All about RC soaring!

Model Airplane News, Dec 2003 by Garwood, Dave

harness the power of the wind

There are RC pilots who think of gliders as nothing more than slow-flying, unimpressive model aircraft to be used mainly for trainers and to entertain old men whose flying skills are not up to flying high-powered aircraft. These fellows are uninformed. While gliders do serve well as trainers and as slow, easy-to-see planes for those whose eyeballs and reflexes have seen better days, there is more to gliders-much more, RC sailplanes are an ultra-exciting component of RC flying, and some can do things that powered planes cannot.

Model sailplanes can be 2-channel (rudder and elevator) slow flyers, aerobats and speed demons, and some are 6-servo, all-out-competition machines (ailerons, flaps, elevator, rudder). They can be flown in thermal lift and slope lift, and they can be engaging enough to fill an RC flier's career.

This article is aimed at RC pilots who may be interested in soaring but perhaps haven't tried it yet, and it covers the two main branches of RC soaring: thermal and slope. I'll talk about both kinds of soaring and mention representative sailplanes, but first a few words on lift.

When they're flying, sailplanes are descending relative to the parcel of air they are in. Gravity gives us the power to fly an unpowered model, as the downward pull is converted into forward speed by the sailplane's wing. For us to keep a sailplane in flight for a significant time, we must find lift, or rising air, and fly it in that lift. We have two main sources of lift: thermal lift and slope lift.

* Thermal lift is generated by the sun's heating the ground unevenly; the warmer ground heats air that expands and rises. This rising air creates the lift in which we see hawks, eagles and vultures circling upward with wings outstretched.

* Slope lift is generated when wind blows into the face of a hill or ridge and is forced upward. When we see gulls cruising by, flying without flapping, they are flying in slope lift.

THERMAL SOARING

The song that plays in the back of my head while I'm thermal soaring is The Eagles' "Peaceful Easy Feeling." Few activities are as relaxing and intriguing as cruising around the sky searching for therrnals and then bringing the plane down when you're good and ready. You can fly therrnals by yourself, with a couple of buddies, or in an organized contest.

Thermal sailplanes cost between $50 and $1,000 and use radio systems that start at $79 and go up to $500. The most popular starter thermal sailplane is a 2-meter-wingspan sailplane (78 inches) built of balsa and plywood or purchased in an ARF package. Polyhedral (curved-wing) sailplanes are controlled by two servos that drive the rudder and elevator. They are inherently stable and tend to right themselves when you make control mistakes. They are also inclined to fly themselves with little input from their pilots. These sailplanes are large enough to fly well while carrying two inexpensive servos of standard size.

The classic beginner polyhedral trainer is the Carl Goldberg Products Gentle Lady; it has been in production for more than 20 years because of its clear building instructions and solid flight performance. Others in this class are the Great Planes Spirit and the Sig Riser. You can find many suitable beginner, intermediate and advanced sailplanes on the websites listed in the "Soaring Resources" sidebar.

LAUNCHING TECHNIQUES

How do you get a model that doesn't have a motor into the air? We have five methods: hand-launch, rubber high-start, bungee launch, winch and aerotow by a powered model airplane.

* Hand-launch is just what the term suggests. The pilot throws the sailplane and immediately begins the search for lift. Today's hand-launch gliders (HLGs) are "discus launched" by one wingtip, and with practice, an average pilot can easily achieve a launch height of 60 feet or more. Dig out your copy of the January 2003 issue of Model Airplane News for an article on flying these amazing planes.

* High-start. Most commonly used by newcomers, a high-start consists of a ground stake, 30 to 100 feet of rubber tubing and 100 to 400 feet of towline that ends with a parachute that has a tow ring on the top. High-starts come in several strengths and sizes and are rated for the wingspan of the sailplanes they're designed to launch. Generally, the larger the plane, the longer the rubber tubing and the towline.

To launch with a high-start, turn on your transmitter and receiver, slide the tow ring onto the sailplane's towhook and walk downwind from the stake to stretch the rubber. With a last wiggle of the sticks and a check that the control surfaces are moving, throw the sailplane upward at a 45-degree angle. It will rise quickly, tracing a curved path upward in the direction of the stake. When it flies over the stake, the tow ring will slip off the towhook automatically, unless the wind is strong, in which case the plane will stretch the rubber tubing and tend to stay on the towline. To release it, push the stick forward to dip the nose, and then pull up, and the tow ring will slip off the towhook.