Design Team 13
Twin-Engine Remote Hovercraft
April Project Report
Raymond Fitzpatrick
B00322395
Martin Mitchell
B00433676
Jake Martell
B00431852
Travis Lunn
B00448582
Jeremy Keans
B00450500
Dr. J.M. Chuang
Submission Date:
Submitted to:
April 9th 2010
Dr. J. Militzer
Abstract
Hovercrafts are multi-purpose vehicles which can travel across various types of
terrain with no alteration. The overall purpose for this design project is to build a
hovercraft which can carry various payloads, up to 100 lbs, across land and water. This
air cushioned vehicle (ACV) can be used for numerous different applications including
military, aid, transportation of building supplies, etc. This report will outline the design
process as well as the final selected design. It also includes sections on fabrication and
testing of the hovercraft and all its components. Also included in this report are detailed
design drawings, detailed budget, a list of calculations done for the project.
i
Acknowledgements
Design Team 13 would like to extend our special thanks to our supervisor
Dr. Chuang for his help throughout this project as well as his patience in working with us
throughout both terms for the duration of this project.
We would like to thank Dr. Militzer for his overseeing of the design
project course. We would like to thank the department staff who assisted us, especially
our assigned technician Mr. Albert Murphy for his help in welding, fabrication and
testing. As well as thanking Mr. Mark MacDonald and Mr. Angus MacPherson for their
help throughout the term.
Finally we would like to thank Mr. Leo Cruickshank, a local hovercraft
expert who provided advice coming from his hovercraft building experiences. Slipstream
hovercraft who gave us a discount on parts we had ordered from them, Shell Canada for
their funding donations, and Dalhousie University.
ii
Table of Contents
Abstract ................................................................................................................................ i
Acknowledgements ............................................................................................................. ii
List of Tables ..................................................................................................................... iv
List of Figures .................................................................................................................... iv
1. Introduction ................................................................................................................. 1
2. Design Requirements ................................................................................................... 3
3. Design Selection .......................................................................................................... 5
3.1. Engine Selection ................................................................................................... 5
3.2. Thrust Powertrain ................................................................................................. 6
3.3. Lift Powertrain ..................................................................................................... 7
3.4. Platform & Skirt ................................................................................................... 9
3.5. RC Control / Steering ......................................................................................... 10
3.6. Buoyancy Compensation.................................................................................... 10
4. Final Design ............................................................................................................... 11
4.1. Thrust Powertrain ............................................................................................... 12
4.2. Lift Powertrain ................................................................................................... 13
4.3. Platform & Skirt ................................................................................................. 14
4.3.1. Platform .......................................................................................................... 15
4.3.2. Skirt ................................................................................................................ 15
4.4. RC Control & Steering ....................................................................................... 17
5. Build and Construction .............................................................................................. 19
5.1. Thrust Powertrain ............................................................................................... 19
5.2. Lift Powertrain ................................................................................................... 20
5.3. Platform and Skirt .............................................................................................. 22
5.4. RC Controls ........................................................................................................ 24
6. Testing ....................................................................................................................... 25
6.1. Size and Weight ................................................................................................. 25
6.1.1. Size ................................................................................................................. 25
6.1.2. Weight ............................................................................................................ 26
6.2. Safety.................................................................................................................. 27
6.2.1. Shrouds ........................................................................................................... 28
6.2.2. Kill Switch ...................................................................................................... 29
6.3. Twin Engine ....................................................................................................... 29
6.4. Terrain ................................................................................................................ 29
6.5. RC Controls ........................................................................................................ 30
6.6. Payload ............................................................................................................... 32
6.7. Steering with Rotating Thrust Fan ..................................................................... 33
6.8. Buoyancy............................................................................................................ 35
6.9. Miscellaneous Criterion ..................................................................................... 36
6.9.1. Maximum speed (5 m/s or 18 km/h). ............................................................. 36
6.9.2. Minimum hover height of 3” .......................................................................... 38
6.9.3. Aesthetics Testing........................................................................................... 40
7. Budget ........................................................................................................................ 42
8. Conclusions ............................................................................................................... 44
References ......................................................................................................................... 45
iii
Appendix A: Calculations ................................................................................................. 46
Appendix B: Drawings ..................................................................................................... 48
List of Tables
Table 1: Engine Design Selection Matrix ........................................................................... 5
Table 2: Thrust Powertrain Design Selection Matrix ......................................................... 7
Table 3: Lift Powertrain Design Selection Matrix .............................................................. 8
Table 4: Platform & Skirt Design Selection Matrix ......................................................... 10
Table 5: Main Parts List for Thrust Assembly.................................................................. 13
Table 6: Main Parts List for Lift Assembly ...................................................................... 14
Table 7: Main Parts List for Platform and Skirt ............................................................... 14
Table 8: Main Parts List for Steering / RC Control Assembly ......................................... 18
Table 9: Weight Testing Results ....................................................................................... 27
Table 10: Terrain Testing Results ..................................................................................... 30
Table 11: Speed Test Results ............................................................................................ 38
Table 12: Hover Height Test Results ................................................................................ 40
Table 13: Final Budget...................................................................................................... 43
List of Figures
Figure 1: Direct Drive Thrust Fan ...................................................................................... 6
Figure 2: Chain Driven Thrust Fan ..................................................................................... 6
Figure 3: Centrifugal Fan .................................................................................................... 7
Figure 4: Horizontal Fan ..................................................................................................... 7
Figure 5: Tilted Lift Fan Assembly .................................................................................... 8
Figure 6: Raised Horizontal Fan ......................................................................................... 8
Figure 7: Diffuser Plate Design .......................................................................................... 9
Figure 8: Bag Skirt Design ................................................................................................. 9
Figure 9: Final Design ...................................................................................................... 11
Figure 10: Thrust Powertrain Assembly ........................................................................... 12
Figure 11: Lift Powertrain Assembly ............................................................................... 14
Figure 12: Platform ........................................................................................................... 15
Figure 13: Airflow Analysis of Bag Skirt (Red=High Velocity, Blue=Low Velocity) .... 17
Figure 14: Steering Control Assembly ............................................................................. 18
Figure 15: Chain Driven Thrust Assembly Construction ................................................. 19
Figure 16: Final Thrust Assembly .................................................................................... 20
Figure 17: Lift Assembly Construction ............................................................................ 21
Figure 18: Top Plate & Skirt Construction Top................................................................ 23
Figure 19: Top Plate & Skirt Construction Bottom .......................................................... 23
Figure 20: Steering Mechanism ........................................................................................ 24
Figure 21: Length Measurement ....................................................................................... 25
Figure 22: Width Measurement ........................................................................................ 26
Figure 23: Weighing of Thrust Assembly ........................................................................ 27
Figure 24: Shrouded Thrust Fan ....................................................................................... 28
iv
Figure 25: Shrouded Lift Fan ............................................................................................ 29
Figure 26: Lift Kill Switch Testing ................................................................................... 32
Figure 27: Thrust Kill Switch Testing .............................................................................. 32
Figure 28: Basic Steering Test Results (Top to bottom: turning left, center, right) ......... 35
Figure 29: Garmin GPS Speed Readout ........................................................................... 37
Figure 30: Hover Height Measurement (front) ................................................................. 39
Figure 31: Hover Height Measurement (back) ................................................................. 39
Figure 32: Aesthetic Poll Results ...................................................................................... 41
Figure 33: Cross Sectional View of Skirt (Jackson, 2004, p. 68) ..................................... 46
v
1. Introduction
Air Cushioned Vehicles, also known as ACVs, are an ideal type of payload
carrying medium as it is amphibious. This allows the hovercraft to carry various
payloads across various types of terrain in a single journey whereas multiples vehicles
would be needed to complete this same journey.
