The goal of our project is to create a compact surveillance device for frontline warfare that will allow for safe reconnaissance missions with minimal causalities. The product should be able withstand small arms fire, be able to relay video and sound signals, have the ability to hover and maneuver in tight environments, be as quiet as possible, and have a minimal manufacturing cost. Our main customer base will be armed forces that are affiliated with the United States government.

As warfare continually evolves, technology must evolve too in order to protect the lives of soldiers. It is becoming more and more commonplace for skirmishes to occur in buildings and houses. In these environments, it is becoming increasingly difficult to execute accurate and safe reconnaissance missions. With the proposed tool, the group hopes to design and create a device that will be able to solve these problems and save lives. Last year, a senior design group initiated the project and successfully built a prototype to present. After performing research, the previous group decided on an enclosed design with two coaxial rotor blades inside. The outside shell was constructed from fiberglass and the motor was powered by batteries. With this design, the prototype was able to fly off the ground with little stability and minimal height.

This year, our new group would like to reevaluate the project and decipher if the design is optimal to achieve our aforementioned objectives. Various issues from last year’s design were addressed, including motor selection, material selection, battery selection, shape determination, and propeller design. Furthermore, we would like to add some of the components and systems that were not included in last year’s design, i.e. video feedback.

The societal impact would be that lives could potentially be saved via this automated reconnaissance tool. Because all customers are involved with some sort of indoor battles, the use of a UAV would allow to examine any area for weapons and enemies without worrying about the losing an individual’s life. By mapping out the area with our product, the customer can then plan their attack and have a greater chance of victory.

Last semester our group finalized our technical model by analyzing all components within the system and understanding its purposes. By addressing the pros and cons of the previous years’ design, we were able to create a model that was about ¼ of the weight, but also supplied more power to a smaller design. The group completed thorough analysis on motors, batteries, propellers, swash plates, material selection, servos, and gyro card selection to ensure a complete and reliable design.

This semester, our goals and objectives stress prototyping and designing. After procuring each component of our system, we will begin assembly and adjust our design as necessary. Procurement process should take a few weeks, but during this time we plan to lay out the plan for the semester so we can maximize the time available. Our fabrication plan and Gantt Chart further address our goals and milestones for the semester. Obviously by the end of the semester we must have a working system to be presented during Senior Design Day. We would like to have our system flying well in advance and then add other components such as video. Our group has made a guarantee that by the end of the semester we will have an Unmanned Spy Chopper that can hover through tight corridors and ready for frontline warfare.

• The team shall evaluate the pros and cons of the design selected by last year’s group.
• The system shall achieve a flight height of at least 20 feet.
• The system shall maintain a sustained flight of at least 20 minutes.
• The system must be able to hover.
• The system must be able to transmit live video transmission.
• The system shall have a compact design to allow for portability and maneuverability.

Industry research and development into unmanned aerial vehicles (UAV) have been occurring since the early 1900’s. The current UAV functions available ranges from remote sensing, such as electromagnetic sensors, biological sensors, and chemical sensors. These sensors can be used to detect microorganisms and elements in the air, and cameras can be used to observe any weapons or enemies. It is also used to transport objects into areas that require supplies like in war zones.

While some of the UAVs in use are radio controlled aircrafts controlled by a human operator, some more modern UAVs contain guidance systems and built in controls to navigate itself. Research was done on automating the navigation process so that the UAV can make decisions without human intervention, such as path planning or reacting to environment changes; however, because of intricate software, we had moved away from the idea and focused more of maneuvering through customer inputs. In many cases having a pre-defined route could cause issues and having direct control of the system would allow for more freedom.

