Team 6: Calvin Supermileage
Final Design Report
Benjamin Beezhold, ME
Jon Hofman, ME
David Kaemingk, ME and CivE
Will Vanden Bos, ME
Jacob Vriesema, ME
Engineering 340 Senior Design Project
Calvin College
9 May 2012
© 2012, Team 6: Calvin Supermileage and Calvin College
Executive Summary:
The Calvin College 2011-2012 senior design Team 6: Supermileage includes the following senior
engineers: Ben Beezhold (ME), Jon Hofman (ME), David Kaemingk (ME and CivE), Will Vanden Bos
(ME) and Jacob Vriesema (ME). In this report the team proposes and documents design solutions for
creating a single-occupant high fuel-mileage car to compete in the annual SAE Supermileage®
competition in Marshall, MI. In such a design, the team resolved to minimize inefficiencies that arose
from tire rolling resistance, aerodynamic drag, and engine performance. The following report outlines
project feasibility as well as highlights design solutions that encompass aerodynamics, engine
optimization, frame design, steering design and power transmission all while observing SAE
Supermileage® competition rules.
Table of Contents
Table of Figures ............................................................................................................................................ 4
Table of Tables ............................................................................................................................................. 6
1
Introduction ........................................................................................................................................... 7
2
Project Management ............................................................................................................................. 8
2.1
Team Organization........................................................................................................................ 8
2.1.1
Team Member Roles in Subcategories ................................................................................. 8
2.1.2
Documentation Techniques................................................................................................... 9
2.2
Scheduling..................................................................................................................................... 9
2.3
Budget Management ..................................................................................................................... 9
2.4
Design Norms ............................................................................................................................. 10
2.5
Method of Approach ................................................................................................................... 10
2.5.1
Minimizing Resistances ...................................................................................................... 10
2.5.2 Maximizing Engine Efficiency .................................................................................................. 13
2.5.3
3
Task Specification and Schedule ........................................................................................................ 14
3.1
Project Breakdown ...................................................................................................................... 14
3.1.1
Engine Integration ............................................................................................................... 14
3.1.2
Aerodynamics ..................................................................................................................... 14
3.1.3
Frame Design ...................................................................................................................... 14
3.1.4
Power Transmission ............................................................................................................ 14
3.2
4
Optimizing Vehicle Operation ............................................................................................ 13
Gantt Chart, Tasks, and Calendar ............................................................................................... 14
Design Process .................................................................................................................................... 18
4.1
Aerodynamics and Vehicle Envelope ......................................................................................... 18
4.1.1
Initial Testing ...................................................................................................................... 18
4.1.2
Material Alternatives........................................................................................................... 20
4.1.3
Final Selection .................................................................................................................... 20
4.2
Frame .......................................................................................................................................... 23
4.2.1
SAE Requirements .............................................................................................................. 23
4.2.2
Frame Overview and Material Selection............................................................................. 23
4.2.3
Overview of Design Process ............................................................................................... 25
1
4.2.4
4.3
Engine ......................................................................................................................................... 27
4.3.1
SAE Requirements .............................................................................................................. 27
4.3.2
Testing................................................................................................................................. 28
4.3.3
Alternatives ......................................................................................................................... 29
4.3.4
Final Modifications ............................................................................................................. 37
4.4
Steering ....................................................................................................................................... 37
4.4.1
SAE Requirements .............................................................................................................. 37
4.4.2
Alternatives ......................................................................................................................... 39
4.4.3
System Selection ................................................................................................................. 41
4.5
Rolling Resistance ...................................................................................................................... 41
4.5.1
Testing and Calculations ..................................................................................................... 42
4.5.2
Alternatives ......................................................................................................................... 43
4.5.3
Final Selection .................................................................................................................... 43
4.6
5
Final Design ........................................................................................................................ 26
Electrical Subsystem ................................................................................................................... 45
4.6.1
Engine and Fuel Injector Circuit ......................................................................................... 45
4.6.2
Brake Lights and Starter Circuit ......................................................................................... 46
Vehicle Costs ...................................................................................................................................... 47
5.1
Cost Estimation Development .................................................................................................... 47
5.1.1
Registration Costs ............................................................................................................... 47
5.1.2
Body and Frame Costs ........................................................................................................ 47
5.1.3
Wheels/Brakes/Transmission .............................................................................................. 47
5.1.4
Electrical Costs ................................................................................................................... 48
5.1.5
Engine and Powertrain Costs .............................................................................................. 48
5.1.6
Shell Costs .......................................................................................................................... 49
5.1.7
Testing Equipment .............................................................................................................. 50
5.1.8
Total Costs .......................................................................................................................... 50
6
Conclusion .......................................................................................................................................... 51
7
Acknowledgements ............................................................................................................................. 52
8
References ........................................................................................................................................... 53
9
Appendices.......................................................................................................................................... 56
2
9.1
Appendix A: Wind Tunnel Stress Calculations .......................................................................... 56
9.2
Appendix B: EES Order of Magnitude Calculations .................................................................. 57
9.3
Appendix C: MathCAD Frame Calculations .............................................................................. 59
9.4
Appendix D: FEA Frame Simulations ........................................................................................ 69
9.5
Appendix E: Detailed Frame Design .......................................................................................... 80
3
Table of Figures
Figure 1: Team organization chart ................................................................................................................ 8
Figure 2: Forces acting on the vehicle during operation ............................................................................. 11
Figure 3: Power losses ................................................................................................................................ 12
Figure 4: Work breakdown schedule with Gantt chart ............................................................................... 15
Figure 5: Funnelback design isometric view and dimensions (in inches)................................................... 18
Figure 6: Kammback design isometric view and dimensions (in inches) ................................................... 19
Figure 7: Drag forces from varied wind velocities in wind tunnel ............................................................. 20
Figure 8: CAD model of final shell design ................................................................................................. 21
Figure 9: Styrofoam mold created and donated by Betz Industries ............................................................ 21
Figure 10: Lamination schedule for upper and lower shell......................................................................... 22
Figure 11: Completed shell utilizing sandwich concept ............................................................................. 22
Figure 12: Roll Hoop Requirements ........................................................................................................... 23
Figure 13: Preliminary frame design .......................................................................................................... 24
Figure 14: Beam 1 loading diagram, all dimensions are in inches ............................................................. 24
Figure 15: Frame Design ............................................................................................................................ 25
Figure 16: Main beam FEA simulation for a 1-inch deep pothole; safety factor of 2.0 ............................. 26
Figure 17: Dimensioned Vehicle Chassis (all dimensions in inches) ......................................................... 27
Figure 18: Specified Fuel Bottle and 3.5hp Base Engine ........................................................................... 28
Figure 19: Schematic of a basic engine dynamometer................................................................................ 29
Figure 20: Modification options for the petrol engine ................................................................................ 30
Figure 21: Increasing compression ratio provides increased engine efficiency.......................................... 31
Figure 22: Temperature increases inside the cylinder will likely not cause engine knock ......................... 32
Figure 23: A basic carburetor draws liquid fuel into the combustion stream. ............................................ 33
Figure 24: The engine control unit gathers information to determine the timing and amount of fuel ........ 33
Figure 25: Left, a typical fuel injector sprays atomized fuel ...................................................................... 34
Figure 26: Fuel injection is costly and complicated, but more efficient than carburation. ......................... 35
Figure 27: Base engine side-valve combustion chamber, offset from cylinder .......................................... 36
Figure 28: Combustion chamber designs: (a) wedge chamber, (b) hemispherical head, (c) bowl in piston,
and (d) bath-tub head (Stone, 104).............................................................................................................. 36
Figure 29: Test track for Supermileage® competition ............................................................................... 38
4
Figure 30: Maneuverability course ............................................................................................................. 39
Figure 31: Wagon style steering mechanism .............................................................................................. 40
Figure 32: Knuckle steering system ............................................................................................................ 40
Figure 33: A knuckle steering system implemented in vehicle .................................................................. 41
Figure 34: Contact area and rolling resistance ............................................................................................ 42
Figure 35: Rolling resistance test fixture .................................................................................................... 42
Figure 36: Optimum tire diameters ............................................................................................................. 44
Figure 37: Engine and fuel injector circuit diagram ................................................................................... 45
Figure 38: Engine and fuel injector vehicle circuit layout .......................................................................... 45
Figure 39: Brake lights and engine starter circuit diagram ......................................................................... 46
Figure 40: Brake lights and engine starter vehicle layout ........................................................................... 46
5
Table of Tables
Table 1: Key design variables ..................................................................................................................... 13
Table 2: List of project tasks with estimated time allocations .................................................................... 16
Table 4: Rolling resistances ........................................................................................................................ 43
Table 5: Registration costs .......................................................................................................................... 47
Table 6: Body and frame costs.................................................................................................................... 47
Table 7: Wheels/Brakes/Transmission/Steering Costs ............................................................................... 48
Table 8: Electrical Costs ............................................................................................................................. 48
Table 9: Engine and Powertrain Costs ........................................................................................................ 49
Table 10: Shell Costs .................................................................................................................................. 49
Table 11: Testing Equipment Costs ............................................................................................................ 50
6
1
Introduction
On July 29, 2011, President Obama announced that automakers have agreed to increase car fuel
efficiency to 54.5 mpg by 2025 (NHTSA). A drastic increase over today’s efficiency standards, this
move underscores an increasing need to reduce the demand for fossil fuels. Pessimistic analysis of
worldwide supply estimates that peak oil production has already occurred ( Aleklet). With alternative
energy vehicles slowly making their way to showroom floors, engineers need little convincing of the
significance of highly efficient cars. It is in this light that the Society of Automotive Engineers (SAE)
sponsors the SAE Supermileage® competition. Engineering students from across North America design
a high efficiency, single-occupant vehicle: the best combination of fuel economy, written and oral
presentation wins. The team represented here designed and built a vehicle to participate in this
competition for their Senior Design Project. A few broad outcomes of such a project included
overcoming design difficulties, expansion of knowledge in respective design niches, and interpersonal
group management.
