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.
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
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
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 amount of backlash.
Base Load Antenna
A short "whip" antenna about 6 inches
long used instead of the long dangly antenna that comes with
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 control 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
A bad condition where the control
adjustments 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.
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 system. 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.
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.
A form of "super glue" commonly used in
model building, do not use it on foam.
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 move 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
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.
The term is more common with R/C
airplanes (because you have enough time to say dead stick),
but it is 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 with 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
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
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.
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
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. You can NOT do autorotation 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
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 rotor blades will be used up before you land
causing the helicopter to drop like a rock and again, slam
into the ground.
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.
Described as an increase of performance
within 1/2 rotor span 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.
The special kind of fuel R/C vehicles
typically use. It contains a good portion of nitro methane
and other chemicals.
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.
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.
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
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 their 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
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 cross-wind conditions.
A transmitter with special features for
flying helicopters, the most important of which is mixing.
Most heli need at least 5 channels to fly. Computer Heli
Remotes allow you do program advanced and custom mixing
rates for various flying styles. Computer remotes also let
you store multiple "models" so you can save all your
programming to memory for multiple aircraft.
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 dangerous because it can catch you
off guard and send your blades into a frenzy.
The process of flying, while not going
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.
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 RPM 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 rotor head will separate from
your helicopter. They're called a "Jesus Bolt" because when
they break the pilot was known to say "Oh Jesus!"
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 valve clockwise makes the mixture more
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 loctite 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.
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 transition 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.
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 helicopter 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
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. This is used to fight slop and
use the servo power more effectively by "balancing" the
The direction the wind his hitting the
rotor blades taking in to consideration flapping and
Every rotating or shaking thing has a
resonance frequency. 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 frequency
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
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
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.
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
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
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 sideways / 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
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 /
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 the 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
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 "safety" switch while you
carry your heli to the flight line, but is more commonly
used to practice autorotation 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 being applied to the rotor / tail
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 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.
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.
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 separation! 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 yaws.
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