A mechanism for diverting the flow in a wind tunnel from the wing of a tested model is described. The wing is mounted on the wall of a tunnel. A diverter plate is pivotally mounted on the tunnel wall ahead of the model. An actuator fixed to the tunnel is pivotably connected to the diverter plate, by plunger. When the model is about to become unstable during the test the actuator moves the diverter plate from the tunnel wall to divert maintaining stable model conditions. The diverter plate is then retracted to enable normal flow

Doggett, R. V., Jr.

Ricketts, R. H.

English

NASA Technical Reports Server

United States Patent 1191 [ I  11 4,372,159 
1451 Feb. 8,1983 Doggett, Jr. et al. 
, ”  
[54] AEROELASTIC INSTABILITY STOPPERS 
[75] Inventors: Robert V. Doggett, Jr., Hampton; 
FOR WIND TUNNEL MODELS 
Rodney H. Ricketts, Newport News, 
both of Va. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[73] Assignee: The United States of America as 
[21] Appl. No.: 274,706 
[22] Filed: Jun. 17,1981 
[51] Int. C I . 3  .............................................. COlM 9/00 
[52] U.S. Cl. ...................................................... 73/147 
I581 Field of Search .......................................... 73/147 
~561 References Cited 
U.S. PATENT DOCUMENTS 
2,721,476 10/1955 Pindzola et al. . 
2,788.661 4/1957 Post et al. . 
3,068,690 12/1962 ODair et al. ......................... 73/147 
3,070,998 ]/I963 Schreiber 
3,587,306 6/1971 Bryan . 
3,903,740 9/1975 Baldwin . 
Primary Examiner-S. Clement Swisher 
Attorney, Agent. or Firm-H. Osborn; J. Manning; W. 
Nelson 
1571 ABSTRAff 
A mechanism 10 for diverting the flow in a wind tunnel 
from the wing 20 of a model being tested therein. The 
wing 20 is mounted on the wall 30 of a tunnel. A di- 
verter plate ll  is pivotally mounted on the tunnel wall 
30 ahead of the model. An actuator 18 fixed to the 
tunnel is pivotally connected to the diverter plate 11, by 
plunger 15. When the model is about to become unsta- 
ble during the test the actuator 18 moves the diverter 
plate from the tunnel wall to divert flow about the wing 
and change the effective sweep angle thereof maintain- 
ing stable model conditions. The diverter plate is then 
retracted to enable normal flow. 
12 Claims, 5 Drawing Figures 
30 29 
20 / 
AIR FLOW 
https://ntrs.nasa.gov/search.jsp?R=19830013233 2020-03-22T00:23:19+00:00Z
U.S. Patent Feb. 8, 1983 4,372,159 Sheet 1 of 3 
AIR FLOW 
FIG. 1 
U.S. Patent Feb. 8, 1983 Sheet 2 of 3 4,372,159 
U.S. Patent Feb. 8, 1983 Sheet 3 of 3 4,372,159 
FIG. 4 
4,372,159 
1 2 
It is yet another object of the present invention to 
provide an instability stopper which is adaptable to use 
in any wind tunnel. 
It is also an object of the present invention to provide 
5 an instability stopper which is noninterfering with the 
dynamic characteristics of the model. 
provide an instability stopper which is noninterfering 
with the flow field around the model. 
SUMMARY OF THE INVENTION 
The foregoing and other objects are attainable ac- 
cording to the present invention by providing a simple 
Wind tunnel testing of aeroelastic models often jeop- &-flow diverter consisting of one or plates 
ardizes the model because aeroelastic instabilities such 15 hinged to the wall of the wind tunnel upstream of the 
as flutter and divergence produce large, rapidly increas- model to be tested, and an actuator mechanism with a 
ing model deformations that can lead to Structural fail- linearly extendable and retractable plunger shaft by 
ure, thus destroying or severely damaging the model. It which the plate(s) is deployed, deflecting the air flow 
is common practice in aeroelastic model testing to take Over the model. 