Team 13 is undertaking the design and construction of a twin-engine remote
controlled hovercraft also known as an Air Cushioned Vehicle (ACV) which will be
capable of carrying a 100 lb payload across various terrains. This payload was picked
because it, when combined with the total weight, was at the upper range of the hovercraft
guidelines for pressure of 15 lb/ft2 to maintain operation. The design was selected via an
iterative design methodology in which many different designs for the four separate
sections; namely, thrust powertrain, lift powertrain, platform & skirt, and RC
control/steering, were considered. The main focus was to find the best balance between
performance, budget, and construction feasibility.
The selected design consists of two engines (one lift & one thrust), a bag skirt
design without holes, single plate platform, and rotating thrust fan for steering. This
prototype hovercraft design will utilize all of the thrust power from the fan by rotating the
fan versus using the conventional flaps which reduce air flow. The hovercraft will be
controlled using a 6-Channel remote and receiver which will control both engine throttles
as well as steering of the craft. In order for safety the craft will be equipped with one kill
switch, for both engines. This report will outline the design requirements set out in
September, the final budget, a list of testing results, as well as recommendations for
future work and improvements on the current design. It will then detail the fabrication
and construction undertaken during the winter term and discuss the modifications needed
to the original design needed in order to meet the design requirements during the testing
phase. It will then discuss the testing process as well as the results obtained from them.
Work during the winter term commenced upon the team's return to Halifax in
January began with the construction of the design from the fall term. As parts and stock
arrived the fabrication was the first step in the building process. The raw aluminum
1
material was fabricated into the thrust assembly, lift assembly, and main plate, and upon
completion of this the task was undertaken to construct the skirt of the durable nylon skirt
material.
After construction of the skirt was complete testing started with the lift
assembly and was immediately deemed successful as the craft hovered effortlessly. Then
after finalizing the chain-driven thrust assembly and testing it with negative results due to
excessive vibrations modifications were attempted including chain tensioners and idler
sprockets. Neither method worked so a redesign which included direct driving the thrust
fan by raising the engine and lowering the fan to meet each other. This new design
proved extremely successful with smooth operation and allowed the testing process to
begin.
During the testing of all the criteria put forward, the project was deemed a
success as it met virtually all of the listed criteria. It lifted payload, steered, and traversed
as desired on all surfaces (asphalt, gravel, sand, water) with the exception of grass.
Research shows that grass is one of the most difficult surfaces for a hovercraft to traverse
because it is often not smooth, and creates very high friction with the craft relative to
other surfaces.
2
2. Design Requirements
The primary objective of the project is to be able to carry a payload of 100 lbs
across various types of terrain while demonstrating the advantages of a hovercraft over
that of either a typical land or water vehicle. There are many secondary design
requirements which are also proposed as follows:
 Powered by twin engines and twin fans (lift and thrust) to achieve maximum
possible performance
 Maximum Size 6' x 4' so that transportation can be obtained in any ordinary
quarter ton pickup trick.
 Maximum weight of 250 lbs was selected as a reasonable number when
considering the weight of 1/4" aluminum used for the design.
 Must move a payload of a minimum 100 lbs. This weight is selected because
15 lb/ft2 is the upper range of operation pressure for hovercrafts. The 100 lbs
payloadbrings our hovercraft weight to approximately this value as well as is
heavy enough to carry many standard items or tools to assist in use.
 Fans must be covered and shrouded for safety.
 Controlled by remote control, two thrust controls, and steering.
 Must include one kill switch for safety shut off of both engines.
 Maximum speed of at least 5 m/s. This speed was selected as it provides an
effective speed as well as being much faster than last year's 1.3m/s craft.
 Steering controlled by rotating the thrust fan.
 Craft must be buoyant in case of emergency engine shut down.
 Minimum hover height of 3”. This value was selected as it will allow the
craft to traverse most small obstacles in its way and discrepancy in terrain.
 Capable of operation on various terrain including:
o Asphalt,
o Grass,
o Sand,
o Snow,
3
o Water, and
o Rough land – gravel.
 Aesthetically pleasing.
4
3. Design Selection
3.1.
Engine Selection
In order to provide the proper amount of thrust and lift the selection of number of
gas engines as well as required horsepower had to be selected. The options which were
weighed were a single 6.5 hp horizontal shaft engine, two 6.5 hp horizontal shaft engines
(one thrust and one lift), and one 5 hp vertical shaft (lift) and one 6.5 hp horizontal shaft
(thrust) engine.
Due to the carrying capacity of the hovercraft the first option of a single 6.5 hp
engine was not selected. Although this would be the most inexpensive option it is not
viable due to the lift requirements of the hovercraft.
The second alternative of two 6.5 hp horizontal shaft engines provided the
necessary amount of horsepower for both thrust and lift but due to the construction
difficulties it was not selected. Ducting the air from a horizontal fan for lift posed
additional flow consideration problems as well as an increase in cost. The horizontal
engines also weigh more than a vertical engine.
The third option was the use of one 5 hp vertical shaft engine for lift and a 6.5 hp
horizontal shaft engine for thrust. This option poses the best power to weight as well as
simplifying the construction of the hovercraft. Although the vertical engine is more
expensive than that of the horizontal, the decrease in construction costs by using it will
lower the overall cost of the hovercraft.
Table 1 shows the design selection matrix for the selection of the engines. Due to
the weight reductions and construction cost reductions Option #3 consisting of one 5 HP
vertical shaft and one 6.5 HP horizontal shaft engine were selected.
Table 1: Engine Design Selection Matrix
Design
Weight
Power
Construction
Control
#1 Single Engine
10
(~30 lbs)
2 (6.5hp)
4
4
#2 Two Horizontal
Shafts (2 x 6.5hp)
3 (~70 lbs)
10 (13hp)
4
7
#3 One Vertical
(5hp) & 1 Horizontal
(6.5 hp)
6
(~60 lbs.)
