Hovercraft lift system and steering - UC DRC Home

HOVERCRAFT: LIFT SYSTEM AND STEERING

A thesis submitted to the

Faculty of the Mechanical Engineering Technology Program

of the University of Cincinnati

in partial fulfillment of the

requirements for the degree of

Bachelor of Science

in Mechanical Engineering Technology

at the College of Engineering & Applied Science

by

KELLY KNAPP

Bachelor of Science University of Cincinnati

May 2011

Faculty Advisor: Professor Elgafy

Hovercraft: Lift System and Steering Kelly Knapp

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TABLE OF CONTENTS

HOVERCRAFT: LIFT SYSTEM AND DESIGN ................................................................... 1

TABLE OF CONTENTS .......................................................................................................... 2

LIST OF FIGURES .................................................................................................................. 4

LIST OF TABLES .................................................................................................................... 5

ABSTRACT .............................................................................................................................. 6

INTRODUCTION .................................................................................................................... 7

PROBLEM STATEMENT........................................................................................................................................ 7 BACKGROUND – HOW DOES THE LIFT SYSTEM WORK? ....................................................................................... 7 RESEARCH, TECHNOLOGY AND EXISTING PRODUCTS ......................................................................................... 8

CUSTOMER NEEDS AND ANALYSIS ................................................................................ 9

SURVEY AND FEEDBACK ..................................................................................................................................... 9 ......................................................................................................................................................................... 10 HOVERCRAFT PRODUCT OBJECTIVES ............................................................................................................... 11

DESIGN .................................................................................................................................. 13

DESIGN ALTERNATIVES AND SELECTION ......................................................................................................... 13 DRAWINGS ....................................................................................................................................................... 14 ......................................................................................................................................................................... 14 LOADING CONDITIONS AND DESIGN- LIFT SYSTEM .......................................................................................... 15 LOADING CONDITIONS AND DESIGN- LIFT DUCT AND BAG SKIRT ................................................................... 16 LOADING CONDITIONS AND DESIGN- RUDDERS AND STEERING COMPONENTS ................................................ 17 COMPONENT SELECTION .................................................................................................................................. 19 BILL OF MATERIALS ......................................................................................................................................... 20 PLAN TO FINISH ................................................................................................................................................ 20 SPECIALIZED TOOLING ..................................................................................................................................... 20

FABRICATION ...................................................................................................................... 21

FRAME FOR LIFT DUCT .................................................................................................................................... 21 T-NUTS FOR SKIRT ATTACHMENT ................................................................................................................... 21 STEERING COLUMN ........................................................................................................................................... 22 RUDDER ASSEMBLY ......................................................................................................................................... 22 SPLITTER DUCT ................................................................................................................................................ 23 EPOXY RESIN ENCAPSULATION AND PAINTING ................................................................................................ 23 PLANNED TESTING ........................................................................................................................................... 24 ACTUAL TESTING AND LOOKING FORWARD ..................................................................................................... 24

PROJECT MANAGEMENT .................................................................................................. 25

LIFT SYSTEM AND STEERING PROPOSED BUDGET ............................................................................................ 25 LIFT SYSTEM AND STEERING ACTUAL BUDGET ............................................................................................... 25 PROPOSED SCHEDULE ....................................................................................................................................... 26 SCHEDULE FOR DESIGN FABRICATION ............................................................................................................. 26

REFERENCES ....................................................................................................................... 27

APPENDIX A - RESEARCH ................................................................................................... 1

APPENDIX B – SURVEY RESULTS ..................................................................................... 1


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APPENDIX C – QFD ............................................................................................................... 1

APPENDIX D – PRODUCT OBJECTIVES ............................................................................ 2

APPENDIX E – SCHEDULE AND BUDGET........................................................................ 1

SCHEDULE: ......................................................................................................................................................... 1 HOVERCRAFT PROPOSED BUDGET:..................................................................................................................... 2


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LIST OF FIGURES Figure 1: Hovercraft Principles Diagram .................................................................................. 7

Figure 2: Lift System Principles ............................................................................................... 7

Figure 3: Assembled Hovercraft Kit ......................................................................................... 8

Figure 4: 19XRW Hoverwing ................................................................................................... 8

Figure 5: Reverse Thrust Bucket Equipped Hovercraft ............................................................ 8

Figure 6: Segmented Skirt ...................................................................................................... 13

Figure 7: Bag Skirt .................................................................................................................. 13

Figure 8: Back of Hovercraft .................................................................................................. 14

Figure 9: Isometric Assembly ................................................................................................. 14

Figure 10: Cross Section of Splitter Duct ............................................................................... 14

Figure 11: Cross Section of Lift Duct ..................................................................................... 14

Figure 12: Rudder System ...................................................................................................... 14

Figure 13: Close up of Rudder Assembly ............................................................................... 14

Figure 14: Segment Area Diagram ......................................................................................... 16

Figure 15: Bag Skirt with Proper Pressure ............................................................................. 16

Figure 16: Bag Skirt without Proper Pressure ........................................................................ 16

Figure 17: Solidworks Drawing .............................................................................................. 17

Figure 18: Effects of Hull Slope ............................................................................................. 17

Figure 19: Bending Moment Diagram .................................................................................... 18

Figure 20: Rudder (Top View) ............................................................................................... 18

Figure 21: Rudder Assembly .................................................................................................. 18

Figure 22: Skeleton Frame ...................................................................................................... 21

Figure 23: Inner Lift Duct ....................................................................................................... 21

Figure 24: T –Nut (front end) ................................................................................................. 21

Figure 25: T-Nut (side) ........................................................................................................... 21

Figure 26: Steering Column Assembly ................................................................................... 22

Figure 27: Steering Column Frame......................................................................................... 22

Figure 28: Rudder Assembly .................................................................................................. 22

Figure 29: Back of Splitter Duct ............................................................................................. 23

Figure 30: Front of Splitter Duct ............................................................................................ 23

Figure 31: Epoxy Resin Application....................................................................................... 23

Figure 32: Sanding of Epoxy Resin ........................................................................................ 23

Figure 33: Painted Hovercraft ................................................................................................. 23


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LIST OF TABLES Table 1: Customer Importance Feedback ................................................................................. 9

Table 2: Engineering Characteristics ...................................................................................... 10

Table 3: Cushion Pressure Vs Air Flow ................................................................................. 15

Table 4: Design Budget .......................................................................................................... 25

Table 5: Fabrication Budget.................................................................................................... 25

Table 6: Schedule for Design Quarter .................................................................................... 26

Table 7: Finalized Schedule .................................................................................................... 26


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ABSTRACT

Owners of recreational vehicles such as ATVs, boats, and jet-skis are limited to travel

depending on whether they are on land or water. The hovercraft is a vehicle that can travel on

any type of surface including land or water by operating on a cushion of air. While several

companies manufacture hovercraft, they are very expensive and usually include minimal

features.

