1. 0
ME 498-SENIOR DESIGN
Portable Hovercraft
Jason Carlstrom, Nolan Davis, John Hamman,
Matt Huff, Darren Popkins, Cory Roberts,
Michael Rogers
Saint Martin’s University
Hal and Inge Marcus School of Engineering
12/9/2013

2. 1
Acknowledgements
Dr. Jung
Dr. Kahn-Jetter
Dr. Slaboch
All our Engineering Faculty and Staff
Our Family and Friends

3. 2
Table of Contents
Acknowledgements 1
CHAPTER ONE:FALL DESIGN
First Design:VolkswagenHovercraft
Chassis / Skirt 3
Lift / Propulsion 4
Weight 5
SecondDesign:Searchand Rescue Hovercraft
Engine 6
Maneuverability/Body/Skirt 7
Design 8
Rescue 9
Final Design:Portable Hovercraft
Engine 10
Thrust and Lift 11
Performance 13
Static Analysis 14
Strength Test of Materials 15
Hull Design 16
Budget 20
Works Cited 22

4. 3
CHAPTER TWO: SPRING CONSTRUCTION
Actual Costs
Build Process
- Cowling
- Body Panels
- Steering
Obstacles

5. 4
CHAPTER ONE: FALL DESIGN
DesignOne: VW Beetle HoverCraft
This design will utilize the chassis and engine from a Volkswagen Beetle. The goals of
this model are to be street legal and hover capable. We chose the VW as the base because of its
simplicity, and light weight construction.
Chassis:
The craft will be constructed
around the Volkswagen Beetle chassis.
We chose the VW chassis because the
major drive components are all contained
in the chassis itself. The body is easily
removed from the chassis as well
making teardown very simple. Our
plans include removing the body and
possibly selling to recoup cost.
Once the body is removed we
are left with the chassis itself. This is
often called the “pan” and will be
referred to that throughout this design.
An illustration of a pan is shown below.
The pan has a solid floor board
Figure 2: VW Chassis
Figure 1: Chassis VW hovercraft design
Figure 3: VW Chassis hover craft design

6. 5
integrated into the construction. This is a major design advantage as compared to a conventional
vehicle chassis that uses only frame rails. This floor board will allow us to create an air tight seal
underneath the craft without needing to fabricate massive patch panels saving on cost and
fabrication time.
Skirt:
Material:
There are multiple options available for skirt material. We have purchased two different
types for testing thus far: Sport Nylon and PVC fabric. These materials will be tested for their
permeability and strength. We also plan to test the skirt construction method. We are currently
considering stitching and or adhesive/glues. These methods must also be tested for strength and
permeability. We must ensure that our seams and seals can withstand the pressure we calculate
for our air cushion ensuring blow outs will not occur.
Positions:
The skirt will need to have two positions; fully deployed and inflated for use in hover
operations, and fully retracted for driving operations. The current design for a multi position skirt
would have straps running under the craft and skirt. To deploy the skirt the straps will be
loosened, to retract the skirt the straps are tightened.
To utilize the wheels during driving operations the skirt will need to leave adequate
clearance for the rear wheels to spin and the front wheels to turn. Taking this into account we
come up with a rough estimate of a skirt footprint of roughly 2700𝑖𝑛2
to 3125𝑖𝑛2
.
Ride Height:
Further research must be conducted on skirt height. In a conventional hovercraft this
would not be of major importance, but due to the wheels on our craft we need to ensure that the
skirt provides enough lift for the wheels to clear the ground. The stock ground clearance for
1960’s era VW is approximately twelve inches. This however is for a suspension under full load,
with body attached. The ride height will certainly be higher once the body is removed and all
unnecessary weight is stripped. This means that our skirt will need to provide more than twelve
inches of lift. If this amount of lift is not possible we may need to find another option. This could
include lowering the ride height of the bug. This is easily achievable in a multitude of ways.
Commercially available lowering kit: We could fit one of the many aftermarket lowering
kits available for VW Beetles. These kits allow for the ride height to be reduced dramatically.
This method would be simple but not cost effective as kits run in the four hundred dollar range.
Smaller Diameter Tires: Another option would be fitting smaller diameter tires. The ride
height improvement will not be as great as the lowering kit but this method would be much
simpler and economical. Smaller tires would also help reduce weight of the craft. This would be
simpler and cost effective.

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Cut Springs: The last option would be to cut a certain amount of coils out of the springs.
This would allow us to lower the ride height to our choosing, but would adversely affect the ride
quality.
Lift:
The lift for our craft will come from 15 HP Briggs and Stratton lawn mower motor
mounted where the passenger seat would originally be located. The motor will be will be perfect
for this application due to its vertical shaft design. This will allow power to be transferred to our
propeller without the need to construct a complicated transmission system. The propeller blade
essentially replaces the lawn mower blade. A cowling will need to be built to surround the blade.
This cowling will allow the air to be directed straight down through a hole cut into the pan,
filling our skirt with air and creating the air cushion our craft will glide on.
Propulsion/Drive:
The goal of our craft is to be drivable on the street. This means that all of the original
drive components must be retained in our final design. All suspension components are mounted
to the front and rear of the pan. The motor and transmission are mounted off the rear of the pan.
Retaining the drivability of our craft should be fairly simply. A mount will need to be fabricated
to mount the steering column as well as pedal assembly once the body is removed. Throttle
cables and other miscellaneous cables may also need to be rerouted.
The plan is to utilize the original VW engine for propulsion as well as drive. The VW
Beetle came equipped with a differing range of engine sizes from 1200cc to 1600cc. These
engines range from 45 to 65 horse power and should have more than enough power.
When in driving mode the engine and drive train will be used in original configuration.
Once in hover mode the VW transmission will be placed in neutral ensuring that the rear wheels
remain stationary. The propulsion fan will be mounted directly behind the original motor. A
clutch mechanism will be designed to connect the propeller to one of the pulleys located on the
rear of the engine. This could be a mechanical clutch or an additional pulley/belt system. Once
the car is in neutral the propeller can be engaged connecting the prop to the engine. The engine
can then be revved to spin the prop up to proper RPM.
Some of our concerns are:
 The strength of the shafts at the rear of the engine. Will they be able to handle the extra
load placed upon them by the prop?
 The gearing, or lack thereof, on the rear shaft. Will we be able to reach the proper prop
RPM without redlining our engine? Also will there be enough torque to spin the fan?
Weight:
The biggest concern of this design is the weight. Standard VW beetles vary on weight
depending on the year and engine options. An average weight can be assumed to be 1900 lbs.