8 (11.5hp)
8
10
Cost
9
(~$200)
6
(~$400)
4
(~$500)
Total
29
30
34
5
3.2.
Thrust Powertrain
In order for the hovercraft to make turns, it was determined that the thrust fan,
which is located at the back of hovercraft, would have to rotate. With a rotating thrust
fan, the thrust force could be applied at different angles on the back of the hovercraft in
order to rotate the hovercraft and make turns. The thrust fan and motor will be placed on
a rotating platform. In order to rotate the platform, three separate designs were examined
in terms of performance, vibration resistance, center of gravity, construction and cost.
The results of these ratings can be found in Table 2. All three designs require the use of a
remotely controlled electric motor.
Design #1 involves attaching the motor
directly to the thrust fan as shown in Figure 1.
This design is simple but has a few significant
flaws. First, the platform would be difficult to
control as the rotating shaft from the electric
motor would rotate very fast. Secondly, this
design would require placing the electric motor
directly beneath the platform which would
Figure 1: Direct Drive Thrust Fan
elevate the thrust fan and create a higher center of gravity for the hovercraft.
Design #2 involves the use of a belt drive to translate rotational power from the
motor to the platform. This design gives better control and performance over Design #1
as the rotational speed can be reduced through the use of different sheave sizes. A
disadvantage of this design would be that it would require a significant amount of tension
in the belts which would create a bending moment on the motor shaft and platform shaft.
Design #3 is similar to Design #2 but uses
a chain drive to translate the power rather than a
belt, see Figure 2. This design would eliminate
the problem of the bending moment in the shafts
because the chain does not need to be in a great
deal of tension.
From the results in Table 2, Design #3,
Figure 2: Chain Driven Thrust Fan
chain driven design, was selected. Design #1 was rated significantly lower. Design #3
6
was selected in order to simplify construction as well as reduce bearing forces as
discussed above.
Table 2: Thrust Powertrain Design Selection Matrix
Design
#1 Direct Drive
#2 Belt Drive
#3 Chain Drive
3.3.
Performance
Vibration
Center of
Gravity
Construction
Cost
Total
4
8
8
4
4
6
4
8
8
10
3
8
8 (~$50)
6 (~$50)
4 (~$60)
22
29
34
Lift Powertrain
Lift Powertrain is a very important aspect of the hovercraft since it creates the air
pressure beneath the hovercraft that lifts it off the ground. This (combined with skirt
design) will give the hovercraft its ability to float and traverse the various specified
terrain. A front mounted engine for lift has been chosen to balance the rear thrust engine
so longitudinal center of gravity remains even without payload. The results of the design
selection matrix can be seen in Table 3.
Design #1: Horizontal shaft engine and a
centrifugal fan directing air downwards, see
Figure 3. This design involves an expensive
centrifugal fan because the fan intakes and
outputs air through different directions. This fan
works similar to a pump and is less efficient than
a standard fan flowing air straight through.
Figure 3: Centrifugal Fan
Design #2: A vertical shaft engine with a
corresponding fan blowing air directly straight
downward, see Figure 4. This design is the easiest
to construct as it requires only a platform to
mount the engine giving space and air access to
the fan mounted directly to the output shaft. This
fan provides an efficient flow of air. The downfall
Figure 4: Horizontal Fan
of this design, which led to it not being selected, is that the close proximity of the fan
blades to the skirt poses a risk of damaging the skirt during shutdown or deflation.
7
Design #3: An angled engine and fan blowing
air towards the rear of the hovercraft, see Figure 5,
which would give a better dispersion of air. The
angled fan would provide better airflow to the rear of
the craft which a straight vertical fan would not reach
as easily, providing a better balance. However this
Figure 5: Tilted Lift Fan Assembly
design is complicated because the engine then must
be mounted at an angle, which makes the mounting complicated. Furthermore, the
engines are designed for fuel and oil flow to be operated with a level engine; it is
questionable how the engine systems will react to an angled position.
Design #4: as seen in Figure 6 is conceptually
very similar to design #2. However by raising the engine
vertically upwards a height of 13 inches gives this design
two major advantages. First it removes the risk of the
fan damaging the skirt during deflation, because the skirt
cannot deflate in close proximity to the blades. The
second major improvement is that it allows us to taper
the duct from the blades to the skirt inlet effectively.
Figure 6: Raised Horizontal Fan
As can be seen in Table 3, Design #4 the raised vertical fan design has been
selected. The main reason for this selection is the ability to funnel the air flow into a
smaller cross section as well as keeping the skirt material out of the vicinity of the fan
blades.
Table 3: Lift Powertrain Design Selection Matrix
Uniformity
of Airflow
Control
Construction
Weight
Cost
Total
#1 Horizontal
Engine with
Centrifugal Fan
4
8
2
2 (~60lbs)
2
(~$350)
18
#2 Vertical Fan
8
5 (skirt
interference)
9
8 (~45lbs)
#3 Fan on angle
10
8
4
6 (~50lbs)
#4 Raised
Vertical Fan
10
10 (no
interference)
8
7 (~50lbs)
Design
9
(~$250)
4
(~$350)
39
32
9
(~$250)
44
8
3.4.
Platform & Skirt
One of the most vital parts of a hovercraft is the design of the platform and skirt.
There are many ways in which a seal can be made with the ground and after reviewing
multiple selections online three different designs were considered. Design #1 shown in
Figure 7, uses a diffuser plate to diffuse the air and create pressure under the hovercraft,
Design #2 is called a “bag skirt” and the air is directly flows into the skirt with holes in it,
and Design #3, is a combination of a diffuser plate with a bag skirt.
Design #1, shown in Figure 7, is one of
the more expensive alternatives for the design.
Due to having multiple plates the construction
of this design is also more complex. The
uniformity of the airflow through the plate is
also a downfall of this design.
Design #2, see Figure 8, is a simple
Figure 7: Diffuser Plate Design
alternative to the diffuser plate. In this design
the air flows directly into the skirt inflating it
and then the air is released under the hovercraft
through designed holes in the skirt. This
design is also the lightest, and simplest to
construct.
Figure 8: Bag Skirt Design
Design #3, is a combination of Design‟s #1 and #2 using two plates and a bag
skirt design. This design complicates the construction and also adds weight and cost.
The airflow through this design is more uniform than that of Design #1.
Table 4 shows the design selection matrix for the platform and skirt. The bag
skirt design was selected for its overall ease of construction, uniformity of airflow as well
as reduced cost and weight.
9
Table 4: Platform & Skirt Design Selection Matrix
Uniformity
of Airflow
Control
Construction
Weight
Cost
Total
#1 Diffuser Plate
6
8
6
8(~75lbs)
32
#2 Bag Skirt
10
8
10
10 (~50lbs)
4(~$250)
8
(~$200)
#3 Bag Skirt w/
Diffuser Plate
8
8
8
6 (~75lbs)
4(~$250)
34
Design
3.5.