some precautions to minimize the risk of model damage 20 To minimize aeroelastic interference the device can 
when an aeroelastic instability is encountered. One be recessed in the wind tunnel wall, fuselage half-body, 
method, called subcritical response technique, is to or splitter plate, depending on the application. 
avoid encountering an instability by taking a series of A more complete appreciation of the invention and 
measurements at conditions below the stability bound- many of the attendant advantages thereof will be 
ary and using these measurements in an analysis to pre- 25 readily apparent as the invention becomes better under- 
dict the conditions at which the instability will occur. stood by reference to the following description when 
Although subcritical response methods show consider- considered in conjunction with the accompanying 
able promise, none has been developed that can be used drawings wherein: 
with confidence in a variety of applications. In applica- BRIEF DESCRIPTION OF THE DRAWINGS 
tions where subcritical techniques are applicable, it is 30 
usually necessary to reach at least one instability con&- FIG. 1 is a top view of the single-plate embodiment, 
in the stored position; tion to verify the method. 
Another of reducing the risk of model damage FIG. 2 is a side view of the single-plate embodiment, 
is to conduct aeroelastic model studies in wind tunnels in the stored position; 
that have a FIG. 3 is a top view of the single-plate embodiment, 
pressure. These means include such things as spoilers in the 
FIG. 4 is a top view of the double-plate embodiment, that are deployed in the tunnel diffuser to provide a for use with a splitter plate, in the deployed position; choking effect and piping and valve arrangements that and 
of the tunnel and the test section plenum. The spoiler is ment, in the deployed position. usually used in small tunnels and is usually very effec- 
tive. The valve-piping system is more applicable to 
large tunnels and is not as effective as the spoiler. How- 
with the device before it can be used, requiring exten- 
sive modifications to the tunnel. Other methods of mini- 
mizing the risk of model damage include physical re- 
straints to the model such as cables which are normally 
reaches a preset value. Although cable and other pas- 
sive restraint methods are usually effective in minimiz- 
ing model damage, their pressure does distort the flow 
Over the model and does affect the dynamic characteris- 
tics of the model. 
There is thus seen to be a need in the art for an im- 
proved aeroelastic instability stopper for wind tunnel 
AEROELASTIC INSTABILITY STOPPERS FOR 
WIND TUNNEL MODELS 
ORIGIN OF THE INVENTION 
m e  invention described herein was made by employ- 
ees Of the United States Government and may be manu- 
factured by or for the Government for governmental 
purposes without the payment of any royalties thereon 
or therefor. 
BACKGROUND OF THE INVENTION 
It is still another object of the present invention to 
for rapidly reducing flow dynamic 35 
position; 
are used to short circuit flow between the low 'peed leg 40 FIG. 5 is a top view of a two-segment plate embodi- 
DESCRIPTION OF THE PREFERRED 
EMBODIMENTS 
bodiments are shown, each as used in studies of swept- 
forward wings. Like numbers in the several e m u i -  
merits refer to parts. 
Referring now to FIGS. 1, 2 and 3, a shgle-plate 
deflection 50 embodiment is shown. The wing is designated 20. The 
invention comprises diverter plate 11, attached to wind 
tunnel wall 30 upstream of the model by hinge 13, =tu- 
ator push rod 15, and pivot 22, actuator 18, and return 
spring 17. Actuator 18 is anchored by pivot 21 to allow 
55 the actuator and shaft 15 to rotate through the small arc 
described by pivot 22, with respect to shaft 15, as di- 
verter plate 11 swings on-hinge 13. Apertures 27 and 29 
models. are provided in the wall 30 to allow the shaft 15 and 
Accordingly, it is an object of the present invention spring 17 to pass therethrough. The plate is recessed 
to provide an improved apparatus for preventing large, 60 into the wind tunnel wall, fuselage half-body, or splitter 
potentially destructive deformations in wind tunnel plate, so that when retracted there is no aerodynamic 
models. interference produced by the plate. For thin plates, a 
It is another object of the present invention to pro- flush mounting with the wind tunnel wall is satisfactory. 
