Remote Control Helicopter
R/C Helicopter Terminology

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Remote Control Helicopter
Terms and meaning to words related to r/c helicopters and heli's.


Helicopter Terms

3D (flying)
High performance flying, usually combining two maneuvers at once. For example, mixing a loop and a roll, to loop while rolling etc...
540 Stall
A high speed climb followed by a 540 degree Pirouette as the heli stops climbing .
ABC / Non-Ringed
These letters stand for aluminum, brass and chrome or a composite such as nickel. These engines have an aluminum piston and a chrome or composite coated brass cylinder sleeve which allows them to be more efficient for higher performance. They have no piston ring and rely on a very tight piston/cylinder fit to obtain a piston/cylinder seal. New ABC engines are normally hard to turn over by hand. Because of the tight fit, it is very important that the engine is broken in properly.
This is really an airplane term, but is easier to say than "cyclic roll." Ailerons are what banks a plane left or right, but does not really exist on a helicopter.
The shape of a wing which produces lift.  
Angle of Attack
The angle between the direction of the cord of the blades and the relative direction of the wind.
A prefabricated model - Almost Ready to Fly Autorotation
A maneuver to land in the case of engine failure; the momentum of the rotor blades can be just enough to slow the heli down just before landing.
An adjustment on many transmitters that allows you to adjust the maximum throw of a servo. This is used to avoid binding. See binding.
Ball Link
Connections that allow for adjusting controls using a ball on one end, and a link that "snaps" onto the ball on the other.
Describes the play in the meshing of two gears. Too much backlash and the gears could slip or break the teeth, too little backlash could cause excess wear and tear. The common rule is the thickness of two sheets of paper for the right am ount of backlash.
Base Load Antenna
A short "whip" antenna about 6 inches long used instead of the long dangly antenna that comes with the receiver.
Bell and Hiller
A control system commonly used for r/c helicopters that allow the pitch of the blades to change depending on where they are in their rotation with the aid of paddles to take a substantial load off the control system. Bell is the co ntrol system that involves the swashplate and linkages to adjust the pitch and Hiller is the part that uses a flybar or paddle to make the cyclic more responsive.
A bad condition where the control ajustments can not move as far as the maximum servo travel. This puts extremely high torque on the servo constantly and can ruin a servo with time.
Boom Strike
A devastating event when a landing is hard enough that the momentum of the rotor blades bends them down to the point that one of them makes contact with the boom. This generally destroys the blade, boom, control wire, and tail drive sy stem. This is also one of the most common events experienced by new pilots who overreacted and pushed the heli into the ground.
Brain Fade
A mental condition where the person flying the heli, suddenly forgets which way to move the controls, or which control to move at all. This can happen for no apparent reason, even when you think you're comfortable at flying.
Buddy Box
Two similar transmitters that are wired together with a "trainer cord." This is most useful when learning to fly -- it's the same as having dual controls. The instructor can take control by using the "trainer switch" on his transmitter
CA Glue
A form of "super glue" commonly used in model building, don't use it on foam.
Cyclic-Collective-Pitch-Mixing, CCPM mounts the servo's pushrods directly to the swash plate at 120 degree increments, like an equilateral triangle. With these three servo's the swash plate can be tilted in any direction, and when they all mo ve in the same direction the swash plate can be raised and lowered. All the mixing is done electronically by the transmitter, which means you MUST have a ccpm compatible transmitter.
CG ("Center of Gravity")
For modeling purposes, this is usually considered -- the point at which the airplane balances fore to aft. This point is critical in regards to how the airplane reacts in the air. A tail-heavy plane will be very snappy but generally very unstable and susceptible to more frequent stalls. If the airplane is nose heavy, it will tend to track better and be less sensitive to control inputs, but, will generally drop its nose when the throttle is reduced to idle. This makes the plane more difficult to land since it takes more effort to hold the nose up. A nose heavy airplane will have to come in faster to land safely.
There are two types of "channels" when talking about R/C. One is the channel the Tx transmits on, the other is how many control surfaces a Tx can control.
A weighted fuel pick-up used in a fuel tank to assure the intake line is always in fuel
R/C helicopters use a clutch so that the engine can idle without the rotor blades spinning. Usually they use clutch shoes which when spinning spread out and rub against the clutch drum causing it to rotate and spin the gears.
Centrifugal Force
The imaginary pulling force the helicopter applies to the blades while they're spinning. 