46
RC Control / Steering
The selection of the radio control was limited to a single design. A controller
with a minimum of 4 channels was selected as it is necessary to have a channel for each
engine throttle, a channel for steering, as well as one channel for the kill switches. Four
servo motor actuators will be used; two to control each individual throttle and two to
actuate the kill switches on each engine. A high torque servo motor will be used and
remote controlled to rotate the steering fan.
3.6.
Buoyancy Compensation
In case of emergency shutdown on water the craft must be buoyant so that it can
float and be retrieved. Highly buoyant material such as solid foam will be added to the
craft to gain buoyancy. Material positioning will be in a location that will not detract
from craft aesthetics such as directly beneath the plate and inside the skirt itself. Inside
the skirt will also be highly beneficial because it will reduce the water which could get in
the skirt when shutdown occurs, and replace that volume with a buoyant volume.
10
4. Final Design
The hovercraft design incorporates many challenges for Team 13 to overcome.
These challenges presented themselves throughout the design and construction processes.
The design minimizes the center of gravity of the overall craft in order to increase the
stability of the overall ACV. The overall final design is one that uses tried and tested
hovercraft design with a state of the art rotating thrust fan for steering, which can be seen
in Figure 9.
The final design accounts for many design alterations from that listed in the
Section 3 Design Selection to account for construction and testing issues. All alterations
are listed in each section under the proposed final design. This is done in order to
demonstrate that the design process was done in such a manner that shows the
engineering thought put into the overall design but also illustrates the problems which
were encountered and how they were overcome.
The hovercraft was designed by separating the craft into four separate sections:
Thrust Powertrain, Lift Powertrain, Platform & Skirt, and the Remote Control, Steering,
and Electronics.
Figure 9: Final Design
11
4.1.
Thrust Powertrain
The thrust powertrain is the system responsible for lateral propulsion of the ACV.
To keep the center of gravity as low as possible the engine will be mounted directly onto
the rotating steering plate, see Section 4.4 for details on the steering. The center of
gravity was largely taken into account in order to maximize the overall stability of the
craft. In order to drive the fan, the drive shaft of the engine will have an attached gear
sprocket which will be attached to the input shaft of the fan via chain. The 22” diameter
thrust fan is attached directly to the input shaft using a key and bolt connection and
produces 20.4 lbf which is calculated in Appendix A: Calculations. The final design
selected for the thrust assembly can be seen in Figure 10 along with a list of parts as
shown in Table 5.
Figure 10: Thrust Powertrain Assembly
12
Table 5: Main Parts List for Thrust Assembly
Item
Engine
Fan
Dampers
Fan Supports
Sprocket
Chain
Fan Shaft
Angular Bearing
Bearing Block
Pillow Block
Mounting Plate
4.2.
Description
Qty
6.5 hp horizontal shaft engine, make Powerfist
22" diameter fiberglass fan
Rubber dampers (from scrap)
Custom manufactured aluminum fan support assemblies
10 tooth V-Series sprocket
Length of chain
3/4" custom shaft 12" length
3/4” bearing for thrust and radial load
Custom built block for angular bearing
Radial bearing
24" OD aluminum mounting plate
1
1
N/A
2
2
1
1
1
1
1
1
Lift Powertrain
The lift powertrain is in charge of providing the necessary pressure underneath the
craft to lift the craft‟s weight off of the ground. This pressure is created using a vertical
shaft engine attached directly to the lift fan. This fan forces air directly into the bag skirt,
see Section 4.3.2 for bag skirt details, which then inflates the skirt and creates the
pressure under the craft.
The lift engine is mounted on a custom made aluminum plate, which has sections
removed in order to allow air flow, and the plate is supported with 6 pillars to hold the
engine and fan in place. Vibration is minimized through the effective use of rubber pads
under the mounts. The overall final design of the lift powertrain is shown in Figure 13
and a list of the main parts can be found in Table 6.
13
Figure 11: Lift Powertrain Assembly
Table 6: Main Parts List for Lift Assembly
Item
Engine
Fan
Key
Dampers
Engine Mounts
Mounting Plate
4.3.
Description
5 hp vertical shaft engine, make Powerfist
22" diameter fiberglass fan, 5 vane
Standard square key way for 7/8” shaft
Rubber dampers (from scrap)
Custom manufactured aluminum fan supports
Custom manufactured aluminum engine mount plate
Qty
1
1
1
N/A
6
1
Platform & Skirt
The most important aspect of design of a hovercraft is the platform and skirt
design. This design is essential as it separates the lift air flow and creates the high
pressured area beneath the craft which lifts the vehicle. The platform is also the housing
for all the mounting of equipment such as engines, electronics, and fans. A complete
listing of parts can be found in Table 7.
Table 7: Main Parts List for Platform and Skirt
Item
Aluminum Plate
Skirt Material
Flotation
Strengthening Ribs
Skirt Bolt Strips
Description
6’ x 4’ with 24” radius and 19” dia. hole
Black-8 linear yards
Added buoyancy
Aluminum rods for added strength
Aluminum strips to pinch skirt to platform
Qty
1
N/A
N/A
N/A
N/A
14
4.3.1. Platform
The platform of the hovercraft is important as it will house all of the components
and must take all of the respective loads. A ¼” Aluminum plate (5052-H32) was selected
due to its lightweight and strength properties.
The overall size of the hovercraft has been selected as 6 ft in length by 4 ft in
width. This was chosen in order to minimize the cushion pressure under the hovercraft.
When the preliminary size was selected of 5.5 ft by 3 ft a cushion pressure was calculated
to be 21.21 lb/ft2 which is much higher than the average hovercraft cushion pressure of
10-15 lb/ft2. Once the new designed size was selected an acceptable cushion pressure of
14.58 lb/ft2 was calculated, which is still relatively high but carries a safety factor
associated with it, for detailed calculation see Appendix A: Calculations. The final
design of the platform can be seen in Figure 12.
4 ft
6 ft
Figure 12: Platform
4.3.2. Skirt
The skirt design will be a „Bag‟ skirt. This design is readily used in industry as
one of the more reliable constructions. In this design the lift air is ducted directly into the
skirt which then inflates. The skirt allows the air to exit under the craft using specified
holes in the skirt. This air flow under the craft creates the high pressure which lifts the
15
ACV. The skirt is constructed using a Polyurethane-Coated Nylon Fabric which is
attached directly to the platform at two separate locations sealed off air tight.
In order to select the appropriate size of skirt, Team 13 followed standard practice
for bag skirt design as outlined in Introduction to Radio Control Hovercraft (Jackson,
2004). Following common practices shown in this book the two different radiuses of the
skirt were selected to be R1=3” and R2=6”, which exceed the design criteria of hover
height of 3 inches. With these values the skirt cross sectional area and volume were
calculated to be 0.49 ft2 and 8.97 ft3, see Appendix A: Calculations for detailed
calculations.
