Author: Louis Joyner
Edition: Model Aviation - 2012/11
Page Numbers: 115,116,117,118
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Built-up glider wings

by Louis Joyner [email protected]

Years ago, one of the model magazines published a hand-launched glider that featured an interesting wing construction. Instead of the usual solid piece of 3/16- or 1/4-inch sheet, the wing consisted of a piece of 1/16-inch balsa with a large cutout in the middle of each panel.

Ribs glued on the underside of the sheet gave it camber. Both top and bottom were covered with tissue. I'm not sure there was much savings in weight or time, but it did eliminate the shavings and sanding dust.

More recently, some large discus-launched models have used built-up construction in an effort to keep weight down. These typically use a solid balsa front section back to roughly 30% chord, and a wide balsa trailing edge with connected ribs. The entire wing is covered with tissue or plastic film. In addition to saving some weight, easier-to-find balsa is used.

For small catapult gliders, built-up construction also offers a way to use some of those scraps of lightweight C-grain balsa left over from building a larger glider.

At a recent contest, Joe Hurdle showed me two catapult gliders with built-up wings. One featured a striking bird-feather color scheme airbrushed on the top of the wing. The other, slightly smaller model, had an elegant elliptical planform and "V" dihedral.

The wing consisted of a 3/16-inch balsa leading edge and 1/8-inch balsa trailing edge connected by 1/16-inch ribs. A wide center rib and filler blocks at the tips complete the wing structure. After assembly, the wing is planed and sanded to the desired airfoil as is a solid balsa wing. Instead of covering the entire wing, Joe only covered the open areas with carefully shaped pieces of plastic film.

Remote Dethermalizer

Remote dethermalizer (RDT) systems allow the modeler to activate the DT remotely at any time during the flight. They can be used to save a power model that goes off pattern and is heading straight for the ground, to prevent a fly-away when a model booms out in a thermal, or to keep a model out of the trees when flying from a small field. When test flying, an RDT allows the pilot to cut a flight short and make trim adjustments.

The simplest RDTs are stand-alone systems that consist of a receiver, battery, and microservo that activates the DT. A small transmitter sends the activation signal when the flier pushes the button. Similar to a garage door opener, the signal is encrypted to eliminate the chance of activating another model's RDT. Systems that can share the battery power of a host electronic timer are also available.

Two popular RDT systems are the Airtek unit from Ken Bauer at Airtek Free Flight Electronics and the Aeris system available from Starlink Flitetech Models or from the manufacturer, Free Flight Electronics. Both the Airtek and Aeris systems are available as stand-alone or as host versions.

Kit Bays showed me the RDT on his tip-launched glider. It is the Bauer Airtek stand-alone system fitted into the nose of the glider instead of lead, so there is no weight penalty (typical stand-alone systems weigh roughly 8 grams). The microservo is located closest to the front of the model, with a small LiPo battery next, and the receiver behind that. Kit has fitted the transmitter with an armband so it is always accessible.

As a battery-conservation measure, the receiver in the Airtek unit that Kit uses cycles on and off. "Sometimes you have to wait a couple of seconds for it to react," says Kit. He has purchased a second Airtek receiver that is always on and provides instant DT. He plans to use that receiver in a scaled-up Civy Boy 61. "It sucks up a little more current," he says, "but it could save the model."

Although a stand-alone RDT setup sells for approximately $300, it reduces the chance of losing a model. Kit has set up all four of his tip-launched gliders for RDT. Each model is fitted with a microservo and a simple mousetrap lever to reduce the loads on the servo arm.

"I move the receiver and battery between models," he mentioned. On his next model, Kit plans to try a linear servo, which is slightly narrower than the servos he is using. This will allow him to reduce the front fuselage width. RDT also opens up free flight (FF) to sites that would not be suitable for a conventional timer or fuse-activated DT. "It's really handy for a small field," says Kit. "The practice fields I have are so small."

