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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
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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)
Hovercraft: Lift System and Steering Kelly Knapp
22
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
Hovercraft: Lift System and Steering Kelly Knapp
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
Hovercraft: Lift System and Steering Kelly Knapp
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
Hovercraft: Lift System and Steering Kelly Knapp
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
Hovercraft: Lift System and Steering Kelly Knapp
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
Hovercraft: Lift System and Steering Kelly Knapp
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
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
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
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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Cra
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esig
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Abili
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Rearv
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Custo
mer
import
ance
Rela
tive w
eig
ht
Rela
tive w
eig
ht
%
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