vide an instability stopper which is mechanically sim- FIG. 4 shows another embodiment of the invention, 
ple. 65 for applications where the wing is mounted off the wind 
It is a further object of the present invention to pro- tunnel wall on a splitter plate. Two diverter plates llu 
vide an instability stopper which is capable of rapid and 12u are used. The inner plate 120 diverts the flow 
actuation at any test condition. from behind the splitter plate 25, so that the air is chan- 
ever* in both cases the wind must be quipped 45 The invention is generally designated 10. Three em- 
but become taut when the 
3 
4,372,159 
neled through a hole in the splitter plate over the in- 
board portion of the wing 20. The outer plate 110 per- 
forms the same function as described previously for the 
single plate. Pivot 22 on the outer plate l l a  is connected 
to rigid linkage 16, the other end of which is connected 5 
by pivot 23 to inner diverter plate 12a The inner di- 
verter plate 1 2 ~  is hinged to the wind tunnel wall 30 by 
hinge lk, and is connected by pivot 24 to actuator push 
rod 15. Extension and retraction of push rod 15 moves 
the inner and outer diverter plates in tandem. A return 10 
spring 17 is used to retract the diverter plates. 
FIG. 5 shows a two-segment embodiment of the 
invention for use if a more gradual turning of the flow 
is required. This embodiment differs from the single 
plate embodiment, described above, in the division of 15 
ihe diverter plate into two portions l l b  and 126 and 
insertion therebetween of connecting hinge 146. Link- 
age 19 is pivotally connected at 40 to the tunnel wall 30 
behind the pivotal connection 136 of the diverter plate. 
The other end of the linkage 19 is pivotally connected at 
41 to the outside surface of the portion 116 of the di- 
verter plate at its approximate center. Since the linkage 
19 is pivoted behind the diverter plate of pivotal con- 
nection 13b it results in a shorter arm which causes the 
portion l l b  of the diverter plate to be positioned at 
greater angle with respect to the wall 30 than the por- 
tion 12b. 
OPERATION OF THE INVENTION 
When it is determined (through other means, known 
in the wind tunnel test art) that the instability limit of 
the model is being approached, the diverter plate (or 
plates) is (are) deployed. Actuator 18 is remotely con- 
trolled and quick acting, powered either electrically, 
pneumatically, or hydraulically. When the diverter 
plate (or plates) 11 is (are) deployed, the air flow is 
diverted over the outboard portion of the model, in the 
FIGS. 1 and 5 embodiments. This results in the airflow 
over the outboard portion of the wing effectively re- 
ducing the sweep angle over the outboard portion of 
the wing. The velocity inboard is reduced by the shield- 
ing effect of the plate; however, the flow may be turbu- 
lent because of eddies produced by flow off the edges of 
the plate. In some circumstances this turbulent flow can 
produce buffet-like response. The double plate FIG. 4 
embodiment is a solution to this problem because the 
flow is diverted smoothly over the inboard portion of 
the wing 20 by the inner plate 12a the inner and outer 
plate 12u and l l a  act in combination to reduce uni- 
formly over the entire wing span, not just the outboard 
portion as with the single plate. Although flow inboard 
is at a higher velocity with the double plate, the flow is 
smoother and produces less buffet-like response. Both 
the single and double plate arrangements have their 
advantages depending on the type model being tested 
and the test circumstances effectively preventing insta- 
bility of the model. This reduction in sweep angle in- 
creases the divergence speed thereby controlling insta- 
bility and possible damage to the model. 
Although the invention has been described relative to 
specific embodiments thereof, it is not so limited and 
numerous variations thereof will be readily apparent to 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 
4 
those skilled in the art. For instance, return spring 17 is 
not needed for certain types of actuators 18. 
What is claimed as new and desired to be secured by 
Letters Patent of the United States is: 
1. A device for diverting the flow over a model air- 
craft in a wind tunnel test comprising: 
wind tunnel means having walls forming a test sec- 
plate means associated with a wall of the test section; 
pivoting means for connecting said plate means to the 
wall of the wind tunnel; and 
actuation means for controllably deploying said plate 
means into said test section to divert flow from a 
model being tested therein preventing instability of 
the model. 
