all about Electrics

All About Electrics

Bob Kopski

This is the wrap-up. In it the author talks about mail received in the past months, gives a look at the future of electric flying, covers some oversights and omissions from previous parts—and more. Part 10 — conclusion (but it's really only the beginning!).

"Conclusion" is a misnomer. While that word does describe this final part of the series, the series is hardly the last word on electrics. "All About Electrics" is not quite an accurate title either, but I can blame that on the editor! I do hope my purpose has been fulfilled — to share enough of my experience to assure you first-time and continuing success with electrics (with understanding).

This installment attempts to review the high points of the series, catch up on loose ends, and respond to some of the most-often-raised points from reader mail. When this was written, Part 7 (the March issue) had just appeared, so there had been no reader feedback yet from Parts 8 and 9.

Review

This series has appeared continuously since the September 1983 issue, covering everything from what electric power is to how to accomplish your own flight objectives.

Part 1 (September 1983) was a sales-pitch of sorts: a reminder of why electric is useful and why you might be reading this series.

Part 2 delved into electric motors to help readers feel at ease with these new prop turners and to prepare for later discussions.

Part 3 (November 1983) demonstrated the relationship of electrical power, motors, and propellers. We saw that most motors discussed were similar in performance and that the electrical input power required to turn a given prop at a specific RPM did not differ greatly between several motors. More importantly, propeller size had a very dramatic effect on power drain from the battery — the model's "fuel tank." These lessons are important when planning your own electric project.

Part 4 covered batteries in depth: battery size, weight, available power, charging methods (including my preferred conservative charge), installation, precautions, and cooling.

Parts 5 and 6 (January and February issues) discussed installations: motor mounting, battery mounting, radio mounting, switches, connectors, fuses, wiring, speed controls, prop stops, and related items crucial to successful electric flight.

Part 7 (March issue) showed, with data from hundreds of flights, what kind of flight performance to expect for four typical electric applications. Four models were described in detail, demonstrating everything from 5-mm stay-stick aerobatics to 15-mm Old-Timer laziness. Part 7 stands on a solid data base.

Part 8 (April) offered suggestions for electric planning and construction. Weight was quantitatively depicted and rules-of-thumb were explained. Suggestions were given for building strong, lightweight models, and the scarcity of suitable kits (but growing number of magazine plans) was noted.

Part 9 tabulated many motor/prop/battery combinations and operating power levels. It provided the means to select combinations that would fly well, given reasonable model weight and construction.

More examples

If you still feel uncertain, review the examples in Part 7: they show what planes of various sizes can weigh and how they fly. Your chosen design may be close enough in size to one of those examples that you can use them as a guide. The one variable you can control is model weight — largely dependent on your construction and materials. Motor and radio weights are relatively fixed. Success often depends on how light (yet durable) you can make the plane. Almost any suitable design and power system will fly well if you don't build the model too heavy.

Many glow-engine kits or sailplane kits are not suited to electric use because of structural weight, but several kit designs can be adapted with structural modifications. Think light and strong. Study the design examples from Part 9, apply the guidance in this series, and electric elation is yours.

The mailbag

So far I have received approximately 150 letters. The maximum mail flow was about a letter a day for five weeks in late 1983. I replied to all but a few that required no answer. Some readers wrote more than once; one person wrote seven times. A few wrote rather important notes that disappeared — if you think yours might have been one of those, please write again.

The most-often-asked questions:

• "What motor should I use in such-and-such a plane?" — I tried to give specific answers when possible, but weight is the most important factor.
• Variable-speed controls in gliders — I personally prefer not to use a throttle in a glider, since most people want to get the plane up and then try to glide for a long time. If you want a throttle, by all means use one.
• Concerns about Part 3’s motor comparisons — the point was that most motors are similar and that the prop largely determines power input. The presentation was not intended as a consumer's report.

Other mail themes:

• Renewed interest from former modelers who had drifted out of the hobby.
• Many designs are being flown; a frequent kit conversion mentioned was the Drifter Two, typically powered in the .05 to .075 range.
• Several experienced electric fliers phoned with suggestions. Jim Zarembski and Keith Shaw both pointed out a potential airflow problem in my preferred battery cooling installation: depending on fuselage shape and flight characteristics, a pressure imbalance can prevent airflow out of the fuselage bottom. Their solution is to put a "reverse air scoop" forward of the air exit holes; the resulting step cures the adverse pressure buildup.
• I monitor battery and motor heat carefully after the first flights of a new model. Good airflow through the battery often deposits brush dust along the airflow path, which is evidence the cooling is working.

Reader preferences and observations:

• Gliders are the most popular electric models; Old-Timers are second most mentioned.
• Few readers wrote about contest interests, which matches observations at club electric fly events: most people just want something electric that flies for fun.
• Many readers noted a shortage of basic electric information and a lack of dealer interest/knowledge.
• Requests included coverage of airfoils for electrics, turning the series into a book, and inquiries about buying pictured models.

Answers to those requests:

• If an airfoil is good for a glow-engine plane, it is almost certainly fine for electric use, assuming the plane is appropriate.
• A book has been discussed but is not certain.
• I do not have models for sale.

