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To some, it means "any maneuver that an airplane cannot perform." Backards and sideways flight, sideways rolls, and so on.

To me, good 3D isn't just about unconventional orientations, it's about interesting and graceful transitions from each orientation to the next.

The FAI is a global organization that sanctions all sorts of contests having to do with flying things, from rubber-band-powered free-flight contraptions to model rockets to full scale aerobatics and racing. RC helicopters are somewhere in there, too. FAI events are known by codes such as "F1A" (for precision aerobatics with RC planks) and "F3C" (for precision aerobatics with RC helicopters).

Learning to auto is one of the challenges that every helicopter flyer must eventually overcome. If your engine should quit unexpectedly, this skill is the only thing that will save your helicopter, not to mention any people and property below it.

Modern helicopter radios include provisions for a flight mode call throttle hold, which tailors the pitch range for autorotations.

If a helicopter hovers with 5 degrees of collective pitch, it will rise vertically when collective pitch is increased above 5 degrees, and it will descend vertically when collective pitch is decreased below 5 degrees.

"Positive" collective pitch is used to keep the helicopter airborne while it is upright; "negative" collective pitch is used to keep the helicopter airborne while it is inverted.

Most helicopter flyers in the western hemisphere use a "mode 2" radio setup that the controls collective pitch with the up-and-down movement of the transmitter's left stick.

Due to gyroscopic precession, the effect of the pitch change happens 90 degrees after the pitch change takes place. In the example above, a helicopter with clockwise main rotor rotation would roll to the right, which probably isn't what you expected!

Most helicopter pilots in the western helisphere use a "mode 2" radio configuration, in which the cyclic pitch is controlled by the transmitter's right joystick.

Dial indicators are also used to check the clutch, and sometimes the tail rotor output shaft.

On the other hand, if you're working on aerobatics, you might want a setup where full stick movements give all of the available servo movement. The advantage is that your rolls will be over quickly and you'll be back to an orientation you're comfortable with. The drawback is that the control response can be uncomfortably 'twitchy' for hovering and close-in flight.

Dual rates solve these problems by allowing you to select between two control rates at the flip of a switch. You can select 'low' rates for precise hovering and 'high' rates for aerobatics. Modern helicopter radios provide dual rates for the cyclic and rudder controls. More expensive radio system provide more than dual rates - you may be able to select between three rates, or more. Some contest flyers like to fine-tune the control rates for specific maneuvers, some go as far as to set up specific rates for every maneuver they will be required to perform.

Take a look at exponential control, too.

Exponential allows you to make the controls softer around the center of the stick movement, while retaining full control movement at the extremes of stick movement. The idea is that while you're hovering you will mostly be making smaller stick movements, and you'll enjoy the reduced control rate. But while you're doing aerobatics you'll be moving the sticks to their extremes, and you'll want the servos to move to their limits as well.

It's best described with a picture, but I don't have a picture yet. Bear with me.

Take a look at dual rates, too.

It's enough to give you wacky brain syndrome!

Modern helicopter radios allow you do set up different flight modes to solve these problems. Each flight mode has its own pitch curve, throttle curve, and tail rotor curve. Flight modes are typically called normal mode, idle-up-1, idle-up-2, and throttle hold.

The throttle hold flight mode is a bit different than the rest because its throttle curve and tail rotor curves (if you can call them curves...) are just flat lines - you get the same throttle and tail rotor trim settings no matter where the collective stick is at. That's ok though, because you want the engine to be idling the whole time, and you do not want the tail rotor trim to vary during the auto.

A few full-scale helicopters also use flybars, but most do not. Everything happens a bit more slowly in a full-scale helicopter, and the pilot is sitting right there inside of it, so the bad habits are considerably easier to deal with.

The term also describes the style of competition at these gatherings, which is typically less rigorous than FAI F3C competition, but still more disciplined (and hence easier to judge) than freestyle competition. Comment events include timed "pad hopping" for novices, timed aerobatic routines for experts, precision "spot landing" autos, and so on.

Contrary to popular suspicion, the position of the header tank has no effect on the mixture. At least until the main tank runs out... but if you run the main tank empty, a change in mixture is not a bad way to remind yourself that you're about to run out of fuel. It beats a surprise autorotation, anyhow.

While standard gyros are based on simple proportional (P) feedback, heading hold gyros use integral feedback as well (PI). Integral feedback allows the gyro to not only damp unwanted yaw movements, but to return to the original heading after an unwanted yaw movement has disturbed the helicopter's orientation. For 3D flyers, heading hold makes life a whole lot easier.

The main drawback is that for normal forward flight, the weathervaning tendency of standard gyros is actually welcome - it keeps the helicopter from 'crabbing' slightly sideways across the sky. This is why some people - especially contest flyers - prefer standard gyro functionality for some maneuvers.

There is no "correct" head speed, but some helicopter/engine/exhaust combinations tend to run best with head speeds within a given range. The combinations are too many to list here, but if you need advice for your specific setup, you should seek out people who are using the same equipment and find out what they have found to work best. Also bear in mind that personal preference is a large factor here!

When you get into aerobatics, you will find yourself wanting more negative pitch to sustain inverted flight. That's what the idle-up-2 flight mode is for.

The only drawback to this flight mode is that with all that collective pitch range at your disposal, the the collective stick becomes rather touchy. This is no big deal with a 60-class helicopter, but when you've hovering a 30-class ship it can be more trouble than it's worth. I'm fond of using idle-up-1 for hovering during contests, even with my 60.

You will usually notice excessive vibration when the helicopter is spooling up at the start of a flight, due to the fact that the rotor blades are not yet in their optimium lead/lag positions. Once centrifugal force has pulled the rotor blades to their optimium positions, the vibrations decrease dramatically.

