Gliding – No Engine, No Problem

 by

 Jim Hanney

 Ever thought of surfing the air currents thousands of feet above the ground, flying hundreds of miles cross country in a day, or looping the loop as part of an aerobatics routine?  These are all possible in a glider or as many do enjoy, a day’s local soaring flying over familiar landmarks.

The sailplane

Gliders fly like any other type of aircraft, airflow over the wings creating an area of low pressure above the wing, and high pressure below it.
 This difference in air pressure causes the area of high pressure (below the wing) to be sucked up into the area of low pressure above it, creating lift.  Unlike an aircraft that has an engine to provide its forward movement through the air (thrust), a glider relies on gravity. Therefore, a glider is always flying down through the air, even when gaining height in a thermal.

Learning to fly
Gliding is no more difficult to learn than driving a car.  However, you can’t stop a glider and get out if you feel tired or need a break! Therefore, the most difficult aspect to master is confidence in you own ability to fly the glider from take off to landing whether that is 5 minutes flight or five hours.  A glider has the same basic controls as powered aircraft; elevator to control pitch, rudder to control yaw and ailerons to control roll.  All three controls along with the trim and airbrakes must be mastered to fly the glider as efficiently as possible. The picture above is of a K13 coming into land at Ayres Field, to the east of Bovington Camp.

Soaring
Thermals start at ground level as bubbles of air, which have warmed in relation to the air around them.  They are, therefore, lighter and begin to rise, forming a thermal.  However as the air rises it expands and cools.  This is at a rate of 3ºC for every 1000 feet (the dry adiabatic rate).  The thermal continues to rise and cool until it equals the temperature of the surrounding air.  It is at this point that on a warm summer’s day, cumulus clouds form.  These clouds act as beacons of lift to the experienced glider pilot.  By studying clouds a glider pilot can ascertain if a cloud is forming or decaying, and by turning under the building cloud, rise with it.  A building cloud will start as an area of “haziness” in the sky and as the cloud builds, it will darken and form a “flat bottom”.  It is at this point that lift is strongest.  It then begins to deteriorate and collapse.  However, to the inexperienced eye, a collapsing cloud and a building cloud can look the same.  Cloud spotting can be an interesting past time!

Hill Soaring
Although thermal soaring is the most popular today, the gliding movement started with hill soaring and continues today at a number of specialist sites.  The theory is straightforward.  As the wind blows up a hill it rises, and the glider pilot is able to fly along the line of the hill, and as long as the wind blows the glider will remain airborne. In the pioneering days of gliding this led to flight of over 48 hours, and a number of deaths due to pilots falling asleep!

Wave Soaring
This is a very specialised form of soaring which utilises the atmospheric conditions caused by air flowing over mountain ranges and causing undulations of rising and falling air, similar to waves in the sea.  As these “waves” build, the gliding pilot can rise with them up to heights of over 45,000 feet.  We don’t get many of these waves in Bournemouth!

I hope this short introduction to gliding gives an insight into this wonderful form of flying.  If you would like more information please contact Dorset Gliding Club at www.dorsetglidingclub.co.uk  

Written by Jim Hanney with help from his son. 

The photograph, right, is of the author Jim Hanney, many years ago (no more years than that!) preparing for a solo trip.  He is glad to say that he has since given up smoking!