ASEN 3112 Structures
Fall 2012
SETUP AND OPERATING PROCEDURE
VIBRATION OF A BEAM -MODEL AIRPLANE
DESCRIPTION OF APPARATUS:
The test article is a beam-model airplane comprised of six elements which are basic
pieces of aluminum (6063-T5) stock. These elements are assembled using simple nuts,
bolts and lock washers. A separate piece is provided for the cantilever beam test.
Dimensions for each piece are as follows:
Fuselage - 1 x 22 x 1/8 (inches)
Wing - 1 x 18 x 1/8
Wingtip - 1 x 4 1/2 x 1/4
Rudder - 1 x 5 x 0.040
Elevator - 1 x 4 1/2 x 1/4
Cantilever Beam - 1 x 22 x 1/8
Weights of each piece are as follows;
Winglet / stabilizer
Rudder
Fuselage
Wing
Gold bracket (ea)
Stop nut
Phillips style flathead screw
Slotted style flat head screw
Allen head screw
All other screw
Lock washer
Cantilever Beam
Fuselage/Wing Center mounting plate
Mounting bolts and washers
51g
12.2g
125.3g
103.8g
2.4g
1.1g
0.7g
1.0g
1.4g
1.1-1.2g
0.1g
129.7g
19.2g
9.2g
A clamp is attached to the APS Vibration Shaker which will securely hold either the fully
assembled airplane, or any of the disassembled pieces, or the cantilever beam, in place
for testing.
A metric ruler scale is attached to the fuselage, wings and cantilever beam. This will help
locate mounting positions for the clamp and accelerometers. Notice that zero locations of
the scale are somewhat arbitrary and ruler alignment should be documented by the user.
The frequency of vibration is controlled by a function generator that applies a sine wave
to the shaker amplifier which electrically drives the shaker. The function generator
frequency is displayed on its front panel. A strobe light is used to visually display the
modes of vibration. With careful manual tuning of the strobe light frequency, the
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Fall 2012
experimenter can observe full displacement of the beam under study. Three single axis
small PCB accelerometers are available to measure displacements of the vibrating beams.
A fourth PCB accelerometer is mounted to the vibration shaker on the airplane support to
measure the shaker input frequency.
SET-UP PROCEDURE:
Before attempting any tests, please check the following:
1) APS Shaker Amplifier is securely in place with the Amplifier cable connected to
Shaker.
2) Four accelerometers labeled 0-3 are available to test the airplane model. The
accelerometers can be placed on points of largest displacement (using Bee’s wax)
along the beam model. One accelerometer is always placed on the shaker location
to measuring the forcing function.
3) Four accelerometers are connected with BNC to the NI 9234 cDAQ module
channels 0-3.
4) Ensure the cDAQ module is on and connected to the computer by means of USB
cable.
5) Check all connections by comparing to Figure 1: Wiring Connections.
PCB Accelerometers (4x)
Laptop
USB cable
Beam
Model
Airplane
NI 9234
Blue cables #0-3
HP 33120A
Function Generator
APS Amplifier
APS Shaker
Figure 1: Wiring diagram vibration of a beam model airplane.
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ASEN 3112 Structures
Fall 2012
6) Turn Amplifier Amplitude knob fully counter clock wise (Off). Also turn
Operating Mode selector knob to OFF position for safety while making initial
settings.
7) Turn ON HP 33120A Function Generator. Load the preset settings by pushing
“Recall” button. Confirm that Recall 1 is shown on the screen. Push Enter. If
needed, the settings can be set manually as described in the Appendix.
8) Confirm BNC cable is connected to HP 33120A Function Generator “Output”.
(Do not mistakenly use the SYNC output.)
OPERATING PROCEDURE:
1) Open “Beam Model Airplane 2012.vi”.
2) Note that the LabVIEW VI displays are:
Accelerometer waveforms (mm/s^2)
Computed displacements (mm)
3) Run the VI and select where to start a datafile.
4) Turn ON Function Generator and APS Amplifier Power Switch. Carefully
monitor that the airplane should not be moving yet because the amplitude knob is
turned down.
5) Push Function Generator Amplitude button to confirm output is 800 mV.
