Soaring is one of my great passions. I owned and flew a Super Dimona motorglider from 1995 to 1998 and a Stemme S10VT from 1998 until 2010. Both were based in the San Francisco Bay Area and allowed "soaring safaris" to places like the Grand Canyon, Telluride (CO), and the Grand Tetons. More usual trips were to Yosemite, shown in this photo of Half Dome and Nevada Falls, as well as to other areas in and around the Sierra Nevada Mountains. Additional soaring photos are on my soaring photos page and two soaring videos are located farther down this page.
Soaring is the sport of riding air currents to gain altitude which then is used to glide some distance through still or sinking air, to another source of lift where the process is repeated. In this manner, modern sailplanes (high performance gliders) have soared well over 2,000 km (1,200 miles) in a single day. Except for a brief initial launch using an auxiliary engine or a powered aircraft tug, this is done entirely on solar power, the source of the lift.
Because web sites can change rapidly, the only external links I have provided are to the Soaring Society of America and the British Gliding Association , which are fairly stable. But web searches such as "soaring", "sailplanes", "paragliding", etc. will produce many other good hits. I also include a brief list of FAQ's below, somewhat tailored to my own experience.
Is it dangerous? There are approximately 5-10 glider fatalities per year in the US and approximately 15,000 active glider pilots, indicating that they bear an annual risk of about a 1-in-2,000 of being killed by participating in the sport. Driving has an annual fatality rate of about 1-in-7,000, so soaring is roughly three to four times more dangerous than driving, on an annual basis. The sport has a danger factor, but one needn't have a death wish to take it up. [Note: There is no way to know the exact number of active glider pilots, so the above number is very approximate.] See the Soaring Safety section of this web site for some additional thoughts.
Is soaring the same as hang gliding? No. People soar in sailplanes, hang gliders, and paragliders, but there are major differences in these aircraft. Hang gliders and paragliders are light weight, with the pilot suspended below the wing. Paragliders can even be carried up a mountain, to the launching area, in a backpack. In contrast, my motorglider weighs 850 kg (1870 lb) and has a 23 meter wing span (75.5'). The pilot in a sailplane is totally enclosed in a cockpit, protected from wind and rain, and also providing much better aerodynamics. On the other side of the ledger, hang glider and paraglider pilots get closer to the pure experience of what it must feel like to be a bird.
What is the difference between soaring and gliding? The terms are sometimes used interchangeably. For example, the FAA licenses glider pilots, not soaring pilots. But most glider pilots soar at least some of the time. Soaring involves climbing in natural sources of lift, thereby replenishing altitude lost in the glides between areas of lift. Most glider pilots would say they only got to glide on days they couldn't find any lift, but say they went soaring if they were able to repeatedly regain altitude in lift.
Some low performance gliders are not intended to soar, notably the troop transports of World War II. These expendable gliders were towed behind powered aircraft and released when they were within gliding distance of their target fields. The advantage over parachute drops was that the troops would all deploy on the ground at the same time and place, whereas paratroopers often get separated.
The video below conveys the feeling of soaring amazingly well. The first minute is non-soaring scenery in the Alps, after which the soaring part starts.
What is a motorglider? Just as some sailboats have auxiliary engines, some sailplanes have auxiliary engines. And, just as with sailing, I hate to turn the engine on. On the other hand, the only thing worse than the noise of the engine is not hearing it when you need it. Having an engine makes a sailplane much more useful. I can take off under my own power, I can motor to areas of good lift and, if the lift should fail, I can get home. On the downside, motorgliders are significantly more expensive than unpowered gliders, both to buy and operate. The video below shows a Stemme S10VT motorglider, the same kind I flew from 1998 until 2010, when I sold it. Another kind of powered glider, often called a self-launching sailplane, is shown in a three minute video. (The first two minutes just show the warmup and can be skipped. The last minute is the good stuff.)
How do gliders without engines get airborne? In the US, gliders without auxiliary engines are usually towed aloft by a tow plane, connected by a rope that can be released. While rare in the US, winch launching (with mile long cables!) is used frequently in other parts of the world where fuel is more expensive. Other launch means are auto tow (again with a rope or cable) and bungee cords. The latter method is usually used to launch off a ridge (see Ridge Lift below) since it is hard to gain much altitude this way.
How far can a sailplane fly? As of August 2004, the world record was 3,009 km (1,869 miles), flights of 500 km (310 miles) are common, and 1,000 km flights are not uncommon. But even a flight that "goes nowhere," just playing within gliding distance of my home field (Hayward, CA) can be a magical experience, with magnificent views of the Bay, the San Francisco skyline, the Golden Gate Bridge, and the Sierra Nevada Mountains in the distance. When the lift is localized, as it often is in the Bay Area, I sometimes go no more than 10-20 miles from my home base. This would be boring in a power plane, but the views, the quiet, and the constant challenge of finding lift can keep me happily occupied for several hours.