This senior design project fulfills the capstone requirement for senior engineering students at Calvin
College. The class is divided into two sections: ENGR 339 during the Fall semester and ENGR 340
during the Spring semester. Class time in ENGR 339 was spent teaching senior engineering students how
to work as a team. Lectures and discussions address topics such as communication, safety and project
management. ENGR 340 focused more on vocation and also allocated the majority of class-time to
building a prototype. The following sections document the feasibility, design, and implementation of this
project.
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2
Project Management
2.1
Team Organization
The Calvin College Supermileage senior design team consists of five mechanical engineers. Design and
analysis work was divided into five subcategories based on team members’ skills, interests, and previous
internship experience. Figure 1, below, shows the organization chart of Calvin Supermileage along with
supporting faculty and mentors.
Figure 1: Team organization chart
2.1.1
Team Member Roles in Subcategories
Ben Beezhold: hails from Seattle, Washington and worked extensively on the shell and aerodynamics
design throughout this project. His degree in engineering with a mechanical concentration and
international designation will be put to the test as he begins working full-time as a structural design
engineer at Boeing, also in Seattle.
Jon Hofman: Jon is a fifth year senior graduating with a degree in engineering - mechanical
concentration and a music minor. In this project, he oversaw all things engine: testing, modification,
8
installation, and operation. He lives in Zeeland, MI with his wife Julie and son William. He anticipates
working full time at Gentex upon graduation.
David Kaemingk: David is a fifth year senior and will be graduating with concentrations in civil and
mechanical engineering and mathematics minor. David primarily worked on the design and fabrication of
the vehicles frame. He eagerly anticipates marring Tara Meyering this summer as well as working at
Gentex upon graduation.
Will Vanden Bos: has greatly enjoyed working on a team developing a more fuel-efficient vehicle. Will
worked mainly with designing steering and powertrain components, and also helped extensively with the
vehicle shell construction. He is passionate about sustainable energy practices, especially with regard to
the automotive industry, and is excited to begin working at Gentex Corporation after graduating in May.
Jacob Vriesema: worked extensively on the CAD models, tire selection and electrical components as
well as helped with much of the paperwork and shell. He hopes to work with energy efficiency someday
or become a CAD consultant.
2.1.2
Documentation Techniques
Accountability for reaching project goals often took the form of informal meetings three days a week.
Team meetings were held each weekend. In the early stages of the project, these meetings mostly
consisted of brainstorming sessions and research. Additional meetings were often called in order to
prepare various assignments for the ENGR 339 class. As time went on into ENGR 340, meetings became
almost daily. At these meetings, important notes were written down and emailed out to the team, as well
as saved in the team folder on one of Calvin’s Servers (Shared/Engineering/Teams/Team06). Note that
all project documents were saved in this folder.
2.2
Scheduling
The ENGR 339 and ENGR 340 course schedule and assignments served as the framework for scheduling
tasks throughout the duration of this project. Course assignments helped move the project from concept
to completion. With such assignments serving as the framework, each task was assigned an estimated
length of time for completion. These assignments provided a schedule with concrete deadlines and also
served as project milestones. In ENGR 339, a program called OpenProj was used to create a Gantt chart
to schedule tasks. The goal here was to break milestones into tasks with a maximum execution time of 8
hours, in order to help emphasize the critical essence of time. Unfortunately, this method did not prove
very beneficial to the team. The chart became very unwieldy with so many items, and as special software
was needed open it, it was not viewed very often. This resulted in missed deadlines and late tasks.
However, in ENGR 340, the team switched to Google Calendar to schedule tasks. This proved to be a
much more beneficial tool. Having the schedule overlaid on a calendar really helped visualize when tasks
were due, and the ease of access allowed it to be checked much more frequently. This method was used
with great success for the remainder of the semester.
2.3
Budget Management
The crux of every project is its budget. Originally, Will Vanden Bos set up an estimated budget that was
updated and adjusted throughout the semester. At the beginning of ENGR 340, a preliminary budget was
approved. The team then kept track of all purchases in a spreadsheet stored on the Team Folder
9
(Shared/Engineering/Teams/Team06/Budget) in order to keep spending documented and accountable.
Section 5.1 (Cost Estimation) provides an in-depth look at estimated costs and budgeting.
2.4
Design Norms
As Christian Engineers, the team has a calling to create designs that have significance and fulfill the
cultural mandate. Their design pushed to incorporate the following principals in the design of their highmileage vehicle.
Stewardship: The overall intention of the vehicle should demonstrate careful use of the Earth’s
resources. The entire project was framed by this idea of stewardship as they strove to alleviate
dependence on fossil fuels.
Integrity: As a team, they strove to promote honesty and professionalism interacting with each
other, the professors, and any outside companies and consultants. They tried to display good
character and sportsmanship throughout the course of the project, and hope to continue this at the
Supermileage® competition.
Transparency: By maintaining an open stream of communication with all who were involved in
this project, they strove to produce consistent, reliable, and predictable solutions.
2.5
Method of Approach
Maximizing the fuel efficiency of the vehicle can be addressed in the following ways:
1. Minimizing the resistances acting on the vehicle
2. Maximizing the engine’s efficiency
3. Optimizing vehicle operation in accordance to competition requirements
Because of time and budget constraints, team Supermileage performed a preliminary analysis to identify
the factors that have the greatest potential to affect fuel economy. This analysis set a basis for project
direction and more in-depth analysis and testing.
2.5.1
Minimizing Resistances
The significant inefficiencies opposing the vehicle motion are wind resistance, rolling resistance from the
wheels, bearing resistance, and power transmission losses. These are depicted as equivalent forces in
Figure 2.
10
Figure 2: Forces acting on the vehicle during operation
A major aspect of the 2011-12 Supermileage vehicle was formulation of a design that minimizes these
resistances. An order of magnitude analysis was performed for the resisting forces using Equations 1-3.
Fdrag  C d A proj
V2
2
Eqn. 1
Frr  C rrV
Eqn. 2
Fbearing  Cb FN
Eqn. 3
Note that Cd, Crr, and Cb are coefficients of drag, rolling resistance, and bearing resistance, respectively.
Variables Aproj, FN, and V represent the projected frontal area of the vehicle, normal force, and vehicle
velocity. All these combine to form design variables for this project. Studies were done to determine the
tradeoffs between these design variables. The values which minimize resistances were then used in the
design of the vehicle. Results showed that at lower velocities, resistance due to rolling resistance
dominated. However, at a certain velocity (approximately 24mph) losses from aerodynamic drag
dominated. Figure 3 shows each resistance as a function of velocity.
11
Figure 3: Power losses
Assumptions made in this analysis are displayed in Table 1. Power loses were also calculated to
illuminate efficiency “offenders.” Note that the estimated range column specifies a maximum and
minimum value for each variable. The estimated power loss range column lists the power losses
associated with the maximum and minimum values. The difference in power loss column represents the
difference between the maximum and minimum values and therefore represents the sensitivity of that
variable to power loss.