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Component Weight (lbs)
complete VW 1900
VW Body -500
Props 50
Lift Mower 75
Single Passenger 200
misc 100
Total 1825
This is very light for a production vehicle but very
heavy for a hovercraft of our scale. The main weight
savings will come from removing the body from the
chassis. The table listed below lists the weights of
various components. A minus indicates that the
component will be removed. We come up with a final
weight estimate of 1825 pounds. Using our estimated
air cushion area we can calculate the psi needed to lift our craft
1825 𝑙𝑏𝑠
2700 𝑖𝑛2 ≈ .7 to
1825 𝑙𝑏𝑠
3125 𝑖𝑛2 ≈ .6 𝑝𝑠𝑖.
converting these values to pounds per square foot we end up with a pressure range of 87 psf to
101 psf. This pressure is too high for our skirt to contain.
Conclusion:
The downfall of this design comes down to weight. We have concluded that starting with
a Volkswagen Beetle chassis will be too heavy for the footprint the skirt will cover. Even after
stripping the chassis of the body and extra parts we still estimate a weight of 1825lbs. This is just
an estimate, as the weight could be much higher. We could compensate by increasing the lift fan
power, but this will increase the weight and require a more robust skirt. We have decided to
change directions and manufacture our own light weight chassis in hopes to decrease weight and
increase speed and maneuverability.
Verdict:
Overall this project proved to be simply too expensive to be plausible. The sheer size and weight
of the hovercraft demand a more powerful (and thus more expensive) engine.
DesignTwo: Search and Rescue Hovercraft
This design is intended to address the unique requirements of a hovercraft designated for
quick response, search and rescue of a single non-ambulatory person in variable amphibious
conditions.
Our goal for this project is to design and build a highly maneuverable hovercraft capable
of speeds of over 35 miles per hour, with the ability to extract one person from water. The
hovercraft will have a 600-800 pound payload to account for one driver, a two-person rescue
crew, medical supplies, and the patient. Our estimated budget is $3200.
Engine:

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We have incorporated a two-engine design, with one engine for lift and the other for
thrust. The advantage of this system is that the thrust engine can be shut off without affecting the
lift, which allows the hovercraft to be stationary on the water, which is a key characteristic for
rescue. The hovercraft will need to remain in one spot while the rescue team enters the water and
moves the patient onto the hovercraft.
Lift:
The lift fan will be powered by a Briggs & Stratton riding lawnmower engine with 15
horsepower. The engine will be positioned near the front of the hovercraft. The vertical shaft will
work perfectly with our lift fan to power it without the need for much alteration. This is the ideal
engine because it is lighter than a more powerful engine, but has enough power to lift the
hovercraft.
Thrust:
The thrust fan will be powered by either another lawnmower engine or a small VW
Beetle 4 cylinder engine. Because our goal includes quick response and speeds of over 35 mph,
we will need more power from the thrust engine than the one for lift. A slightly more powerful
lawnmower engine might be enough, but our preferred engine would be a VW Beetle engine
because it is air cooled, not terribly heavy and would produce plenty of horsepower. This
decision will depend on what kind of budget we have to work with.
Handling / Maneuverability:
One of the main disadvantages of the typical hovercraft is that it is extremely difficult to
maneuver and movements are not precise at all. This design incorporates several features that
aim to increase both maneuverability and precision of our movements. Our initial design
included side thrusters, which took a portion of the air from the lift fan and directed it out the
sides through vents, which could be opened to provide lateral movement without turning the
hovercraft. We tested this design in our small-scale model, but our tests revealed that the airflow
was not sufficient to move the hovercraft from side to side. Our other idea to increase the
precision of movement addresses the other main issue with a hovercraft, which is braking. By
including a cowling around the thrust fan which can close and redirect the air flow, our fan
creates a reverse thrust, which will slow the hovercraft considerably, allowing for much more
responsive braking and stopping.
Body:
This design will use a foam core chassis with wood reinforcements for structural
integrity. The chassis will be formed by layering sheets of foam in the shape of our hull, then
applying fiberglass to the foam and wood. We will use several sheets of foam for the floor, and

10. 9
put in wood reinforcements underneath the lift fan, thrust fan, and the rest will be spaced evenly
along where the crew will be seated.
General dimensions for the current design show the hovercraft roughly 9 feet wide by 14
feet long. The width needs to be adequate to hold a patient lying horizontally after being rescued,
with enough room for the rescue tube and guardrails. As is discussed later, the surface area
requires roughly 130 square feet, which drives our length dimension to be at least 14 feet. This
allows plenty of room for the engines, all 4 passengers and the fan.
Skirt:
Material:
We have purchased two different types for testing: Sport Nylon and PVC fabric. These
materials will be tested for their permeability and strength. We also plan to test the skirt
construction method. We are currently considering stitching and or adhesive/glues. These
methods must also be tested for strength and permeability. We must ensure that our seams and
seals can withstand the pressure we calculate for our air cushion ensuring blow outs will not
occur.
Design:
Our initial plan for the skirt was a solid one-piece tube skirt. The advantage of this design
is that it is much cheaper and easier to manufacture. It is also the most stable skirt design, which
is important for such a large hovercraft, especially when loading a patient on board. An
alternative option we considered was a “finger skirt”, which consists of many small individual
sections that connect near the top. This type of skirt is much harder to make and is more
expensive, but is much more durable than a tube skirt. This is because if one section or “finger”
on the skirt rips the rest of the skirt remains intact. The downside of this style is that it is much
less stable and more expensive to produce. After further research, we decided that the best option
to help us achieve our goals would be a hybrid design featuring a finger skirt in the front and a
tube skirt in the back. The advantage of this design is that the front of the hovercraft can
withstand a small tear in the skirt without losing too much air pressure, but the back of the
hovercraft will provide enough stability to keep the hovercraft stable while bringing the patient
on board.

