project overview - calvin college | grand rapids, · web viewthe lift engine will be a briggs...

Team 1: On Wings Like A

Penguin– Philip Baah-Sackey – Eu Sung Chung – Joe Englin – Chris Lowell –

Calvin CollegeEngineering 339

6 December, 2007Abstract

The primary objective of this project was to design an air cushion vehicle capable of transporting two people over earth and water. The chosen design was a 13 foot by 6 foot bullet-shaped craft lifted and propelled by two separate engines. It was determined that the power output required from these engines was 5.5 horsepower and 16 horsepower, respectively. The design chosen meets the team’s requirements while remaining at relatively low cost. The craft was designed while keeping the Christian principles of integrity and humility in mind.

2Team 1: On Wings Like a Penguin

Table of Contents1 Project Overview...................................................................................................................................62 Design Requirements.............................................................................................................................63 Christian Perspective.............................................................................................................................6

3.1 Background....................................................................................................................................63.2 Transparency..................................................................................................................................63.3 Integrity..........................................................................................................................................73.4 Humility.........................................................................................................................................7

4 Project Organization..............................................................................................................................74.1 Task Delegation.............................................................................................................................74.2 Project Timeline.............................................................................................................................84.3 Methods of Communication..........................................................................................................8

5 Patent Research......................................................................................................................................86 Initial Design Specifications..................................................................................................................9

6.1 Hull................................................................................................................................................96.2 Landing Skids and Attach Strips....................................................................................................96.3 Cockpit.........................................................................................................................................106.4 Lift Duct.......................................................................................................................................116.5 Air Splitters..................................................................................................................................126.6 Thrust Duct..................................................................................................................................136.7 Lift Engine Mounts......................................................................................................................146.8 Thrust Engine Mounts..................................................................................................................156.9 Lift Engine...................................................................................................................................156.10 Thrust Engine...............................................................................................................................156.11 Lift Fan.........................................................................................................................................156.12 Thrust Propeller...........................................................................................................................166.13 Rudders........................................................................................................................................176.14 Steering........................................................................................................................................186.15 Bag Skirt......................................................................................................................................19

7 Method of Approach............................................................................................................................208 Alternative Solutions...........................................................................................................................21

8.1 Craft Shape...................................................................................................................................218.1.1 Circular................................................................................................................................218.1.2 Rectangular..........................................................................................................................218.1.3 Triangular.............................................................................................................................21

8.2 Craft Size.....................................................................................................................................218.2.1 Eight Feet by Four Feet........................................................................................................218.2.2 Ten Feet by Five Feet..........................................................................................................22

8.3 Skirt Design.................................................................................................................................228.3.1 Full Flow Bag Skirt..............................................................................................................228.3.2 Bag and Finger Skirt............................................................................................................22

8.4 Engines.........................................................................................................................................229 Feasibility of Design............................................................................................................................23

9.1 Similar Product Case Study.........................................................................................................239.2 Lift Fan Design and Lift Engine Choice......................................................................................23

9.2.1 Lift Fan Calculations............................................................................................................239.2.2 Jerry Shover’s Hovercraft Case Study.................................................................................239.2.3 UH-13P Sportsman Case Study...........................................................................................239.2.4 UH-13PT Twin Trainer Case Study....................................................................................24

9.3 Thrust Propeller Design and Construction...................................................................................24


9.4 Fan and Propeller Safety Concerns..............................................................................................259.5 Material Availability and Budget Considerations........................................................................259.6 Time Limitations and Scope........................................................................................................25

10 Fiscal Analysis.....................................................................................................................................2611 Test Plan...............................................................................................................................................27

11.1 Engine Testing.............................................................................................................................2811.1.1 Lift Engine...........................................................................................................................2811.1.2 Thrust Engine.......................................................................................................................28

11.2 Propeller Testing..........................................................................................................................2811.2.1 Lift Fan.................................................................................................................................2811.2.2 Thrust Propeller...................................................................................................................28

11.3 Duct Assembly Testing................................................................................................................2811.3.1 Lift Assembly.......................................................................................................................2811.3.2 Thrust Assembly..................................................................................................................28

11.4 Skirt Testing.................................................................................................................................29

Appendix A: Lift Calculations for Required Horsepower...........................................................................30A.1 Lift Fan and Engine Calculations................................................................................................30A.2 Lift Calculation Results...............................................................................................................31

Appendix B: Thrust and Drag Calculations.................................................................................................32B.1 Thrust Propeller Calculations......................................................................................................32B.2 Thrust and Drag Results...............................................................................................................33


Table of FiguresFigure 1: Hull Components............................................................................................................................9Figure 2: Skid Components.........................................................................................................................10Figure 3: Skids on Bottom of Hull...............................................................................................................10Figure 4: Skeletal Frame of Cockpit............................................................................................................11Figure 5: Lift Duct with XPS spacers..........................................................................................................11Figure 6: Lift Duct in Cockpit.....................................................................................................................12Figure 7: Air Splitters..................................................................................................................................12Figure 8: Air Splitters Diverting Air into Skirt............................................................................................13Figure 9: Thrust Duct Mounted on Hull......................................................................................................13Figure 10: Lift Engine Mounts....................................................................................................................14Figure 11: Lift and Thrust Engine Mounts..................................................................................................14Figure 12: Thrust Engine Mount..................................................................................................................15Figure 13: Lift Fan.......................................................................................................................................16Figure 14: Lift Fan with Components..........................................................................................................16Figure 15: Thrust Propeller..........................................................................................................................17Figure 16: Thrust Propeller with Components.............................................................................................17Figure 17: Rudder Assembly.......................................................................................................................18Figure 18: Steering Assembly......................................................................................................................18Figure 19: Rear View of Steering................................................................................................................19Figure 20: Hull with Skirt Attached.............................................................................................................19Figure 21: Angle of Attack Due to Changes in Radius...............................................................................24

