Author: Dave Garwood
Edition: Model Aviation - 2009/08
Page Numbers: 112,113,114
,
,

Radio Control Slope Soaring

Dave Garwood [[email protected]]

Let's fly a "moldie"

Starting in slope soaring with an EPP-foam glider is the most commonly taken path these days, but there may come a time when a pilot wants a better-looking sailplane—one that is smoother, rounder, and sleeker.

Perhaps he or she needs a lighter glider for small air or small hills. It's possible that a person needs a heavier slope rocket for big air and big hills. Maybe he or she has taken up slope racing, and a stronger, stiffer airframe would improve lap times.

"Moldies," or sailplanes with molded composite parts, can be designed and built lighter than EPP-foam sailplanes or heavier when ballast is added. If any of the preceding capabilities are a siren song to you, a moldie may be in your future.

"Moldies" is a nickname for molded-fuselage airframes. "Composite" means that a combination of dissimilar materials are mixed during construction, such as epoxy resin and fiberglass cloth.

Additional materials are often introduced to take advantage of special properties, such as carbon fiber for tensile strength and stiffness and Kevlar for strength and toughness. Some sailplane designs even have hollow molded wings. Aircraft designers go to this time and trouble to achieve more accurate wing-airfoil sections, lighter wings, or both.

Some slope fliers advocate the advantages of foamies over moldies, and they might miss out on some top-end speed. Other slope pilots won't fly anything but molded composite super sailplanes, and they may have fewer flying sites to choose from, leaving out especially those with rock-strewn or manzanita-bush-infested landing areas.

I like both foamies and moldies. I prefer to build a fiberglass-fuselage airframe. I prefer flying a bounceable foam airplane when I have to land between bushes or even in bushes. But for pure flying ability, I prefer composite construction. For appearance points, moldies win again.

I remember flying my first fiberglass model—a Sig Samurai—a huge step up from the Sig Ninja balsa-and-plywood glider. Although it was nearly 20 years ago, I can remember the adrenaline rush that the Samurai's speed and precision delivered.

In a review of the kit in the April 1993 Model Airplane News, I wrote:

"The semi-symmetrical airfoil (1/64-inch plywood sheeted wings) and the slippery fuselage let this airplane pour on the speed, and it's really at ease when traveling fast. Of the 24 sailplanes I've built and flown, only one is faster, and none are as relaxed at speed."

At the World Soaring Jamboree in 1994, I saw my first high-performance WWII warbird: a Slope Scale Mitsubishi A6M6 Zero fighter. The molded-fiberglass-fuselage model was not only tearing up the slope at Eagle Butte, Washington, with speed and maneuverability, but it looked like an airplane while doing it. I had to have one of those, too. Then another, and another.

The Slope Scale warbirds can be ordered with light, medium, or heavy fiberglass-and-epoxy layups, and it's awesome to be able to have one of each to match different lift conditions. Right now I have four Slope Scale warbirds with receivers installed, ready to fly.

Also at this point, molded slope racers were starting to fill my quiver of slope aircraft—notably a Charlie Richardson Fun-1 One Design Racer (ODR) and a full-on screamer: a CR carbon Renegade. Man, I had arrived, stylin' and flyin' real fast. Oh happy day.

Stage three for me began when I learned to use an airbrush. My first Slope Scale models were finished with Krylon and a paintbrush, but three flying buddies urged me to learn airbrushing, and I am glad I did.

Then came more molded scale airplanes: a Doug Buchanan BAe Hawk in a British camouflage scheme and another Hawk in air-show-team colors. There's no shame in wearing out an airframe. Then I built and finished a Jeff Fukushima Focke-Wulf Fw 190 Dora, which was a great-flying large-scale warbird.

My airbrush high-water mark so far is a Carl Maas Sukhoi Su-25 Frogfoot, which you might remember from the cover of the April 2008 Model Airplane News. There's an article about airbrushing in that issue.

Stage four for me (I hope) will be making molds and pulling composite fuselage parts from that mold. I know enough about this process to respect and admire the high level of engineering, craftsmanship, and attention to detail that is needed to produce quality molded parts, but I have not done it myself. In the meantime, "support your local molder."