Collective (Variable Pitch)
Describes the control which adjusts the pitch of the rotor blades; causing the heli to ascend or descend without the need to change the rotor RPMs. This is usually the up and down movement of the left stick on the Tx. Having the ability to do this means you can use the momentum of the blades when spinning to do an autorotation if the engine dies and gives quicker response time as well.
Describes the controls which adjust the horizontal attitude of the helicopter, as in roll left-right and pitch forward and backward. Both of these movements are controlled by the right stick.
Dead Stick
The term is more common with R/C airplanes (because you have enough time to say dead stick), but it's a term that describes an emergency landing due to a power loss when the engine quits.
Dialed In
The term used to describe when you're power / cyclic / tail rotor mixing is set up just right, so that when you add power / cyclic the mixing adds / removes tail rotor thrust to maintain the exact same heading without needing input from t he pilot. Usually, you must spend quite some time making the mixing more or less sensitive via trial and error, by rapidly adding and removing power / collective. All heading hold gyro's are already "dialed in" by nature, all that needs to be done is to adjust the sensitivity so the tail does not wag / act sluggish. All mechanical and non hh piezo gyro's will need to be dialed in manually by tweaking the mixing on the Tx. Heavy cyclic inputs also affect the torque on the helicopter and must be mixed w ith the tail if that is possible on the Tx you are using. Again, this is already taken care of with a heading hold gyro and only applies to standard mechanical and piezo gyros.
Dissymmetry of Lift
Describes how the advancing side of the rotor disk is moving faster and thus produces more lift than the retreating side. This causes the helicopter to bank in forward flight and is dampened by flapping blades.
The force that air pushes back onto a moving object when resisting it's movement.
Dual Rates
A feature of some Tx models which allows a person to flip a switch to make the controls more or less sensitive.
This is another airplane term, but is easier than saying "cyclic forward / back." The elevator is what pitches the plane forward or back, to dive or climb, but does not really exist on a helicopter.
A feature of some Tx models that allows a person to program in different control sensitivities depending on the position of the stick. Usually, this means the further the stick movement, the faster the controls. This allows the middle area of the controls to be less sensitive, but also allows full servo travel on the outer limits of the controls.
A feature of some Tx and Rx models that support PCM. Failsafe is used so that the servo's go to a predefined position if the signal is lost. In an airplane this can be to go to a low idle while putting the plane in a gentle turn, but in a helicopter it is not as useful since helicopters are naturally unstable there is no predefined setting to prevent a crash.
Feathering Shaft
A rod which helps support the rotor blades and give them more ridged strength. A flapping head has two feathering shafts (one for each blade) and a sea-saw head has one feathering shaft (running the span of the head)
An abbreviation for Fast Forward Flight. Usually in excess of 50 MPH, or near the maximum speed of the helicopter.
Fixed Pitch
A term that describes a helicopter with no collective adjustments. This means that you control the height strictly with the rpm's of the rotor blades. These are easier to maintain, stronger, and simpler to build but lack major feature s of the collective (variable pitch) type. For one: you can NOT do autorotations with these helicopters and the "vertical control" is much less responsive than the collective of a "standard" heli.
A type of rotor head where the two rotor blades are not connected directly through the feathering shaft (a thick wire), each blade can move somewhat independently of the other resulting in smoother control of the helicopter and the to some degree the feel of a .60 size heli. 
The slang term which describes a R/C heli that has a motor which runs on gasoline.
A device used to automatically hold the rotor RPM constant. Used in conjunction with idle-up modes. This device is not needed, but aids when flying 3D.
Ground Effect
Described as an increase of performance within 1/2 rotorspan of the ground. Which means, near the ground your blades produce more lift.
Ground Resonance
This describes the phenomena that can make a helicopter shake itself to bits on the ground, even when it is perfectly balanced in the air. This is more common in seesaw type heads which aren't as dampened as flapping heads, and is also more common on pavement or hard surfaces which don't absorb vibrations.
Usually a term associated with gyros, it describes the sensitivity of the gyro. Too much gain causes the tail to wag back and forth, while too little gain won't hold the tail steady.
Glow Fuel
The special kind of fuel R/C vehicles typically use. It contains a good portion of nitromethane and other chemicals.
Glow Heater
A device you connect to the glow plug on a engine which heats the coil element so that the fuel can ignite and the engine can start.
Glow Plug
A plug that looks like a small spark plug, but has a wire coil in it which stays hot enough once the engine is running to ignite the next combustion cycle, and keep the motor running.