What happens if the wind stops? Sailboats can't get home without external power when the wind stops, and it is a common misconception that the same is true for sailplanes. But altitude, not wind, determines whether a sailplane can make it home. My sailplane has a 50:1 glide ratio, meaning it can glide 50 miles horizontally for every mile of altitude. So, if I am 50 miles from my home field at an altitude of 10,560' (two miles), I have a 100% safety margin and have often done such a "final glide" into Hayward, burning off the altitude safety margin in a high speed glide toward the end. (The glide ratio drops at higher speeds.)
Any fixed wing aircraft needs air flowing over the wing to fly, but creates its own wind by moving through the air. A sailplane gets the energy to do this by always flying slightly downhill, which is why it loses altitude in the absence of lift.
What creates lift? Lift, an upward moving parcel of air, is part of the weather. Weather is created by unequal heating of different parts of the earth's surface, mostly from solar energy but with small contributions from geothermal and other sources. The unequal heating causes motion of the air in an effort to equalize temperature.
Thermals are rising chimneys of hot air, created when the sun heats the ground to a higher temperature than the surrounding air. The air near the ground heats up, becomes lighter than the cold air above it, and wants to rise, while the heavier, cold air above wants to sink. These two tendencies are in conflict and create an unstable equilibrium, during which time a bubble of hot air is formed near the ground. A catalyst is needed to trigger the thermal and break the tug of war. Thermal triggers are varied and include:
Because thermals concentrate power from a wide area into a narrow chimney of rising air, they can be very powerful. The Great Basin in Nevada, Utah, and Arizona is an excellent thermal generator in the summer with thermals that can exceed 2,000 feet/min (10 m/sec) to altitudes of over 20,000' although soaring in the US is usually limited to 18,000' to avoid conflict with airliners.
While thermals occur most often in summer, it is a temperature difference that creates thermals, so they can occur in winter if the air mass is colder than normal (e.g., after a cold front passes) and can be absent in summer if the air mass is warmer than usual or solar heating is reduced (e.g., by overcast). Thermals are usually separated by large regions of sink, in which case the pilot circles in the thermals until they top out and then flies at high speed through the sink to the next thermal.
This stopping to "tank up" in thermals makes the flight's average speed lower than the sailplane's typical flying speed. But thermals can also form lines of lift, particularly in areas of convergence (see below), allowing high speed flight without circling. In this mode, the glider pilot slows down in lift and speeds up in sink, thereby spending more time in lift and recovering the altitude lost elsewhere.
Ridge lift is created when wind hits a slope and is forced upward. Ridge lift is usually confined to an area close to the hill and is known for its adrenaline rush as the wing seems to brush the tree tops. When conditions are right, the Appalachian Mountains can produce ridge lift along much of their length, allowing very fast, long flights. [Note: Because this form of lift is usually found very close to the ridge, there is an added danger factor. While I am in the distinct minority among glider pilots, I will not use ridge lift unless it extends much further out than usual thereby allowing a somewhat higher safety factor.]
Convergence occurs when two air masses move in different directions and collide (converge). One air mass is forced up, over the other, creating a line of lift, similar to ridge lift, allowing high speed (no stopping to circle) flight. When convergence occurs in an area of thermals, it can trigger a line of thermals, allowing high speed thermal flight as well, although technically the lift is a mixture of convergence and thermal.
Mountain wave is created on the lee side of mountain ranges when strong winds (greater than 20 kts) hit the range at approximately a right angle. This produces ridge lift on the windward side, with turbulence and sink on the lee side. But, with the right conditions, a standing wave is created downwind of the sink that can rise much higher than the mountains. For example, the world altitude record of 49,009' for a glider was set in wave created by the Sierra Nevada Mountains, whose highest peak is under 15,000'. Wave can be localized, but in the right conditions (a seemingly constant caveat or prayer, depending on how you look at it), systemic wave can be set up which produces wave lift along much of the mountain range, again allowing very fast flights without circling.
How do you find lift? Lift is rising air. The energy to lift the air comes from heat stored in the air, so as it rises it cools. Cool air can hold less moisture than warm air, so the relative humidity in the air increases as it rises. If it rises high enough to reach 100% relative humidity, a cloud is formed. Thermals produce puffy, cauliflower shaped clouds called cumulus clouds, or cu's for short. Mountain wave produces a stationary lens shaped cloud, called a lenticular (lennie to the cognoscenti) or wave cloud. These clouds mark the areas of lift. The picture below, taken over the east end of Yosemite Valley in wave lift, shows both cumulus and wave clouds.
When convergence and thermals mix and form a line of thermals, this will often be marked by a "cloud street", a line of cu's. Soaring pilots will fly along these cloud streets, often dolphin flying (slowing down in lift, speeding up in sink), so the sailplane spends more time in lift without stopping to circle. The picture below, taken over Yosemite's high country in the east end of the park, shows a cloud street. There is also probably lift in the blue patch between the end of the cloud street and the few puffs to its left. If I have to traverse a blue area, with just a few little puffs of cloud, I often play "connect the dots," flying from one puff to the next, and am often rewarded by this effort.
If the air is very dry or the lift doesn't go high enough, lift does not generate clouds to act as markers. On such "blue days" (i.e., the sky is only blue, no white), you use other techniques:
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