12
Table 1: Key design variables
Design Variables
Symbol
Assumed
Value
Estimated
Range
Estimated Power
Loss Range [W]
Difference in
Power Loss [W]
Vehicle Mass [kg]
Mvehicle
52.2
40 - 90
63
77
14
Vehicle Velocity [m/s]
V
6.7
6.7 - 11.2
69
163
94
Coefficient of Drag
Cd
0.12
0.1 - 0.25
66
86
20
Projected Area [m2]
Aproj
0.75
0.5 - 1
63
74
11
Rolling Resistance
Coefficient
Crr
0.0055
0.005 -0 .01
65
102
37
Coefficient of Bearing
Friction
Cb
0.0005
0.0001 0.001
60
63
3
This analysis suggested that aerodynamic drag and rolling resistance have the greatest effect on the car
while bearing resistance is less significant. Therefore our team focused on reducing aerodynamic drag and
rolling resistance.
The easiest and most effective way to reduce aerodynamic drag is to simply reduce the vehicle’s projected
area. Other factors which effect aerodynamic drag are more difficult to quantify using basic calculations,
such as the effects of surface texture and humidity.
At low velocities, rolling resistance is the largest resistance on the vehicle. Therefore, much time was
devoted to selecting wheel components (e.g. wheel diameter, width, and tire pressure) and minimizing
vehicle weight.
The preliminary resistance calculations described above did not consider the effects of wheel alignment or
transmission losses. However, these factors still required design work and will be discussed in greater
detail in their respective sections.
2.5.2 Maximizing Engine Efficiency
Preliminary calculations suggested that increasing the efficiency of the engine by 1 percent would result
in an increase of fuel economy by roughly 86 mpg (see Appendix B for calculations). For this reason,
Team Supermileage spent significant time maximizing the fuel efficiency of the engine. With the help of
Baker Engineering, the team was able to attach the engine to a dynamometer coupled with fuel and air
flow rate instrumentation in order to determine the vehicles optimum operating rpm.
2.5.3
Optimizing Vehicle Operation
The competition requirements state that the vehicle must maintain an average velocity between 15mph
and 25mph. Rolling resistance and aerodynamic drag are proportional with velocity and thus are
minimized when velocity is minimized. However, maintaining 15mph may require the engine to operate
at a less than ideal rpm. Many successful teams in the past have approached this problem by fine tuning
13
gearing in the transmission as well as coasting and accelerating alternately. This allows the engine to
operate around its most efficient rpm. The team plans on implementing this coast and burn strategy when
they compete in the SAE Supermileage® competition.
3
Task Specification and Schedule
3.1
Project Breakdown
In working towards the ultimate goal of high fuel efficiency, the team divided major vehicle components
into subsystems. This helped clarify design and research needs. Subsystems included the following:
Engine Integration, Aerodynamic Design, Frame Design, and Power Transmission.
3.1.1
Engine Integration
The Engine Integration team handled engine modifications and engine testing procedures. Most
importantly, this group worked with Baker Engineering to test the engine on a dynamometer. This device
recorded the amount of fuel used for different engine power outputs, driving efficiency and performance
optimizations.
3.1.2
Aerodynamics
The Aerodynamics group focused primarily on devising test methods to confirm design decisions relating
to decreasing aerodynamic drag. Wind tunnel tests were one method by which this was attempted. In
addition, this group decided which material to use for the vehicle shell and how to fabricate the entire
vehicle envelope.
3.1.3
Frame Design
Team members working on the frame design subsystem were concerned primarily with creating a
lightweight yet durable frame that meets competition rules. The main tradeoff for this subsystem
included balancing material properties with weight. Steering design and wheel selection also took place
in this group.
3.1.4
Power Transmission
While the engine integration group looked at modifications to the engine, the power transmission group
focused on how to efficiently transmit power from the engine to the wheels. Shifting speeds and
coast/burn techniques were also considered in this group.
3.2
Gantt Chart, Tasks, and Calendar
As discussed earlier, a Google Calendar was used to schedule tasks and meetings for ENGR 340 in place
of the Gantt chart system. Please see the Team Folder (Shared/Engineering/Teams/Team06) for
screenshots of this calendar. An example of how the team separated deliverables with time can be found
in Table 2, below, while Figure 4 shows the work breakdown schedule (as of December 9, 2011).
14
Figure 4: Work breakdown schedule with Gantt chart
15
Table 2: List of project tasks with estimated time allocations
TASK NAME
Engine Work:
Engine Research:
Research designs from previous
teams
Research fuel injection
Research Increasing compression
ratio
Research carburetor devices
Begin contructing a dynomometer
HOURS PER
PERSON
TASK NAME
HOURS PER
PERSON
Materials Work:
Materials Research:
6 hours
First order calcs for chassis design
2 hours
6 hours
Determine 3 material choices
8 hours
6 hours
Research steering assemblies
7 hours
6 hours
Research braking assemblies
Determine frame design and
material
Materials Implementation:
Order of magnitude calcs for
various materials
Choose prefered chassis design
Constuct a CAD model of the
vehicle
Perform FEA analysis on key
components
Obtain materials
Construct chassis
Construct shell
Construct steering assembly
7 hours
4 hours
10 hours
10 hours
5 hours
Construct braking assembly
5 hours
10 hours
Engine Implementation:
Test engine with dyno
7 hours
Generate and interpret dyno data
5 hours
Modify engine componants
10 hours
Adjust to get best MPG
10 hours
Test adjustments
Iterative adjustment and tests
Aerodynamics Work:
Aerodynamic Research:
Research aerodynamic concepts
and equations
Determine how coefficient of drag
and lift affect vehicle
Design 2 shapes: models with
interior / exterior wheels
Draw 2 shapes in CAD
Create 3D plots using Steelcase
Printer
Create list of wind tunnel
components
Aerodynamic Implementation:
Build a wind tunnel test section
Perform wind tunnel tests
Generate and interpret wind
tunnel data
Make recommendation on body
shape
10 hours
10 hours
10 hours
8 hours
6 hours
6 hours
8 hours
8 hours
Optimization Work:
8 hours
6 hours
Optimization Implementation:
2 hours
Test Vehicle
Modify/Optimize vehicle based on
testing
20 hours
Race in Competition
8 hours
10 hours
8 hours
Documentation:
Verbal presentation #1
Verbal presentation #2
1 hour
1 hour
2 hours
Prepare PPFS
1 hour
-
PPFS Draft Due
Verbal presentation #3
Verb al presentation #4
Prepare final paper
20 hours
20 hours
1 hour
1 hour
20 hours
16
4
Design Process
4.1
Aerodynamics and Vehicle Envelope
The success of teams entering the Supermileage competition depends heavily upon minimization of fuel
consumption. Two key design elements in this include the shape of the vehicle shell (coined “vehicle
envelope”) and its total weight. If projected area is large, the vehicle’s drag will also increase. In
addition, increasing shell weight has a negative impact on rolling resistance (See section 4.5). The
following subsections describe initial testing, material selection, and final design specifications.
4.1.1
Initial Testing
Most Supermileage vehicles fall into two categories: wheels internal to the shell and wheels external to
the shell. The Aerodynamics group decided that an ideal way to test these alternatives was with Calvin’s
wind tunnel under the supervision of Professor DeJong. Two models were created using Pro/Engineer
software. Steelcase Inc. assisted in manufacturing these models using a Fused Deposition Modeling
(FDM) machine. The first vehicle modeled internal wheels and was called the Funnelback design. Since
the shell must cover the internal wheels, its projected area was relatively large. Figure 5 illustrates the
first model.
Figure 5: Funnelback design isometric view and dimensions (in inches)
The second model placed the wheels outside the envelope of the shell. It utilized what is known as a
Kammback design. Kammback technology, embodied on hybrid vehicles such as the Toyota Prius and
18
the Honda Insight, has been shown to increase fuel efficiency by forcing the air to separate from the end
of the chassis sooner. Figure 6 illustrates the second model.
Figure 6: Kammback design isometric view and dimensions (in inches)
The above models were tested using Calvin College’s wind tunnel over a range of velocities from roughly
40mph up to 110mph. The resulting force of drag was detected using strain gages mounted inside a test
structure. Equation 4 could then calculate a drag coefficient:
Cd 
2 Fd
v 2 Aproj
Eqn. 4
Where Fd is the drag force,  is the density of the air, and Aproj is the projected frontal area. While the
notion of finding a clear winner between the two test models might seem straightforward, the test results
were not indicative of such information (See Figure 7, below).
