Advantages of Electric Power

Author: Bob Aberle

Edition: Model Aviation - 2010/07
Page Numbers: 39,40,41,42,43,44

Advantages of Electric Power

I wrote an article about electric-powered flight, titled "Introduction to Electric Power," that was published in the July 2003 Model Aviation. You can find that feature at the Web site address included in the "Sources" list at the end of this article.

Seven years later, electric-power technology has changed tremendously. Because of the technical advances that have been made, "e-power," as it is sometimes called, now offers many more advantages than ever!

With that in mind, I am presenting this updated article. It is a basic introduction to let you know what is going on and what is available in the realm of electrics. As time goes on, I plan on writing more detailed information that will enable you to fully appreciate this exciting form of model propulsion.

If you have thought about trying electric power, please read on.

by Bob Aberle

What Is Electric Power?

It is a system that operates a motor using electrical energy stored in a battery, as opposed to a fuel tank feeding an engine. Electric power offers the model aircraft enthusiast several basic and important advantages, such as:

Quietness: Minimal noise is created when the motor is operated. It is so quiet that no mufflers are necessary. This major advantage has helped aeromodelers obtain flying fields; silent models will not annoy the public.

Soundless flying capabilities have contributed to the establishment of small aircraft we refer to as "park flyers" or "backyard flyers." The inference is that these models can be flown at local fields without attracting attention. Public acceptance of electric-powered models has led to the development of the AMA's Park Pilot Program membership category.

Cleanliness: No residue is left on an airplane after a flight. As a result, no special finishes need to be applied to the aircraft. Even more important is the fact that residual fuel, or spilled fuel, will not get into our groundwater and create serious ecological problems. This is another way our hobby supports the "green" movement.

What Comprises an Electric Power System?

This means of propulsion basically includes a motor (that turns the propeller), a speed controller (ESC), and a battery that provides electrical energy to operate the motor.

The most efficient motors that modelers use are brushless types. These are basically AC motors that do not require brushes; therefore, they have nothing to wear out or need replacing.

Motors are available in two categories: "outrunner" and "inrunner." The outrunner type is the most popular. By design, it can turn a propeller directly, without a mechanical gear train.

Essential Tools for the Electric Modeler

One of the most important tools you will need to fully enjoy and use electric power for your models is a device that can read the most important motor parameters: current (amperes), voltage, and the product of the two, which is watts (power).

The second thing you need is a meter—preferably digital. Plan on spending probably $50–$60 for one. There are several good ones on the market, and all will do the same job.

I especially like the Watt’s Up wattmeter because the manufacturer, RC Electronics, supplies a 35-page user’s manual that covers all of the various applications for this product. You can find the manual on the company’s Web site.

There are numerous types of battery chargers on the hobby market. Many are designed for a specific type or brand of battery.

My favorite is the FMA Direct Multi4 because it can charge almost any battery chemistry, packs with as many as four cells, and up to 4 amps of current. FMA Direct also sells a variety of node connector adapters that will allow you to charge nearly any brand of battery you can obtain.

Rather than spend several pages describing all that the Multi4 can do, check out the user’s manual located on the FMA Direct Web site. FMA Direct also sells the Cellpro 10S charger for those who need to charge packs with as many as 10 cells at 10 amps.

Connectors are a vital part of electric power systems. These connectors allow you to plug together all of the components that make a full system. Many of the individual components come with connectors already installed. Unfortunately not all do, so you might be required to install your own. In some cases you can do that with a mechanical crimping tool, but you will usually need to solder the connectors.

When you get down to the multipin node connectors that allow you to balance-charge battery packs, there is no industry standard. There are currently at least six types of node connectors you might have to deal with:

PolyQuest
Thunder Power
FMA Direct Revolution
Kokam
Horizon Hobby (E-flite and ParkZone)
Great Planes (ElectriFly)

Most manufacturers sell balance-charge adapters to satisfy these connectors.

Bob Aberle [email protected]

Motor, ESC, and Battery Basics

Unlike fueled engines, which are categorized by cubic-inch displacement, motors are generally rated by input power measured in watts. If you multiply the motor current (in amperes) by the voltage applied from the battery, you obtain the wattage, or the power input.

