, to measure also wing models in which the structural details have already been given practical consideration

Klemperer, W

English

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,--
PROB”&M OF THE SLOTTED WING.
A Cotinication from the Aerodynamic Institute of the Aaohen
Technical Hi@ SGQOO~.
BY .TJ.Klemperer.
Fron l’Zeitsch:;Mhfihrl?lugtechnikund Motorluftschiffahrt,’1
October 31, 1921.
.
June, 1922.
.
https://ntrs.nasa.gov/search.jsp?R=19930082657 2020-06-17T22:13:26+00:00Z
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31176014405386
PROBLEM
A Gommunication,fromthe
,,, ,:. ..-.—,..,,,..,.,,..,,.
OF m SiJOTTEbtiNG.*
Aerodynamic Institute of the Aachen ‘
Technical’Hi&” School” “,
By W. Klemperer.
It is to be expected that the advantageous prqxzties,
hitherto discovered in many slotted wing sections, depend very
largely on the contour of the slot and the structural de~ails
of the wing. The formation of the slot presents many,difficml-
ties *O the constructor. In the first place, the lazgernl@@eX(..
of sharp curves requires a complicated wood or metal construction,
The attaching of the ailerons, the s“~rutsand the stay wires de-
mand special consideration. With unsupported wings with several
spars there is the further task of finding a way for the slots
betweenthe spars. Lastly, it is not inconceivable that the di-
hedral, sweep-back and the interruption of the slot in the middle
by the fuselage may cause surprises. It is therefore of intezest,
aside fTom mea~urements on wings of constant cross-sectionalong
the span, to measure also,wing models in which the structural det-
ails have already been given practical consideration. such an
experiment was performed in the aerodynamic laboratory of the
Aachen Technical High School by the writer in ~omPanY with Mr.
F“;ornm.
. .
!Bheexp.ezimentswere made with a-model of an unsupported
monoplane wing, which had the following measurements. Its ground
* From !IZe”itschriftfirFlugtechnik und Motorluftschiffahrt,1!
October 31, 1921. . .
—plan was trapezoidal (J?i&
of maximum cross-sectional
formrd”’”third‘of-W% ’’’ilbs.-..—..
4.- 2-
~)L The m~ddle dash line is the line
thickness, which was located & the
‘?be””V=sh”apehag the ra%~o of 1 : 10
along’the top surface on the l“ineof the maximum thickness. The
section perim~ter p - p is similar to No. 422 of the (.X5ttingen ~
experiments. The sections at other points of ‘thespan are ob-
tained from this one by extending its coordinates. Theiz perim-
eters are determined by the data which are written at several
points of the wing for the maximum height of the ribs. The sus+..’
face was first tested without slot. Then a slot was made and the
test repeated. Then the slot was closed for verification and,
since the result was less than the original value, other methods
were tried in order to reproduce perfectly the original unim-
paired shape. Thereupon several systematic modifications in
shape of the slot were tried.
In introducing the slot, and indeed, only a single one,
the
al-
lowan~e had to bt~made for the employment of three spars in the
unsupported front section of the wing. The slot was accordingly
placed between the front and main spar, the location of which is
indicated in the drawing. As a result of the diminishing thick-
ness of the wings toward their outer ends, the slot was quite
steep in the middle of the wing and became flatter toward the
ends. The front side,of the slot,was S-shaped,..whileits rear
side was intended to form a sort of leading edge of the adjoin-
ing part of the wing secticm. The modifications made in the slot
L
—affected its
front side.
.
n~t’”e-xtended
-3-
width and the concavity of the upper port~oh of Itd
The slot shapes are shown in Fig. 2. The 61Gts w~re
%fi&”&llclelsrigth”ofthe span, but were interfipted
in the middle (whew in actual practice they would be inter-rupt-
ed by the fuselage] for a distance of about one-tenth of the ~~all.
Moreover,. the slot was interrupted in the middle and at the end
of each sezni-spanfor the sake of holding the two’portions of the
wing together. The remaining wood partition was somewhat rounded
or sharpened, but perhaps this shaping was not aerodynamically
perfect. No fuselage was included in the model. The airplane
model was copied,from the design of an airplane glider p~ovided
with a slot.
Since a multi-component balance was not available for the
experiments and was moreover not
of the normal effect of the slot
Of attack ~d the ~a~j.~~ lift),
necessary for the demonstration
(increasing the maximum angle
the lift component was first
measured as a function of the angle of attack. Any very accurate
determination of tb.erefe~ence line for the angle of attack was
not essential, sincn the angle of vanishing lift was very accu-
rately determined, It was about -7°, measured with reference
the chord.
The measuring device consisted essentially of a balance,
one’arm of which one end of the wing was
spindle, so that the air foxce conponent
could alone exert a torsion moment, with
attached by means of
to
to
a
noxmal to the air stresm
known lever arm, on the
I
Jr’”” Q ... ,,
*-J
.,,.,,,,, .,. ...-..— ,.,,,,..
-., ,..
I
1
i
balance beam. .
of the balance
- ‘4
::
The free end of
beam by a small
attadwl to the end
To the end Of the
balame beam was attached an oil”dsmptng devi”ee,with a damping
faqtor adjustable during the measurement.. Between the balance
arm ‘supportingthe model and the one holding the ‘scalepan there,
was, during the experiment, a changeable conversion device, which,
on account of the importance of maintaining the sensitiveness
was
the
the
did