A device used to help stabilize the yaw of a helicopter. They come in three forms right now. Mechanical, Piezoelectric, and Piezoelectric with heading hold. Mechanical gyros use a real spinning disk inside a small enclosure and help resist the yaw due to the torque of the main rotor blades by adjusting the tail rotor pitch. Piezoelectric gyros do the same thing, but are more accurate / responsive. See Heading Hold for the third type.
Gyroscopic Precession
A physical property of a spinning object too complicated to explain, but to put it simply, is the same reason when you're holding a spinning bicycle tire and you try to turn it, it banks and when you try to bank the wheel, it turns. The rotor blades act the same way, so then when you want to pitch the helicopter forward, the force that the blades must apply would make it seem like it should bank left.
Header Tank
A small fuel tank connected between the main tank and the engine. It purpose is to capture air bubbles / foam that would otherwise be going into the carburetor. This extra fuel tank is mostly used by 3D fliers due to the nature of the ir flights. This small tank can also be used to see when you're about to run out of gas, if you can't see your main fuel tank while the canopy is on.
Heading Hold (HH) or Heading Lock
A feature mode of some gyros that stands out by its property to hold the heading of a helicopter and resist the tendency to weathervane. Once trimmed, the tail needs very little input to hold a directional heading, even in high c ross-wind conditions.
Heli Transmitter
A transmitter with special features for flying helicopters, the most important of which is mixing. Most heli's need at least 5 channels to fly. Computer Heli Remotes allow you do program advanced and custom mixing rates for vario us flying styles. Computer remotes also let you store multiple "models" so you can save all your programming to memory for multiple aircraft. I use 1 model for real flight and a 2nd model for Sim flight.
Hot Start
The ability for the engine to start itself (without the glow-warmer) if you turn the start shaft after the engine has been running a while. This is because the engine is so hot the heater is not needed to cause ignition. This is also da ngerous because it can catch you off guard and send your blades into a frenzy.
The process of flying, while not going anywhere.
Hydraulic Lock
A condition where the cylinder has filled with fuel and can not complete a rotation. Forcing the cylinder to rotate if you try and start the engine can ruin the connecting rod. You remedy the situation by removing the glow plug and letting the fluid drain. This can be caused by over-filling your gas tank which 'spills' into the muffler, from where it has direct entrance into the cylinder.
Idle up
A feature on most transmitters that will not allow the throttle to fall below a minimum setting. This is useful because the vertical portion of the left stick simultaneously controls throttle and collective. When flying inverted you need negative collective, you do not want your engine to go to idle when you move your stick all the way down, so idle-up will keep the RPMs high so you can maintain inverted flight indefinitely. Effectively putting a "cap" on the low-end of the throttle.
Internet Relay Chat, a real-time chat medium that has been part of the internet before the world wide web existed. Here you can talk to many people real-time in groups called "channels." Each channel has a specific topic you're supposed to ta lk about, but as you can imagine, the topic usually drifts.
Jesus Bolt
Most helicopters have two of these bolts. The Jesus bolts are the bolts that hold the main mast to the frame, and the head to the main mast. If you loose either one of these bolts your entire rotorhead will seperate from your helicopter. They're called a "Jesus Bolt" because when they break the pilot was known to say "Oh Jesus!"
Too Lean
This means that fuel to air ratio is too low, and the engine will run hot. This can damage the engine rapidly, so it is recommended to start adjusting the engine on the rich side and work toward the lean end. Usually, turning a needle va lve clockwise makes the mixture more lean.
Loctite (Red / Blue)
A special glue for holding metal to metal screws in their sockets so they don't come loose in a strong vibration environment. Loctite is color coded by strength, red being the strongest and blue being medium. Most people use blue locktite because if red is used the screws may never come out again.
A term that describes a function of many transmitters that allows one control movement to affect more than one control surface at a time. Revolution Mixing is an example of this, but mixing can also be used to add power when you input large cyclic movements.
As in "Fuel / Air" mixture. This balance of fuel and air is what determines the effectiveness of the engine, as well as how fast the engine runs. You tune the mixture with the needle valves.
Needle Valve
A small dial near the carburetor of the engine that adjusts the mixture of fuel and air into the combustion chamber. Some carbs have two needle valves, one for high rpm and one for low. The low RPM also controls how smooth the transi tion is from low to high. .
A term that describes hovering or maneuvering with the nose of the helicopter pointed at the person controlling it. This is a advanced step in the learning stages of flying a helicopter because both roll and yaw are backwards in relation t o the controller.
These are the shorter stubby blades on the end of the two rods opposite the rotor blades. These aid in pitching the main rotor blades for quicker responses and less servo stress.
