Draper, John W

Rose, Robert W

English

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RESTRICTED Copy RM L9J07a 
NACA 
RESEARCH MEMORANDUM 
INVESTIGATION OF THE DYNAMIC LATERAL STABILITY AND
CONTROL CHARACTERISTICS OF A MODEL OF A FIGHTER 
AIRPLANE WITHOUT A HORIZONTAL TAIL AND EQUIPPED
WITH EITHER SINGLE OR TWIN VERTICAL TAILS
By John W. Draper and Robert W. Rose 
Langley Aeronautical Laboratory
Langley Air Force Base, Va. 
CLA3.I'ICATION 
fiss document Centel—classified Information 
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thereto, and to United States citizens Of known 
lovolty and disorettoes who of nooennity most be 
ri: ernst Gervof. 
NATIONAL ADVISORY COWY 
FOR AERONAUTICS 
WASHINGTON 
November 15, 1949 
RESTRICTED
https://ntrs.nasa.gov/search.jsp?R=19930086067 2020-06-17T13:05:35+00:00Z
NACA 1*4 L9J07a	 RESTRICTED 
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 
INVESTIGATION OF THE DYNAMIC LATERAL STABILITY AND 
CONTROL CHARACTERISTICS OF A MODEL OF A FIGHTER 
AIRPLANE WITHOUT A HORIZONTAL TAIL AND EQUIPPED 
WITH EITHER SINGLE OR TWIN VERTICAL TAILS 
By John W. Draper and Robert W. Rose 
SUMMARY 
An investigation has been conducted in the Langley free-flight 
tunnel to determine the dynamic lateral stability and control character-
istics of two configurations of a model of a fighter airplane without a 
horizontal tail, one with a single vertical tail mounted on the fuselage 
and the other with twin tails of about the sane tail volume mounted on 
the wing. The results of the investigation indicated generally similar 
flight characteristics for the two configurations. 
INTRODUCTION 
Interest has recently been shown by aircraft designers in the 
relative merit of single and-twin vertical-tail configurations on 
fighter airplanes with sweptback wings and without a horizontal tail. 
An investigation has therefore been conducted in the Langley free-flight 
tunnel to compare the dynamic lateral stability and control character-
istics of two configurations of a model of such an airplane, one with a 
single vertical tail mounted on the rear of the fuselage and the other 
with twin vertical tails located approximately halfway out on the wing 
semi spans. The-two tail configurations had about the sane tail volume. 
The model used in the investigation had a wing with 350 sweepback of the 
quarter-chord line, an -aspect ratio of 3, and a taper ratio of 0.65. 
The present investigation consisted of force tests. to determine the 
static stability and aileron control characteristics of the model with 
the two tail configurations and flight tests to determine the dynamic 
stability and the controllability of the model with the two tail 
RESTRICTED
2	 NACA RM L9JO7a 
configurations. Flight tests were also made to determine the effect of 
decreased directional stability on the flying characteristics of the 
model.
SYMBOLS 
All force and moment measurements were referred to the stability 
axes. A sketch . showing the positive directions of the forces, moments, 
and angles is given in figure 1. 
S	 wing area, square feet 
mean aerodynamic chord, feet 
b	 wing span, feet 
St	 vertical-tail area, square feet 
tail length (longitudinal distance from center of gravity 
to c/4 of vertical tall), feet 
V	 airspeed, feet per second 
q	 dynamic pressure, pounds per square foot (v2) 
P	 air density, slugs per cubic foot 
M	 angle of attack of fuselage center line, degrees 
angle of sideslip, degrees (-r) 
angle of yaw, degrees 
CP angle of roll, degrees 
CL lift coefficient (-Z/qS) 
