Selecting an rc helicopter can be a daunting task, especially for the beginner. The first step is to know your options. To begin, we will examine the different types and configurations of rc helicopters available.
RC helicopter rotor blades can be fixed pitch, or collective pitch. An rc helicopter relies on the lift generated by it’s rotors. These rotors are comparable to the airfoil on the wing of an airplane. When the blades are locked at one angle, we refer to the rc heli as fixed pitch. This means that the blades always cut into the air at the same angle. This design has several advantages. The design is simpler, more durable, and easier and therefore cheaper to manufacture. The overall cost of a fixed pitch rc helicopter will be less than the cost of a comparable collective pitch model. The major disadvantage of the fixed pitch design is that the vertical component of flight becomes less controllable. Because the angle at which the blades cut through the air is constant, the only way to vary the amount of lift produced is to increase the rate at which the blades spin. This is accomplished by increasing the engine speed. The problem with this system is that because of inertia, the speed of the engine cannot be changed or controlled as rapidly as the servo you would use to control vertical thrust in a collective pitch rc helicopter.
In a collective pitch rc helicopter, the angle of the blades is changed to control the amount of upward thrust. Unlike a fixed pitch helicopter, when the command is given for the helicopter to climb or descend, the pitch of the rotor blades changes and the engine speed remains constant. The servo controlling the pitch of the blades (and the climb rate of the rc helicopter) only has to alter the position of the the rotors, which can be done rapidly with relatively little resistance. This is capable of a more rapid response than the engine having to accelerate the entire drive train and rotors up to a new speed. Clearly, the collective pitch design provides better control but at a higher price.
Cyclic pitch is the term applied to an rc helicopter which maneuvers by changing the pitch of each individual blade at different points along the path of rotation, causing them to generate more thrust on one side of the rc helicopter than the other. This will tilt the rc helicopter and result in horizontal motion.
An important option is known as auto rotation. In a fixed wing aircraft, if the engine were to stop, the plane becomes a glider with the wings still producing lift. The same can happen in an rc helicopter that is equipped with auto rotation. In an rc helicopter without auto rotation, the engine is connected to the rotors with out the ability to disengage – meaning that if the engine were to stop, the blades would do the same. This would result in the pilot losing control and the helicopter crashing. With auto rotation, the blades will spin freely during an engine failure. They will still generate some lift, allowing the pilot to maintain control and land. This is normally accomplished by a one way clutch or bearing. Auto rotation is a good feature to have because it may save your rc helicopter if the engine were to fail.
When manufactures refer to the size of a helicopter they are most likely talking about the displacement of the engine, rather than the size of the helicopter itself. Engine displacement commonly ranges from .30 to .90 cubic inches. Each size has it’s advantages and disadvantages, and these will be examined in depth in part two of this guide. For now though, the rule of thumb is that a larger engine is more powerful and will burn more fuel.
Pod and boom is a term applied to the type of helicopter where the body is composed of a ‘pod’ where the radio, engine, gears and other components are kept. The ‘boom’ is the part of the helicopter that holds the tail rotor. This is a common type of rc helicopter, accounting for the majority of the models available. This is different from the scale model style, where the entire model is designed to look just like the real thing. These generally have large fuselages which make them easier to see. They are also more aerodynamic. But for the beginner, pod and boom design is recommended, because of availability and durability.
Now that you are familiar with the different types of rc helicopters available, you are ready to make an informed choice on the type of model to buy. We will show you different points to consider when buying your first rc helicopter in the second part of this guide.
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Posted in RC Helicopter Flying School