Paddle Timing
A term to describe how far off the rotation cycle the paddles rotation should be. There is a delay from when the pitch is applied to a paddle and when the paddle is actually moved up or down, it turns out that the paddle pitch must b e applied about 90 degrees before you want the paddle to have risen or lowered. This delay is designed to work with gyroscopic precession which is why the movement of the paddles and blades may make it SEEM like forward cyclic would actually make the hel icopter pitch backwards. 90 degree timing offset + 90 degree gyroscopic precession turns the backward control into the correct movement. This is also why you should look at the swash plate to test the servo reversing, and not look at which way the blade s / paddles move.
PCM is Pulse Code Modulation which means the signal is somewhat digital, meaning the receiver can tell the difference between the transmitter signal and rf noise. Most PCM receivers can be set for a "default" so that when transmission is lost you can have the controls go to a predefined position, this is also called failsafe. PPM is strictly FM, and is susceptible to RF noise, but not as much as AM. PPM, or FM, is the most common because it's cheaper than PCM and the failsafe abilities of PCM are not as useful to a helicopter as it is to an airplane, since airplanes can somewhat fly themselves if trimmed right.
Peak Charger
A peak charger automatically shuts off when your battery is fully charged. This means longer run times for your vehicle. Peak chargers are nearly foolproof, if you forget to turn it off, the charger does it for you. No more overcharged batteries
A maneuver described as a high yaw rate of a helicopter, when the tail spins around the canopy one or more times.
Pitch Meter
A measuring device used to check the varying pitch settings of your rotor blades and paddles. You need the pitch of the corresponding blades to be very close or they will not track evenly.
Pressure Patterns
The distribution of pressure over an airfoil. 
A method of connecting servos to the control points with two connections, one on either end of the servo connection / control connection. This allows the servo to push a connection on one end and pull the connection on the other end. Th is is used to fight slop and use the servo power more effectively by "balancing" the pivot point.
Relative Wind
The direction the wind his hitting the rotor blades taking in to consideration flapping and retreating blades.
Resonance Frequency
Every rotating or shaking thing has a resonance freqency. When something is at it's resonance frequency, every imbalance adds to itself at every cycle. This leads to a force which mathematically goes to infinity and no helicopter can handle those stresses for long. Using large training gear usually change the resonance frequance to right around that point your helicopter likes to hover. This can result in violent shaking even if your blades are balanced and all your mechanics are good. What you can do is change the resonance frequency, or avoid it by changing your hover rpm. Shorten or lengthen your training gear to easily solve this problem, or increase your rpm a bit.
Retreating Blade Stall
A dangerous situation resulting when in fast flight where the blade that is flying towards the helicopters tail looses enough airspeed to generate lift. This can result in loosing control of the helicopter.
Revolution Mixing
This is a mixing function on a transmitter which lets you program a throttle to rudder mix so that as you add more power the transmitter automatically adds more rudder to compensate for the increase in torque. This function should be inhibited if you're using a heading hold gyro.
Rotary Wing Platform
Term which describes the main rotor blades of a helicopter. 
Rotational Velocities
Describes how the airspeed over the tips of the blades is different that that over the other parts of the blade.
Yet another airplane term, but not as common as aileron and elevator. This is what controls the yaw of an airplane, and is synonymous with the tail rotor / vertical stabilizer aka "tail fin."
Rudder Offset
This is a transmitter function that lets you specify a additional amount of rudder trim for idle-up modes which usually have a higher RPM or different blade pitch curve and thus different amounts of torque to compensate for. This function should be inhibited if you're using a heading hold gyro.
Too Rich
This means that the Fuel to Air ratio is too high, and the engine will garble. This does not damage the engine, but it does drastically reduce the power output. Usually, turning the needle valve screw counter-clockwise makes the carburet or run more rich.
Abbreviation for Receiver, the portion of the radio system that is mounted in the helicopter and adjusts the servos according to the transmission from the Tx.
See-Saw Head
A form of rotor head where the two rotor blades are "connected" through a feathering shaft (thick wire) so that when one pitches up the other pitches down. This makes for a more stable helicopter an a simpler design, but does not hand le as well as a flapping head type.
A device that can turn a lever arm one way or the other with many points between the two extremes. These adjust all the control points of a R/C vehicle.
Settling with Power
A dangerous condition when descending from a hover where the helicopter's rotor blades enter their own down-wash. This can cause a crash if you don't recover soon enough. Note: This is not a fatal condition on model helicopters because they have such a huge power to weight ratio, however it can catch you off guard and it does require more time to stop descending if you're in this state.  