6) Turn Amplifier Operating Mode Switch to “Current” mode.
7) Slowly turn “Amplitude” knob CW about ¼ of a turn to increase the vibration
level seen. Be ready to turn the “Amplitude” knob back down in case you excite a
resonance too much and risk causing damage to the beam model, especially for
Mode #2 where the tail section is easily damaged!
8) Push Freq button and push right arrow until the digit you wish to change is
flashing. Adjust to desired starting frequency using up/down arrow or rolling
knob.
9) Test the following Modal Frequency Ranges:
5.0 - 6.5 Hz
* Do not use accel on vertical tail, is impeded the resonance significantly
12.5 – 13.5 Hz
* Recommend accel on horizontal tail tip and vertical tail top.
* Ampl knob no more than 9 o’clock position.
24.0 – 30.5 Hz
* Recommend accel on nose and wing(s)
37.0 – 38.0 Hz
* Recommend accel on nose and wing(s)
48.0 – 50.8 Hz
* Recommend two separate accels on horizontal tail tip.
10) Once you get close to a mode shape region change the sensitivity of the
Frequency generator to increment in 0.1 Hz increments to narrow in on the
precise resonance frequency.
11) For higher mode shapes you will need to increase the amplitude:
i) First you can turn up the amplitude knob to the far right.
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ASEN 3112 Structures
Fall 2012
ii) Secondly, you can adjust the Ampl” setting on the Function Generator to get
measurable vibrations. You can go as high as 1.3 Vpp for mode #5. When you
are narrowing in the resonance frequency in 0.1 Hz increments, make sure the
amplitude to the shaker remains constant while comparing relative
accelerometer readings at each frequency.
12) If desired turn ON the Strobe light to aide in viewing the vibration amplitudes.
Adjust the Strobotac frequency using the dial. Note: When Strobotac frequency
exactly matches Function Generator, the light will be in sync and you may not see
any vibrations. By slightly de-tuning the Strobe light, you can see full
displacements. This is especially useful in Mode #5.
13) This VI saves ALL the data during the running time of VI, which could result in
inconveniently large datafiles. Use the “Stop and Save” button to close the
program.
14) Rerun the VI once the resonance is found.
15) Update the comment field as needed, and then use the “Stop and Save” button to
save a short run time version datafile.
16) Always turn down the amplitude knob when switching to a new mode shape!
17) Modes 2 and 5 specifically will be modeled and data will be compared to
theoretical results.
18) Repeat as necessary to complete the experiment and investigate and describe all 5
mode shapes.
Last updated: March 14, 2016
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ASEN 3112 Structures
Fall 2012
Appendix A : Additional Setup Notes:
1) Instructions for attaching accelerometers:
a. PCB Accelerometers have been attached as needed using Bee’s wax. If
they need to be moved, they are pressed on firmly while twisting slightly
onto airplane element. Test attachment with a sideways force on
accelerometer to confirm attachment is solid. Provide appropriate strain
relief for all accelerometer cables using electrical tape.
b. NOTE: DO NOT DROP ACCELEROMETERS AS THEY WILL BE
DAMAGED!! PLEASE REPORT ANY ACCIDENTS TO TA FOR
DOCUMENTATION.
c. Here is the list of accelerometers serial numbers per channel:
i. CH 0 - SN 102548 – 9.55 mV/g
ii. CH 1 - SN 101415 – 5.59 mV/g
iii. CH 2 – SN 102547 – 9.70 mV/g
iv. CH 3 - SN 101414 – 5.59 mV/g
2) Instructions to set the Recall settings on the Function Generator
a. Push “Freq” button. Push sine wave symbol button. Observe display has
one flashing digit.
b. Push the → button until KHz is flashing. Push the ↓button until Hz is
flashing.
c. Push the → button until tens digit is flashing. Push the ↓button to
approximately 5 Hz.
d. Push Frequency Generator “Ampl” button and observe tens digit flashing.
Push the ↓ button to set the output to 800 mVpp.
e. To save these settings to the Waveform Generator, simply press the ‘shift’
button, followed by the ‘Recall/Store’ button. Select State 1 and press the
‘Enter’ button.
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