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Next Generation Carbon Fiber Airframe
(turn in TWO copies)
Team Members
David Edwards | Alex Kollen | Danny Johnson | Alex Chan | Nicholas Cho
Academic Advisor
Jun Jiao
PSAS Progress Report -- Winter 2015 8 March 2016Executive Summary
This is a progress report for a capstone project funded by the Portland State
Aerospace Society (PSAS). PSAS’s ultimate goal is to build a rocket capable of
deploying a small satellite into the earth’s orbit. This capstone team was assembled to
start development on the next generation of carbon fiber airframes. The diameter of the
new airframe will be increased from the previous design of 8” to a much larger 14”. For
this capstone project, the goal is to develop a simplified and improved carbon fiber
airframe manufacturing process and improve the surface finish of the airframe. The
intention is to have this rocket achieve a speed above Mach3, so the surface roughness
of the airframe must be greatly improved to reduce drag forces at this velocity. In
addition to designing 14” airframe modules, the capstone team must also design and
fabricate module coupling rings. Goals will be achieved by improving upon existing
processes and developments made by previous PSAS teams.
After the internal and external research, several possible design solutions have
been generated; however, their implementation is contingent on funding and access to
materials. Currently, the team is in the final stages of acquiring the necessary materials
for the rocket. While awaiting the arrival of material, further initial design analysis will be
performed. This report will summarize the major decisions that led to the current design.
Table of Contents
Executive Summary 1
Introduction 3
Mission Statement 3
Project Plan 4
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Product Design Specification Summary 5
External Search 5
Internal Search 6
Top Level Design Evaluation 7
Detailed Design Progress 8
Conclusion 10
Appendix 11
Introduction
The primary goals of PSAS are to be the first university to send a rocket to the
Karman line and set a small satellite into orbit. To accomplish this feat, weight and
surface roughness of the rocket must be improved for Mach3 flight. Multiple iterations
are required to optimize the design of the rocket, so it is important to have a relatively
simple yet repeatable manufacturing process. As a step along this iterative process, the
design and analysis of an optimized rocket will provide information for future teams to
build upon. The next step to achieving the goal of reaching the Karman line requires the
design of a new, much larger, 9” diameter rocket (the current rocket is 6.6” in diameter).
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This larger rocket will be made almost entirely out of carbon fiber and will feature a
single stage liquid fuel rocket engine. The combination of a light airframe, coupled with
the highly energy dense liquid fuel, should bring PSAS much closer to achieving their
goals.
Mission Statement
The purpose of this capstone project is to design a 9” diameter rocket with an
improved surface finish and manufacturing process. By the end of the capstone project,
a larger and improved rocket will be designed and built according to the specifications
outlined in the Product Design Specifications. A time and energy efficient manufacturing
process will be developed and implemented to enable PSAS members to easily
fabricate multiple carbon fiber airframe modules. Proper documentation will be provided
to PSAS; this documentation will thoroughly describe not only the design process used
by this capstone team, but also the specific instructions to recreate the fabrication
process of the carbon fiber airframe. Once the project is completed, a prototype will be
delivered to PSAS along with the relevant analysis and documentation.
Project Plan
Current progress is shown by the Gantt Chart in Figure 1 below. The Gantt Chart
shows us slightly behind schedule in the following categories: Process Design, FEA
Modeling, Pre-Fab assessment for both the rings and mold fixture and Fabrication of the
rings and mold fixture. This schedule was designed with the intent of having a flexible
time frame due to material acquisition problems, etc. This time deficit will be resolved in
the coming weeks. Additionally, we had originally allotted time to manufacture these
parts ourselves, but Machine Sciences Corporation has agreed to donate their material
and time, so the fabrication aspect will consume very little of our time.
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Figure 1: Current project plan
Product Design Specification Summary
The Product Design Specifications (PDS) outlines the major criteria a project
design has to meet. It is compiled by the customer (PSAS), and describes the
specifications in terms of relative importance and engineering metrics. The PDS is
referenced to ensure that the project design is on the right track. A list of the most
important parameters is shown below, while a more detailed list is shown in Appendix A.