19
Drag Forces of Two Models
2.5
Drag Force [N]
2
Kammback
Funnelback
1.5
1
0.5
0
40
50
-0.5
60
70
80
90
100
110
Wind Velocity [mph]
-1
Figure 7: Drag forces from varied wind velocities in wind tunnel
Vibrations affecting the test equipment and imprecisions in the measurement techniques caused
uncertainty to propagate throughout the results. Since forces cannot be negative, sensible data should
only be observed above the x-axis. Note that these inconsistences could be the result of inaccurate wind
tunnel calibrations. Given more time, this team would have pursued retests.
4.1.2
Material Alternatives
Before proceeding onto shell shape design, it was important to first select a building material. While
some materials could be used in most any design, others might present challenges in the presence of
contoured surfaces. The primary materials of choice were the following: acrylic, fiberglass, Dacron, and
carbon fiber. In all these choices, the best candidate ought to demonstrate high rigidity, light weight, and
low cost. While acrylic would be ideal for a canopy-type cockpit for the driver, its manufacturability is
extremely low and its density is quite high. Fiberglass presents an excellent lightweight choice for
general use. However, initial testing using small curved molds indicated that fiberglass could not
maintain its integrity around a tightly curved surface. While carbon fiber would present an extremely
strong and lightweight solution, funds were unavailable for such an exorbitant cost. Finally, Dacron was
selected because it fulfilled all three specifications; Dacron also exhibits heat-shrinkability. The final
design utilized Dacron laminated with epoxy.
4.1.3
Final Selection
Using CAD software, the final aerodynamic shape was formed around the completed frame. This
allowed our group to visualize exactly where components such as wheels, roll bars, and engines needed to
be placed. The final shape integrated several inspirations: aspects of the wind tunnel models, small
airplane nose design, and vehicle designs from top Supermileage competitors. In the end, this group
20
produced a CAD model with an aerodynamic shell that perfectly fit outside the frame. Note that the final
design placed wheels inside the shell. Figure 8 shows such CAD model.
Figure 8: CAD model of final shell design
Note also that the internal wheels are shielded frontally by fairings. This will ideally ensure that the
airflow around the wheels remains undisturbed.
Typically when working with a laminated material like Dacron, the builder uses a mold to shape the cloth.
The process of laminating includes pinning Dacron to a mold, heat shrinking until taut, then applying a
thick coat of epoxy; together these form a single layer. Betz Industries (a Grand Rapids, MI foundry)
played a significant role in mold fabrication. Using enormous Computer Numerical Control (CNC)
machines, Betz created a 1:1 Styrofoam model per our CAD design. Figure 9 shows Betz’s contribution.
Figure 9: Styrofoam mold created and donated by Betz Industries
The final shell design also utilized a theory called sandwich concept. In an effort to maximize the
material’s efficiency, the two faces were “placed at a distance from each other to increase the moment of
21
inertia, and thereby the flexural rigidity, about the neutral axis of the structure. A comparison could be
made with a solid beam.”1 Thus the lamination schedule was as follows: 1 layer Dacron, 1 layer of 1/8 th
inch thick polyvinyl foam, 1 layer Dacron, finished with extra coats of epoxy. A schematic of this
lamination schedule is shown in Figure 10.
Figure 10: Lamination schedule for upper and lower shell
When creating the shell, the team resolved to implement a monocoque structure. In other words, the
structure would remain rigid without the help of internal structural members but rather would derive its
support through a continuous, rigid form. This design primarily works to reduce shell weight. Ultimately,
white paint was added for aesthetics. Figure 11 illustrates the finished shell (pre-paint).
Figure 11: Completed shell utilizing sandwich concept
1
"DIAB Sandwich Handbook." DIAB, 3 Sept. 1952. Web. 8 May 2012.
<http://www.diabgroup.com/europe/literature/e_pdf_files/man_pdf/sandwich_hb.pdf>.
22
4.2
Frame
The frame is an integral part of the vehicles design; it must provide the adequate structural integrity to
support vehicles loads, provide the overall shape of the vehicle, and satisfy competition safety
requirements. In addition, rolling and bearing resistances are proportional to the vehicles weight and thus
it is advantageous to reduce the vehicles total weight. For these reasons, material selection and a careful
design is important to the overall success of the vehicle.
4.2.1
SAE Requirements
Competition requirements mandate a roll bar that extends a minimum of 5 cm above the driver’s helmet
and is wider than the driver’s shoulders as shown in Figure 12. The entire vehicle must also withstand a
250 lbf force applied to the top of the roll bar at any angle. The vehicles structure must also include a
steel or aluminum fire wall that completely separates the driver from the engine. (SAE, 16-17).
Figure 12: Roll Hoop Requirements
4.2.2
Frame Overview and Material Selection
Early in the design phase the team selected a teardrop-shaped vehicle design utilizing a three-wheeled
configuration as show in Figure 13. The vehicle is divided into front and rear sections by the roll
bar. The driver, two front wheels, and a four bar linkage steering assembly occupy the front half of the
vehicle. The rear section houses the engine, starter motor, batteries, fuel container, power transmission,
and the driven rear wheel.
23
Figure 13: Preliminary frame design
The frame team developed a basic failure analysis of the main beams of the vehicle. The goal of this
analysis was to guide the team’s selection of feasible materials for the rest of the frame. Figure 13Figure
14 shows a simplified diagram of the main beams approximated loads. In this analysis, the beam was
assumed to be simply supported at both ends and all of the loads were assumed to be static with the
exception of the driver which was analyzed as an impact force calculated using the energy method
Equation 5.
[
√
]
Eqn. 5
Where δst is the static deflection resulting from the weight of our driver, h is the height the load is falling
from, and n is a correction factor. A height of 1 inch was assumed in the analysis—this accounts for the
driver entering and exiting the vehicle as well as simulating the vehicle encountering over uneven roads
and pot holes (Norton108-111).
Figure 14: Beam 1 loading diagram, all dimensions are in inches
24
This preliminary study found aluminum, steel, and wood to be feasible materials for the vehicle frame.
Our team selected aluminum 6061-T6 for its high strength-to-weight ratio, weldablility, and local
availability.
4.2.3
Overview of Design Process
After selecting aluminum 6061-T6 as the frames primary material and GR Iron and Steel our aluminum
vendor, the frame team iterated through several designs for the rest of the vehicle. This iterative process
included hand calculations, Autodesk Simulation finite element analysis, and reviews with Phil Jaspers
and Richard DeJong. Considering the lifetime of this vehicle is under a year, fatigue was not considered
in this analysis. The frame design was split into three main assemblies: main beams, front end, and roll
bar as seen in Figure 15.
Figure 15: Frame Design
The main beam assembly is composed primarily of 1.5in x 1in x 1/8in channels connected by rigidity
braces. These main beams are capable of withstanding an impact load of the vehicle hitting a 1 inch
pothole with a safety factor of 2 as seen in Figure 16. This analysis is very conservative as it does include
the additional supports added to the channels, nor the effect of the sway bars. See the appendix for
complete frame drawings and detailed stress analysis of each assembly.
25
Figure 16: Main beam FEA simulation for a 1-inch deep pothole; safety factor of 2.0
4.2.4
Final Design
The final dimensioned chassis design can be seen in Figure 17 showing a side, front, and top view. The
side view includes the approximate profile of how the driver fits into the vehicle.
26
Figure 17: Dimensioned Vehicle Chassis (all dimensions in inches)
4.3
Engine
4.3.1
SAE Requirements
Each SAE Supermileage team is given a common engine, donated by the Briggs and Stratton
Corporation. The 3.5hp base engine (Figure 18, below) is four-cycle, air cooled, carbureted, and equipped
with side-mounted valves. Teams may modify the base engine within certain bounds. For example, the
piston and crankcase may be machined or altered, but must still be identifiable as components of the base
engine. In addition, a common fuel bottle is provided to each team at the competition. Design of the
engine and body must allow for the swift (45 seconds) removal and replacement of the fuel bottle so that
competition organizers can easily measure fuel usage at the competition.
27
Figure 18: Specified Fuel Bottle and 3.5hp Base Engine
4.3.2
Testing
Internal combustion engines have been the subjects of over a century of research and implementation,
both by academia and the automotive industry. Engine efficiency is often a function of many
interdependent features and components; theoretical analysis can be very complicated and unreliable. For
this reason, the team decided to implement the use of an engine dynamometer. With the ability to
empirically test the engine, the team would be able to objectively quantify engine improvements.
Additionally, the team could discover optimum engine operation parameters, e.g. the rpm at which the
engine performs most efficiently.
Dynamometers are extremely expensive and hard to make. Fortunately however, a local business, Baker
Engineering Inc, from Nunica, MI, was receptive to the idea of partnering with the team in testing and
modifying the engine. They have professional-quality small engine dynamometer test equipment. Baker
Engineering has years of experience designing and building performance gas engines, both large and
small.
