Table of Contents
1.0 Summary of FRR Report .......................................................................................... 3
1.1 Team Summary ..................................................................................................... 3
1.2 Launch Vehicle Summary ...................................................................................... 3
1.3 Brief Payload Description ....................................................................................... 3
2.0 Vehicle Summary ...................................................................................................... 4
2.1 Simulation Data .................................................................................................. 5
2.2 Flight Results ..................................................................................................... 6
3.0 Payload Summary ..................................................................................................... 8
4.0 Budget Summary..................................................................................................... 14
5.0 Educational Engagement Summary ........................................................................ 14
6.0 Conclusion .............................................................................................................. 15
University of Nebraska - Lincoln | USLI FRR 2
1.0 Summary of FRR Report
1.1 Team Summary
University of Nebraska – Lincoln Rocketry Team
Location: Lincoln, Nebraska
Faculty Advisor: Dr. Kevin Cole
Professor-Mechanical and Materials
Engineering
Certified Mentor : Thomas Kernes
National Association of Rocketry #82141
Project Director: Matthew Mahlin
Payload Team Leader: Alexandra Toftul
1.2 Launch Vehicle Summary
Length:
Diameter:
Nose Cone:
Fin Span:
Weight:
Motor Mount:
124.5”
5.5”
27.5”
14.5”
23.7/39.5 lbs
98mm
Von Kármán (LD-Haack), 1:5 Fineness
(3-fin configuration)
Unloaded weight / Launch weight
37” long – rear retaining ring
Launch Motor:
Designation
Aerotech L1170FJ-P
Total Impulse (N*S)
4214
Thrust/Weight
6.82/1
Recovery System:
Component
Main Parachute
Drogue
Shock Cord
Wadding
Characteristic Dimension
108”
36”
52’ Main / 50’ Drogue
24”
Comment
Hemispherical with 24” Spill hole
Mach 1 Ballistic X-Form
1” Tubular Nylon
2 x Fire resistant protective cloth
1.3 Brief Payload Description
The scientific payload consists of a deployable UAV designed to serve as a test bed for
an ambient wind energy scavenging experiment. The goal of the experiment was to
determine whether the amount of power generated by a windbelt can be maximized by
using an active control system to maintain the fundamental mode of vibration in the belt,
even as the wind speed varies throughout descent.
University of Nebraska - Lincoln | USLI FRR 3
2.0 Vehicle Summary
Figure 1 Dimensional Drawing of Entire Assembly.
A dimensional drawing of the entire assembly is provided in Fig. 1. An exploded
assembly of the vehicle is shown in Fig. 2. As can be seen, the launch vehicle consists
of three major sections. The first section being the Nosecone housing the
communications bay. Second, the Forward Sustainer to house the main parachute in a
forward bay, the avionics in the center, and the drogue parachute in the aft. Lastly, the
Rear Sustainer to hold the deployable payload, motor mount tube, and join the stabilizer
fins.
Materials used in construction of the vehicle were fiberglass, polyester vinyl resin,
bluetube, and plywood. The Nosecone is a commercially purchased filament wound
structure. The remaining sustainer sections are bluetube wound in 4oz fiberglass cloth
and hardened with polyester vinyl resin. The fins and vehicle bulkheads are composed
of plywood reinforced with fiberglass.
Figure 2 Exploded view of vehicle components.
University of Nebraska - Lincoln | USLI FRR 4
2.1 Simulation Data
What follows are the dimensions and models used in OpenRocket simulations. After the
test flight, the drag characteristics of the vehicle were accounted for by increasing the
surface roughness in the model. The motor used in the simulation is an Aerotech L1170
FJ and this is what the vehicle was flown on in April.
Figure 3 OpenRocket model of vehicle with selected motor and 5.0lb payload.
Table 1 Motor evaluated in simulation.
The conditions of our simulation match the conditions of the launch such as winds
averaging 15 MPH and the 5 degree angle of the launch rail. The only difference is for a
launch in this wind speed it was calculated that no ballast should be used. So, there is a
0.3 pound difference in launch mass between the calm wind condition launch and the
launch configuration used. The predicted altitude was overshot intentionally as well.
Ultimately, the result was a difference of about 1.4 % from the simulation’s predicted
altitude.
