How to be Successful Building & Flying Electric Powered RC Planes(ERCITS)
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NOVEMBER, 2002 Newsletter

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How to be Successful Building &
Flying Electric Powered RC Planes

A talk given to the MARCS Club in the Spring of 1998 by Ron Martone

Introduction

I got interested in electric powered radio controlled model planes (eflight for short) about four years ago, after learning to fly on a glo trainer and then graduating to a glo shoulder wing plane. I have completed 4 electric powered models and have several others in construction. I am going to assume that I am talking to experienced modelers who already know how to build and fly RC planes, have some equipment and might be interested in eflight as a way to get in more flying time or just enjoy another facet of the hobby. In addition to my talk and demonstration tonight, I want to leave you with these notes in case you get interested enough to want to try modern eflight. I have also brought my eflight flying buddy, Chuck Davenport and some planes, equipment, books, articles and hardware for us to look at. Feel free to ask questions as I go along and I hope you find it all worthwhile.

First off, we need to understand that things have really changed recently- batteries, motors, controllers and chargers are all much better than even a few years ago. Today, among the fastest (more than 200 MPH), most powerful (sustained, straight up 80 MPH {7000fpm} climb), longest duration (at least several hours) and highest altitude RC planes are all electric. Today, electric power flies trainers, aerobatic ships, old-timers, sailplanes, scale, ducted fans, helicopters, free flight, control line, indoor, park fliers and giant scale. Electrics can weigh as little as 2 ounces and go up to over 20 pounds. So just because eflight did not work for you or someone else in the past does not mean it cannot not work for you today.

Skills You Will Need to Be Successful

Don’t think that just because you can build and fly an internal combustion (IC) powered plane (glow, gas or diesel) that you can build and fly an electric one- there are new skills you may have to master, for example:

* how to pick a successful plane/motor/battery combination

* how to build good electric structures

* how to charge and handle flight batteries

* how to maintain electric motors

* how to optimize prop selection

* how to check out a plane for possible electrical noise problems and solve them

* how to deal with the safety issues involving a motor that can start very easily and batteries that can weld

* how to really "fly" a plane that is not overpowered

* learning to manage power usage while flying, and

* practicing until you can reliably land a plane so it does not have to be built like a battleship (Keith Shaw, a leading expert in eflight, estimates that half of the weight of a glow plane is there just so it can survive really rough landings)

How to Guarantee You Will Fail

Don’t try to convert an old glow plane using a "can" motor and a cheap battery pack - it is absolutely doomed to failure! Instead- and especially for a newcomer to eflight, pick a combination of plane, motor, battery pack, prop and controller that has a long track record of being successful.

Electric Planes Compared to IC Planes

Electrics are not better or worse than IC planes - just different -and they ought to be enjoyed for the pleasure and challenge they can bring. Electrics are much more popular in Europe (and most of the rest of the world) than they are in the US because those European countries have anti- noise laws, are more concerned about the environment and have much less space for flying fields. Some think the US will become much more involved in electric powered RC in the near future, especially in clubs located near big cities. There are a number of signs of this happening- you may have noticed a lot more articles about eflight in the magazines lately or the increasing number of eflight equipment at the Toledo show.

ADVANTAGES OF ELECTRIC PLANES

* quiet- essentially silent

* clean-no fuel or exhaust oil or afterrun oil on your plane/clothes/car/floors at home

* more convenient- all you need is a plane, your radio and a few charged packs

* very reliable starting (like in winter) and running

* can fly them in many places like vacant fields and parks

* you can be a pioneer, try something new

* with less vibration you can build lighter planes which fly better

* no fuel or exhaust to pollute the air, ground or ponds

* can save fields threatened by noise complaints

* are easier to use by physically challenged people

* you can run the motor up in your workshop

* no lumpy mufflers or cylinders to spoil a scale ship

* easy to build a twin or multi- "engine" plane

* easy to build/balance a pusher and reverse the prop

* you can shut the engine off and on in flight

* easier to fly more often like on a lunch break

* you can fly them indoors in the winter in places like gyms

Motors

-- Types

+ "can" ferrites- inexpensive- not very efficient (20 to 60%), can have acceptable performance for low powered sport planes if used correctly. Are disposable-brushes and bearings are not replaceable.

