TiCHF r C.AL liJOTES
rATIOlTAL ADV I SORY COi.fJl.1I TTEE FOR AERONAUTICS.
No . 2 1 4
IWTE
on
THE:
L~ TZ:.::AY:a.
By
f~assachusetts
EFFECT 0 - AINOlL DRAG.
Shats~ell
Ober,
Ins t i tute of Technology .
Feb ru2,ry, 1925.
I ATIONAL ADVISORY ~.mI'!TEE FOR AZRONrlUTICS,
TECHNI CAL NOTE
~JO.
214.
NO'::E ON THE KATZ)6AYR ZFFECT ON AIRFOIL DRAG.
By
Shats~ell
Ober.
The re{uction in drag of an airfoil vhen the air stream is
oscillating is cE'J_led the Katzmayr effect.
This effect
l"rcJ8
first
described by Dr. Kat z 'i1ayr , eli rector of t:he Vienna Aeroc.yn&mical
Laboratory, in IIZei ts chrif t f~r Flugtechnik unci .~otorluftscnif­
fahrt,
II
March 31 and Ap ri 1 15, 1922 (Ref erence 1).
Oo.n fi rming ex-
periments have aeen made by Toussaint, Kerneir and. Girault, and
are given in a report translated by t he National Advisory Co mmittee for Aeronautics in Technic a l Note No . .;) 02 (Reference 2).
That re)ort conf irms Kc.tzmayr ' s :results,
~ret
contains no expla na-
tion or reason 1':1Y e.n osci llating vr ind should rec.uce the airfoil
drag.
Ti.1e purpose of thi s note is to offer a simple expl2.na tion
of the CBllSe of the Katzmayr effect.
Consider first the condition in a
~erfectly
steady air streem.
The d:rag, of course, is measured by a balance tlle linkE'..ges of
v/~1.ich
are so ali gned that t e com·ponent of force 210ng the '·{ind stream
can be re ad directly.
As no art ifi oi s l air stream is ebsolutely
steady in velocity or: direction, it is necessa.ry that the balance
be heavily G.E'[:ped ty
dash~ots
or equ ivalent
rrange:l lents.
Further-
more, as the forces to be mes.sured are not inconsiderable, the balance rfill inevi tably have a lar ge rtlonent of ine:;.'tia and a long nat-
,r
N. A.C·A· Techn ica l Kote Yo . 214
ura l pe riod of oscillation .
f o lloTT
8,
2
The c1rc.g ba lance therefo:r;-e v'ill not
r eDid oscillation in t h e true mag:li tud e of t he d r ag
CO;::l1-
po nent, even though t h e amp litude of t he variation be l&rge , but
wi ll ~iv e a mean rea ding represent i ng t he integ r a l of the in stant _ neous 0.rag vIi t h respe ct t o ti me (h vi c.ed by the ti me of a co mp l ete oscillation .
If t h e ai r stream is osci _l a ti ng in direction a correctly
a.li gnec1 d.r ag balance will re a.0. tile me a n of the componsllts of forc e
parallel to the nor mal
stead.y vn.nd.
As the nind
direc-r,:L~n
changes
from normal t he d r ag balance is no lon g er in correct altgnmert t
.~ri
th t he inst2ntaneous d irection, so a co rroonent of lift is added
to or subtrc.cteo. f ro m t he true dr ag .
1 n the ca se of
2n
airfo il
ithin the ordinary working r a.n g e of angles of attack the compon en ts to be subtra ct e& a re l a r ge r tha n those to be added, as the
corJpone n t of lift rr.easu red on t he drag arm is negat ive v:hen the
che n ge of ,rind d irection i s
S UCD
as t o increas e the true angle of
a tt ack Gnd t h erefore l'ih en the li ft i s l e.r ges t (8 ;.Josi t ive, as
ShOl'fTI in F i g . 1 ) .
The r. san co myonent parallel to the .ri nd d irec-
tion, 1.7h i ch is liihat t he ba l a nc e rea c5.s,
by t he exi stence of the
0
Jill t herefore be reduced
sci llation (Reference 3).
When the fre-
quency of the oscillation i s such th at t he Fin3 chord is only a
small fr2ction of a
1~rave
l ength , the 2.ngle of atta c k may be con-
s j.dered c011st2nt a long the chord at an} inst ant d:u.ri!1 ?; an 08ci 11ation, and. t~l. e lift a nd d r ag com onents pa.rallel to the nO:'lYlal 'wind
ca re ction ce.n be c a lcula ted f l'om values made i n a normal steady
.
Tech n ica l Note No . 214
l'J .rl .......~.
vJind.
:3
If the ';iav e is so short that it approaches th e vring chord,
the abov e assumption cannot be made and the calculation becomes
The chcmging dir e ction of the str~am, like the j.nduced.
invalid._
dra g on an airfo il of low a spect r atio, then acts to change t he
effective curvature of the section.