Moldie Advantages

  • Shape: Who doesn't appreciate the attractive appearance of rounded and curved parts? If it's a curved shape you need and you want a smooth finish on it, molding is the way to get it. It's far less work than building the form from sticks and a far smoother final finish than any reasonable EPP construction effort. Shape is important in scale models, and rounded shapes are strong and make efficient use of interior space on nonscale airplanes—look at airliners.
  • Stiffness: The composite materials' stiffness allows lightness in airframe production. EPP foam is soft and floppy, and foam aircraft need spars and fuselage stiffeners—often wood (heavy) or carbon-fiber tubes (expensive). Molded-fiberglass models can be made both lighter and heavier than foam or balsa-and-plywood airplanes. Lighter because the strength and stiffness allow lighter materials to be used; heavier because a design can have room inside for removable ballast.
  • Easier construction: A hollow fuselage makes radio installation easy. There's no cutting pockets in foam that let the servo wiggle under load; just install servo rails and mount with screws—the way servo designers intend them to be installed. Need a hard point for mounting a wing? Epoxy a bit of plywood in place and tap some threads to receive a bolt. Want to attach a fin or a horizontal stabilizer? Glue it on with epoxy.
  • Takes paint well: Sometimes you need more subtle colors than are available in iron-on covering. Sometimes you need a matte finish or a feather edge for camouflage markings. Paint is the answer, and fiberglass seems like it was made to be painted. Even the simplest and cheapest rattle-can spray finish will be more durable than almost any iron-on finish. Are you ready to dive into airbrushing for decorating your models? You'll like the way airbrushed paint lays down on fiberglass.
  • Repairability: I've smashed plenty of sailplanes in my time—wood, foam, and fiberglass—but I'd rather repair a fiberglass model than a foam or wood model. Sure, there are several tricks to learn about adhesives and reinforcing broken areas, but you can get a moldie back to its original shape and strength. For me, balsa models come out of the repair slightly crooked and much heavier, and foamies gain weight from repeated applications of Goop and tape, and they still tend to develop soft and weak spots.
  • Fly better: Molded sailplanes penetrate into headwinds better. Molded sailplanes accelerate quicker, have higher top speeds, and fly better in off-direction lift. The successful racing sailplanes and dynamic soaring (DS) models are molded composite. Yes, there are trainer racers and DS airplanes, but the real-deal, go-fast models are moldies. Toss out a fiberglass slope airplane after flying a foamie and you're in for a pleasant surprise.

Moldie Disadvantages

  • Higher cost: The cost of building a composite model is generally higher than an equivalent-size wood or foam design. Building time will probably be longer with composites, which adds to the cost as well.
  • Learning curve: The methods and techniques used to build and finish moldies can be new for some modelers, depending on previous experience. You may have to do some reading or get advice from experienced builders.
  • Fear of breaking: This is likely the single largest fear that keeps pilots from trying moldies. Although they can be broken, they can be repaired back to 100%. Hey—no guts, no glory. If you let the fear of crashing and repairing hold you back, you might miss the experience of higher speed and the superior ability to penetrate.

When I began this piece about molded slope sailplanes, I was hoping that after the EPP revolution and well into the period of rising demand for prebuilt sailplanes, there were enough composite molding houses in operation to supply the need. I knew that Dan Sampson had taken over production of the Slope Scale line. I knew that Jeff Fukushima at Vortech Models was still molding fuselages and making new designs.

While researching for this column, I learned that there were at least 28 companies in the US and Canada that supplied molded-fuselage kits and composite-built sailplanes suitable for slope flying. Many thanks to correspondents on RCGroups for helping to complete the list of sources.

Sources

  • AMD Hobby — Ventus 3.8-meter scale glider: (+852) 2858 6698; www.amdhobby.com
  • F3X.com — Racers and high-performance sailplanes: (949) 645-7032; www.f3x.com
  • Great Planes Manufacturing — Spirit 100 ARF, Spirit Elite ARF: (800) 637-7660; www.greatplanes.com
  • Northeast Sailplane Products — Composite gliders: (802) 655-7700; www.nesail.com
  • Slope Scale Models — Airacobra, A6M6 Zero, F-20, F-86, Tucano, U-2, BD-5: flybyudan.blogspot.com/2009_02_01_archive.html
  • Tom Martin Radio Control — Schweizer SGS 2-32 (the vista cruiser of sailplanes): (816) 392-8640; www.tmrcsailplanes.com

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