+ higher quality ferrites (at least 70% efficient), usually have replaceable brushes, ball bearings, adjustable timing.

+ cobalts, - usually more reliable, longer lived than ferrites- usually more expensive, more efficient (also at least 70% efficient), Don’t lose their magnetism due to use and abuse like ferrites. Astro is a good brand at reasonable prices.

+ neodym-offer very high power for short bursts only (like 10 or 20 seconds).

+ brushless- very expensive and require an expensive dedicated controller, very efficient (70 to 90%), low electrical noise (minimizes radio interference), least mechanical wear and longest lived, very versatile.

-- Break-in--needed to match flat brushes to round commutators, most can motors need it - power increases 10 to 30 % and motor lives longer, have to do it on a new motor, some others do not need break-in like Astros. To break in a motor, run motor at 1/3 to ½ of rated voltage with no load for several hours and check how well brushes match the commutator, one trick is to hook up 2 alkaline D cells (no prop) to an unloaded motor and let them completely discharge.

-- Timing -timing optimizes the position of the brushes compared to the comm for a particular task. Neutral timing is most efficient; advancing the timing increases the power and current draw but just up to a point. Motors may have to be retimed if gearing is used. If timing is too advanced or if it is retarded, lots of electrical noise will be generated and the brushes will wear out quickly.

-- Interference suppression capacitors- on brushed motor, use disc ceramic capacitors from each brush to the case and one between the motor terminals. If not supplied by the motor manufacturer, use 0.01microfarad caps at 50 working volts direct current (WVDC) which you can get at Radio Shack.

-- Number of Cells - manufacturers recommendations are often too conservative- find out, from an experienced modeler, what really works. It can make a big difference; for example-a 7.2 volt motor is rated to run on 6 cells but using 7 can boost power by 20% while increasing overall weight by only 5%.

Direct and Gears/Belt Drives

-Direct drive is preferred for sprint type flying like pylon racing and high performance sailplanes. It can also work well on small schoolyard planes. Gear or belt reduction drives produce more thrust and usually more overall efficiency (and therefore a longer flight) but at slower top speed for the aircraft and can benefit general sport, scale and certain duration types. Another benefit of gear or belt drives is that they are one way to prevent bent motor shafts in hard landings. For comparison, a direct drive cobalt 40 turns the same prop at the same RPM as a glow 40 but with a gearbox, a cobalt 40 performs more like a 4-stroke .65

Controllers

--Types

* switches- just switch on the power and fly until you run out of charge- the cheapest approach.

* servo controlled switches- turn full power on and off at will-inexpensive, -don’t use with geared systems or you can shear the motor off.

* relay type controls-also full on and off, some have BEC (see below for definition), are inexpensive.

* low rate (also called frame rate) Electronic Speed Controllers (ESCs) work by turning the power fully on to the motor for part of the time (for half power, half of the time) and they do this at about 50 times per second. These are OK for on/off type of control but waste battery power and heat up the motor at part throttle.

* high rate Electronic Speed Controllers (ESCs) also work by turning on the power to the motor for part of the time- for half power, it is 50% of the time but at about 2000 or 3000 times per second. Worth getting. Astro and Jomar make good controllers. The better controllers offer a number of safety features to protect you, other people and your plane.

* dedicated brushless motor controllers- work only with a particular brushless motors

--Brakes-apply almost a dead short across the motor to stop rotation and force a folding prop to fold. Good idea on direct drive, may cause too much stress for gear or belt drives.

--BEC- (Battery Eliminator Circuit)-powers your receiver from the flight pack, saves weight, cost and taking care of another battery but can kill your Rx when the flight battery runs low. This can be offset by a cutoff circuit that shuts off the motor while there is still (hopefully) enough juice in the battery to let you land safely. Use with caution- if you run out of charge, you lose your plane (Keith Shaw does not think they are worth the risk, Bob Kopski and Bob Aberle use them all the time successfully). Don’t use a car controller in a plane -they do not have a cutoff.

--Opto isolation- keeps noise from the ESC from getting back to the receiver. Worth having if possible. You cannot have BEC and opto isolation at the same time.