A hovercraft will be developed that would entice the power-sports enthusiast by offering

the features of all the other recreational vehicles. This hovercraft will be a total replacement

and will be priced below $10,000 to compete against current recreational vehicles.

Team Members and Responsibilities:

Kelly Knapp: Lift System and Steering

Dave Louderback: Thrust System and Drivetrain

Jeremy Siderits: Hovercraft Body and Frame


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INTRODUCTION

PROBLEM STATEMENT A properly designed lift system will be required to raise the hovercraft at least ½‖ off the

ground while traveling anywhere from 0 to 65 mph. This will provide the proper amount of

lubrication, which will alleviate scrapping against the bottom of the hull and the ground. For

the steering system, handlebars, cables, pulleys, and rudders will be made into an assembly

that will be able to withstand the forces from the thrust fan and alter the direction of the craft

effectively.

BACKGROUND – HOW DOES THE LIFT SYSTEM WORK? Air generated from the single fan and engine system propels hovercraft forward with

thrust air and lifts the craft up by producing an air cushion as shown in Figure 1.

When the lift air is sent past the fan it goes down to the hull by a splitter. Then, the air

coming from the splitter fills the air duct along the perimeter of the craft. At this point,

the bag skirt begins to inflate and sends air to the underbelly of the hull. As a result, air

pressure will increase until the hovercraft begins to raise and reach its hover-height, or

maximum hover elevation. As seen in Figure 2, the air begins to bleed underneath the

skirt; it is at this point the hovercraft is in its optimum state.

Figure 1: Hovercraft Principles Diagram

Figure 2: Lift System Principles


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RESEARCH, TECHNOLOGY AND EXISTING PRODUCTS

Despite small customer demands, there is actually a variety of hovercraft across the

market. While each type of hovercraft has its own benefits, there are also corresponding

disadvantages such as price, safety, or power. For example, some manufacturers offer kits to

build. However, they usually come with limited features and can be small in size. An

example of a home-built kit is shown in Figure 3 (1).

Figure 3: Assembled Hovercraft Kit

Another type of hovercraft is the ground-effect vehicle. While this vehicle offers the

most excitement, it costs around $85,000. The Hoverwing™, shown below in Figure 4,

includes wings that allow it to lift off the ground at speeds of at least 35 mph (2). However,

this craft requires a very skilled driver and increases danger due to higher operating speed.

Other hovercraft in the market offer effective braking systems. These crafts use reverse

thrust buckets that redirect the thrust air flow. The buckets typically allow for a braking of

40% – 50% of the acceleration rate (3). This feature, depicted in Figure 5, also allows for

reverse operation which is not possible in other hovercraft (4).

Figure 5: Reverse Thrust Bucket Equipped Hovercraft

Besides the technology shown above, most manufacturers rely on other vehicle parts

to build the hovercraft. Therefore, most of the technology in the hovercraft market is directly

related to the technology currently used for other vehicles such as boats, ATVs, and jet-skis.

For example, the engines used in hovercraft are typically the same two or four stroke

combustion engines commonly found in small cars or riding lawn mowers. Therefore,

hovercraft are now being built with electric start engines. Additional technology related to

other vehicles includes drain holes and engine hour gauges which can be ordered through

boat catalogs.

Only fits one

person.

Winged hovercraft

are more dangerous

due to high speeds

and airborne flight

Reverse thrust

buckets.

Hovercraft

wing

Figure 4: 19XRW Hoverwing


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CUSTOMER NEEDS AND ANALYSIS

In order to determine what the customer wants in a hovercraft, characteristics were

determined and then listed in a survey. The audience surveyed included two recreational

vehicle enthusiasts, five hovercraft manufacturers, and six people interested in the hovercraft.

Since a variety of groups were surveyed, the results were not biased and they portrayed a true

average of the potential buying market. Since most people surveyed do not own a hovercraft,

current satisfaction was not included in the survey.

SURVEY AND FEEDBACK

The table below lists the customer importance that directly relates to the survey

feedback. There were a total of 13 surveyed and the level of importance is listed from top to

bottom.

Table 1: Customer Importance Feedback

The results show that the top five characteristics are durability, reliability,

maneuverability, speed and safety. These five factors will receive the most attention in the

design of the hovercraft in order to uphold the features that the customers want. The lowest

three features were low noise, cargo space, and the ability to tow skiers and tubers. These

features will not receive as high importance in the design since they are not very important to

the customer. In addition, since the ability to tow skiers ranked very poorly, it may be

removed from the design in order to increase product satisfaction levels when the hovercraft

is complete.

Rank Average Relative Weight %

1 4.54 11%

2 4.54 11%

3 4.31 11%

4 4.23 11%

5 4.15 10%

6 4.15 10%

7 3.92 10%

8 3.15 8%

9 2.92 7%

10 2.23 6%

11 2.00 5%

Customer Importance

Effective Brakes

Cost

Ability to Travel in Reverse

Low Noise

Cargo Space

Ability to Two Skiers/Tubers

Survey Characteristic

Durability

Reliability

Manueverability

Speed

Safety


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In order to achieve the features shown above, specific engineering characteristics were

established. Using a QFD (Quality Deployment Function), these characteristics were given

absolute weights to find the level of importance. They are listed in Table 2.

Engineering Characteristic Absolute

Importance

Proper tip speed 4.90

Hull constructed with fiberglass seamed marine

grade plywood 4.16

Reverse thrust buckets 3.83

Sturdy construction 3.57

4 cycle engine powered at 85% 2.28

Crash bumper 2.27

Emergency stop 1.96

Rearview mirrors 1.82

Screen to cover the fans 1.71

Aerodynamic design 1.06

Warning labels/fire extinguisher 1.03

Mufflers 0.95

Ability to seat 3 passengers 0.95

2ft3 cargo space 0.60

Tow rope 0.55

The top five engineering characteristics were: proper tip speed, hull constructed with

fiberglass seamed marine grade plywood, reverse thrust buckets, sturdy construction, and an

engine that would only be powered at 85% during operation. These importance levels are a

direct correlation of the features shown in Table 1. Notice how proper tip speed and seamed

fiberglass are all steps made to make the hovercraft more durable, reliable and safe. These

characteristics will be a top priority during construction. In addition, similar to the ability to

tow skiers and tubers, the tow rope also scored very poorly. The feature will receive little

importance during design.

