NART Report Drag Effects Faye Clawson-1
Published on: Mar 3, 2016
Transcripts - NART Report Drag Effects Faye Clawson-1
Drag Effects of Corrugated Plastic Rocket Fin Design and Corrugation Orientation
Navajo Technical University
Gary L. Brandt2
Northwest Indian College
Cd = Coefficient of drag
CPLE = corrugations parallel to leading edge
CPRC = corrugations parallel to root cord
FML = Fluid Mechanics Lab, NASA Ames Research Center
LE = Leading edge
mV/V = millivolts per volt
NART = Native American Research Team
RC = Root chord
RotCFD = Rotor Computational Fluid Dynamics software
SP = Span
TE = Trailing edge
TP = Tip
fpm = Feet per minute
fps = Feet per second
Corrugated plastic such as used in making political and other outdoorsigns,is often used to make fins for
air/water rockets. It is light and durable. A question often asked by the rocket builders is, “Which way do the
corrugations go, into the air flow, or does it matter?” This investigation will provide information about which
corrugation orientation, parallel to the air flow or parallel to the fin’s leading edge, is more efficient during flight.
The test goal is to learn which corrugation orientation will have less drag. Two clipped delta shaped (trapezoid) fin
plan forms were evaluated: one plan form has corrugations parallel to the fin’s root chord (CPRC) and one fin has
corrugations parallel to the fin’s leading edge (CPLE); Testing evaluated fin drag at constant angle of attack (0
degrees) and varied wind speeds for comparison. All testing was performed in the 24” x 24” Wind Tunnel
(Lifesaver) located in the Fluid Mechanics Lab at NASA Ames Research Center, (Figure 1) The two fins were also
analyzed in the RotCFD for comparison to the wind tunnel results.
1 Student, Industrial Engineering, Navajo Technical University
2 Faculty, Information Technology,Northwest Indian College
Figure 1. 24” x 24” Wind Tunnel (Lifesaver)
Corrugated plastic is an ideal material for water/air pressure rocket fins because it is readily available,
inexpensive, durable, and easy to shape with household tools. Many people have made rocket fins out of corrugated
plastic. Corrugated plastic stockis similar to corrugated cardboard in that there are corrugations or openings
between an upperand lower skin. Figure 2 presents a conceptualdrawing of corrugated plastic as well as an edge
view of a representative sample. The openings may have an effect on the air flow over the fins where one orientation
may exhibit less drag compared to the other orientation. To the knowledge of the author, no testing for drag has been
done on rocket fins made from this type of plastic. Two delta shaped (trapezoid) fins were tested to investigate
which corrugation orientation, parallel to the air flow or parallel to the fin’s leading edge,is more efficient during
flight. One fin had corrugation orientation parallel to the leading edge, and the other had corrugations parallel to the
root chord. RotCFD is used in the rotorcraft industry as a design tool that can carry out aerodynamic simulations.
Additional analysis was done with RotCFD by running simulation for both fin designs in order to view the simulated
Figure 2. Corrugated plastic drawing and edge view showing corrugations
It is hypothesized that the CPRC will be more efficient during flight by creating less drag. It is thought that
the drag will be reduced with the corrugations parallel to the air flow (Figure 3) because the air will flow through the
openings in the fins. It is thought that the drag will be higher with fins that have the corrugations parallel to the fin’s
leading edge (Figure 4) due to air blockage from the leading edge.
Figure 3. Corrugations parallel to the root cord. Figure 4. Corrugations parallel to the leading edge.
III Design Description
Testing was performed in the 24” x 24” Wind Tunnel (Lifesaver) in the Fluid Mechanics Lab (FML) at
NASA Ames Research Center. A test stand to hold the fins in place was made of light wood, wire, and Velcro
(Figure 5) and was mounted on the torque sensor (Figure 6) and then that assembly was mounted on the wind tunnel
along with an anemometer (Figure 7). An anemometer measured the tunnel’s wind speed in feet per minute and the
torque sensormeasured the torque generated by the drag over the test fin’s surface created by the wind. The torque
sensorwas calibrated to measure in grams.
Figure 5. Test stand concept (dimensions in inches) and the stand mounted on the torque sensor
Figure 6. Omega TQ201 Series Torque Sensor and digital display
Figure 7. Test stand in place with anemometer sensor and display unit
Test models were made of corrugated plastic (Figure 2). The trapezoid shaped fins, known as clipped delta
fin design, (Figure 8) have dimensions of: RC = 6”, LE = 6.18”, TE = 6.18” SP = 6”, TP = 3” having a total area of
27 in2 Figure3 shows the corrugations parallel to the leading edge and air flow direction. Figures 3 and 4 showthe
corrugation orientation to the air flow direction.
Figure 8. Clipped Delta Fin
The torque load cell sensor has an output of 2 mV/V with a load range of 25 ounce-inches.The test stand
was mounted on the rotating shaft of the torque sensorwhich meant that any rotating movement of the test stand
would cause the torque sensorto display a reading.
