Hanson, P. W.

Levey, G. M.

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RM SL58H08a
RESEARCH MEMORANDUM
for the
Bureau of Ordnance, Department of the Navy
EXPERIMENTAL INVESTIGATION OF FLUTTER AND DIVERGENCE
CHARACTERISTICS OF THE ROCKET-MOTOR FIN
OF THE ASROC MISSILE
COORD NO. N-AM-66
By Gilbert M. Levey and Perry W. Hanson
Langley Aeronautical Laboratory
Langley Field, Va.
X 7 1 - 7
(ACCESSJQ^ NUMBER) -' -
(PAGES)
-{THJRU)
(CODE)
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CES AND NASA
S ONLY
NATIONAL ADVISORY COMMITTEE
FOR AERONAUTICS
WASHINGTON
Restriction/Classification Cancelled
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NACA RM SL58H08a
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
RESEARCH MEMORANDUM
for the
Bureau of Ordnance, Department of the Navy
EXPERIMENTAL INVESTIGATION OF FLUTTER AND DIVERGENCE
CHARACTERISTICS OF THE ROCKET-MOTOR FIN
OF THE ASROC MISSILE*
COORD NO. N-AM-66
By Gilbert M. Levey and Perry W. Hanson
SUMMARY
Some 0.4-scale models of rocket-motor fins of the ASROC missile were
investigated for flutter and divergence in the Langley 9- "by 18-inch
supersonic flutter tunnel in the Mach number range from about 0.6 to l.J*
Results of this investigation indicate that both divergence of the over-
hung leading edge and flutter occur within the sea-level operating condi-
tions of the missile at Mach numbers above about 1.0. Tests of models
with altered .root fixity and plan form and of some relatively thicker
models indicated that these aeroelastic problems could be overcome either
by extending the root clamping plates the entire length of the root chord
or by increasing the thickness of the fins by about 25 percent.
INTRODUCTION
At the request of the Bureau of Ordnance, Department of the Navy,
an investigation was conducted in the Langley 9- by 18-inch supersonic
flutter tunnel on O.U-scale models of the ASROC rocket-motor fins at Mach
numbers from about 0.6 to 1.3. The purpose of this study was to obtain
flutter and divergence characteristics. The models were built by the
Langley Aeronautical Laboratory and were scaled in such a way that the
test dynamic pressures for the models were equal to the full-scale dynamic
NACA RM SL58H08a
pressures. In addition to the 0.4-scale models, other models approxi-
mately 25 percent and ^5 percent thicker than design thickness and
several models having variations in plan form and root fixity were tested.
Test conditions and results of this investigation are presented
herein. The Bureau of Ordnance has requested that results of this study
be considered proprietary.
SYMBOLS
a velocity of sound, fps
fp flutter frequency, cps
fn natural frequency of nth mode (n = 1, 2, 3, M, CPS
M Mach number
q dynamic pressure, Ib/sq ft
t thickness, in.
T absolute stagnation temperature, R
p air density, slugs/cu ft
Subscript:
max maximum
MODEL DESCRIPTION
The basic models used were O.^-scale replicas made of 202^  aluminum
alloy. This scaling was accomplished by multiplying all plan-form dimen-
sions and the thickness of the full-scale model by O.k, thus making the
model thickness a nominal 0.050 inch. In addition to the basic models,
some thicker models which had the same plan-form dimensions as the
0.050-inch models but which were 0.063 and 0.072 inch thick (repre-
senting a 25-percent and 45-percent increase, respectively, in thickness
of the full-scale fin) were tested. Models of the same thickness as the
basic models, but with different root fixities and plan form, were also
tested. A drawing of the basic model is shown in figure l(a), and the
NACA RM SL58H08a
variations in root fixities and plan form are shown in figure l(b).
Natural frequencies and thicknesses of the models are presented in
table I.
In order to facilitate mounting the model in the wind tunnel, two
clamping plates, each equal to the model thickness, were riveted to the
model with the same pattern that was used on the full-scale fin. In
order to compensate for the possibility that the root restraint on the
basic model might not be as good as the root restraint on the full-scale
fin, a piece of material was left integral with the model between the
two previously mentioned plates. (See fig. l(a).) At the forward end
of the root, a cut was made as shown in figure l(a) to simulate the
fixity of the overhung leading edge. In order to determine the effect
of not having this filler piece integral with the main surface, two
models (BF-7C and BF-14) were built the same as the full-scale fin would
be, with the filler piece butted to the model. (See fig. l(b).) The
models were bolted between two 1/2-inch-steel plates, which in turn were
bolted to the wind-tunnel model support.