Table 2: Engineering Characteristics


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HOVERCRAFT PRODUCT OBJECTIVES

The following is a list of product objectives and how they will be obtained or measured

to ensure that the goals of the project are met. The product objectives will focus on the

various aspects of a hovercraft.

Reliability (11%): 1. A four cycle engine will be used, instead of the unreliable 2 cycle that is used on many hovercraft.

2. All electrical connections will be soldered and then covered with heat wrap to ensure

no bare wires will be exposed to water and corrosion. 3. All fasteners will be fastened with locknuts and/or Loctite for sturdy construction.

4. Engine will be powered at 85% during normal operation in order to obtain longer engine life.

Durability (11%): 1. A rubber crash bumper will be placed around the craft and attached to the exterior frame.

2. The hull will be constructed using ½‖ marine grade plywood coated with an epoxy primer and an

enamel grade finish for waterproofing.

3. All seams will be joined by fiberglass for superior strength and waterproofing.

4. All metal used for engine mounts or frame support will be primed and painted to prevent corrosion.

Speed (11%): 1. The craft will be designed to travel in excess of 40 mph on calm water.

2. Sloped shapes will be used to reduce drag.

Maneuverability (11%): 1. Reverse thrust buckets can be used in addition to the normal rudders to control the movement of the

craft.

2. A turning radius of zero is achievable with minimal thrust but increases with speed.

Safety (10%): 1. A screen will cover the thrust and lift fans.

2. Fan tip speed will be kept below the manufacturer’s maximum tip speed in order to keep the fan

blades from breaking and possibly injuring people.

3. Warning labels will be placed on:

a. Any electrical device to prevent shock

b. Around the fans to prevent injury

c. Near engines to prevent burns

4. A fire extinguisher will be placed on board in the event that the engine catches fire.

5. All other safety requirements will be upheld based on part manuals.

Effective braking system (10%): 1. The hovercraft will feature reverse thrust buckets that cause the hovercraft to reduce speed.

2. Fifty percent of the thrust airflow will be redirected for braking allowing a deceleration equal to one

half of the acceleration rate.


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3. An emergency stop feature will be used to cut power to the lift fan. Pads on the bottom of the hull

will prevent damage when this feature is used.

Cost (10%): 1. The hovercraft will be priced similar to an ATV or Jet Ski, around $10,000 new.

Ability to travel in reverse (8%): 1. The hovercraft will be equipped with reverse thrust buckets to allow the craft to travel in reverse by

pulling a lever.

Low noise (7%): 1. Normal operation will be at less than 85 decibels.

2. The engines will be equipped with mufflers.

3. The fan tip speed will be below the manufacturer’s maximum tip speed. This will minimize excessive

sound.

Cargo space (6%): 1. The design will allow at least 2 ft

3 of cargo space, located under the seat or in the front of the hull.

Ability to tow skiers/tubers (5%): 1. A tow rope will be able to be attached to the back of the craft.

2. In order to legally tow a skier, the craft will be able to seat 3 passengers (5).

3. It will have rearview mirrors so the operator can verify the safety of the skier.


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DESIGN

DESIGN ALTERNATIVES AND SELECTION

The lift system could be powered by either one or two engines. The comparison below best

demonstrates the pros and cons between the two systems (3).

Twin Engine

Pros

Independent control is possible. One engine

lifts the craft while the other engine propels it

forward. This allows the users to hover in

place.

Easier to balance.

Cons

Twice as many engines, twice the

maintenance.

More expensive

Heavier since two engines creating a total of X

horsepower are usually heavier than one

engine producing the same X horsepower.

Single Engine

Pros

Only one setup required – fewer moving parts,

oil changes, and fuel tanks

Aesthetically looks better

Less expensive

Less noise

Fewer Vibrations

Lighter

Cons

More difficult to pilot

A minimum rpm of the fan must be held at

all times

A single engine setup was chosen since it had fewer moving parts, lower costs, lower noise

levels, and it weighed lighter. With the engine setup selected, the skirt system could be

analyzed. The two primary options for skirt options are the segmented, or finger, skirt and the

bag skirt. A better representation is shown in Figure 6 and 7 (6).

Segmented ―Finger‖ Skirt

Pros

Easier to repair

Easier to balance

Better climbing capability

Cons

Higher costs

Bouncy ride

Bag Skirt

Pros

Cheaper costs

Lower weight

Better stability

Cons Higher drag

Poor take off performance when floating

The bag skirt was chosen because it has better stability, it weighs less, and it is several

hundred dollars cheaper.

Figure 6: Segmented Skirt Figure 7: Bag Skirt


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DRAWINGS Assembly Drawings

Splitter Duct Assembly

Inner Duct

Rudder Assembly

Figure 9: Isometric Assembly Figure 8: Back of Hovercraft

Figure 10: Cross Section of Splitter Duct

Figure 11: Cross Section of Lift Duct

Figure 12: Rudder System

Figure 13: Close up of

Rudder Assembly


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LOADING CONDITIONS AND DESIGN- LIFT SYSTEM

Lift Area and Perimeter

Area = 6.5 ft x 13 ft = 84.5 ft

Perimeter = 2*(6.5) ft + 2*(13) ft = 39 ft

The perimeter of 39 ft does not include the slope of the outer hull. In order to take into

account of the lost space, a perimeter of 90% was used since the hover gap centerline will be

in between the slope of the outer hull.

Perimeter = 39 ft x 90% = 35.1 ft

Hover Gap

Hovercraft hover gaps are generally between ½‖ and 1‖. At least a ½‖ is required to provide

sufficient lubrication underneath the hull, which will minimize skirt surface scrapping.

However, hover gaps above 1‖ create excessive spray from high air escape. Soil, sand, and

water can all be blown towards nearby sightseers and passengers. Therefore, a ¾‖ hover gap

will be designed. This hover gap will fluctuate with fan rpm in a direct relationship.