2. The combination of claim 1 wherein said pivot 
means is a hinge. 
3. The combination of claim 2 wherein said actuation 
means includes a longitudinally extendable and retract- 
able shaft passing through an opening in, the wall of the 
wind tunnel, and the projecting end of said shaft being 
hingedly connected to said plate means, whereby linear 
motions of said shaft are translated into angular motions 
of said plate appropriate to divert the air flow over the 
model wing as desired as said shaft is extended and 
retracted. 
4. The combination of claim 3 wherein the said plate 
means further includes, at approximately its midsection, 
hinge means and linkage means whereby the said plate 
means deploys to form two surfaces, the surface adja- 
cent the wind tunnel wall at a first angle, and the other 
surface at a greater angle, to the air flow. 
5. The combination of claim 3 wherein splitter plate 
means is mounted in said test section, a second plate 
means hinged to said splitter plate, and linkage mans 
connecting said other plate means with said second 
plate means enabling said plate means to be deployed 
together. 
6. The combination of claim 5 wherein said splitter 
plate is spaced from said test section wall and has an 
opening to allow flow therethrough, said other plate 
means diverting flow from between said test section 
wall and splitter plate through said splitter plate open- 
ing; and 
said second plate means diverting flow from said 
splitter plate opening and in said wind tunnel sec- 
tion to control flow about said model. 
7. The combination of claim 1 wherein elastic means 
is attached to said plate means for retracting said plate 
means. 
8. The combination of claim 7 wherein said elastic 
means is a spring. 
9. The combination of claim 1 wherein said test sec- 
tion wall is recessed to receive said plate means and 
pivot means. 
10. The combination of claim 3 wherein said actua- 
tion means is electrically operated. 
11. The combination of claim 3 wherein said actua- 
tion means is pneumatically operated. 
12. The combination of claim 3 wherein said actua- 
tion means is hydraulically operated. 
tion; 
* * * * *  


Aeroelastic instability stoppers for wind tunnel models

A mechanism for constraining models or sections thereof, was wind tunnel tested, deployed at the onset of aeroelastic instability, to forestall destructive vibrations in the model is described. The mechanism includes a pair of arms pivoted to the tunnel wall and straddling the model. Rollers on the ends of the arms contact the model, and are pulled together against the model by a spring stretched between the arms. An actuator mechanism swings the arms into place and back as desired

United States Patent [191 [ I  11 4,372,158 
Feb. 8, 1983 Doggett, Jr. et al. ' 1451 
[54] AEROELASTIC INSTABILITY STOPPERS 
[75] Inventors: Robert V. Doggett, Jr., Hampton; 
FOR WIND TUNNEL MODELS 
Rodney H. Ricketts, Newport News, 
both of Va. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[73] Assignee: The United States of America as 
[21] Appl. No.: 274,705 
[22] Filed: Jun. 17, 1981 
[51] Int. c1.3 .............................................. GOlM 9/00 
[52] U.S. C1. ...................................................... 73/147 
[58] Field of Search .......................................... 73/147 
[561 References Cited 
U.S. PATENT DOCUMENTS 
2,721,476 10/1955 Pindzola et al. . 
2,788,661 11/1957 Post et al. . 
3,068,690 12/1962 ODair et al. ......................... 73/147 
3,070,998 1/1963 Schreiber . 
3,587,306 6/1971 Bryan . 
3,903,740 9/1975 Baldwin . 
Primary Examiner-S. Clement Swisher 
Attorney, Agent, or Firm-H. Osborn; J. Manning; W. 
Nelson 
[571 ABSTRACT 
A mechanism 10 for constraining models 20 or sections 
thereof being wind tunnel tested which is deployed at 
the onset of aeroelastic instability, to forestall destruc- 
tive vibrations in the model. The mechanism includes a 
pair of arms 110 and l l b  pivoted to the tunnel wall 30 
and straddling the model. Rollers 1% and 126 on the 
ends of the arms contact the model, and are pulled 
together against the model by a spring 17 stretched 
between the arms. An actuator mechanism 18 swings 
the arms into place and back as desired. 
