Tilt Rotor UAV Laxmi Narasimha Sai Abhinand T Faculty of Electrical and Computer Engineering, National University of Singapore Objective The objective of this UROP was to create a prototype of an unmanned aerial surveillance vehicle which can probably be used by the defense as a scout. This means the vehicle must be able to carry a lot of surveillance equipment. This being an unmanned vehicle not only gives us the advantage of making it small but also adds to its stealth. The best choice which satisfies this purpose is a tandem rotor designed helicopter, much like a miniature CH 47 Chinook. General design and Uses of a tandem rotor Helicopter The general and basic design of a tandem rotor helicopter is a bit different from a traditional helicopter. This bread of helicopters has two rotors placed horizontally, connected by a driveshaft and one smaller rotor at its back for forward motion. Unlike and ordinary helicopter which need one rotor to push itself up and the other to fight the angular momentum caused by the first, the tandem rotor design uses both its engines to push itself up. This is possible because one of it turns clockwise and the other rotates counter clockwise balancing the torque created by the first. The third, small rotor is used to guide it laterally. The advantage of this design is 1. All the engine power is used to lift itself and none of it is wasted on balancing torque. 2. This added power allows it to carry heavier load. 3. If one engine fails, the other can help the helicopter continue its flight (due to the connected drive shaft). F-16 is being carried here.
A Walk Around of a CH-47 Chinook The CH-47 Chinook is one of the most accomplished tandem rotor helicopters. Its main purpose is to carry heavy loads at great speeds to distant places. The basic specifications of are shown below. The CH-47 comes with a glass cockpit with glass on either side from the waist down. This enables the pilot and the co-pilot to get a better look of the surroundings. It also enhances the pilot s depth perception. There is a bubble window at the port side which helps examine the ground better (Picture located at top right). A closer look on the aerodynamic rotor blades shows us that it is much like a fixed wing aircraft. The wings are made out of fiberglass. Note the scratching on the forward outer edge of the blade (top right picture). That is erosion from debris in the air. Sand, for example, is hard on the blades. Leading edge cover protectors have been developed to reduce the erosion. The rotor at the forward pylon is the one that has all the transmission equipment. The fuel tank of this helicopter is located along side the side of the fuselage (top left picture). This not only helps it carry a lot of fuel (due to the helicopter s length) but also helps the helicopter balance itself.
The twin turbines (top left picture) present at the rear of the helicopter help it to move in front. They are mounted just below the rear rotors. The transmission housing is beneath the rotor blade, aft and forward. The inside of the cockpit (top right picture) is fitted in with a lot of dials and many other electronic equipment. This would help pilots fly the CH-47 more efficiently. It is expected that the new F-model will digitize all those dials and have colored map graphic presentations on the main panel, all to reduce workload of the pilots. The CH-47 is known mostly for its ability to carry a lot of external and internal cargo. It can carry up to 33 fully equipped solder or 6000lbs of internal cargo. She can carry a total weight of 13,000 lbs externally. To maintain the stability of the helicopter, the troops are asked to sit on the seats placed on the two sides of the fuselage. The remaining can be seated on the floor in-between the two rows. As show in the other picture (to the right), the interior can be reconfigured for casualty evacuation. This ends a brief walk around the CH-47 Chinook.
THE PROTOTYPE The following is a table of the components of the helicopter, along with the weight distribution. Component Multiplex Permax 400 6V Motor Multiplex 400L Gearbox Master Airscrew (Electric Only Series) 8.5 x 6 in Rotor Aeronaut Carbon Elektro 8.5 x 6 in Rotor Futuba RX R116FB Balsa Wood Frame and Perspex Supports Supporting Aluminium Rods Total Electronic Speed Controller (50 amp) Futuba TX T6XA 9V Battery Pack Weight (g) 70g x 2 = 140g 10g x 2 = 20g 40g 40g 20g 20g 10g x 8 = 80g 360g Overboard Overboard Overboard This model is based pretty much on the design of a tandem rotor model. There are two main horizontal rotors which are each 8.5 inches long connected to a Permax 400 motors with the help of a gear box provided with it. The motors were fixed in place with the help of a Perspex support and four aluminum rods surrounding each of them. There was some extra Perspex placed on top of the wood mounted on each of the motor to kill the vibrations generated by the motors. The rotors needed to be overlapped and hence the rear motor was lifted slightly above the first motor. This would avoid any collision of rotors. The extra space created below the rear
rotor was used for a signal receiver from the remote control used to control the helicopter s motion. The motors are used to generate a lift and are controlled by a speed controller which is connected to the receiver of a remote control. This enables the remote to control the speed of the rotors and by extension, the height of the helicopter. The electronic speed controllers are devices which can control the speed of a motor connected to it. They are made of Field Effect Transistors (FETs) which constantly keep switching off and on. The rapid switching of the transistors is what causes the motor connected to it emit its characteristic high-pitched whine, especially noticeable at lower speeds. It also allows much smoother and more precise variation of motor speed in a far more efficient manner than the mechanical type with a resistive coil and moving arm once in common use. This coupled with the remote control gives a good control over the helicopter. Improvements There are some suggested improvements. I had worked with the Parallax Boe-Bot kit and completed the tasks laid out in it such as programming the micro Processor in that car to move in certain directions or to sense obstacles with sonar or IR sensors. This was possible by writing programs in BASIC. Some improvements could be, adding a Micro Processor to incorporate some other features into the helicopter, like, height detectors using sonar or IR sensors, or control all the motors (without speed controllers). We could then vary the speed of the motors with the help of a simple program. This can be used to vary the speed of individual motors which can help turn the helicopter. This is possible because a varied change in speeds of the rotors will cause an imbalance in the angular momentum caused by both the rotors, thus causing the helicopter to turn in a particular direction. The next step is to make the helicopter be controlled by a laptop. This can be done by fixing a receiver on the Microprocessor aboard the helicopter and a transmitter on the land connected to the laptop (as shown in the Beo-Bot Kit). The next step is to make the helicopter move forward. This can be achieved by fixing a motor to the back of the model (after that weight has been balanced in the front) and connecting it to the microprocessor. This way, the whole helicopter will be controlled by a laptop and the laptop will also keep getting a regular feed of the height above the ground and if there are any obstacles coming from any side (this can be done by installing sensors on either side of the helicopter). Bibliography Advanced Tandem Rotor Helicopter, Retrieved November, 2008 http://www.globalsecurity.org/military/systems/aircraft/atrh.htm America's "Happy Hooker," the CH-47 Chinook, Retrieved November, 2008 http://www.talkingproud.us/military121306.html
CH-47 walk-around, Retrieved November, 2008 http://www.talkingproud.us/military121306b.html CH-47 Chinook Helicopter, Retrieved November, 2008 http://www.chinook-helicopter.com/