Monday, 18 August 2008



Electric helicopters are hot. Motors are improving, batteries are getting better all the time and kit manufacturers have responded with some really good helicopter kits designed for electric power.

The emphasis here is on getting started in electric helis. This doesn't cover everything you need to know, but hopefully explains some concepts and jargon to make radio-controlled helicopters less of a mystery. If you already fly fixed wing, you can experience the exhilaration of learning to fly again. But you may need to allow a few months to get everything together.

I still have a lot to learn about helicopters. What I have learned so far is still fresh in my mind. I have not tried a small indoor helicopter yet, so my knowledge is limited in this area.
So far, my experience is limited to the following machines:

Kalt Whisper - my first heli and the first commercially available electric helicopter that flew well. I learned to hover with this helicopter.

Hirobo Shuttle - this is the helicopter I learned to fly around on. It is a "30 Size" glow helicopter converted to electric. The Brushless power system used in this helicopter gives it enough power to fly with authority.

Logo 20 - this is a very good electric helicopter roughly equivalent to a "45 Size" glow heli. It is very stable and capable of full aerobatics. With 24 cells it performs very similar to an aerobatic glow-powered heli

Electric helis have improved a lot over the past few years. The larger ones now fly very similar to their glow counterparts and indoor helis that fly well are available. As a testament to how well the new breed of electric helis fly, some accomplished glow heli pilots have added electric helis to their fleet. That is not to say they are replacing glow helis in competition yet, but they are certainly capable of impressive aerobatics and their relatively quiet turbine sound and smooth flight characteristics make them pleasant to fly.

A Few Heli Basics

Unlike fixed wing aircraft, helicopters employ a rotary wing. The wing rotates at a nearly fixed speed moving throughthe air constantly to give the heli the ability to hover. The characteristics of the rotary wing can be changed somewhat by swapping main rotor blades.

Helicopters store a lot of kinetic energy when the rotor is up to speed. Just tipping a helicopter over with the rotor atfull speed can cause quite a bit of damage.

To avoid unwanted reactions that would tend to rotate the helicopter, it is very desirable to maintain a constant headspeed at all times. This is not possible with fixed pitch helicopters as they require speed changes to increase and decrease lift.

In most helicopters, the tail rotor is a variable pitch propeller driven by a shaft or belt from the main motor. This isbetter than a variable speed prop because it is capable of faster thrust changes. The tail rotor has two key functions.
Firstly, it allows the yaw (direction of the nose or tail) of the helicopter to be controlled, particularly in a hover.
Secondly, it counteracts the reaction torque resulting from drag in the main rotor blades. In a hover, the tail rotorblades will have a small pitch to counteract this torque. This also causes the helicopter to have a slight tilt in a hover to counteract the sideward thrust of the tail rotor. Cool.

What is Revolution Mixing? Revolution mixing increases the pitch of the tail rotor blades as the pitch of the main rotorblades increases or decreases from 0 degrees. This is necessary because the drag in the main rotor blades increases as their pitch moves farther from 0 degrees. Revolution mixing should never be used with heading hold gyros because they are absolute and control yaw (the direction the nose is pointing in the horizontal plane) on their own.

What is cyclic pitch and what is collective pitch?
All helicopters have cyclic pitch control, which is the ability tovary the pitch of the main rotor blades as they revolve. This gives the helicopter the ability to tilt, and therefore the ability to direct thrust to move in any direction. The extra mechanical linkages in the rotor head facilitate mechanical mixing (usually Bell-Hiller mixing) for added stability in flight. Collective pitch, as the name suggests, tilts all the main rotor blades in the same direction at the same time, giving the helicopter the ability to ascend and descend in a very responsive manner without changing the rotor head speed. This is a very desirable feature.

Helicopters fly quite differently with different head speeds. When the main rotor is rotating relatively slowly, more pitchis required to lift off the ground and the helicopter becomes sluggish with poor control of the tail. At high head speeds, the helicopter transforms into a spritely beast that is more sensitive to control inputs at the cost of somewhat reduced flight time.

