Author: Dave Garwood
Edition: Model Aviation - 2011/08
Page Numbers: 110,111,112
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Radio Control Slope Soaring

Dave Garwood <[email protected]>

Guest column: Bruce DeVisser (San Jose, CA)

In the RC skies, few models look as serene and as sophisticated as a long-wing scale glider in flight. For nearly 20 years, the South Bay Soaring Society (SBSS) has run the impressive Los Banos Scale Sailplane Event at the magnificent Los Banos Reservoir RC flying site in north-central California.

In the current context, "scale" means a radio-controlled model of a full-size sailplane, either modern or vintage. "Power scale soaring" (PSS) refers to a radio-controlled, powered model of a full-size, powered prototype, either propeller or jet.

What attracts modelers to scale slope soaring? The answer is simple—slope soaring is a lot of fun, and those who are interested in scale models want to fly their scale sailplanes on the slope, too.

There is no fundamental difference between PSS and scale sailplane slope soaring—ok, roll rate is much higher with a PSS model. Another advantage of slope flying is that, as long as the wind blows, you can keep flying. There is no dependence on finding a thermal to maintain altitude, and if you want to loop or roll there is typically lift available for recovery to the original altitude.

If you ask a group of RC pilots what types of models are used for slope soaring, most answers would describe sport sailplanes, purpose-designed slope or racing models, and PSS aircraft. Many people think scale sailplanes are used only for aerotowing, and while that is true for a large segment of the scale community, many dedicated slopers only fly their "scalies" on the slope and forgo a tow release—practically a standard feature on many scale sailplanes.

Scale sailplanes can be launched off a hilltop or by bungee or winch. Slope models generally are gliders because they cannot rely on thermal flight at the site, but they do very well in the much stronger lift found on ridgelines.

Vintage sailplane models, such as the well-known Minimoa, often have light wing loading and thick airfoils, which produce a lot of drag and can make them difficult to fly in strong slope winds unless ballast is added. Modern sailplanes benefit from years of airfoil research that have produced thinner profiles with better lift-to-drag characteristics. Designers have followed a parallel path in producing efficient airfoils scaled for models. It is possible to fit a more efficient modern airfoil to a vintage fuselage, but the appearance may not be prototypical—so ballast is a readily available remedy for vintage types.

The thinner airfoils of full-scale modern sailplanes, such as the DG-600, don't often scale directly to small models until you approach about 1/2 scale. Efficient model airfoils have been developed that look the part while providing the performance modelers need: models that fly as well as they look.

Launching and flying scale sailplanes on the slope

Successful launches into slope lift require planning and technique. A simple push-off will not accelerate a typical scale model to a stable flying speed. Instead, launch the model directly into the wind in a slightly nose-down attitude, following the slope face until safe flying speed is reached before leveling off.

One common issue is wing lift at the point of release if the model isn't pointed directly into the wind, which can lead to loss of control. Larger wingspans increase this tendency, so assess wind conditions carefully and, when possible, have an experienced person launch the model for you.

Once airborne, scale sailplanes emphasize style: large, graceful maneuvers and the ability to climb to the top of a lift wave or bubble. At good sites you can fly to the limit of eyesight in multiple directions while remaining only a few hundred feet above the launch point. Lift can shut down suddenly at many sites, so always keep a landing plan in mind.

Landing areas and model construction

Slope fliers often accept difficult landing areas to take advantage of great wind and lift, so models are built with that in mind. Scale sailplane construction ranges from all-balsa to all-molded fiberglass, and these models are not designed to withstand repeated rough landings.

Typical scale sailplane size and weight:

  • Wingspan: about 120–240 inches (3–6 meters)
  • Weight: about 6–36 pounds (3–16 kilograms)

These sizes require larger landing areas and gentle touchdowns—no slamming these models into terra firma. A large shallow-angle slope face is often easy to land on headed up the hill or even across the face, provided the surface is good. Even full-scale sailplanes use similar landing techniques at some sites. When you see scale slope-soaring articles online and in print, they mostly show the best sites—Los Banos, CA; Point of the Mountain, UT; Lake Wilson, KS; Torrey Pines, CA; and similar places—but there are many suitable sites around the country.

Getting started

If you're a slope flier curious about scale sailplane sloping, the best introduction is time with an experienced pilot and a suitable model so your first flights avoid launch and landing concerns. A competent aileron pilot should handle a scale model, though experience with rudder and coordinated turns is beneficial. Vintage types, in particular, often turn much better when rudder is used along with aileron and elevator.

When buying your first model, start smaller, lighter, and simpler. Two forgiving slope sailplane trainers are scale EPP sailplanes such as a 3-meter Ka-6 or a 60-inch (2-meter) Schweizer 1-26. Both are designed by Dave Sanders and available from Sky King RC Products; they are easy to build, fly reasonably, and tolerate some rough landings.

If you have experience and a suitable site and want a hard-body sailplane, consider staying in the lighter and cheaper 2.5- to 4-meter range—examples include the Hobby Club semiscale series and the ICARE RC standard series. Most of these have a fiberglass fuselage and balsa-covered foam wings.

If you build your own, there are many plans and kits for vintage and modern sailplanes, many designed with slope flying in mind. Check Island Models (laser-cut vintage kits), Traplet Plans Service, and Tom Martin RC. There are also many accessories such as pilots, instrument panels, and more.

Further information can be found on web forums, club websites, and in specialty magazines such as Flying Scale Models (UK) and Aufwind (Germany). Articles and plans by Chris Williams (various British model magazines) are highly recommended. For local involvement, the South Bay Soaring Society (SBSS) is a great resource.

Sources

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