Table of TablesTable 1: Tasks Assigned to Each Group Member.........................................................................................7Table 2: GANNT Chart for First Semester....................................................................................................8Table 3: Budget for Building a Larger Prototype........................................................................................26Table 4: Second Semester Construction and Test Plan...............................................................................27Table 5: Lift Calculation Results.................................................................................................................31Table 6: Thrust and Drag Results................................................................................................................33


1 Project Overview

In the modern world, there are myriad vehicles for many different purposes. Some can travel by land, some can travel by water, and some can travel by air. It was noticed by team members that there is only a small supply of vehicles that can make a seamless transition from travelling on land to travelling on water. The team believes that such a vehicle is very beneficial for situations when neither aquatic vehicles nor land vehicles can access certain locations. Therefore, the team decided to design an air cushion vehicle (ACV), otherwise known as a hovercraft, that would solve this problem. Besides being able to access both land and water locations, an ACV is not bound to roads like most cars or trucks. Because of a hovercraft’s unique means of lift and propulsion, it can traverse virtually any terrain. A hovercraft has the capabilities of both an off-road vehicle and a marine vessel, making it more useful than many vehicles in a variety of circumstances.

2 Design Requirements

To be useful to those who desire to effectively travel both on land and water in one vehicle, the team’s ACV was designed with the following requirements. First and foremost, the vehicle should be aesthetically pleasing as well as aerodynamic. The vehicle will be able to attain speeds of at least 5 miles per hour and remain safe to operate. It is very important that the user feels safe while operating the craft and that the user can correct any steering mistakes quickly and efficiently. The ACV will be large enough to transport 2 passengers or carry a 400 pound payload. Being able to transport 2 people translates to a more fun and enjoyable ride for both the driver and passenger. The ACV will be able to clear small obstacles littered on the ground such as small rocks. This means that the ACV will be hovering approximately half an inch off the ground from the bottom contact point of the hovercraft skirt. This is one of the greatest benefits of a hovercraft; a hovercraft can “float” over any debris on the ground. Lastly, the hovercraft will be lifted and propelled by two separate motors. Designating one engine to be a thrust engine provides greater control in steering and having one engine for the sole purpose of hovering the ACV off the ground helps to lift the craft higher (in order to clear obstacles) since some of the engine power is not being diverted into steering.

3 Christian Perspective

3.1 Background

As engineers at a Christian liberal arts college, it was important for the team to design a prototype that integrated faith and beliefs with the design process. As Christians, each member of the team is ultimately responsible to God for their choices. There were several moral guidelines, or “design norms”, that employ Christian ways of thinking which the team believed could be applied to this particular project. During every design stage, the team made sure to apply each of these design norms.

3.2 Transparency

For this project, it is imperative that the ACV can be easily understood and operated. While a simple on/off switch is not feasible for this design, a basic knowledge of how to drive a car is all that is necessary to maneuver the hovercraft. Both engines are recoil start, so all that is required to start them is to pull a cord. Steering is very simple as well, only requiring the user to move the joystick left to turn left and right to turn right. Speed is controlled by a cable and lever, similar to how a handbrake works. Designing these components this way allows the user to become quickly familiar with the basic operation of the hovercraft. A smooth, easy transition from car to hovercraft makes the ride more enjoyable and less frustrating.


3.3 Integrity

Building a hovercraft with integrity requires the team to double-check calculations, even if it takes more time. The team’s prototype will not be a product of careless craftsmanship, and will be able to perform the functions that the team proposed. The end user should be satisfied with this craft for a long time. If the product lasts a long time, this maintains the team’s integrity as well as the product’s integrity. The team does not want to design a product that customers will be largely unsatisfied with because it falls apart every time the customer uses it. Designing the craft with integrity also bears witness to the team’s Christian faith.

3.4 Humility

As Christians, the team believes that humans are fallible creatures. The team does not believe that this prototype is the best hovercraft ever brainstormed. There will inevitably be flaws and imperfections in the prototype design, and it is the team’s job to minimize these faults. The team should not brag about all that is correct about the design and instead should maintain a humble, Christ-like attitude about the design. The team realizes that there is a good chance the design will fail miserably and that this project needs to be approached as realistically as possible. Approaching the design process with a humble attitude will allow the team to catch any errors that may occur rather than conceitedly ignoring any problems. Such an attitude results in a better designed hovercraft.

4 Project Organization

4.1 Task Delegation

After analyzing the team’s dynamics and skill sets, the team realized it would be beneficial to entrust certain tasks to certain team members. For example, Chris had a great deal of previous experience with developing websites, so the task of creating the team website was given to him. Joe was a very assertive, vocal person so many of the public relations issues, like calling around to find materials, were delegated to him. Jim and Phil were both obtaining math minors, so they were placed in charge of calculations and completing the feasibility study. In order to ensure the project’s design was completed on time, the work was divided as shown in the following chart.