One of the biggest challenges that the industry faces is flight time. The flight time depends on the aircraft size and the engine used. Our group initially looked into various technologies such as solar power which would require no refueling, helium to allow for a zero weight, and material selection to reduce overall weight. Research is also put into in flight UAV refueling to extend flight time. By analyzing each respective area, we can optimize our flight time to be able to compete with other competitors. Various competitors exist on the market, but none are quite as small as our design. The Boeing Condor has a record maximum flight time of 58 hours, and the QinetiQ Zephyr, a solar electric UAV, recorded an 82 hour flight time. But these two systems are very different in design as it can be almost 200ft wide, with a target towards outdoor missions. Another competitor is the DraganFlyer, which similar in size to our product, but is target towards the everyday consumer and not towards military or federal agencies. Because of this reason, our product is unique for the industry and involves start of the art technology for a target niche market.

The counter-rotating horizontal rotors allow the helicopter to balance without the assistance of a tail rotor. The action and reactions to the forces of the overhead rotor causes the body of the helicopter to rotate about the shaft, thus causing the body to spin around. One of the main issues this design address is the effects of angular momentum. In single rotor designs, the helicopter body tends to spin in the opposite direction of the rotors due to conservation of angular momentum. When the engine spins the blades, the blades apply an opposite torque to the body, causing the body to spin. Another issue this design solves is the dissymmetry of lift. This is when there is an uneven amount of lift on the opposite sides of the rotor disc caused by the difference in relative airspeed between the advancing blade and retreating blade. The advancing blade has faster than normal airflow, while the retreating blade has slower than normal. This in turn could cause the rotor blades to flap up and down, such that that it develops a smaller angle of attack and the helicopter can no longer maintain lift. The helicopter would then start to rotate. This design also reduces the size of the shape and creates a design easier to weight balance. Given the inability to control the movement of last year’s design, the group wants to ensure that the final design can be weight distributed.

Rotor System Design

The swash plate is an integral part of the counter rotating rotor design because it is used to change the helicopter’s roll and pitch. The swash plate consists of a stationary swash plate and a rotating swash plate. The stationary piece can tilt in all directions and move vertically to adjust the angles of the other plate and the rotors. The rotating plate is connected to the rotor’s mast and rotates along with the rotor. Push rods or hydraulic actuators are used to tilt the static swash plate to adjust the helicopter’s roll and pitch. The difference in the lift around the blade will cause the helicopter to tilt toward the side with less lift.

Swash plate

The camera that we have selected for this application is the 2.4Ghz HeliCam which is a Micro Wireless Video Camera. This camera is very well suited for or application. As far as connectivity needs, this camera allows us to connect it to a television for live streaming video or any portable monitor that can accept video input to provide mobile streaming video. As far as our strict weight and size limitations, this camera and transmitter measures 5/8" x 7/8" x 1 1/4" and has a weight of only 9 grams. Lastly this camera suited our range requirements, this units is capable of transmitting video up too 450 ft. All if these key features singled out this camera over the rest.

Ease of operation will be extremely important to the functionality of the vehicle. A minimum four channel remote would be needed to provide the user with enough control to properly maneuver the aircraft. The LP5DSM radio is a 5 channel proportional transmitter that we have selected. It offers all of the stability and performance of the new 2.4 ghz Spectrum technology. The first four channels will be used to control the crafts, left and right, forward and backward motion. The final channel is fully programmable and we plan on using it to control our video system. This controller is also has a very low power consumption, according to specs on standard AA batteries over 30 flights can be performed.

The transmitter in the remote utilizes a thin band in the FM radio frequency to communicate with the receiver located in the helicopter. Typical line of sight range is upward of half a mile. However, in buildings this distance drops due to interference from walls and building materials. The radio should be able to remain connected to the vehicle in a normal sized building while the operator remains outside. Large, complicated buildings with thick brick walls would cut the controllable distance further. However, in most buildings the useable range should be upwards of several hundred feet, allowing thorough investigation from outside.

Before completing a detailed analysis on a new design, it is important to analyze last year’s design and understand its strengths and weaknesses. Last year’s objective was to create a UAV to be used in combat by hovering and maneuvering through small crevices. There were many reasons why the system was not successful including, restricted airflow-shell design, weight, and weight distribution. Each of these issues contributed to a system that could barely thrust off the ground.

