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How Do RC Helicopters Work?

January 12th, 2008 · 19 Comments ·

Helicopters are one of the most versatile modes of transportation in existence and give the pilot complete access to a fully 3-dimensional space. Because of this, helicopters, whether RC or full size, are one of the most difficult vehicles to learn to control.

For example:

A train can travel in 2 directions: forwards and backwards.

A car can travel in 4 directions: forwards, backwards, left and right.

An airplane can travel in 5 directions: forwards, left, right, up and down.

Whereas a helicopter can travel in 6 directions: forwards, backwards, left, right, up and down. Plus it can also rotate 360 degrees in either direction and do all of that while inverted.

In a traditional full size helicopter, the pilot is facing forwards controlling the cyclic with one hand and the collective with the other.

However, in an RC helicopter, you’re not always looking the same way the helicopter is flying which makes it quite difficult to keep oriented and stay in control. I’ve even heard full size helicopter pilots say that an RC helicopter is harder to fly – though in reality it’s probably not – but keeping orientated when you’re not facing the same way the helicopter is can be extremely difficult to master.

How Do RC Helicopters Fly?

So, how does an RC helicopter fly? Someone once said that it beats the air into submission – and in fact, it kind of does.

RC helicopter flight can be broken into 5 basic components and their functions. The main rotor, tail rotor, swash plate assembly, collective control and cyclic control.

The Main Rotor

A conventional RC helicopter has its main rotor above the fuselage (its body) which consists of 2 or more rotor blades extending out from a central rotor head, or hub assembly.

The main rotor of an RC helicopter is what produces the lifting force that allows the RC helicopter to fly. The rotors on a collective pitch RC helicopter are shaped just like the airfoils of an airplane wing, only they are thinner, narrower and both sides are symmetrical.

As the rotor blades rotate through the air, they generate lift. The amount of lift generated is determined by the pitch angle (and speed) of each rotor blade as it moves through the air. Pitch angle is referred to as the angle of attack when the rotors are in motion.

Some cheaper RC helicopter models which use fixed pitch rotors, generate lift by speeding up or slowing down the motor and therefore the speed of the main rotors. This results in a much slower responsiveness of the heli, since it takes some for the motor speed to speed up or slow down. As far as I know, there aren’t any real RC helicopters which use fixed pitch available on the market anymore an don’t go picking one up at a garage sale – there’s a reason they’re no longer made.

Depending on how the RC helicopter is set up, the main rotors typically spin at a constant headspeed ranging anywhere from 1,500 RPM to 3,000RPM. Larger size .60 or .90 RC helicopters will usually have a headspeed of 1,500RPM to 2,000RPM where smaller .30 or .50 size heli’s might have a headspeed in the 2,000RPM to 3,000RPM range.

To increase thrust, or lifting power, you simply need to increase the pitch of the main rotor. On an RC helicopter, the angle of attach (pitch) can be anywhere from +15 degrees to -15 degrees, though most RC heli’s are somewhere in the +11 to -11 range.

The pitch angles of the blades are controlled by the collective and the cyclic control which are transferred to the main rotors through the swash plate.

The Tail Rotor

Since Newton’s law states that “For every force, there is an equal and opposite reaction force,” as soon as the RC helicopter leaves the ground, there is there is nothing to keep the helicopter from spinning in an opposite direction to the torque force generated main rotors.

To stop the spinning of the body, a force which counteracts the force of the main rotors needs to be applied to stop it. In a single rotor RC helicopter, this is usually done by a smaller set of rotors attached to a long tail boom called the tail rotor, which is used to control the yaw, or rotation, of the helicopter.

The amount of thrust the tail rotor produces is determined by their angle of attack.

Increasing the angle of attach (pitch) of the tail rotor blade will increase the thrust, which will push the helicopter in the same direction as the main rotor blades, while decreasing the pitch decreases the amount of thrust, allowing the natural torque force of the main rotors to take over letting the helicopter rotate in the opposite direction to the main rotors.

A gyro, either mechanical or piezo-electric, measures the difference in rotational force between the helicopter and tail rotor and adjusts the pitch of the tail rotor accordingly to hold the RC heli steady.

The tail rotor is typically mounted at a 90 degree angle from the main rotor and provides a sideways thrust which counteracts the rotational force applied by the main rotors to hold it straight.

Depending on the gearing ratios, the tail rotor typically turns 3 – 6 times faster than the main rotor.

Tail rotors in RC helicopters are typically driven by a belt or a torque tube which is powered off the main gear which also powers the main rotor. In some cheaper models, a separate motor is used to power the tail.

The Swash Plate Assembly

The swash place on an RC (or full size) helicopter is used to translate the pilots commands into the motion of the main rotor blades and / or flybar.

The swash plate assembly fits on to the main rotor shaft beneath the head of the heli and consists of one rotating and one non-rotating disc.

The lower, non-rotating disc is linked directly to the cyclic and collective controls which are controlled by servos under the command of the pilot’s transmitter inputs.

This non-rotating disc is attached by a bearing to the second rotating disc, which turns with rotor and is linked to the main rotor blade pitch horns.

The swash plate can be made to tilt in any direction according to the cyclic controls, or move up and down to change the pitch of the rotors under the collective control, which allows the pilot to control the RC helicopter in a 3-dimensional space.

Collective Control

The collective control raises the entire swash plate assembly as a unit. As the swash plate rises or falls, it changes the pitch (angle of attack) of all rotor blades simultaneously and to the same degree. This is known as collective control.

Therefore, when the collective control is increased, it will raise the entire swash plate assembly increasing the angle of attack. Increasing the angle of attack increases the lift of the main rotor, causing the heli to gain altitude, while decreasing the angle of attack decreases the lift.

