Helicopter Terms and Considerations for the Beginner
The new modeller may find our technical language confusing at first. This does not help a person easily understand early conversations intended to help set-up the helicopter. With this in mind we have developed a short list of terms in a very basic format or easy to understand manner.
Cyclic control :
The right radio transmitter stick controls the cyclic. Think of the main rotor disk as a big plate, whichever way you move this stick is the way the big plate tilts. The helicopter will move in the direction the main rotor tilts as its thrust vector is redirected. How exactly this mechanism works is rather complicated.
Collective control :
The left transmitter stick controls the amount of main rotor thrust by varying the main rotor blades together in pitch. Rotor rpm or speed is constant so lift is changed by overall blade pitch variation. The pitch to the blades is varied together in a collective manner! The throttle is also controlled by the left stick since when the collective is altered the engine loading is different. We are after all performing different magnitudes of work.
Because the way in which a helicopter feels with respect to the main rotor controls will change with different rotor rpm, we try to maintain a constant rotational speed of the rotor. Moving this left stick up or forward in the hover causes the helicopter to climb. If the cyclic is moved forward at the same time as the collective the machine will accelerate forward.
The heart of all helicopters. This mechanical component controls the main rotor cyclic and collective parameters. It changes a non-rotating control output from the on board radio servos to a rotating control out put to the blades. The swashplate has a rotating and non-rotating portion. The servos connect to the non-spinning part while the blades connect to the rotating portion. This exchange is completed by means of two bearings.
The swashplate rises and falls on the mast or main rotor drive shaft to change collective pitch. The tail rotor pitch change mechanism has a very similar operation in this regard but this is where the two rotors part technical company. The swashplate also tilts. This imparts a reciprocating action through the rotating control directed to the blades.
The low tilt will pull a rotating control rod away from the main rotor blade while the upper tilt will do the opposite. This happens every rotation of the rotor. Since the device can be made to tip every which way the main rotor blades will be rotationally synchronised to the way the unit tilts. Basically we are causing the blades fly higher or lower at specific points of rotation rather than trying to physically move the rotor to the desired flight path.
Tail Rotor control :
The purpose to the small rotor at the rear of the helicopter is to control the yaw axis. This control is on the left stick or part of the collective stick. Moving the left stick side to side controls this axis. It can be compared to the rudder on an airplane or boat since it steers the back end to point the nose left and right. It also compensates for the torque applied to the main rotor which tends to twist the fuselage in the opposite direction of main rotor rotation.
The tail rotor uses a form of collective control to the blades in much the same manner as the main rotor even though it has no cyclic control. The more main rotor collective pitch we apply will demand more engine power, more engine power will create more torque to the main rotor. This torque change will have to be compensated for or the helicopter will change its heading or yaw.
An electromechanical device which changes electronic commands into proportional mechanical control movements. It receives its information from the radio receiver installed on the helicopter. The radio receiver as expected is controlled by the radio transmitter flown by the modeller. The servo has a shaft which rotates about 120 degrees.
An arm is attached to the servo shaft to output control rod movements. The cheapest ball bearing servo type will serve the beginner. Helicopters require at least 5 servos to function correctly.
This is an electronic device connected electrically between the receiver output to the tail rotor servo. The tail rotor is the hardest parameter of the helicopter to control. Because of this we install a gyro to better manage this control axis. It basically damps out many unwanted yaw movements the pilot has not commanded. It makes flying the model possible for the beginner and for the honed individual control matters become enjoyable.
Everyone uses this device and there are many types available. The cheapest gyro will best serve the beginner.
The model helicopter engine of choice. It has no ignition system and functions like a diesel engine in that it needs no ignition system or spark plug once running. The engine burns a mixture of methanol, oil and nitromethane. Larger helicopters are available with a gasoline engine similar to what one would find in a weed-eater. Bigger machines are much more expensive to repair and are not recommended to a beginner.
Glow engines have a higher power to weight ratio that makes them very desirable as a model helicopter power plant. Glow fuel however is more expensive than gasoline but the smaller 30 sized helicopter is very frugal in consumption.
Support equipment :
Electric starter, starter wand, glow plug electrical connector, fuel, fuel pump, a small 12 volt battery from a motorcycle or similar application, a glow driver to power the glow plug for engine starting, small hand tools and a container to carry this equipment.
Sounds like a lot but it really isn’t that bad. Hobby shops sometimes carry support packages but very often used stuff is available and the equipment lasts a long, long time.
Purchasing decisions :
– Consider a 30 sized glow helicopter.
– Pick a Thunder Tiger Raptor, Century Hawk, Hirobo Shuttle or a Kyosho Caliber.
– Choose the machine best represented at your local area. Check with a model helicopter club before buying. You may well pickup good cheap equipment. The locals without sales motivation, but with ample technical skills will help you best during the decisions. Have any used machine gone over by an experienced modeller.
– Select a modern 6 function (channel) or better helicopter radio system from Futaba, Hitec, JR or Airtronics. You want 5 point pitch and throttle curves which are spec’d in the advertising documentation. Try to get a 4.8 volt 1200-1800mah nicad battery pack with the system. You can upgrade the radio package easily and cheaply at the time of purchase.
Pick a piezo gyro (solid state with no moving parts). Check with the locals for the best place to buy.