One of the major design flaws from last year included an enclosed shell that covered the propellers. In essence, it was done to protect the propellers from contacting any objects and causing the system to crash. Although it was a protective measure, it greatly diminished the air flow into the system by restricting it to the shape of the shell. From the designs below, we can see the optimal design would be the image on the left as it allows a flow through a large volume, while the image to the right restricts the volume into a vertical direction.

Air Flow

The next major issue with the design included its weight. Last year’s design was estimated at over 2 lbs. Many of the contributing factors to the weight were two motors that weighed over 5 oz. each, two batteries that weighed 2.5 oz. each, a fiberglass shell that weighed nearly 6 oz., a wood frame that weighed over 4 oz., along with servos, a micro-circuit board, and a few other factors. Our new design uses many similar components but achieves a total weight of only 8oz, which is less than 25% of last year’s design. Our system includes one battery at 1.52 oz, two motors that weigh 3 oz. combined, a foam frame that weighs less than 0.5 oz., a micro-circuit that weights 1.5 oz., and an outer shell of 1oz. By reducing the weight we can reduce the thrust required to launch the system off the ground and reduce the output power of the motors. This would in turn help reduce the number of batteries required and expand the choice of batteries available.

The choice of batteries is a very important consideration as it must be powerful enough to support our motors for a prolonged period of time, while also being small in size. Our group was able to find a battery with equivalent amperage output that provides the same flight time as the previous design that weighed less. But by reducing it to one battery, we remove almost 3.5 oz overall.

The design of last year’s system was also a major reason for its issues. Because of its large 14” diameter, weight distribution was an issue. The majority of components were placed in the center of the design creating center of gravity issues. Further the previous system did not have enough time to address stabilizing issues, making it difficult to have a constant center of gravity to allow it to fly. By addressing all of these issues early, our new design can be successful.

Lift

Calculation’s Reference Area

Lift Results

Lift Formulas

In order to perform these calculations, the group needed the air density, aircraft velocity, reference area, and coefficient of lift. The coefficient of lift was found using a 10 degree angle of attack for the rotors. The reference area is the surface area of the rotor blades while spinning. Air density was found at 70 degrees Fahrenheit.

Drag

Drag Results

Drag Formulas

Only a few components of this equation were needed to calculate the drag. The reference area could be found by taking a cross sectional area from the group’s SolidWorks model. A drag coefficient of 1.2 was used because the body design was curved and similar to figures that that shared this drag coefficient. The mass density of air was again found at 70 degrees Fahrenheit and velocity was estimated using a current RC helicopter.

Thrust

The helicopter rotors are the mechanisms in the design that produces thrust. Thrust is the force along the intersecting axis of the helicopter which is produced by the resultant aerodynamic force of the rotors. In equilibrium, these forces will be equal and opposite to each other [8]. Notably, there are two established theories that exist to calculate the force produced by the rotary wings of a helicopter: the momentum theory and the blade element theory. The momentum theory actually takes precedence over the other in this instance because it is much simpler method to calculate thrust and is reasonably accurate.

Thrust produced by propeller

Momentum theory/Thrust Formula

The momentum theory is a mathematical model of an ideal propeller or helicopter rotor and represents one of the simplest explanations of the problem of thrust generation by a propeller. Consequently, there are a few assumptions that are made which are indicated by Gessow and Myers[9].

1. The rotor is composed of an infinite number of blades, uniformly accelerating through the air through the disk with no loss of thrust at the blade tips. Essentially, uniform flow is assumed.
2. A frictionless fluid is assumed so no profile drag occurs. Drag is produced by the surface friction and the shape of the airfoil.
3. There are no discontinuities in velocity on both sides of the rotor which allows the tip losses to be ignored.
4. Thrust is in static conditions.