Batteries

(We are talking here about flight packs (not Rx & Tx packs))

* Nickel Cadmium (written sometimes as Ni-Cd or nicad) cells are still the best bet for charging easily, safely and reliably. Certain types can be fast charged and then deliver lots of power because their internal resistance is low. Taken care of, they can be good for hundreds of flights.

* Size ranges from 500 to 2000 milliamp hours (mAh), mAh is a measure of total charge or energy just like ounces of fuel is to an IC plane. More mAh means more charge stored which means more energy is available so you can have more power or duration but the size of the pack and weight also go up which leads to higher wing loading, more power needed to fly, etc. so tradeoffs exist.

* Voltage =1.2 volts/cell but drops to more like 1.0 volt/cell under heavy load.

* Expert disagree on how to store flight packs after a flight - Keith Shaw says to store them as discharged from flight and fast charge before use. This works well for sport use and I recommend it. (Some other opinions are: Larry Sribnick of SR Batteries says to slow charge overnight, unplug or trickle charge all week, top up with a fast charge ,consider the first one or two flights as throw aways and then the next flight will be the best possible - this approach is ideal but only makes sense for competition; Bob Aberle recharges at the overnight rate, recharges at the overnight rate once a month if in storage, considers his first flight as "soft" and OK for sport use but the next quick charge and flight is optimum for competition.) They all work but for sport use, but Keith Shaw’s approach works well and is a lot easier.

* new packs should be first slow charged and discharged to 1 volt per cell a few times to "break them in".

* as a general rule, packs should only be connected in series when you make up a pack

* to avoid battery memory problems, ( if they really exist) regularly fast charge your batteries and occasionally discharge them to 1.0 volts/cell under light load

* don’t discharge packs below 1.0 volt/cell or you risk damaging cell reversal

* nuse Sanyo "R" type batteries for virtually all your needs- they are efficient, reliable and tolerant of mild overcharging and other abuse.

* do not recharge batteries until after they cool down or you will greatly reduce their lifespan.

* a good supplier of battery packs is SR Batteries

* a good supplier of cells is B&T

* for anything other than a beginners system, buy quality packs from SR Batteries or learn how to make packs which will supply high currents without self destructing by using Keith Shaw’s instructions in his August 93 article in Model Airplane News (available free at Ken Myer’s web site).

Wires and Connectors

* use only Sermos or Anderson Powerpole connectors and solder them. See Bob Aberle’s book on how to use them.

* use at least 14 gauge multistranded wire in the power circuit and up to 12 gauge for long runs or very high current draws (above 40 amps). Wire composed of many thin strands flexes more easily and puts less stress on connectors.

Chargers

* trickle-rate charger- puts in about one or two % of C ( the cells capacity)- just replaces charge lost in storage

* overnight (also called slow) charger- rate equals C/10 and recharges pack safely in 14 to 16 hours.

* fast charger with timer - to use, first discharge pack to a low level ( about 1 volt/cell) then charge to just replace the cells capacity so you do not overheat and possibly destroy the pack. (the fast charge rate for Sanyo R cells is 3C) These chargers are usually limited to charging packs with a maximum of 7 cell from a 12 volt battery.

* peak detector charger- work automatically to fast charge the pack and then shut off when the battery reaches almost full charge. You will get better charges, better flights, take better care of your batteries and be more successful with a good peak charger. Astro 110D and 112D are good choices.

* Note: most chargers work from 12-volt batteries in the field. It can be your car’s battery if you are careful not to strand yourself. Your best bet is a deep discharge (Marine) battery- trolling motor size for sport planes, 40 Ah or bigger for more serious stuff.

Planes

* Since electric power systems are heavier, usually planes need to be lighter but this is possible because of less vibration. Any kind of plane can be flown with electric power if the special tradeoffs are dealt with. The basic issue is that a battery holds only about 1/5 the energy of a tank of glow fuel of the same weight (and it does not get any lighter when it is discharged). Wing loading, duration and power have to be carefully balanced to get a successful design.

* avoid ARFs- there are many dogs on the market. Get advice from an experienced modeler.

* proven designs are shown below.

