More frequently asked questions
What actually makes a glider fly?
The simple answer is “the wings”. The special shape of the wing of a glider creates a suction effect above the wing and a pressure effect below the wing. The result of this is that the wing is lifted by the air passing over it. When enough lift is generated then the wings lift the entire glider off the ground.
It has no engine – how does it go forward?
A glider moves forward by putting its nose down and losing height. In a sense it “falls” and the energy gained by this drop in height is converted into forward motion. Things are not as bad as it may seem at first glance. Gliders are very efficient and for each metre of height lost a typical club glider will move forward 30 metres (written 30:1). This is known as the Glide Angle and is a measure of the efficiency of the glider. The very best gliders have a glide angle of 60 : 1
How long does a glider flight last?
A glider flight can last for less than a minute or for more than 12 hours. Admittedly both of these times are extremes. You can expect a flight to last at least five minutes, but if the weather conditions are good then flights of 30 minutes or more are usual.
How does the glider get off the ground?
There are two main methods – aerotow and winching. At North Wales GC, winching is used. This involves using a winch with a long cable. The winch is placed some 1100 yards away from the launch point and the glider is attached to a winch cable. The cable is then reeled in at around 60 miles per hour and this causes the glider to climb steeply. After 30-40 seconds the glider will be over 1000 feet high and possibly as high as 1700 feet.
What is a “thermal”?
A thermal is a bubble of warm air that is rising. On a sunny day the Sun heats the ground and air near the ground becomes warm. Eventually this bubble of warm air detaches itself and starts rising. If the glider stays within this bubble it will be carried upwards. Using thermals gliders can ascend several thousand feet into the sky.
What is “Ridge Lift”?
Occassionally there are features in the landscape which force the wind to move upwards. Ridges and hills are particularly good at this and if the glider gets into the rising air it is lifted up. Such lift is known as ridge lift.
Why does a glider only have one big wheel?
The wings of a glider are very efficient at generating lift. As soon as the glider starts moving the wings start generating lift and the aircraft can easily balance on its wheel. When landing the aircraft stays balanced on its wheel right until it stops. Weight is important and one wheel only weighs half as much as two wheels, so gliders make do with one wheel.
Can anyone learn to fly?
The answer is yes – but there are some restrictions. The design of the glider places some physical constraints on the size of the pilot. Most gliders cannot accommodate people who are very tall (over 6ft) or who weigh more than 16 stones (224lbs / 102kg). There are also some medical constraints – pilots must have reasonable eyesight in both eyes, must not suffer from epilepsy, major coronary problems, etc. In general – and this is only a “rule-of-thumb” guideline – if you are healthy enough to drive then you are healthy enough to fly a glider.
To keep flying, gliders need lift from the surrounding air. One form of lift is a thermal. Thermals are created when the sun warms the air near the ground until. When this pocket of air becomes significantly warmer than the surrounding air, it starts moving upward through the atmosphere. This bubble of air can be several hundred feet across and involve as much as 50,000 tonnes of air moving upward at (typically) 500 feet per minute. When the bubble rises high enough any water vapour in it cools and will form a small fluffy cloud with a rounded top and a flat bottom.
Cross section of a thermal
The thermal consists of several bubbles of air moving upwards in a loose column. Within the thermal there is a movement of air such that the centre of the thermal can provide very strong lift whilst the outer edges provide very little lift. The glider will attempt to centre in the thermal’s core and will fly in a circle to stay in the strongest lift.
To get a series of thermal bubbles providing plentiful lift, it helps if the warm air on the ground is regularly disturbed to “unstick” the thermal bubble from the ground. Cars and agricultural machines are good sources of disturbance and are said to “trigger” the thermal.
Cross Country Soaring
Finding a thermal
There are three basic techniques for finding a thermal. One is to look for the cumulus cloud that can form at the top of a thermal whilst another technique is to fly downwind from a ground-based feature that is likely to create warm air, for example a dry, freshly ploughed, brown field or a large car park. The final trick is to look for somebody who has already found a thermal – either another glider or a bird.
To keep flying, gliders need lift from the surrounding air. One form of lift is ridge lift. This is caused when the wind blows across a feature in the landscape such as a long ridge or a hill. As the wind meets the obstruction it is forced up and over the ridge or hill and any glider flying in front of the ridge will also be lifted up.
As the wind moves over the top of the ridge it may become very turbulent instead of flowing smoothly. This is known as “curl over” or, more colourfully, as “the clutching hand”. The glider is dragged down by the descending air almost as if someone had reached up and grabbed it. Fortunately curl over is easily avoided by simply staying in fron of the ridge.
To keep flying, gliders need lift from the surrounding air. One form of lift is wave lift. This is caused when the wind blows across a feature in the landscape such as a hill or mountain and, if the wind is of sufficient strength, then the airflow begins to oscillate up and down like a large wave. This sort of lift is glider heaven. Wave systems can provide lift up to 20,000 feet and is very smooth to fly in.
Wave systems are easy to find. Their position is usually marked by very odd clouds which are very, very smooth and often very long and thin. The only problem is getting high enough to contact the wave system. At North Wales, we get strong wave from Snowdonia when the wind is in the west and blowing at just the right strength.