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This article is intended for those who have previous experience with nitro/gas powered helicopters, and wish to explore what the modern electric technology has to offer. During my involvement with this hobby in the past 12 years, I have experimented with a few electric helis including Kalt Whisper and Kyosho Concept EP. Needless to say, the technology available back then didn't provide the power/duration needed to make flying electric heli enjoyable. Therefore, glow/gas was still the power of choice. That is about to change. You are currently in the beginning of an electric revolution like never seen before. The advent of brushless motors and recent development of lithium battery technology has made electric power practical. With power and duration that will rival the best of internal combustion (IC) engines, soon you will see more and more electric powered helis zooming across the sky at your local field. Obviously the main advantage of electric power is the cleanliness and quietness they have to offer, but also think about the equipment you have to bring to the field to supposrt glow helis. No more gallon fuel jugs, starter, fuel pump, glow plugs, etc. Just bring your heli, a couple of battery packs, and a charger. Theoretically, three battery packs should last you all day, with one in flight, one on charge, and one cooling down in between flight and charge. That is assuming your power source (usually12V car battery) will last all day. What are not obvious are the disadvantages of going with electric power. Contrary to popular beliefs, duration and power is no longer a disadvantage of electric power. With the proper setup, similar sized electric heli can out fly its glow counterpart. The real disadvantage of electric power is the startup cost. A brushless motor and matching speed control can easily exceed the cost of its glow engine counterpart. On top of the power plant, there is the cost of batteries and a suitable charger. Therefore, if your motivation for going electric is cost savings, you might be in for a sticker shock. Similar to glow powered helis, electric helis are categorized based on their sizes. But instead of designating the category based on engine sizes (cubic inches), electric helis uses the number of battery cells. Generally speaking, a .30 size heli would need between 10 to 14 cells, .40-.50 heli would need 20-24 cells, while the larger .60-.90 helis would need 30+ cells. They use similar blade length as well, such as 500-550mm, 600mm, and 680-710mm, respectively. What intrigues me the most about electric powered helis is the dynamic nature of power system. Glow flyers will know what to expect from a certain power package consisting of engine, pipe, and fuel type. This makes selecting a power plant a no-brainer; pick OS or YS and stick with what pipe works, then you will have a heli with similar power as any Joe at the flying field. On the other hand, electric power introduces many variables, which can affect the power output dramatically. Variables such as motor winding, pinion gear size, speed control type, motor timing, battery type, cell count, or even charging method all contribute to the resulting flying characteristics. One power system can be configured to provide long duration, as well as power to perform aerobatics routines. The construction between glow and electric helis is very similar (except for the fact that electric heli frames can be built lighter), so I will not go into details there. What distinguish electric power from glow/gas power are the following: This is the powerhouse for the heli. While brushless motors are the preferred technology for electric helis, brushed motors can also be used. Many may have the impression that brushless motor is a new technology, it actually is just a three phase AC motor that has been around for years. These motors have three leads instead of the two commonly seen on brush motors, and are controlled by speed controller sending alternating currents into the three wires. These motors are preferred due to their high efficiency and longevity. Theoretically, the only thing that can wear out in a brushless motor are the bearings. Compared to the number of parts that wears out in IC engines, these brushless motors present much better value in the long run. This is the brain that controls how fast the motor spins. Usually they have three wires for connection to the motor, two wires for connection to battery pack, and a 3-lead signal wire that connects to the throttle channel on receiver. Some BEC (Battery Eliminating Circuitry) equipped ESCs will even provide regulated power through the signal wires to the receiver, saving the weight from having a separate receiver pack. It truly is the center of the electric power system. There are ESCs built specifically for airplanes and cars, but for helicopter application it will need to have soft motor start, brake disabled, and no low voltage motor shutoff. Soft motor start and disabled brake will save the heli transmission from shocks created by sudden changes of speed during spool up/down, while the absence of low voltage cutoff will ensure the motor won't stop in flight by getting every last bit of juice out of the batteries. While you can purchase heli specific ESCs with these features, there are programmable units which allows user to enable/disable individual functions, in case you want to explore other brushless motors applications. Recent advancement in brushless motor technology have enabled them to incorporate circuitry to maintain constant RPM, similar to the Futaba GV-1 governor used in glow powered helis. With the speed governor setup, the throttle curve is set to a flat line, and the ESC will increase or decrease voltage automatically to compensate for the load incurred by collective pitch. Generally, throttle is at 0% across for normal mode, and a fixed percentage at idle up (usually 80%). The 0% is to keep the motor off when battery is plugged in. Flying is done completely in idle up mode, where collective is controlled by pitch curve, with throttle remain constant. Consider these the solid form of nitro fuel that powers your heli, except you can re-use them. The sub-C sized batteries commonly found in RC car circuit are the cell of choice for helis, primarily due to their availability and performance. Their capacity (measured in amp-hours, or how many amps it can produce for an hour) has increased from 1.3 Ah back in early 1980 to todays 3.3 Ah, utilizing Nickel Metal Hydrate (NiMh) chemistry to achieve the higher capacity to weight ratio. Although NiMh cells provides larger capacity, they usually provide less power output than equivalent Nickel-Cadmium (Nicd) cell, cannot be charged at a high rate. Due these reasons, Nicd is still preferred by pilots who prefer higher power output, but with the sacrifice of slightly shorter duration. The battery technology is probably the fastest evolving element in electric power system. For example, Sanyo has recently introduced NiMh cells with Nicd characteristics, meaning they can be fast charged/discharged, while providing long duration. But the biggest breakthrough is the much talked about Lithium technology. The latest Lithium Polymer (LiPo) technology provides extremely long duration, and also allows higher discharge rate unlike the old Duralite cells. With these LiPo cells, powerful aerobatic power is available for up to 30 minutes! Currently, most of the popular electric heli kits are manufactured by European based companies. While familiar names like Kyosho and JR Heli Division offer electric kits, they are usually limited to smaller 10 cell sized helis. Here are some of the electric heli kits manufacturers and their electric heli product: Mikado (http://www.mikado-heli.de): Logo series Minicopter (http://www.minicopter.de): The Joker Ikarus (http://www.ikarus-modellbau.de): Eco, Piccolo Graupner (http://www.graupner.de): Uni-Mechanik-Elektro Vario (http://www.vario-helicopter.de): Silence Gensmantal (http://www.gensmantel-heli.com): Heaven JR Heli Division : (http://www.jrpropo.co.jp): Voyager E Kyosho: (http://www.kyosho.co.jp): Concept EP So how do these electric helis really fly? Since the mechanical construction between electric and glow helis are similar, flight characteristics are similar as well. Like Mr. Fred Bronk said on the E-zone (www.ezonemag.com), the heli itself does not know what ís powering it. As a matter of fact, glow helis converted to electric power should have near identical performance. With brushless motors providing similar power as IC engines, and the new LiPo battery to provide duration exceeding that of glow helis, soon there will not be any incentives to fly IC engine helis. |