In most cases, a new model was used for every test because it was
found that once the leading edge of a model had diverged, even though it
could be straightened and its frequencies did not change, there was an
appreciable lowering of the dynamic pressure required for divergence the
second time the model was tested. All the data shown in table I pertain
to models which had not experienced flutter or divergence prior to the
points listed, except for test 33 in which a previously diverged model
was used with the overhung leading edge restrained. Test 38 was a rerun
of test 37 except for the manner in which the model was clamped. The
forward portion of the two clamping plates was cut away as shown in
figure l(b) for test 38.
Typical vibration node lines of the models tested are shown in fig-
ure 2, and the natural frequencies for each model are listed in table I.
Since the full-scale fin frequencies and nodal patterns are not avail-
able, it is not possible to assess the accuracy with which the models
simulated the dynamic characteristics of the full-scale fin. Since the
basic models used were replicas made of the same material as the full-
scale fin, it would be expected that the full-scale frequencies would
be O.k times the model frequencies.
INSTRUMENTATION
Continuous records of wind-tunnel conditions and model behavior
were obtained for each test on an oscillograph. The outputs from pres-
sure cells and from a thermocouple were recorded and used to obtain
tunnel static and stagnation pressures and stagnation temperature,
NACA RM SL58H08a
respectively. Strain gages located on the models as shown in figure 1
were used to record the natural frequencies and flutter frequencies of
the models as listed in table I. In addition, the forward strain gages
were used to obtain the divergence conditions. High-speed motion pic-
tures at a speed of about 1,^ 00 frames per second were taken of the model
during each tunnel test.
TEST PROCEDURE
The tests were conducted in the Langley 9- by 18-inch supersonic
flutter tunnel. This tunnel is of the intermittent blowdown-type using
fixed nozzle blocks and operating from a high-pressure source to a vacuum.
The transonic tests were made by using a slotted test-section nozzle
employing a choking device in the diffuser to obtain the desired Mach
number in the test section.
The tests were made at approximately constant Mach number and con-
stantly increasing dynamic pressure until the desired results were
obtained. The maximum dynamic pressure of the tunnel is limited in the
range of these tests to those obtainable with a pressure of 35 pounds
per square inch absolute in the test section.
RESULTS AND DISCUSSION
The test results obtained for the basic models are listed in table l(a)
and are shown in figure 3 where the dynamic pressure required to produce
flutter or divergence is plotted as a function of Mach number. Also shown
in figure 3 is a. curve showing the sea-level operating conditions of the
rocket.
The flutter boundary parallels the operating curve with a small mar-
gin of safety at subsonic speeds and then appears to cross over into the
operating region at Mach numbers greater than 1.05- The dynamic pressure
at the static-divergence boundary appears to be roughly constant within
the scatter of the data and crosses into the missile operating region at
a Mach number of about 1.1.
The type of flutter encountered was relatively mild and involved
predominantly torsional motions as indicated by the flutter frequencies
listed in table I(a) and by examination of motions pictures taken during
the tests. In some cases when flutter occurred, the dynamic pressure was
increased without causing damage to the model until divergence of the
overhung leading edge was encountered. After the model diverged, the
flutter became less violent or stopped completely. In general, the
NACA RM SL58H08a
divergence produced a permanent deformation which is illustrated by the
photograph of a typical model shown in figure 4.
Some possible solutions to the problem have been examined. Results
of these tests of modified configurations are listed in table l(b). For
one test (test 33) the overhung leading edge was restrained by attaching
clips to the tunnel wall. Divergence was eliminated but flutter occurred
within the missile operating region. Other models which were about
25 percent and 45 percent thicker than the basic models were tested. No
aeroelastic instabilities were encountered within the maximum dynamic
pressure to which the tests were extended which, as indicated in figure 3,
is well beyond the sea-level operating condition of the ASROC. Tests of
configurations with modified plan form and root restraint (see fig. l(b)
and table l(b)) indicate that extending the root clamping plates from the
leading edge to the trailing edge eliminated aeroelastic instabilities
within the flight boundary. Other configurations with portions of the
leading edge unsupported experienced flutter within the flight boundary.
The possible effects of the nondestructive type of flutter of the
fins encountered in these tests on the flight path of the ASROC would be
difficult to assess. However, it would be expected that the occurrence
of divergence would produce large deviations from the intended flight
path. In addition to the uncertainties regarding adequacy of model
simulation, another question of concern is the possible effects of the
relatively large longitudinal accelerations acting on the fins during
the boost phase. It would seem that these effects would be smallj how-
ever, their evaluation is beyond the scope of the present investigation.