HO Nev cr, even at the highes t
frequency and the slowest s pe ed of t es t mentioned in
N. ~ .
C. ; .. . Tech ~
nical Hate No . 202 (Refel' 8hce 2), the wave length in the Toussaint
experi ments was five times the l:-ing chord.
On the assump tio n that the a.ngle of at tac k is constant along
the chord thQ p rocess of ca lculation b ecomes compa ra t i ve ly si;:rpl e.
In Fi g . 1
a
~
L
~
tTl..1.e lift at
0.0
D
~
true drag at
0.0
S
hypothetica l an g le of Qtta ck, baseQ on the mean
~ ind di rection
angle bet we en Dean wi nd di rer:tion and. p i nd (irectio n
a t any inst a nt, + vvhen angle of attack is incr ea sed.
:::
11 2nQ Dl
= true lift anQ d.rag a t
( a + 8) °
12 l and D2 = true lift and drag at ((1
Dt
=
read ing of 00.l anc8 '\Then
e
:::
-!..J II
=
read ing of balance " hen
f3
=
D'
=
T'
:..,) 1
co S
D"
=
I
cbs r\ + T.- 2 sin 6"l
-'-' z
[31 -
11 sin
- S)0
+ 6 ~°
[3~
[31
Fro m t he method of genera tion t he 'lave form of the o scillatio :n
is appr oxi mat e l y har monic, or
f + K sin t,
yohere
"KII
i s the
i"T . A. O· A. Techni ca l Note No . 214
ampl i tude and
11
tTl
ti m~ .
the
4
The mean effect may be founc_ by in-
te g r a ting the mean f orce when the osci l l ation is
one- nA.lf
of the cu!'v e f or a complet e cycle bei ng fOlded back on the
ot~1e r
part, that is:
F
= mean drag r ead ing =
If
+ DII
2
dt
DI
J
J dt
is s mal l, t ':le slope of the lift ano_ the change of slope
K
of th e dreg may be conside:r ed cons t a nt.
The form of the mathemat-
i c a l s olution was or i g ine. lly due to P Tof. Zd17ard P . Warner.
cu rvatur e~
introduction of
The
giving a somewhat closer approximation ,
was su gge s ted by Dr- H. L. Dryden .
Dt + DII
2
Replacing
by
cose
+ D2
D,
:::
2
s inS by
-- anc~
D1 + D,2 -=
c-,
~
2
c~ 2:0
1
2
+ -
11 - 12
e in
2
cos B -
do.. 2
S
e
82
since C:;'2 Ylge of slope is
assumed constant.
D' + Dtt
2
=
D +
2
d D S2
d 0..2'
I
2
-
elL 3 2
do..
'
co r.'-Din2" tion of tbe posi tive
Int egra ti ng over a hal f c yc le ( ,-(';le
a nd ne gat iv e angl es maki n g th i s equ iva lent to inte grat lon for
B.
COl'i -
o l ete cycle) .
n
F
=
D' +
2
J0
In
0
n/w
/
0
~2 cit
=
n/w
1(2/
0
DII
n/iJ.j
dt
=
dt
Ri n
DJ0
.2
dt + (1 d D
\ 2 d 0..2
jnlw
dt
n/w
c.l
/
dC'
0
c
2
u.lt dt
1(2
= 2
(t
,
122
dt
n/w
~
w t\
I
2w
sin
0
=
1(2
x
n
2w
N.A.C ;A: Technical Note lTo. 2 1f
F = D +
F = D +
K2
4
K2
4
2
d D
eto.2-
5
K2
dL
do.
2
K and
K2
d2.D
d 0.2 - 114.6
dL
d O.
K
in r ad ians
0.
anci
0.
in degrees
I n the use of this formula it is more convenient to replo ce
f o rces by coeff icien ts
F i g . 6 of Techni cal Note to .
0
this paper, at
o
CD is . 041 ,
202~
reprodu ced as F i g. 2.1 in
2.
dCT,
d Cn
is .070,
is about . 0007.
d O.
0.0.2.
+10 0
Wi th an all1;.Jl i tude of oscilla t ion of
CF = . 041 +
100
100
4 .0007 - 114.6 . 070
The experiment2.l value is
dCL
do:.
+. 003 .
=
.041 + .018 - .061= -.002.
