I should cover the basics of helicopter safety first, i wont go into flight safety, or pre-flight checks just yet. Just basic precautions to take on the ground whilst building or modifying your helicopter.
Specifically, until you are confident with the mechanics of the RC helicopter, and are in a informed position to start the mechanical set-up of the aircraft, do not connect the Li-Po battery to the helicopter. There are many reasons for this, but all will end in the helicopter trying to spin its blades at 2000 rpm, causing injury and/or damage. Once in a position to setup the helicopter mechanically, it is ok to connect the battery to the speed controller, but remove prior to this the three wires going to the motor, to prevent the helicopter trying to spool up.
This is valid specifically for a electric helicopter, but is also valid for a nitro heli, except it is more difficult to accidently start a nitro heli. This guide is written in a fashion aimed towards electric helicopters, as this is what most new pilots will encounter. Most of the principles are the same, except the motor and speed controller is replaced by an engine and a servo. That is not to say electric helicopters are for beginners, its just a lot of the simple ready to fly sets are electric. Electric helicopters are available up to the 90 size IC range, and perform as well as, if not better than there IC counterparts.
I will cover the basics of all of the components in this guide as well, but i go into more detail about specific articles on other pages within this site. Also, see my subsequent articles on how to learn the basics of RC helicopter flight, and achieve a stable hover.
In this guide i will use the T-Rex 500 as the example, to guide you through the various components of the helicopter. I am not however recommending this as a beginners model. Under one-on-one tuition it is possible to learn on this aircraft, and in fact its flight characteristic can be set to be very docile and beginner friendly. But it is aimed more towards the mid to high end range and competition flight, they are also many times more expensive than a basic ready to fly box set, that a beginner should be aiming for.
NoteThis section is essentially a glorified glossary of terms. I will go into detail on all of these subjects in other sections of the site. Such as radio setup, mechanical setup, flight training etc.Tthis is also a multipart series, so check back soon for more updates.
Helicopter Mechanics
Airframe Usually injection moulded. But also on more expensive models constructed from carbon fibre, and Aluminium. Providing a rigid frame to piece all of the components together, and transfer the power between the motor and rotor head. It also serves as a frame to hold the electronics. Modern pod and boom sport models, are semi exposed except for a fiberglass painted canopy that covers the first half of the airframe via some simple retaining clips. This aids in orientation of the aircraft whilst in flight, and helps to improve aerodynamics.
Tail Between the tail unit and main frame is the tail boom, it provides a route for the tail drive system and control linkages. It is necessary to have the rear rotor blades at a larger diameter than the main rotor blades away from the main frame. Usually there are also two support structures coming from the base of the helicopter frame, to a fixed point along the boom to aid structural rigidity. This is also where the horizontal stabilizer fins are located, a bit further towards the rear we find the vertical stabilizer connected to the tail drive unit. The power is normally transferred to the tail from the main motor via a belt drive, but it is also possible to have torque tube drives, that have a fixed drive shaft powering it. The rudder control on the radio controls the yaw of the helicopter via changes in pitch of the tail blades.
Swashplate This is one of the most important parts of a RC helicopter, it is how the movements from the servos are transferred to the rotor blades, and finally translated into a movement of the helicopter in the direction required. It allows the stationary helicopter frame and servos to apply movement to the spinning blades pitch. In order to produce propulsion in a certain direction, as the blades spin, at certain points along the circumference of the rotation, the pitch of the blade changes, thereby creating more lift on the left side than the right for example. This will then cause the helicopter to move to the right. This is the Aileron control on the radio, and produces a sideways banking motion. It is the same theory for the Elevator control, it rocks the swashplate forwards and backwards, like the Aileron moves it from side to side.
Rotorhead Relatively simple compared to the swashplate, as most of the control mixing has been done there. The main components here are the blade grips, they are able to rotate to allow for the changes in pitch of the individual blade. Also on the rotor head is the flybar, this is to provide a mechanical form of stabilization to the inherently unstable aircraft. To provide control to the rotor head, we have a complex mixture of washout arms, bell crank arms, mixer arms, pitch control arms and flybar control arms. All working together to keep the helicopter in the air. I wont go into detail on these in this section, as the particular setup varies from one helicopter to another. I will however go into more detail in the mechanical setup section of this website.
A combination of rotor pitch and head speed gives the helicopter lift. When applying increasing pitch on both blades at the same time, this will produce lift, but also increased drag effects will reduce the head speed. On a modern transmitter, the throttle, and pitch are mixed to counter act this and keep a constant head speed, this is also where a engine governer comes into force on a nitro model.
To calculate head speed, we look at the rating of the motor, so a 3000 Kv motor will rotate at 3000 rpm per volt. So the T-Rex 500 runs at 22.2 v. This means the motor will spin at 66,600 rpm when the full voltage is applied, it then makes sense that at half throttle, we will have 33,300 rpm. It is then a simple case of working out the ratio between the teeth on the motor pinion and main gear to give us our head speed. So as an example, if for every one turn of the main gear, the motor turns 40 times, we would have a head speed of 1665 rpm.
Speed Controller and Motor Unlike a nitro model where we have a mechanical mixture control and servo, on a electric helicopter we have a brushless motor and electronic speed controller [ESC]. The speed controller acts as many units in one. Supplying the appropriate voltage to the motor, providing power to the electronics, controlling headspeed, battery level warnings, and many more features. Most ESC's will have a built in battery eliminator circuit (BEC) to maintain the correct voltages to the receiver and ultimately the servos and gyro. If you have a nitro model, this will be a separate unit, and the helicopter electronics will have there own, smaller Li-Po batter pack. The ESC usually will connect to the motor via 3 cables, positive, negative and data. it is important when working on your helicopter on the ground, to disconnect the motor from the speed controller, to avoid accidental arming and spooling up.
Servo's and Gyro If you have a 120 degree swashplate you will have 3 servos mixed to control the swashplate movement. This is known as eCCPM, the controls are mixed on the transmitter, to allow the three servos to control the four directions of motion applied on the cyclic control. Some helicopters use 90 degree non-ccpm swashplates, but on the majority of current helicopters these are much less common. A quick visual inspection of your swashplate will allow you to identify easily which type you have.
Lastly we have the tail servo, usually attached directly to the tail boom, or tucked away inside the main frame below were the tail boom interfaces with the frame. This provides the control for the pitch of the rear tail blades, to allow the model to yaw and rudder control. However, it is necessary to incorporate a gyro between the receiver and servo, to control the position of the tail. Due to the force of the tail rotor, it will generally always want to move. Also looking at the laws of motion, once moving it will want to continue on that path until operated on by an external force. So a gyro counteracts this. It keeps the tail locked steady in one position, when you give some left rudder, it moves left, but the moment you stop the control input the tail comes to sharp stop. Without this you would have to be constantly balancing the tail, and the other controls. No easy task.
Overview So that completes are introductory lesson to the basics of remote control helicopters, this was meant as a simple overview, check back soon, and explore other parts of the site for more in-depth tutorials on RC helicopters. It may all seem confusing at first, but it will become second nature within no time at all.
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