University of Nebraska - Lincoln | USLI FRR 5
2.2 Flight Results
According to the Perfectflite Stratologger altimeter, our primary altimeter, the altitude
reached by the vehicle was 5228 feet AGL. This was officially confirmed immediately
after the flight. The vehicle was just under 1% off from the target altitude. The
secondary Raven2 altimeter recorded a very similar 5231 feet AGL. Both values are
based on barometric pressures. The close agreement of the two altimeters shows that
they are similarly calibrated and have been deemed reliable because of the small
difference of two feet. The data from the Primary altimeter is graphed in Figure 4 and
the secondary altimeter in Figure 5 on the following page.
During the flight, the avionics successfully deployed the drogue at apogee. First
detonating the primary apogee charge and then the secondary apogee charge after a
second of delay. The tethered payload was also successfully drawn out of the payload
bay during this event. A small pressure leak to the avionics caused a few hundred foot
drop in altitude recorded due to the charge, but was nowhere near enough to cause
premature ejection of the main parachute. The affect of the pressure leak was much
improved since the test flight due to plugging the wiring tunnels. The main parachute
was then successfully deployed at 1000 feet above ground level. All recovery
components operated as intended during the flight.
Looking at data from the flight computers, the descent rate under drogue was an
average of 79.76 feet per second. Under the main parachute, the descent rate was
slowed to just 11.27 feet per second. While the drogue descent rate matched closely
with calculations, it appears that the moderate winds during the flight and reduction in
launch mass do to winds slowed the descent under main parachute by a third of the
expected 18 FPS. This resulted in favorable low descent energy but didn’t cause the
vehicle to drift out of the launch field.
Upon recovery, the vehicle was completely intact and in relaunchable condition. The
robust structure was able to withstand nine times the force of gravity during launch, use
shear pins to ensure two recovery events, land at a low velocity, and get dragged
through the dirt. In addition, it also continuously transmitted its location with the BRB900
and was able to transmit video during part of the flight. All objectives and vehicle criteria
for the competition were met by this design.
University of Nebraska - Lincoln | USLI FRR 6
Figure 4 Perfectflite Stratologger primary altimeter altitude data.
Figure 5 Raven2 Secondary altimeter altitude and velocity data.
University of Nebraska - Lincoln | USLI FRR 7
3.0 Payload Summary
The scientific payload design is shown in Fig. 6. Following separation from the rocket,
two rigid ‘wing’ structures fold outward from the UAV body. Each of these houses a
windbelt assembly consisting of a flexible ribbon, a pair of permanent magnets attached
to the ribbon, and two fixed conducting coils. These systems take advantage of ambient
wind to harvest electrical energy from the mechanical motion of the ribbon throughout
descent.
The main objective of the payload is to analyze the effectiveness of an active control
system for maximizing the power output of a windbelt energy scavenging system. Other
objectives include investigating the relationship between various factors affecting the
windbelt system’s performance, and determining the practically of using such an energy
scavenging scheme on an airborne system.
Figure 6. Payload design
While a full-scale flight test of the windbelt system was not realized due to scheduling
constraints, a detailed benchtop test was conducted to determine several important
relationships relevant to the experiment. In particular, the relationship between was
wind speed, windbelt tension, and windbelt resonant frequency was investigated, as
well as the relationship between wind speed and voltage output for several windbelt
tensions.
University of Nebraska - Lincoln | USLI FRR 8
Data Analysis and Results of Payload
A benchtop test was conducted to investigate the relationship between was wind speed,
windbelt tension, and windbelt resonant frequency, as well as the relationship between
wind speed and voltage output for several windbelt tensions.
Windbelt Design and Construction
The payload airframe is shown in Fig. 7. It was constructed out of thermoplastic, which
was chosen because it is relatively low cost, readily available, and lightweight yet
adequately rigid when fully solidified. Hinges were attached to both wing structures to
allow the payload to fit compactly inside the rocket during ascent. A rotating eye bolt
was used to attach the payload airframe to its parafoil, allowing the UAV to spin freely
throughout descent to prevent tangling of the parafoil lines.
Figure 7 Airframe of scientific payload with extended windbelt arms.
