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TECHNICAL MEMORANDUM X-519

EFFECT OF VERTICAL-TAIL MODIFICATIONS ON THE STATIC

STABILITY CHARACTERISTICS AT A MACH NUMBER

OF 2.2 OF A SUPERSONIC VTOL AIRPLANE

MODEL HAVING A BROAD FUSELAGE

AND SMALL DELTA WINGS

By Ross B. Robinson and M. Leroy Spearman

Langley Research Center ~--------------, Langley Field, Va.

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NA TIONAl AERONAUTICS AND SPACE ADMINISTRATION

WASHINGTON April 1961

CONFIDENTIAL

https://ntrs.nasa.gov/search.jsp?R=19630007289 2018-05-15T21:32:07+00:00Z

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CONFIDENTIAL

NATIONAL AERONAUTICS AND SPACE A_INISTRATION

TECHNICAL MEMORANDUM X-519

EFFECT OF VERTICAL-TAIL MODIFICATIONS ON THE STATIC

STABILITY CHARACTERISTICS AT A MACH NUMBER

OF 2.2 OF A SUPERSONIC VTOL AIRPLANE

MODEL HAVING A BROAD FUSELAGE

AND SMALL DELTA WINCS*

By Ross B. Robinson and M. Leroy Spearman

J

An investigation has been conducted in the Langley 4- by 4-foot

supersonic pressure tunnel at a _ch number of 2.2 to determine the

effects of various tail modifications on the stability characteristics

of a model representative of a supersonic VTOL airplane. The original

model had a broad fuselage, small delta wings_ and twin vertical tails.

The tail modifications included a center-line vertical tail having the

same area as the original twin tails and the addition of twin ventral

fins.

The results for the configuration with the original tail indicated

an initially low value of directional stability Cn_ that decreased

rapidly with increasing angle of attack until directional instability

occurred above an angle of _.5 °. Changing to a single tail or adding

ventral fins resulted in an increase in directional stability at low

angles of attack. However, with increasing angle of attack, the con-

tribution of the single tail to Cn_ decreased more rapidly than that

for the original twin tails whereas the contribution of the ventral

fins remained essentially constant. As a result, the most effective

means of increasing the angle-of-attack range for positive Cn_ was

through the addition of ventral fins to the configuration with the

original vertical tail.

*Title, Unclassified.

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...... v

2 CONFI DENTIAL

INTRODUCTION

Among the types of manned aircraft currently being proposed are

those that combine the features of supersonic operation with the ability

to take off and land vertically (VTOL). Some of the configurations

being considered make use of lifting-fans in order to achieve the VTOL

characteristics. If these fans are installed in the body, the result

may be a rather broad, flat fuselage that might be expected to have a

pronounced effect on the aerodynamic characteristics of the vehicle.

Accordingly, an investigation has been undertaken in the Langley 4- by

4-foot supersonic pressure tunnel to determine the aerodynamic char-

acteristics of a model representative of a supersonic VTOL aircraft

having a broad fuselage, small delta wings, and twin vertical tails.

Results of the investigation at a Mach number of 2.01 (ref. i) indi-

cated that the original configuration had low directional stability.

An extension of the investigation has been made at a Mach number of 2.2

for which, in addition to the original configuration, tests were made

with a single vertical tail and with ventral fins. The results of this

investigation, with a limited analysis, are presented herein.

SYMBOLS

All data presented herein are referred to the body system of axes

except the lift and drag data which are referred to the stability sys-

tem of axes. The moment reference point is at a longitudinal station

corresponding to 65.35 percent of the body length.

CL llft coefficient, Lift/qS

C D

Cm

Cn

C Z

Cy

L/D

q

(See fig. l(a).)

drag coefficient, Drag/qS

pitching-moment coefficient,

yawing-moment coefficient,

rolling-moment coefficient,

side-force coefficient,

llft-drag ratio

Pitching moment/qS_

Yawing moment/qSb

Rolling moment/qSb

Side force/qS

free- stream dynamic pressure

O

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S

b

c_

Cn_

CZ_3

Cyf?

wing area, 1.488 sq ft

wing mean aerodynamic chord, 1.08 ft

wing span, 1.77 ft

angle of attack, deg

angle of sideslip, deg

directional stability parameter

effective dihedral parameter

side-force parameter

MODEL AND APPARATUS

Details of the original model with twin vertical tails are shown

in figure i_ details of the ventral fins and of the sin_le vertical

tail are shown in figure 2. Geometric characteristics are given in

table I. The ventral fins were located at the same spanwise station

as the twin vertical tails. The body was designed to provide for an

internal flow system composed of twin horizontal-ramp inlets on the

sides of the body that were ducted to six simulated jet exits side by

side at the base of the body. All tests were made with 0.10-inch-wide

transition strips of No. 80 carborundum grains affixed 2 inches behind

the fuselage nose and at the 10-percent-chord stations of the wing and

tail surfaces. All control surfaces were set at zero deflection.

The model was mounted in the tunnel on a remote-controlled rotary

sting. Six-component force and moment measurements were made through

the use of an internal strain-gage balance.