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Rescue
In order to save
weight and reduce cost, our
system for extracting a
patient from the water will
be as simple as possible.
Our rescue system takes
cues from lifeguard
practices and applications.
The craft will carry two
dedicated rescue swimmers
and be equipped with; two
lifeguard “rescue tubes”, a ring buoy and back board. This equipment will allow the craft to
handle a multitude of rescue situations. The ring buoy can be utilized to rescue victims within
tossing range while keeping the rescue swimmers safe inside the craft. The back board will allow
possible head or spine injuries to be handled in the correct manner. The sides of our hovercraft
would be angled down to allow for a smooth transfer of the back board from water to the
hovercraft, and guide rails would help guide the board back onto the hovercraft for a gentle
rescue without further aggravation of any injuries the patient may have suffered. There will be a
dedicated seat for the victim once he is on board. In the case of a head or neck injury there will
be tie downs to keep the back board safely secured to the deck.
Concerns
Figure 4: Search and rescue craft design mock up Figure 5: An example of a finger skirt
Figure 6: Example of a Hybrid Designusing both Finger Skirt (front) and solid tube
(back).

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Our biggest concern for this project is our budget. Building a hovercraft capable of
carrying four people (roughly 800 pounds) requires a large surface area and a skirt pressure high
enough to support the craft. The average hovercraft has a skirt pressure of about 10 psf
(pounds/square foot). Our initial design for the hovercraft produced an estimated total weight of
500-600 pounds. Adding the weight of 4 passengers, the hovercraft would need to lift a total of
at least 1300 pounds. Assuming that we maintain the average skirt pressure for a hovercraft, ours
would need a skirt surface area in contact with the ground of 130 square feet (just over 9 ft. by
14 ft.). This is a very large project to build and using lightweight (but cost effective) materials
our budget came to an estimated $3200. Major components include our two engines, skirt
materials, propeller, and foam sheets for our main body.
Verdict:
Overall this project proved to be simply too expensive to be plausible. The sheer size and
weight of the hovercraft demand a more powerful (and thus more expensive) engine, as well as
large amounts of foam and skirt material. Unfortunately, it would not be reasonable to focus on a
smaller rescue hovercraft because it takes at least two people to perform the physical rescue, and
a hovercraft is not reliable enough to leave running without a driver. Therefore, 4 is the smallest
number of people that the rescue hovercraft is practical for, and so it cannot be downsized to
save on cost.
Final Design: Portable Collapsible Hovercraft
This design is designed to make a recreational hovercraft that can be folded up by a
single driver and stored in the bed of a pickup truck easily.
Our goal for this project is to
design and build a lightweight (under
200 lbs) hovercraft that’s capable of speeds of over 20+ miles per hour, with the ability to be
folded flat along 2 hinge points, support the weight of an average sized person (200 lbs) and fit
in the bed of a truck.
Engine
We have decided to go to a single engine design that will be able to provide both the lift
and the thrust for the engine. The engine we have decided to go with is a Briggs & Stratton 1150
Snow Series engine with 6 horsepower. The engine will be positioned in the back of the craft and
Figure 7: Hull design mock up

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the horizontal shaft will work perfectly to provide the fan blades for the thrust. This is the ideal
engine because it is only 15 pounds which is the heaviest individual component of the hovercraft.
Dimensions and General Craft Design
The craft will be made out of three
panels, each three feet by three feet. The
panels will be connected by hinges, so that
the craft can be folded up and easily
transported and stored. The panels will be
constructed of foam core with wood support
and fiberglass laminated skin. A seat will fold
out of the center panel, as will control levers
(one for throttle, the other for steering).Figure
8 shows a final design overview.
The foam we plan to use is expanded
polystyrene foam; this is available at Lowes
or Home Depot in a variety of sizes. We have discovered through testing that polyester resin will
eat through our foam. After further research we have found that epoxy resin will not eat the
foam, thus our hull will be constructed of polystyrene foam coated with epoxy resin and
fiberglass cloth.
Thrust and lift design
For the sake of easing calculations, all units have been switched to SI:
Total engine output power 𝐸̇ = 6.5 ℎ 𝑝 = 4849 𝑊
Fan diameter 𝐷 = 30 𝑖𝑛 = 0.762 𝑚
Skirt pressure 𝑃𝑠 = 12.12
𝑙𝑏𝑓
𝑓𝑡2 = 579 𝑃𝑎
Standard atmospheric pressure 𝑃𝑜 = 101 𝑘𝑃𝑎
Craft weight 𝑊𝑐 = 300 𝑙𝑏𝑓 = 9.32 𝑠𝑙𝑢𝑔 = 136 𝑘𝑔
Density of air at sea level, and room teature 𝜌𝑜 = 1.225
𝑘𝑔
𝑚3
Thrust Output
Research on fan thrust designs shows us that thrust fan/duct setups rarely exceed 50%
efficiency (Brooks). So, for the sake of being conservative, we estimate our final fan will have
about 30% efficiency. This should be a fairly good estimation, as we will do all we can to match
the proper fan to our engine’s power and speed range, but we do not have access to the resources
needed to fully design our own system. Because of this, much of these calculations are simply
estimations, and the final design will depend on what engine we procure, and what fan is within
our budget.
Figure 8: Final design mock up