Each windbelt system consisted of a ribbon, a pair of magnets, and a pair of conducting
coils. Materials considered for the windbelt ribbon were Mylar-coated taffeta, Dacron
tape, metalized Mylar tape, and gorilla tape. Considerations in choosing the ribbon
material included weight, flexibility, availability, and cost. Mylar-coated taffeta is often
mentioned in relation to small-scale windbelt prototypes, however it is not readily
available in the United States. It was determined through testing that two pieces of
metalized Mylar tape stuck together resulted in the maximum ribbon motion at all wind
speeds tested, and this was therefore the material selected.
Magnets were selected based on strength, weight, surface area, cost, and availability.
Testing showed that magnets that were too heavy would significantly limit the motion of
the windbelt ribbon, adversely affecting performance. For this reason, magnets were
selected to be as strong as possible for the greatest allowable weight. It was also
University of Nebraska - Lincoln | USLI FRR 9
observed that ribbon motion was maximized when the magnets were placed at the ends
of the ribbon, rather than toward the middle.
The conducting coils were placed as close as possible to the magnets in order to
maximize magnetic field coupling and induced voltage. The coils were secured with
thermoplastic approximately 3/8 inch from the magnets as shown in Fig. 8.
Figure 8 Spacing of magnets and conducting coils.
Experimental Setup
The test setup is shown in Fig. 9. A test rig was constructed out of wood to hold the
ribbon in place, and a hairdryer was used as a wind source. The hairdryer was
positioned such that the airflow was always perpendicular to the ribbon, and was moved
closer or farther from the ribbon to provide the desired wind speed. Wind speed was
measured with a handheld digital anemometer.
A pulley system was used to tension the ribbon. The end of the ribbon was attached to
a weight that could be increased or decreased incrementally. Finally, an oscilloscope
was used to measure the voltage generated in one of the conducting coils during
testing.
University of Nebraska - Lincoln | USLI FRR 10
Figure 9 Bench test set up of tuned windbelt.
Experimental Procedure
Three sets of data were taken at three nominal winds speeds (10, 20, and 30 mph). The
wind source was fixed in the vertical direction (distance from the table), and horizontal
direction (relative to the length of the test rig), and only moved closer or farther from the
test rig in order to obtain the desired wind speed at the ribbon. The ribbon tension was
varied at each wind speed from 0 oz to 1.5 oz in increments of 0.5 oz by adding 0.1 oz
weights to the end of the ribbon.
One of the conducting coils was connected to the oscilloscope, and the voltage was
recorded every 5 seconds for 70 seconds at each wind speed and tension. These
values were then averaged together. The resonant frequency condition was determined
by observing the voltage signal on the oscilloscope. At the resonance condition, this
was observed to be a single-frequency sinusoid, whereas at other times the signal
contained various harmonic components. An approximate value for the resonant
frequency was then determined at the ribbon tension that yielded the greatest average
generated voltage.
University of Nebraska - Lincoln | USLI FRR 11
Data
The experimental data collected is shown in Table 2. It can be seen that there is one
ribbon tension at each wind speed for which the average generated voltage is
maximized. The differences are more pronounced for wind speeds around 20 or 30 mph
than for those as low as 10 mph. These maximum voltage values were observed near
the ribbon resonance condition, which was different for each wind speed.
A plot of ribbon resonance frequency versus wind speed is shown in Fig. 10. A
logarithmic trendline was fitted to the data, with an R2 value of 0.891 indicating a
moderately good fit. The resonance frequency is low for low wind speeds, increases
quickly as wind speed increases, and then stays approximately the same for higher
wind speeds.
Table 2 Summary of Experimental Data
Wind Speed
(mph)
Tension
(oz)
Voltage (mV)
Fres (Hz)
Nominal: 10
(Actual: 10.1)
0
0.5
1
50.40
49.87
41.33
2.14kHz
1.5
44.27
0
0.5
1
63.60
84.93
36.53
1.5
37.33
0
0.5
1
1.5
62.13
74.93
32.93
33.73
Nominal: 20
(Actual: 19.9)
Nominal: 30
(Actual: 30.2)
5.31kHz
5.50kHz
University of Nebraska - Lincoln | USLI FRR 12
Resonant Frequency, kHz
Resonant Frequency vs. Wind
Speed
7
6
5
4
3
2
1
0
y = 3222.8ln(x) - 5041.3
R² = 0.891
0
5
10
15
20
25
30
35
Wind Speed, mph
Figure 10
Scientific Value
The collected data indicates that performance of a windbelt system depends on the
oscillation mode of the belt, and that this in turn depends on the windbelt tension and
ambient wind speed. It was determined that for a given wind speed, there is a certain
ribbon tension that results in significantly better performance than others, and that this is
occurs when the ribbon is in a resonant condition.