TESTS, CORRECTIONS, AND ACCURACY

The tests were made in the Langley 4- by 4-foot supersonic pres-

sure tunnel with the following test conditions:

Mach number ........................... 2.2

Stagnation temperature, OF ................... i00

Stagnation pressure, ib/s_ in .................. i0

Reynolds number, based on _ .............. 2.44 × 106

CONFIDENTIAL _-_j

4 CONFIDENTIAL

The stagnation dewpoint was maintained sufficiently low (-25 ° F

or less) so that no condensation effects were encountered in the test

section.

Tests were made for an angle-of-attack range of about -8° to 16°

at _o = 0° and for an angle-of-sideslip range of about -12 ° to i0° at_ and of about -8 ° to i° at _ = 4.6 ° , 9.1 °, and 13.6 ° .

The angles of attack and sideslip were corrected for deflection

of the balance and sting under load. The drag data have been corrected

for the effects of internal flow, base pressure, and balance chamber

pressure.

The estimated accuracy of the individual measured quantities is

as follows:

CL .............................. ±0.0004

CD .............................. ±0.0007

Cm .............................. ±0.0004

Cn .............................. ±0.0001

C_ .............................. ±0.0003

Cy .............................. ±0.0007

_, deg ............................ ±0.2

_, deg ............................ ±0.2

SUMMARY OF RESULTS

Modifying the vertical tail or adding ventral fins had little

effect on the longitudinal characteristics shown in figure 3 other than

to increase slightly the drag and reduce the lift-drag ratio.

The aerodynamic characteristics in sideslip for various angles of

attack are shown in figure 4; the sideslip derivatives are shown in

figure 5. The configuration with the original twin tails indicates a

low value of directional stability Cn_ at _ = 0° that decreases

rapidly with increasing angle of attack until directional instability

occurs at _ = 4.5 ° (fig. 5)- Changing to a single tail or adding

ventral fins resulted in an increase in directional stability Cn_ at

low angles of attack. With increasing angle of attack, however, the

contribution of the single tail to Cn_ decreased more rapidly than

that of the original twin tails_ whereas the contribution of the ven-

tral fins remained essentially constant throughout the angle-of-attack

range. As a result, the most effective means of increasing the angle-

of-attack range within which positive directional stability could be

CONFIDENTIAL

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CONFI DENTIAL 5

maintained was through the addition of the ventral fins to the configu-

ration with the original twin tails. As pointed out in reference i,

the rapid decrease in vertical-tail effectiveness with increasing angle

of attack is probably caused by a disturbance created by the inlet lips.

The existence of such an adverse flow field is indicated by the results

for the single tail wherein the effect of increasing the span of the

tail within the adverse flow field causes the tail effectiveness to

decrease even more rapidly as the angle of attack is increased so that

at the higher angles of attack the single tail is less effective than

the original twin tails.

Langley Research Center;

National Aeronautics and Space Administration,

Langley Field, Va., January 26, 1961.

REFERENCE

i. Driver, Cornelius, and Spearman, M. Leroy: Stability and Control

Characteristics at a Mach Number of 2.01 of a Supersonic VTOL

Airplane Model Having a Broad Fuselage and Small Delta Wings.

NASA TM X-441, 1961.

CONFIDENTIAL _,_

6 CONFIDENTIAL

TABLEI.- GEOMETRICCHARACTERISTICSOFTHEMODEL

Wing:Span, in ............................ 21.30Theoretical root chord, in .................. 19.50Tip chord, in ........................ 0.62Meanaerodynamic chord, in .................. 13.00Area, sq ft ......................... 1.488Aspect ratio ......................... 2.12Taper ratio .......................... 0.032Leading-edge sweep, deg ................... 63.5Trailing-edge sweep, deg ................... 13.05Sweepof quarter-chord line, deg ............... 57.45Dihedral, deg ........................ 0Incidence, deg ........................ 0Thickness, percent chord ................... 3Elevon area, sq ft ..................... 0.322

Body:Length, in .......................... 39.02Maximumwidth, in ...................... 10.68Body station for maximumwidth, in .............. 36.98Maximumdepth (excluding canopy), in ............. 1.95

Original (each) Single4.13 5.57

Vertical tails:

Span, in .....................

Root chord:

Theoretical, in ................ 7.44 12.05

Exposed, in .................. 6.25 9.00

Tip chord, in .................. 1.09 1.60

Leading-edge sweep, deg ............. 63.5 63.5

Trailing-edge sweep, deg ............. 25.0

Area:

Theoretical, sq ft ............... 0.122 0.233

Exposed, sq ft ................. 0.086 0.172

Ventral fin (each):

Span, exposed, in. . ........ .......... 1.90

Root chord, in ........................ 8.17

Tip chord, in ........................ 0

Leading-edge sweep, deg ................... 40

Area, exposed, sq ft ..................... 0.067

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CONFIDENTIAL ] 2

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Effect of tail modifications on the aerodynamic character-

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CONFIDENTIAL I t

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CONFIDENTIAL

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CONFIDENTIAL 17

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NASA- Langley Field, Va. L-1459 CONFIDENTIAL -_ 2)

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