Table 1: Tasks Assigned to Each Group Member

Task Group MembersPhil Jim Joe Chris

Research P P S SPosters x x P xWebsite x x x P P Primary task

Calculations P P S S S Secondary taskFeasibility P P x x x Not assigned

Budget x x x PAutodesk model x x P x

Material sourcing S S P PPPFS S S P P


4.2 Project Timeline

Many of the tasks during the course of this project were structured around due dates for the team’s senior design class, Engineering 339. Having these due dates helped to keep the team focused on the important milestones and to complete the work assigned according to schedule. A detailed GANNT chart can be seen in below in Table 2.

Table 2: GANNT Chart for First Semester

September October November DecemberWEEK 1 2 3 4 1 2 3 4 1 2 3 4 1 2 Form team Determine project Initial project research Project objectives defined PPFS Outline - Table of Contents Oral presentation In-depth design analysis Project website and sign Material sourcing and cost estimation Project brief Determine final specifications Complete AutoCAD model Finalize budget Draft PPFS Oral presentation Final PPFS

4.3 Methods of Communication

The team often communicated in person and rarely by email. The team tried very hard to build good relationships and tried to foster an environment where no team member would be afraid to voice an opinion. In order to achieve this goal, the team deemed it best to speak with each other after senior design class, in between classes, and most commonly during team meetings. This method of continual face to face contact worked extremely well and overall, the team was very pleased with the results; work was completed efficiently and with minimal confusion.

5 Patent Research

As part of the team’s resolve to follow necessary ethical codes applicable to this project, the team researched various patents, with the objective of determining the aspects and ideas of the team’s hovercraft design that were borrowed from other people. This way the team was able to acknowledge the engineers who came before them. The team looked at 38 available patents that dealt with hovercraft manufacturing or design. Even though similar fundamental designs were used in the team’s work, none of the technologies specific to the patents were being used in this project, primarily due to the very specific nature of the patents.


6 Initial Design Specifications

6.1 Hull

The craft will be 13 feet long (from the tip of the craft) by 6 feet wide. The sides of the craft will follow the contour of the craft and will be ¼ inch thick and 4 inches deep. See Figure 1 below.

The hull will be shaped like an overhead view of a bullet, combining triangular and rectangular aspects. The bow will be roughly triangular in shape with curved sides. The curve will taper off into the stern which will be rectangular in shape. The hull platform will also curve down at the outer edges.

Figure 1: Hull Components

6.2 Landing Skids and Attach Strips

There are two parts to the landing skids. There is a thin layer of marine plywood following the contour of the ACV that is 8 inches wide and 125 inches long. Centered and glued onto this wood are the attach strips, which are 1 inch by 1 inch. The width of this setup is 56 inches. See Figures 2 and 3 below.


Figure 2: Skid Components

Figure 3: Skids on Bottom of Hull

6.3 Cockpit

The cockpit portion of the ACV is 28 inches high, 56 inches wide (at the widest point), and 123 inches long. The bench where the passengers will be seated is 50 inches wide, 14 inches long, and 18 inches high.

The shape of the cockpit follows the contour of a canoe if looking straight down at the canoe from above. The back end of the cockpit flattens out into a square platform where the engine will be mounted. See Figure 4 below.


Figure 4: Skeletal Frame of Cockpit

6.4 Lift Duct

The lift duct will be 24.25 inches in diameter. This dimension allows for an ⅛ inch clearance on each side of the duct once the fan is put in place. The duct is set at an angle of 20 degrees into the hull because the engine is not recommended to run at over 20 degrees. See Figures 5 and 6 below.

Figure 5: Lift Duct with XPS spacers


Figure 6: Lift Duct in Cockpit

6.5 Air Splitters

The air splitters are made out of ⅛ inch thick marine plywood roughly 14.5 inches wide and 10.5 inches long. These pieces will have 1 inch diameter dowels mounted on top of them in order to alleviate erosion from the lift fan. See Figures 7 and 8 below.

Figure 7: Air Splitters


Figure 8: Air Splitters Diverting Air into Skirt

6.6 Thrust Duct

The thrust duct will be 42 inches in diameter at the propeller entrance, and 36 inches in diameter at the duct’s exit. The duct will be 18 inches in depth. See Figure 9 below.

Figure 9: Thrust Duct Mounted on Hull


6.7 Lift Engine Mounts

The lift engine is mounted to a metal frame that bolts into the lift duct. The frame is constructed of two aluminum box beams that are 1 x 2 x 24 inches in size. These beams are joined together by two cross braces 1 x 2 x 10 inches in size. The main supports have aluminum plates welded onto their ends with holes drilled in them for the bolts that hold the engine frame to the lift duct. See Figures 10 and 11 below.

Figure 10: Lift Engine Mounts

Figure 11: Lift and Thrust Engine Mounts


6.8 Thrust Engine Mounts

The thrust engine is mounted to an aluminum frame constructed of 1 inch by 1 inch box aluminum. These bars are welded together in a box shape that is 19 x 19 x 28 inches in total size. See Figure 11 above and Figure 12 below.

