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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