¾‖ in. hover gap *

= 0.0625 ft

Hover-gapAREA = 0.0625 ft X 35.1 ft = 2.194 ft² (slot hover gap)

Cushion Air Pressure

Lift Area = 84.5 ft x 90% = 76.05 ft²

Estimated Total Weight (including passengers) = 1200 lbs

x

Cushion Air Pressure = 0.109 Psi

0.109 Psi / 0.0361 water constant = 3.019 in water

Air Velocity

Using the relationship table shown in Table 3, the air velocity was

interpolated from the cushion air pressure. This was calculated to an

Air Velocity = 115.3 ft/s. Air velocity losses due to friction from

asphalt, grass, or water are equal to an average of 40%

Actual Air Velocity = 115.3 ft/s x 60% = 69.18 ft/s

Minimum Lift Air Volume Needed

69.18 ft/s * 2.194 ft² hover gap = 151.76 ft³/s = 9105 CFM

Normal cruising speeds will generate about 30000 total CFM. Since only 30% is directed to

the lift system, only 9000 CFM will be generated at normal cruising speed. For safety

concerns, (6)6000 CFM will still generate an adequate ½‖ hover gap (3).

Theoretical HP Requirement

152 ft³/s x 0.109 lbs/in² x

= 2385.8 ft-lb/s

≈ 4.34 HP

An integrated setup is only 25% efficient due to limited air flow.

= 17 HP

Engine is to run @ 85% to prevent engine wear and tear

= 20 HP

Table 3: Cushion Pressure

Vs Air Flow


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Figure 14: Segment

Area Diagram

LOADING CONDITIONS AND DESIGN- LIFT DUCT AND BAG SKIRT

Serial Feed Method

From the lift design calculations, approximately 9000 CFM will be required for a ¾‖ hover

gap. However, during maximum thrust, the maximum volumetric rate will be approximately

83000 CFM

83000 CFM * 30% = 24900 CFM

This will create a 2‖ hover-gap. This is very high and will cause high spray of soil or water.

Therefore, maximum CFM will be avoided.

Lift Duct Area

Total area of duct = π*r² = π * 21² = 1385.44 in²

Approximately 30% of Duct Area Required for Lift

1385.44 * 30% = 415.6 in²

areaK = –

=

–

= 404.78 in

The design for the splitter was chosen to be 14 inches for

ease of fabrication. In order to verify that this will produce

the proper area, h=14 inches was calculated.

When h=14.0, = 141.06

This results in an area (K) of approximately 405 in², or 29.2% of the thrust duct area (8).

Area of holes around hovercraft perimeter

The area of the holes around the hovercraft that empty into the bag skirt must be equal to the

area of the thrust duct underneath the splitter which was about 495 in². This is so that there is

equal flow of air and a 1:1 pressure ratio (3).

Area of lift input = 405 in²

Holes around perimeter need to be equal to this for adequate flow

= 6.75 in² per hole

π * r² = 6.75 in² r² = 6.75 in/ π r = 1.45 in = 1.5 in

Area of holes in skirt

The area of the holes in the skirt that allows the air to flow underneath the hull should be

lower. In fact, it should be low enough to fill the bag with 20% percent higher pressure (6).

This yields a radius = 1.34 in

Figure 15: Bag Skirt with Proper Pressure Figure 16: Bag Skirt without Proper Pressure


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Hull Slope

The proper angle for the hovercraft perimeter of the hull should be 25° to 35° to prevent side

plow-in, or the skirt getting sucked underneath the hovercraft. See Figure 17 and 18 for

clarification. The top illustration in Figure 6 shows what will happen for angles much greater

than 35° (3).

LOADING CONDITIONS AND DESIGN- RUDDERS AND STEERING COMPONENTS

The loading conditions for the steering system are caused by the thrust force of the fan. This

force was used to calculate the proper materials and sizes of the steering system

Thrust Dynamics

The total thrust force from fan is 426 lbs with only 70% of the force hitting the rudders.

426 lbs *70% = 298.2 lbs

Total Area of Duct = π*r² = π * 21² = 1385.44 in²

1385.44 in² *70% = 970 in²

Thrust Pressure =

= 0.307 psi

Rudder Forces

Large Rudder Area = 25.625 in High x 8 in Wide = 205 in²

205 in² x 0.307 psi = 63 lbs

Small Rudder Area = 22 in High x 8 in Wide = 176 in²

176 in² x 0.307 psi = 54 lbs

Stresses on Rudder

Force = 63 lbs

Angle of rudder direction = 45°

Actual Force = 63 lbs x sin(45) = 44.55 lbs

Figure 17: Solidworks Drawing Figure 18: Effects of

Hull Slope


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With the forces calculated, the force on the rudder was set up as a beam calculation. Notice

from Figure 19 that there will be two pins holding the rudder. These will act as supports for

the ―beam.‖ The rudder was designed out of balsa wood and was tapered from 1‖ thick to a

point, therefore, a ½‖ beam thickness was assumed and the stresses were calculated (9).

Summation of Moments

ΣMA = 0 = 44.55 (3 in) - RB (2 in) RB = 66.825 lbs ΣMB = 0 = 44.55 (1 in) – RA (2 in) RB = -22.275 lbs

Maximum Shearing Force

V3 = R2 – V4 = 66.825 – 27.844 = 38.981 lbs

Maximum Bending Moment

M2 = -

= - (

) (

) (5²) = -69.609 lb-in

Section Modulus

s =

=

= 0.333 in³

Design Stresses on Rudder

σmax =

=

= 208.8 psi

σd = σmax * 6 = 208.8 psi * 6 = 1253 psi

Douglas Fir Wood Minimum Sy = 2176 psi (acceptable)

Figure 19: Bending Moment Diagram

Figure 20: Rudder

(Top View)

Figure 21: Rudder Assembly


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Diameters for Holding Pins

Shear Stresses (9)

*1020 Cold Drawn Steel; Sy = 51000 psi

F = 44.55 lbs /2 pins = 22.28 lbs

A = π*d²/4

Safety Factor = 4

τ = sy/4 = 51000/4 = 12750 psi

Let τ = τd

A = F/ τ = 22.28 lbs / 12750 psi = 0.0017

in²

D =√(4*A/ π) = 0.047 in

Diameter chosen is 1/8‖ in

Bearing Stress Verification (9)

DIA = ⁄ ‖ , Length = 3‖

Ab = 3 in x 0.125 in = 0.375 in²

At Vmax = 38.981 lbs

σb = F/A =

= 103.95 psi

σbd = 0.90 sy sy = σbd / 0.90

sy =

= 115.5 psi

1020 cold drawn steel sy = 64000 psi

(acceptable)

COMPONENT SELECTION Bag Skirt

The bag skirt was chosen to be made out of 30‖ wide 16 oz neoprene coated nylon. It is

approximately $6.00 / lineal foot. Nylon is a very strong, resilient material that will survive

repeated frictional abuse. The neoprene coating provides additional features such as (7):

Resisting degradation from sun, ozone and weather

Remaining useful over a wide temperature range

Displaying outstanding physical toughness

Outstanding resistance to damage caused by flexing and twisting

Protection from skirt dragging and scraping wear

Splitter Duct

For the splitter duct, 0.030‖ stainless steel was chosen for superior strength and durability. It

was donated for the project.