Figure 12: Thrust Engine Mount

6.9 Lift Engine

The lift engine will be a Briggs and Stratton engine with 6.0 horsepower. The engine is recoil start with a 3-5/32 inch long vertical crankshaft. The crankshaft is 7/8 inch in diameter, has a 3/16 inch wide full keyway, and 2 Woodruff key slots. It is drilled and tapped with 3/8 inch 24 UNF threads.

6.10 Thrust Engine

The thrust engine will be a PowerMax engine with 16 horsepower. The engine is recoil start with a 2-3/4 inch long horizontal crankshaft. The shaft is 1 inch in diameter with a 1/4 inch wide keyway. It is drilled and tapped with 3/8 inch 24 UNF threads.

6.11 Lift Fan

The lift fan will have 4 blades and will be 24 inches in diameter. The blades will be 6 inches wide and 7 inches long with an average pitch angle of 16 degrees. The center of the fan will be 10 inches in diameter. See Figures 13 and 14 below.


Figure 13: Lift Fan

Figure 14: Lift Fan with Components

6.12 Thrust Propeller

The thrust propeller will be 42 inches in diameter with 2 blades at an average of 22 degree pitch angle. The center will be 6 inches in diameter. See Figures 15 and 16 below.


Figure 15: Thrust Propeller

Figure 16: Thrust Propeller with Components

6.13 Rudders

The rudders are 18 inches in length, 1 inch wide and 48 inches tall. They have dowel rods mounted in them to connect them to the hull of the craft and the top of the lift duct. They will be shaped like an airfoil. See Figure 17 below.


Figure 17: Rudder Assembly

6.14 Steering

The steering tube will consist of a ¾ inch diameter pipe that is 6 feet long. A perpendicular rod will be connected at the rear of this tube that is 24 inches tall. This rod will connect to a horizontal rod that runs between the rudders. See Figures 18 and 19 below.

Figure 18: Steering Assembly


Figure 19: Rear View of Steering

6.15 Bag Skirt

When inflated the skirt will be approximately 6 inches in radius and follow the contours of the hovercraft. If laid out flat, the skirt will be 34 inches wide. See Figure 20 below.

Figure 20: Hull with Skirt Attached


7 Method of Approach

Before designing a hovercraft, the team elected to research other hovercraft projects that people had completed. This research yielded a good knowledge base of general construction techniques and helpful hints for the operation of an ACV. After obtaining this knowledge, the team was able to design an ACV with specifications that would result in an aerodynamic, aesthetically pleasing, and safe craft.

The first part of the design process was to graphically represent the team’s desired hovercraft. Each component of the craft was modeled in Autodesk Inventor then attached to the appropriate section of the ACV.

Once the graphic representation of the team’s hovercraft was complete, the team carried out a material selection process. The materials needed to be chosen carefully in order to fit with the design requirements, mainly the weight of the craft. Materials that would be able to withstand water also needed to be selected. The team decided upon a combination of marine plywood, extruded polystyrene foam (XPS), epoxy, and fiberglass for the majority of the hovercraft. Other materials like clear pine wood, aluminum, and spray can expanding foam were chosen for the more specific applications.

After the team selected materials and parts, they needed to be sourced at lowest cost to remain within budget constraints. The team looked around and found many components needed for the construction of the hovercraft, some of which were obtained at no cost. The information found from this search allowed the team to make changes in the design if components were cheaper than expected, or more expensive. Once a final list of materials was compiled, the team made a few last tweaks to the Autodesk design to reflect any changes that occurred during this design process.

Finally, after the hovercraft design was confirmed, the team laid out a construction plan. The hovercraft will be built as closely to the original design as possible, only making modifications when necessity dictates, as not all difficulties can be foreseen for actual construction. A variety of tests will be performed during the construction process to ensure proper functionality of the ACV. Any problems discovered will be corrected with the intent of following the original design as closely as possible.


8 Alternative Solutions

8.1 Craft Shape

An ACV can be designed in a variety of shapes, mainly circular, rectangular, and triangular. Each shape has its merits, and depending on the purpose for which the hovercraft is being used, one shape might be better than the other.

8.1.1 Circular

Most, if not all, ACVs that are circular in nature are typically personal hovercraft scooters. A round shape is best suited for small hovercrafts due to the ease of maneuverability and because the circular shape provides a platform for the user to stand on. Having a circular shape also minimizes the size of the hovercraft. However, since the purpose of this project is not to design a personal hovercraft, a circular design will not be used.

8.1.2 Rectangular

A rectangular design for an ACV is a very good option for those seeking simplicity of design and minimal wood-cutting. A rectangular design does not have any complex curves and allows more room for error when cutting a hole for the lift duct. A rectangular shape makes it easier to design a skirt as well. However, while a rectangular hovercraft is easier to construct, it requires more material and is not as aesthetically pleasing to the eye as a sleeker design would be. Since this project’s budget is tightly constrained, cutting down material costs is necessary.

8.1.3 Triangular

A triangularly shaped hovercraft is the most aesthetically pleasing design. A sleek design reduces drag on the vehicle and increases its aerodynamic properties. The triangular design is slightly more complicated to construct, but drastically decreases the amount of material needed for the craft. However, decreasing the size of the platform increases the pressure required on the underside of the hovercraft to lift. Increasing the pressure means a more powerful, heavier engine is needed to lift the ACV. For this reason, a perfectly triangular design cannot be implemented.