It may be noted that the U. S. Proving Ground (Dahlgren, Va.) reported
in unpublished data that flutter was observed in a tracking film of an
ASROC firing; however, the effect on the trajectory was not mentioned.
CONCLUDING REMARKS
The results of the experimental studies (neglecting acceleration
effects) on 0.4-scale models of the ASROC rocket-motor fins appear to
indicate some aeroelastic instability within the sea-level operating
conditions of the missile in the higher Mach number region. The flutter
is mild and nondestructive, its effect on the trajectory being difficult
to assess. On the other hand, the divergence of the overhung leading
edge could produce large trajectory deviations. Results of tests on
models about 25 percent and 45 percent thicker than the scaled model and
on models with a variation in plan form and with clamping plates extending
MCA RM SL58H08a
*••••
• • •
•• •
• • •
•• •
the full length of the root chord indicated no aeroelastic instability
within the operating conditions of the missile.
Langley Aeronautical Laboratory,
National Advisory Committee for Aeronautics,
Langley Field, Va., July 2k, 1958.
NACA RM SL58H08a 7
TABLE I
EXPERIMENTAL RESULTS
(a) Basic configuration
Test
10
16
25
27
28
29
50
31
32
Model
BF-I|
BF-5
BF-8
BF-9
BF-11
BF-10
BP-10
BF-12
BF-10
t,
in.
0.050
.050
.050
.050
.050
.050
.050
.050
.050
Frequency, cps
fl
114
111
118
113
117
112
115
115
113
i2
185
178
179
184
178
169
169
187
170
5
250
288
—
296
298
272
290
290
270
f4
31*0
333
337
350
340
328
320
350
320
1F
150
164
160
151
149
11.5
—
—
M
1.30
.81
.81
1.15
1.15
.89
.89
• 78
• 78
.61
.69
1.04
1.30
T,
°R
544
558
564
544
545
549
549
552
557
559
546
548
545
P,
slugs/cu ft
0.00189
.00345
.00484
.00245
.00297
.00350
.00368
.00347
.00477
.00410
•00353
.00273
.00206
a,
fps
988
1,090
1,096
1,023
1,02?
1,067
1,067
1,088
1,093
1,121
1,097
1,042
990
Ib/sq ft
1,557
1,337
1,894
1,606
1,955
1,576
1,655
1,250
1,734
823
1,010
1,598
1,707
Legend
(a)
D
F"
D
F
D
F
D
F
D^
F
F
D
D
Remarks
Diverged mildly
Fluttered and then diverged while
fluttering
Fluttered only; q^ ^ reached at
1,290 Ib/sq ft
Fluttered only
Diverged
Diverged mildly
(b) Modified configurations
Test
33
19
5
6
18
21
34
37
38
39
40
Model
BF-10A
BF-7C
BF-2
BF-3
BF-2
BF-2
BF-J
BF-13
BF-13A
BF-14
BF-15
t,
in.
0.050
.050
.072
.065
.072
.072
.063
.050
.050
.050
.050
Frequency, cps
fl
114
113
147
137
150
148
128
130
133
128
128
f2
170
164
234
215
233
234
213
213
214
184
197
f3
250
400
350
430
406
352
—
—
—
—
f4
310
500
"»55
410
460
460
420
392
380
336
363
fF
155
145
—
:::
—
...
—
225
162
172
M
1.30
.60
1.30
1.30
.60
.96
1.50
1.50
1.30
1-30
1.30
T,
°R
542
559
544
532
566
536
545
555
556
552
548
P,
slugs/cu ft
0.00183
.00246
.00424
.00378
.00552
.00571*
.00378
.00356
.00338
.00220
.00288
a,
fps
986
1,123
988
977
1,130
1,044
989
999
999
995
992
Ib/sq ft
1,507
887
3,500
3,060
1,264
2,865
3,125
3,000
2,850
1,846
2,400
Legend
(a)
F
F
Q"
Q
Q
Q
Q
Q
F
F
F
Remarks
Leading edge restrained at root
Root restraint altered by cutting root
(see fig. l(b))
No flutter - no divergence
Low damping near maximum conditions
Ho flutter - no divergence (see
fig. l(b) for model modifications)
Fluttered - no divergence (see fig. l(b)
for model modifications)
Fluttered - no divergence (see fig. l(b))
Fluttered - no divergence
aThe test-condition legend is as follows:
F - test conditions at flutter
D - test conditions at divergence
Q - maximum test conditions reached without flutter or divergence
Full-scole: all dimensions in inches
-Beveled leading
edge
Aluminum
rivets
-.5-
- Clomping plates
same thickness
as model
• • • • tl •
• • • • • * •
Half-scale: all dimensions in inches
4.22
2.0
I
Model root
extension
-10.66 •
.2R
~45
2024 aluminum-alloy
flat-plate model
Clamping plates
each side of model
•Aluminum
rivets
O O O O
Mount—-O
bolt
O
Clamping plates -
and model root
extension
1.75-H
39°
.62
O
5-inch-steel
mount blocks
6.0
12.0 •
(a) Basic model.