If, ins t ead of the v alues of
t h e nea n ve lue s from - 10
o
to +10
0
"re
t he agre ement vi t h the expe ri mental result is even bet t er .
use ~
It
t~en
s eems cleaT that the inst an t aneous lift and d rag of an airfoi l are
functions only of the a l ti tude a t that instant, and quite ino.epen<ient of
t~1e
fa ct th2.t the angle of B.ttack may be in process of
The mean dr ag coeffici ent
OF
cha~e .
may elso be found by an arith-
metical integration 17hich makes due allommce for all variations
in
00
0D
•
an~
CD'
0L'
The wo r k i s g i ven in Table I for a mean angle of
i s ca lcu12.ted for va lues of
from +10 0 to _100.
Assum i ng tha t each
8 spaced a t
CD'
cP
intervals
affects the meen
OF
N. A.C·A. Technica l No te No. 214
6
in propo r tion to the time it persists, and using 0 o as the mean
00000
o
from - 1 to 1 ,2 from +1 t o +3
and so on (9i is used in place
of 10 0 as the las t point, for obv ious reasons), the mean
found .
OF
OF
is
works out by this me t hod , in the case just given, at
-. 003.
Similar comput ati ons have been made by the mathematical and
each with 10 0 amplitude.
arithmetica l methods fo r
r i th.
Exper.
a
Math .
i
_4 0
-. 026
- .022
~.015
0
-. 002
- . 003
+.003
+40
+ . 027
+ . 028
+.031
The agreement between the ca l culated and eXi.Jerimental results is
fair, certainly good enough to indicete that the explanation offered is correct.
By the mathematical analysis it
ap~ears
that the reduction in
drag coefficient should vary as the square of the
cillation.
In Fig . 9 of Techni cal Note
10.
~mp litude
of os-
202 (Reference 2), the
reduction of coefficient due t o a 10 .. 50 8mplitude is .038, "rhile
that due to 16.5 0 is only . 058 , insteEd of .094, if the square law
held.
But in Fig. 12, the
rec~uctions
Amp l l' tu d e
l
80
2 re:
13°
17°
Reduction
. 036
.079
. 110
Var i ed as square
based on 13 0
. 030
.079
.135
N. A,C · A· Technical Not e No. 21 4
7
Tl-c.ese vEriF'.tiOl1s 8re ne a l'° r t he squ8:ce .
Such a 1::erra-:;ions as exi s "\:;
fo r tLe lo r ge ampli tudes a::.-·S ac count ed fo r by t h e increase of t:':::e
at t ~c~
angl e o f
i n the. course o f t h e o s cillat ion to far beyond the
po int of rnax i rJur1 , i nve.lidat ing th e a ssump ti ons
OIl
'which the a naly-
s is '<7as ba.sed .
A fUT"cher app li ccd i on of t he K2, tzmayr
Hr.
-,~:21te::c
y. 3:e,c:..e , is the. t it
G2.y
effect , suggestec_ 'by
be the cause of
v a ria tion of d r ag s mea sured i n v a rious tunnels .
~Jart
of the
A sma l l natura l
o s cillat i on of d ire c tion of the v'i nd s tr eam "'ould have exactly
t he
effec t as an
S?::'18
e. :.:' t i iic ~ al l y
p r odu c e6 oscil l at i on .
deL, and
-_a.a
t he mathematica l 8l1.8,lY 5i s e,nc:" val ue of
Usi:n.g
for a
go oa. '-ing nea r r.1i n i mu m dr ag, the reduc t i on in drag , due to 2.n 080
0
' e J 18
. 5 . 2d'
C1"11
_ cVC" 10n 0 -1.<: 1-'- amp 1_ 1. tuC'~
~o} a n d t h 8 t O
CLue t 0 1 / 2 l'S
=
( Cn
;J
C-OT.
dO
2
l
. 0120 , -:-=- = . 100 , ---=;:c a e : a'"
=
. C01 ) .
It is cert2inly not inco:"1-
c e i vable that there may be an osc i llat i on in pin'. C.irection of 1/2
at
SOt,18
r'in<i spee0_ i n almos t an] t ype of tun:'1s1 .
fa ct th a t
t~:. i s
osci ) l a tio n
i'.12.~- C~18. nge '-'it~1
i7inc
Furt~1err..:oIe,
s ~Je e(
t~:e
,.,ould offer
en explanat i on of t he st r ildngl y c':. i fferent character istics sll.o';'n
by
11
sC81e Gife ct
Ol.~r
es"
t 2.~(8L
i l1 cL i fferent tun:"1els .
0
r .A.C·.8.· Tecl1nica110te No. 214
8
TABLE 1.
Effect ive Drc::.g Re2.o.ing Cl.t 0
CD cos~
_9_21 0
0
IJean .~.ng 1e
7'1
.!..)
-. 0 2
. CIS
. .. 016
-.003.
.013
.451
.0059
-8
.n.