First the stand was mounted to the torque sensor the combination of sensorand stand hereinafter referred to
as the fin mount, and then the torque sensorwas connected to a digital display instrument. A near frictionless pulley
was mounted and place behind the fin mount in such as fashion that the calibrating weights could be tied to a piece
of string in order to cause the torque sensorto register movement (Figure 9). Increasing gram weights were tied to
the string in order to collect a set of data points that would be used to convert the torque load cell readings to
equivalent grams. The fin mount was mounted in center of the exit end of the wind tunnel. The wind tunnelwas
turned on and torque readings were recorded to ensure that the drag of the fin mount did not exceed the load
capacity of the torque sensor.
Figure 9. Torque sensor calibration setup
Next a fin was mounted on the fin mount. The fin was aligned at 0 degrees angle of attack to the wind flow
in order to eliminate drag created by any non-zero angle of attack. Angle of attack was determined by comparing its
position with graph paper placed on the wind tunnel's floor (Figure 10). Torque sensorreadings were recorded for
wind speeds from 0 to 1900 fpm and from 1900 to 0 feet per minute in approximately 200 fpm increments. Each
step increase or decrease took place after the anemometer indicated steady flow and the torque sensorsettled to a
near steady reading. This procedure was repeated for the second fin. Ten readings were recorded for the CPLE fin
and 9 readings were recorded for the CPRC fin.
Figure 10. Angle of attack calibration
IV Analysis and Results
Added Weights and Torque
Figure 11. Calibrating torque sensor for converting its readout to grams
Figure 11 illustrates how the weights and torque sensorreadouts were plotted and the data slope was
calculated to be 8.277. This meant that each torque reading had to be divided by 8.277 in order to obtain grams.
All of the data was converted in post processing to the appropriate units of fps, square feet, and pounds.
Coefficient of drag (Cd) was computed by using the formula
D = Cd½ ρ𝑣2
Drag=Drag Coefficient x ½ x Air Density x Air Velocity^2 x Area.
y = 8.2778x + 0.3889
0 5 10 15 20
Torque Sensor Calibration
Linear (Read out)
Figure 12. Data collection
After the conversions,the data was plotted,and the results are shown in Figure 12.
Figure 13. Graphical results of wind tunnel tests. Velocity is in feet per second.
Calculating the difference between the Cd of the CPLE and the Cd of the CPRC gave an average of a 2%
difference. This indicates that the fin with the CPRC has slightly less drag than a fin with the CPLE.
Wind tunnel test results supported the hypothesis that a fin with the corrugations parallel to the air flow has
less drag than a fin with the corrugations parallel to the leading edge.
In all of the RotCFD images, the airflow is from the left. RotCFD analysis also supported the hypothesis.
Figures 14-16 are RotCFD generated images of the flow about the fin with the corrugations parallel to the leading
edge. Figures 17-19 are RotCFD generated images of the fin with the corrugations parallel to the air flow. Arrows
are vectors representing pressure with brightness indicating increasing pressure. Examining Figures 17-19, one can
see that the air flow over the fin with the corrugations parallel to the root chord has little turbulence. This creates
0.0 10.0 20.0 30.0 40.0
Corrugated PlasticCoefficient of Drag
RotCFD images of fin with corrugations parallel to its leading edge
Figure 14. Cross section with Leading Edge on left Figure 15. Top view with Leading Edge on left
Figure 16. Front view looking down the span toward the root
RotCFD images of fin with corrugations parallel to air flow
Figure 17. Cross section with Leading Edge on left Figure 18. Top view with Leading Edge on left
Figure 19. Front view looking down the span toward the root
Wind tunnel tests and RotCFD modeling indicate that fins with CPRC have slightlyless drag than fins with
I would like to express my deepest appreciation to everyone who provided me the possibility to complete
my report. A special gratitude I give to my mentors Gary Brandt and Kurt Long, whose contribution to my project,
testing,and encouragement, helped me to coordinate my project especially in writing this report. I would also like to
thank AIHEC, TCUP, Navajo Technical University, the NART Team, Ames Aeromechanics Branch, Dr. William
Warmbrodt, and Jessica Williams. Special thanks to Christine Gregg and Larry Young for editing and offering
Brandt, Gary. July 17, 2013.
Department of Physics, http://van.physics.illinois.edu/qa/listing.php?id=2140. July 17, 2013.
Long, Kurt. July 17, 2013.
NASA, The Coefficient Drag. http://www.grc.nasa.gov/WWW/k-12/rocket/dragco.html. July 29, 2013.
NASA, Rocket Stability. http://exploration.grc.nasa.gov/education/rocket/rktstab.html.July 17, 2013.
NASA, http://www.nasa.gov/. July 15, 2013.
THE PHYSICS HYPERTEXTBOOK, Aerodynamic Drag. http://physics.info/drag/.July 19, 2013.
U.S. DEPARTMENT OF TRANSPORTATION FEDERAL AVAITION ADMINISTRATION.ROTORCRAFT
FLYING HANDBOOK. Washington,DC: 2000. Print.