Design and Implementation
of a
Single-Manned Hovercraft
Caitlin Del Zotto
Keith Gooberman
Matthew Mayerhofer
Noah Weichselbaum
Senior Design Project
Advisor: Professor William Keat
Table of Contents
1. Introduction
1.1 Purpose of the Project
1.2 The hovercraft and how it works
1.3 Review of the Technical Literature
2. Definition of the Problem
2.1 Design Objective
2.2 Design Requirements
3. Conceptual Design
3.1 Functional Decomposition
3.2 Lift Alternatives
3.3 Thrust Alternatives
3.4 Skirt/ducting Alternatives
3.5 Steering Alternatives
3.6 Design Concepts
3.7 Selection of a Concept
4. Final Design
4.1 Main Features and How it Works
4.2 Design Details
4.2.1
Lift System
4.2.2
Thrust System
4.2.3
Skirt/ducting System
4.2.4
Structure/cockpit
4.2.5
Controls
4.2.6
Safety Features
4.3 Results of Analysis
4.4 Results of Prototyping
5. Summary of Accomplishments and Future Work
6. Detailed Design
6.1 Overview of Final Design
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6.2 Selection of Lift and Thrust Engines
6.3 Structure of Platform and Cockpit
6.4 Skirt
6.5 Lift Engine Mount
7. Conclusions
7.1 Summary of Accomplishments
7.2 Recommendations for Future Work
7.3 Lessons Learned
Appendix
List of Individual Responsibilities
Caitlin:
-helped build prototype
-got engine specifications
-organized and assigned weekly individual tasks for team
-divided up and outlined design report and design presentation
-completed some SolidWorks parts
-constructed Cockpit
- steadily worked on manufacturing final product
Keith:
-completed CosmosWorks stress analysis
-found the Center of Gravity of platform
-designed lift motor mount
- steadily worked on manufacturing final product
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Matthew:
-researched skirts
-completed lift calculations
-got fan specifications
-helped build prototype
-steadily worked on manufacturing final product
Noah:
-completed SolidWorks model of hovercraft
-completed some SolidWorks parts
-found prototype design
-ordered much of the material for manufacturing
- steadily worked on manufacturing final product
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1. Introduction
1.1 Purpose of the Project
The purpose of this project is to design and build and hovercraft that will carry one
person over many types of terrain. It must have the ability to complete a maneuverability
course and have a top speed of at least 4 mph. It should have the ability to travel on
smooth pavement, water, over grass, up a small incline (approximately 15 degrees), and
over a parking lot curb. The finished product should cost less than $2800 (provided not
all new material must be purchased) and must be completed by March, 2006.
1.2 The hovercraft and how it works
The hovercraft, also known as an air cushion vehicle (ACV), was first proposed in
1716. This machine was to consist of a lightweight timber frame that would be covered in
canvas. After further thinking and experimentation it was concluded that the resources,
needed to make the hovercraft work, were not available. In the late 1800s, Culbertson, an
American, designed a ship with channels in the bottom in which air was to be pumped in
by compressors. This air would then provide a cushion intervening between the hull and
the ground. Culbertson is considered the forefather of the hovercraft idea (History of the
Hovercraft).
Culbertson’s idea was later improved upon by an Englishman, Christopher Cockerel.
His theory was that air would be accelerated by a large fan and then some of the air
would be diverted to the cushion area. This would create a jet of high pressure air under
the hull to create lift. The remaining air would then be ejected out the rear of the craft and
used for propulsion. The main problem with Cockerel’s idea was that a large amount of
power would be needed to maintain the air pressure under the hull because there was
nothing retaining the air under the machine. This problem lead to an unacceptable ‘hover
height’.
This problem was then addressed and fixed by a group of English engineers at
Westland Aircraft. To retain the air under the hull, engineers created a skirt that would fit
around the outside of the hovercraft. Now that the pressure under the hull could be
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retained, the previous power requirements would be reduced greatly and the ‘hover
height’ was increased significantly.
The knowledge and technology of the hovercraft has only increased since the first
primitive design of a wooden frame to today’s ocean traversing Marine hovercrafts. The
hovercraft has proven so far to be an extremely versatile and useful mode of
transportation. In recent years, the hovercraft has become more and more popular for
commercial use and rescue missions such as ice patrol and flood rescue. They are even
used for ocean and river tours, water taxi service and for farming purposes. One day the
hovercraft might become more integrated into society as a mean of transportation but for
now it’s primarily relegated to private ownership and operation.
1.3 Review of the Technical Literature
There are many technical resources available on the internet. The Hovercraft Club of
Great Britain published two readings on hovercrafts. There is one book on hovercrafts
that is no longer in print, but has all of the information one would need to build one.
DiscoverHover.com gave free AutoCad plans of a hovercraft to students, which our
group utilized. One site, Hoverhawk.com supplies all of the materials needed to build a
hovercraft,
including
fans,
skirt
material,
and
even
complete
kits.
Neoterichovercraft.com gives a fantastic history on the development of the hovercraft,
and also is a site where we purchased a video on how to build a hovercraft. One other
website has a lift calculator online entitled “Hovercraft Lift Calculator”. The project that
our group took ideas from for the prototype was a science fair project, posted by the
American Science Foundation.