28
Figure 19: Schematic of a basic engine dynamometer
Similar to that of Figure 19, a dynamometer couples the petrol engine to a DC motor. The power then can
be dissipated through resistance wires powered by the DC motor. Because the motor is mounted on nonfixed trunnions, a fixed lever-arm mounted to the DC motor gives the torque acting on the motor by
applying a force to the load cell. A tachometer then measures the angular velocity of the output shaft.
The engine power then, is given by Equation 6, when ω is in radians per second.
Eqn. 6
From this equation, the peak engine power can be found as a function of rpm. To find peak efficiency, the
rate at which fuel is consumed must also be measured. The addition of a fluid flow-meter giving the fuel
consumption rate can give the effective fuel-volume efficiency (Joules/mL), calculated by Equation 7.
̇
Eqn. 7
By using a dynamometer, Calvin Supermileage had the ability to quantify any modifications made to the
engine. This allowed the team to definitively know if a modification had improved the efficiency of the
engine. By running the engine at different rpms, the team was able to determine the most efficient engine
speed. This information was then used when designing the gear ratios in the transmission and power train.
4.3.3
Alternatives
Of the hundreds of ways the engine could be modified, the team chose just three to consider. Many other
options exist, but time and budget constraints forced the team to limit the scope of possible engine
modifications to those that initially seemed most feasible, effective and affordable. Figure 20 shows the
options considered.
29
Figure 20: Modification options for the petrol engine
Compression Ratio and “Running Lean”
Without any major design modifications to the engine itself, certain parameters can be adjusted to
increase fuel efficiency. With fuel delivery executed by the carburetor, adjustments can be made to the
air-to-fuel mass ratio or AFR.
̇
̇
Eqn. 8
When the AFR matches the molecular ratio for a complete combustion of the fuel, it is called the
stoichiometric AFR, and is about 14.7:1 for gasoline (Stevens). Typically, a richer AFR (more fuel and a
smaller AFR) can produce more power, while a leaner AFR can product more efficiency. The AFR for
best efficiency varies from engine to engine and is a function of many design variables. Modern cars have
found peak efficiency anywhere from 15.7:1 to 17.6:1 (Stevens, and Edgar). The team, using the
dynamometer, could adjust the carburetor to test various AFRs and establish the best ratio for fuel
efficiency.
Another engine modification under consideration was the compression ratio. The compression ratio is the
ratio of the cylinder volume at the bottom of the stroke (bottom dead center, or TDC) to the volume at the
top of the stroke (TDC), Equation 9 (Cengel, 361).
Eqn. 9
A higher compression ratio results in greater pressures during the combustion phase of the engine cycle.
The CR could be increased by adding material (through welding) to the combustion chamber, thus
reducing the VTDC. These higher pressures can in turn result in greater energy release from the combustion
cycle. In an ideal engine cycle (Otto cycle) with air modeled as an ideal gas, the efficiency of the engine
is given by Equation 10 (Cengel, 361). Here, k is a constant specific heat ratio for gasoline equal to 1.4.
Eqn. 10
Even though no engine can perform as thermodynamically ideal, it is interesting to see the increase in
efficiency as a function of compression ratio. The base engine provided by Briggs and Stratton has a
compression ratio of 6:1 (Briggs and Stratton FAQ); increases up from 6 are shown in Figure 21.
30
Efficiency Increase with Higher Compression Ratios
30%
25%
20%
15%
10%
5%
0%
6
7
8
9
10
11
12
13
14
Compression Ratio
Figure 21: Increasing compression ratio provides increased engine efficiency
There are several drawbacks to increasing the compression ratio. First, an increase in CR drives an
increase in cylinder pressure during the engine cycle. The materials and construction of the engine head
and cylinders might not withstand the pressure increases. Second, with the pressure increases come
temperature increases. At higher temperatures, engine components see greater stresses and could melt. In
addition, if the fuel reaches its auto-ignition temperature before the spark plug fires, a spontaneous
combustion could take place creating engine knock. Figure 22 shows the nominal ignition temperature
(Transportation Energy Data, 1) for the competition fuel (isooctane) in relation to the increased
temperatures.
In a thermodynamically ideal engine model, any compression ratio greater than 8 could produce
temperatures above the auto ignition temperature for isooctane. Several things, however, will likely allow
for these high temperatures. First, the actual engine is not thermodynamically ideal and will therefore lose
heat loss during the compression cycle. Note also that the temperature will not increase as dramatically as
shown in these calculations. Second, the nominal ignition temperature is not measured in conditions at all
similar to the inside of an engine, and may in fact be several hundred degrees higher than nominal (Smyth
and Bryner 247). Because of this, it is not likely that engine knock will be a problem.
31
Corrected AI temperature = 1291 deg F
Nominal AI temperature = 781 deg F
Figure 22: Temperature increases inside the cylinder will likely not cause engine knock
Fuel Injection
The stock 3.5hp Briggs and Stratton comes with a fixed jet carburetor. Essentially, carburetors deliver
fuel to the combustion chamber as a function of the flow-rate of air into the cylinder. The intake air passes
through a venturi “throat” in the carburetor. The increase in air velocity creates a pressure drop which
draws in liquid fuel through a small orifice in the sidewall. The flow-rate of the air (controlled by the
throttle) then determines the amount of fuel drawn into the combustion stream. The carburetor can be
adjusted (as suggested above) to different proportions of fuel and air (AFR, air-fuel ratio). A basic
diagram of a carburetor is found in Figure 23.
32
Figure 23: A basic carburetor draws liquid fuel into the combustion stream.
Fuel injection is another technology for delivering fuel to the combustion stream, but does so quite
differently from carburation. Whereas the carburetor draws liquid fuel into the air with a venturi pressure
drop, a fuel injector uses tiny jets to atomized the fuel and spray it into the combustion stream based on
parameters such as air flow rate, engine speed, throttle, temperature and others (Stone, 122). The
parameters are measured with sensors and processed by an engine control unit, or ECU. The ECU
determines the amount of fuel to inject based on algorithms programmed into the ECU. The flow diagram
showing a fuel injection system is shown in Figure 24.
Figure 24: The engine control unit gathers information to determine the timing and amount of fuel
The injector can either be located before the intake valve (port injection) or as part of the combustion
chamber itself (direction injection). In either case, atomized fuel is mixed with air for combustion in the
cylinder, Figure 25.
33
Figure 25: Left, a typical fuel injector sprays atomized fuel2
For maximum efficiency, fuel injection has several advantages over traditional carbureted engines. First,
the fuel is atomized when ignition occurs versus a liquid fuel mixture in carburation. This atomized fuel
burns more efficiently than liquid fuel and results in greater engine efficiency (Walton, 98). Second, fuel
injection is much more responsive to the operating environment; the ECU can vary the amount of fuel
based on sensor data and react instantly to changes in temperature and pressure. This means less wasted
fuel, and better AFR at all operating speeds. Third, there is no venturi “throat” that constricts the intake
flow which results in easier engine “breathing” and less flow-power loss.
Unfortunately, converting a carbureted engine to one with fuel injection is no easy task. A host of new
engine components must be affixed to the engine: sensors, injections, pumps, an ECU, etc. It would be a
challenge merely to get all these new components to work together to that the engine operates at all; it is
another challenge to optimize the operation so that the engine runs more efficiently. Figure 26 shows
some pros and cons of fuel injection fuel delivery system.
2
http://upload.wikimedia.org/wikipedia/commons/2/29/Injector3.gif). Middle: direct injection sprays fuel into the cylinder. Right, port injection
sprays fuel upstream of the intake valve (Walton, 99)
34
Figure 26: Fuel injection is costly and complicated, but more efficient than carburation.3
Without the advice of engineers at Baker Engineering Inc., it is unlikely that Calvin Supermileage would
be able to convert the engine to run with fuel injection.
Combustion Chamber and Head
The Briggs and Stratton base engine has a side-valve arrangement, similar to the one shown in Figure 27.
In this arrangement, the valves and spark plug are offset from the center of the piston. The theoretical
fluid dynamics involved in the flow and combustion are very complicated and difficult to perform
accurately. Despite this, there are some generalizations than can be made about combustion chamber
design.
Side valve configurations have an upper limit of 6:1 for the allowable compression ratio. This is because
the explosion trajectory is not in line with the piston motion, and the zero-clearance “squish” region on
one side of the piston can cause pockets of high pressure resulting in engine-knock (Stone, 100). In
addition, the flow of the air-fuel mixture can create poor burn profiles in a side-valve configuration. Many
other designs exist, each with a particular design benefits. Figure 28 shows several common combustion
chamber designs.