To size a motor, use the parameter called power loading; it relates power input (watts) to the total weight of an aircraft. The resulting watts-per-pound figure is the key to determining the correct-size motor for your model. Later you will find many references to this all-important parameter.

Each motor can provide a broad range of power. The size, weight, and armature windings are one consideration. The choice of propeller size is a second. Voltage applied to the motor is a third. Coordinating those three variables is the secret to enjoying all of the advantages of electric-powered flight.

The ESC is inserted between the motor and the battery. It essentially takes the place of the servo that would control the carburetor of a fueled engine. The servo cable that exits every ESC is plugged into the throttle port on your RC receiver.

Moving the throttle-channel control stick on an RC transmitter will turn a motor on or off and provide variable speeds from idle to full power. Besides the servo cable, there is a three-wire cable that goes to the brushless motor and a two-wire cable that goes to the battery pack.

Modern ESC technology includes sophisticated electronics that provide many advantages for electric flight. A modeler can program most of today’s ESCs for specific operations, such as the direction of motor rotation.

An ESC will also prevent a motor from starting unless the transmitter throttle stick is at the low or idle position. This eliminates any chance of a motor accidentally starting and causing an injury.

An ESC will shut down the motor when a preset voltage level is reached. This is necessary because Li-Poly batteries can be permanently damaged if the voltage drops too low. And if any kind of interference hits your RC system, the motor will be shut down as a warning that you should land your model immediately.

A unique feature of most ESCs is the battery eliminator circuit (BEC). This enables your motor battery to also provide power to your RC system. By doing this, only one battery pack is required on your aircraft. Although the BEC feature had limits years ago (such as current demands and voltage), most airplanes today—except for the very large models—can be flown off a single battery pack using the BEC.

Currently, the most popular battery for electric-powered flight is the Lithium Polymer type, or Li-Poly. This technology emerged in our hobby approximately seven years ago and completely changed the way we fly electric models.

Li-Poly batteries offer much more capacity and are available in packages that weigh much less than the older Ni-Cd and NiMH batteries. Because of their popularity, Li-Poly prices have come down considerably.

Li-Poly battery cells have a nominal fully charged voltage of about 4.20 volts per cell. They should be recharged at a 1C rate, which can take as long as an hour depending on the state of charge at the time charging started. Improved Li-Poly cells can charge at 2C rates in 30 minutes and 3C rates in 20 minutes. Another characteristic of Li-Polys is that they should not be discharged lower than roughly 3.0 volts per cell.

Early on it was determined that Li-Poly batteries, contained in packs of two or more cells, needed to be balanced. This simply means that every cell in the pack should have the same voltage at full charge. To make that happen, battery packs are assembled so that each cell can be separately charged and monitored. This requires a special connector that is attached to every Li-Poly battery pack containing two or more cells. These multipin connectors are referred to as node connectors. Modern battery chargers provide the necessary interface with the various node connectors used throughout our hobby.

Besides Li-Poly, popular battery chemistry involves Lithium-ion (Li-ion) technology. Some Li-ion cells and packs are produced by A123Systems.

I urge you to read the three-part article titled "Those Things We Call Batteries," which you can find on Model Aviation's Sport Aviator Web site. Also read MA's bimonthly "The Battery Clinic" column by Red Scholefield, a noted battery expert.

Where Are Electrics Today?

There are many more advantages to using electric power for models than the fact that it is quiet and clean. Following is a summary of other benefits:

Improved motor efficiency by going brushless.
Reduced system weight: motors and batteries weigh less than engines and related components.
Longer motor run times: batteries have become lighter and have more capacity.
Faster battery recharging: quickly gets your aircraft back into the air.
Safer operation.
Improved linear throttle response for more precise flight control, especially with 3-D-type hovering maneuvers.

Electric-power enthusiasts enjoy several prominent events across the country. It is common to see 300–500 registered electric-power pilots and several thousand spectators at these gatherings.