employed only witlainmoderate limits.
The wing mddel was not installed in the middle, but nearer
edge of the two-meter”diameter air stream at a ‘pointwher:e
latter was the most uniform and where the dynamic pressure
not vary more than Zfifrom the readings of the stationary
Pitot tube, as shown by tests with a second movable tube. By
this manner of installing, it was possible to get along with so
little suspended apparatus, that its influence on the measure-
ments could be disregarded. The accuraoy of the balance adjust-
ment for high lift values was well within ~~ of the maximum lift
and was somewhat greater for smaller angles of attack, The de-
termination of the mean value of the dynamic pressure (by means
of a Prandtl micromanometer) probably attained an acouraoy of l%.
The moment of the drag component was offset by the lateral
loading of the balance beam, so that the balance knives were
equaily loaded.
,.
As a matter of secondary importance, a separate measurement
of the drag was undertaken, by turning the balance 90° and taking
I I ——,..,.——-. .,..——:.—..
up tinelift
through the
termination
measurement
by means of a steel wire ancho%cd in a line passing
knife edges of the ‘m.lance. The accuracy of the de-
of the angle ‘ofattack from the values of the lift
was within about 1/2$.
The results of the lift measurements are shown collectively
by Fig. 3. The surprising result is the decided superiority of
the first model without slot. The maxim lift of (la= 147
could not subsequentlybe again fully attained by closifigthe
slot with paper oz paraffin or plaster of paris. That the first
curve must nevertheless be considered accurate, follows from the
fact that two ezperlme~ts performed on different days agreed well.
The utilizable angular range of the wing extended from -7° to
about 15°. Experiments with the slot nom showed a noteworthy de-
crease “inlift from small angles of attack up. No further @-
crease of the lift up to very large angles was Observed, although
there was not so decided a decxease from 15 to 20°, as with the
unslotted wings. In no case, did the slotted wings give better
zeeuits t-nanthe unslotted, Hence, in the experiments wi%lnslot-
ted wings, those with the narrowest slots naturally gave better
results. It is also to be noted that= with the slotted wings at
angles between
the slot would
ble, which may
15 and 20°, wheze accordingly the real effect of
be expected, a mhist3ing so~d was clearly audi-
have been comnected with the unexpected disturbance
of the air flow. While with anunslotted wing section, the bal-
ance adjustment experi~nced strong oscillations in the vicinity
s
. ...*.- -
.of 18 to 20° and consequently the lift,valuewas tsm;~ora~ilyvery
,_.,!?%?e@Y.#~?is..wa?}e,q,~,.~ot.iceablewith slotted wings. It was,., ... ...----
not possible to polish the wing model. In order to determine
whether the influence of the roughness of the wood could have
caused the non-appearance of the !lLachmanneffect,!?the wing was
covered with a collodion film and again tested both with and with-
out the slot. The differences in the results were however so
..
slight, that they were not introduced in the diagram.
.,,
The measurements of the drag (only made for the unslotted
wing) are plotted in Fig. 4, and giwe the best L/D (of about 13)
between O and 1°. The result was due to the roughness of the
surface.
The experiments were performed in an air stream of 20 to 25
m/see. Confirmatory experiments at a lower velocity showed no
dependence on this.
In so far as it is allowable in this sort of experiments,to
draw conclusions from a model for the full size, with 15 to 20
times larger dimensions, it may be inferred that the special form
of slot, tested in these experiments, would not simply give no
advantage, but would do positive harm. To what these disappoint-
ing facts are due has not yet been fully explained. It is howev-
er possible and even probable that the non-appearance of the
lILachmanneffecttii&du8 to the interruption of the slot”. A con-
tinuation of the experim~nts should settle this point. In any
event, however, the experiments show what a complicatedproblem
-?-
tbat of the slotted wing is, in that structural umsideration
can exert such an extraordin~ _inf3.u%nge.__On%.tsap.rody~~c
,.. ., ,,..,,,. ....
properties and that it consequently appears neoessary to pursue
this’particularproblem still further with experiments on models,
while taking into account the practical details of construction.
Translated by the National Advisory Committee for Aeronautics.
Front elevation
.
.-.
Wing section p-p,
L/D Fig.
14
12
10
8
I
P ?!
main spar.
1’
Wing section q-q.
.
——
— -— ._
I
———-———————~.I
I
—:—_.
I —-——---— +.. .__..__.
t
..- .— -----
+ .—_
I
i
“ I
I
6I—.L____ i
_..l
_loo _50 Oc 5° loo
Fig. 4. Angle of attack.
,,, . ... ,.,,..-. -, — —.. ..
. 16
i ‘:
pq .r
.—
k
“:
*14:. ,
A“ -
,.-,.,. -
,—— .—.—. -.
.12~
T
.
~ 10
~
D03
~;
%@ ; --- ––. -_—.-.– .—
1+0
v+ Withdut slotQ%4 I(D
o0
!4
o
7 ‘“—-
1 ~’
-— —
~
-
e
,.,
L
/
--. .—-. —
I-. —... — - -- - -— -—-. .—,—L ——.
1e T.’ithoutslot.(D 11 11 (check)..— -t-Closed with plaster.h S1O @ Turbu7.ent.
—.- X Closed with paraffin.
0 Paper pasted “ontop.
o It If II—— bottom.
0 Ylideslot.
0 Concave s102.
_— ----
0 Narro;; ‘f
l Wide and concave slot.
Fig. 3, ‘ Angle of attack. ~G% ,.,,,,,- . ..——
,,’ —
..-, . ._. k..>. .. .L --- >+._ . — -------- —e
1
I
.
,.. ,
.“
. . .
“
.,.
.. .
. .
..
.
. .
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Problem of the slotted wing : a communication from the Aerodynamic Institute of the Aachen Technical High School

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