Design and installation of vibration testing system for spring mounted model of wing

TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 18, SOÁ K7- 2015 
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Design and installation of vibration 
testing system for spring mounted 
model of wing 
 Tran Tien Anh 
 Hoang Ngoc Linh Nam 
Ho Chi Minh city University of Technology, VNU-HCM 
(Manuscript Received on July 08th, 2015, Manuscript Revised September 23rd, 2015) 
ABSTRACT: 
This paper presents the design and 
installation of measuring vibration system in 
wind tunnel area 1m x 1m. The theoretical 
analysis of the spring structure in this model 
help we possible to design a system for wind 
tunnel by yourself with suitable area, wind 
speed as well as survey wing model to obtain 
results desire. 
This system helps us to observe the 
oscillation of wing survey by eyes, but to 
know exactly how wing fluctuates, also the 
pitching angle of wing, we use ultrasonic 
sensors to measure the distance variation, 
will be presented in more detail in the text. At 
the same time, the article also shows how to 
make a simple and durable wing model with 
NACA 0015 airfoil - wing model will be 
surveyed ranged in system above. 
The aerodynamic phenomena affect to 
the vibration of the wing are also mentioned 
and overcome in the design of the wing. 
Finally we process the data after 
measured to see the similarities between the 
experiment and the theoretical dynamics of 
aviation. 
Key words: wind tunnel, measurement computing, ultrasonic sensor, ultrasonic transducer, 
measuring instruments. 
1. INTRODUCTION 
1.1. Aerodynamic Elastic Phenomena 
Aerodynamic elastic phenomena are 
phenomena involving simultaneous of three 
forces: aerodynamic forces, elastic force and 
inertia force. General characteristic of these 
phenomena is oscillation. There are some 
characteristic phenomena of aerodynamic elastic 
phenomena: 
- Flutter phenomenon is phenomenon of 
vibration, bending wings. The nature of this 
phenomenon is the harmonic oscillations of a 
self-stimulate certain structural components 
while at the same time the participation of the 
three forces (elastic forces, aerodynamic and 
inertia). During oscillation, structures appear 
drag oscillations and stimulate oscillations 
texture [1]. Increasing the cruising speed, 
increasing force of maintain oscillations, to catch 
critical speed, oscillation structure will has 
constant amplitude. If the cruises speed much 
more than critical speed, the structure will be 
destroyed. 
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- Buffeting phenomenon is shaking a certain 
structural components. The nature of this 
phenomenon is the forced oscillation structure, 
by vortex of broken gas line runs through the line 
as structural components in the front of the 
swirling effect (act of force excitation frequency) 
coincides with own oscillator frequency certain 
structural parts of aircraft will generate resonance 
and thus the structure was destroyed [3]. 
- Dynamic reaction phenomenon is 
phenomenon occurs when simultaneous effect of 
three structural forces and when flying through 
turbulence flow (often impact pulse or cycle) or 
by pulses collide when landing planes grounded. 
Due to such effect that might appear too large 
overload causing structural destruction. 
Figure 1. Experiment examined the aerodynamic 
phenomenon in wind tunnel of NASA. 
(
/WindTunnel.html) 
In this study, we just only care about two 
phenomena flutter and buffeting. 
To observe the phenomenon, we compute 
the natural frequencies of the system and the 
frequency of the external force, equal two this 
frequency to the resonance phenomenon occurs, 
will observe the phenomenon [2]. 
1.2. Objectives 
The motivation of this thesis is design and 
installation a measuring vibration system in wind 
tunnel, along make an aircraft wing to put it 
inside that system. The aim is measured the 
vibration of wing by ultrasonic sensors (measure 
the distance). 
Data after being measured will be shows in 
excel format, base on that we process the data to 
find out the vibrate amplitude and swivel angle. 
2. PARAMETERS OF SPRING MOUNTED 
MODEL 
2.1 Vibration Natural Frequency 
To calculate the natural frequency, we put 
the wing into the model to simulate the oscillation 
as shown below: 
Figure 2. Wing model before oscillation 
Figure 3. Wing model during oscillation 
Applying Newton second law and moment 
theorem to the model showed above, we have the 
following dynamics equations: 
2211
21
22
22
llxkllxkJ
lxklxkxm
o 