2. Definition of the Problem
2.1 Design Objective
Our overall objective is to design a hovercraft which is capable of transporting
one person. In order to do so we will need to create a platform which floats freely, even
when loaded with hundreds of pounds of weight. This vehicle must be capable of
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running for extended periods of time, and therefore it must use a fan to increase the
pressure under the platform as opposed to compressed air tanks. Once freely floating the
hovercraft must be able to provide itself with enough thrust to propel forwards. This
energy must also be provided with the use of a fan. After we have completed our design
and created a moving hovercraft, there are a series of requirements we must address.
2.2 Design Requirements
The design requirements translate into a series of tests. First, the hovercraft must
navigate through a course designed by William Keat. In order to determine a fair time in
which the hovercraft must complete the course William Keat’s two year old son, Ian
Keat, will perform a time trial. In this course the hovercraft must be able to travel over
grass, concrete, gravel, and water. Second, our vehicle must be able to climb over a
parking curb without bottoming out. Third, we must be able to drive this hovercraft up
an incline of an angle of 15 degrees.
Course Requirement
The first of these is a course designed by William Keat. Although the course has
not been laid out yet, we can still assume there are going to be a variety of turns, both
sharp turns and gradual turns. The goal of this test is to challenge our vehicles speed and
handling capabilities. Initial tests on our competitor, Ian Keat, provided he travels at
about four miles per hour. This will be a test on our thrust system and our control
system. The thrust fan must be able to provide enough energy to drive our hovercraft
faster than four miles per hour, in order to deliver a low time trial. The steering system
must be able to navigate through the course with some control. Depending on the
difficulty of the course, the amount of control we will need will be determined. The
course will also have different types of terrain, which the hovercraft must be able to
travel over. This terrain includes grass, concrete, gravel, and water. On concrete or
water where the skirt will remain tangent to the ground all the way around the perimeter
of our hovercraft, keeping the pressure underneath will not be a problem. On the
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contrary, when the hovercraft is traveling over grass or gravel, more air will escape
underneath the skirt and therefore our lift system must overcome the pressure loss.
Curb Requirement
Our vehicles second requirement is to climb over a parking curb. This curb will
be the usual parking curb which translates to about a two inch jump. Once the front of
the hovercraft has encountered the curb, the skirt is going to lift up and create huge
escape vents for the air in the skirt. Our lift system must be strong enough to handle the
tremendous pressure loss and keep the hovercraft off the ground. If our thrust system is
strong enough to get us going at high speeds, the curb jump will not be as hard since the
kinetic energy might push us over the curb before the skirt is lifted up long enough to
diminish the pressure beyond the critical point.
Incline Requirement
Finally, our finished vehicle must be able to drive up an incline. The angle of the
incline has not been determined, but either way driving up the incline will be a difficult
goal. The pressure under our vehicle must remain high enough to support the weight the
vehicle is carrying.
This weight is always applied in the direction of gravity, and
therefore directly straight down. Once we attempt to drive up the incline, the angle of
gravity shifts and we are now using the lift fan and the thrust fan to overcome gravity.
The angle of the ground will also have an effect on the skirt, probably allowing air to
escape, in turn requiring more lift. Once we can test our vehicle it will be easier to grasp
a concept of what the incline requirement will entail.
3. Conceptual Design
3.1 Functional Decomposition
A hovercraft can be decomposed into several subsystems. In our research we
found the most important subsystems of the hovercraft are the lift and thrust systems. The
lift system has two primary jobs. The first job is to create enough air pressure under the
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hull of the craft to lift it off the ground. This is done by using a lift fan with many blades
and also keeping the blade tip clearance tight so that the amount of air lost between the
duct and the blades is minimized. The second job is to replenish the amount of air lost.
For a hovercraft to work properly, a certain amount of air is needed to create enough
pressure to lift it. If this air lost, due to leakages and surface changes, is not replenished
as quickly as it is lost, the craft will lose hover height. The “backbone” of the lift system
is the skirt. The skirt must perform three key functions: It must contain the air supplied
by the lift fan, it must be able to contour to the changing terrain and it must also offer
some stability. The thrust system has one primary job and that is to create enough
horizontal force to move the craft. The overall speed of the craft will be dependent on the
size of the thrust fan and motor.
3.2 Lift Alternatives
There are two basic configurations for producing lift and thrust, they are using a
dual fan system or employing a single fan system. Each concept has its pros and cons.
With a dual fan system (Figure 1) the lift fan and thrust fans are controlled separately.
This gives the operator the ability to independently control the speed of the lift fan.
Figure 1: Picture of a Dual Fan System
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This is important when changing terrain because more air is going to be lost from under
the skirt when going over grass compared going over concrete. This concept also allows
the operator to independently control the horizontal speed of the craft as he makes the
transitions over different terrains. The downsides to a dual system are the extra expenses
in buying two motors and two fans and also there is extra weight to be compensated for.
The single fan system (Figure 2) uses one fan, usually bigger than either of the
fans on the dual system, to create enough air flow to pressurize the hull and propel the
hovercraft. The air is displaced both into the hull of the craft and horizontally for thrust
by a splitter. The splitter system is beneficial because of the lower costs to buy the fan
and motor and also because its payload will be lower. The downside to the single system
is the lack of ability to increase or decrease velocity without increasing or decreasing hull
pressure separately. Also it is more difficult to calculate the position of the splitter to
optimize lift pressure and horizontal thrust at the same time.