Props

Special props are made for electric planes. Folders reduce drag on gliders, are less likely to break in a hard landing and help prevent bent motor shafts, fixed props are thinner and lighter, have smaller hubs and are optimized for slower turning geared systems. Since geared motors can swing big props like 12 or 15 inches, the standard IC props are unnecessarily heavy. For direct drive, IC props like APCs are sometimes used. Do not use an electric prop on an IC engine- the vibration can cause them beak up and fly apart.

Radio Equipment

Keep it as light as possible. Use lightweight receivers, micro servos( when possible) and usually you only need 250mAh receiver packs.

Additional Useful Equipment - an ammeter (or shunt) to measure current, a tachometer, a digital voltmeter, a battery discharger, light bulb loads, Ace Dual Metered Vari-Charger, end- of -charge beeper, a digital scale to weigh parts, a digital fish scale to measure thrust, a deep discharge 12 volt field charging battery and a charger for it.

Guaranteed Packages for Success

If you want to try eflight, I can recommend the following packages:

* Bare Minimum Performance- 2 meter glider (The Goldberg Electra), building materials, one 6 cell pack and an AC/DC fast timed charger-cost about (~)$155 plus radio. Add ~$30 for an electronic on/off switch or ~$60 for a speed control.

* Better Performance - High wing .05 size trainer (the Great Planes PT Electric or the Goldberg Mirage), 2 each 7 cell 1700 or 2000 mah SCR packs, speed control (Astro 210, Ace Smart throttle), peak charger, building materials- cost ~$ 335 plus radio. Nice flying planes and equipment you can use on your next plane. Mirage works even better on a geared cobalt 05 with a 12/8 folder. The PT electric should have only ¼" of washout.

* Best Performance- High wing .25 size trainer- (the SIG Seniorita converted using Bob Kopski’s article in Model Aviation July 91- available from the AMA), geared Astro cobalt 25 motor, building materials, 1 battery pack, speed control (Astro 217D), peak charger - cost ~$410 plus radio.

Other Packages Recommended for Experienced Modelers

* Concept Models Fleet Bipe with geared cobalt 40 on 18 to 21 1400 mah cells

* Spirit of Yesteryear Amptique on 6 or 7 cells and any geared 05-a very gentle trainer

* Great Plains Electro Streak- quite aerobatic with the supplied motor (better with a geared Cobalt 05-Kopski) or amazing with an Astro 15 on 10 SCR 1400mah cells with a Jomar SM-4 controller in an enlarged fuse (K. Shaw)

* Astro Porterfield Collegiate with geared 25 cobalt on 14 SCR 1400 mah cells with a 13/8 prop

* Sig Senior with an Astro geared 40 on 18 or 20 SCR cells

* Astro Viking on Astro cobalt geared 035 on 6 SCR 1000mah cells or a geared 05 on 7 SCR 1000mah cells

* Spirit of Yesteryear Playboy and Lanzo Bomber on a geared 05 on 7 SCR 1000mah cells

* Today’s Hobbies Skyvolt on an Astro 15 direct

* Great Planes Cub on an Astro geared 05 and 7 SCR 1400 mah cells or an Astro 15 direct on 10 SCR 1400 mah cells and an 8/6 prop.

* Astro Challenger with a geared cobalt 05 on 7 cells with a 12x7 or 13x7 folder

* Great Planes Spectra also with a geared cobalt 05 on 7 cells with a 12x7 or 13x7 folder

Flying

- most electric planes fly "on the wing" like most full scale planes and not "on the prop" like many IC models. if you have any glider experience, you probably have already developed the skills you need. If not, you have to learn them. You do not usually have available gobs of extra power to save your butt if you stall the wing. Some newcomers to eflight, even though they are skilled IC fliers, stall and crash planes and blame the planes when the problem is they never learned to fly on the wing.

Important Safety Precautions

* always use an arming switch but do not break current with it, (Digikey part # CKN 1035-ND is a reliable part)

* always use a fuse (automotive spade type) of proper rating, (and in the correct part of the circuit if you use a BEC). This can save you from serious hand injuries and avoid setting planes and fields on fire. Sermos makes a nice connector for fuses or you can use properly insulated, soldered on, push on terminals. Some people solder the fuses into their battery packs or into the circuit.

