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Cool Product of the Moment
Kyosho Caliber .30 Radio Controlled Helicopter
Recently I have become very interested in Radio Controlled Helicopters, because, let's face it, they're pretty cool. It's amazing to me that somehow, this complicated lump of plastic, wood, and metal parts come together to form an ultra precise flying machine. RC helis come in all shapes in sizes, from tiny electric powered micro-helis that fit in the palm of your hand, to large .90 class competition helicopters which are able to pull maneuvers that a real helicopter could never dream of. My helicopter falls somewhere in between, being a .30 sized heli, which is an excellent size for a beginner. Larger helicopters are more stable, but are much more expensive to fix when you crash them, which is inevitable in the beginning.
The Caliber .30 is quite a complex beast. The heli is broken down into numerous components which all have to be assembled to make a flyable unit. The main components are as follows:
Pod or fuselage- The main structure of the aircraft to which all of the other components are mounted.
Boom- The tailboom to which the tailrotor and associated components are connected. On this heli, the tailrotor is driven by a toothed belt, although some are driven by a shaft. The rudder servo changes the pitch of the tailrotor blades to control the anti-torque function
Engine- The engine is a very impressive piece of machinery, with turbine-like performance from a very simple, inexepensive engine. It is an air cooled, 2 stroke glow engine of .32 cubic inch (5.25 cc) displacement. Output is a little over 1 horsepower at around 18,000 rpm from a weight of around .75 lbs., putting it into a very high power to weight engine class. The fuel is glow fuel, which is a blend of a methanol base with around 15% nitromethane and 18% blend of synthetic and castor oils. Power and mixture is controlled by a simple carburetor, and the fuel tank is pressurized for fuel delivery via a pressure line coming off the muffler.
Mechanics- The Mechanics is RC Heli terminology for the transmission and drivetrain. The Caliber .30 features a centrifugal clutch driven directly by the engine. The outer clutch bell is connected to the mechanics via a large toothed belt. The belt drives a larger pulley that sits on an overrunning sprag clutch to allow the rotors to freewheel in the event of an engine failure. The overrunning clutch is a trait common to all helicopters. The overrunning clutch transmits torque to the tailrotor drive pulley and to a set of spur gears which provides the final reduction to drive the main rotor mast. The mechanics reduce the engine speed of 18,000 rpm down to a rotor speed of around 1,600 rpm or so.
Main Rotor Mast and Swashplates- Like a real helicopter, the Caliber .30 is a collective pitch machine, which means that rotor rpm is kept constant while the collective and cyclic pitch of the blades is changed to move the helicopter around. Changing the collective and cyclic pitch of the blades is accomplished by moving the fixed swashplate. The fixed swashplate then moves the rotating swashplate to which links are connected. Those links change the pitch of the blades and the flybar. To move the fixed swashplate, there are three linkages which are connected to three electrically powered servos mounted where the cockpit would be in a real heli. Those servos move the linkages in combinations to move the swashplate in the desired direction. The swashplates are mounted around the main rotor mast, which comes up through the center of the heli, and carries the flybar and the main rotor grips, which in turn carry the wood or composite main rotor blades.
Electronics- As one would imagine, an RC heli is electronics-intensive; much more so than an RC car or even an RC airplane. Unlike an RC airplane, where each motion of the control stick on the transmitter corresponds to the movement of a respective servo, a helicopter with EMS (electronic mixing system) actually utilizes a computer built into the transmitter to interpret the movement of the control sticks and then blend the functions of all of the servos on the heli to perform the desired operation. This is particularly true for the three servos that move the swashplate. For example, when one wants the helicopter to move to the right, he wants to increase the left cyclic pitch of the blades. He moves the right control stick on the transmitter to the right, and the computer commands the right servo to move forward and the left servo to move rearward, while the center servo remains stationary. This causes the swashplate to tilt toward the right, increasing the left cyclic pitch on the rotor, causing the helicopter to move to the right. In another example, when one wants the helicopter to rise, he wants to increase the collective pitch of all of the blades. He moves the left control stick forward, and then the computer commands the three servos connected to the swashplate to all move backwards in unison, thus uniformly raising the swashplate, increasing the collective pitch, and causing the heli to rise. To further complicate things, sometimes the computer will also incorporate a throttle curve and revo-mixing, bringing the remaining two servos into action. For example, as collective pitch is increased, two things happen aside from the heli rising. One, the load on the engine increases, and two, the torque on the main rotor shaft increases. The increased engine load wants to slow the engine down, so a throttle curve is programmed to automatically increase the throttle opening via the throttle servo to match the load and maintain constant rotor rpm. The increased torque wants to make the helicopter yaw in the opposite direction, so revo-mixing can be used to correspondingly increase tail rotor pitch through the tail rotor servo as collective pitch is increased, countering the increased torque.
Fortunately, I have equipped my heli with two devices that allow me to forego setting a throttle curve and revo mixing. These are two devices that really add to the performance of an RC heli, and they are the gyro, and the engine speed governor.
The gyro is common on just about all RC helis, and even on some aerobatic planes. The gyro is an electronic unit that sits in the nose of the heli and senses any unwanted yawing of the aircraft, and will adjust the pitch of the tail rotor blades to maintain a desired heading.
The speed governor is not as common as a gyro, but its has become very popular on RC helis. A magnetic sensor measures engine speed, and when the governor is switched on, the governor will move the throttle servo to maintain the set rpm. Then, by simply raising or lowering collective pitch, the engine power can automatically be increased or decreased, and rotor rpm remains constant.
The battery and the receiver round out the electronics package. The battery provides power to operate all of the servos and electronic controls, and the receiver converts signals from the transmitter top operate the 5 servos.
So far I've really enjoyed flying my RC helicopter, and I would like to get further into this very challenging but rewarding hobby. I'd eventually like to get a .90 class heli so I can do some crazy aerobatics. There are turbine powered helicopters available as well, although I don't think I could justify the much higher cost of them knowing that the performance is not as great as a glow powered helicopter.
Here is a video of my first successful flight with my heli, in my back yard: (I've gotten much better since then!)
Here is a video of a turbine powered RC heli
For more information on this exciting hobby, check out these fine websites:
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