At any rate and as mentioned earlier, the momentum theory is a simpler model. Thus, it requires the aforementioned assumptions but also compromises accuracy in comparison to the blade element theory. Blade element theory is a mathematical process that involves breaking an airfoil down into several small parts and determining the forces on them. These forces are then converted into accelerations, which can then be integrated into velocities and positions. The blade element theory is an extremely accurate model but is extremely difficult to calculate without the proper software.

The Momentum theory is based on the power efficiency required to hover (within static conditions) and can be replaced with a figure of merit of 1 to represent ideal conditions, or less to represent more real life applications. In this case, multiple figures of merit were modeled but we chose to use 75% as the baseline to calculate the expected pounds of thrust needed to lift our design off the ground. Actual thrust values have been shown to be approximately 80% of the thrust produced by an ideal rotor of the momentum theory[9]. The power required was supplemented with actual figures from both electric motor and gas motor output.  By optimization, the induced velocity was able to be calculated to support the formula and produce appropriate outputs. The outputs of both a gasoline powered motor and electric motor are shown in the graph below. To illustrate, the larger a figure of merit of the rotor is then more power will be required to produce a certain amount of thrust with a margin of error.

Electric Motor vs. Gas Motor

Here we have two compared models of thrust versus the rotor blade size which applies the momentum theory and accounts for the power produced by an electric motor and gas motor, respectively. As you can see, a gas motor would provide much more thrust as oppose to an electric motor. Our system will have a 6 ½ inch blade, in order to keep within a diameter than will allow our design to maneuver through tight spaces. Accordingly, a blade radius of 6 ½ inches along with a gas motor would produce approximately 50 more pounds of thrust. As desirable as this may seem, other factors have been considered (such as increased weight, cost, and added complexity to design) and for these reasons, the electric motor takes precedence. Regardless, the electric motor will produce more than the necessary amount of thrust to overcome drag as it ascends.

 

After many discussions by the team in choosing a conceptual design, the team felt that none of them would be suffice. Our preliminary design will be considerably different than last year’s design, created from the previous group. The design will still consist of two rotor systems that are counter-rotating, opposite each other. The shell of the new design will be much smaller and more enclosed than last year’s model. It will only cover part of the mechanical components of the system and will leave the rotor blade systems exposed to the outside environment. The team feels that enclosing the rotor blade system will only create more problems in trying to get the design to lift off the ground. Allowing the blades the freedom to create thrust from all around will produce the most efficiency and the best lift force. Our blades will be the widest part of our design. The blade system will be 15.1 inches from end to end. The second longest part will be the landing skids which will be 6 inches long. The shell will be 4.5 inches wide by 4.5 inches long. The height of the entire design will be 5.24 inches high which is much smaller than the previous design.

The team will try to make as many parts as possible to minimize the costs of buying from third party manufacturers. All of the parts that will be created from Styrofoam will be created in house. These parts consist of the shell, landing skids, battery box, and battery support. The rest of the parts will be purchased from outside vendors because these parts are currently on the market and tested for compatibility with each other. Purchasing these parts will reduce the problems associated with items not working well with other items.

The product will be pre-assembled by a product tester and inspected for problems. Once approved, the item will be flown and tested for functionality. If the product passes these tests, it will be disassembled and packaged into a box. Once this process is completed, the product will be ready for shipment to the customer. Instructions will be provided for the customer to assemble the product on their own. An instruction manual will also be included in the package for the customer. It will include flying and maintenance instructions as well as a parts list in case additional parts need to be purchased for repair on the product.

Additional parts can be purchased by the customer if they would like to use the product as training. A training gear set could be purchased separately in case the customer is not experienced with the product. It will consist of four training gear rods that attach to the bottom of the product. These rods will be the longest parts of the product when equipped. They will be equipped with Styrofoam balls at the end as guards in case the product hits a hard surface. Because most of the mechanical components are inside the Styrofoam shell, they will be protected from damage in case the product hits a wall when in flight. The customer must be very careful when flying the product because the rotors will be exposed to damage. The operator must make sure they have experience and know how to properly maneuver the product. The camera attached to the front of the shell will allow the operator to see what is ahead of the product. Sensors could be included to the product to increase product collision prevention but will not be included at this time.