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Thrust force is defined by the mass being moved times the velocity at exit, or𝑇 = 𝑚̇ 𝑉𝑑 .
In this case, the net thrust can be defined as the change in velocity from the front of the fan, to
the back or𝑇𝑛𝑒𝑡 = 𝑚̇ ( 𝑉𝑑 − 𝑉𝑜). The mass flow rate will also depend on the speed of the air, the
density of the air and the area of flux. So, the final equation for thrust is𝑇𝑛𝑒𝑡 = 𝑉𝑑 𝐴 𝑑 𝜌 𝑑( 𝑉𝑑 −
𝑉𝑜). It should be noted that as the free stream air𝑉𝑜, reaches the same speed as the discharge air
(such as when the craft nears its maximum speed) then the thrust force goes to zero. So, the
highest thrust is when the fan is subjected to static conditions, such as when there is zero outside
wind speed, and the fan is not moving, or 𝑇𝑛𝑒𝑡 = 𝑉𝑑
2
𝐴 𝑑 𝜌 𝑑. The power is defined as𝐸̇ =
𝑚̇ 𝑉𝑑
2
2
. So,
swapping in the equation for thrust, we get𝐸̇ =
𝑇𝑉 𝑑
2
=
𝑉𝑑
3
𝐴 𝑑 𝜌 𝑑
2
. This equation is useful to allow us
to find the discharge velocity, given fan power
consumption.
Small engines typically exhibit fairly flat
power curves. The lower end of the RPM range
should only be about 22% less power than the
peak output, as seen in Figure 8. So, using 2.6 kW
as our low end of the power range, and 30% fan
efficiency, the velocity of air at the discharge
should be about 14.1 m/s. The high end of the
engine’s power should give a discharge velocity of
17.3 m/s.
Estimating Lift Pressure and Required Airflow
The fan will be giving thrust, as well as lift power to the skirt. This means we will have to
section off an area of the fan for lift air. Looking at Bernoulli’s equation, we can see that the
velocity of air will create a certain pressure if the velocity is brought to zero. This is the ideal
case for the craft, where there is zero air leakage from the skirt. Of course, there will be much air
leakage, and some is actually required in order to keep the skirt off the ground. For the sake of
determining available lifting pressure, we can use Bernoulli’s equation, coupled with ideal gas
law. In the case of the hovercraft, we will assume negligible change in potential energy, so the
resulting equation comes to be
𝑉𝑑
2
2
+
𝑃 𝑑
𝜌 𝑑
=
𝑃𝑠
𝜌 𝑠
. Using the ideal gas law,𝑃𝑉 = 𝑚𝑅𝑇 we can
find
𝑃 𝑑 𝑉 𝑑
𝑚 𝑑
=
𝑃𝑠 𝑉𝑠
𝑚 𝑠
, or
𝑃 𝑑
𝜌 𝑑
=
𝑃𝑠
𝜌 𝑠
. We are assuming standard atmospheric pressure and density of air,
and we know the skirt pressure should be 579 Pa, so𝜌𝑠 = 1.232
𝑘𝑔
𝑚3 . Using these values we can
find that the required minimum velocity at the discharge should be 0.0055 m/s. This figure is
very low compared to the velocity of our idealized fan at its low power setting, but keep in mind
this is the velocity required to only lift the craft. It does not provide a layer of air between the
skirt and the ground, nor does it take into account air leakage.
Figure 9: Sample power curve for similarengine selected

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If we arbitrarily set the hover height (that is, the air gap between the skirt and the ground)
to 2.5mm, then we can find a volumetric flow rate required to keep this gap. The perimeter of the
skirt envelope was found using the dimensions
of the craft, a skirt height of 8 inches (0.2 m),
and a 45° skirt angle, the perimeter comes to
6.919 m. assuming the air inside the skirt
envelope is not moving initially, then
Bernoulli’s equation simplifies to
𝑃𝑠
𝜌 𝑠
=
𝑃 𝑔
𝜌 𝑔
+
𝑉𝑔
2
2
.
So,𝑉𝑔 the velocity at the air gap comes to
0.055m/s. The area of flux is the gap times the
perimeter, equaling 0.0346 m2 with a 2.5 mm
gap. With these conditions we would require a
volume flow rate of 0.00095 m3 /sec. So, with
the air velocity flowing at the minimum speed
for pressure buildup, we would require 0.173 m2
of fan area.
Lift Section of Fan
To find the area of the fan we must section off for lift, we can use simple geometry.
Figure 10 shows the area of the fan output, the shaded region showing the area sectioned off for
lift. The area of the quadrant of the circle, with angle 𝜑, is found by the equation 𝐴 𝑞 =
(
𝜑
360
) 𝜋𝐷2
4
.
The area of the triangle ABC, is 𝐴 𝐴𝐵𝐶 =
ℎ2 𝑆
2
=
𝐷2
2
sin2 𝜑
2
. The angle 𝜑, is simply 𝜑 = 2sin−1 𝑠
𝐷
.
The area of the sectioned fan is the area of the quadrant minus the area of the triangle, thus 𝐴 𝑠 =
𝐴 𝑞 − 𝐴 𝐴𝐵𝐶 . So the area of the lift section is 𝐴 𝑠 =
(
𝜑
360
) 𝜋𝐷2
4
−
𝐷2
4
𝑠𝑖𝑛
𝜑
2
cos
𝜑
2
. Using this equation
𝜑comes to 158 degrees., which gives ℎ1 = 0.374 𝑚, or about the radius of the fan.
It must be noted, all of the lift and thrust calculations are very tentative. These
calculations are very simplified, and when actually building the craft, some tests must be
conducted in order to maximize the system.
Craft Performance
Estimating the crafts acceleration can be accomplished using Newton’s Second Law
𝑇𝑛𝑒𝑡
𝑚 𝑐𝑟𝑎𝑓𝑡
= 𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛. The initial acceleration is easy enough to find, since 𝑉𝑜, the free stream
velocity, is zero. The initial acceleration is 0.467 m/s/s. As the craft accelerates, the thrust
decreases, so to find the velocity as a function of time, the following differential equation must
Figure 10: Diagram of fansections