8.2 Craft Size

The size of the craft is dependent on the available budget. For this project, a sufficiently large enough craft will be designed in order to seat two people comfortably. There needs to be enough room behind the passengers’ heads so that the engine is not too close as well. A general design principle for ACVs is that the craft should be about twice as long as it is wide.

8.2.1 Eight Feet by Four Feet

This size is mainly suited for a single person ACV. Trying to seat two people in a craft this size causes the craft to be much more unbalanced and causes a small degree of discomfort for the passengers since they have to sit extremely close together. The thrust engine must also be located extremely close to the passengers’ heads which is very unsafe.


8.2.2 Ten Feet by Five Feet

An ACV of these dimensions is still mostly suited for a single person, but could fit two passengers much more comfortably than the previous alternative. The benefits of this design are that the engine can be located sufficiently far from a passenger’s head and it is somewhat easier to balance the craft. This craft does not need as much material as the project’s current design, and if budget constraints are too tight, this design will be implemented to cut costs.

8.3 Skirt Design

A good skirt design yields optimum hovercraft performance. When the craft encounters debris on the ground while hovering, a good skirt design should minimize any turbulence felt on the craft as well as give adequate stability. The skirt should be flexible enough to efficiently conform or contour over obstacles to minimize drag and minimize the loss of cushion pressure. The skirt should also be able to contain the air under the craft to keep the ACV afloat.

8.3.1 Full Flow Bag Skirt

This type of skirt is like the bag skirt being used for this project, but instead of using air splitters to pressurize the skirt and push air into the hovercraft cushion, all air flow is directed into the skirt. Once the air is in the skirt, there are holes all along the inner edges of the bag where air can escape and pressurize the cushion beneath the ACV. By controlling the number and size of the holes it is possible to alter the pressure differential between the loop and the air cushion. However, due to the complexity of this design and the small margin of error allowed, this design was not chosen.

8.3.2 Bag and Finger Skirt

A bag and finger skirt is a skirt with numerous segments. The advantage of a bag and finger skirt is the great amount of flexibility when driving over bumpy terrain. The skirt does not receive as much wear and tear as a bag skirt would. This skirt design is much more difficult to build due to all the sewing work required. This project is not expected to be used in very vigorous applications either, so a bag and finger skirt was not chosen.

8.4 Engines

An alternative for engines in the ACV is using one motor to drive both lift and thrust propellers. Using one engine means a more powerful engine is required rather than two lesser powered engines. Higher horsepower engines are generally more expensive than purchasing two smaller engines. Using only one engine also entails designing and rigging up a belt and pulley system to lift fan and thrust propeller since they would no longer be driven directly. For the sake of simplicity two engines were desired, ergo this project was not designed with one engine.


9 Feasibility of Design

One of the main objectives for the senior design project was to complete a feasibility study in order to determine whether the proposed design project was within the bounds of the team’s resources, time, and abilities. The results of the study are presented below.

9.1 Similar Product Case Study

It was crucial to the success of this project to look at what other people had worked on to learn techniques as well as the intricacies of hovercraft design. An organization called Universal Hovercraft (UH) was considered to be the authority on hovercraft design here in the United States so much of the team’s knowledge was gleaned from their website. Universal Hovercraft also hosts a “Homebuilders Showcase” page with links to personal websites of people who have designed UH crafts. Many of these homebuilders have made improvements or modifications to UH crafts. The team viewed many of these personal websites, which aided the team in the brainstorming process. After looking at these websites and the UH site, the team came up with a design that they believe improves upon other hovercraft designs.

9.2 Lift Fan Design and Lift Engine Choice

One of the greatest challenges in this project was designing the optimum lift fan given the conditions of 800 pounds of total ACV weight and a 13 foot by 6 foot craft. Closely related to the lift fan design was the choice of an accompanying engine, as it needed to generate a certain amount of power in order to maximize the lift fan’s potential. Research was done to determine the most effective design and size of the lift components that would successfully lift the team’s hovercraft.

Based on calculations performed by the team and supported by various case studies, the team was able to design a lift fan and select a matching engine. The fan chosen was 24 inches in diameter with an average pitch angle of 16 degrees. The lift engine power required was 5.5 horsepower, as shown by calculations in Appendix A as well as the case studies below.

9.2.1 Lift Fan Calculations

The team carried out calculations to determine appropriate lift engine and fan specifications for the craft. An ACV lift fan operates best when the fan is able to absorb all of the horsepower from the engine. The team found that to use a 24 inch diameter lift fan on a craft of this size and weight required about 5.5 HP. This amount of horsepower is best matched to this size fan and the fan will efficiently utilize this power. See Appendix A for detailed calculations.

9.2.2 Jerry Shover’s Hovercraft Case Study

The team came across this hovercraft design and made comparisons. His hovercraft utilized a 3.5 HP engine and carried a total weight of about 400 pounds. The craft was somewhat similar in size to the team’s hovercraft (10 by 5 feet compared with 13 by 6 feet).

9.2.3 UH-13P Sportsman Case Study

This hovercraft was designed by Universal Hovercraft. It only used one 20 HP engine with a belt and pulley system for lift and thrust, and had dimensions of 13.5 feet by 6.25 feet. The craft was rated to carry a total weight of about 900 pounds and used a 26 inch diameter fan with 28 degree pitch.