Figure 2: Picture for a Single Fan System
3.3 Thrust Alternatives
This term we have focused primarily on the lift system and have plans on finishing our
research on the thrust system. From what we have seen and know so far, the thrust system
has to be able to create enough horizontal force to counteract the frictional forces created
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between the skirt and the ground, while achieving a velocity requirement of 6 ft/s or 4
mph, and climb an incline of 15 degrees.
3.4 Skirt/Ducting Alternatives
There are three main types of skirts: a bag skirt, a finger skirt and a bag and finger
skirt. The bag skirt (Figure 3) is the easiest type of skirt to construct and apply to the hull
of the craft.
Figure 3: Hovercraft with a Bag Skirt
It also gives the greatest stability because it offers a high stiffness in roll and pitch. The
bag skirt offers the roughest ride between all the skirts and it is also has a limited
clearance height depending on the pressure ratios between the hull and bag. The second
skirt concept we looked at was the finger skirt (Figure 4).
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Figure 4: Hovercraft with a Finger Skirt
The finger skirt is made up of many pouches that individually become inflated with air.
These individual pouches give the finger skirt that ability to contour very well to
changing surfaces. The finger skirt offers the smoothest ride quality and also has very
low friction characteristics. It is also ideal for high speeds and rough terrain. Although the
finger skirt offers many qualities someone would look for in a skirt, our greatest concern
is the stability or lack thereof.
Lastly, we looked at the bag and finger skirt (Figure 5). This is a combination of
the two previous skirts. The bag and finger skirts bring most of the qualities of the other
two skirts: smooth ride, fingers contour well to surface changes and the craft will be
stable with this concept. Even though it seems the bag and finger skirt would be the best
of both worlds, it does have its disadvantages. This concept has a high weight, a lot of
material and is extremely difficult to integrate both systems together.
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Figure 5: Hovercraft with a Bag and Finger Skirt
An important aspect of the lift and skirt system is the pressurization of the hull
under the craft. We researched both a free flow system and a ducted system. This system
has the lift fan simply blowing air downwards into the hull. Even after our research we
are still not certain that this type of system will be able to uniformly pressurize the hull.
In order to better ensure that our hull is evenly pressurized, we decided to look at a duct
system in the hull. The lift fan will force air into the ducts which will evenly disperse the
lift air due to holes in the ducts.
3.5 Steering/Braking Alternatives
Due to the zero friction of the hovercraft both steering and braking seem to pose
some problems. We first took a look at different steering possibilities. The first concept
we looked at was the rudder system (See picture below).
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The rudder system is controlled by the operator via a steering wheel or joystick.
This system is light in weight. The second system we researched was a dual thrust fan
system. For this system, turning is done by increasing or decreasing the speed of one of
the fans. This gives a greater horizontal force on one side of the craft, hence turning the
craft. This system is not optimal for our requirements because it is going to increase both
our payload and the overall cost of the project.
4. Final Design
4.1 Main Features and How It Works
The hovercraft design selected for construction is one which incorporates a dualfan system. The dual fan system was decided upon mainly because it allows for a lot of
benefits that the single fan system lacks. The thrust can be varied or even stopped without
affecting the lift.
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Figure 6: Final Design of the Hovercraft
This design will be assembled on an 11’x5’x1” plywood platform, which will be
the base structure of the hovercraft. As can be seen in Figure 6 the lift system will be
located at the front end of the platform and the thrust system will be located at the rear so
as to balance the center of gravity.
The direction of thrust will be controlled by two rudders behind the thrust fan.
These rudders will be controlled from the cockpit via a mechanical linkage. The cockpit
will be located in the center of the platform.
The skirt chosen for this final design is a bag skirt which will be 1’ in height.
4.2 Design Details
4.2.1 Lift System
A four cycle engine with a vertical shaft will be mounted on top of a ducted fan.
This fan will be mounted in the platform, with the airflow directed to the underside of the
hovercraft in order to create the plenum. A hovercraft of our projected weight of 800lbs
will require approximately 12,000 cfm’s of airflow.
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To obtain this requirement a 22” diameter ducted fan with 8 blades will be
implemented which will be powered by a 20hp engine. This system should produce
enough airflow to lift the hovercraft off the ground up to approximately 1.5”.
4.2.2 Thrust System
This system will be powered by a 21hp horizontal shaft engine. The shaft will be
connected to a ducted fan. The ducted fan for thrust will be slightly larger than the lift fan
with a diameter of 26” and 10 blades.
4.2.3 Skirt/Ducting System
A bag skirt was chosen for the final. Of all the skirts investigated, it is the lowest
cost, least complex to manufacture, and is the most stable. The skirt will be constructed
out of 1050 denier ballistic nylon that is coated in polyurethane. This is a very durable
material that will withstand the rough treatment the skirt may face. The shape of the skirt
can be seen in Figure 1. The dimensions of the actual skirt are 11.5’x5.5’x1’. When
inflated the skirt balloons out slightly from the platform, as represented by the extra .25’
on both sides of the platform.