What is an "Auto" and why is it important?
"Auto" is short for autorotation. Autorotation is basicly the spinning upof the main rotor blades using only the helicopter's kinetic energy (speed) and potential energy (height). An auto is used to fly the helicopter down to the ground without power. Assuming the helicopter is upright, this is done by giving the main rotor blades a negative pitch (say -4 degrees or so) so that they act as a windmill to maintain sufficient rotating speed to control the helicopter as it descends. Knowing how to auto can save a helicopter in the event of a motor failure. An auto is not possible with a fixed pitch helicopter.

How tight should the bolts be securing the main rotor blades?
This is a question I originally had difficulty findinga good answer for. It appears it is not extremely critical, but it is beneficial to have them tight enough to avoid unwanted pivoting of the blades when spinning the rotor up at startup and for autorotations.

What is a pitch curve?
Helicopter radios usually have 5 set points on the left stick for setting a pitch curve. Thepitch of the main rotor blades at various positions can be set to control the vertical ascent/descent rates.

What is a throttle curve?
The throttle curve works hand-in-hand with the pitch curve. The speed of internalcombustion (glow) engines varies drastically as the load changes. This makes the use of a throttle curve (or a speed governor) mandatory in glow powered helicopters. Many throttles for electric helis have speed governors built in. To some extent, it is possible to get away without a throttle curve in electric helis that don't already have a built-in speed governor. This is because electric motors do not spin up above their specific speed when unloaded and they increase power output much more rapidly as the torque load increases. In helis, the load on the motor increases a lot as the main rotor pitch moves farther from 0 degrees during flight. It also increases when cyclic pitch is increased or as the tail rotor pitch increases but this is often ignored. If a speed governor is used, a flat throttle curve or throttle control via another variable radio channel is required.

What are Normal, Idle Up 1 and Idle Up 2 modes?
There is a switch on helicopter radios that allows one of several preset pitch and throttle curves to be selected. Normal mode is set up to allow the motor to stop at minimum throttle stick throw and uses gentle pitch changes around hover for smoother control. Negative main rotor pitch is usually
limited to a few degrees. Idle Up modes are intended for maintaining power to the main rotor at all times - even with negative main rotor pitch. This gives the helicopter the ability to hover inverted and is used for sport and "3D" aerobatics.

What is Throttle Hold?
Throttle Hold shuts off the motor while maintaining control of all other helicopter functions. It is used mainly for practicing autorotation landings, but can also be used as a safety switch for electric helis to make sure the motor remains stopped prior to, or after a flight. In the event of tail rotor or gyro failure, Throttle Hold can save a helicopter that would otherwise spin hopelessly out of control with a safe autorotation landing.

Because it is constantly spinning, the main rotor of a heli is not as visible in flight as the wing of an airplane. Also, in a standard "pod and boom" helicopter configuration, the fuselage cross section is small. These combine to make it a bit more difficult to pick up the orientation of a helicopter in the air. This can be compensated somewhat by fitting a scale fuselage or by buying a larger helicopter. :-)

Unlike the tail of an airplane, the tail of a heli can easily rotate - mostly when the aircraft is stationary or moving slowly.Needless to say, this can cause severe orientation and control problems for the beginning pilot! Today, gyros are universally used to stabilize tail (yaw) of the helicopter. A good gyro and tail rotor pitch servo combination can transform a slow or squirrelly tail into one that is rock solid and responsive.

There are two types of gyro - rate and heading hold (HH). A rate gyro applies a corrective control input based on therate at which the helicopter is rotating in the yaw axis. A heading hold gyro is absolute and tries to maintain the heading or rotation speed input by the pilot. Heading hold gyros can also operate in rate mode.

Gyros are often sold paired with a servo because the characteristics of the servo has a great impact on the ability ofthe gyro to control the tail. The Futaba GY401 solid state gyro is sold with the S9253 digital servo for example and is an excellent combo. All good gyros sold today are of the solid state variety.