Rudder material

The rudders will be comprised of 8‖ wide Douglas fir wood. The rudder will be one inch in

diameter and tapered to a small radius. It will also be covered with fiberglass resin to provide

a smoother surface.

Pin Material and Cables

Cold drawn steel will be used for the holding pins and cables. While this material is heavy,

the parts being used are very small so only a small amount of weight will be added. Cold

drawn steel is also very strong so it is perfect for the application.

Rudder Base Brackets

The rudder base brackets holding the pins will be made out of ¼‖ thick aluminum plate.

Since the brackets will have a thicker cross sectional area, a lighter, weaker material such as

aluminum is ideal for the application.


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BILL OF MATERIALS 20 linear feet of 60‖ wide neoprene covered nylon bag skirt

1 sheet of ¼‖ marine grade plywood

10 lbs of fiberglass resin

50 linear feet of fiberglass mesh tape

25 linear feet of ¼‖ x 1‖ nylon insert

1 Gallon Epoxy wood sealant

(2) 22‖ x 8‖ Douglas Fir wood

(2) 26.625‖ Douglas Fir wood

(4) 1‖ x 4‖ aluminum sheet

(4) 1‖ x 3.5‖ aluminum sheet

(8) DIA 1/8‖ x 3‖ long holding pins

20 linear feet of 1/4‖ cable

(4)DIA 3‖ x 0.5‖ thick pulleys

Set of aluminum angled handle bars

PLAN TO FINISH

The order of fabrication is as follows. The areas in bold symbolize my responsibility of the

project

1. Construct ribs and stringers

2. Cover Inside ducts with foam and panels 3. Attach outside shell and cargo area with plywood

4. Attach thrust duct and splitter

5. Install engine and mounting hardware

6. Install fan

7. Install Rudders 8. Remove all parts not to be painted

9. Paint 10. Re-assemble

11. Attach skirt and make final adjustments

SPECIALIZED TOOLING

Rudders

Band saw to cut aluminum base brackets

Drill press to cut holes

Fiberglass resin

Splitter and Lift Ducts

Table saw for long cuts

Jig saw for odd shaped cuts

Fiberglass mesh to hold seams


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FABRICATION

FRAME FOR LIFT DUCT Initially, the skeleton was made (shown in Figure 22) and then the buoyancy foam was

poured. When the foam was rising, 1/8‖ plywood panels were set in place so that the airflow

in the lift duct would be undisturbed. See Figure 23.

T-NUTS FOR SKIRT ATTACHMENT In order for the bag skirt to be easily removed, t-nuts were installed on the sides and bottom

along the perimeter of the hovercraft. In all there are 128 secure points for the bag skirt each

including a ¼‖ stainless steel bolt, washer, and t-nut. See Figure 24 and 25.

Figure 22: Skeleton Frame Figure 23: Inner Lift Duct

Figure 24: T –Nut (front end) Figure 25: T-Nut (side)


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STEERING COLUMN The steering column was constructed with Douglas fir 2x2s. The steering column was built

using a wheel and pulley system. Plastic-coated stainless steel was wrapped around the wheel

and tightly connected to the rudder brackets. Figure 26 and 27 show clarification.

RUDDER ASSEMBLY The rudders were hand-crafted out of a Douglas fir 2x8 and mounted on a sliding bracket that

pivoted on base mounts. The top of the rudders were held in place by brackets and a pin that

spins freely as shown in Figure 28.

Figure 27: Steering Column Frame Figure 26: Steering Column Assembly

Figure 28: Rudder Assembly


23

SPLITTER DUCT The splitter duct was made out of 0.030‖ stainless steel. It was shaped and welded so that it

diverted air in all three axis. See below.

EPOXY RESIN ENCAPSULATION AND PAINTING The entire hovercraft was then coated with epoxy resin and sanded down. Once wiped clean,

a coat of marine grade epoxy enamel was sprayed. The figures below show clarification.

Figure 30: Front of Splitter Duct Figure 29: Back of Splitter Duct

Figure 31: Epoxy Resin Application Figure 32: Sanding of Epoxy Resin

Figure 33: Painted Hovercraft


24

PLANNED TESTING A manometer as shown in Figure 22 will be placed in various areas around the inner duct of

the hull to test for correct pressures.

Another testing measure will be to ensure bag skirt

inflates to the proper shape. The correct shape as outlined in

the design for the bag skirt verifies that the 20% pressure

differential is being obtained.

ACTUAL TESTING AND LOOKING FORWARD Testing is yet to be done, but will be completed when the

project is finished. Even with very an average of 14 hour

days, we were not able to get completed.

Figure 34: Manometer


25

PROJECT MANAGEMENT

LIFT SYSTEM AND STEERING PROPOSED BUDGET

Our original budget for the lift system and steering was $675.00. However, we decided to go

with a single engine setup which reduced the costs of the lift system and steering by $235.00.

Please see the proposed budget in Appendix E. The actual budget is shown below in Table 4

and 5.

Table 4: Design Budget

System Component Qty Description Price

Bag Skirt Bag Skirt 1 Neoprene Coated Nylon $200.00

Splitter System 1 0.030 stainless steel $25.00

Steering Handlebars 1 Jet-Ski Handlebars $50.00

Inside Rudders 2 Douglas Fir - 25.625" x 8" $20.00

Outside Rudders 2 Douglas Fir - 22" x 8" $20.00

Cables and

Pulleys 1 Aluminum cables and

pulleys $25.00

Total $340.00

LIFT SYSTEM AND STEERING ACTUAL BUDGET

Due to donated materials and discounts on our materials, the actual budget was slightly less

than anticipated. This was not the case for the other parts of the project.