● Rocket must withstand Mach3 forces within a safety factor of 2.
● Outer surface roughness must be less than 0.1 m.𝜇● Outer diameter must be about 14”.
● Weight of the rocket must be 50% or less than the previous model.
● Manufacturing process must be simpler and more repeatable.
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● Simulations, new module design, and manufacturing must be documented.
● All necessary tests must be performed.
External Search
The capstone team researched designs and processes used to create a previous
carbon fiber PSAS rocket. The goal of this research was to determine which method
would result in a simpler and more repeatable manufacturing process. The overall
design of the previous rocket was found to be more than sufficient to meet the
requirements of the customer but it was apparent that the manufacturing process
needed to be improved. The previous process resulted in a surface finish that was much
less than what is acceptable for our surface finish requirements. It was determined that
the surface could be smoothed out after the curing process but this would add time and
complexity to the manufacturing process. Additionally, the surface finish may be
obtained by using an external mandrel, which may be faster, simpler and more
repeatable. Some limiting factors to potential design solutions include material and
budget limitations as well as epoxy/adhesive procurement and compatibility.
Internal Search
After external research, the team brainstormed possible solutions and two
manufacturing process were identified as potential replacements for the current method
of using prepreg carbon fiber sheets with heat shrink tape. The proposed solutions were
based partly on current manufacturing processes in related fields. These potential
design solutions are presented below:
1. Vacuum MoldMechanism: After a vacuum seal is placed over the mandrel, a vacuum is
created to form an external surface finish that is dependent on the mold.
Comment: This method is less skill oriented and more repeatable than the
current manufacturing process. However, it is expensive and requires skills to
obtain the proper seals.
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2. Clam ShellMechanism: A product called AirPad HTX is used to make a flexible mandrel
with the clam shell and vacuum pull through design solution. The clam shell
method is shown in Figure 2.
Comment: This method is most likely to get us the best surface finish out of the
two alternative methods and would be the simplest to repeat. These benefits
come at a cost as the required material is not as readily available as some
alternative methods.
Figure 2: Clam Shell around the mandrel
Top Level Design Evaluation
Both of the proposed design solutions have the potential to work and fit the
criteria of the PDS document, but they each have their strengths and weaknesses. It is
the objective of the team to determine which method is superior. The team is very
limited by funding so it is unlikely that both methods can be tested at full scale to
determine which method is best, so concepts were evaluated using a Concept Scoring
Matrix (Figure 3).
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Figure 3: Concept Scoring Matrix
The post-cure finishing method is added to the concept scoring matrix to highlight
the improvements of new manufacturing methods. It is also important for the team to
consider potential issues, such as the unavailability of materials to implement the new
manufacturing processes, which would force the team to use less efficient processes.
The results of the concept scoring matrix show both the vacuum mold and the clam
shell processes at essentially the same level. It must be noted that in the creation of the
concept scoring matrix, there was no way to objectively rate these processes and all
scoring is entirely speculative. However, both the new processes seem to show
significant benefits over the current process, especially in terms of time and
repeatability, which are key components of the PDS.
The team is severely handicapped by the limited availability of crucial materials
as well as the funds to procure these materials. At this point, the team has decided to
pursue both the vacuum mold and clam shell method. Ultimately the decision of which
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method we select will be determined by the materials the team is able to acquire. If
both become available to us, we will pursue both and compare the results.
Detailed Design Progress
The main objectives required to meet the requirements of the PDS are as follows:
● Determine design of mandrel mold
○ The design is almost complete for the mandrel mold. Further design will
be finalized once we procure the necessary materials. Design and
material selection may or may not change if we do not get the material
required for carbon fiber.