9.2.4 UH-13PT Twin Trainer Case Study

This hovercraft was designed by Universal Hovercraft and most closely resembled the team’s hovercraft design. This ACV used a 5 HP engine for lift with craft dimensions of 13.5 feet by 6.25 feet. It was able to carry a total weight of 800 pounds and used a 24 inch diameter fan with 14 degree pitch.

9.3 Thrust Propeller Design and Construction

For the thrust calculations, the primary principle used was that at a given craft speed, the force of exiting air must be greater than the drag force on the craft in order to accelerate. The first step in these calculations was therefore finding the drag force. The minimum force of exit air needed to overcome the drag at the given speed was then calculated. Then, using the amount of horsepower selected for the thrust motor, the maximum speed and acceleration generated by the thrust was found. To determine the maximum attainable speed, the acceleration was set to zero. It was realized that by setting the acceleration to zero and choosing the desired velocity of the craft, the pitch of the propeller could be calculated. See Appendix B for detailed calculations.

After calculating the pitch of the propeller needed to produce the required amount of thrust to move the hovercraft, the next step was to calculate the angle of attack of the propeller, which would determine the optimum design of the propeller for this hovercraft. Since the pitch of the blade must be constant throughout the propeller, the angle of attack varied as the radius of the propeller changed. Figure 21 shows the required angle of attack at any given position on the propeller blade.

5 9 13 17 21 255

10

15

20

25

30

35

Rblade [in]

Angl

e of,a

ttack

[de

g]

Figure 21: Angle of Attack Due to Changes in Radius

Even though the team’s thrust propeller calculations may be slightly off due to non-ideal operating conditions, the results found were very similar to other hovercrafts of similar size and shape. Based on these calculations and other hovercraft designs, the optimum thrust propeller was found to be 42 inches in diameter with an average pitch angle of 22 degrees.


9.4 Fan and Propeller Safety Concerns

The team will perform a stress analysis on the propeller blades in order to determine whether the blades are strong enough to tolerate radial and bending stresses generated on them. These stresses are due to the centrifugal and drag forces on the blades.

Due to the overwhelming force tending to tear the fan and propeller blades radially off the hub, the team will incorporate safety measures to prevent putting the user or any bystanders in danger. To prevent a broken blade from potentially injuring someone, the outer layer of the ducts will be covered with sheet metal to reinforce them. Also, the front and back of the thrust duct will be covered with wire guards to prevent accidental injury from contact with the propeller blades. The team plans to perform a strength analysis on the ducts in order to determine that they will be strong enough to prevent any serious accidents if the blades exploded off the hub.

9.5 Material Availability and Budget Considerations

Most of the materials required for this project can be obtained easily at local stores. Other materials that are more difficult to find locally can be purchased online or fabricated in metal shop at no cost. Fortunately, the team was able to obtain a free lift engine with ample power so one engine at least is accounted for and does not impact the budget in a negative way. Some other materials may be donated and almost all stores provide student discounts for projects. The Calvin metal shop stocks many of the materials needed in this project which will also be free for the team. Because of the low cost of the bulk of materials used in this project, a good portion of the budget will be devoted to purchasing a new thrust engine as it is nearly impossible to find a free or inexpensive 16 HP engine. A detailed budget can be seen in Section 10.1.

9.6 Time Limitations and Scope

The project has a relatively large scope with respect to its time frame. There are multiple components being designed in the ACV and many must be designed at the same time. This complicates planning schedules, especially if problems arise and parts of the ACV must be fixed before continuing to the next part. The team is expecting to work throughout Interim term and most days during the weeks of second semester in order to construct and complete the prototype on time. A detailed schedule can be seen in Section 11.


10 Fiscal Analysis

The cost of building the designed ACV is as follows. Currently, many parts can be fabricated in metal shop. Most of these components are parts that will hold the propeller and fan together as well as connect them to the engines. The team has received a free lawnmower engine from Physical Plant to be used as a lift engine. The team has also purchased a go-kart engine to be used as a thrust engine.

Table 3: Budget for Building a Larger Prototype

bold signifies a verified numberItem Size Quantity Low Price High Price

Horizontal engine 16 HP 1 $327.96 $327.96Vertical engine 6.0 HP 1 $0.00 $0.00

XPS foam 2" x 4' x 8' 0 $0.00 $0.00XPS foam 1" x 4' x 8' 1 $9.88 $9.88Marine plywood 1/8" x 4' x 8' 6 $166.80 $160.80

Epoxy resin (105B) 1 gallon 3 $188.97 $188.97206B hardener 0.5 gallons 3 $74.97 $74.97Pump kit 2 pumps 1 $7.99 $7.99

Fiberglass cloth (6 oz) 38" x 1 yd 10 $69.50 $69.50Skirt (18 oz vinyl nylon) 60" x 1 yd 8 $79.60 $79.60Skirt screws 3/4" 300 $8.95 $16.95Skirt glue HH-66 1 pint 1 $14.95 $14.95Spray can foam 12 oz 4 $22.40 $22.40

Thrust propeller 1" x 6" x 8' 3 $38.58 $121.95Lift fan 1" x 6" x 8' 2 $25.72 $140.95Hub 4.5" diam 2 $0.00 $99.90Hub backing plate 4.5" diam 2 $0.00 $33.90Bushing/nut ? 2 $0.00 $23.90Balancing plugs ? ? $0.00 $0.00Keys 2 $0.00 $6.00Aluminum supports $0.00Guard wire $0.00

Contingency $200.00 $200.00======== ========

TOTALS $1,236.27 $1,600.57


11 Test Plan

A detailed construction and testing plan can be seen below. This schedule will be used to keep the group on task and working toward the final objective of a working ACV.

