Slope Sailplanes

About Slope Soaring

Slope sailplanes are a form of R/C glider that were designed for the slope or edge of a hill. I used to say that slope sailplanes needed to be medium to large in size, but with the advent of new radios and small, powerful servos, you can build a slope plane that's teensy. Most sailplanes or gliders tend to be made as light as possible, but slope soarers don't worry so much about the overall weight — they concentrate on precision and speed. And some are just built for combat on the slope.

Some slope planes tend to look like fighter planes and others can have long, thin, razor-sharp wings. However, I have flown some of my older, retired engine-powered planes on a slope too (minus the engine as you don't need it there).

Slope sailplanes are usually launched by tossing or throwing your planes into the wind while standing near the top of a slope. As the plane leaves your hand and enters the lift generated by the slope, the plane will either rise (if made to fly slower, usually by pulling back on the elevator "stick" to give it up elevator) or gain speed. On the slope or in a thermal, sailplanes are always moving downwards through the air. If the air below the plane is rising, either from the slope or thermal, faster than the plane's descent rate, the plane will rise.

Some slope lift can be quite strong. Strong enough, in some cases, to fly planes designed for gas or electric power (without the engine or motor running) quite well. On some of those 'booming lift' days it feels as though you could fly your radio transmitter or a sandwich from your lunchbox...

Finding a Good Slope

Most good flying slopes are hills or cliffs where the wind strikes the surface of a slope and rises as it is forced upwards due to the shape of the hill. The wind should blow directly against the face of the slope for maximum lift. However, if the prevailing wind doesn't strike the hill nearly 'straight on' or mostly perpendicular, the wind might end up blowing around the face of the hill instead. This will result in lots of wind blowing in your face, but no lift available for flying.

Another thing that can affect the lift on a slope is whether there is a mountain or other hill within a half mile or so in front of the slope. Instead of the air lifting as it reaches the slope, it has a tendency to rise and fall often containing severe turbulence and unpredictability. It can make it impossible to control your plane or have any fun while flying on this kind of slope.

Also note: on top of the slope, just back from the edge of the hill, the lift sometimes stops abruptly or spins toward the ground causing turbulence and other "rotors" that can cause the plane to pitch wildly as it nears the ground — or there sometimes is no lift at all.

If you're shopping around for a slope that no one flies, it is better if you find a slope with a smoother, more rounded top. Hopefully not covered by rocks either, as the rocks have this ability to 'jump' in the way of a landing plane!

All classes of thermal sailplanes will work well in a slope environment. The only potential problem about flying, say a handlaunch sailplane, on a slope is the amount of available lift can be too much for a sailplane designed for extracting every breath of lift available — i.e. you can't get the plane down on the ground again easily! For a slope, you can sacrifice lightness of construction and other efficiency in the airframe for a plane designed for speed and strength. It is not uncommon for some slope gliders to fly at speeds in excess of 120 mph or faster as long as the conditions permit.

Unfortunately there are not that many beginner-level planes these days to choose and the ones that are out there tend to have an electric motor and folding propeller. Having power come from a motor can come in handy, but on the slope you can just ignore the motor or even remove it and fly it on the slope without it.

Also, there is a type of slope soaring that has become very popular: Combat slope flying. The goal is to essentially knock others out-of-the-air. There are companies producing sailplanes specifically for this purpose.

Slope Soaring in Action