16. 15
be solved
𝑑𝑉
𝑑𝑡
=
( 𝑉𝑑
2
−𝑉 𝑑 𝑉( 𝑡)) 𝜌𝐴 𝑑
𝑚 𝑐
. A second order differential equation is formed as
𝑑2
𝑥
𝑑𝑡2 = −
𝑉 𝑑 𝜌𝐴 𝑑
𝑚 𝑐
∗
𝑑𝑥
𝑑𝑡
+
𝑉𝑑
2
𝜌𝐴 𝑑
𝑚 𝑐
. The differential equation was solved, and the velocity as a function of time is found
to be 𝑉( 𝑡) = 𝑉𝑑 (1 − 𝑒
−
𝑉 𝑑 𝐴 𝑑 𝜌𝑡
𝑚 𝑐 ). So, this equation limits the top speed of the craft to that of the
discharge speed. Using this function, it appears that it should take the craft about 19 seconds to
accelerate to 50% of its max speed, or 8.65m/s (19 mph). It will take much longer to accelerate
from 8.65 to 16 m/s (65.5 more seconds), but it is likely the craft will not be operated in this
range often. Of course, these speeds neglect drag, but hopefully the low profile design does not
slow it down too much.
Static analysis of the craft
The hull of the hovercraft is flat, and consists of three individual sections which are 3x3
feet. Because of the nearly uniform width of the craft, and the linear arrangement of the weights
(the rider and engine/fan assembly), it can be modeled as a beam. To do this, first an estimate of
the pressure it takes to lift the craft must be made. In this case, assuming a rider of 200 pounds
and an engine weight of 100 pounds, with a lifting area of 24.75 ft2, the pressure to lift the craft
comes to 12.12 lb. / ft2.
The engine’s weight was
set at 1.5 feet from the aft
edge, and to fully balance
the forces, the rider’s
center of mass must be set
at about 3.5 feet from the
front edge.
To find a linear
distributed load, which
accounts for the lift force,
the width of the craft can be multiplied by the pressure. This is relatively simple for most of the
craft, as the distributed load becomes 12.12*3, or 36.36 lbs/ft. The very front section makes this
rather difficult, however, since it is circular. To simplify the math required, the front was
assumed to be triangular (see Figure 11). So for the first 1.5 feet of the craft, the distributed load
equals 24.24*x. Integrating the distributed load functions gives the sheer force as a function of x.
Integrating this once more gives the bending moment as a function of x. These functions were
put into excel, and can be seen in Figure 12. So, with a 200 pound rider, and the configuration
Figure 11: Side view of static forces on hover craft

17. 16
shown in Figure 11, the maximum sheer force comes to be 101.4 pounds, and the maximum
bending moment is 145 ft.*lb.
Figure 12: Bending moment and sheer force diagram
Strength test of actual materials
We conducted a strength test on a piece of simulated
structure from the hover craft. The piece was a sheet of
foam, one inch thick, 15.375 inches long, and six inches
wide. On one end was epoxied a piece of wood, used to
simulate the hinge section on the folding hovercraft. On the
two largest faces and around the wooden insert, fiberglass
and epoxy resin was attached. The goal of this experiment
was two-fold. We wished to get a better sense of the strength
of the materials we intend to use, as well as insuring that the
design of the hinge section will be acceptable.
First, the test piece was clamped on the wooden
section between two flat pieces of steel, in a bench vise. A
pulley was set up across from it, at the same height as the
predetermined attachment point of the piece. To test the
deflection at the varying weights, an arrow shaft was
attached to the base of the vise. As the piece flexed, an
accurate measurement was taken from the straight arrow rod.
-100
-75
-50
-25
0
25
50
75
100
125
150
0 1 2 3 4 5 6 7 8 9
X (Feet)
Sheer Force (lbs)
Bending Moments (ft*lbs)
Figure 13: Materials test setup

18. 17
Results
Hinge strength
The wooden section used to
simulate the hinge section on the final
hover craft performed well. The test piece
failed in the foam and fiberglass section
about 4 inches above the wooden joint.
This is a rather simplified set up,
compared to what will actually be
employed, as it has no holes for screws,
and was clamped together. Even with the
differences in the set up, it still shows that
the joint between the foam and wood
should hold up.
Foam and laminate strength
The results of this strength test are somewhat inconclusive.
Even still, much has been gleaned from the test. The first test failed at a
force of 12.74 pounds, the face pointed towards the force buckled
inward. The test clearly failed in compression, which was expected, as
fiberglass is known to be weak in compression. Since the side in tension
was relatively undamaged, we decided to test the piece again, after
turning it around. This, of course, was not intended to give any real
data, but actually turned out quite useful. The failure limit for the
second test was right at 12.5 pounds, nearly identical to the first. This
shows that the fiberglass laminate, at least on a piece with only one
layer thick, provides little strength in compression. This later
determined how we calculated the configuration of our final design.
We also were able to find approximate values for E*I (the
modulus of elasticity times the moment of inertia). The data gained for
this value proved to be quite varied. For both tests, it decreased as the applied force increased.
For example, the first test with the lowest applied weight (7.71 pounds) gives E*I as 37.1 lb.*ft2 ,
whereas the second weight of 12.74 gives E*I as 26.8 lb.*ft2. This is likely due to compressive
damage, and the foam core being pushed beyond its elastic range. The second test ranged from
Figure 14: Shows compressive failure, but still intact wood
structure
Figure 15: Compressive failure