The skirt has dual purpose of both sealing off the high pressure area under the
craft as well as providing emergency buoyancy in case of a shut down over water. In
order to compare the amount of volume required to have the craft float in water the
overall weight of the craft is divided by the density of water which is then compared with
the volume of air in the skirt. With our current design there is 59% excess volume of air
in the hovercraft skirt in order to keep the craft afloat. For detailed calculations see
Appendix A: Calculations.
An airflow analysis has been conducted on the bag skirt to ensure that the
designed airflow will exit the craft evenly. This airflow analysis can be seen in Figure
13.
16
Figure 13: Airflow Analysis of Bag Skirt (Red=High Velocity, Blue=Low Velocity)
Although at first glance this airflow seems to be uneven, this is only due to the
limitations of the airflow software. This case as shown in Figure 13 shows the hovercraft
at start up, with 5220 cubic feet per minute (cfm) of flow. Initially the pressure under the
craft will be the same as atmospheric but as the pressure underneath increases the flow
out of the skirt will become more stable and even.
4.4.
RC Control & Steering
A majority of RC control components have already been obtained free of charge,
such as a 6 channel controller and receiver along with 5 servomotors. These have all
been salvaged from previous design projects and will work perfectly for our
requirements.
It was decided that minor modification of the engines such as removing throttle
leavers and connecting directly to the throttle would be the most cost and time effective
way of utilizing RC controls. Through minor modifications of the stock engine setups
(adjustment and replacement of levers and springs), the servomotors on hand will
accomplish the tasks of engine throttles as well as kill switches. For simplicity of design
and construction, and because the controller and receiver have additional channels than
we initially desired, the engine kill switches will be on the same channel for quickest
17
shutoff. In addition, the controller can be pre-programmed so that if signal from the
controller is lost, the kill switches can be automatically activated so the craft does not
continue on out of control.
Steering control will be performed by rotating the horizontal engine mounting
plate around a single shaft in a thrust and radial bearing block in the center of the plate.
This is achieved through the use of a high torque servo motor which will be directly
attached to the mounting shaft. This complete assembly is shown in Figure 14 along with
the parts list in Table 8.
Figure 14: Steering Control Assembly
Table 8: Main Parts List for Steering / RC Control Assembly
Item
Bearing
Shaft
Sprockets
Chain
Bearing Plate Supports
Steering Motor
Remote Control
Servos
Battery 6 Volts for Receiver
Description
Thrust and radial bearing w/ housing
Shaft
10 tooth V-Series sprocket
Size and length of chain
Caster wheels to distribute load
Ultra torque servo motor (manufacturer TBD)
6 Channel
Small Servos
6.0V for more power (optional)
Qty
1
2
1
6
1
1
5
1
18
5. Build and Construction
5.1.
Thrust Powertrain
The chain driven system was constructed as shown in Figure 15, with an
additional support frame over the engine to support the fan shaft which included two
bearings one being a thrust roller bearing. For safety reasons there is also an aluminum
frame which encases the chain to protect any user from being able to touch as well as be
hurt by the assembly. The final assembly can be seen in Figure 15 below. Once this
assembly was built it was tested and found to have excessive vibration as well as chain
slop, therefore a new design was proposed, see Figure 16.
Figure 15: Chain Driven Thrust Assembly Construction
Although the original design selected a chain driven system, this thrust assembly
caused many more problems than originally anticipated. Due to the large force which the
fan imposed on the drive shaft and support frame there was an extremely high degree of
vibration which resulted in chain slop. In order to minimize the chain slop a chain
tensioner was first installed, but was found not to have enough force to eliminate this
vibration. Next an idler sprocket was installed to put tension on the chain with the
overall same result. After having tested the thrust system with both types of tensioners it
19
was found that the welds in the corners of the support frames had started to crack due to
excessive vibrations and force.
After spending a substantial amount of time trying to get the chain driven system
to perform to standard it was decided to abandon the chain assembly. In order to
minimize the vibrations, a direct drive with a flexible coupling was installed. Although
this option was looked at in the design selection it was abandoned due to the height of
installation of the engine. It was found with the assembly on hand that the fan could be
lowered and this would only result on increasing the height of the engine 5” which was
deemed acceptable.
With this decision in mind the direct drive system was constructed as can be seen
in Figure 16. This new design also minimized the weight of the assembly for better
performance.
Figure 16: Final Thrust Assembly
5.2.
Lift Powertrain
During construction the design selection for the raised vertical fan with a funnel
type front design selected in January was slightly altered to give a combination of two
designs proposed.
In late January to become more familiar with the construction of hovercrafts a
local hovercraft expert Leo Cruickshank was approached and asked for suggestions on
our proposed designs. One of the main suggestions he had was to put a larger hole in the
20
front of the craft as the amount of air we were using would be plenty to fill the skirt and
the rest can go directly under the craft to create the intense pressure to lift the hovercraft.
This design was then looked into in more detail and the construction of it would also be a
lot simpler while there would also be an efficiency increase of the airflow.
With this in mind the design was altered to be a combination of designs #2 and #4
where a raised vertical fan was used but was funneled directly down and only a third of
the air was used to inflate the skirt. To do so a 19” diameter hole was put in the front of
the top plate, as shown in Figure 17.
There was also a slight design alteration in the support plate for this assembly. In
the original design there were square type sections which were cut out of the plate for the
airflow. When construction of this plate began it was decided upon that it is much easier
to use two different radius‟ circles and create the same cross section for the airflow.
Therefore as shown in Figure 17 the cut outs are actually round as opposed to the
quadrilateral type shape originally designed.
The final design constructed is shown in Figure 17. As shown in this photo, the
air is ducted down from the fan into the skirt and directly under the hovercraft while the
overall height proposed for the raised vertical fan was maintained.
Figure 17: Lift Assembly Construction
21
5.3.
Platform and Skirt
Once again there was a slight design alteration made to the top plate due to the
aforementioned visit with Leo Cruickshank. In order to synchronize the top plate design
with the lift assembly the size and position of the air entry hole was changed. A 19” hole
was cut, as shown in Figure 18, in replacement of the 6” hole and it was moved further
towards the rear of the hovercraft. The final construction of the top plate can be seen in
Figure 18.
The skirt design was also changed to compensate for the lift assembly alterations.
Because there is only a third of the air entering the skirt it was not found necessary to
place any holes in the skirt as previously selected. The skirt was constructed to allow air
to exit under the craft through the small gaps between the bolts on the inner perimeter
where as the outside perimeter is air tight optimizing the use of the air. The final skirt
design can be seen in Figure 19. The construction of the skirt was difficult as the shapes
of the corners were not intuitive and therefore through an iterative process the proper
shapes were cut and glued together and the overall design has performed very well.