Book Review

The Compressed Air Engine Book, edited by Sergio Montes and Chris Stoddart, provides an in-depth look at one of the earliest forms of free flight propulsion. Dating back to before the turn of the century, compressed air motors (similar to steam and CO2) provided a quiet, compact power source.

Although supplanted by internal combustion engines and more recently by electric power, compressed air motors have endured throughout the last 100-plus years in a variety of forms, both homebuilt and manufactured. The ready-to-fly Air Hog is one recent example of a compressed air model for mass consumption.

Published by Free Flight Quarterly, the book explores the history, design, and construction of compressed air motors. Detailed drawings and instructions for building compressed air motors are included. One, designed by David Kerzel, can be built with only a drill press and hand tools utilizing brass tubing, rod, and sheet from the local hobby shop.

Constructing John Morrill's .015 cu. in. Zephyr motor requires a small lathe and milling attachment. Most of the parts are aluminum, with Delrin used for the piston and drill rod for the crankshaft. His plans also detail construction of air tanks from two small aluminum juice cans.

Also included are small-scale plans for Jim Sprenger's Scirocco, a 30-inch-span Sport model utilizing the Zephyr motor. The model uses traditional stick-and-tissue and the book includes full-size patterns for wing and stabilizer ribs, propeller blank, and fuselage formers.

Another motor plan is from a 1928 issue of The Modelmaker magazine and was designed by Ed Packard, founder of Cleveland Model Supply. This opposed-twin design uses brass tubing and sheet for most of the parts. The original plans called for a 14-inch propeller; Roger Schroeder constructed one that turned a 7 x 3 propeller at 2,000 rpm on 60 pounds of air pressure.

Information about ordering The Compressed Air Engine Book can be found on Free Flight Quarterly's website listed in the Sources. The 84-page book is $25.

FAI Model Supply

In the mid-1990s, John Clapp and his wife, Sally, purchased FAI Model Supply from Ed Dolby, who had started the mail-order company roughly 50 years earlier. At that time, the company's major product was rubber strip for free flight models.

John worked closely with the manufacturer to develop rubber of consistently high quality and power output. Now FAI Super Sport rubber is used by virtually every competition rubber flier in the world. In addition, the Clapps expanded the company to include a wide variety of kits and free flight supplies.

This past summer, John and Sally decided to sell FAI Model Supply to another husband-and-wife team: Charlie and Geralyn Jones. Charlie is an active F1B and F1G modeler, as are the couple's two sons, Ryan and Kyle. The new contact information for FAI Model Supply is listed in Sources. Best wishes to the Jones family in its new venture.

All rubber fliers owe John and Sally a big thanks for their work keeping us supplied with quality rubber strip and hundreds of hard-to-find free flight items.

Retrieval Pole

Getting a model out of a tree has always been a part of free flight. Throughout the years, many methods have been tried, but the two that seem to have survived are the tall pole and a professional tree climber.

The late Tommy McLaughlan had a homemade retrieval pole of telescoping sections of aluminum and magnesium tubing. Everyone who flew at Tommy’s Pensacola, Florida, contests probably used his retrieval pole at least once.

For the last 20 years or so, the retrieval pole of choice has been the telescoping fiberglass one used by power company linemen. The Telescoping Hot Stick, made by Hastings and sold through local dealers, is available in extended lengths from 12 to 40 feet.

At the Carolina Free Flight Association contest last summer, CD John Diebolt showed me a lighter alternative to the industrial-strength lineman’s pole. It’s a fiberglass pole used for flying decorative kites.

Sold by Jackite, Inc., the pole measures 46 inches collapsed and extends to 31 feet. At 5 pounds, it weighs much less than a Hastings pole. Although the Jackite comes in green, the orange one makes the most sense for our intended use in the trees. The price for the 31-foot model is approximately $70 plus shipping. Shorter ones are also available.

As with any pole, the Jackite product should be used from directly below the model. This makes handling much easier and prevents the pole from bending excessively. You will need to fit the end of the pole with some sort of hook or fork so you can carefully move the model from the tree limb.

Sources

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