The final design also incorporates a ducting system into the lift system. The actual
design of this system still has yet to be finalized, however the general idea is shown in
Figure 7.
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Figure 7: Ducting System for Hovercraft
4.2.4 Structure/cockpit
The cockpit, as seen in Figure 8 will be constructed mainly of out of plywood and
will be accompanied by fiberglass mat for reinforcement. It will house the control
systems steering, lift and thrust. The cockpit will also safely house the driver of the
hovercraft. The dimensions of the cockpit will be 3’x3’x2’.
Figure 8: Cockpit Design for Hovercraft
4.25 Controls
The control system for steering is comprised of a linkage system, which connects
the steering column located in the cockpit to the two rudders behind the thrust fan, as
seen in Figure 9.
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Figure 9: Design of Steering System for Hovercraft
When pressure is applied to the steering column on one side, as seen in Figure 4,
it will move the linkage it is connected to forward while the other linkage moves
backward. The horizontal axis that the rudder lies on is fixed, so as the linkage it is
connected to moves, the rudder will rotate accordingly.
4.26 Safety Features
The safety of the driver of the hovercraft, as well as those that may be in the
surrounding area is of the utmost concern. The driver of the hovercraft will be secured in
the cockpit by means of a safety harness that will be attached to the seat. The driver of
this vehicle will also be equipped with a helmet, life-jacket (the hovercraft may be over
water and lifejackets are required by boating law), and earplugs (the noise produced by
two 20hp motors can be quite deafening).
The engines on the hovercraft will both be equipped with kill switches that will be
located in the cockpit in case the hovercraft happens to lose control. The fans that are
attached to these engines will be safely housed in fiberglass ducts with filters over them
to keep out debris and prevent human contact with the fan blades.
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Finally the cockpit will be equipped with a fire extinguisher.
5. Summary of Accomplishments of Fall Term and Future Work
As a team of four members, we accomplished a great deal in the past ten weeks.
Beginning with nothing but a vague notion of a hovercraft we determined the decisions
that needed to be made, compiled the research to aid us in making those decisions,
produced a design and did some prototype testing. The necessary pressure under the
vehicle was determined with the aid of an online calculation and a simple free body
diagram. With that knowledge we determined the fan and motor size we would need to
lift our vehicle. Solidworks drawings were constructed for a detailed design. With a
layout of our structure and the power sources determined, we focused on details such as
the skirt type, the control system, and the safety features. Once our conceptual work
neared completion, we concentrated on prototyping a model and running stress tests on
our proposed plywood base.
By the end of next term we must have an operational hovercraft. To continue our
ongoing progress, the stress tests will become more detailed and a frequency analysis will
be run. We will also determine what type of ducting system we are going to use, and
how effective it needs to be. Once the motors and propellers have been obtained,
manufacturing will begin construction of the lift platform. We must construct our vehicle
in a timely fashion in order to have enough testing time. As a team we are aware our
project poses hundreds of problems, and the testing period must be extensive. Finally,
with the finished design, the hovercraft will be tested to see if it meets the design
requirements discussed earlier.
6. Detailed Design
6.1 Overview of the Final Design
For the final design we loosely followed the drawings and dimensions supplied by
Universal Hovercraft. For the base we used Concrete Adhesive (available by the gallon
from Lowe’s Hardware) and adhered 1” x 8” x 4” thick foam board. The final design
19
was 12’ x 6’ x 4”. From here we attached 5/32” thick wooden boards using Liquid Nails
(also available at Lowe’s) on both sides. From here we made two cuts from the front two
corners. The cut away section measured 2.5” x 4” and went through the entire craft on
both corners.
Finally, from here we had the machine shop make a 10.5o hole 19” back from the
front of the craft for the lift duct. The hole measured 33.5” diameter and the edge on the
bottom was centered 4.5” back from the edge on the top. An engine mount sits inside
this duct and will be attached to two truss like supports on the sides to attach the motor to
the hovercraft.
The cockpit sits right behind the back side of the lift duct and is 3’ x 3’ by 2’ high.
The controls will sit in this cockpit and will be simple bike-break-like controls for the
rudders. Behind the cockpit will be the mounted thrust duct & fan. Both the lift fan and
the thrust fan were ordered through Universal Hovercraft. With these came the brackets
to mount the fans to the engines and the fiberglass cloth which covers the blades. Both
the lift fan and the thrust fan will have chicken wire protective cages over them.
The skirt is attached to the bottom of the craft. Two rods holding the skirt cut
some of the lift fan’s air away into the bulge part of the skirt. The other part of the skirt
is attached to a ½” board which is Liquid Nailed to the sides of the foam. The skirt
attaches with 1/8” screws provided by Universal Hovercraft.
In this section there will be detailed accounts of each part of the hovercraft and
how we built them.
6.2 Selection of the Lift and Thrust Engines
Selection of the lift engine and thrust engines varied, depending on what was
required by each respectively.
