Leroy R. Grumman Cadet Squadron, NER-NY-153

Civil Air Patrol - The official auxiliary of the United States Air Force

Background

 

 

Description

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 using thermals and ridge updrafts as the source of the lift.


 

History

In 1848 Sir George Cayley, an eminent British scientist, is credited with having designed and built the first successful heavier-than-air device, a glider said to have carried a 10-year-old boy several yards after its launching from a hill. From the 1890s onward, research and development of gliders, flying techniques, and similar subjects were being notably pursued in Germany, England, and the United States.

 

Cayley Glider - Replica

 

A Cayley replica glider in flight

 

Otto Lilienthal Glider - 1894 test flight

 

World War I halted glider development, but when the Treaty of Versailles prohibited powered flight in Germany, one result was enormous progress in the development of soaring flight. The first world championships were held at Wasserkuppe, Germany, in 1937. Progress continued, but was slowed again during World War II when military applications of gliding forced sport flying into the background.

 

From then until now, the sport has flourished, and several countries boast aggressive, healthy soaring programs. At least 5,500 pilots throughout the world have earned diamond badges and over 150 have now flown flights farther than 1,000 kilometers (620 miles).


 

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.


 

What is the difference between soaring and gliding?

The terms are sometimes used interchangeably. 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. Most glider pilots soar at least some of the time.

 

 

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.

USAAF Waco Assault Glider

 

RAF Horsa Assault Glider in tow


 

 

Hang Glider - Launch

 

Hang Glider - In Flight

 

Is soaring the same as hang gliding?

People soar in sailplanes, hang gliders, and paragliders, but there are major differences in these aircraft. Hang gliders and paragliders are lightweight, with the pilot suspended below the wing. Paragliders can even be carried up a mountain, to the launching area, in a backpack. The pilot in a sailplane is totally enclosed in a cockpit, protected from wind and rain, and also providing much better aerodynamics for greater efficiency in utilizing lift. 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.

 

Paraglider

 

Paragliders

 


 

Grob Motorglider

 

What is a motorglider?

Just as some sailboats have auxiliary engines, some sailplanes have auxiliary engines. Having an engine makes a sailplane much more useful. It can take off under its own power, it can motor to areas of good lift and, if the lift should fail, it can get home. On the downside, motorgliders are significantly more expensive than unpowered gliders, both to buy and operate, are heavier (the weight of the engine) and have less efficient aerodynamic details/properties (i.e., engine cooling inlets, propeller, more robust landing gear to handle the additional weight) than a typical sailplane. They also require the pilot to have a powered aircraft license.


 

How do gliders without engines get airborne?

In the US, a tow plane, connected by a rope that can be released, usually tows aloft gliders without auxiliary engines. 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.


 

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. For example, a sailplane may have a 50:1 glide ratio, meaning it can glide 50 miles horizontally for every mile of altitude.  A fixed wing aircraft needs air flowing over the wing to fly but creates its own wind by moving through the air due to engine/propeller thrust. A sailplane gets the energy to do this by always flying slightly downhill, which is why it loses altitude in the absence of lift.


 

Is it dangerous?

There are approximately 5-10 glider fatalities per year in the US and approximately 15,000 active glider pilots, indicating about a 1-in-2000 chance of dying from participating in the sport on an annual basis. Soaring has a danger factor, but one needn't have a death wish to take up the sport.

Lift

 

What creates lift for a Sailplane since there is no 'Thrust" force component?

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:

 

  • turbulence created when two cars pass on a road
  • a discontinuity in topography (e.g., a mountain peak or pass)
  • wind hitting a mountain
  • a local hot spot, such as an asphalt parking lot

Thermal Lift - Animation

 

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/Hill Lift - Animation

 

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. Because this form of lift is usually found very close to the ridge, there is an added danger factor.


 

A Cold Front (High Air Pressure Air Mass) moving in - Animation

 

A Warm Front (Low Pressure Air Mass) moving in - Animation 

 

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 Lift - Animation 

 

A 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 less than 15,000'. Wave can be localized, but in the right conditions, a 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, 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 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:

 

  • "House thermals" are locations that frequently produce thermals. Most local pilots know the location of these faithful life savers, use them, and will share the knowledge with visitors or new comers.
  • Soaring birds have an uncanny ability to find thermals. If you see a soaring bird, following it will usually lead you to lift. If the bird leaves a thermal, follow it. It probably senses an even stronger thermal nearby. We don't know how birds find thermals, but they are better at it than any human or instrument we have yet devised.
  • Look for other sailplanes that are climbing.
  • Look for dust devils. The lift can extend well above the top of the visible portion.
  • Look for topographic features that are likely to trigger thermals. In addition to those enumerated earlier, rocky slopes facing the sun, steep canyons, mountain peaks or passes, and airports (lots of asphalt to soak up the sun's energy) are good examples.

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