CD drag coefficient (-X/q.S) 
Cm pitching-moment coefficient (M/qSë) 
Cy lateral-force coefficient (Y/qS) 
Cn - yawing-moment coefficient (N/qSb)
NACA RM L9JO7a	 3 
C2	 rolling-moment coefficient (L/qsb) 
Z	 normal force, pounds 
X	 longitudinal force, pounds 
-	 M	 pitching moment, foot pounds 
Y	 lateral force, pounds 
N	 yawing moment, foot pounds 
L	 rolling moment, foot pounds 
ba	 aileron deflection (perpendicular to hinge line), degrees 
Cy	 rate of change of lateral-force coefficient with angle of 
sideslip in degrees (Cy/) 
Cno	 rate of change of yawing-moment coefficient with angle of 
sideslip in degrees (Cn/3) 
rate of change of rolling-moment coefficient with angle of 
sideslip in degrees (Ci/) 
Subscripts: 
r	 right control surface 
2	 left control surface 
APPARATUS AND MODEL 
The investigation was conducted in the Langley free-flight tunnel 
whichis designed to test free-flying dynamic models. A description of 
the tunnel and the testing technique is presented in reference 1. 
Force tests to determine the static aerodynamic characteristics of the 
model were made on the Langley free-flight-tunnel six-component balance 
which is described in reference 2. 
Three-view drawings of the model configurations used in the 
investigation are presented in figures 2 and 3 and photographs are 
given in figure 1. Table I presents the dimensional and mass character-
istics of the design.
NACA RM L9JO7a 
The wing of the model had a modified Rhode St. Genese 35 airfoil 
section. The use of this section is in accordance with the Langley 
free-flight tunnel practice of using an airfoil that will attain a 
reasonable maximum lift coefficient at low Reynolds numbers. The wing 
was set at 00 incidence with respect to the fuselage center line and 
the control surfaces on the wing were set at an upward deflection to 
balance out, the pitching moment due to camber. The control surfaces 
were deflected in opposite directions from this trim setting for aileron 
control and in the same direction for elevator control. The -tails were 
built in several sections, as shown in figures 2 and 3, in order that 
the directional stability of the model could be easily reduced by 
removing the various sections. 
A comparison of the geometry of the to different tail configura-
tions can be obtained from figures 2 and 3 and from table I. In 
estimating the tail volume (Stlt) of the twin tails, the area of the 
landing-gear fairings located under the wing was neglected since this 
area is a low-aspect-ratio, rounded surface which probably contributes 
very little to the directional stability, except possibly at large yaw 
angles. On this basis, the total area of the twin tails is about 
55 percent greater than that of the single tail. The single tail, how-
ever, has a tail length 55 percent greater than that of the twin tails 
so that its tail volume is about equal to that of the twin tails. The 
aspect ratio of the single tail was approximately 10 percent greater 
than that of the twin tails.
TESTS 
Force tests were made to determine the static lateral stability 
characteristics of the model for the single-tail, twin-tail, and tall-
off configurations. Rolling and yawing moments produced by aileron 
deflections and basic longitudinal stability characteristics were also 
determined for the two tail configurations. 
All force tests were run at a dynamic pressure of 3.0 pounds per 
square foot, which corresponds to an airspeed of about 34 miles per 
hour at standard sea-level conditions and a Reynolds number,
 