The annual NEAT (Northeast Electric Aircraft Technology) Fair in upstate New York, held every September, is one of the largest electric-flight gatherings.
The SEFF (Southeast Electric Flight Festival) in the Atlanta, Georgia area is held every May.
For micro and indoor electric-power aeromodelers, KIEF (Keystone Indoor Electric Fly) takes place each October in Muncy, Pennsylvania.

These are just a few of the fly-ins on the schedule. More are being added each year.

Electric Events:

NEAT Fair — www.neatfair.org
SEFF — http://seff2010.com
KIEF — www.pafunfly.com
National Electric Fly-In (NEFI) — www.modelaircraft.org/events/NEFI.aspx
Arizona Electric Festival (AEF) — www.azmodelaviators.com

Most SIGs in our hobby are using electric power. It has been integrated into almost all aspects of aeromodeling, including trainers, sport fliers, park flyers, standoff-scale, Scale (national and international), Aerobatics (national and international), 3-D (hovering and demonstrations), sailplanes, Old-Timers, free flight, micro and indoor flyers, control-line (national and international), vintage RC, helicopters, and giant scale.

The AMA Nats, held each July at AMA Headquarters in Muncie, Indiana, now has many competitors who use electric power, especially in CL, Scale, Aerobatics, and helicopters.

Further advancing the popularity of electric power is the fact that many manufacturers now offer ARF and RTF models. Many arrive with the motor, ESC, and batteries installed at the factory, and numerous fueled aircraft can be converted to electric power.

This increased popularity has resulted in considerable component price reductions that make electrics affordable. With more manufacturers and more options, aeromodelers have a wider choice of motors, ESCs, and batteries.

Today's electric power systems for models are generally easier to operate than fueled engines. Ample information is available about electrics, and you can get all the details you need to assemble, install, and operate your own system. You don't need an electrical engineering degree to enjoy electrics—though you will need to learn to solder. Battery care is improving with better products and more sophisticated chargers that do much of the work for you. With so many people into electrics now, you can usually find experienced aeromodelers to answer questions as you learn.

Sizing electric power systems to fit your models is probably the most important aspect of this type of flight and will require you to learn several things. Recognizing that this might prevent some modelers from getting into electrics, I wrote a two-part feature on the subject. The feature covers all aspects of the watts-per-pound parameter that is key to motor selection—make sure you read every word.

References for Electric Power

Several print and online magazines cater to the electric-powered aeromodeler. A few to which you can refer:

Model Aviation (MA) features five columns that contain information about electrics: "Electrics" by Greg Gimlick; "The Battery Clinic" by Red Scholefield; "Small-Field Flying" by Paul Bradley; "Micro-Flying" by Joe Malinchak; and "Frequently Asked Questions," which I write. MA also publishes product reviews and articles about electric power.
Park Pilot magazine continually publishes product reviews and articles that feature electric power.
Model Aviation’s Sport Aviator online magazine contains reviews and feature articles about electric-powered aircraft and electric power.
Flying Models has a column titled "Electric Flight," alternately written by Don Belfort and Stew Meyers.
RC Micro World Online Magazine is for micro and indoor electric-power fliers.

Hobby forums provide an excellent opportunity to ask questions and receive answers. Not all those who respond are experts, but replies can still be helpful. Five forums I recommend:

AMA’s Forum — www.modelaircraft.org/forums/default.aspx
WattFlyer — www.wattflyer.com/forums
The E Zone — www.ezonemag.com/pages
RCGroups — www.rcgroups.com/forums/index.php
RC Universe (select "Electric Flight") — www.rcuniverse.com

Some useful books and guides:

Everything You Wanted To Know About Electric Powered Flight — an online e-book by Ed Anderson, available on the Tri-County Wing Snappers site.
How to Build and Fly Electric Model Aircraft by Robert Schleicher — available from Barnes & Noble.
RCadvisor’s Mini-Fly by Carlos Reyes — a guide to designing and building an electric-powered model from scratch in one day (available from RCadvisor.com).
Getting Started in Backyard Flying — written by Bob Aberle, available from AMA Headquarters' retail store.
The World of Indoor/Micro Radio Controlled Model Aircraft (all electric) — by Bob Aberle on CD, available from RC Micro World.