The requirements for the lift engine revolved around being able to lift the
estimated total weight of the hovercraft, which was approximated at 800lbs. Based on
rough calculations as well as documented results from Universal Hovercraft, it was found
that to lift this weight the lift engine needed to produce approximately 12,000cfm’s. After
consulting with Donald Small, an employee at Universal Hovercraft, it was concluded
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that to obtain the desired airflow a 30in diameter 4 blade propeller would be implemented
in our lift system, and it would be powered by a 15.5hp Briggs and Stratton engine (see
Figure 1). This engine is equipped with a 1in. x 3 5/32in keyed vertical shaft which
allows it to be attached directly to the fan blade, which is an advantage to our final
design.
Figure 10: Briggs and Stratton Vertical Shaft Lift Engine
In our original design we had called for a 20hp engine, however based on cost as well as
considerations for weight it was determined that this engine would be better suited for our
final design.
The thrust engine chosen for our final design was not under as significant
constraints as the lift engine. This engine simply needed to be powerful enough to move
our hovercraft. Based on the fact that our craft is hovering over the ground, the amount of
friction on the bottom is minimal, so the amount of force necessary to move the
hovercraft is much less than it would be to say move a car. Based on these requirements,
it was concluded that an 11.5hp horizontal shafted Tecumseh engine would be ideal (see
Figure 2). This type of engine is still relatively powerful, and along with the 2-blade 36”
propeller being attached directly to the horizontal shaft, more than enough airflow would
be produced by this system to move the hovercraft. Originally we had planned on using a
21hp engine for the thrust system. However, the 21hp engine was a few hundred dollars
more, which with the amount of money we received from the IEF grant was not a
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possibility, also the 11.5hp engine weighed about 30lbs less which was beneficial to the
overall weight of our hovercraft.
Figure 11: Tecumseh 11.5hp Horizontal Shaft Thrust Engine
6.3 Structure of Platform and Cockpit
The structure of the platform was 4 inches of foam board adhered together with a
¼” piece of plywood on top of the foam. The sides of the craft were equipped with ½”
plywood to later attach the skirt to.
Because the foam board is not in the exact
dimensions of our 12’x 6’ craft, the places that were bonded together were attached with
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Figure 12: Platform of Hovercraft
foam caulk. To layer the 1” sheets, we used foam adhesive. We then placed weights on
the platform to assure that the pieces adhered well. From the blueprints given to us from
Universal Hovercraft, we decided on the dimensions of 12’x 6’. The prints showed us
what material to use for the platform, which was extremely helpful. The front of the craft
is cut at an angle because the space in the front of the craft was not necessary besides the
lift duct. It was deducted that we did not need the excess weight, and it would be safe to
remove it. Below is a picture showing a better view of the plywood attached to the sides
for the skirt attachment:
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Figure 13: Platform of Hovercraft with view of skirt attachment segments
The bottom part of the craft has two 10’x 1’ foam segments at which the “feet” of the
skirt were placed, and the other set of wood for the skirt attachment (See Figure 15
below).
The structure of the cockpit is similar to the designed cockpit in the fall. The
dimensions are the same, but made from masonite to keep the weight at a minimum. It is
a 3’x3’ square with side walls 1’ high. The back is 2’ high. The pieces of masonite were
secured together by screwing them to small pieces of wood to act as supports. The
manufactured cockpit looks like this:
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Figure 14: Cockpit
Figure 15: Bottom view of the platform
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The above picture shows the extra layer of foam and ¾” wood used to attach the skirt to
the bottom of the craft.
6.4 Skirt
Figure 16: Picture of a simple bag skirt
When it came time to choose a skirt type we took many things into consideration.
Since we had a strict deadline, a limited source of money, we chose to use the bag skirt.
There are also two genres of bag skirts: full flow and no flow. Full flow means that all of
the air is fed into the skirt and is released into the cushion through holes. And no flow
means a small amount of the lift air is diverted into the skirt and the rest is used to
pressurize the hull. We chose the no flow bag skirt because we felt this would give us the
best opportunity to get a floating platform. The bag skirt was chosen for other reasons
also. Bag skirts will give our craft the most support. This is due to the craft being
supported by both the air in the bag of the skirt and also by the air that is pressurizing the
hull. One of the best qualities of the bag skirt was the simple implementation to our
design. The bag skirt was the simplest skirt to make and also attach to our craft. Once this
design choice was made the material was ordered. We were advised to use 1050 denier
ballistic nylon coated in polyurethane. This is a very durable material that will withstand
the rough treatment the skirt may face. The skirt material was then cut in widths of 30”
and fitted to the different sides of the craft. We used six separate pieces of skirt material,
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one for each side. Each piece was attached to the next using H-66 vinyl cement. On the
bottom of the platform is a sequence of ½” x ½” pieces of wood following the outline of
the craft but offset inwards from the platform edges. These pieces of wood are used to
attach the skirt to the underbelly of the craft. As can be seen in Figure 17, these pieces
overlap the lift duct. These pieces act as splitters in a sense. A small amount of air is used
to blow up the bag while the majority of the air is used to pressurize the hull.
Figure 17: Splitters and skirt attachment
We attached the skirt using a few hundred ¼” screws, spaced every three inches.
6.5 Lift Engine Mount
The lift engine mount was designed with the suggested mount supplied by
Universal Hovercraft in mind. The duct the mount had to stretch over was 33.5” long.