Table 5: Fabrication Budget

System Component Qty Description Price

Bag Skirt Bag Skirt 1 Neoprene Coated Nylon $150.00

Splitter System 1 .030 stainless $25.00

Steering Handlebars 1 Jet-Ski Handlebars $25.00

Inside Rudders 2 Balsa Wood - 25.625" x 8" $30.00

Outside Rudders 2 Balsa Wood - 22" x 8" $30.00

Cables and

Pulleys 1 Aluminum cables and

pulleys $25.00

Total $285.00


26

PROPOSED SCHEDULE

Figure 9 shows the proposed schedule for the design quarter. In the beginning we did work

on design, but our approach was admittedly casual. By mid-January, however, we began

working very hard and were able to keep the schedule on track. Since then we have kept up

an intense pace and we have made a great deal of progress.

SCHEDULE FOR DESIGN FABRICATION We were able to stay on the schedule shown in Figure 7, but did not get completely finished

with the project.

Table 7: Finalized Schedule

Table 6: Schedule for Design Quarter

Proof of Design Contract 11/24/2010

Design Freeze 1/31/2011

Oral Design Presentation 2/28/2011

Design Report 3/7/2011

Tech Expo 5/20/2011

Oral Final Presentation 5/23/2011

Final Report Due 5/30/2011


27

REFERENCES

1. Universal Hovercraft. UH-10F Entry Level Hovercraft. Universal Hovercraft. [Online]

Universal Hovercraft. [Cited: 09 29, 2010.]

http://www.hovercraft.com/content/index.php?main_page=index&cPath=33_40.

2. —. 19XRW Hoverwing. Universal Hovercraft. [Online] Universal Hovercraft. [Cited: 09

29, 2010.] http://www.hovercraft.com/content/index.php?main_page=index&cPath=2.

3. Perozzo, James. Hovercrafting as a Hobby. Bend, OR : Maverick Publications, 2001.

4. Neoteric Hovercraft. 4 Passenger Recreational Specifications. Neoteric Hovercraft.

[Online] Neoteric Hovercraft. [Cited: 09 20, 2010.]

http://neoterichovercraft.com/specifications/4Lspecifications.htm.

5. Ohio Department of Natural Resources, Division of Watercraft. The legal

requirements of boating: towing a person with a boat or PWC legally. BOAT-ED. [Online]

Ohio Department of Natural Resources, Division of Watercraft, 04 02, 2010. [Cited: 09 29,

2010.] www.boat-ed.com/oh/course/p4-15_reqspectotowing.htm.

6. Mott, Robert L. Machine Elements in Mechanical Design. Upper Saddle River : Pearson

Prentice Hall, 2004.

7. Fitzgerald, Christopher and Wilson, Robert. Light Hovercraft Design. Foley, AL : The

Hoverclub of America, Inc., 1995.

8. Springer, Ryan. Hovercraft Manufacturer. Rockford, IL, 09 29, 2010.

9. Baker, Larry and Kathleen. Power Sports Enthusiasts. Cincinnati, OH, 10 01, 2010.

10. Simons, Chuck. Power Sports Sales Specialist. Cincinnati, OH, 10 01, 2010.

11. Hovercraft Forum. Hoverclub of America. [Online] June 6, 2008. [Cited: September 20,

2010.] http://www.hoverclubofamerica.org/forum/index.php?showtopic=1569.

Appendix A1

APPENDIX A - RESEARCH

Problem:

Owners of recreational vehicles such as ATVs, boats, and jet-skis are limited to travel

depending on whether they are on land or water. The hovercraft is a recreational vehicle that

can travel on any type of surface including land or water. While several companies

manufacture hovercraft, they are very expensive and usually include minimal features. A

hovercraft will be developed that would entice the power-sports enthusiast by offering the

features of all the other recreational vehicles. This hovercraft will be a total replacement.

Also the hovercraft to be developed will be built for less than $10,000 in order to compete

against present-day recreational vehicles.

Closest MET Projects:

OCAS 1:4 Jet Propulsion Boat

Joseph Duffey, Douglas Weber, Adam Patterson, 1987

One-Man Propeller Driven Airboat

Sean Nguyen, 1990

These two projects are similar to a hovercraft in that they both use the propulsion of air to

move the craft, rather than using a propeller in the water. However, these two projects differ

from ours because they are still boats, and being so, they are limited to use only on water.

Our hover craft will float on a cushion of air and as a result, will be able to easily travel on

nearly any terrain, whether it is land or water.

Appendix A2

Interview Notes:

Interview with power sports sales specialist, Oct. 1, 2010

Chuck Simons (513-752-0088)

Beechmont Motorsports, 646 Mount Moriah Drive, Cincinnati, OH, 45245.

Sells recreational vehicles including ATVs, Jet-Skis, and Dirtbikes.

All vehicles offer excitement but are limited by either land or water.

Chuck stated that the reasons why people buy recreational vehicles are:

Fun and enjoyment

Hunting

Farm Help

Convenience (carrying big loads)

Features or specifics that most customers are interested in include:

Automatic Transmission

Fuel-Injected Engine

Speed

Noise Levels

Cargo area

Carrying racks (For ATVs)

Interview with power sports enthusiasts, Oct. 1, 2010

Larry and Kathleen Baker (did not want to give contact number)

Beechmont Motorsports, 646 Mount Moriah Drive, Cincinnati, OH, 45245.

Owners of an ATV and a Jetski.

Larry and Kathleen said that the newer engines are very electrical and their brand new

ATV and jet-ski models had broken down several times and were difficult to repair.

They stated they would never buy a newer model again and that older style engines

were more reliable and much simpler.

They stated that their jet-ski was fun because they could tow their children on a tube.

(In our research, we found that in the state of Ohio, a motorsports vehicle is only

capable to pull a third party if it is rated to carry at least three people on-board and it

has mirrors to see behind the vehicle).

Interview with hovercraft manufacturer, Sept. 29, 2010

Ryan Springer (815-963-1200)

Universal Hovercraft, 1218 Buchanan Street, Cincinnati, OH, 45245.

Ryan stated that:

The hovercraft’s hull should be slightly tapered and buoyant so that it floats in water

in case of engine failure.