* do not connect the battery until ready to launch or take off.

* take the prop off your motor whenever working on your plane.

* don’t turn on your Rx until ready to take off or launch and turn it off soon after landing.

* make sure throttle is off before turning radio on.

* use a helper for radio-on checks.

* sand flash off your props.

* use properly constructed and insulated battery packs (they can put out 100 amps which can melt a watch band or ring).

Cost to Try Eflight

As we saw earlier, you can try out eflight for not much money. A powered glider with an inexpensive car battery pack and a timed charger goes for about $155. If you want more performance, convenience, parts that you can use in your next plane, etc. then it will cost more. In the long run, eflight costs about the same as IC planes - with the higher cost of eflight equipment being offset by no fuel costs.

Good Sources Of Information

* Tap the knowledge of modelers who have electric experience- for example, my electric flying buddy, Chuck Davenport (440-942-0752) or me (440-352-9040).

* Dig out your magazines and read the last few years of the electric model columns and electric construction articles.

* If you have access to the WWW, start with Jim Bourke’s website- "The Ezone" ( http://www.ezonemag.com) and Ken Myers’ website-"The Future is Electric" (http://members.aol.KMyersEFO/) There is a ton of great information here and I highly recommend your using it. If you do not have a computer, many libraries now have them and will help you use them to get to this information.

* Ask your favorite local hobby shop for advice- as interest grows, so will their knowledge.

* Write to the electric columnists for advice- for example Bob Kopski of Model Aviation and include a SASE.

* Call or write the electric suppliers for advice- New Creations, SR Batteries, and Astroflight are among those whose advice you can trust- their numbers are included later on in the Suppliers section.

* Go to an electric meet like the KRC in Lancaster PA- see hundreds of successful electric C planes.

* Write to Keith Shaw at 2756 Elmwood, Ann Arbor, MI 48104 and include a SASE. He is a wealth of knowledge.

Computers Also Can Be Very Helpful

In addition to access to the World Wide Web, and its vast amount of information, which was mentioned above:

* There are a number of design programs available. These are not necessary to be successful but they can help make it easier to design your own planes and pick the best components. Examples are AeroComp, Electroflight Design Program, and Motocalc. You can get similar good advice from quality suppliers like New Creations, Astro and Modelair Tech.

* Some flight simulators-like Dave Brown’s -have an option for electric planes so you can get some "flying" experience.

Odds and Ends, Rules of Thumb and General Advice

It is really nice to have three battery packs for a plane so you can fly with one while one is on charges and one cools. You can fly indefinitely with this arrangement.

A motor will draw about 75% of the current when flying compared to what it draws when the plane is tied down on the ground.

Hand launching saves energy and makes people wonder what you are doing with a plane with a "dead" engine on the flight line.

Electric fliers love to argue about how to charge and store batteries, whether or not to use BEC and how to make up and use battery packs with a lot of cells.

If you design your own planes always make sure you have a path for cooling air for your motor, controller and flight pack.

Make sure your flight battery can’t shift in flight-this almost guarantees a crash.

Be sure to range check you plane with the motor running.

A Special Interest Group (SIG) for CRCC?

Maybe- if enough of you get interested in electric flight, you can start a SIG and locate one or more flying fields in the immediate area (like glider pilots do) where silent electric planes would be welcomed. A number of other clubs have done this successfully. I suggest you give it some serious thought.

Suppliers

First try your favorite local hobby shop and try to order uot; by Keith Shaw in Model Airplane News December 1991 - available free at Ken Myers website

""Electric Conversion" ( of the SIG Seniorita) by Bob Kopski-Model Aviation July 91- available from the AMA

Sources Of Information for This Talk

My thanks to Keith Shaw, Jim Bourke, Bob Kopski, Ken Myers, Bob Aberle, Bob Boucher, Larry Sribnick, Rod Wooley and many others for sharing their knowledge about what it takes to be successful with electric flight. It was from their writings, their talks and our correspondence, combined with my own experience and that of my MARCS eflight buddy, Chuck Davenport, that most of this talk was developed.

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Updated November 14, 2002.

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