With: 
- m: weight of wing model 
- k: stiffness of the springs (four springs 
have the same stiffness) 
TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 18, SOÁ K7- 2015 
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- l1: distance from A to M 
- l2: distance from B to M 
- Jo: inertia moment of structure 


2
2
2
121
21
22
24
llkxllkJ
llkkxxm
o


022
024
21
2
2
2
1
21
xllkllkJ
llkkxxm
o 



With 
  tXx cos 
   tcos 
Equations become: 
 




0
0
22
24
2
2
2
1
2
21
21
2

 X
llkJllk
llkkm
o
 022
24
det 2
2
2
1
2
21
21
2
llkJllk
llkkm
o
 
Solutions of that equation deduce natural 
vibration frequency: 
o
ooo
mJ
llmJllmJllmJ
k 21
22
2
2
1
222
2
2
1
1
842 
 
o
ooo
mJ
llmJllmJllmJ 21
22
2
2
1
222
2
2
1
2
842 
 
We can see that 021  (3). 
2.2. The Frequency of the External Force 
Wing lift is given by equation [4]: 
 ftAVctF 2sin
2
1 2 
With: 
- f: Vortex shedding frequency 
- c: constant 
- : the density of fluid 
- V: characteristic velocity of fluid 
- A: the biggest area perpendicular to the 
direction of the velocity V 
Figure 4. Simulation of wing model section to 
specify the area A 
I will examine vortex shedding phenomenon 
occurs with wing model when put it into wind 
tunnel. 
Vortex shedding phenomenon is the 
phenomenon of fluids as water or air flow over 
an obstacle with certain velocity and depending 
size and shape of obstacles will split into two 
interleaved flows. 
Alternatively, vortex shedding frequency 
depends on the Strouhal number through the 
following equation [5]: 
V
fdSt 
With: 
- f: vortex shedding frequency 
- d: max thickness of obstacle. In this 
wing model, d = 4cm 
- V: velocity characteristic of fluid. Max 
velocity of wind tunnel is 8m/s 
We know as Strouhal number is a 
dimensionless number, it depends on object’s 
shape and value of Reynolds number. 
In that Reynolds number is a dimensionless 
value, which is showed the relative magnitude 
between impacts caused by inertia and in friction 
(viscosity) to flow [6]. 
With: 

 Vd
 Re 
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Including: 
- d: max thickness of wing model 
- : kinematic viscosity of air 
Figure 5. Strouhal number acts as function according 
Reynolds number for cylindrical. 
( 
Figure 6. Value of Roshko number in graph link 
between Strouhal number and Reynolds number. 
In that, Roshko number is a dimensionless 
number described mechanism of flow when 
oscillate [7]. 
Ro = St x Re 
For different values of Reynolds number, 
flow over various objects also different. 
We choose the stiffness k so that vortex 
shedding frequency 