Fixed pitch helicopters have cyclic pitch only. The average pitch of the blades through one revolution is fixed suchthat ascent and descent in a hover is controlled only by changes in rotor speed.

Collective pitch helicopters add the ability to independently control the pitch of the main rotor blades. This makes thehelicopter much more responsive to vertical control inputs and makes autorotation possible provided the helcopter is equipped with an autorotation clutch. An auto clutch is a one-way bearing that allows the main rotor to freely rotate when the motor has slowed or stopped.

What's all this about 120-degree CCPM?
CCPM stands for Cyclic Collective Pitch Mixing. 120-degree CCPM is a variant characterized by minimal mechanical complexity and servo-to-swashplate connections that are 120 degrees apart. The benefits and drawbacks to this approach are often debated at length on discussion boards, but the main impact of 120-degree CCPM is the need for a suitable program in your helicopter radio to handle it. Basicly, the simpler mechanics of 120 degree CCPM requires a more sophisticated program in the radio. Many helicopters can be configured for several different CCPM modes so if you don't have all the latest radio equipment you are not necessarily out of luck.

Helicopters, particularly larger ones, require strong, reliable servos. These are often coreless or even digital. Toincrease the gyro feedback gain and better stabilize the yaw of the helicopter, a good tail rotor servo is very fast and employs digital technology.

There is no substitute for a good gyro/tail servo combination. This can make tremendous changes in the yaw stabilityand response of the helicopter.

It is extremely important that the linkages in helicopters operate smoothly and freely but not loosely. Stiff linkages willmake the helicopter handle poorly and cause premature failure of the tail servo. Free linkages are not automatic - many helicopters kits require extra effort during assembly to ensure smooth operation. In this regard, do not assume that just following the instructions will result in a good flying heli. The JR Ball Link sizing tool or similar is almost mandatory for assembly of most helicopters.

A proper heli radio (or at least a radio modified to emulate a heli radio) is strongly recommended. Radios for helishave switches in different places than aircraft radios and have a smooth (unratcheted) throttle stick action. It is best for student and instructor to use the standard heli configuration. If you are learning to fly and you hand your non- standard radio to your instructor, the result may not be pretty.

Base loaded ("Deans") antennas can be useful in a heli. It is nice not to have a long antenna wire strung outside theheli. In some instances, it is also easier to keep a short base-loaded antenna away from the electro-magnetic interference generated by the electric power system.

What rotor blades should I use?
Depending on the type of helicopter, there may be many choices of helicopter blades. Semi-symmetrical blades provide more lift but are not suitable for so-called 3D aerobatics. These are
commonly used in smaller helis. Full symmetrical blades are most often used. Wood blades are fine for general
flying around. Glass and carbon fibre blades should be stiffer and provide crisper performance.
What about upgrade components? Many heli upgrades seem to be more "show" than "go" and do little to improvethe flight characteristics of the heli. There are a few exceptions. For example, the Carbon Fibre Vertical Stabilizer upgrade is almost mandatory to protect the Logo 20 tail rotor in less-than-perfect landings.

Generally speaking, the more ball bearings a heli has the better. Ball bearings (also called anti-friction bearings) haveless friction and maintain clearance better over time than sleeve bearings. In good helis, double ball bearings are often used in linkages to further improve precision. The races of ball bearings will brinell (get small imperfections that result in increased roughness and noise) if static loads are too high. Shock loads and improper installation (for example, pushing hard on the outer race of a bearing to force it onto a tight fitting shaft) can cause this brinelling of the races and reduce bearing life. Reasonable precautions should also be taken to keep dirt and grit out of the races of ball bearings.

Tools for helis

Some different tools are required for helis. Some recommended tools include:

Good small slotted and cross-recess screwdrivers
Small (Ignition) wrenches
Ball sizing tool
Ball link removal/installation tool
Balancer - i.e. High Point
Blade pitch measurement device

Characteristics Unique to Electric Helicopters
Unlike glow powered helis but like electric airplanes, electric helis are self starting. Depending on the smoothness ofthe throttle, the main rotor may start up fairly quickly.

