Sears, Richard I

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NATIONAL ADVISORY cOMMITmE FOR AERONAUTICS
Wm’rmm lUWOIW
ORIGINALLY ISSUED
April 1942 as
Res&lcted Bulletdn
CAUULATICM OF TAB CHARACTERISTICSFCYRFIZGm
C(X?DITIQ!WFNM WIND-TUNNEL DATA
By Rlchexd 1. Seam
Langley Memarial Aeronautical Mmratory
~ey Field, Va.
WASHINGTON
,,
NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of
advance research results to an authorized group requiring them for the war effort. They were pre-
viously held under a security status but are now unclassified. Some of these reports were not tech-
nically edited. All have been reproduced without change in order to expedite general distribution.
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ilATIOl?ALADVISORY 00MMITTEn FOR AHROHAUl!IOS
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OALCULA!TIOM 037 TA3 OHAMCTERISTIOS FOR l?LI~H!C
.3
y COHDITIOHS FROM WIND-TUNNEL IIATA
.4
By EichariL I. Sears
Certain tail-surfaoe oharaoterlsties ealoulated from
wind-tunnel data have been reported not to check with
flight-test neasurementta. ~hia discrepancy might have
been caused by failure to aooount for the changes in equi-
librium conditions that occurred in flight when the wind-
tunnel data neasured in etatio-force tests wsre applied.
The problem under consideration Is the calculation of
the effect of tab deflection upon the free-floating angle
of tiie elevator, EIS in a servocontrol. Flight-test meas-
urements are re~orted to k~e shown nearly twioe as great
a change in elevator deflection per degree tab deflection
as wind-tunnel tests have Indicnted. The followlng illus-
tration may be given in order to show that such a discrep-
ancy nay be expecte~ If the tab characteristioO are aom-
puted ~jlthout consideration of the response of the air-
plane to a Ceflectios of the elevator.
It can be shown that, for zero pitching velocity, the
hinge-moment ooeffioient of the elevator nay be expreseed
by the following relation:
Ohe = Che ,d + Ghe ae + Ch 8t
a 8e ebt
or
where
at angle of attaols of tall
a angle of attack of atrplane
_ .. .— .—
_ .
..- -.— .. . . . .. -
.
... . . ..—
1
angle of attnok of airplane at zero llft
angle of incidenoe of tail
elevator deflection
tab def?.ectlon
angle 05 dovnwash
elevat5r hlnge=noment coefficient
Thus, when c~e = o, the free-floatlng angle of
vator is
Che , (Go + it) +oh 6~a ‘8t
8
‘free
=-
Ch
%3e + ‘heal (1 - cm) ‘e
The rate of change of free-floating angle of the
with tab deflection is
cl-
the ele-
elevator
.
a8e() ‘%t=-% free
‘h
‘8e $ ‘h%, (1 - ‘a)%
. .
From reference 1, It oan be seen that, for typical air-
....-
.3
-1
u
J1
,.
-.,.
.=. -’-:ab - - - . -.: .: ,... . .. . . . ..
* lies betweenplanes, O and -1.0 and ha’s “’ti-tie”do”ti-
nended value of =0.5. It should be noted that the sign of.
Be is taken opposite to that used” In referenoe 1. Por
airplane 3 of referenoe 10 with various center-of-gravity
positions
From reference 2,
1
~
= -1.08, -2-220 -2~85
SF
the seetion parameters for an lJAd.&0009
airfoil with a 0.300 flap are:
Ch = -0.0130
’80
Ch =
-0.0C94
‘8t
=
-0.0130
. .
x -0,0160
Thus, for a 0.20
for m 0.10 Ce tab
for a 0.20 Ce t~-b
for m 0.30 Ce tab
Ue tab, when *
a~e
= -2.22
at)e -0.0130
~ = - (-0.0130) + (-0-0075)(1 - 0.6)(-2022) = ‘2”06
The curves of figure 1 have been oonputed in this man-
a8e
nero They give the paraneter
~
for various amounts of
the airplane reeponee factor ~ . Thus , It oan be seen
a8e
4-..
...-—
that the reported discrepancy between oonputed ree-ults and
the flight-test measurements might well be explainea If
the computation neglected the response of the airplane to
elevator movement. Suoh computations would be represented
by the points at - = O.
~8e
Langle~ I.iouorialAeronautical Laboratory,
Hc.tional Advisory Comntttee for Aeronautics,
Langley Field, Va.
. .
REFERENCES
10 Gilruth, R. E., and White, M. D.: Analysis and Pre-
diction of Longitudinal Stability of Airplanes.
Rep. No. 711, NACA, 1941.
2. Aries, Uilton B., Jr., and Soars, Richard I.; Determi-
nation of Coatrol-Surfaoe Charactoristlcs fron NAOA
Plain-Flap and Tab Dctn. Rep. No. 721, l?ACA, 1941.
.
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Ylgare 1.- Variation of tab offectivuoss wi+~ airp@ac raepcnso to
olovator dafloction. I-MA 0009 airfoil Q.30c alovator.
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Calculation of tab characteristics for flight conditions from wind-tunnel data

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