2
2 f 
 2122221222221
2
842
11025
llmJllmJllmJ
mJk
ooo
o
3. EXPERIMENTAL APARATUS 
3.1. Design of Spring Mounted Model 
Figure 7. 3D design of model experiment 
As stated above theory, we will carry out the 
design of the pivotal portion size pilot based on 
oscillations of wing model. It is clamped tightly 
to 8 springs with stiffness k foresee mimicking 
wing oscillations which model will be 
implemented from the initial conditions to the 
active vibration and finally the oscillation 
combined vibrations on until wing model is 
destroyed when we turn change factors such as 
velocity in tunnel wind, angle of attack of 
experimental models to the following objectives: 
- Check the correctness of the initial 
theoretical calculations for model when the angle 
of attack of the wing by wing is 0. 
- Surveying the effects of the change to 
oscillation angle of attack of the model wing 
simultaneously drawing conclusions. 
Inside, wing model is hanging by 8 springs 
which have same stiffness k. 
Figure 8. Wing model is hanging by 8 springs which 
have same stiffness k 
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Accordingly, the wing model is attached to 
the rails by the structure as shown by below. 
Figure 9. Joints between the wing model and springs 
structure 
In that frame bar (4) is through a rectangular 
hole cut size 5cm × 8cm in mica plates (1) and 
mounted on the frame between the structure as 
above, connection with the above structure will 
facilitate the fitting, and to facilitate expanding 
upgrade later when we conducted experiments 
with the other model towards expanding as stated 
at the beginning of the thesis in all countries. 
Wing model fitted with 8 springs by 
structure of hooks (1) and screws fixed through it 
with bolts (2), it can be moved in the grooves 
between the vertical aluminum frames on the 
picture to change distance as the theoretical 
calculations above then connected to the springs 
(3). Three connected structures have the same 
idea. 
In that, hanger (1) hang on screws are 
screwed into the trench as shown above, and it 
can move back and forward by turning the screw 
loose to be able to sync move with the screw rod 
between the bottom frame, mounted on steel bars 
V3.5 donuts yellow donut plate as above, this is 
an important part bearing that have function to 
bear and fixed the frame rail experiment with 
structural model as Figure 12 below: 
Figure 10. Overall of bracket structure 
Figure 11. Structure of fixed the donut plate to the 
gudgeon 
In that, iron roller (1) screws fixed by screws 
(3) to the groove (2) is welded steel frame fixed 
to the above illustration, in which yellow donut 
plate is fixed to four edges of the iron frame as 
listed on four red rollers. This fixed structure 
makes donut plate is fixed but can be rotated to 
make the frame wing angle of incidence change 
from that implementation goal 2 of the 
experiment. 
Then the model is mounted to shield blanket: 
- One mica plate 1m×2m×10mm in size. 
- Three wood plates 1m×2m×8mm in size. 
After completing the design model with size 
of 2m x 1.4m x 1,62m placed on the rollers 10, 
is tightly coupled to the wind tunnel mouth 1m x 
1m size to conduct experiments. 
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Figure 12. Realistic picture of the experimental 
model 
Accordingly experiment, we will calculate 
vortex shedding frequency given on the basis of 
theory. Followed that, we choose spring which 
have stiffness k that guaranteed to the separate 
oscillation frequency equal vortex shedding 
frequency, as calculated above to be able to 
observe the Flutter phenomenon of wing model 
in wind tunnel. 
3.2. Wing Testing Model 
The experimental wing model was designed 
in standard of NACA 0015 for airfoil: 
Figure 13. 3D drawing of wing model 
In that, 
- Shield wingtips will be used to reduce the 
impact of the Horseshoe Vortex phenomenon on 
the wing (just like wing tip), 40cm x 16cm x 8mm 
in size. 
- Frames of NACA 0015 wing model make 
by wood 8mm. 
- Rib of wing model by wood 10mm. 
- Decal outer wing model. 
- The part fixed wing model with a stainless 
steel bar of diameter 25mm x 25mm. 
Figure 14. Preliminary wing models after assembled 
Figure 15. Wing model after completed 
3.3. Ultrasonic Sensors and Devices 
Devices are used to measure in this 
experiment include: 
DC Power BK Precision: is a power supply 
device, voltage regulator suitable for the 
Ultrasonic sensor during measurement oscillator. 
Figure 16. DC Power BK Precision 
MC Measurement is a device to transmit 
measured data to PC, offers easy-to-use data 
acquisition and data logger hardware and 
software for test, measurement, and industrial 
applications. MC measurement computing is the 
market leader in the design, manufacture and 
distribution of value-priced data acquisition 
hardware, and test and measurement software 
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solutions for both programmers and non-
programmers. 
Ultrasonic sensors: major device for 
measuring oscillations. In this experiment, we 
use two Sensick UM30-21-118. 
Our sensors have operating range about 30 to 
250 mm, limiting range is 350 mm, so the 