11 Claims, 2 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19830013232 2020-03-22T00:23:38+00:00Z
U.S. Patent Feb. 8, 1983 4,372,158 
FIG. 1 
FIG. 2 20 
22 
7 
I3 
I7 
12b 
4.372,158 
1 
AEROELASTIC INSTABILITY STOPPERS FOR 
WIND TUNNEL MODELS 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the U.S. Government and may be manufactured 
by or for the Government for governmental purposes 
without the payment of any royalties thereon or there- 
for. 
BACKGROUND OF THE INVENTION 
Wind tunnel testing of aeroelastic models often jeop- 
ardizes the model because aeroelastic instabilities such 
as flutter and divergence produce large, rapidly increas- 
ing model deformations that can lead to structural fail- 
ure, thus destroying or severely damaging the model. It 
is common practice in aeroelastic model testing to take 
some precautions to minimize the risk of model damage 
when an aeroelastic instability is encountered. One 
method, called subcritical response technique, is to 
avoid encountering an instability by taking a series of 
measurements at conditions below the stability bound- 
ary and using these measurements in an analysis to pre- 
dict the conditions at which the instability will occur. 
Although subcritical response methods show consider- 
able promise, none has been developed that can be used 
with confidence in a variety of applications. In applica- 
tions where subcritical techniques are applicable, it is 
usually necessary to reach at least one instability condi- 
tion to verify the method. Another means of reducing 
the risk of model damage is to conduct aeroelastic 
model studies in wind tunnels that have a means of 
rapidly reducing flow dynamic pressure. These meth- 
ods include such things as spoilers that are deployed in 
the tunnel diffuser to provide a choking effect and pip- 
ing and valve arrangements that are used to short cir- 
cuit flow between the low speed leg of the tunnel and 
the test section plenum. The spoiler is usually used in 
small tunnels and is usually very effective. The val- 
vepiping system is more applicable to large tunnels and 
is not as effective as the spoiler. However, in both cases 
the wind tunnel must be equipped with the device be- 
fore it can be used. Both require extensive modifications 
to the tunnel. Other methods of minimizing the risk of 
model damage include physical restraints to the model 
such as cables which are normally slack but become taut 
when the model deflection reaches a preset value. 
Although cable and other passive restraint methods 
are usually effective in minimizing model damage, their 
presence does distort the flow over the model and does 
affect the dynamic characteristics of the model. 
There is thus seen to be a need in the art for an im- 
proved aeroelastic instability stopper for wind tunnel 
models. 
Accordingly, it is an object of the present invention 
5 
10 
I5 
20 
25 
30 
35 
40 
45 
50 
55 
to provide an improved apparatus for preventing large, 
potentially destructive deformations in wind tunnel 
models. 
It is another object of the present invention to pro- 
vide an instability stopper which is mechanically sim- 
ple. 65 
It is a further object of the present invention to pro- 
vide an instability stopper which is capable of rapid 
actuation at any test condition. 
2 
It is yet another object of the present invention to 
provide an instability stopper which is adaptable to use 
in any wind tunnel. 
It is also an object of the present invention to provide 
an instability stopper which is noninterfering with the 
dynamic characteristics of the model. 
It is still another object of the present invention to 
provide an instability stopper which is noninterfering 
with the flow field around the model. 
SUMMARY OF THE INVENTION 
The foregoing and other objects are attainable ac- 
cording to the present invention by providing a simple 
constraining device including a pair of parallel arms 
that are hinged at one end to the tunnel wall. A pair of 
soft wheels, or rollers, is attached to the other end of the 
arms. When the device is actuated, the arms rotate away 
from the wall, and the wheels roll along the upper and 
lower surfaces of the model, thus returning the model to 
its undeformed shape and preventing the model from 
deflecting either statically or dynamically. The device 
is operated by a remotely controlled electrical, pneu- 
matic, or hydraulic actuator. 