Most electric heli throttles feature a built-in speed governor mode. Glow heli pilots have to buy additional hardware forgovernor control. It is also possible to control the throttle without using the normal throttle channel of the radio. If an extra channel can be controlled by a variable knob or slider this can be used to control the speed setting for the governor. This is preferred approach for some heli pilots.

Electric helis are very stable in a hover thanks to the stable power output of the electric power system.

Electric helis do not require a clutch. Clutches are not 100% reliable so not having a clutch is a good thing.

Like electric airplanes, electric helis have noticeably reduced reserve power when the batteries are near exhaustion.
This is even more noticeable in helis than in fixed-wing aircraft.

Because of the high currents present, the potential for electric disturbances is fairly high in an electric heli.Precautions such as careful routing of signal wires away from power wires should be taken. Sometimes, winding signal wires though ferrite rings can help filter out unwanted noise and reduce glitches.

Just like with electric airplanes, there is more variability in the motor system through changes to the number of cellsand to the final gear ratio. Also just like in airplanes, this affords more opportunity for optimising the motor system after installation. At first, it also provides more opportunity to get it wrong, but most manufacturers web sites now provide good guidelines for power systems. It can be a good idea to buy pinions one size larger and smaller than the one that "should" work for tweaking purposes.

What about BEC's in helis? A typical electric helicopter has four servos. All these servos can consume quite a bit of current, especially the new digital servos. It is extremely important that the Battery Eliminator Circuit (BEC) have sufficient capacity to supply sufficient current for all servos operating simultaneously under flight loads. A Battery Eliminator Circuit is often built into the speed controls used in smaller helicopters to avoid the weight of receiver batteries. Recently, a separate, high voltage "Ultimate BEC" has become commercially available from Kool Flight Systems and is being used quite successfully in the larger electric helicopters. Otherwise, standard receiver packs
are used. Receiver batteries should be sized to last a reasonable number of flights.

What about motor batteries?
Some exciting advancements are being made in batteries. Lithium chemistries are just starting to emerge and have been used with amazing results. In most heli applications, they are probably not
ready for "prime time" so for the average user, NiCds remain the most reliable and cost effective solution. NiCds charge quickly and deliver high currents with ease.

Brushless motors have been a boon to electric helicopters. Helicopters require constant power - this is hard on theless-efficient brushed motors. Brushed motors in helicopters run hot and tend to wear brushes quickly. Brushless motors remain virtually maintenance free even in helicopters.

Benefits of a Simulator

In my view, it is difficult to overstate the benefits of a simulator. If you are new to R/C flight, a simulator is a great wayto start. If you are already a fixed wing pilot, I would say the similator is just as important when learning to fly helis.
When in forward flight, helis fly somewhat similar to fixed wing aircraft. But helis require new skills - hovering,transition to and from forward flight and more dexterity of the left thumb for control of collective and yaw. Since every (successful) heli flight begins and ends in a hover, these new skills are very important and required immediately. This makes the simulator a very valuable tool for the beginning heli pilot unless of course you have several backup helis at your disposal. :-)

Best Starter Heli

Question: What is the Best Heli to Start With?
Answer: The one in the flight simulator.

When it comes to the real thing, I feel strongly it is not necessary to start with glow helis as some would suggest. Inmy case, it would have meant getting a bunch of glow equipment I know I'll never use again just to learn to fly helis.
Dumb. Using a simulator further minimizes the argument for learning on one type or another.

If I had to choose, I would say the best choice for learning to fly helis of any kind is a Lite Machines Corona. It is hard to go too far wrong with the Corona as a first heli. It is relatively inexpensive and very durable. It runs very reliably with electric power. Its only major drawback is it is a fixed collective pitch heli.