For maximum efficiency, it is important to ensure an even fuel mixture throughout the chamber, minimize
flow-power losses through valve and port design, and low-mechanical wear (Stone, 100. Pulkrebek, 249,
Second Chance Garage. Morgan.). With the cooperation of a local machine shop, Calvin Supermileage
would be able to design a new combustion chamber with an overhead valve configuration. Additional
3
Stone, 121. Walton, 95-99, Pulkrebek, 179-181
35
design would be needed to arrange the valve push-rods. Both designs (a) and (b) could be implemented
with the need for additional piston modification. Head modifications are quite common among
performance enthusiasts, and so the feasibility is quite high for this engine modification.
Figure 27: Base engine side-valve combustion chamber, offset from cylinder
Figure 28: Combustion chamber designs: (a) wedge chamber, (b) hemispherical head, (c) bowl in piston,
and (d) bath-tub head (Stone, 104).
36
4.3.4
Final Modifications
Calvin Supermileage examined several options for engine modification, and determined the need for
dynamometer testing. They also implemented a new carburetor and exhaust, new flywheel and starter,
and an altered head design.
A Mikuni carburetor was installed in place of the standard. It offers an adjustable air-to-fuel ratio (AFR).
Maximum efficiency is typically produced by “running lean,” i.e. running the engine with excess air.
During dynamometer testing, an oxygen sensor was used to monitor the AFR. Depending on the
atmospheric conditions, maximum engine efficiency was found with and AFR between 16:1 and 17:1.
This ensures that the fuel is as completely burned as possible. The carburetor was mounted to the intake
port with a straight-shaft aluminum intake, fabricated by the team.
To start the engine during the competition run, an electrical starter was needed. The stock engine
flywheel was replaced with a purchased flywheel that had starting teeth on one side. The electric starter
was mounted to a custom bracket fit to the engine. The starter is powered by a 12V battery, and can be
fired by a switch mounted on the steering column of the vehicle.
To increase the engine efficiency, the head was modified for higher compression ratios. The stock B&S
engine has a compression ratio of 6.6:1. The engine head was filled in with aluminum weld, bringing the
compression ratio up to 7.2:1.
4.4
Steering
4.4.1
SAE Requirements
The steering mechanism is an important characteristic of the vehicle, which must both enable safe and
effective maneuvering of the car, and satisfy the specifications set out by SAE. The track that the vehicle
will compete on is a 1.6-mile oval test track shown in Figure 29, below.
37
Figure 29: Test track for Supermileage® competition
This in itself doesn’t require much of a turning radius, however the vehicle must also pass a
maneuverability course before it is allowed to compete. This course, as illustrated in Figure 30, consists
of completing an untimed 180 degree turn, and then weaving in and out of 4 cones placed 25 feet apart in
under 15 seconds.
38
Figure 30: Maneuverability course
In order to successfully complete this course then, the vehicle must have a maximum turning radius of 50
ft. Another requirement by SAE is that the steering must have a “natural” response. In other words, if the
driver turns the steering wheel left, the car will go left, and vice-versa.
4.4.2
Alternatives
As the basic components of the Supermileage vehicle are quite similar to a go-kart, go-kart steering
systems were studied and analyzed. There are two main designs for go-kart steering systems: Wagon
Style systems, and steering knuckle systems.
Wagon Style System:
The first type of system is the most classic, but also the most elementary. This simple system simply
consists of two wheels permanently fixed to an axle, which is then rotated by the steering column. See
Figure 31 below.
39
Figure 31: Wagon style steering mechanism
Steering Knuckle System:
This system is more complicated; however it also solves many of the problems of the Wagon wheel
type. The steering knuckle system consists of wheels mounted to “knuckles”, which are in turn mounted
to an axle. These knuckles are then driven by a 4-bar linkage connected to the steering column, as shown
in Figure 32. Because it is driven by a 4-bar linkage, this system is much more stable. Another advantage
of being driven by a 4-bar linkage is that by adjusting the lengths of various bars, optimizations and
changes can be implemented (Steering Systems).
Figure 32: Knuckle steering system
40
4.4.3
System Selection
Because of its many advantages, the steering knuckle system was employed in our Supermileage
vehicle. The final product is similar to Figure 33.
Figure 33: A knuckle steering system implemented in vehicle
4.5
Rolling Resistance
Rolling resistance is a major inefficiency that occurs between the tires and the ground. For a cyclist,
rolling resistance can account for up to 80% of drag at speeds of 6mph and as much as 20% at speeds of
25mph. Therefore, decreasing rolling resistance would make the Supermileage vehicle much more
efficient. When a tire holding up weight bulges against the ground it increases the contact area (See
Figure 34). This area is directly related to the amount of friction the tire feels from the ground. To
minimize the friction one needs to decrease this contact patch by investing in a thinner tire or increasing
the tire pressure.
41
Figure 34: Contact area and rolling resistance
4.5.1
Testing and Calculations
There was no testing on different tires due to the high upfront costs of buying tires and lack of a testing
fixture similar to Figure 35. Typically, tires are tested on a rolling drum while a known weight is pressed
down on the tire. The drum rolls at a known speed and the torque required to keep the drum rolling
equates to a rolling resistance coefficient.
Figure 35: Rolling resistance test fixture
To simplify, the team considered the power to propel the vehicle forwards as a function of the rolling
resistance, weight and velocity. Thus with just a researched rolling resistance constant the team could
determine the power to overcome this drag using Equation 11, below.
Prr = Crr Nv
Eqn. 11
42
Where Crr is the rolling resistance coefficient, N is the weight on the tire and v is the velocity of the
vehicle. Since the Supermileage vehicle is much heavier than a road bike, it was very important to note
the weight in these calculations.
4.5.2
Alternatives
Among bike tire enthusiasts, there is some rolling resistance data—but it is not common for a bike tire
company to publish these numbers as they are dependent on too many factors: weight, tire pressure,
temperature, speed...etc. However, as one can see in Table 3, rolling resistance coefficients for high-end
tires are quite small, but when multiplied by weight and velocity the magnitude of the power loss due to
the rolling resistance can be upwards of 70 watts.
Table 3: Rolling resistances
Tires
Crr
Veloflex Carbon
0.0049
Gommitalia Platinum
0.0053
Vittoria Corsa Evo CX
0.0054
Vittoria Corsa Evo KX
0.0057
Continental Competition 0.0059
Many cyclists choose a larger diameter tire for its lower rolling resistance. As said before, the rolling
resistance is a function of several variables. To simplify, the analysis only considered the diameter.
Equation 12 relates the coefficient of rolling resistance to the diameter D of the tire and the amount of
vertical deflection z.
Crr =
z
D
Eqn. 12
Using this equation, tires from Table 3 have a vertical deflection of about 700-1000 micro-inches. Note
that this analysis assumes a constant deflection amongst tire options. Using the constant deflection
assumption and a 28-inch tire, the coefficient of rolling resistance becomes 0.0057 for a high-end tire.
4.5.3
Final Selection
There are hundreds of bike tires to choose from with differing coefficients of rolling resistance, price and
size. The order of magnitude calculations discussed in section 2.4 was used to determine which tire
diameter would optimize the aerodynamic drag and rolling drag. Figure 36, below, shows the power loss
(in watts) of the combined drag and rolling resistances as a function of the tire diameter. An optimum
diameter was found using the following equations for power loss in the aerodynamic drag and rolling
resistance.
Eqn. 13
43
√
Eqn. 14
Eqn. 15
By taking the derivative of Presist with respect to D and setting it equal to zero, a minimum was
determined. The optimum tire diameter becomes:
é zW ù
Dopt = ê
2ú
ë rC1Cd v û
2/3
Eqn. 16
Plotting this for a few velocities between the required 15-25mph yielded Figure 36. For example, the
optimal tire diameter that minimizes the power losses due to aerodynamic drag and the rolling resistance
for the vehicle traveling at 20mph is about 24 inches. However, this poses an interesting dilemma:
lowering the vehicle diameter also increases the rolling resistance coefficient. Ultimately the team
decided that it was more important to reduce rolling resistance than aerodynamic drag given the vehicle
operating speeds. Using large diameter tires will provide excellent rolling at the cost of lowered
aerodynamic performance. Again, this was justified given the SAE competition speed regulations (must
maintain an average of between 15-25 mph). After these considerations, the team selected Velocity
Escape 700c 32H Black MSW rims with Continental 22mm tubular tires. These tires have a maximum
internal pressure of 200 psi, about double what many bikes use.
