ME 441 Senior Design
CUA Hovercraft – Class of 2008-2009
ME 441 Semester Summary
12/4/08
Joe Cochrane, Aldo Glean, James McMahon, Omar Monterrubio, Kalin Petersen
Presentation Outline
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Project purpose
System requirements
Hull and deck
Lift calculations
Skirt construction
Lift engine modifications/mount
Lift fan justification
Thruster justification/testing
Thruster housing design
36 V Power system/alternator testing
Goals for next semester
Purpose
To develop an autonomous hovercraft for
carrying landmine detection hardware for the
facilitation of humanitarian efforts to de-arm
post conflict mine fields.
System Requirements
• Sufficient deck space to accommodate
components
• Cushion pressure less than 8 psi (pressure
required to trigger a landmine)
• Remote maneuverability
• Minimum payload capacity: ~562 lb
- Does not include weight of hull or possible counterbalance weight
Hull and Deck
• Equipment requirements:
• Minimum area: ~50 ft2
• Does not include obscure equipment footprints or additional
equipment
• Radar antenna spacing
• Modeled deck layout
• Proposed size: 7’x10’
6’x10’ Deck Size*
7’x10’ Deck Size*
*configurations are tentative
Hull and Deck
• Hull is ~3x bigger than last year’s, but conceptual
design was retained
• Proven design
• Simplicity
• Time and money invested
• Took approximately 6 weeks to complete
construction
• Next semester:
• Waterproofing: drain holes and polyurethane
Hull and Deck
Hull: I-beam Testing
• Conducted “pullout test” on sections of base to Ibeam and deck to I-beam connections
• Test shows connections can withstand over 15 psi
• Connections must be able to withstand at least 7.7
psi
• Factor of safety of at least 1.94
Calculations
Hull: I-beam Testing
Lift Calculations
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Fluid dynamics reexamined for the lift system
Cushion pressure: 0.065 psi
Required flow rate: 4010.6 cfm
Inside hull pressure: ~0.72 psi
Calculations
Skirt
• Maintained previous skirt design
• Used same material (ballistic nylon)
• Went to Cambridge Canvas & Sail Loft in
Cambridge, MD to have skirt professionally
sewn
Skirt
Hull and Skirt Assembly
Lift Engine
• Zenoa G50 Fan Cooled Engine
– 45 hp @ 5800 rpm
– 2 stroke, Twin Cylinder, Horizontal Opposed
• Engine reorientation required intake manifold modifications
• Intake manifold modifications are complete
• Engine fully functional in new orientation
• Next semester:
– Exhaust modifications
– Engine shaft-lift fan-alternator connection
– Engine mount
Lift Engine
Modification
Original
Conceptual Engine Mount Design
Top views
Side view
Lift Fan
• Previous lift fan model and size determined sufficient for
project requirements
Thrusters
• During the summer, gas engine was tested
extensively
• Decision was made to switch to electric motors due
to difficulty with tuning and inconsistency of gas
engine
• Researched electric model airplane motors, went
with largest model
Thrusters
• Electrifly Rimfire 63mm Out-Runner Brushless
Motor
– Weight: 22.4 oz. (635 g)
– Suggested prop size: 18x6W - 20x8E
– Input Voltage: 29.6-37 V
Thruster Testing
• Wooden 20x8 (diameter x pitch) and plastic 20x8 propellers
tested
• Concluded that the wooden and plastic props produced the
same amount of thrust force
• Plastic props were chosen: less expensive
Thrust Measurements
25
Thrust (lb)
20
15
20x8 Wooden prop
20x8 Plastic prop
10
5
0
0
20
40
60
80
Motor Range
100
120
Thruster Testing
Thruster Housing
• Electric motor is lighter and smaller
• Thruster housing design modified for space
conservation
• Decision to use 0.01” thick galvanized
steel for thruster shroud in place of
bending wood
• Next semester:
– Motor mount strength testing
– Thrust reduction testing
Thruster Housing
36 V Power System
• 250 Amp externally regulated alternators
• 36V system using alternators to power electric
motors
• Basic testing completed
Alternator Testing
• 28.9 V produced on unloaded alternator at
approximately 3300 rpm
• Tested electric motor powered by single alternator
• Motor was run successfully, but only produced
maximum of 12.6 lb of thrust
Voltage Output of Alternator vs.
RPM
Thrust Force vs. Alt. Voltage
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8
26
Force (lb)
Voltage (V)
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25
24
4
2
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22
3800
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4000
4200
4400
Alternator RPM
4600
4800
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23
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25
Alternator Voltage (V)
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27
Goals for Next Semester
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Final engine mount design and construction
Working hovercraft
Functioning 36 V power system
Thruster controls
Employment of radar, GPS and other system
components
Questions?
For more information:
http://students.cua.edu/51mcmahon/