The support must hold the Briggs and Stratton 87lb 15.5HP Vertical Shaft Motor
securely. The mount was designed to hold the engine in the duct, about six inches down
from the top of the hole. The mount was built out of soft-carbon steel since that was all
that was deemed necessary by Team Hovercraft as well as the Union College Machine
Shop. We assumed the deeper the blades sit in the lift duct the more pressure it will be
able to provide since no air can escape through a faulty angle or air missed by the end of
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the blades. Ensuring that the distance between the edge of the propellers and the lift duct
is very small is important and according to Universal Hovercraft can account for losses as
much as 15% of the CFMs if the distance is much greater than 1/8 inch. A screen shot of
the final design, as well as the final engineering drawings, can be seen below in figures
18-20.
Figure 18: Engine Mount Screenshot
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Figure 19: Engine Mount Design Drawings Sheet #1
Figure 20: Engine Mount Design Drawings Sheet #2
Just to make sure this engine mount would support the weight of the engine
(87lbs), the engine mount was run using the help of the Finite Element solver,
COSMOSworks. The four brackets that will mount into the wood were restrained and
the four brackets holding the motor shared the 87lb force. This was meshed at a normal
mesh and run. Both the loads and the displacement plot can be seen below in figures 21
& 22.
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Figure 21: Engine Mount With Loads & Restraints
Figure 22: Engine Mount Design Displacement Plot
Although the displacement chart seems to fail, the displacements are actually less than
0.045”. This is also not a very accurate display since the motor will not allow the
brackets in the middle to deform outward since the motor will hold them at the same
distance apart. Even with this being considered, there will be another metal bar welded
across from one side to the front of the hole to ensure the mount will remain steady. The
engine will be mounted to this with rubber vibration dampers in between all bolts, nuts,
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and brackets. The mounts will be attached to two wooden trusses, built by 2” x 4” wood
rods. The bottom of the truss system will be I-bolted through the entire craft to ensure
the motor is securely mounted to the body of the hovercraft. A proposed truss system can
be seen below (all bolts are 5” x ½” diameter) in figure 23.
Figure 23: Proposed truss system
The implemented lift engine mount can be seen below in Figure 24:
Figure 24: Lift Engine Mount over duct
6.6 Lift Fan
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The lift fan selected for our final design was a 4-blade 30in diameter propeller.
We had originally planned on using an 8-blade 22in diameter propeller, however this
decision had to be modified for a number of reasons. The main one being that we wanted
to significantly increase our airflow, and longer propeller blades meant increased airflow.
The other consideration we had to take into account was not a constraint that could have
foreseen. This being that the company Universal Hovercraft, which we ordered our
propellers from, had a fire in their factory and they’re production had been inevitably
halted temporarily. Therefore, the time it would have taken to make an 8-blade propeller
would have been too long based on our time constraints. A 4-blade propeller could be
made in a shorter amount of time, and was still acceptable for our requirements.
Therefore the 4-blade 30in diameter propeller was selected for our final design (see
Figure 25).
Figure 25: Lift Fan
However, another problem arose from these problems experienced by Universal
Hovercraft. This problem was that in order for them to ship the propeller to us in a timely
manner, they would not be able to fiberglass the propeller for us. So in Figure 25, the
propeller is unfinished, being only composed of wood at this point.
The process used to finish the propeller involved using a two part epoxy and 6oz
fiberglass cloth (see Figure 26).
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Figure 26: Lift Fan with First Layer of Fiberglass
In this process the first step involved carefully mixing the epoxy in its two-to-one ratio.
Then this epoxy was spread evenly over the propeller blades and the fiberglass cloth was
laid over the epoxy. The cloth was then saturated in epoxy, and any excess epoxy was
removed with a squeegee. At this point it was made sure that no air bubbles were present
in the cloth, as this would affect the fans performance, after which the epoxy and
fiberglass were allowed to set.
This procedure was repeated twice so as to give the propeller the necessary
strength and dexterity to weather rough conditions that could be present during operation
of the hovercraft. The finished lift propeller can be seen below in Figure 27.
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Figure 27: Finished Lift Propeller
6.7 Safety Features
Currently the major safety features have not yet been incorporated into our final
design due to our time constraints. However, one major one that is present is the kill
switch for our lift motor, there is also one present on our thrust motor however this
engine has yet to be mounted on the hovercraft.
Other key safety features that will be implemented include placing 1/8 inch
plywood, about 4 inches wide, that run halfway around the inner side of the lift duct.
These plywood pieces are placed 6 inches above as well as 6 inches below the plane of
rotation of the lift fan. The pieces provide protection to the person in the cockpit as the
fan is not able to move out of its plane of rotation with the additional pieces maintaining
it in its designated place. Another safety feature for the lift fan is that it will be covered
with 1/2inch grid-screen wire which will protect the driver or other persons from being
hit with debris that may enter the fan.
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Other safety features that will be implemented with the hovercraft include:
seatbelt, helmet, fire extinguisher, ear plugs, and life jacket (should the hovercraft be
driven over water).