Figure 36: Optimum tire diameters
44
4.6
Electrical Subsystem
The SAE competition rules state that each vehicle must exhibit brake lights as well as three kill switches.
Team Supermileage designed two internal circuits to connect the engine to the fuel injector, as well as the
lights to the starter. All circuits will be fitted with appropriate fuses.
4.6.1
Engine and Fuel Injector Circuit
According to competition rules, each of the three kill switches must be able to stop the engine and any
fuel injection system. The difficulty of this circuit design comes in how each of the components shuts
down: the engine requires a closed circuit to stop; the fuel injector requires an open circuit to stop. The
circuit shown in Figure 37 designed to comply with the rules.
Figure 37: Engine and fuel injector circuit diagram
Most of the wires were fit inside the frame. The circuit will use a 12V battery, firmly mounted behind the
firewall. The vehicle-wiring scheme can be seen in Figure 38, below. Colored wires help distinguish
circuits.
Figure 38: Engine and fuel injector vehicle circuit layout
45
4.6.2
Brake Lights and Starter Circuit
The second circuit contained brake lights and the engine starter. Lights and engine starter both will
require a momentary single pull single throw (SPST) switch to allow them to be turned on only when they
are being used. Figure 39 shows the circuit diagram. Figure 40 shows the vehicle circuit configuration.
Figure 39: Brake lights and engine starter circuit diagram
Figure 40: Brake lights and engine starter vehicle layout
46
5
Vehicle Costs
5.1
Cost Estimation Development
5.1.1
Registration Costs
The registration costs for the SAE Supermileage® competition are unfortunately not cheap. Registration
cost $600, although this did include a “donated” engine.
Table 4: Registration costs
Registration
Item Description
Registration Fee
Cost/Item
$
Qty
600.00
Total Cost
1
Sub Total
5.1.2
$
600.00
$
600.00
Body and Frame Costs
The body/frame portion of the budget was surprisingly cheap. The team purchased about $30 worth of
aluminum, a few shoulder bolts, and a few other miscellaneous parts. This brought the total spent on the
Body/Frame to be $50. In addition, Calvin College donated about $10 worth of aluminum and brass,
which the team used to make the axles for the front wheels. The team did all part fabrication and welding
themselves in an effort to keep costs down.
Table 5: Body and frame costs
Body/Frame
Item Description
Aluminum Channel (1.5"x1"x0.125")
Aluminum Tubing (1.5"x1.5"x0.125")
Shoulder Bolt
5.1.3
Cost/Item
$
$
$
Qty
1.80
14
1.85
3
10.22
2
Sub Total
Total Cost
$
$
$
$
25.20
5.55
20.44
51.19
Wheels/Brakes/Transmission
The wheels/brakes/transmission/steering aspect of the budget was a little pricier. As mentioned earlier,
minimizing rolling resistance was a huge priority, and so our team was willing to spend heavily on wheels
and tubes to aid this minimization. Another pricy item in this category was the thermoplastic bearings.
These were not cheap, but enabled us to save several pounds of weight.
47
Table 6: Wheels/Brakes/Transmission/Steering Costs
Wheels/Brakes/Transmission/Steering
Item Description
Front: rims + spoking
McMaster Steering fasteners
McMaster Steering tie-rods
McMaster transmission sprocket
McMaster transmission keyed shaft
Comet: Al sprocket and hub
Rear wheel: (w/ Int. Hub)
Tubes
Thermoplastic Bearings
Cost/Item
$ 140.00
$
9.81
$
11.88
$
9.96
$
31.50
$
62.00
$ 248.00
$
85.00
$ 138.85
Qty
2
1
1
1
1
1
1
3
1
Sub Total
5.1.4
$
$
$
$
$
$
$
$
$
Total Cost
280.00
9.81
11.88
9.96
31.50
62.00
248.00
255.00
138.85
$
1,047.00
Electrical Costs
The electrical costs were pretty reasonable. The taillights cost about $45, but otherwise most of the cost
came from miscellaneous wires and switches.
Table 7: Electrical Costs
Electrical
Item Description
Mcmaster wire organizers
DPDT Switches
Lights
Lowes: 14gage wires
RadioShack: wires and connects
Cost/Item
$
28.72
$
3.99
$
45.22
$
32.37
$
16.26
Sub Total
5.1.5
Qty
1
2
1
1
1
Total Cost
$
28.72
$
7.98
$
45.22
$
32.37
$
16.26
$
130.55
Engine and Powertrain Costs
The Engine expenses stemmed mainly from the purchase of a fuel-injection kit. This cost the team
$512. Other items purchased included fuel-lines and insulation to wrap the engine in. In addition, the
team received support from Baker Engineering in testing and modifying the engine. They allowed us to
run our engine on a dynamometer and gave advice on how to best proceed with modifications and fuelinjection installation. This was estimated to be about $750 worth of time and help which Baker
Engineering donated.
48
Table 8: Engine and Powertrain Costs
Engine
Item Description
Fuel Injection Kit
Nunica Marathon Engine Petrol
Gasket Material/Exhaust
Insulation
Cost/Item
$ 512.00
$
18.62
$
35.00
$
20.00
Qty
1
1
1
1
Sub Total
5.1.6
$
$
$
$
Total Cost
512.00
18.62
35.00
20.00
$
585.62
Shell Costs
The Shell cost about $1,000 for Dacron material, epoxy, resin, and foam. This was laid up over a
Styrofoam plug in a “sandwich-core” manner to create the shell. The Styrofoam plug was donated by
Betz Industries and is estimated to be valued at about $500.
Table 9: Shell Costs
Shell
Item Description
Betz Styrofoam molds (donation)
Dacron Covering
Dacron Covering (reorder)
Vinyl Foam
Vinyl Foam (reorder)
Duratec StyroShield
FibRelease
MEKP Hardener
System West Epoxy
System West Epoxy (reorder)
Paint Brushes (Harbour Frieght)
Fields Fabric: layup fabric
System West Hardener
Mcmaster shell rubber strip seal
Sawhorse Materials
Lowe's Paint Supplies
Epoxy Pumps
Cost/Item
$
$
6.85
$
7.34
$
29.85
$
34.93
$ 133.27
$
33.61
$
6.27
$
99.99
$
39.99
$
15.30
$
2.97
$
45.99
$
63.05
$
46.41
$
42.45
$
14.99
Sub Total
Qty
2
10
5
7
2
1
2
3
1
1
1
10
1
1
1
1
1
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
Total Cost
68.50
36.70
208.95
69.86
133.27
67.22
18.81
99.99
39.99
15.30
29.70
45.99
63.05
46.41
42.45
14.99
$
1,001.18
49
5.1.7
Testing Equipment
Testing equipment included a load cell that had to be purchased for dynamometer testing and strain gages
that were used in wind tunnel testing. This totaled about $400.
Table 10: Testing Equipment Costs
Testing Equipment
Item Description
Baker: Test Load Cell
Strain Gages
Cost/Item
$ 374.76
$
19.60
Sub Total
5.1.8
Qty
1
1
$
$
Total Cost
374.76
19.60
$
394.36
Total Costs
Total monetary costs spent on this project totaled $3,809.90. Note that our team received a $300
donation, which brought the total cost to the engineering department down to about $3,500. It is difficult
to quantify donations of parts and time in financial terms, but it is estimated that without the donations
received, this vehicle would have cost around $5,000.
Because this vehicle is a one-time project, it is a little difficult to have a “production cost.” For the
purposes of this project, production costs were assumed to take into account the cost of designing,
constructing, and optimizing the vehicle. This total cost would then be exactly the same as shown above,
with the addition of design and construction time. It is estimated that this project required at least 500
hours per person. Therefore if we assume that each team member was paid $25/hour, the total cost of this
project was $125/hr. At this rate, the total cost of labor/design/construction works out to be $62,500, and
total vehicle value equals $67,500.
50
6
Conclusion
The above sections document the feasibility, design, and fabrication of a vehicle to compete in the SAE
Supermielage® completion by Team 6. Specific design solutions outlined above provide insight into the
following vehicle categories: aerodynamics, engine optimization, frame design, engine design, and power
transmission. These design solutions were selected in effort to minimize vehicle inefficiencies while also
maintaining the SAE Supermileage® rules. Looking back, in addition to successfully implementing these
designs, Team 6 believes they have learned valuable team skills throughout this project. Team 6 has
greatly enjoyed assessing and overcoming the many challenges that came their way throughout the year,
and is looking forward to seeing how the vehicle holds up in competition!