During construction of the skirt wire mesh was used to frame out the desired
shape of the skirt so that when the loose fabric was draped in place it would hold the
desired shape. This allowed a better visualization of the panels needed to shape the skirt
so that the proper panels could be cut to shape the rear corners and the front radius so that
when glued together created an effective skirt design which we wanted. During final
application of the skirt onto the plate, waterproof caulking was used to seal the bolt holes,
and on the outside bolt line of the skirt corner bead was layed so that it clamped the skirt
100% airtight and air could not leak on the outside of the craft. This bolting strip was
deemed unnecessary because if any small holes occurred on the inside of the skirt it
would only leak to the underside of the craft where it would aid in the lifting of the craft
and would not be a performance loss.
22
Figure 18: Top Plate & Skirt Construction Top
Figure 19: Top Plate & Skirt Construction Bottom
23
5.4.
RC Controls
The original design called for the use of a servo motor to rotate the thrust
plate to give the steering control but problems arose with this design. The high torque
servo motor was able to turn the assembly but the plastic attachments for the servo were
quickly stripped due to the torque imposed upon them. A brass piece was then
constructed but without the ability to make the inner splines for the servo it was
impossible to get it to stop slipping.
With this design problem in mind, Team 13 was able to borrow a
previously used electric motor and gear box from Team 5 as it was undersized for their
use. With this electric motor a speed controller was taken from an RC car and
implemented to rotate the plate directly, see Figure 20.
Figure 20: Steering Mechanism
With the use of the electric motor and gear box the steering was then able
to become very reliable and found to have excess power.
24
6. Testing
In order to ensure that the designed and constructed hovercraft meets the design
requirements as shown in Section 2: Design Requirements each of the requirements had
to be specifically tested.
Some of the design requirements were met without testing being required as the
construction of the hovercraft itself ensured that the requirements would be met. The
following section will outline each design requirement, testing methodology, the results
of each test, as well as any conclusions or recommendations which were made post
testing.
6.1.
Size and Weight
6.1.1.
Size
This design requirement was fulfilled during the construction phase of the
hovercraft and is therefore satisfied without testing; see Figure 21 and Figure 22. The
craft plate was cut to fit within the criteria and sized at 4'x6'.
Figure 21: Length Measurement
25
Figure 22: Width Measurement
The size restriction set on the hovercraft was accomplished during fabrication and
the hovercraft can successfully be carried by 3 people and placed in the back of a pickup
truck as well.
6.1.2.
Weight
The maximum weight of 250 lbs was selected in order to be able to move the
hovercraft around by 3 people with little restriction. The hovercraft was built in a piece
set up where the lift and thrust assemblies can be removed as well for ease of
transportation.
In order to substantiate that the hovercraft met the maximum weight of 250 lbs the
following steps were taken.
1. A digital scale was borrowed from the civil department.
2. The thrust assembly, lift assembly, and plate were all weighed separately,
see Figure 23 for example of thrust assembly.
3. The sum of the weights is the total weight of the craft.
The result of the maximum weight was that the hovercraft came in weighing in at
232.2 lbs. This is therefore a success for meeting this design requirement and does not
require any further testing. For specific weight of each assembly see Table 9.
26
Table 9: Weight Testing Results
Component
Weight
Top Plate
116.2 lbs.
Thrust Assembly
74.8 lbs.
Lift Assembly
41.2 lbs.
Total
232.2 lbs < 250 lbs
Figure 23: Weighing of Thrust Assembly
6.2.
Safety
Due to the inherent safety hazards with a moving craft with two high
speed rotating fans safety is a major concern. We want to design a safe craft so we will
concentrate our safety concerns with isolating the fans with shrouds and providing a kill
switch to quickly shut down the craft
27
6.2.1.
Shrouds
In order to ensure the hovercraft can be used safely by any user the fans were
required to be shrouded and the ability to reach them had to be restricted. This was done
through the construction phase of the hovercraft. The shrouds are used to increase the
efficiency of the fans and therefore were installed first. In order to reduce the chances of
things getting into contact with the fans there was a chicken wire placed on both sides of
the thrust shroud and on the upper side of the lift shroud.
With these safety pieces constructed this design requirement was satisfied without
testing. See Figure 24 and Figure 25 for shroud coverage.
Figure 24: Shrouded Thrust Fan
28
Figure 25: Shrouded Lift Fan
As the pictures above demonstrate the fans are adequately shrouded in order to
protect the user while still allowing the fans to draw enough air to create the required
cubic feet per minute of airflow.
6.2.2.
Kill Switch
The testing of this requirement is included in Section 6.5 ,see below
6.3.
Twin Engine
This design requirement was fulfilled during the construction phase of the
hovercraft and is therefore satisfied without testing, see Figure 21.
6.4.
Terrain
One of the main capabilities of the hovercraft is established that it must be able to
work on various types of terrain. This has been established through many other tests but
is a simple pass or fail scale whether the hovercraft worked or didn‟t on these types of
terrain.
1. Hovercraft was placed on the various surfaces.
2. Both engines were turned on.
3. Hovercraft was driven around and if performance was satisfactory
a pass grade given.
29
Table 10: Terrain Testing Results
Terrain
Test #
Pass
Cement
1
X
2
X
3
X
1
X
2
X
3
X
1
X*
Gravel
Grass
2
Water
Sand
Fail
X
3
X
1
X
2
X
3
X
1
X
2
X
3
X
* only lift was tested on first test.
Terrain tests were deemed a large success as the hovercraft was capable of
operating on all smooth services, while grass provided it much difficulty to thrust.
However literature available online shows that grass is one of the hardest surfaces for a
hovercraft to traverse because the craft does not get good lift separation between the
ground, grass, and skirt. On all other surfaces (cement, gravel, water, and sand) the
hovercraft was able to both lift and thrust and steer adequately to provide control of
operation.
This test was also deemed a success, as in almost all cases the hovercraft was able
to perform as desired. With respect to the low performance on grass, this could be solved
through a more powerful motor in either lift, thrust, or both. This would allow the craft to
lift higher and gain more separation, power through the separation which is already
occurring, or both, respectively.
6.5.
RC Controls
The first design requirement was that the hovercraft must be remote controlled.
This was selected instead of the proposed design of a manned hovercraft due to safety
concerns. This design criteria was met as all the kill switches, throttles, as well as
30
steering are remote controlled. The steering is controlled through a speed controller
which varies the speed of a gear reduced electric motor.
The remote control design requirement was tested very simply. In order to
substantiate that the remote control functions were functional, the following steps were
demonstrated.
1. Hovercraft was placed in a well ventilated area and tied down.
2. The gas switch on the thrust engine was manually turned on as well as the
choke.
3. The kill switches were tested to ensure the on/off capabilities were
working before the engines were started.
4. The kill switches were then turned to the on position so the engines could
be started.