Since all blades are changing pitch together, the change in lift remains constant throughout every full turn of the blades.

Cyclic Control

The cyclic control works by tilting the swash plate up or down and increasing the pitch angle of a rotor blade individually as they revolve, so the angle of attack on one side of the helicopter is greater than it is on the other.

As the pitch angle changes, the lift generated by each blade changes and this unbalanced lift causes the helicopter to tip towards whichever side is experiencing the least amount of lift.

This allows the helicopter to move in any direction around a 360-degree circle, including forwards, backwards, left and right or any combination of the 4.

For example, when the cyclic control is pushed forwards on your radio transmitter, the swash plate tilts forwards increasing the angle of attack (and lift) in the rear of your helicopter which causes it to move forwards.

Because of the cyclic and collective pitch control of the main rotor blades and the pitch control of the tail rotor, your engine RPM and therefore the speed of the main rotor blades, can be kept at a constant rate increasing maneuverability response time.

Your radio transmitter handles all the mixes and translations between cyclic and collective movement, so all you need to think about is which way you want your helicopter to fly, not angles of attack or swash plate tilting.

Have a question about this article or anything else RC Heli related? Ask it in our brand new RC Helicopter Forum and you'll get expert answers quick.

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Tags: RC Helicopter Articles

19 responses so far ↓

  • usman shahzad // Jan 31, 2008 at 1:08 am

    very nice description

  • Ramesh // Mar 28, 2008 at 6:08 pm

    im very interested about RC Heli and this is good stuff

  • sunoor batra // Apr 18, 2008 at 10:33 am

    very easy to understand and satisfactory
    description.

  • Opal // Sep 2, 2008 at 9:22 am

    It’s a great description,however it will be better if you put some more photo on this article to make it easier to understand

  • cp2 // Sep 29, 2008 at 8:08 pm

    Does Collective Control have only in CCPM helicopter? And Cyclic Control? Nice site! Thanks

  • admin // Sep 30, 2008 at 1:28 am

    Hi Cp2, all regular and model helicopters (besides the cheap fixed pitch ones) have full collective and cyclic control.

    It’s necessary to control the altitude and maneuver during flight.

    Hope that answer your question…

  • Hobo // Oct 20, 2008 at 7:05 am

    on a helimax450, in what direction does the main and tail rotor blades turn? Does this apply to all helis in all countrys. Thank you.

  • admin // Oct 20, 2008 at 1:45 pm

    Hi Hobo,

    The Helimax 450′s main blades spin clockwise and the tail rotor spins counter clockwise.

    The direction of rotation of the blades for an RC helicopter depends on how the manufacturer designs it, though most heli’s have both main and tail blades that spin clockwise.

  • Hobo // Oct 27, 2008 at 12:15 pm

    Ihave been trying since my last question on oct 20 to get the main motor to arm, am using a futaba t9cap transmitter with a FP_R14BDF reciever. it will not arm with the throttle stick, only with the elevator stick in the up position, and when i push the stick forward i get an increase in the rpms. Again HELP!! thank you HOBO

  • admin // Oct 27, 2008 at 3:00 pm

    Hobo, it sounds like you need to reverse the throttle stick direction in your radio settings.

  • Hobo // Dec 11, 2008 at 5:22 pm

    Thanks admin. you solved my throttle problem. OK, again on my heli-max450, is it possible to set main blade pitch without using a pitch gauge? Again, thanks for all the help.

  • admin // Dec 13, 2008 at 4:37 am

    Hey Hobo, glad you got that worked out.

    Yes, you can set the pitch visually without a pitch gauge using the flybar (after making it level) as a reference point. You just won’t know how many degrees of pitch you’re running each way, but you can easily set 50% collective at 0 degrees and make sure there’s equal travel in each direction.

  • Hobo // Dec 14, 2008 at 10:14 am

    Its me again. Am having difficulty with getting the right pitch on the main blades, instead of getting lift i get the opposite effect. Alao there is a greag deal of slop in the linkage. Am still using a futaba 9c radio. Im sure you know by this time im somewhat new to this and how to do it. I do have a blade CP i learned to fly with but this heli max 450 has got me buggered. Your assistance in the past has been most helpful, hope you dont mind my asking you for help again. Again. thank you. HOBO

  • admin // Dec 19, 2008 at 5:07 am

    Hobo, it sounds like you may need to reverse the collective in your radio if you are getting negative pitch when you should have positive.

  • enki // Feb 16, 2009 at 12:14 am

    heli-rc…i’m very eager to learn this as a new hobby. I’m thinking of having a Llama V4 for a start.

    My reason why such model/brand?
    -price
    -avilability
    -if i did get bored the investment aint that big :)

    things i’d like know:
    -battery requirement specs (volts?, mah?, etc)
    -other interesting facts

  • rohit pande // Feb 19, 2009 at 9:28 am

    hi.. i want to design my own rc helicopter.. could u advice me on the types of components to be used for the following specifications..
    -max payload 25kg
    -electrical engine (battery operated)
    -flight time of 6 hours max
    -travel radius of 200 mts max

  • surfer with a heli // Feb 26, 2009 at 1:02 am

    I also would like to put together a heli capable of extended range and flight time (thinking something controlled via my laptop with fuel cell battery maybe?), any suggestions would be very much appreciated.

  • Esky Shop // Feb 26, 2009 at 7:45 am

    Do you have some post about “How To Balance Your RC Helicopter Head” ???

  • abby // Apr 14, 2009 at 7:30 pm

    very good article , what you say is very interesting and also very useful , thank you for your good work , it seems that you are a big RC Helicopter , here I recommend you a good place , there you can find out different kinds of good RC Helicopter , believe me , I will not let you down!
    that is : tradestead
    why not have a try!

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