51
7
Acknowledgements
Many people offered technical assistance and gave advice toward this project. We would like to
especially thank the following people:
Professor Ned Nielson (Calvin College)
Professor Richard Dejong (Calvin College)
Professor Matthew Heun (Calvin College)
Phil Jasperse (Calvin College)
Briggs and Stratton
Ren Tubergen (Industrial Consultant)
Dave Jones (Steelcase)
Bryan Stratton (Intertek)
Evert Klomp (Kentwood Cycle)
Craig Overweg (Reliable Automation)
Jeff VanKuiten (Betz Foundry)
Mark Dorner (Baker Dorner)
Joe Flickweert (Supermileage 2011 team member)
In addition, we would also like to thank our families and friends for giving us support and encouragement
in undertaking this project.
52
8
References
"2012 SAE SUPERMILEAGE® RULES." SAE International. Web. 17 Nov. 2011.
<http://www.sae.org/domains/students/competitions/supermileage/>.
Aleklett, Kjell, Mikael Hook, and Kristofer Jakobsson. "The Peak of the Oil Age." Energy Policy 38.3
(2010). Mar. 2010. Web. 17 Sept. 2011.
<http://www.tsl.uu.se/uhdsg/publications/peakoilage.pdf>.
"Carburetor." Wikipedia, the Free Encyclopedia. Web. 09 Oct. 2011.
<http://en.wikipedia.org/wiki/Carburetor>.
engel, unus A., Robert . Turner, and ohn M. Cimbala. Fundamentals of Thermal-fluid Sciences.
Boston: McGraw-Hill, 2008. Print.
"Combustion Chambers (and a Little Engine Theory)." Antique Auto and Classic Car Restoration How
To. Web. 09 Oct. 2011. <http://www.secondchancegarage.com/public/585.cfm>.
"Dynamometer." Wikipedia, the Free Encyclopedia. Web. 17 Nov. 2011.
<http://en.wikipedia.org/wiki/File:Dynamometer01CJC.svg>.
Edgar, Julian. "AirFuel Ratios." Auto Speed. Web. 17 Oct. 2011. <http://autospeed.com/cms/title_TuningAirFuel-Ratios/A_1595/article.html>.
"File:Dynamometer01CJC.svg." Wikipedia, the Free Encyclopedia. Web. 09 Dec. 2011.
<http://en.wikipedia.org/wiki/File:Dynamometer01CJC.svg>.
Engineering Scratch Drive. <S:\Engineering\Scratch\ENGR 339\SAE Supermileage SDP>.
53
"Frequently Asked Questions." Briggs & Stratton. Web. 17 Oct. 2011.
<http://www.briggsandstratton.com/engines/support/frequently-askedquestions/Engine%20compression%20ratio/>.
"Fuel Injection." Wikipedia, the Free Encyclopedia. Web. 09 Oct. 2011.
<http://en.wikipedia.org/wiki/Fuel_injection>.
"Getting A Head." Ex-LibrisOzebook, Rare, Out-of-print, Collectible, Historic and Originalelectronic
Books (ebooks, E-books or Digital Books) on CD ROM, CD-ROMor DVD, Email or Download.
Web. 09 Nov. 2011. <http://www.ozebook.com/compendium/t500_files/morgan/head.htm>.
Norton, Robert L. Machine Design: an Integrated Approach. Upper Saddle River, N.J: Pearson, 2010.
Print.
"President Obama Announces Historic 54.5 Mpg Fuel Efficiency Standard." NHTSA. National Highway
Traffic Safety Administration, 29 July 2011. Web. 17 Sept. 2011. <http://www.nhtsa.gov/>.
Pulkrabek, Willard W. Engineering Fundamentals of the Internal Combustion Engine. Upper Saddle
River, NJ: Prentice Hall, 1997. Print.
Riley, William F., Leroy D. Sturges, and Don H. Morris. Mechanics of Materials. Hoboken, NJ: John
Wiley, 2007. Print.
Smyth, Kermit C., and Nelson P. Bryner. "Short-Duration Autoignition Temperature Measurements For
Hydrocarbon Fuels Near Heated Metal Surfaces." Fire on the Web. NIST, 1997. Web. 17 Oct.
2011. <http://fire.nist.gov/bfrlpubs/fire97/PDF/f97188.pdf>.
Stevens, Derek. "Fuel Economy Tuning - Tech Review - Honda Tuning Magazine." Honda & Acura
Tuning, Engine Tuner, Parts Review, Drag Racing - Honda Tuning Magazine. Web. 17 Nov.
2011. <http://www.hondatuningmagazine.com/tech/0510ht_fuel_economy_tuning/index.html>.
54
Stone, R. Introduction to Internal Combustion Engines. London, UK: MacMillan, 1985. Print.
"Transportation Energy Data Book." Untitled. Web. 17 Oct. 2011.
<http://cta.ornl.gov/data/appendix_b.shtml>.
Walton, H. "How Good Is Fuel Injection." Polular Science Mar.-Apr. 1957: 88-93. Web.
55
9
Appendices
9.1
Appendix A: Wind Tunnel Stress Calculations
Derivation for Equation 7:
56
9.2
Appendix B: EES Order of Magnitude Calculations
57
58
9.3
Appendix C: MathCAD Frame Calculations
59
60
61
62
63
64
65
66
67
68
9.4
Appendix D: FEA Frame Simulations
1.
2.
3.
4.
Main Beam Stress Analysis
Rigidity Bracing for Main Beams
Front End Stress Analysis
Roll Bar Stress Analysis and Material Removal
1. Main Beam Design.
Calvin Supermileage
2/15/12
Selection: 1.5x1x1/8in Channel. Length = 66in
Beam Loading
Static Loads for one beam.
Loads
# of loads
Point Shell
5.56 lbf
4
Point driver
45 lbf
1
Point engine
22.75 lbf
1
Dist driver
0.938 lbf/in
1
Dist overall
10/66 lbf/in
1
Assumes vehicle weight of 110 lbf; driver weight of 135lbf.
Subtotal weight / Beam
22.24 lbf
45 lbf
22.75 lbf
22.5 lbf
10 lbf
Reality Check:
Compare theoretical and algor results for a simple loading case. 100lbf applied in the center of the beam
(33in).
69
Theoretical deflection = 0.415in; Algor simulated deflection = 0.435 in.
Impact Force Simulation
To simulate the vehicle hitting a pothole, the drivers load is considered to be an impact force. The Impact
force is calculated using the energy method as described in Norton on page 108.
Impact Load Determination For Channel 1.5x1x1/8 in. Length = 66in.
70
Deflections due to drivers static load.
At point load, deflection =0.130in; distributed load, deflection range from 0.130in to 0.192in
“if the weight is dropped on a beam, the static deflection of the beam at the point of impact is used”
(Norton P109 middle paragraph).
CASE 1: impact load height = ¼ in
CASE 2: impact load height = 1 in
CASE 3: Static Load
Case 1: Impact Loading height = 0.25in
71
Minimum factor of safety = 2.96 (impact load height = 1/4in)
Maximum deflection = 0.79in (impact load height = 1/4in)
Case 2: Impact loading height = 1in
72
Minimum factor of safety = 2.0 (impact load height = 1in)
Maximum deflection = 1.14in (impact load height = 1in)
Case 3: No Impact loading, assume static loading.
Minimum factor of safety = 6.49 (static loading)
73
Maximum deflection = 0.375in (static loading)
Case 4: Static Loading Under Roll Bar Test
Minimum factor of safety = 2.86 (static loading)
Close up
Maximum deflection = 0.69in (static loading)
74
2. Rigidity Bracing
Displacement in the horizontal direction. Loading: 1in impact. 30 degree, NO BRACING!
Displacement in the horizontal direction. Loading: 1in impact. 30 degree
Displacement in the horizontal direction. Loading: 1in impact. 30 degree, WITH 2 BRACING! (25,51in)
3. Front End Stress Analysis
Calvin Supermileage
2/15/12
Selection: 1.5x1.5x1/8in Tube. Length = 20in
75
Reactions for no impact loading (static) (Ra = 78.8lbf, Rb = 48.7lbf)
Max displacement magnitude = .0081in (static loading condition)
Minimum factor of safety = 20
4. Roll Bar Stress Analysis
76
Mesh Percent
Max Stress
(PSI)
Roll bar with no material removed. Meshing example
100
70
40
20
1700
2700
4700
5700
10
6000
With material removed for weight.
MODEL: LOTS
Top beam stresses match models above, verifying the model.
Vertical 250 lbf load; overall
77
Vertical 250 lbf load; bottom
Vertical 250 lbf load; side joint
Simulated at an angle.
78
Angled 250 lbf load; overall
79
9.5
Appendix E: Detailed Frame Design
80
81
82
83