Table 4: Second Semester Construction and Test Plan

Dec January February March April May 1 2 3 4 5 1 2 3 4 1 2 3 4 1 2 3 4 5 Obtain lift engine Ensure lift engine works Obtain thrust engine Thrust engine test Purchase materials Construct hull and skids Construct lift fan Cut hole for lift duct Build and install lift duct Build/install air splitters Lift engine mount Cockpit skeleton frame Metal components Balance lift fan Finish front of cockpit Cut and sew skirt Attach skirt Install lift engine and fan Test to see if it hovers Construct thrust duct Construct thrust prop Balance thrust propeller Thrust engine mount Finish back of cockpit Install thrust duct Install engine and prop Test run of thrust prop Construct rudders Install rudders Install steering Test entire hovercraft Compose final report Deliver final results


11.1 Engine Testing

11.1.1 Lift Engine

Once the lift engine is in the team’s possession, it will be tested to ascertain its functionality. Depending on the condition of the engine (whether it was purchased new or used), the team may need to take the engine apart and clean it to get the engine running. The engine will be run for at least 15 minutes to make sure there are no glaring problems.

11.1.2 Thrust Engine

The thrust engine will inevitably be purchased new, which implies the engine is almost guaranteed to work on first test. Basically, the team will pour gasoline into the tank, crank the motor, and ensure that it works. This engine will have throttle control installed, so the team will also test the throttle control to make sure it is in working order.

11.2 Propeller Testing

11.2.1 Lift Fan

The lift fan must be properly balanced in order to get good power output from the fan and not put undue stress on the engine. To balance the fan, a shaft will be threaded through the center of the fan, then placed on two level rails. If the fan is unbalanced, the heavy portion will gravitate toward the bottom as it rolls on the rails. If the fan is found to be unbalanced, holes in the center of the fan will be drilled, and metal weights will plug the holes.

11.2.2 Thrust Propeller

This propeller will use a slightly different method of balancing. Instead of using metal weights to balance out the blades, small amounts of material will be sanded off of the propeller blades. The center of the thrust propeller needs to be as solid as possible since there is less material (only 6 inches in diameter).

11.3 Duct Assembly Testing

11.3.1 Lift Assembly

The lift assembly consists of the lift duct, lift fan, and lift engine. These parts will be assembled together and then tested to guarantee their functionality. The fan must be able to fit inside the duct with about ⅛ inch of clearance at the tips. The tips obviously cannot touch the sides or the fan and lift duct will be wrecked. If the fan fits and does not need to be sanded down, it will be attached to the engine shaft and mounted inside the lift duct. Finally, the engine will be started to make sure that the whole assembly functions.

11.3.2 Thrust Assembly

A similar procedure will be carried out for the thrust assembly. The propeller will be sanded down as necessary if it does not fit inside the duct. Once the propeller fits inside the duct, it will be attached to the engine. The engine will be turned on to ensure the proper functioning of the whole assembly.


11.4 Skirt Testing

This is the most important test of the project and determines if the project is a failure or a success. This test will happen as soon as the hull, lift duct, and lift fan are completed. The skirt will be attached to the hull using screws initially. If the ACV successfully lifts off the ground, once the project is reaching completion, the skirt will be glued as well as screwed. However, until the project is getting close to being finished, the underside of the craft will need to be readily accessible and a skirt would get in the way if attached right away. To test if the skirt functions or not, the lift fan will be mounted with the lift engine inside the lift duct. The engine will be turned on, and if the air splitters were designed correctly, the bag will inflate, a cushion of air will be created underneath the craft, and the ACV will hover. Otherwise, it will be back to the drawing board.


Appendix A: Lift Calculations for Required Horsepower

A.1 Lift Fan and Engine Calculations

Length = 13 [ft]

Width = 6 [ft]

AirGap = 0.5 [ in ] ∙| 0.0833 ∙ftin |

Weight = 800 [lbf]

LengthBow, sides =√[Length2 ]

2

+ [Length2 ]

2

HullPerimeter = Width + Length2

+ Length2

+ 2 ∙ LengthBow, sides

LiftPerimeter = 0.9 ∙ HullPerimeter “lose small amount of length to lifting by cushion pressure, 90%”

HoverGap = AirGap ∙ LiftPerimeter

Area = 0.5 ∙ Width ∙ Length2

+ Width ∙ Length2

LiftArea = 0.9 ∙Area “front slope, 90%”

LiftPressure = WeightLiftArea ∙ | 0.006944 ∙ psi

lbf / ft2 |AirVelocity = 7111 ∙ LiftPressure3 - 3809 ∙ LiftPressure2 + 1099 ∙ LiftPressure + 31.78ActualVelocity = 0.6 ∙ AirVelocity “more realistic estimate of air escaping underneath ACV"