In reality, there is no such thing as one "best" heli to learn on. Those who learn quickly, build more precise and aremore patient and careful can start with a more advanced heli than the one recommended above. Those who already fly glow powered helis will choose an electric heli that suits their skill level.

The Mikado Logo 10 and 20 are probably the best mainstream electric helis available. These helis are well designed,fly well and are made with quality components. The micro helis such as the Piccolo and Hornet are somewhat more difficult to make fly well but are fun machines for indoor and calmer weather. The Minicopter Joker CX is a sophisticated (and expensive) large "60 size" machine that is generally considered the best large electric heli currently available. Other popular electric helis of note include the Ikarus Eco series, the Kyosho Concept EP and the JR Voyager E.

What about converting a glow heli? This works too and can result in a good flying, robust and relatively inexpensive heli. Recently, the 50 Size Raptor has become a popular conversion candidate and there is even a conversion kit available from ElectraFlight. However, all things being equal, conversions are a bit heavier with shorter flight times and/or less performance than a machine designed from the ground up for electric power. It will also require the necessary skill and labour to convert the power source if you are starting from scratch. If done right, the performance difference isn't that great so there is no reason not to try. It is rewarding and sometimes less costly to convert a glow heli so if you have the tools and access to a suitable candidate by all means go for it!

Final Thoughts

"OK. I've decided to take the plunge and get an electric heli, what else should I know?"

How much will it cost? Well, if you have to ask......

It is certainly true that an electric helicopter of any size is not an inexpensive thing. Again, the LMH Corona isprobably the lowest cost heli available. A simulator can also save hundreds in repair costs. Somehow I have managed to conveniently forget how much it has cost to get my Logo 20 in the air. But what a nice heli. :-)

Can I save money by using a brushed motor?
A qualified yes. Some brushed motors work quite well, especially in smaller helis. Even if the motor works well, however, you can expect a lot more maintenance to keep the heli in the air. In many heli applications, the joy of initial cost savings for a brushed motor will be quickly overcome by the frustration of poor reliability.

Where do I turn for help?
Find someone with knowledge of electric helis. Glow pilots can help you fly, but may be little help if your electric set-up needs adjustments or has problems. Ray's Helicopter Manual is a good resource for model helicopters in general. Get advice and support online from one or more of the online discussion groups. The on line glow heli groups can also be very helpful to the beginning electric heli pilot. The Ezone, RunRyder, and RC Universe are a few I would recommend.

What setup to use?
Should I get a tame setup for more flight time or a more aggressive setup that will grow with me as my flyingskill improves? To a large extent, only you can answer this question. I wouldn't lose too much sleep over this because the characteristics of the power system can be changed somewhat after purchase. A tame setup generally uses a motor with a lower speed constant and achieves a lower head speed. By varying the number of cells and the drive ratio to the main rotor, the characteristics can be varied quite a bit with a given motor. All I can suggest is try to be realistic about your goals and abilities.

Do I need to use a speed control made for helis?
This isn't absolutely mandatory, but as the size increases it becomes more important. Throttles made for use in helis have a "heli" mode that makes important changes to the operation of the throttle. For example, it engages a governor mode that is ideal for maintaining rotor head speed. It often also makes changes to other operating parameters such as thermal and voltage cutoff settings that are more suited to helis. No throttles for brushed motors that I am aware of have a governor mode. Another drawback of brushed controllers is they often have a poor transition to full throttle (jump abruptly from say 90% to 100%) that can negate any possibility of using a proper throttle curve.

How hard is it really to learn to fly a heli?
It isn't as difficult as it is different. The first hurdle is the hover. Buy, beg or borrow a simulator and use it! First learn to hover with the tail towards you. Then learn to hover viewing the heli from the left and right sides and then nose in. I know this simulator advice is being repeated ad nauseum here but
there is no substitute for stick time on a sim. Practice autorotation landings soon after you are comfortable flying around on the sim. This could save your heli later.

Finally, start acquiring the components early. Depending on the model and the motor/speed controller/gyro/servoschosen, you may have to allow as much as several months for all the materials to come together.

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