of 11.20,000 'based on the ,
 mean aerodynamic chord of 1.31 feet. All forces 
and moments for the model are referred to a center-of-gravity position 
at 0.20 mean aerodynamic chord and at a vertical position of 0.018 mean 
aerodynamic chord-above the fuselage center line. 
Flight tests were made to determine the effect of tail configura-
tion on the dynamic stability and controllability characteristics of 
the model. The effect of reducing the directional stability was also 
studied. The flights were made at a lift coefficient of approximately 0.6
NACA RM L9J07a	 5 
and with a static margin (-Cm/CL) of about 0.16. The mass character-
istics were approximately as shown in table I. A relatively light wing 
loading was used to minimize damage to the model in crashes. 
RESULTS AND DISCUSSION

Force Tests 
The results of force tests made to determine the static longitudi-
nal and lateral stability characteristics of the model are presented in 
figure 5 to 7. The differential setting of the ailerons indicated on 
the figures corresponded to the flight-test trim conditions which were 
necessary because of asymmetry of the model due to warping and deforma-
tion resulting from crashes. 
The data presented in figure 5 show that the model had about the - 
same drag and longitudinal stability characteristics with either tail 
configuration but that the lift coefficient was generafly slightly 
higher for the single-tail configuration. This can probably be 
accounted for by the difference in the interference effects on the wing 
for the two configurations. 
The variation of the lateral coefficients with angle of yaw 
(fig. 6) is essentially linear over a range of yaw angles from 200 
to -200
 for either the twin or single tails or tail off at m = 120, 
which corresponds approximately to the angle of attack of the model in 
the flight tests. The variation of the lateral-stability parame-
ters -C, C 13 , and -Cy, with lift coefficient for the model with 
tails on and off is presented in figure 7. These parameters were 
obtained from force tests made at 50 and 0 yaw. The values of Cn 
were larger for the single tail than for the twin tails. Inasmuch as 
the tail volumes of the two configurations were about the same, this 
difference is probably due to the fact that the aspect ratio of the 
single tail was greater than that of the twin tail. With the tails 
removed the model had a small positive value of directional stability 
at the higher lift coefficients. The effective-dihedral parameter 
was about the same for both configurations over the lift-coefficient 
range.
NACA FM L9J07a 
The results of aileron effectiveness tests made at cx. = 120 
with 170
 deflection of each aileron (which corresponds to the deflections 
used in the flight tests) are presented in the following table: 
Configuration C1 Cn 
Single tail 
Twin tails
0.028 
.021
0.0045 
.0040
These data show that the aileron rolling moment was somewhat lower for 
the twin tails than for the single tail. The aileron yawing moment was 
small and favorable for each tail configuration, apparently because of 
the initial upward setting of the surfaces, and was relatively 
unaffected by tail configuration. 
Flight Tests 
The results of the flight tests showed that the vertical-tail 
configuration had very little effect on the general flying character-
istics of the model. With either the twin-tail or single-tail arrange-
ment the model was easy to fly. Oscillations resulting from normal 
control or gust disturbances were small and well damped. The model 
could be controlled as well with ailerons alone as with coordinated 
aileron and rudder control except in cases where the model was rather 
violently disturbed either inadvertently or intentionally. In these 
cases, recovery was effected more easily when the rudder was used in 
conjunction with the ailerons. 
The flights made with the directional-stability parameter Cn 
reduced, progressively from a large positive value to a small negative 
value, by removal of tail sections, indicated that the directional 
stability could be reduced considerably before any effect was noted. 
(See fig. 8.) With fairly small positive values of Cn the model 
was more easily disturbed in yaw and was more difficult to control 
once it was disturbed. Even with the tails removed, however, fairly 
good flights were obtained and it was difficult to disturb the model 
sufficiently by abrupt aileron deflection to cause the model to become 
uncontrollable. 
The flying characteristics of a model with such low directional 
stability are usually unsatisfactory because of large-amplitude yawing 
motions which are excited by the adverse aileron yawing moment and the 
yawing moment due to rolling velocity. When the effective dihe-
dral (-Ci) is moderate or large, this adverse yawing produces large 
NACA RM L9JO7a	 7 
rolling moments which tend to counteract the aileron rolling moments 
and thereby make the flying characteristics even more unsatisfactory. 
In the present investigation, however, flights were obtained with 
approximately zero directional stability and a moderately large value 
of -C1 (0.0015) apparently because the disturbing yawing moments due 
to aileron deflection and rolling velocity were very small. The force-
test results of figure 7 indicate that with tail off the model had 
negative Cn at the flight lift coefficient (0.6), but fairly satis-
factory flights were obtained. Although these results might appear to 
be in disagreement, it is theoretically possible for no directional 
divergence to exist even when Cno is slightly negative, especially if 
the effective dihedral -Cj has a moderately large positive value as 
it has in the present case. 
During the tail-off flight tests the lift coefficient was reduced 
from about 0.6 to 0.5 and it became impossible to fly the model because 
of directional instability. This result substantiated the force-test 
results which showed a decrease in directional stability with decreasing 
lift coefficient.
CONCLUDING REMARKS 
.The results of the investigation to determine the dynamic lateral 
stability and control characteristics of a model without a horizontal 
tail and equipped either with a single vertical tail mounted on the 
fuselage or with twin tails of about the same tail volume mounted on 
the wing indicated generally similar flight behavior for the two con-
figurations. 
Langley Aeronautical Laboratory 
National Advisory Committee for Aeronautics 
Langley Mr Force Base, Va.
8	 NACA RN L9J07a 
REFERENCES 
1. Shortal, Joseph A., and Osterhout, Clay-ton J.: Preliminary 
Stability and Control Tests in the NACA Free-Flight Wind Tunnel 
and Correlation with Full-Scale Flight Tests. NACA TN 810, 1941. 
2. Shortal, Joseph A., and Draper, John W.: Free-Flight-Tunnel 
Investigation of the Effect of the Fuselage Length and the 
Aspect Ratio and Size of the Vertical Tail on Lateral Stability 
and Control. NACA ARR 017, 1943.
NACA RM L9JO7a	 9 
-	 TABLE  
DIMENSIONAL AND MASS CHARACTERISTICS OF FIGHTER AIRPLANE 
RESEARCH MODEL TESTED IN LANGLEY FREE-FLIGHT TUNNEL 
Weight, w, lb .......................... 9.1
 Wing loading, W/S, lb/sq ft .. . - 
........ . 1.83 
Relative-density factor, (Mass/pSb) ............... 6.78
 Center-of-gravity location, percent M.A.0............20 
Moments of inertia (approx.) 
About X-axis,
	