Figure 1.- Model geometry and mounting details,
Tunnel
wall line
G
I
CD
NACA RM SL58H08a
••••
• •
«•••
• •••
• • •
•• •
/f Oj O Oif .42
t
O
0 0
O
O O O Oj
~*\ ~
^^
O
^
- Model cut
here
Model BF - 7C
/~ ~~
/ O O
h— 2.15— •
ing plates c
1°
k,
ft
o o o o o o o o o
O O O
0 0
• — Trailing edge
extended to
root
Clamping plates extended 1
here and forward portions
removed for BF-I3A
Models BF-13 and BF-I3A
Y— 2.15 —
O O O_ __O_ _O_ _O_ O_ O O O
_j|' Model cut here for BF~I4^
O O O
K- -6.40
.42
1. 5 5-*
Models BF-14 and BF-15
(b) Modified models. All dimensions are the same as those of the basic
model except as noted.
Figure 1.- Concluded.
NA.CA RM SL58H08a 10
Mode Node line
I
2
* 3
4
The third mode appeared to be a leading-edge flapping mode,
the rest of the model being motionless.
/
/ /// // /
J /
o o o o o o o o o
(a) Basic model.
Figure 2.- Vibration node lines considered typical.
NACA RM SL58H08a 11
• •••
• •
• • •
•• •
Mode
I
2
3
Node line
(b) Modified models. Node lines for configuration with clamping plates
extending length of root chord are same except that there are no node
lines near leading edge.
Figure 2.- Concluded.
4000
3200
cr
en
O)
2400
o
"£
o
c.
1600
800
O Divergence
D Flutter
Maximum test—
dynamic pressure
Rocket operating curve
.6 .8
Mach number
1.0 1.2 1.4
o
>
800
Figure 3-- Flutter and divergence boundaries for rocket-motor fins. Basic models, ro
L-58-2760 
Figure 4.- Pho-t'ograph of typ ica l  diverged model mounted i n  the Langley 9- by 18-inch . r - supersonic -. ,- 
flutter %-xi> .;- -; 3F-.-,. rz  "ri: , .:%.il&*' ' ' " .- - .+*;.I s .  :%+* -< , 3- 
, >h . '- *'b- "z . .- ", .% .-*. 3&,-- , ;h#:*=> . .. - 12% ;.? > <% %, < $>;qg 
NACA RM SL58H08a
EXPERIMENTAL INVESTIGATION OF FLUTTER AND DIVERGENCE
CHARACTERISTICS OF THE ROCKET-MOTOR FIN
OF THE ASROC MISSILE*
COORD NO. N-AM-66
By Gilbert M. Levey and Perry W. Hanson
ABSTRACT
Some OA-scale models were investigated in the Langley 9- by 18-inch
supersonic flutter tunnel in" the Mach number range from about 0.6 to 1.3.
Results of this investigation indicate that both divergence of the over-
hung leadiug edge and flutter occur within the sea-level operating condi-
tions of the missile'at Mach numbers above about 1.0.
INDEX HEADINGS
Mach Number Effects - Wing Sections 1.2.1.8
Missiles, Specific Types . 1-7.2.2
Aeroelasticity 1-9
Vibration and Flutter k .2
NACA RM SL58H08a
FLUTTER AND DIVERGENCE
CHARACTERISTICS OF THE ROCKET-MOTOR FIN
OF THE ASROC MISSILE
COORD NO. N-AM-66
Gilbert M. Levey
Perry . Hanson
Approved: Cx 'c •
I . E . Garrick
Chief of Dynamic Loads Division
Langley Aeronautical Laboratory
mjg(7-2^-58)


Experimental Investigation of Flutter and Divergence Characteristics of the Rocket-Motor Fin of the ASROC Missile

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