ME 441 Senior DesignCUA Hovercraft – Class of 2008-2009

Joe Cochrane, Aldo Glean, James McMahon, Omar Monterrubio, Kalin Petersen

ME 441 Semester Summary12/4/08

• 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

Presentation Outline

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 counter-balance weight

Hull and Deck

6’x10’ Deck Size* 7’x10’ Deck Size*

• 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’

*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 I-beam 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

• 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

• 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

Lift Engine

Modification

Original

Conceptual Engine Mount DesignTop views

Side view

• Previous lift fan model and size determined sufficient for project requirements

Lift Fan

• 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

Thrusters

• 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

Thruster Testing

Thruster Testing

• 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 ofbending wood

• Next semester:– Motor mount strength testing– Thrust reduction testing

Thruster Housing

Thruster Housing

• 250 Amp externally regulated alternators• 36V system using alternators to power electric

motors• Basic testing completed

36 V Power System

• 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

Alternator Testing

• Final engine mount design and construction• Working hovercraft• Functioning 36 V power system• Thruster controls• Employment of radar, GPS and other system

components

Goals for Next Semester

For more information:http://students.cua.edu/51mcmahon/

Questions?