19. 18
E*I equaling 22.4 168.3 lb.*ft2. Because of the varied nature of the E*I values, we are not able to
use the data gained for E*I.
Designing for hull thickness
Using the maximum bending moment from our test, we can get an accurate idea of how
wide our hull should be. For both tests, the moment applied to the test piece was about 16 ft.*lbs.
Since the moment of inertia varies linearly with the hull width, we can use this value to find the
max bending moment that can be applied to the craft. With an identical setup of material
configuration and foam thickness, our hull should be able to withstand six times the bending
moment of the test piece, as the hull is six times as wide. The width was predetermined by size
constraints we chose earlier. This means, our hull should be able to take a bending moment of
about 100 ft.*lbs. The statically determined max bending moment is actually 140 ft.*lbs., so with
one inch thick foam, we are still far below the required strength.
Another way we decided to look at the problem is by using the compressive limit of the
foam. The manufacturer gives the foam we used in our test piece a maximum compressive limit
of 25 psi (Foamular). If we assume the fiberglass in tension will exhibit negligible deformation,
and be indestructible compared to the compressive strength of the foam (which it is certainly
many times stronger), then we can find the thickness of foam needed for our 36 inch wide craft.
Put another way, the neutral axis would be located right at the surface where the foam and
fiberglass meet (seen in Figure 16). The static calculations show that the maximum static
bending moment is about 145 ft.*lbs. The equation for maximum stress in the given conditions is
𝜎 =
𝑀𝑦
𝐼
, where M is the moment, y is the thickness, and I is the moment of inertia (in this case,
equal to
𝑏𝑦
3
). Simplifying, we get 𝜎 𝑚𝑎𝑥 =
3𝑀
𝑏𝑦2 , and solving for y yields 𝑦 = √
3𝑀
𝑏𝜎 𝑚𝑎𝑥
. Using this
equation, we find that the thickness of the craft needs to be 2.41 inches. Unfortunately, this
thickness is rather impractical. The foam only comes in one or two inch thick sheets, so we
would have to use four inch thick sheets, which raise cost and weight issues, and most
importantly there is no safety factor. Another option could be to use multiple sheets of fiberglass,
which would provide rigidity to the laminate and offer some compressive strength, but again, we
run into the cost wall.
The Final Design
Figure 16: Diagram for finding the thickness of the hull

20. 19
Since the strength of the foam and fiberglass was not strong enough on its own, we decided the
most cost-effective method to remedy the situation was to add a wooden spine down the middle
of each panel of the craft. Following is the strength calculations and factor of safety attained
thereof.
The modulus of elasticity of a composite is calculated by𝐸𝑐 = 𝑥𝐸𝑓 + (1 − 𝑥) 𝐸 𝑚 , where x is the
ratio of cross sectional area of the fiber to the matrix, 𝐸𝑐is the elastic modulus of the composite,
𝐸𝑓 is the elastic modulus of the fiber, and 𝐸 𝑚 is the elastic modulus of the matrix (Kalpakjian).
Using this equation, we found the elastic modulus of our fiberglass composite will be 6.3 ∗
106
𝑝𝑠𝑖, which assumes a 50/50 ratio of glass to resin. Using the same model, the tensile strength
of the composite comes to 2.58 ∗ 106
𝑝𝑠𝑖.The elastic modulus for the wood we will likely use to
build the craft (Douglas fir) will be about 1.95 ∗ 106
𝑝𝑠𝑖 (WoodBin). For the sake of
computation, we assume that
the modulus of elasticity of
the foam core will be
negligible, as it is far lower
than either of the other two
structural components. We
also will assume that the
fiberglass composite will
offer no strength in compression.
An excel program was created to be able to change the width of the wooden sections, in order to
achive the desired safety factor. By using a total width of wood of 5 inches, there is a safety
factor of about 8 for the wooden sections. Of course, this is without considering the added
strength of the foam core, and the top layer of fiberglass, so the safetly factor should be
somehwat higher in actuality. The final configuration can be seen in Figure 17.
Table 1: Neutral axis, and strain calculations
Componen
t yi Ai Ai*yi Y ybar
Ai*y^
2 I-x I-i Stress-i
Max
Stress n
1 0.52 5 2.6 0.165 0.136 0.417 0.553
501.36
08 3940 psi
7.8586
12
2 0.01 2.39 0.0239 0.345 0.284
7.757E
-05 0.285
-
6957.3
3
6.34*10
^6 psi
370.83
2
Sum 7.39 2.6239 0.355
Re-adjustment of Bending and Sheer Forces
Figure 17: The final configuration and modulus of elasticity used for each material
Figure 18: Diagram illustrating the values for the neutral axis location and
strain calculations.

21. 20
Now that a theoretical thrust for the engine has been found, we must make sure the
moment caused by the thrust force is still within structural limits. Assuming half the fan is
sectioned off for lift, which leaves the other half to supply 83.5 N, or 18.75 lbf. of thrust, at
maximum output. The centroid of thrust would be located 18.2 inches above the deck of the
craft. This adds an extra torque of 30ft*lbs at x=7.5 feet. The bending moment at this location
was only 40 ft.*lbs., giving a total of 70 ft.*lbs., which is still far below the maximum already in
place from static loading, of 140 ft.*lbs.
Hinge and bolt calculations
From earlier calculations, it is observed that the most shear force and moment a hinge or
latch will face are 81.84 lbs. and 96.48 lb.-ft. respectively at the foremost joint. The chosen latch
is capable of operating under forces up to 2000 lbs, which is greater than one order of magnitude
of the calculated shear force assuming a 200 lb. rider. No failure is expected to occur through
shear therefore as it is expected that the steel has homogeneous strength properties.
From the stress analysis shown below, which assume a static loading, it is clear that the
moment at the intersection is sustained entirely by the hinges and latch system. We therefore get
that the maximum shear sustained by all bolts in the front joint is 1157.76 lbs. We must then find
whether this joint will fail by the wood beam or the steel bolt.
From Mechanics of Materials, 8th edition by R.C. Hibbeler, we get the following equation :
𝜏 𝑚𝑎𝑥 =
𝑉𝑄
𝐼𝑡
, simplified for a regular bolt this becomes 𝜏 𝑚𝑎𝑥 =
4
3𝜋
𝑉
𝑟2 . Assuming a standard A36
steel bolt, we can alter our earlier formula as follows; additionally we will add a safety factor of
2:
𝑟 = √
8
3𝜋
𝑉
𝜏 𝑚𝑎𝑥
As we assume that the stress will be sustained by at least 4 bolts per section, we
get that our bolts must be at least 0.1652 inches in diameter, of which bolts of this diameter are
very practical and easy to obtain.
Figure 19: Depiction of the expected forces and stresses on thejoint
section at a maximum