Suppliers: I could compile a list, but magazines and catalogs are a reliable source of vendor information; catalogs usually have a nominal handling fee.

A memorable letter came from 14-year-old Tracy in Reno, asking about electric-powered ducted fans. I had no relevant experience and had to dampen enthusiasm; sorry, Tracy.

A new product

Part 4 described commonly used cell capacities of 0.55 Ah and 1.2 Ah and noted the growing popularity of the larger size. Since then a new 0.8 Ah cell has become available from both Astro and Leisure. A seven-cell battery I have weighs 9 oz., implying individual cells weigh about 1.3 oz. The 0.8 Ah cell weight agrees with the expected ratio: 0.8/1.2 × 2 oz. ≈ 1.33 oz. There’s no magic — cell capacity and weight are closely related.

I haven't used this new pack yet (it was winter when this was written), but view it as another option in an increasing selection of electric parts and supplies.

SEAM

The Society of Electric Aircraft Modelers (SEAM) is a recent organization now recognized by the AMA as a Special Interest Group. This places SEAM in an important position to guide electric matters including competition rules, team selection, records, and safety. AMA recognition assumes SEAM to be the unified voice of those interested in electrics.

If you're interested, write to: Society of Electric Aircraft Modelers 11632 Flamingo Dr. Garden Grove, CA 92644 Ask for the latest info and an application for membership. Ten dollars adds your name to the growing voice and gets you a regular newsletter. SEAM is organized by AMA district; each district has a SEAM director, and I am the director for District 3.

The future

I expect growth and popularity for electrics. They are quiet (increasingly necessary), convenient, applicable to many modeling interests, and fun. I also expect the introduction and refinement of electric classes and organized competition. Everything has to start somewhere — most good things grow and get better. We stand at this electric threshold now.

As for electric products, I don't see significant changes in present-day performance levels for a long time. Major breakthroughs in motor efficiency are improbable — many motors are already quite good. Ni-Cd batteries are likely to remain much as we know them, and I know of no other battery technology on the horizon that will soon replace them for affordable hobby use. Even if a magical battery existed, it would likely appear first in mass-market devices before becoming affordable for modeling.

That said, new products and refinements will continue to appear, making current products longer lasting, easier to use, better buys, and more available.

Things I'd like to see

• Armature shafts that are harder to bend.
• More sophisticated chargers to accommodate varied battery configurations.
• Motors with flow-through cooling ducts directed into the brush-commutator area.
• More kits designed for electrics.
• More versatile motor designs (for example, removable flux rings or optional armature windings).

Some of this may be asking a lot, but five years ago I would not have expected the current market. It is bound to keep improving, and suppliers need sales to justify making more and better products.

If you're interested in getting into electrics, waiting probably won't make a major difference. Read the series again if needed, decide what you'd like to fly, figure out what it will take, and do it.

Some oversights

A few things could have been covered more thoroughly:

• In Part 7, the Playboy table listed a completed empty fuselage weight of 3-1/2 oz. That is correct only without the landing gear. I modified my gear so it could be attached after covering rather than built in as per the plans.

• A more difficult area: choosing among several motor/prop/battery combinations that produce the same power level. From the tabulations in Part 9, similar power can be achieved with higher voltages and lower currents, or with lower voltages and higher currents. Cell sizes for various voltages often cost about the same, so you can purchase similar energy storage at different voltages. However, higher current is generally harder to handle than higher voltage. Remember that current squared times resistance determines power losses (I^2R), so system efficiency suffers more as current rises. Serious modelers should consider this when optimizing a system; beginners should choose simpler, easier-to-charge, and less costly systems to start enjoying the flying.

• In Part 8, Rule of Thumb One described power needed to "cruise." That term might have been misleading; I meant the motor input power needed to just barely maintain altitude and maneuver a bit — essentially the power to keep you in the ballpark. Twice that value usually yields a very flyable airplane.

• Variable power controls (an electronic "throttle") are worthwhile only when you have an excess power margin. If the plane is marginal at full power, a throttle provides little benefit. For adequately powered planes, proportional control adds pleasure and precision to flying and landing.

• Correction: In Part 2 I incorrectly wrote that many small motors use hard-to-get 5-40 screws for prop adapters. They actually use 6-40 screws.

The ending

Yes, the series is ending as originally announced, but there are follow-up plans. The Spectra construction article is coming, and I will write a continuing column titled "RC Electrics" to offer how-to information monthly, along with news and views. I welcome input (information and photos) from interested readers; I can't promise if or when everything will be printed, but I'll do my best.

I also plan occasional longer features covering electric topics too long for a column. You can expect continuing electric coverage of varying length and particulars. A regular column in Model Aviation was one of the most requested items in my mail, and that's what you'll be getting.

Any comments or questions on this series may be sent (with SASE) to: Bob Kopski 25 West End Dr. Lansdale, PA 19446

Meanwhile, a sincere "Thank you" for staying with this series, and may electric elation be yours!

Transcribed from original scans by AI. Minor OCR errors may remain.