5. The thrust engine was pull started manually to lift the hovercraft.
6. The lift throttle was then throttled up and down to demonstrate that the
servo was in control of the throttle.
7. The thrust engine was then pull started manually and once started the
choke was shut off manually.
8. Once the engine was running smoothly the thrust throttle was throttled up
and down to demonstrate throttle control.
9. To ensure kill switches were working the kill switch was then turned off to
verify that both engines would shut down.
The servo motor controls of the kill switches as well as throttles worked well each
and every time they were tested. The first test was a pure servo motor test as outlined in
this section, it was a success. The kill switch testing photos are shown in Figure 26 and
Figure 27. The throttle testing was also successful but no photos are shown in the report
due to little range of throttle design.
31
Figure 26: Lift Kill Switch Testing
Figure 27: Thrust Kill Switch Testing
The servo testing was a full success in which all the servos used worked well. All
of the custom servo mounts held the servos in place with little to no induced vibration
from the motors. Over the series of tests which were conducted on the hovercraft this
test is essentially repeated and there was not a single failure of the system.
Every test outlined from this section is inherently retested every time the
hovercraft is used and therefore is ultimately a success.
6.6.
Payload
The payload design criteria stated that the hovercraft should lift and move
a minimum of 100lb payload. The 100lb payload was selected so the hovercraft overall
weight with payload divided by its footprint was approximately 15 pounds per cubic feet,
which is the upper range of a hovercrafts operating pressure.
Testing of the payload is fairly simple, 100 lbs is to be fitted to the hovercraft
platform, and then the hovercraft is to be started up to see if it will inflate its skirt and lift
up as it would if it did not have a payload on it.
32
Testing results for the payload were extremely positive as the hovercraft was able
to lift the 100lbs easily on all surfaces tested. With the additional weight, it took an
additional second or two for the skirt to inflate and lift in comparison to the unloaded
craft, this was deemed normal as it had to lift the additional weight. The hovercraft thrust
also worked sufficiently, on all surfaces except grass (which was expected from the
terrain clips). With the payload the thrust assembly turned the craft and pushed it
forward, and similar to the lift assembly startup, it took slightly longer for the loaded
craft to gain headway in contrast to the unloaded craft due to the extra force needed to
build up to push the increased mass. The 100 lbs payload was achieved on all surfaces,
including sand, grass, asphalt and pavement, (water was left out just as a precaution to
not lose the weights in the lake). In some cases like on asphalt, gravel, and grass, the craft
was capable of lifting up to 160 lbs. This however severely retards the thrust response.
The payload criteria tests were deemed a success as the craft could lift the payload
sufficiently and traverse with it on all terrain which it could traverse normally.
Recommendations for payload are that a larger thrust engine would generate sufficient
power as to provide more nimble operation of the craft under loaded situations.
6.7.
Steering with Rotating Thrust Fan
The most innovative piece constructed for the hovercraft was the rotating thrust
fan which turns the thrust assembly instead of using a rudder system. In order to test this
assembly the hovercraft is lifted and thrust turned on and the hovercraft is then steered
using the remote control.
The testing methodology for the steering mechanism was done through two tests.
First, a basic test where the servo was used to turn the plate without the thrust fan on, and
secondly, as a full scale test turning the hovercraft under full operation.
Basic Test:
1. Hovercraft was fully assembled with thrust engine off.
2. Remote control was used to turn the thrust assembly both right and
left.
Full Test:
1. Hovercraft was placed outside on a flat surface.
33
2. The electronics were all set up and the lift and thrust engines
turned on.
3. Once the hovercraft was driving the controller was used to
maneuver the hovercraft right and left.
4. On thrust engine idle the turning radius to the right and left were
recorded.
The results for the steering tests were all once again successful. In the basic test
where the electric motor was used to turn the plate without the thrust assembly on there
were absolutely no problems, see Figure 28.
34
Figure 28: Basic Steering Test Results (Top to bottom: turning left, center, right)
Based on the test results which are shown in the previous section the steering
mechanism was shown to be performing well. The recommendation which is made is
that the steering mechanism is not very affordable or realistic due to its constructability
and complicated set up. If the hovercraft were to be mechanically driven as opposed to
remote controlled then this would be a more viable alternative.
6.8.
Buoyancy
It is extremely important for a hovercraft to be able to float during an emergency
shut down over water. This ensures that the craft itself and the payload can be recovered.
35
This was a simple test to perform in which was performed only once to ensure
that the hovercraft was buoyant.
1. Hovercraft and all electronics were turned on.
2. The craft was driven onto water where team members had the craft roped
off in case the craft did not float.
3. The kill switch was turned off and both the thrust and lift engines shut off.
4. The hovercraft was left to rest in the water to ensure buoyancy was met.
During this test the hovercraft was started up and slid from the beach onto the
water where it was then shut down. The hovercraft skirt deflated and the plate lowered to
the water, where it then proceeded to float under no power and moved with the current.
The flotation material which was installed in the skirt and underneath the craft to assist
buoyancy provided sufficient buoyant force to keep the craft above water.
This test was deemed a success because the hovercraft did float under an
emergency shutdown condition. It was noticed however that under emergency shutdown
the craft could not handle additional weight added to it and therefore it is recommended
to add some more buoyant foam so that there is a larger factor of safety for buoyancy
during shutdown.
6.9.
Miscellaneous Criterion
6.9.1.
Maximum speed (5 m/s or 18 km/h).
The design criteria for a minimum speed of 5 m/s (18 km/h) was established in
order to have an overall better performance than the hovercraft built in 2008-2009 at
Dalhousie University.
The testing of the speed test was conducted on pavement terrain as it is the best
for performance hence why it was selected for the test. If time is adequate speed test will
be completed on other surfaces.
1.
Hovercraft was placed on a flat surface with adequate room to open full
throttle.
2.
A Garmin GPS unit was strapped down to the hovercraft to measure the
velocity, see Figure 29 for an example of readout.
36
3.
Controller was turned on, battery plugged in, and kill switch was put to the
on position.
4.
Lift engine was started following by the thrust engine.
5.
Thrust engine was then throttled up to full throttle.
6.
Once hovercraft meets what is perceived as max speed, the throttle was
released and the kill switch turned off.
7.
The GPS was removed and the average and maximum speeds are read off
and recorded.
The following are the results of the speed test on the hovercraft. Each
measurement was repeated twice to ensure accuracy. Table 11 shows the test results for
each of the various surfaces in which we were able to perform the speed testing on. An
example of the Garmin GPS readout can be seen in Figure 29. Water is not included in
this test as we did not want the Garmin GPS unit to get wet and therefore this was not
completed.