51u-ft2	
.................... 0.13 
About Y-axs,	 slug-ft2	
..................... .18 
About Z-axis,	 slug-ft2	
....................
.29 
Ratio of radius of gyration to wing span (approx.) 
X-axis	
............................ 0.19 
Y-axis	
............................. .22 
Z-axis	
............................ .29 
Wing 
Airfoil section
	 ...........Modified Rhode St. Genese 35 
Area,	 sq ft	
.......................... 4.96 
Span,	 ft	
.......................... 3 
Aspect	 ratio	
......................... 3.00 
Sweepback of quarter-chord line, deg
	
............ 35 
Incidence,	 deg	
.......................... 0 
Dihedral,	 deg	 ..........	 ...	 ............ o 
Taperratio	
......................... 0.65 
Washout, deg 
M.A.C., ft 
Longitudinal distance between leading edge M.A.C. and 
leading edge root chord, ft
	 ............... 0.696 
Root	 chord,	 ft	
........................ 1.60 
Tip	 chord,	 ft	
........................ 0.967 
Distance from nose to leading-edge root chord, ft
	 ....... 0.946 
Elevators and ailerons 
Area, percent wing area (one)
	
................ 9.7 
Span, percent wing semispan (one)
	
.............. 43 
Chord, percent wing chord (inboard end)
	
........... 22.9 
Chord, percent wing chord (outboard end)
	 ............ 29.2 
Vertical tails (twin) 
• Area, sq ft (total, neglecting landing-gear-fairing 
areaunder wing) ........................ 0.99 
Area, sq ft (total	 including landing-gear-fairing 
area under wing5
	
..................... 1.16 
Tail span, ft 
Aspect
	 ratio.	
....................... 1.13 
Tail length, ft (center of gravity to tail 	 /4)	 ...... 1.09 
Tail volume (Stt) (area above wing only)
	 .......... 108 
Vertical tail (single) 
Area,	 sq ft	
.......................... 0.64 
Tail	 span,	 ft	
........................ 1.20 
Aspectratic......................... 0.875 
Tail length, ft (center of gravity to tail
	 /4)	 ...... 1.69 
Tail volume
	 (St i t)	 ...................... 1.08
x 
Wind direc
10	 NACA RN L9JO7a 
V 
Wind direction 
into page 
M z 
a 
x  
Wind direction
VA 
Figure 1.- The stability system of axes. Arrows indicate positive 
directions of moments and forces. This system of axes is defined 
as an orthogonal system having its origin at the center of g'avity 
and in which the Z-axis is in the plane of symmetry and perpen-
dicular to the relative wind, the X-axis is in the plane of 
symmetry and perpendicular to the Z-axis, and the Y-axis is 
perpendicular to the plane of symmetry.
INACA BM L9JO7a	 11 
PARTING LINES FOR 
REDUCTION OF TAIL 
AREA
44.40 
Figure 2.- Twin-tail configuration of fighter airplane model. (All