7. Conclusions
7.1 Summary of Accomplishments
We began the winter term ready to order all of our parts and begin building our
hovercraft. We started off by buying all of the necessary supplies needed to create the
platform. This included wood, foam, adhesives, etc. We then adhered four layers of 1”
polystyrene foam together to give us our base platform. We then added a layer of 1/8”
plywood on top of that to add a little rigidity to our craft and also so we had something to
screw into. Once the platform was created we began to construct our lift duct. This
consisted of very little engineering and a lot of luck. We had the machine shop cuts us
two circles of our desired lift duct diameter and we bent a piece of 1/8” plywood around
the circles. We then created a cylinder out of paper board that was 2” wider in diameter
and filled that extra space in with expansion foam. Once this was done we were able to
cut the hole in our platform for our lift duct. We then glued the lift duct into position
again using expansion foam and an all purpose adhesive wherever we could. While all of
this is going on the motors and fans are being shipped to us. As soon as the adhesive had
dried on the lift duct we were able to move the craft around and begin working on the
skirt. We encountered some trouble in understanding how the skirt was to be designed
exactly but once that was figured out there was a lot of cutting and screwing going on.
The skirt used approximately 600 - 1/4” screws to be properly attached to the craft. While
these steps are being taken in the Engineering Lab, one of the group members began the
design of the motor mounts and had the Solidworks drawings sent to the machine shop
for construction. By this time, both our lift and thrust motors have come in along with
their respective fans. Each of the fans needed to have a few layers of fiberglass applied to
their blades. This was done to increase the strength and performance of the blades. We
also had the correct size hole bored out of the centers of the fan so they would fit the
driveshaft of their respective motors. Once we got the lift motor mounts back we were
35
able attach the mounts to the craft and set the lift fan and motor in place. Unfortunately,
due to a few bumps along the way we were only able to get as far as installing the lift
motor and fan. So as for the terms accomplishments, we were able to fully build the
hovercraft’s platform, lift duct and cockpit. We did not spend any time working on or
dealing with the thrust system because all of our efforts were put into building a hovering
platform for the end of the term.
Figure 28: Final Product at end of Winter term
7.2 Recommendations for Future Work
For Steinmetz Day, we plan to attach the thrust system, and cosmetically enhance
our hovercraft. We can recommend to ourselves for next term, and anyone who may
want to dabble in building a hovercraft to assume every step will take twice as long. Our
struggles existed mainly in the time crunch, and if this project was given three terms, I
really think that it could have been 100% completed and able to complete all of our
design requirements. To assure that the thrust system is secure and running by Steinmetz
Day, we will continue our work and meet twice a week until the thrust system is
completed.
7.3 Lessons Learned
In this twenty-week period, we have certainly learned that it is difficult to rely on
other people. Unfortunately there is not a large market for hovercraft parts sales, so we
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worked with only one company. This company suffered a minor fire in their stock room,
which delayed the shipping of many of our materials. To build something this complex
in ten weeks, absolutely nothing can go wrong. We did not have enough time to plan for
mistakes, and at often times were rushed. This is the reason why we were unable to attach
the thrust system. The lift system was completed, and technically is all that is required to
make a hovering platform.
Our group certainly thinks that the project was a great learning experience, and a
lot of fun. If anything could have been done differently, it would be having the 10 weeks
of design during spring of Junior year, giving 20 weeks to build the hovercraft.
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References
http://www.neoterichovercraft.com/general_info/historyof.htm#intro
http://www.rqriley.com/hc-calc.html
http://www.amasci.com/amateur/hovercft.html
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Final Itemized Budget
Material
Cost ($)
Plywood sheets
250.00
Foam caulk
30.00
Foam adhesive
40.00
Sheets of 1” thick Foam board
100.00
10 HP Tecumseh Vertical Shaft Motor
390.00
Skirt Material
100.00
Skirt cement
12.50
Skirt screws
20.00
Lift Propeller
155.00
Bushing
20.00
Mounting hub
80.00
Fiberglass
50.00
Fiberglass epoxy kit
118.00
Backup Plate
30.00
15.5 HP Briggs & Stratton Horizontal Shaft Motor
600.00
Thrust Propeller
200.00
Masonite sheets
30.00
Various shipping charges
100.00
Total Cost
2295.50
39
IEF GRANT REQUEST FORM
CATEGORY B
STUDENT INITIATED
RESEARCH
(PLEASE TYPE or WRITE CLEARLY)
STUDENT ID # 1842831
***all information given in order of name
#1843077
#1798368
#1841975
1.
Student name, class, major:
Caitlin Del Zotto, MER 497, Mechanical Engineering
Keith Gooberman, MER 497, Mechanical
Engineering
Noah Weichselbaum, MER 497, Mechanical
Engineering
Matthew Mayerhofer, MER 497, Mechanical
Engineering
2.
Student addresses (Include college box number and home address):
Box # 0583, Reamer Campus Center, Union College, Schenectady, NY 12308
P.O. Box 703, Altamont, NY, 12009
Box # 899, Reamer Campus Center, Union College, Schenectady, NY 12308
KEITH”S HOME ADDRESS
Box# 2087, Reamer Campus Center, Union College, Schenectady, NY 12308
224 Pine Grove Street, Syracuse, NY 13210
40
Box# 1509, Reamer Campus Center, Union College, Schenectady, NY 12308
15 Barbara Lane, Wappingers Falls, NY 12590
3.
Title of proposed research:
Design of a HoverCraft
4.
Is this research for academic credit?
Yes
5.
If Yes, Please list course(s):
MER 497 & MER 498
6.