measurement process must install additional 
shields in measuring range of sensors. Supply 
voltage about DC 9 to 30 V and power 
consumption less than 2.4 W. (UM30-2 
ultrasonic sensors). 
Finally, we install all equipment together, 
ready for measurement. How to connection this 
circuit will be shown in DASYLab software of 
chapter 4. 
Figure 17. Assembly all equipment together 
4. OSCILLATING MEASURE OF WING 
TESTING MODEL 
Results after measured as the difference of 
distance between two points A and B fitted with 
two sensors above the ground (x1 and x2), as 
proposing picture: 
Figure 18. Simulate the vibration of points A and B 
Figure 19. Result file after measurement 
In excel file after exporting, it has three main 
columns, the first column is the measurement 
time, here we adjust for the signal is taken every 
0.01 seconds. The two columns after are about x1 
and x2 fluctuations, the distance between A and 
B respectively to a fixed plane below. 
Then from the oscillation of two points A 
and B, we interpolate the vibration of the wing 
center - point M and the pitching angle of wing 
model. 
So that we will study the oscillation of wing 
axis, follow the equation: 
2
21 xxx 
And the pitching angle of wing: 
120
arctan x 
With the distance from wing axis to sensor is 
120mm. 
Completed the preparation and measurement 
metrics, the following are the results of the 
process. Firstly, we examine the oscillation of 
wing with incidence angle =0. 
Once enough data, we marked all three 
columns and run scatter, results are as follows: 
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Figure 20. Chart of wing oscillation over time with 
 =0 (4.6 m/s wind speed). 
In that, the blue line is the graph of the wing 
fluctuates, the red one is pitching angle of wing. 
We noticed that although the angle of incidence 
by 0, wing still fluctuating, it is due to error 
during installation. But it’s not oscillation too 
large due to wind velocity too small. 
Similarly, we gradually increase the wind 
speed until reaches the maximum allowed speed 
(about 8.5 m/s), then we change the angle of 
incidence and examine. 
Figure 21. Chart of wing oscillation over time with 
 =12o (wind speed of 5.5m/s ) 
Figure 22. Chart of wing oscillation over time with 
 =21o (wind speed of 4.6 m/s ) 
5. CONCLUSIONS AND PERSPECTIVES 
5.1. Achievements 
This thesis has achieved all of its goals. 
Firstly, we learned the structural how to make a 
wind tunnel; thereby we design a wing 
accordingly to it and installation of wing on it. 
During installation, it was generated some 
problems, but we had solved, such as the wind 
tunnel can’t open the door to get the wing model 
into it, position of the screws do not outsourcing 
exactly so the installation encounter a little 
difficult, ... This stage also helps us have more 
knowledge about machining with CNC cutting 
machine to manufacture wing model. 
Second, this thesis helps us to know and 
come into contact with the ultrasonic sensors – 
the expensive sensors. It also helps us to using 
Dasylab software a brief. 
Finally, the measurement and processing 
data stages help us to verify empirically with 
what they have learned in theory about the factors 
effect to wing when the airflow passing it. 
5.2. Limitations and Further Research 
There are some limitations in this thesis: 
- Wind tunnel was outsourcing with some of 
the details have not exactly fetch to the 
installation of the associated have some 
difficulties. 
- The maximum allowable speed of the wind 
tunnel is not large enough to be able to observe 
the oscillation of wing model by eyes. 
- The maximum distance that the ultrasonic 
sensor can measure quite small, so we have to 
add some details to shorten the distance. 
For expand research, as presented at the 
domestic situation in the first research thesis, this 
is a subject that has wide applicability in the 
aviation, construction, architecture, etc. So in 
designing the model was optimized ability to 
install additional accessory devices to be able to 
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expand into different research directions on the 
same model in order to save costs still effective 
in studies. 
We have explained on aerodynamic theory 
of bending and twisting phenomenon of wing 
model aircraft when operating outside reality. 
However, wing model that we put in this thesis is 
symmetrical airfoil, in fact wings have 
symmetrical airfoil were no longer in use on 
airplane, but instead is the airfoil with the 
camber, wings were added with control surfaces 
as: slat, flap, aileron 
On both experimentally and theoretically 
demonstrated that modern wing models are 
designed according to the new theory can 
improve the shape of wings, wing curvature 
(degrees Camber) and new control surfaces help 
technological improvements to air a new altitude. 
An altitude that there can make available the non-
engine aircraft but could fly for hours in the air 
just based on improvements in wing patterns and 
materials. 
Acknowledgements:This work was support
ed by the research grant of AUN/SEED-Net over 
a total period of 2 years for Collaborative 
Research with Industry (CRI) project 
(Project No. HCMUT-CRI 1401).