dimensions are in inches unless otherwise noted.)
) 
12
	
NACA RN L9JO7a 
PARTING LINES FOR 
REDUCTION OF TAIL 
AREAS
H— IaOO-
FIgure 3.- Single-tail configuration of fighter airplane model. (All 
dimensions are in inches unless otherwise noted.)
H 
CH 
rd 
zt 
0 
4) 
I I j
NACA RM L9J07a	 13 
NACA RI.! L9J07a	 15 
H 
Cd
zui 
O A 
Iz Ow C 
zu 
ILL 
OLL 
cIo
(DEG) DEG 
VAIL —24 —28 
NACA RN L9JO7a	 17 
o--TWIN TAIL —23 —29 
4d8iiiiiii. 
p2.3 
Z 
Ui
- 
Z 
Ld
- --
or_ oO._J - -
0	 4	 8	 12	 16	 20	 .1	 0	 H ANGLE OF ATTACK, a, DEG	 PITCHING—MOMENT COEFFICIENT, Cm 
Figure 5.- Longitudinal characteristics of fighter airplane model. 
•1UR•UlR1 
•lUURlU 
••uiuuu• 
R"HEMEMEM
ANGLE OF YAW, Y, DEG '-4 
18	 NACA RN L9JO7a 
2 
Lii> UU
.1 
0I-
LLZ 
'Lii
0 
111L 
luLL 
I—lu 
<0 - 
_J0
.04 
I-c
.02 
Oz
0 
'0. 
ZLL
—.02 
>0
• 
I— 
ZO2 LiJO i 
0I—
I Li	 0 
00 
4: JLL 
jLiJ 
—02 00. 
cr0
M.
(DEG) (DEG) 
—24 —28 
—23 -29 
—27 —30 
2Z_ /. 
fSINLE TAIL 
0--TWIN TAIL 
---TAIL	 OFF 
-
-- ^c- -  
- 
Figure 6.- Lateral characteristics of fighter airplane model. a. 
= 
120. 
- - -
I — - - - 
- - - 
- 
.--
--- --t /
OMENS-1-APH EMNEEMEEMU 
ENUMMMMM 
MMMMMM I I M 
NACA RN L9J07a	 19 
• 
,NONNI 
uJQ 
>.-
a: I-
LLW 
-1-uJ 
LLK i—cr 
-J°- -.01 
.00; 
ED 
')u .00 
<a: 
U
0 
0< 
LJJa: 
cr<
-00I 
-j 
0 
Ld
002 
.001 
LiJ< 
LJ1 
LL< I_uo_	 (•
i 
I (DEG) (DEG) 
 SINGLE TAIL -24 -28 
-- TWIN TAIL
-23 -29 
TAIL	 OFF -27 -30 
0	 .2	 4	 .6	 .8	 1.0
LIFT COEFFICIENT, CL 
Figure 7.- Static lateral stability characteristics of fighter airplane model. 
20
	
NACA RM L9JO7a 
SINGLE TAIL	 TWIN TAILS 
002 
Little yawing. Quick to return when	 Little yawing. Quick to return when 
di disturbed.	 sturbed. 
Slightly more yawing than initial 	 Slightly more yawing than initial 
condition.	 I	 condition. 
J- .001 
Increased yawing and slower to return. 	 Increased yawing and slower to return. 
Large angles of yaw when disturbed. 	 Large angles of yaw when disturbed. 
Sometimes impossible to recover from 	 Sometimes impossible to recover from 
yawed position.	 j....	 yawed position. 
Fairly good flights until yawed, then model usually 
became uncontrollable. No noticeable adverse yawing 
In aileron rolls. 
Figure 8.- Effect on flight characteristics of progressively reducing 
the directional stability for both configurations. 	 - 
I4ACA_LaflgleY - 11-15-49 - 250


Investigation of the dynamic lateral stability and control characteristics of a model of a fighter airplane without a horizontal tail and equipped with either single or twin vertical tails

Investigation of the dynamic lateral stability and control characteristics of a model of a fighter airplane without a horizontal tail and equipped with either single or twin vertical tails

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