For which academic terms is support sought?
Fall, Winter
7.
Amount of support requested:
$700 per person x 4 people =
$2800
(A detailed budget must be provided under Item #10)
8.
Faculty Research Supervisor:
William Keat
Student Signature
Student Signature
41
Student Signature
Student Signature
Faculty signature indicating
willingness to serve as research
supervisor for this project
10-22-06
Date
9.
Research Proposal (description of project)
The purpose of this project is to design and build a hovercraft that will carry one
person over all types of terrain. It must have the ability to execute a course designed by
Professor Keat consisting of water, sand, grass, an incline of 30 degrees, and a curb
(height=6”).
The hovercraft, also known as an air cushion vehicle (ACV), was first proposed in
1716. The idea behind a hovercraft is that it is a vehicle or craft supported by a skirt that
is full of air being forced downwards to provide a vertical lift. Then a second force is
applied to the craft in the horizontal direction by means of a thrust fan. The purpose of
42
this is that it makes the hovercraft a versatile form of transportation that can go over
almost any type of surface whether it is land or water. Since its’ first conception,
hovercrafts have continued to be developed allowing for the multi-terrain vehicles that
are available today.
Figure 1: Hovercraft in Action
www.hovercraft.demon.co.uk/
Our hovercraft will be a one person hovercraft similar in some respects to the
design in Figure 1. Like the design above it will have a two fan system. One fan powered
by a 2-cycle engine (20-30hp) providing horizontal thrust, and one fan powered by a 4cycle engine (10-15hp) that will provide vertical lift. Characteristics of the hovercraft that
we intend to improve upon include such items as: safety (i.e. roll-bar over cockpit), ideal
lift system (will prototype different hole patterns in the tubing of the skirt to get the best
levitation), and maneuverability (will determine ideal number of rudders and their
orientation behind the thrust fan for maximum control).
Technical Approach:
Design and construction of the hovercraft needs to be done methodically in order
to be completed and tested within a time span of two terms. The following list of tasks,
summarizes how this will be accomplished.
i.
Generate alternative ideas.
43
ii.
Decide on the best design for the hovercraft- this includes deciding on the best
materials for the hull, single vs. dual fan design, skirt type, and hole patterns for
ducts for vertical lift.
iii.
Analyze the design to size major components such as the lift and thrust fans.
iv.
Develop the detailed design and represent it in the form of dimensional drawings
with the aid of a CAD solid modeling package.
v.
Manufacture the design.
vi.
Test- hovercraft will be tested on Professor Keat’s course of varying terrains and
obstacles carrying one person of less than 300 lbs.
vii.
Document the design and the results in the form of a final design report.
Outcomes:
Through this project we hope to learn valuable information about the design
process and how to create a working finished product. In addition to this we intend to
figure out ways to improve upon current hovercraft designs so that they can be even
more versatile than they already are. This union of research, design, and physical
construction in creating the hovercraft, will provide us with knowledge that we can
use down the road, may it be in grad-school or on a job site.
10. Budget
The main purchases are lift and thrust systems which consist of two gasoline
powered engines and two fans. The engine for thrust needs to have a significant
amount of power (typical hovercrafts are 20-90hp depending on size), while the
engine for lift needs a reasonable amount as well (typically between 10-15hp). Below
is a breakdown of all anticipated expenses for which funding is being sought.
Lift Engine (10hp)
400.00
Thrust Engine (20hp)
850.00
Lift Fan
250.00
Thrust Fan
350.00
Fiberglass Housing for Thrust Fan
100.00
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Steering cable
25.00
Rudders for Fan Direction
100.00
Skirt (polyurethane-coated nylon fabric) 180.00
Skirt Glue/Screws
30.00
4 sheets of 1/8” Plywood
220.00
Cockpit Seat and Safety Harness
150.00
Build Your Own Hover/Trek Video
45.00
Total Hovercraft Budget
$2800.00
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Finite Element Analysis
Once the loads on our hovercraft platform were determined we performed a stress
analysis using the CosmosWorks add-in to Solidworks. Performing this analysis would
determine how thick we need the sheet of plywood to be. Once the original plywood
sheet was drawn in Solidworks, a sheet eleven by five, a hole was cut away where the lift
fan vents the skirt. Data was obtained on the motors we planned on using, an 87lb thrust
motor and a 57lb lift motor (which was changed to a more powerful, heavier motor after
this analysis was performed). The fan weights were four pounds for the lift propeller and
eight pounds for the thrust propeller. Finally, the displacement boundary conditions
needed to be determined. Since Cosmoworks is left with too many variables if nothing is
constrained, leaving the platform free floating was not an option. Since the hovercraft is
actually free floating, this analysis is only an approximation of the actual stresses,
especially near the holes. Below is a diagram showing how the loads were applied.
Different sets of displacement boundary conditions were tried, restraining the lift
fan was the results that gave us the lowest factor of safety.
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Cosmosworks predicted a factor of safety of 1.43 based on Von Mises failure
criterion. It calculated this with 22484 elements and 7647 nodes. These results were
slightly unsettling due to the low factor of safety, but it also determined our half inch
thick board (the thickness analyzed) is probably too thin. The ducting system and the
cockpit may serve to increase the factor of safety.
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