LiftAirVolume = ActualVelocity ∙ HoverGap

HorsepowerTheoretical = LiftAirVolume ∙ LiftPressure ∙| 144 ∙ lbf / ft2

psi | ∙ 1 [hp]

550 [ft∙ lbf

s ]HorsepowerActual = HorsepowerTheoretical

0.6 “60% efficient lift duct”

FanDiameter = 24 [in]

FanArea = π ∙ FanDiameter24

∙ FanDiameter24

T = FanArea ∙ LiftPressure ∙ 144

TBL = 35( Pressure ∙ 144 )0.5


HP = TTBL “horsepower matched to fan”

FanCircum = π ∙ FanDiameter ∙ | 0.0833 ∙ ftin

|Revolutions = 3000 [ rpm ] ∙ | 0.0167 ∙ rev/s

rpm |

TipSpeed = Revolutions ∙ FanCircum1 [rev]

A.2 Lift Calculation Results

Table 5: Lift Calculation Results

INPUTLength 13 [ft]Width 6 [ft]Weight 800 [lbf]AirGap 0.5 [in]FanDiameter 24 [in]Revolutions 3000 [rpm]OUTPUTActualVelocity 68.21 [ft/s]AirVelocity 113.7 [ft/s]Area 58.5 [ft2]FanArea 3.142 [ft2]FanCircum 6.283 [ft]HorsepowerActual 3.924 [hp]HorsepowerTheoretical 2.355 [hp]HoverGap 1.249 [ft2]HullPerimeter 33.32 [ft]LengthBow, sides 7.159 [ft]LiftAirVolume 85.23 [ft3/s]LiftArea 52.65 [ft2]LiftPerimeter 29.99 [ft]T 47.74TBL 8.979RESULTSLiftPressure 0.1055 [psi]HP 5.316 [hp]TipSpeed 314.2 [ft/s]


Appendix B: Thrust and Drag Calculations

B.1 Thrust Propeller Calculations

Tair = 65 [F]

Pair = 1 [atm] ∙ | 14.7 ∙ psiaatm |

ρair = ρ( 'Air' , T = T air , P = Pair )

vcraft = vcraft, req ∙ | 1.467 ∙ ft/smph |

Fd = 0.5 ∙ ρair ∙ vcraft2 ∙ A craft ∙

Cd

32.2 [ lbm ∙ft/ lbf ∙s2]

Afrontal = [ 56.008 ∙32+ π ∙ 7.62 + 64.124 ∙2 ∙7.6+ (582 ∙ π- 45.52 ∙ π ) ∙ 2458 ] ∙ 1 [ in2 ] ∙ | 0.006944444 ∙ ft2

in2 |Acraft = Afrontal

Cd = 0.7

Pitch = 12 [in/rev]

FN = Fd ∙ | 4.448222 ∙ Nlbf

|Vair =Pitch ∙ nprop ∙ | 0.83333333 ∙ ft/s

in/s | ∙ | 0.016666667 ∙ rev/s

rev/min |

dprop = 4 [ft]

Aprop = π ∙ dprop

2

4F thrust, min = Fd

F thrust,min = 0.5 ∙ ρair ∙ V air2 ∙

Aprop

32.2 [ lbm ∙ft/ lbf ∙ s2 ]

Powerprop = nprop ∙ Torque ∙ π ∙ 233000 [ft∙ lbf ∙rev/min∙hp]

Torque = 23 [ft∙ lbf ]

Vair,mph = Vair ∙ | 0.6818 ∙ mphft/s

|F thrust, act = 0.5 ∙ ρair ∙ Vair,act

2 ∙ Aprop

32.7 [ lbm ∙ft/ lbf ∙ s2 ]


Vair,act = Pitch ∙ nprop,act ∙ | 0.016666667 ∙ rev/srev/min

| ∙ | 0.083333333 ∙ ft/sin/s

|nprop,act = 3000 [rev/min]

Powerprop = nprop,act ∙ Torqueact ∙ π ∙ 233000 [ft∙ lbf ∙rev/min∙hp]

Vair,mph,act = Vair,act ∙ | 0.6818 ∙ mphft/s

|m craft = 800 [ lbm ]

acccraft

32.7 [ lbm ∙ft/ lbf ∙ s2 ]

∙ mcraft = F thrust,act - Fd

acccraft = 0

B.2 Thrust and Drag Results

Table 6: Thrust and Drag Results

INPUTacccraft 0 [ft/s2]Cd 0.7dprop 4 [ft]mcraft 800 [lbm]nprop,act 3000 [rpm]Tair 65 [F]Pair 14.7 [psia]Pitch 12 [in/rev]Torque 28 [ft-lbf]OUTPUTAcraft 32.15 [ft2]Afrontal 32.15 [ft2]Aprop 12.57 [ft2]Fd 36.32 [lbf]FN 161.6 [N]Fthrust,act 36.32 [lbf]Fthrust,min 36.32 [lbf]nprop 2977 [rpm]Powerprop 15.87 [hp]rhoair 0.07561 [lbm /ft3]Torqueact 27.79 [ft-lbf]Vair 49.62 [ft/s]Vair,act 50 [ft/s]Vair,mph 33.83 [mph]Vair,mph,act 34.09 [mph]


vcraft 37.07 [ft/s]RESULTSvcraft,req 25.28 [mph]


project overview - calvin college | grand rapids, · web viewthe lift engine will be a briggs...

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