The data may indicate that the increase in performance resulting from an active tuning
scheme may be significant enough to outweigh the input power required to run the
active control system, however further testing is required. While the system tested is
mainly a proof-of-concept, a larger system that generates relatively large amounts of
power may be able to produce several times the amount of energy by employing a
tuning scheme. In such a case, the power necessary to run the control system would be
far outweighed by the gain in energy output.
If this is found to be true, this may have significant applications to the improvement of
ground-based windbelt energy scavenging systems used for power generation in
developing countries, as well as those on airborne systems, which many be used to
power various sensors and instrumentation on board the aircraft.
University of Nebraska - Lincoln | USLI FRR 13
4.0 Budget Summary
The total budget of the project was $10,000 provided by the NASA Nebraska Space
grant. The Vehicle frame was constructed for around $800 and another $2000 extra
construction supplies. A total of 4 L motors were purchased for $1000. A total of $2500
was devoted to the vehicle payload. This included the communications equipment and
the scientific payload. Then an additional $750 was put in to the construction of a launch
pad. The remaining funds were put towards motor hardware, miscellaneous hardware,
paint and protective equipment.
Travel and accommodations for 6 team members to the competition was estimated at
$2,000. Ultimately the team that went down to Huntsville came down to just 4 members.
Rental of a 12 passenger van was $802. One member had to fly down for another $288.
Fuel was $501. Meals for the team make up the remaining expenses. The total cost was
$1767 for the trip.
5.0 Educational Engagement Summary
The Outreach efforts of the Nebraska USLI team started in the fall with a three day
water rocket workshop in the science classrooms of a local middleschool. There young
students were introduced to rocketry concepts and quizzed on them on the first day.
The second day they built their own water rockets. This culminated on the third day
where students flew their water rockets. All the lessons learned from this hands on
experience were built upon by reviewing what worked and what didn’t work so well on
the rockets they built. The event was successful enough that the team was invited back
for a second event in the Spring.
In the spring, the event had to be compressed in to a single day. So we endeavored to
teach students the basics of rocketry using stomp rockets. First though, they were
inspired by showing them our subscale and full scale rockets and explaining how they
functioned. This garnered many questions from the young students. From there, we
decided to hold a competition to see whose stomp rocket would go the farthest.
Unfortunately, the class ended and we were unable to see the students compete. All in
all it was a very rewarding experience for the team and we were able to inspire students
to learn and be curious. With this being our second educational engagement we tallied
up a total of 121 students affected by the University of Nebraska-Lincoln USLI team.
Other outreach event that we present at were Engineering week open house and
Astronomy day. These events both brought in hundreds of students. The Astronomy
day event was especially popular because Nebraska’s own Astronaut, Clayton
Anderson, was there to give a speech.
University of Nebraska - Lincoln | USLI FRR 14
6.0 Conclusion
Figure 43 All associated equipment and hardware for the project.
Overall, the project was highly rewarding for the team. We were even able to share our
knowledge with the public and try to engage young minds. Valuable experience in
rocketry, project management, and hands on construction was gained by our members.
The design and built vehicle proved to be highly successful in reaching our altitude goal
and ability to deploy a payload. It was unfortunate that our team ran out of time to fully
integrate the deployable payload with the vehicle. Still, the payload system has proved
to be quite insightful in to aircraft mounted tuned windbelts used for energy scavenging
based on our ground testing.
It was hard for our small team to bring everything together, but we were satisfied with
our first showing at the USLI competition. We tried to aim high ourselves with lofty goal
and what we were able to accomplish turned out well. It was also truly amazing to see
all the ideas from other teams on the launch field. The next year we will be even more
prepared and remain ambitious. Thank you for making it possible.
University of Nebraska - Lincoln | USLI FRR 15