22. 21
If we assume that the joint will fail by fracture of the wood beam, we must make the
following assumptions: the bolts go through the full wood beam, the bolts will experience a
maximum potential stress intensity factor of 3, and the stress is uniform in the axis of the bolt,
furthermore the failure stress of pine wood from MATWEB.com was observed to be around 508
psi. The maximum stress the wood beam will experience is defined by the following equation:
𝜎 𝑚𝑎𝑥 =
𝑉
𝐷𝑡
and comes to approximately 5266.6 psi, which would mean catastrophic failure. We
must therefore reinforce the area around the bolts, which is accomplished by the Plexiglas
coating and small pieces of sheet metal around the bolt holes. As the Plexiglas coating is at least
0.2 inches and has a yield strength of around 14,504 psi, and any steel plate reinforcement will
have a yield stress of approximately 36000 psi, we can safely assume that the bolts will not cause
failure of the material and of the craft hull.
This design includes foam and wood sections, fiberglass overlay, and reinforcement steel which
are bonded to the fiberglass.
The hinge used is a long piano hinge opposite the latch. As there will be significantly
more screws used to hold this section and a much longer hinge, failure in the hinge is extremely
improbable and can be ignored.
Budget
1) Snowblower 6 HP engine $100.00
2) Propulsion fan and hub $249.95
http://www.ebay.com/itm/45-Arrowprop-Air-Boat-Prop-w-Aluminum-Hub-No-45AB36-Use-It-or-Man-
Cave-/171103051253?pt=Boat_Parts_Accessories_Gear&hash=item27d6895df5&vxp=mtr
3) Chicken wire, for prop cage $19.97
http://www.amazon.com/308476B-48-Inch-50-Foot-Galvanized-
Hexagonal/dp/B000XFX6TY/ref=sr_1_1?ie=UTF8&qid=1381036054&sr=8-1&keywords=chicken+wire
4) Plywood for lift fan, propulsion cowling. 2 sheets at $23.76 each $23.76
5) http://www.homedepot.com/p/Project-Panels-3-4-in-x-2-ft-x-4-ft-Pine-Plywood-2-Pack-
1502108/203444162#.Uo0d7OLOT8c
6) 2x4x8 foot studs forframe structure,10 total at $2.29 each $22.90
Figure 20: Detailed view of hinge section with steel reinforcement

23. 22
http://www.homedepot.com/p/Unbranded-2-x-4-x-8-Premium-Kiln-Dried-Whitewood-Stud-
161640/202091220#.UlEBZBCWn8c
7) Sheet metal for creation of control fins $21.98
http://www.homedepot.com/p/MD-Building-Products-3-ft-x-3-ft-Aluminum-Sheet-
57000/100351161?N=c27v#.UlEDGhCWn8c
8) Piano wire for control systems $11.48
http://www.amazon.com/Carbon-Smooth-Diameter-Precision-
Tolerance/dp/B000VYNE3A/ref=sr_1_12?ie=UTF8&qid=1381042095&sr=8-12&keywords=piano+wire
9) Skirt material, $7.00 per yard, 11 yards $77.00
10) 5 gallons unleaded gasoline, at $3.50 a gallon $17.50
11) Foam sheets for platform, 4 at $20.37 each $81.48
http://www.homedepot.com/p/R-Tech-2-in-x-4-ft-x-8-ft-Foam-Insulation-
310891/202532856?N=baxxZ1z0z6k1#.UlMZBRCWn8c
12) Skirt glue $9.95
http://www.hovercraft.com/content/index.php?main_page=product_oversize_info&cPath=189_62&product
s_id=159
13) Fiberglass sheets,at $6.65 per yard, 10 yards $66.50
http://www.uscomposites.com/cloth.html
14) Fiberglass epoxy for hull, 1 gallons at $39.00 each $39.00
http://www.uscomposites.com/polyesters.html
15) Hinges for steering assembly. 5 sets at $2.77 each $13.85
16) Aluminum tubing for fin assembly, 2 at $19.54 each $39.08
http://www.homedepot.com/p/Crown-Bolt-1-in-x-48-in-Aluminum-Square-Tube-with-1-16-in-Thick-
40620/100337956#.Ul83uxDOT8c
17) Steel tube for engine mounts, load bearing structures.4 at $11.22 each $44.88
http://www.homedepot.com/p/Crown-Bolt-1-2-in-x-72-in-Plain-Steel-Square-Tube-with-1-16-in-Thick-
42310/100338243#.Ul85gxDOT8c
18) Wood screws for hull, deck etc. 2 boxes at $8.47 each $16.94
http://www.homedepot.com/p/Grip-Rite-8-x-2-1-2-in-Coarse-Polymer-Plated-Steel-Bugle-Head-Phillips-
Wood-Screws-1-lb-per-Box-PTN212S1/100173447#.Ul86XRDOT8c
19) Heavy duty Loctite construction adhesive.2 at $4.57 each $9.14
http://www.homedepot.com/p/Loctite-9-fl-oz-Clear-Power-Grab-Heavy-Duty-Construction-Adhesive-
1589157/203009262#.UosW5uLOT8c
20) 2 canisters paint primer, at $6.49 each $19.47
http://www.oreillyauto.com/site/c/cat/Paint+%26+Body+Repair/C0171/C0014.oap?year=2010&make=Wo
rkhorse&model=W42&vi=5161417
21) 1 canisters red paint, $21.99
http://www.amazon.com/Dupli-Color-BSP303-Candy-Finish-
System/dp/B003TQEY4A/ref=sr_1_1?s=automotive&ie=UTF8&qid=1382123745&sr=1-
1&keywords=red+car+paint
22) Conduit for control systemcables, 2 at $9.99 each $19.98
http://www.homedepot.com/p/AFC-Cable-Systems-1-2-in-x-25-ft-Non-Metallic-Liquidtight-Conduit-
6002-22-00/202286718#.UmGMNhDOT8c
23) Electrical wire $6.99
http://www.oreillyauto.com/site/c/detail/CTI0/85700/N1278.oap?ck=Search_N1278_1314373_3190&pt=N
1278&ppt=C0335al
24) Electrical tape, 2 at $4.49 each $8.98
http://www.oreillyauto.com/site/c/detail/MMM0/03799NA/N0226.oap?ck=Search_electrical+tape_131437
3_3190&keyword=electrical+tape

