Radio Controlled Helicopters

So what are they all about?

RC helicopters have always held a mystery for a lot of people, how can these marvels stay in the sky without wings, why are they so maneuverable and how the heck do you fly them.

RC helicopters hold a unique attraction, their presence in the sky, their maneuverability coupled with the sound of the air through the rotor blades, makes them so exciting to fly.

The basis of rotary flight uses a set of rotor blades which spin around a central mast cutting into the air to produce lift. The spinning rotors are considered to be a virtual rotor disc. Tilting the spinning rotor disc will cause flight in the direction of the tilt.

The main rotors are attached to the control system through a swash plate. The swash plate acts as the heart of the control system translating control inputs from the non-rotation fuselage to the rotating rotor disc.

When we have a spinning rotor disc attached to a central mast anchored to the body of the helicopter, the body of the helicopter will spin in the opposite directions this is know as torque reaction and is the reason many helicopters have tail rotor blades.

The control plane of a RC helicopter is illustrated below.

The control mechanism used to influence the control planes of an RC helicopter, vary depending on the helicopter type.

We have 3 main types of RC helicopters which include the following:

•         Co-axial helicopters
•         Fixed pitch helicopters
•         Collective pitch helicopters

 

RC Heli Types

Co-axial helicopters use two sets of fixed pitch rotor blades, one positioned above the other, which are controlled by two separate motors.

Anti torque reaction is archived by spinning each of the two rotor discs in the opposite direction.

Pitch and roll are controlled by the swash plate by tilting the primary rotor disc, while yaw is controlled by varying the speed of the secondary rotor disc.

The height is controlled by changing the rotor speed of the motors by the same amount which will in turn changes the speed of both rotors, changing the amount of lift.

Fixed pitch helicopters by contrast use one set of rotor blades and a separate tail rotor.

Both the main rotor and the tail rotor are normally controlled by two separate motors.

Anti torque reaction is achieved with the tail rotor.

Pitch and roll are again controlled by the swash plate by tilting the primary rotor disc, while yaw is now controlled by varying the speed of the tail rotor.

The height is controlled by changing the rotor speed of the main motor which is turn affects the lift generated by the main rotor blades.

Collective pitch helicopters use one set of rotor blades and a separate tail rotor.

The rotors blades can be independently pivoted to change the angle of attach and influence the lift produced by each blade.

All the rotors are controlled by the main motor, with the tail rotor being driven by the main motor using either a drive belt or drive shaft running down the tail/boom of the helicopter.

Anti torque reaction is achieved with the tail rotor.

Pitch, roll and height are now all controlled by the swash plate by varying the pitch of the main rotor blades, while yaw is now controlled by varying the pitch of the tail rotor using tail control links and a pitch slider. Height can also be controlled by varying the motor speed.

The humble flybar?

The flybar is a long bar attached to the rotor head usually at 90 degrees (depending on the rotor head phasing) to the rotor blades.

The flybar has paddles (or weights) at each end to assist with flight stability, the control system from the swash plate, connects to the flybar, usually through mixing arms, which help to dampen or smooth control inputs into the rotor disc.

So what is a Gyro?

A common device used on our RC helicopters is the gyro.

The gyro is normally used on yaw axis to hold the tail at a constant heading.

When a side wind hits a model RC helicopter which is hovering on the spot, the helicopter will start to rotate so that it is heading into the wind, just like a weather vain. The gyro holds the tail in a constant heading, making sideward and backward flight possible.

So how do flybarless heli’s work?

Flybarless flight takes the heading hold gyro a step further, by also acting on the roll and pitch (cyclic) axis of the helicopter. These 3-axis gyros are referred to as flybarless controllers and provide electronic flight stabilisation replacing the functionally of the flybar.

Removing the flybar reduces the complexity and part count in the head, while reducing drag, allowing for more power from the motor and longer flight times. Flybarless heads provide direct control to the rotor blades without requiring mixing arms, which provides a more locked in feel in the air.

[headline htype=”h4″]Are RC Heli’s hard to fly?[/headline]

This is probably the most frequently asked question, and the best answer I have every heard to this question is that RC helicopters are easy to fly, but hard to master.

Of course this also depends on the type of helicopter you are flying.

Co-axial helicopters tend to be easier and more stable to fly, and are very popular with pilots learning to fly for the first time.

Fixed pitch helicopters are less stable but more agile and controllable and are able to achieve fast forward flight and mild aerobatics.

Collective pitch helicopters are the most challenging to master but they also have the widest flight envelope, being capable of advanced aerobatics and sustained inverted flight. Some collective pitch RC helicopters can reach forward speeds of over 100mph.

I would advise anyone considering learning to fly a RC model helicopter to invest in a computer flight simulator.

Simulators are invaluable training aids and will save you a lot of money in repair costs when starting out and for practising new manoeuvres when your skills improve.

Popular simulators include Phoenix v4, Realflight v6 and Aerofly.

Although learning to fly RC helicopters can very rewarding and exhilarating, make no mistake it is not easy and it can require a considerable investment of time to acquire the necessary skills to become a proficient RC helicopter pilot. Although the time it takes varies, depending on the individual pilot, but the key to success is practice, practice, practice.

The Hover?

One of the first and hardest manoeuvres to master is the hover. And again this varies between the type of helicopter being flown.

Hovering a co-axial helicopter can be described as putting a small marble into a round bowl.

You can tilt the bowl and the marble will move around, if you let go of the bowl the marble will sink into the bottom of the bowl.

The same is true for the co-axial helicopter, moving the sticks will move the helicopter around in a sedate fashion, releasing the sticks will see the helicopter settle into a stable hover.

Now contrast this to the collective pitch helicopter, which can be compared to turning the bowl upside down and balancing the marble on top (or bottom) of the bowl. If you let go of the bowl the marble will roll down the side of the bowl.

Hovering a collective pitch helicopter is a careful balancing act, of constantly making control corrections to attain a stable hover. Releasing the sticks the helicopter will roll/pitch to the ground.

Does size really matter?

In the world of RC helicopters, size does actually matter.

The larger and heavier the helicopter is, the easier it is to see in the sky and the more stable and predictable they tend to be.  Large helicopters are also a lot less susceptible to the influence of the prevailing winds.

Although Larger RC helicopters rarely survive a spill or crash intact, and the cost of repairs can be substantial.

POD and Boom or Scale?

Most RC helicopters which have only a canopy covering the avionics are referred to as POD and boom. Where as replica models that have detailed fuselages and are made to look like their full size counterparts are referred to as scale.

So which helicopter should I buy?

As a beginner the obvious choice would be a co-axial helicopter and there is now a large range of RC co-axial helicopters available ranging from the toy style helicopters right up to the hobby class scale helicopters from a large number of manufactures.

For a hobby class co-axial helicopter, Horizon hobby have a number of very popular models in their blade range to choose from.

These include: scout CX, Red Bull BO-105, Blade mCX, blade mCX2, blade CX2.

A more proficient pilot should consider a fixed pitched helicopter and examples of these from the Horizon Hobby blade range would include the blade mSR, blade 120SR, blade mSR-X.

The advanced pilot would no doubt prefer to consider the collective pitch helicopter and there are a large number of manufactures providing a number of different models varying from basic POD and Boom, scale and competition level helicopters.

Popular makes include the likes of Align, Blade, Thunder Tiger, Mikado, Guai, Synergy, Next D, SAB to name but a few.