● Determine design of coupling rings
○ The core design for the rings is complete. We are currently in the process
of optimizing the design for weight and strength around the screw holes,
where the clear stress concentration indicates that failure is most likely to
occur at that location (see Figure 4). Design changes will be driven by
stress analysis performed in ABAQUS. Our preliminary design indicates
that the additional support should be added around the screw holes, as
this our weakest point when the rings are in tension.
Figure 4: FEA stress analysis of the rings
● Acquire materials (carbon fiber, aluminum, adhesive)
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○ This has become a severe limiting factor for progress. We have been
unable to acquire sufficient adhesive layer material required for the layup
of carbon fiber. This may require us to rely on a contingency plan of not
using aerospace grade materials to achieve proof of design for the rings
as well as giving us the ability to determine a proper manufacturing
process to achieve the desired surface finish.
● Build and compare methods (process and results)
○ Once again, this is limited to materials and funding. If possible, we will
develop processes for both the clam shell and vacuum mold methods and
compare the results.
Conclusion
At this point, two potential concept designs have been identified and most of the
resources required for those manufacturing process has been secured. Although not
typically done in these types of capstone projects, the team was able to successfully
fundraise and recruit sponsorship for materials and services. A major setback the team
faced was the unavailability of carbon fiber for rocket fabrication. The team was able to
find support in this regard and a surplus of quality carbon fiber was donated to PSAS.
Another difficulty the team faced was the cost to fabricate the mandrel mold as well as
the coupling rings. The initial budget provided to the team was estimated to be barely
enough to cover the cost of the raw materials for these components. Fortunately, the
team was able to gain support from Machine Sciences Corporation in the form of raw
materials and machining services. Not only will this cover the expenses of the coupling
rings but also the entire mandrel and fixture. The remaining major hurdle for the team in
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regards to material acquisition is the adhesive layers, which are more expensive than
the carbon fiber itself.
Before fabrication, the team must determine which method will be used to create
an external mold that will achieve the desired surface finish. Currently the team is
looking into either a vacuum exterior mold or a clam shell type external mold. Once a
method is selected, the team will start the process for fabrication and documentation.
Appendix A: Detailed PDS Criteria
In this appendix, the detailed PDS of the project is shown below. The
specifications of the project are group together in terms of relative importance.
HIGH PRIORITYCriteria Requirement Customer Metrics Target Basis Verification
PerformanceWithstand Mach3
ForcesPSAS Safety Factor 2 Group
DecisionDesign Analysis
and Testing
Smooth Surface PSAS m𝜇 <0.1 Group Decision
Prototype
Size Diameter PSAS Diameter in inches
14 PSAS Prototype
WeightLess Than
Previous Model PSAS% of Weight
from Previous
Model
50< PSAS Prototype
Installation Ease of Assembly PSAS Low Skill PSAS Prototype
Simulations PSAS Documented 0 Missing Documents
PSAS Report
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Documentation
New Module Design
PSAS Documented 0 Missing Documents
PSAS Report
Manufacturing Process
PSAS Documented 0 Missing Documents
PSAS Report
TestingPerform All
Necessary TestsProject Team
Max Stress, Shear Stress, Temperature Profile, Heat
Flux100% verified
Group Decision Testing
Table A.1: High Priority product design specifications
MEDIUM PRIORITYCriteria Requirement Customer Metrics Target Target basis Verification
Quantity At least 2 PSAS Number 2 PSAS Prototype
MaterialReasonable Prices Self $ Inexpensive Budget Design
Aluminum Rings PSAS yes/no yes PSAS Design
Timeline
PDS PSU Deadline 1 Report PSU Report
Progress Report PSU Deadline 1 Report PSU Report
Final Report PSU/PSAS Deadline 1 Report PSU/PSAS Report
Gantt Chart Self Deadline 1 Table Self Report
Table A.2: Medium Priority product design specifications
LOW PRIORITYCriteria Requirement Customer Metrics Target Target basis Verification
Environment Not Environmentally
Hazardous
Self Contamination of
Surrounding
No Detectable Contaminants
Group Interest Design
Table A.3: Low Priority product design specifications
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