24. 23
25) SHIPPING COST AND TAXES. May be up to %20 or more of each products cost.
Estimated to be around: $170.60
TOTAL COST: $853.01 pretax/shipping
TOTAL COST: $1023.612
Conclusion:
We fully expect this craft to be completely operational if built to the design specifications
listed above and will be able to be built to be within a more realistic budget compared to the
previous designs. The design should prove to be quite robust, unique, and reliable, owing to the
use of lightweight composites and innovative design.
Works Cited
Brooks,Ian."EstimatingThrustand LiftPerformance."buildandcalculationguide.n.d.Document.
efunda.n.d.web.3December2013.
Foamular.n.d.web.5Dec 2013.
Hibbeler, R. C. . Mechanics of materials. 8th. Pearson Prentice Hall, print.
Kalpakjian,SeropeandStevenR.Schmid. MaufacturingEngineering and Technology.UpperSaddle
River,NJ:PearsonPrentice Hall,2010. print.
Resin Research.n.d.web.5 Dec 2013.
WoodBin.n.d.web.5 Dec 2013.

25. 24
CHAPTER TWO: SPRINGCONSTRUCTION
ACTUAL COSTS
After tallying up our costs for building the portable hovercraft, our total cost is $1,150. This is
$150 under our estimated budget from fall semester, so we came in 11.5% under our original
estimation. We feel this is a significant achievement because there were a lot of unforeseen
circumstances that resulted in higher costs. The main change that occurred was an increase in the
width of our craft from 3 feet to 5 feet, which resulted in an increase in surface area from 27
square feet to 45 square feet. This greatly raised the price for some of our materials, including
foam, fiberglass cloth and epoxy. A table of our costs is included below to show our most
expensive items.
BUILD PROCESS
Our build process was determined by a few key pieces of information that needed to be tested
before we could determine some of our other designs.
Cowling
The most important measurement for our hovercraft is the pressure that is being created by our
fan and cowling. This meant that the first thing that had to be built was our cowling and fan, so
that we could see what pressure we had to work with. The cowling proved difficult in
construction because of its size and shape. In order to make the shape out of foam without having
a lot of wasted foam, our team decided to cut each section in quarter circles out of 2-inch foam.
One quarter circle section example

26. 25
Our cowling is approximately 16 inches in diameter at the front, and is 14 inches from intake
toexit. This meant that our cowling had to be constructed in seven 2-inch layers, each with 4
quarters of a circle. In total, 28 quarter-circular pieces had to be traced and cut, and then glued
together with epoxy.
Once the epoxy was dry, the blocky cowling could be sanded and shaped into a smooth curve.
To make a round shape, with a
smooth finish, a lathe was built
to shape the cowling. The lathe
proved to be a big project in
itself. A bicycle wheel was
mounted to a table. On the wheel
a rack was made to hold the
cowling. To turn the lathe, a
skate board wheel was attached
to an angle grinder. It was linked
to the wheel by a belt made of
rubber tubing. Once the lathe
was turning, a knife was used to
cut the foam down. This process
was slow, and took quite a few hours of work. It ultimately left us with a nearly perfectly round
cowling.
Cowling formed using foam and epoxy.

27. 26
After the cowling was shaped, some wooden blocks were inserted, which would later be used for
mounting the cowling. We then laid two base coats of resin down, and one layer of fiberglass.
This resulted in a very sturdy, very well built cowling.
Body
Because the pressure that our cowling was able to achieve was lower than we were expecting,
the surface area of our craft needed to increase to lower the amount of pressure needed. The
easiest way for us to do this is to increase the width of the craft, so that our original idea of it
being collapsible would not have to be compromised. In order to ensure that our foam would be
strong enough to withstand the new dimensions, two wood inserts would be added lengthwise to
each section to add reinforcement. These would be spaced about 2 feet apart and would be held
together by epoxy and fiberglass.
Completed cowling with fiberglass.

28. 27
Skirt
The skirt was designed in Autodesk Inventor. It consists of eight straight tubular sections, with
bounce webbing attached inside. The CAD
files were very necessary to achieve proper
skirt fit, size, and layout. The CAD files were
printed out to create templates. The fabric was
cut out, using a heavy nylon, with a
rubberized backing. We were at a loss for a
way to actually join the fabric, as sewing it
seemed to be too time consuming. Luckily,
the rubberized backing heat sealed together
with a very strong bond. So, after all of the
panels were cut out of the fabric, they were
joined together by hot iron.
To attach the skirt to the hull of the craft, thin
wooden strips were stapled to the inside of the
skirt. These were then screwed to the craft
using wood screws and fender washers (to
ensure the screws did not sink into the foam of
the hull).
A duct was needed to take the fan’s thrust air,
and force it down into the skirt, and underside
of the craft for lift. The first idea was to create
a duct out of solely fabric, but unfortunately this was unable to hold up to the stresses involved.
So a hybrid duct was made of extra foam, and fabric. It utilizes nearly half of the fan’s output,

29. 28
and connects directly to the skirt in the back of the craft. The fabric was heat sealed together, and
attached to the foam sections via long screws.
Steering
For our steering setup, a bike was cannibalized for its handlebars and a brake handle. By simply
turning the handlebars vertically, it became a steering level similar to an airplane, and the brake
handle will be used to control our throttle. The steering assembly sits between the user’s legs and
uses bike cables to turn the rudders. The cables will run along horizontally out to the sides of the
craft, and run through bike cable sleeves.
The cables are pull only, so a circuit of cables runs from the lever to the rudder linkages. To keep
slop out of the system, two springs are put in series with the cables.
OBSTACLES
The two biggest obstacles that we faced in this project were time and money. As discussed in the
previous section, our build process was determined by our fan and cowling setup. We ordered
the propeller in mid-February, and did not receive it for over a month. This really set us back
because we couldn’t start construction on the rest of the craft until mid-to-late March. Once we
finally got the propeller we could test the pressure.
Our other biggest concern was money.