High performance flying, usually combining two maneuvers at once. For example, mixing a loop and a roll, to loop while rolling etc...
A high speed climb followed by a 540 degree Pirouette as the heli stops climbing. See Pirouette.
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
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.
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.
Battery Eliminator Circuitry (BEC)
A circuit that eliminates the need for a separate receiver battery by using the battery pack that powers the vehicle or aircraft to also power the servos.
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.
When a blade on the upper rotor of a coaxial helicopter strikes a blade of the lower, opposite rotating rotor, usually resulting in the destruction of both blades. Usually only happens when attempting extreme maneuvers.
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.
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.
In brushed motors the magnets are attached to the case and the windings (coils of wire) are wrapped onto an iron armature and shaft. The power is fed in through brushes which together with the "commutator" changes the direction of the current through the motor's windings as the armature rotates.
There are a few problems with this layout. The windings are pretty heavy to rotate and they are in the middle of everything so they have trouble getting rid of any waste heat that is created. The brushes make imperfect contact with the commutator especially as currents and speeds get higher. There are quite a lot of losses in this setup. In practise a brushed motor will rarely be more than about 65-70% efficient and many are difficult to get more than 50% efficient in our sort of high-power application.
Coreless motors are very similar to the above except that the coils are not wrapped round a metal armature but are simply fastened into shape with glue, generally epoxy. This makes the armature much lighter and hence faster to accelerate which makes them good for servos. On the other hand it means they will not stand sustained high speed (revs/min) or loads without falling apart. Coreless motors are generally very small, low speed, low power devices. As flight motors they are only of any use for small indoor planes. E.g. Wes-Technic have a range of coreless motors for just that purpose. Normal brushed motors do come in different qualities. The main difference is in the material of the magnets. Standard (also called can or ferrite) motors have magnets made of ferric oxide. These include probably the most common type of motor used for electric flight, the Graupner Speed xxx series (where xxx denotes the size, 400/500/600 etc). These come in a wide range of sizes, styles (plain bearing, ball bearing, race etc) and different voltage ratings. Note that the voltage ratings refer to how the motor is wound. For electric flight we invariably use a higher voltage than nominal and therefore use more power than the "official" design powers. E.g. a Speed 400 7.2V motor will usually be run on 7 or 8 cells (8.4V or 9.6V), sometimes more.
The conventional brushless motor has the windings attached to the case and the magnets attached to the rotating part. Brushless motors work by electronically switching the motor current on and off in the different windings so there is no commutator and no brushes to bounce and loose efficiency. This is why brushless motors need special controllers.
Because the coils are in contact with the case they can get rid of the waste heat better. This allows the brushless motor to use more power and run faster. The brushless motor is both more efficient (using more of the power in the pack for flying and less for heat) and able to work efficiently over a greater range of cells and currents.
The two main sub-divisions of brushless motors refer to how the current through the windings is sensed and controlled. The original motors had small sensors inside to sense the position and movement of the armature and allow the electronics to control the current to the windings. These have typically 3 main heavy duty wires which carry the drive current and additionally a set of small wires (often 5 or 6) connected to the internal sensors. They generally work only with specific controllers from the same maufacturer.
Advances in electronics now allow the current to be controlled without the need for these sensors, which are relatively fragile and take up space which could otherwise be used for magnets or windings. You will be surprised to hear that this newer type of motor is known as "sensorless". This technology allows you to select the controller and motor separately again (for best of breed). There used to be a considerable cost to this. The sensorless controllers were VERY expensive but the latest improvments in software and electronics have made them a lot more affordable. Almost all the current production brushless motors are sensorless. In fact a sensorless controller can also be used with a conventional brushless motor (you just don't connect the sensor harness).
The latest type of brushless motor available is the so-called "outrunner" like the Model Motors AXI types. At first sight these are rather odd. They are arranged the same way round as a brushed motor with the coils in the centre and the magnets on the can. But...it is the CAN which rotates NOT the centre armature. This means they are a bit tricky to mount since you obviously can't just clamp them down but it does have one BIG advantage. These motors generate much more torque than a conventional arrangement. In practise what this means is that they will turn a much larger and more efficient propeller without needing a gearbox. Gearboxes of course add complexity, cost and weight so that's a real advantage. As far as the motor designations go there are no standards for brushless motors. Each of the manufacturers has their own style. You need either to be able to read and understand motor constants or, better yet, to ask the manufacturer/seller. Since these motor/controller combinations are still relatively expensive you can expect to get individual attention to your queries from the better suppliers in a way that is not possible for the cheap "can" motors.
Brushless Motor KV (kilovolt)
Brushless motors are given a Kv rating, which is RPM per volt, that lets you determine how fast that motor will rotate with a given voltage supplied to it. A 980Kv motor powered by an 11.1V battery would spin at 980 x 11.1 = 10878 RPM with no load.
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 (cyanoacrylate)
A form of "super glue" commonly used in model building, don't use it on foam. (They do make a "foam safe" CA.)
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.
The imaginary pulling force the helicopter applies to the blades while they're spinning.
A helicopter possessing two main rotors that rotate in opposite directions and no tail rotor. The rotor shafts rotate about the same axis, one being hollow and the other being solid and nested inside the hollow shaft.
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.
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.
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.
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.
Electronic Speed Controller. An electronic device that takes the power from the battery pack and the signal from the receiver and measures a certain amount of power to the motor.
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.
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.
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.
Mostly used when talking about airplanes and landing. To flare is when your about to land and pull up just before touchdown and hold until you run out of enough airspeed to fly any more and the airplane sets itself on the ground. With helicopters this is usually referring to the end of an autorotation where you start to add positive pitch back in the blades to slow down your decent. Flare too late and you slam into the ground. Flare too soon and all the energy in the rotorblades will be used up before you land causing the helicopter to drop like a rock and again, slam into the ground.
A free-swinging, weighted bar linked to a rotor that stabilizes the helicopter.
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.
Described as an increase of performance within 1/2 rotorspan of the ground. Which means, near the ground your blades produce more lift.
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.
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.
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.
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.
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.
The process of flying, while not going anywhere.
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.
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!"
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.
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.
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 / PPM
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.
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.
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.
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.
The direction the wind his hitting the rotor blades taking in to consideration flapping and retreating blades.
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.
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.
The rotating wings that are found atop a helicopter. The rotor blades swing, generating lift in the process. The blades perform the same function as an airplane wing (they provide lift).
Rotary Wing Platform
Term which describes the main rotor blades of a helicopter.
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."
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.
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.
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.
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. (contols cyclic/pitch on collective heli's)
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.
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.
TBE (Toilet Bowl Effect)
A behavior, mainly with coaxial helicopters, where the helicopter will start moving in ever-widening circles, with or without tail rotation. It can have a number of causes such as non-tracking rotors or a restriction in the swing of the flybar.
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.
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: --
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.
The extra lift that occurs as a helicopter starts transitions from hover to, especially forward, flight. The lift increases because the main rotor efficiency improves as it begins to cut into relatively undisturbed air.
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.
Woof and Poof
Named after the sound it makes when the rotor blades go wildly out of track, 4 inches or more vertical seperation! The cause of this is debatable, and there seem to be many ways to help fix it, such as lubricating the rubber dampeners, replacing the blades, tightening the blades, reducing slop and reshrink-wrapping the blade covering.
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