Although the illustration is for application to a for- 
ward swept wing, the device is equally applicable to aft 
swept wings. For aft wings, the device would be 
mounted downstream of the model. 
To minimize aeroelastic interference the device can 
be recessed in the wind tunnel wall, splitter plate, or 
fuselage half-body, depending on the application. 
A more complete appreciation of the invention and 
many of the attendant advantages thereof will be 
readily apparent as the same becomes better understood 
by reference to the following description when consid- 
ered in conjunction with the accompanying drawings 
wherein: 
BRIEF DESCRIPTION O F  THE DRAWINGS 
FIG. 1 is a top view of the invention, the dotted lines 
showing the retracted position and the full lines the 
extended position; and 
FIG. 2 is an elevational view, across the direction of 
flow of the wind tunnel, showing both upper and lower 
constraining arms in their deployed position. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
Referring now to the drawings, the invention is gen- 
erally designated 10. It consists of upper constraining 
arm lla and lower constraining arm 116 which are 
attached to the tunnel wall by pivot 13. The constrain- 
ing or restraining arms lla and 116 are of minimum 
mass, slender and of a lightweight material such as, for 
example, tubular aluminum, in order that they may be 
quickly accelerated and decelerated to change their 
position. They and other structure also may be faired or 
streamlined to reduce interference with flow thereabout 
when in the restraining position. The arms should be of 
the length necessary so that the arc described by their 
deployment appropriately corresponds to the shape of 
the model wing being constrained. 
Constraining arms l la  and 116 are provided at their 
radially outward ends with small wheels or rollers 120 
and 12b. These rollers should turn freely in order to 
minimize friction and allow the quickest possible de- 
ployment of the arms. The rollers should be made of 
soft, elastic rubber or plastic to assist in absorbing vibra- 
tions of the model section. 
4,372,158 
The pivot 13 is constructed from a piece of hollow 
pipe or cylindrical material which is free to rotate about 
a pin 22. The pin 22 is carried by a support bracket 23 
which is fixed to the wind tunnel wall 30 by screw or 
other fastening techniques. A sleeve or other type bear- 
ing may be placed between the pin and the interior 
surface of the pivot pipe 13 to ensure ease of movement. 
The arms lla and 116 are properly spaced and secured 
to the pivot pipe 13 by welding or equivalent fastening 
arrangement. 
Pivot 13 allows the arms to rotate together in the 
plane of the model wing 20 to be constrained. This is the 
rotation between the retracted and extended positions 
of the arms. Since the model wing 20 may vary in thick- 
ness (typically tapering from the fuselage outward to its 
tip), the arms 110 and 116 are made of a material that 
will bend with respect to each other so that the roller 
equipped ends will remain in contact with the model 
section. 
The two arms lla and 116 are held together against 
the model wing 20 by a low tension spring 17 of suffi- 
cient preload to keep the wheels or rollers 12u and 126 
firmly in contact with the model wing. The preload 
5 
10 
15 
20 
tension is not so high as to impede rapiddeployment of 
and retraction of the arms, or to cause the wheels or 25 
rollers to damage the model wing surface. 
An actuator 18 is mounted on the outside of the wind 
tunnel wall 30. It is of a conventional type, and its spe- 
cific construction would not be known to one skilled in 
the art. It may be operted either electrically, pneumati- 
cally, or hydraulically. Actuator 18 has a linear plunger 30 
shaft 15 projecting through a hole (made for this pur- 
pose) in the wind tunnel wall. 
The projecting end of shaft 15 is connected to arms 
lla and 116 by a combination sliding sleeve generally 
designated 14 and hinge 16. The sleeve 14 has two sides 35 
14u and 146 which encompass respectively both of the 
arms 110 and 116, and has a bridge portion 14c connect- 
ing the inside surfaces thereof. Hinge 16 is mounted on 
bridge 14c. 
all subject to friction. Provision must be made to mini- 
mize this friction, either by application of a suitable 
lubricant or use of a material such as self-lubricating 
nylon or other friction reducing bearing arrangements 
OPERATION O F  THE INVENTION 
The constraining device is applicable to both flutter 
and divergence testing. At the start of a wind tunnel 
test, and until the tunnel speed has built up to the speed 50 
of onset of aeroelastic instability, the shaft 15 is in its 
retracted position, holding constraining arms lla and 
116 folded substantially flush against the tunnel wall 30. 