Universal Hovercraft is proud that they only use four-stroke engines. A two-stroke

engine produces loud winding noise levels and they are less reliable.

A bag skirt is more customer-friendly since they are thicker than finger skirts and

repairing is easy to do in the field with scrap PVC coated nylon and skirt glue. Also,

the bottoms of the finger skirt deteriorate quickly since they are typically made of

thinner material.

Appendix A3

Related Products:

The UH-10F Entry Level Hovercraft is a great design for first time

builders, high school technology classes and home science projects.

First time builders and students get hands-on experience in

woodworking, fiberglass, small engines, propellers, as well as gaining

knowledge in engineering, aerodynamics and physics.

A single 10 hp Tecumseh horizontal shaft engine turns a two blade 36-

inch ducted propeller that provides both lift and thrust. This single

engine design is both simple and reliable, and has been successfully

built and flown by students in hundreds of schools and colleges

throughout the world. The 10F complies with the Hoverclub of America Entry Level racing requirements.

It's built from a foam and plywood sandwich construction. The

combination of these materials makes a low cost, high strength

composite structure that is un-sinkable.

Driving the craft is easy as it has only two controls; steering and

throttle. Slowly advancing the throttle will bring the craft up on

cushion. Adding a little more power accelerates the craft. Speed is

easily controlled by increasing or decreasing engine rpm. First time pilots can learn to operate the craft in a very short period of time.

The craft will operate on land, water, snow, ice, mud, parking lots,

football fields, ponds and rivers. Speed varies over each terrain.

Smoother terrain will allow the craft to achieve higher speeds while rough terrain will slow the craft.

The Hoverclub of America has designed a racing program specifically for the 10F & 10F2 Entry Level Hovercraft. The program is designed to allow close competition between individual competitors, High Schools and Universities at a very affordable price. See Hoverclub of America for more information.

Offered in a kit priced at $1,499

Very reasonable price

Price does not include wood,

hardware, upholstery, wire, or paint

costs

Only accommodates one person

Only one engine - limits power and

speed

Low HP

25 – 35 MPH

Travels on all surfaces

Very limited design

http://www.hovercraft.com/content/index.php?main_page=in

dex&cPath=33_40

9/29/10

UH-10F Hovercraft

http://www.hoverclubofamerica.org/

http://www.hovercraft.com/content/index.php?main_page=index&cPath=33_40



Appendix A4

Neoteric is the original light hovercraft manufacturer and

the Hovertrek™ is the culmination of Neoteric’s 40 years

of experience in light hovercraft design, development and

engineering. Its aesthetically appealing design embodies

all the advantages and advances Neoteric has innovated:

side-by-side seating, fully enclosed cabin, highly

developed reverse thrust for braking and maneuverability,

more cockpit room, increased thrust and low weight.

Engineered to satisfy expectations and to give long life

and value for money, the Hovertrek™ is recognized as the

industry standard for recreational personal hovercraft.

4 person, 750 lb payload

60 mile range

45 mph max forward speed on calm water

25 mph max reverse speed on calm water

83 dB (A)

Reverse buckets offer braking

and reverse capabilities

Limited to max 2 foot waves

16.7% slope gradient max

Expensive – 20-30K depending

on options

http://neoterichovercraft.com/specifications/4L

specifications.htm 9/20/10 Hovertrek,

Neoterichovercraft.com, Neoteric Hovercraft

http://neoterichovercraft.com/specifications/4Lspecifications.htm

http://neoterichovercraft.com/specifications/4Lspecifications.htm

Appendix A5

Universal Hovercraft is proud to offer the UH-

19XRW Hoverwing™ ground-effect vehicle for

recreational, industrial, commercial, military sales.

It is available to our customers on a ready to run

turnkey basis. The Hoverwing™, designed as a

high performance hovercraft, is unique because of

the ability to add wings for flight in ground-effect.

Flying in ground-effect enables you to clear

obstacles and fly over rough water at speeds in

excess of 75 mph. Cruise altitude is 2 to 6 feet and

the craft can jump up to 20 feet to clear large

obstacles. Operating in ground-effect does not

require a pilot's license, and the craft is registered

as a boat which brings a wide range of new

opportunities to the commercial and tourism

industry.

Removing the wings from the Hoverwing™ takes

just 10 minutes. With the wings removed the

Hoverwing™ converts into Sport mode, a sleek

high performance hovercraft, able to carry 4 to 6

passengers into areas that can't be reached with

any other vehicle. The Hoverwing™ can be

configured in many different ways to

accommodate your passengers or equipment

needs.

Ability to ―fly‖ at very low heights

Extremely expensive - $85K

Must have a skilled operator

Increased level of danger

Very high speeds necessary to fly

Large, open terrain needed to fly

http://www.hovercraft.com/content/index.ph

p?main_page=index&cPath=2 , 9/29/10,

19XRW Hoverwing, hovercraft.com,

Universal Hovercraft

http://www.hovercraft.com/content/index.php?main_page=index&cPath=2

http://www.hovercraft.com/content/index.php?main_page=index&cPath=2

Appendix B1

APPENDIX B – SURVEY RESULTS

HOVERCRAFT CUSTOMER SURVEY

Please fill out this survey so we can get a better understanding of what the public wants in a

hovercraft.

How important is each feature to you for the design of a recreational hovercraft?

Please circle the appropriate answer. 1 = low importance 5 = high importance

AVG

Safety 1 2 3(5) 4(1) 5(7) N/A 4.15

Durability 1 2 3(1) 4(4) 5(8) N/A 4.54

Reliability 1 2 3(1) 4(4) 5(8) N/A 4.54

Maneuverability 1 2 3(1) 4(7) 5(5) N/A 4.31

Effective brakes 1 2(1) 3(3) 4(2) 5(7) N/A 4.15

Ability to travel in

reverse 1 2(3) 3(6) 4(3) 5(1) N/A

3.15

Low noise 1(1) 2(5) 3(3) 4(2) 5(2) N/A 2.92

Cargo space 1(4) 2(4) 3(4) 4 5(1) N/A 2.23

Speed 1(1) 2(1) 3 4(3) 5(8) N/A 4.23

Ability to tow

skiers/tubers 1(6) 2(2) 3 4(4) 5 N/A

2.00

Cost 1(1) 2(1) 3(2) 4(3) 5(6) N/A 3.92

How much would you be willing to pay for this vehicle?

