There are several reasons for flying electric sailplanes. They are a nice change of pace. They are beautiful to watch. They improve your piloting sensitivity. And they are quiet.

This article outlines the basics of electric sailpianes, and is intended for builder/fliers of moderate proficiency. I've been flying them for about five years; my knowledge is based on five aircraft.

The most popular and simplest type of electric sailplane has a 72 to 78" wingspan, a wing area of about 600 sq.", weighs about 45 ounces ready to fly, uses a three-channel RC system, is powered by a "500"-or-so size direct drive ferrite motor, swings an 8x4 prop, and has a six-cell 1200 mAH power battery. There are two readily available kits on the market with these stats, the Goldberg Electra and the Great Planes Spectra. Of course there are ARFs, but they tend to be heavy, and this article is intended for those who fly what they build.

I've built two versions of the Electra, and I recommend it highly as a good aircraft to start with. I built two fuselages with one wing and tail. One fuselage has a direct drive motor; the other is geared. This allowed me to compare performance. I've found that they are about equal, with maybe a slight performance edge for the geared Electra. The direct drive model has a Mabuchi 550 motor, a six-cell 1200 or 1400 mAH battery, and swings a rigid 8x4 prop or an 8x4 Great Planes folder. The geared model has an Astro geared ferrite motor, a seven-cell 800 or 1000 mAH battery, and swings a Master Airscrew 12x8 folder.

Weight and trueness of flying surfaces is essential for good glider performance, so you must build light and carefully. The wing is the most demanding part of glider construction, but the fuselage is rather packed with equipment -- the radio control system and the power system, together with all the wires that connect them. One way to address the problem of a crowded interior is to frame up the fuselage to the point where everything can be installed and properly positioned. Once this is done everything is removed and fuselage construction completed. That's not a bad practice for any aircraft.

While we're on construction, color schemes should be mentioned. Since sailplanes fly very high, visibility must be given serious consideration. As distance increases visibility is less matter of color or decorative pattern than it is of contrast between the model and its background, the sky. (Study highway signs and sign lettering on its background while driving and you'll see.) A model at altitude or distance is seen in silhouette, mainly. The sky can be blue and the model illuminated by bright sunlight. But it can also fly in the shadow of a cloud, or be seen against a cloud, or in hazy conditions. At altitude, you want the greatest contrast possible, the strongest silhouette. Stripes won't help much, even broad ones. My recommendation is transparent coloring for the wing and stab, solid for the fuselage and rudder. One of my sailplanes is transparent yellow; two have red wings and tail with white fuselage; one has transparent blue wings and flying surfaces, white fuselage. Ail have good visibility, the blue being one of the best because of its darkened silhouette. A good reason for a white fuselage and rudder is that it aids visibility in case you land in a tree or thick brush, against which white stands out strongly.

Among the variables in electric sailplane components are the motors, the size and number of the motor batteries, the motor on-off mechanism, and the electrical connectors. Lets take them one by one.

I've described direct drive and geared motors, recommending both. Motors may have ferrite (iron) magnets or they may be made of cobalt for high performance. Start with ferrite; then if you like sailplanes graduate to cobalt. Either type needs a capacitor across the motor terminals to prevent radio interference. Good ferrite motors are made by Leisure Electronics; good cobalts are made by Astro.

I've used three types of motor cut-off mechanisms, all of which work very well. The first is a simple toggle switch, which is actuated by a servo. A short length of tubing is slipped over the toggle shaft. A shod length of wire with Z bends at each end links the toggle arm to the servo arm. The tubing prevents strain on the servo. Simple and very effective.

The second type is a micro switch which has a metal actuating arm. (Radio Shack sells a small one, but I prefer a larger one obtainable from Leisure.) Again, tubing is slipped over the actuating arm, and a wire connection is made with a servo, which can be micro size since the arm requires little force.

The third method is to use an Electronic Speed Control (ESC). There are many available, but for sailplanes the Astro 217D model works just fine and is relatively inexpensive. It also eliminates the motor control servo.

A fuse is recommended. An U-shaped auto 20 or 30 amp fuse works quite well.

As for connectors, the most common type is the nylon Tamiya connector. This works well, but I've switched to Sermos connectors, and found that they improve performance markedly. Deans connectors are also very good.

I've mentioned batteries-- number and mAH capacity-- and what I've found to work well for direct drive or geared motors. I'd urge experimentation. Vary the number of cells (say seven rather than six cells for direct drive), and vary the size of the cells (say seven rather than six cells for geared drive). The key is to remember that with electrics you trade power with weight and hence performance. Build light and you need less power to get to altitude. Increase battery size, either number of cells or cell capacity, and you get more thrust and a longer motor run, but only up to a point of diminishing returns. Finding that point is the reason for experimenting. Adding weight diminishes both climb and glide. In my view the ideal battery is one that gets you up quickly and smoothly without the aircraft seeming to labor, has enough capacity for two good climbs, and which still allows a slow glide. That's my criteria. Experiment.

Some fliers use battery eliminator circuits (BEG). That’s a personal preference. It means a special radio receiver. I don't like BECs because they shutoff the motor when the battery has run down to a certain level. It means you can't have a reserve of motor propulsion to help align your landing. My big fear is that I might catch a thermal, and not be sure that I have enough Rx battery power left. But its a personal matter.

There are several CBRC members who fly electric gliders, and like all CBRC'ers have experience to share. Among them are Ken Gustavson, Jim Prouty, and myself.

What about a good local hobby shop for electrics? I recommend Roy Smith at Suzie Goose Hobbies, 718 E Gude Drive, Rockville, MD, 20850, tel (301) 279-5572.

A specialized mail order house is Hobby Lobby, which handles a lot of German aircraft and accessories. MasterAirscrew makes folding props and a simple power unit (motor, prop, wiring harness, toggle switch). I also recommend Leisure Electronics, 2950 Airway Ave, Bldg A4, Costa Mesa, CA, 92626, tel (714)435-9218, as well as Asfro Flight, 13311 Beach Ave, Marina del Rey, CA, 90292, tel (213) 521-6242.

Try electric sailplanes. They're a great part of model aircraft experience and pleasure.

Paul Spreiregen (202) 337-2887