In this position the arms do not significantly interfere 
with the gas flow through the tunnel or the dynamic 55 
characteristics of the model. Further in order to mini- 
mize such interference, the arms may be encased in 
fairing body 21 or recessed in the wall 30. If the model 
is of a design that includes a fuselage the mechanism can 
be installed in the fuselage of the model and the restrain- 60 
ing mechanism recessed in the fuselage. Actuator 18 is 
of a rapid actuating type, so that deployment of the 
arms may be delayed as long as possible. When it is 
determined through a sensor, the design and operation 
of which are known in the art that the instability limit of 65 
the model is being approached, the constraining a r m s  
are deployed. Shaft 15 is extended, pushing sleeve 14 
outward and along the length of arms 110 and 116 as the 
Pivot 13, hinge 16, sliding sleeve 14, and rollers 12 are 40 
known in the art. 45 
4 
arms rotate on pivot 13. Rollers 120 and 126 move to 
the free end of the model wing 20, constraining it from 
destructive vibrations or deformations. 
The constraining device is retracted when the wind 
speed is decreased, through retracting shaft 15. 
The small size and light weight of the pair of con- 
straining arms enable them to be deployed quickly, and 
result in a minimum of interference with the flow char- 
acteristics of the model and wind tunnel. 
It is thus seen that the present invention enables useful 
wind tunnel testing through a greater range of model 
types and air speeds than was possible with prior art 
methods. 
Although the invention has been described relative to 
a specific embodiment thereof, it is not so limited and 
numerous variations thereof will be readily apparent to 
those skilled in the art. For instance, pivot 13 might be 
recessed into the tunnel wall if such modification to the 
tunnel wall were feasible. 
What is claimed as new and desired to be secured by 
Letters Patent of the United States is: 
1. A device for constraining and forestalling destruc- 
tive aeroelastic vibrations in models being wind tunnel 
tested comprising: 
a wind tunnel having walls forming a test section; 
a model mounted in said wind tunnel test section; 
restraining means; 
said restraining means being connected to test section 
structure and being movable from a positon against 
a wall of the test section to a position engaging said 
model; and 
actuation means for controllably deploying said re- 
straining means when said model is subjected to 
excessive vibrations. 
2. The combination of claim 1 wherein said restrain- 
ing means consists of a pair of slender lightweight arms 
approximately in parallel, arranged to straddle the 
model desired to be constrained. 
3. The combination of claim 2 wherein said restrain- 
ing means further includes roller means of elastic com- 
position on the end of each of said arms for contacting 
said model section with a minimum of friction. 
4. The combination of claim 3 wherein said restrain- 
ing means further includes tensioning means which 
ensures that said roller means bear against said model. 
5. The combination of claim 2 wherein said arms are 
pivotally connected to the test section to rotate together 
in the plane of the model to be constrained. 
6. The combination of claim 4 wherein said tension- 
ing means is a spring. 
7. The combination of claim 2 wherein said actuation 
means includes sleeves slidably engaging said arms; 
a bridge connecting said sleeves; and 
hinge means pivotally connected to said bridge. 
8. The combination of claim 1 wherein fairing means 
cover the restraining means when positioned against the 
test section. 
9. The combination of claim 1 wherein the test sec- 
tion is recessed to receive the restraining means when 
not deployed. 
10. The combination of claim 7 wherein a prime 
mover is carried by said test section; and 
linkage means connecting said prime mover and said 
11. The combination of claim 7 wherein said roller 
means, said pivoting connecting means, said hinge 
means, and said sliding sleeve all employ self-lubricat- 
ing synthetic materials for their parts subject to friction. 
hinge means. 
* * * * *  


Aeroelastic instability stoppers for wind tunnel models

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