$1000-$2000 $2000-$5000(1) $5000-$10,000(3) $10,000-$15,000(6) $15,000+(3)

AVG Cost Range – High end of $5000 - $10000

Thank you for your time.

Appendix C1

APPENDIX C – QFD

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Rela

tive w

eig

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Rela

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%

Safety 9 9 9 3 9 9 9 9 9 1 9 4.2 0.10 10%

Durability 3 9 3 9 9 9 4.5 0.11 11%

Reliability 3 9 9 9 1 9 4.5 0.11 11%

Maneuverability 3 1 9 1 1 4.3 0.11 11%

Effective brakes 3 9 9 4.2 0.10 10%

Ability to travel in reverse 3 9 3 3.2 0.08 8%

Low noise 9 3 9 2.9 0.07 7%

Cargo space 1 9 2.2 0.06 6%

Speed 3 1 1 3 9 1 4.2 0.11 11%

Ability to tow skiers/tubers 3 9 9 9 2 0.05 5%

Cost 1 1 1 3 3 1 9 3 1 3 1 3 1 1 3.9 0.10 10%

Abs. importance 1.71 4.90 1.03 2.28 3.57 2.27 4.16 3.83 1.96 0.95 0.60 1.06 0.95 1.82 0.55 31.6

Rel. importance 0.05 0.16 0.03 0.07 0.11 0.07 0.13 0.12 0.06 0.03 0.02 0.03 0.03 0.06 0.02

Jeremy Siderits, Kelly Knapp, Dave LouderbackHovercraft9 = Strong3 = Moderate1 = Weak

QFD (Excel file) later Appendix C (pasted as picture)

Appendix C2

APPENDIX D – PRODUCT OBJECTIVES

Hovercraft Product Objectives

The following is a list of product objectives and how they will be obtained or measured to ensure that the goals of the project

were met. The product objectives will focus on the various aspects of a hovercraft. The hovercraft is a recreational vehicle and will

be designed to provide safe enjoyment for its users.

Reliability (11%): 5. A four cycle engine will be used, instead of the unreliable 2 cycle that is used on many hovercraft.

6. All electrical connections will be soldered and then covered with heat wrap to ensure

no bare wires will be exposed to water and corrosion. 7. All fasteners will be fastened with locknuts and/or Loctite for sturdy construction.

8. Engine will be powered at 85% during normal operation in order to obtain longer engine life.

Durability (11%): 5. A rubber crash bumper will be placed around the craft and attached to the exterior frame.

6. The hull will be constructed using ½‖ marine grade plywood coated with an epoxy primer and an enamel grade finish for

waterproofing.

7. All seams will be joined by fiberglass for superior strength and waterproofing.

8. All metal used for engine mounts or frame support will be primed and painted to prevent corrosion.

Speed (11%): 3. The craft will be designed to travel in excess of 40 mph on calm water.

4. Sloped shapes will be used to reduce drag.

Maneuverability (11%): 3. Reverse thrust buckets can be used in addition to the normal rudders to control the movement of the craft.

4. A turning radius of zero is achievable with minimal thrust but increases with speed.

Appendix C3

Safety (10%): 6. A screen will cover the thrust and lift fans.

7. Fan tip speed will be kept below the manufacturer’s maximum tip speed in order to keep the fan blades from breaking and possibly

injuring people.

8. Warning labels will be placed on:

a. Any electrical device to prevent shock

b. Around the fans to prevent injury

c. Near engines to prevent burns

9. A fire extinguisher will be placed on board in the event that the engine catches fire.

10. All other safety requirements will be upheld based on part manuals.

Effective braking system (10%): 4. The hovercraft will feature reverse thrust buckets that cause the hovercraft to reduce speed.

5. Fifty percent of the thrust airflow will be redirected for braking allowing a deceleration equal to one half of the acceleration rate.

6. An emergency stop feature will be used to cut power to the lift fan. Pads on the bottom of the hull will prevent damage when this

feature is used.

Cost (10%): 2. The hovercraft will be priced similar to an ATV or Jet Ski, around $10,000 new.

Ability to travel in reverse (8%): 2. The hovercraft will be equipped with reverse thrust buckets to allow the craft to travel in reverse by pulling a lever.

Low noise (7%): 4. Normal operation will be at less than 85 decibels.

5. The engines will be equipped with mufflers.

6. The fan tip speed will be below the manufacturer’s maximum tip speed. This will minimize excessive sound.

Cargo space (6%):

Appendix C4

2. The design will allow at least 2 ft3 of cargo space, located under the seat or in the front of the hull.

Ability to tow skiers/tubers (5%): 4. A tow rope will be able to be attached to the back of the craft.

5. In order to legally tow a skier, the craft will be able to seat 3 passengers.

6. It will have rearview mirrors so the operator can verify the safety of the skier.

Appendix D1

APPENDIX E – SCHEDULE AND BUDGET

SCHEDULE:

Appendix D2

HOVERCRAFT PROPOSED BUDGET:

System Component Price

Lift Bag Skirt $125.00

Lift Engine $100.00

Lift Fan $250.00

Muffler $50.00

Thrust Thrust Engine $100.00

Thrust Fan $350.00

Belt System $50.00

Reverse Buckets $50.00

Muffler $50.00

Body 1/2" thick marine grade plywood $150.00

misc wood $100.00

Fiberglass and resin $125.00

In-line Seating $40.00

Paint $75.00

Warning Labels $10.00

Duct Screen $20.00

Steel Tube Donated

Steering Handlebars $100.00

Rudders $50.00

Electrical Temperature Gauge $25.00

Temperature Gauge $25.00

Tachometer $25.00

Tachometer $25.00

Battery $50.00

Alternator $50.00

Misc Misc parts and hardware $375.00

$2,370.00

Material used for the bottom of the hull

Handlebar system

Temperature guage for lift engine

Temperature guage for thrust engine

RPM guage for lift engine

RPM guage for thrust engine

Joint support and waterproofing material

Enamel based paint for superior protection

Keep hand away, hot, electrical hazard

Fabric and support for seating

Hovercraft Budget

4-stroke engine

Muffler system

Mult-blade fan

Rudder system

Belt and pulleys

Fabricated fiberglass shell

Material used for ribs and top of the hull

Description

Vinyl coated nylon fabric

4-stroke engine (Discounted)

Multi-blade fan

Muffler system

Wire sceen for fan protection

N/A

Tube stock for engine support

12v Battery

System to charge battery

Total

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