Figure 29: Garmin GPS Speed Readout
37
Table 11: Speed Test Results
Terrain
Test #
Pavement
Gravel
Grass
Water
Avg. Speed (m/s)
Max Speed (m/s)
1
1.81 (6.5 km/h)
5.47 (19.7 km/h)
2
3.44 (12.4 km/h)
6.36 (22.9 km/h)
1
2.92 (10.5 km/h)
4.33 (15.6 km/h)
2
2.72 (9.8 km/h)
3.97 (14.3 km/h)
1
<1
<1
2
<1
<1
1
N/A
N/A
2
N/A
N/A
As shown in Table 11 the results of the speed test were mostly successful. The
hovercraft performed really well on pavement and exceeded our design requirement of 5
m/s. Although on the gravel the craft did not meet the 5 m/s, the team believes that the
craft performed effectively. The run which was used for the gravel test was less than 100
m in length and therefore the craft was not able to reach maximum speed. Given a longer
run of gravel the team believes that the craft could meet the requirement of 5 m/s.
Performance on grass was not admirable as there was too much friction which restricted
the craft from travelling up to speed. This is usual as it is the toughest surface for
hovercrafts to hover. Overall, the speed test was deemed a success.
6.9.2.
Minimum hover height of 3”
The design requirement of a minimum hover height of 3 inches was established in
order for the hovercraft to be able to traverse across various rough terrains with rocks,
etc.
The testing of this requirement was very simple as it required only the thrust
portion of the craft be activated.
1.
Hovercraft was placed on the terrain listed below.
2.
Lift engine was turned on and left at idle for first measurement of height
(measurement taken between ground and bottom of plate) at both
the front and back of hovercraft, see Figure 30 and Figure 31
respectively.
38
3.
Lift engine was throttled up to full throttle and another measurement was
taken for both the front and back.
Figure 30 and Figure 31 show an example of the lift height being take on concrete
at idle. This was repeated both at full throttle and idle for all of the different surfaces.
Table 12 shows the results of the various hover height measurements.
Figure 30: Hover Height Measurement (front)
Figure 31: Hover Height Measurement (back)
39
Table 12: Hover Height Test Results
Terrain
Position
Idle Height (inches)
WOT Height (inches)
Cement
Front
8
8
Back
5.75
6.75
Front
8
8.25
Back
6.75
8
Front
8
8.25
Back
6.75
8
Gravel
Grass
The hovercraft performed admirably in this category as the skirt was well inflated
at idle speed for the lift engine. The craft had trouble a bit more to get off of the grass
surface due to the amount of air escape which happens because of the tendency of the
grass. The center of gravity of the craft is also slightly to the back as can be seen by the
hover heights being higher in the front then the back. This can be fixed with simple
ballasting of the front.
6.9.3.
Aesthetics Testing
The aesthetic test is a very qualitative and subjective area and is therefore difficult
to get an accurate test. However the team decided to design the craft as to give it a
rounded looking front section, and finished in the raw, polished aluminum look to give it
an attractive appearance.
Testing data was taken by inquiring with people who viewed the craft what they
thought of the overall appearance. A survey sheet was passed about classmates and
acquaintances who viewed the craft and a poll showed the overall thoughts of its
appearance as can be seen in Figure 32. As can be seen, the majority of people agree that
the hovercraft does look aesthetically pleasing or 'good'. Although the largest majority
opined that it would look better painted a stealthy 'matte black', while zero people
referred to it as being 'ugly'. With this result in mind it is recommended to finish the
hovercraft with a matte black appearance to gain maximum aesthetic benefits.
40
Figure 32: Aesthetic Poll Results
41
7. Budget
The following section outlines a detailed budget of all the necessary parts which
were purchased in order to build the hovercraft. Team 13 was able to find outside
funding through the sponsorship of an anonymous source which donated the aluminum
plate, Slipstream Hover which gave a 10% discount on the skirt material, and Leo
Cruickshank owner of LE Cruickshanks Sheet Metal who donated the aluminum shrouds.
The final budget can be seen in Table 13. The budget is within the allotted budget
which the Department of Mechanical Engineering at Dalhousie University gave to Team
13.
42
Table 13: Final Budget
43
8. Conclusions
In conclusion the twin-engine payload hovercraft project was deemed a success.
The craft fulfilled virtually all design criteria which it set out to accomplish.
The rotating steering fan which was the largest design departure from
conventional hovercrafts proved itself a great success as the electric motor installed
effortlessly rotated the engine and fan assembly and provided interactive steering and
good performance. However the RC controls did provide some added difficulty to this as
the original servo motor which was designed had adequate power but sufficient
attachments were unavailable which could handle the repeated loading as they were made
of plastic. It is recommended that if this design were to be scaled to a manned hovercraft,
a direct steering linkage to a 'steering wheel' of sorts would easily provide power and
responsiveness. This proof of concept was deemed a total success.
The hovercraft overall performance was excellent on all surfaces with exception
to grass. It performed in handling, lift, and thrust adequately on all other surfaces. To fix
the grass performance deficiency, as stated before it is recommended to increase engine
power so the craft can help overcome the added resistance of grass surfaces. In addition,
additional thrust power would also help improve the performance of the craft under
payload operations, and would also increase general performance on other surfaces more
as well.
Finally, we believe this project was also a huge success as it provided real world
experience to the design of a physical entity and provided necessary challenges we
worked to overcome to design around any issues which occurred such as the thrust
vibrations. It also provided excellent first hand experience with the fabrication of the
parts in the machine shop and the overall project provided an excellent experience in a
teamwork environment.
44
References
ASM Aerospace Specification Metals Inc. (n.d.). Aluminum 5052-H32. Retrieved from
http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA5052H32.
Engineering ToolBox. (2005). Air Temperature, Pressure and Density. Retrieved from
http://www.engineeringtoolbox.com/air-temperature-pressure-densityd_771.html.
Jackson, K., & Porter, M. (2004). Introduction to Radio Control Hovercraft.
Germantown, MD: Flexitech LLC.
National Aeronautics and Space Administration. (2008). General Thrust Equation.
Retrieved from http://www.grc.nasa.gov/WWW/k-12/airplane/thrsteq.html.
45
Appendix A: Calculations
Skirt Volume Calculation:
Figure 33: Cross Sectional View of Skirt (Jackson, 2004, p. 68)
(Introduction, 2004)
Where,
C = circumference of the skirt
cross sectional area of skirt
perimeter of hovercraft
volume of skirt
Buoyancy Calculation:
The buoyancy calculation above assumes no loss of air when emergency recovery
required, which will not be the case in reality. The craft does have more buoyancy than
required but in order to add more safety to the craft buoyant materials will be added to
increase this buoyancy ratio.
46
Thrust Calculation (National, 2008)
Given
Where,
= volume flow rate of air
= density of air at a given temperature and pressure
Then the thrust (T) is defined as
Where,
= mass flow rate of air
= discharge velocity of air
= total cross sectional area of the fan
Therefore,
Convert the thrust to lbf,
47
Appendix B: Drawings
48