Most engines have at least two mixture adjustment valves, which let you tailor the amounts of fuel into the engine at idle and full throttle. Many engines also have a 'midrange' mixture valve, which lets you adjust the air/fuel ratio around half-throttle as well.

If carburetors only did mixture adjustments, the engine would run at full speed all the time. That's why carburetors also have throttle control built into them.

Unfortunately, mufflers don't just make engines less noisy, they also make them less powerful. Tuned pipes were invented to address that problem.

When you're first learning to fly, you will use this mode all of the time, just to keep things simple. When you graduate past the training gear stage, you should start using idle-up-1 for most of your hovering. The problem with flying in normal mode is that the bottom half or bottom quarter of the collective stick movement will allow the throttle to drop off too far, causing the rotor head speed to decay, which in turn causes the controls to feel mushy, which in turn makes it much too easy to crash.

When you're learning, you will want to set this up with a limited pitch range, perhaps 0 to +8 degrees. Having less negative pitch available makes it less likely that you'll accidentally slam the helicopter into the ground. Once you're confident with hovering, I suggest setting up this flight mode with the same pitch curve and throttle curve that you use for idle-up-1, with the sole exception of the low-stick throttle setting, which should be set to whatever gives you a nice idle.

(1)Pitch can mean the angle of a rotor blade, measured in degrees. More pitch generates more thrust. Zero pitch generates no thrust. Positive collective pitch causes the helicopter to rise, negative collective pitch causes the helicopter to descend very quickly, or climb inverted.

(2)Pitch can mean rotation of the helicopter about a horizontal axis. If you pitch 360 degrees, you've done a loop. Airplanes use elevator to control their pitch.

British folk sometimes reduce the confusion by using the word "nick" for this instead. The transmitter's right stick controlls "nick" and roll, for example. Damn foreigners.

Take a look at yaw and roll too.

Modern helicopter radios use a feature called a 'pitch curve' to allow you to determine exactly how much collective pitch you want at high stick, low stick, mid-stick, and often the 1/4 and 3/4 positions as well.

It can mean a change in orientation about a horizontal axis. If you roll a little bit to the left, the helicopter starts moving to the left.

It can also mean an aerobatic maneuver in which the helicopter rolls 360 degrees, usually while travelling forward. In this case, the helicopter said to have 'done a roll.'

Airplanes use ailerons to control roll, helicopters use cyclic pitch to control roll, but lots of us call it aileron anyhow.

See also yaw and pitch.

• one for collective pitch
• two for cyclic pitch
• one for throttle
• one for tail rotor (rudder)

The horizontal stabilizer is mostly just there to cover up the places where the tail boom supports attach to the tail boom (it looks nicer that way), and the vertical stabilizer is there to keep the tail rotor blades from hitting the dirt during those imperfect landings that we all have from time to time.

When the swashplate tilts, it imparts cyclic pitch upon the rotor blades. When the swashplate slides up and down the main shaft, it imparts collective pitch upon the rotor blades. When the swashplate comes apart, you're screwed.

Note that a few helicopters use the swashplate for cyclic control only. A separate set of links runs parallel to the main shaft (or through the center of the main shaft) to carry collective servo movements to the rotor head, where they are mixed with the swashplate movements. It's not a better or worse way to do things, just different.

The tail rotor blades are attached with a mechanism that gives them collective pitch, so the tail rotor thrust can be varied to accomodate different amounts of force on the main rotor (not to mention the pilot's occasional desire to point in a different direction).

A very few helicopters used a fixed-pitch tail rotor, whose thrust is varied by changing the tail rotor's speed. These helicopters use an electric motor whose sole job is to spin the tail rotor. It works well enough for small electric helicopters, but that's about all. The delay while you wait for the tail rotor to speed up and slow down is short, but it's still long enough to result in sloppy response, and unwanted yawing movements.

Look at mixture too, that's the other thing carburetors do.

Modern helicopter radios use a feature called a throttle curve to allow you to set the exact amount of throttle you want at various throttle stick positions. Further, most radios allow you to set up different throttle curves for starting, hovering, aerobatics, and so on.

See the section on flight modes for more information.

When learning autorotations, a pitch curve with a range of approximately -3 to +11 degrees is suggested. For advanced autorotations, a most symmetrical pitch curve works better - perhaps -10 to +11 degrees.

The throttle should be set for a reliable idle. I'm personally fond of a fast idle, to reduce the chance that the engine will flame out if I botch the autorotation and need to switch out of throttle hold in a hurry.

The classic training gear system is two wooden dowels, 3/8" diameter and 3 feet long, zip-tied or rubber-banded to the landing gear in an X pattern, with whiffle balls attached to the ends. More sophisticated versions allow the helicopter to yaw idependently of the training gear (e.g. the RotoPod) or provide more shock absorption.

Before spending large sums of money on your training gear, remember that you are trying to quit using the gear as soon as possible. How much money do you want to sink into something that you'll stop using as soon as possible?

In forward flight, trim can change. I have one helicopter that needs a bit of extra forward cyclic in order to maintain straight-and-level forward flight. I have another that requires a bit of left cyclic. With a standard gyro (not heading hold), some left tail rotor trim is usually required to keep the tail directly in line behind the helicopter.

Without uniflow, you will usually lose fuel pressure as the tank empties, which causes the mixture to go lean. This can be annoying.

British folk sometimes use the word 'weathercock' instead, presumably because most weathervanes are cut out with a rooster shape. Damn foreigners.

Airplanes use rudder to control their yaw. Helicopters don't have rudder, but they use tail rotor thrust to accomplish the same thing.

Yaw control would be extremely difficult if not for the gyro. You wouldn't believe how slippery a helicopter is without a gyro, unless you've tried it yourself. Quite a challenge. I don't recommend it.