. C16
. 016
.015
.031
.3 43
.0107
-6
. 27
. 018
. 01B
. 028
.046
. 253
.')117
-4
. ~2
.023
.023
.029
.052
. 219
.0114:
-2
. 58
.03 1
. 031
.020
.051
. 205
.0104
o
. 72
. 041
.041
. CO
.0( 1
. .200
. 0082
2
. 86
. 054
.054
-. 030
.024
.205
. 0049
4
. 98
.057
.067
- . 069
-. (J02
.219
-. 0004
6
1.10
. OB4
.084
-. 115
-. 031
. 2 53
-. J0 79
8
1 . 21
.104
.103
-.1 68
-.065
.343
-.0223
. 1 21
.119
-. 210
-.091
.451
-. 04·10
3.142
-. 0084
Values of
CL and CD
No. 2 0 2 (Ref e rence 2) .
f ro m Fig . S, N..-;..C · .-,. .
Technic ~ l
Not e
E •.';' ·C· A· Tec..1. i1i cal
9
No t e No . 214
TASLE II.
Effect ive Drag Reading at _ 4°
a.+~
f3
~fea
n Ang1 G·
CL
CD
CD'
CD ! t
-1 3-2
_91.0
-.31
. 027
-. 018
-.0081
- 12
-8
-. 21
.021
-. 008
-.0027
-10
-6
-. 05
.016
+.011
.0028
-
8
-4
.11
.01 6
. 024
.0053
-
6
-2
. 27
. 018
.029
.0059
- 4
0
. 42
. 023
,023
.0046
-
2
2
.58
. 031
. 01 1
.0023
0
4
.7 2
.041
-.009
":.0020
2
0
r
. 86
. 054
-.036
-.0091
4
S
. 98
. OS7
-.070
-. 0240
51-2
9.1.
2
1.07
. 078
-.100
-. 0451
1 0
2
~
-.0701
N.A·O·A- Technical Note No. 214
10
TABLE III.
Effe ctiv'? Drag Reading at +40
a+f3
1ean Angle-
f3
CL
CD
CD t
CDlt
- 52
- 9 21°
.30
.019
.068
.0306
-4
-8
.42
. 023
.081
.0278
-2
-6
· 58
.031
.092
.0233
0
-4
.72
. 041
.091
.0199
2
-2
.86
.054
.084
.0172
L1.
G
.98
.OS7
.067
.0013
6
2
1.10
.084
.045
.0094
8
4
1.21
.104
.019
.0042
10
6
1.30
.127
-.010
-.0050
12
8
1 . 37
.156
-.037
-.0127
131.
2
91.
2
1.40
.175
-.059
-.0266
1°
.0894
N. A.C·A. Technical Note No . 214
11
References.
1.
R. Katzmayr:
Effect of Periodic Cbanges of Angle of Attack
on Behavio r of AirfoIls. Translation from
lIZeitscbrift ffu Flug~echnik und. Motorluftscbiffabrt,1I rEarch 31 and lipri1 13, 1982.
N. A. O·A . Technical l1emorandum No . 147. 1922.
2.
Toussaint,
Kerneis
and
Giraul t
Experimental Inves tigation of the Effect of an
Osci lla ti ng Air Stream (Ka tzmayr Ef:ect) on the
Oharacteristics of \ irfoils. Translation from
the French. N .~. O . h ' Technical Note No. 202.
1924.
3.
A. F. Zahm:
Influence of 1 ode1 Surface and Airflow Texture
on Resistance of Aerodynanlic Bodies. N. .ri..O.A .
Technical Report No . 139. 1922l.
.
N~.C.A*
Technical Note No.214
I\L
1
1
1
I
1
L
---c..::",.>----===---~;,L.__d.
_______
Normal wind direction
---
l'I
D'
Fig 1.
•
/
D
~---------------I --~-----~--~~------~~'~--
N.A.C.A. Technite 1 Note No, ' 214
-
--
I
Fig. 2
-~ ---r----.--
.?o
. / - ' - - - - - ' - -1 _
-_ ••
I
-j---
18
14
- - i - - - - - ; - - -- j •
--t--~-,
.12
-4+--~--+---r-~
un
~
-
.--l.- - .-
-
.02 '
I
- -----l . lO
- -~--l--
LlC
n_
6
0~~~~~~~~~~~~~~r_7t~~~~r_~~.08
i
- .1
i
. ~c.,-_J'--r-~- -.
1
_...l -
I
--t- - LTC - -I--.tB
!
I
L
I
----r---r---+-.-I
I
.04 - --- ~ - __ 1____
C
D
I
-.- ---. ~-+l-==-.j;~
+-_1
\+ - --t----; .
06
-J---t----t---; .
04
-.3
--r -
I
,
;
I
.02 ~r-.-t-
-An - i e
00
~f-a+-t-a-c+'-,-+---+--+F-i-g-,t--r.2
----J
140
80
12 0 I
16 0 ~_. o ~