The estimated total weight of the unit will be 8.95 ounces. This is a considerable difference compared to last year’s design with 48 ounces. By reducing the weight, the group believes that the airplane will be easier to maneuver and control.The two motors account for almost 1/3 of the system's total weight. Given our calculations, the amount of power generated by the motor would be more than enough to support this weight. The remaining weight comes from the various motor and rotor parts that are required to make the system work. The Styrofoam shell is a significant aspect part of the design since it dramatically reduced the weight of the unit compared to other materials while still providing the necessary rigidity to encase the parts. The total weight is a reasonable expectation, since it uses compatible parts which will most likely be used for the final build. The battery charger and 5-Channel Transmitter controller are not factored into the final weight since it is separate when the unit is in use.

Final Weight Estimation

The two motors account for almost 1/3 of the system's total weight. Given our calculations, the amount of power generated by the motor would be more than enough to support this weight. The remaining weight comes from the various motor and rotor parts that are required to make the system work. The Styrofoam shell is a significant aspect part of the design since it dramatically reduced the weight of the unit compared to other materials while still providing the necessary rigidity to encase the parts. The total weight is a reasonable expectation, since it uses compatible parts which will most likely be used for the final build. The battery charger and 5-Channel Transmitter controller are not factored into the final weight since it is separate when the unit is in use. 

 

The estimated cost for the prototype has changed once again. Our original estimations were inaccurate because the team focused efforts on reducing cost, mistakenly overlooking compatibility. However, we cannot afford to compromise smooth integration of the system thus the team has modified the bill of materials. Our costs have increased from a modest $343.83 to $419.21, as displayed in Table 2.

Final Cost Estimation

The Gantt chart above explicitly shows the breakdown of what our project is working towards within the final phases. Between Phase IV and Phase V, the team will be assembling the main components of the prototype together. Shortly after Phase V, the electronics and controllers will be fully integrated and ready for complete synchronization with the remote and receiver. Furthermore, most of the testing and performance analysis will occur during Phase VI. The team is likely to have the system fully integrated well before Senior Design Day.

The Gantt chart above explicitly shows the breakdown of what our project is working towards within the final phases. Between Phase IV and Phase V, the team will be assembling the main components of the prototype together. Shortly after Phase V, the electronics and controllers will be fully integrated and ready for complete synchronization with the remote and receiver. Furthermore, most of the testing and performance analysis will occur during Phase VI. The team is likely to have the system fully integrated well before Senior Design Day.

Lift: It is a mechanical force generated by solid objects as they move through a fluid.

Thrust: A reaction force that occurs when a system expels or accelerates mass in one direction causing a proportional but opposite force on that system. Torque: A force about the vertical axis to rotate an object.

Aerodynamic Drag: The force on an object that resists its motion through air.

Coaxial rotors: A pair of rotors mounted on a center mast with the same axis of rotation but turning in opposite directions one above the other.

Helicopter Rotor: The rotating part of a helicopter which generates an aerodynamic force, it provides both lift and thrust. Rotor Pitch: Controls the altitude of the helicopter.

Angle of attack: A term used to describe the angle between the chord line of an airfoil and vector representing the relative motion between the airfoil and the air. It can be described as the angle between where the chord line of the airfoil is pointing and where the airfoil is going.

Swashplate: Consists of two parts, an inner and other swashplate. The other swashplate is stationary and is mounted on the main motor mass, it accepts cyclic and collective inputs. The inner swashplate rotates along with the main rotor shaft and is connected to the rotor blade assembly. By raising or lowering the swashplate it causes the rotors to tilt.

Fiberglass: A composite material made of extremely fine fibers of glass reinforced with an epoxy resin.

Vehicle Chassis: Encompasses the outside shell of the helicopter, as well as the center motor case and the structural supports to keep it all together.