Describes the imprecision of a control system, meaning the controls can be "wiggled" without the servo's moving. Slop can make the helicopter more unpredictable and less responsive to control input.
There are two stabilizers, the horizontal and vertical. These help the helicopter to weathervane, so that while in forward flight, the helicopter points into the wind. 3D fliers will have smaller stabilizers so that they can fly sidew ays / backwards faster without weathervaneing. The vertical stabilizer also prevents the tail rotor from hitting the ground.
This is a feature of many transmitter models that allows you to adjust the trim of control surfaces while still having the trim control on the Tx centered. This way you have full trim adjustment while flying.
Swash Plate
A device that the control arms spin around on so that the pitch of the blades is changed depending on their relative position to the helicopter.
A particular subject being discussed on a news group, or the grooves that a screw has / grooves that a screw screws into.
Throtle Curve / Pitch Curve / Programmable Points
Somewhat like exponential in that you change the way the servos move as you move the stick. Usually you would have a different curve setting for each idle up mode. In idle up one you might have th e throttle at 100% when the left stick is full down, at 50% when it's in the middle, and back to 100% when the left stick is full up. This way you can fly upside down. Some radio's have more curve points than others, which means you could have parts of the stick less sensitive than others, so you could make it easier to hover gracefully on a machine with a very sensitive collective.
Throttle Hold
A feature that comes with many transmitter models. The opposite of Idle-Up, as in, this switch will keep the throttle at idle so that you can increase the collective without gaining high rpms / power. This switch can be used as a "s afety" switch while you carry your heli to the flight line, but is more commonly used to practice autorotations or if tail rotor control is lost causing the heli to pirouette rapidly opposite rotor blade direction, because when the engine is at idle, the tail rotors loose power so the heli will slow down it's pirouettes and you can autorotate to the ground in a more controlled manner. It is also advisable to hit this switch in the case of an emergency so that if the heli hit something it has no power bei ng applied to the rotor / tail blades.
Torque is applied to the body of the helicopter because of the engine spinning the rotor blades, this causes the helicopter to want to spin in the opposite direction of the rotors.
Total Aerodynamic Force
The net force vector applied by the various forces of lift.
TR or T/R
Short for Tail Rotor. Used to counter the torque then engine puts on the rotor blades which left unbalanced would make the heli spin like crazy.
Training Gear
Larger landing gear so that landing at a angle is less dangerous. Beginners use these while learning to hover and they typically are made of two crossing sticks with whiffle balls on the ends.
If the pitch of both rotor blades is not exact, one rotor blade will be slightly off axis of the other blade, it will look like one blade is higher then the other. Viewed from the side with blades at eye level rotor blades would look like this: >< Ideally, you want perfect tracking, so that the blades appear to be perfectly flat and look from the side like this: --
Translating Tendency
When holding a heading with a helicopter hovering level the force the tail rotor puts on the helicopter to keep it aligned causes the entire helicopter to move the opposite direction of the tail thrust. This is compensated wit h right-cyclic in most US helis, but depends on the direction the rotor blades spin.
Transitional Lift
When in forward flight, the spinning rotor disc produces more lift than in a hover. 
Transverse Flow Effect
When in a slow forward flight, wind in the rear part of the disk enters at a lower angle of attack due to the leading edge of the disk pulling air down, which results in vibrations. 
Abbreviation of the remote control unit. "Transmitter"
When you're talking about a wing or a rotorblade, washout is a twist in the blade so that part of it is at a different angle of attack than the rest, allowing you to recover from a stall before it's too late. The term washout mixers, levers or arms are also used in the rc helicopter community and are referring to the mixing arms that connect directly to the top of the swashplate and are mixed with the paddles and main blades through a set of linkages and joints.
The property of the helicopter to point into the wind like a windsock. The amount of weathervaining is determined by the size of the vertical stabilizer.
A funnel shaped tube of fabric that generally signifies a 10 knot wind when fully extended.
Yaw Rate
A term that describes the control input of a heading hold type gyro. Instead of the rudder control adjusting strictly the tail pitch, as it does with a other gyro, a yaw rate gyro will uniformly control the rate at which the helicopter ya ws.
Yaw / Pitch / Roll
Terms that describe the change of attitude of a helicopter. Yaw is the movement about the vertical axis; Pitch describes leaning forward or backward; and roll describes leaning to the left or right (bank).

A simple Z-shaped bend in the wire end of a pushrod, which is used to attach the pushrod to a servo output arm

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