Here are some brief answers to questions we are often asked.  As with most things in the universe, the detailed answers are far more fascinating.

 

Q. What’s the difference between a “glider” and a “sailplane”
A.  “Glider” is a general term … There are paragliders, sugar gliders and hang-gliders   … Even the space shuttles were gliders.  The more precise name for our type of aircraft is “sailplane”.  However, most people just call them gliders and we’re happy with that.

By the way, did you know that hang gliders were invented right here in Grafton, Australia!  [See Link]

… and that several of those pioneers went on to form our Gliding Club!

Q. Is it difficult to fly a sailplane?
A.  Sailplanes are probably the most docile of aircraft other than balloons.  Fortunately they are way more controllable than balloons.  The geometry built into sailplanes creates “positive stability”.  That is,  when you take your hands off the controls, the sailplane will establish itself in stable flight … much like a dart or an arrow will do.  A large part of the skill in piloting a sailplane is trusting that your aircraft “wants to fly well”.  As pilot, you use control inputs to “tell” the sailplane what you want it to do.  You can then relax the controls (or even take your hands off them) and let your sailplane sort out the rest for itself.

Q. Are sailplanes fragile?
A.  Quite the opposite. The strength of an aircraft is usually expressed as the amount of “g-force” that it can withstand.  Our sailplanes are designed to handle a force of 5.3g.  By comparison, a Boeing 747 is designed to handle 2.5g and a Cessna light aircraft is designed for 3.8g.  In short, sailplanes are often the toughest characters on any airfield!  Having said that, every aircraft has lightweight control surfaces that have to be handled with care.

Q. How does a glider fly without an engine?
A. Pretty much like a paper aeroplane … A glider is always flying “downhill” towards the ground, trading height for forward speed. When we fly our two-seat training sailplane, we angle the nose down about two degrees. At this angle, our sailplane uses gravity to trade about 150 feet of height per minute to create a forward speed of 42 knots.

Q. Why don’t you talk in metres and kilometres per hour?
A. I’d love to, but aviation is international. The international agreement for aviation is to measure height in feet, horizontal distance in nautical miles and speed in  knots (nautical miles per hour). To convert our previous answer into metric measurements, our training sailplane descends at about 3 km/h in order to achieve a forward speed of 78 km/h. Pretty slippery when you think about it!

Q. So, how can a glider keep flying for more than a few minutes at a time?
A. The trick is to fly in areas where the air is rising faster than 3 km/h!  That way the air will carry the sailplane upwards faster than it is descending.

Q. What makes air rise?
A. It all comes down to the heat from the sun. The sun heats the atmosphere unevenly as it travels across the sky. Think of how the temperature changes from dawn to midday … from winter to summer … and from the grassy banks of a river to a bitumen carpark.  Well, as they say… “hot air rises”.  As warmer air leaves the ground, it leaves behind a “hole” … a partial vacuum (area of low pressure) that pulls in nearby cooler air.  In this way, the sun stirs the atmosphere into a “boiling” motion … 24/7.  We ground creatures are familiar with cooler air that’s moving horizontally to fill areas of low pressure … we call that “wind”.  Pilots also become familiar with air that’s moving up and down … like water simmering in a saucepan. Pilots call rising air “lift” and descending air “sink”.  Airline passengers experience lift and sink as “turbulence”.

Q. How can you find these areas of lift?
A. At Grafton, we mostly search for “thermals”.  These are “columns” of air that form over warm areas on the ground and channel the warmer air up through the atmosphere.  They’re much like those big round cooling towers that you see near power stations … except they’re way bigger (about 200 metres across) … and they’re invisible!  Although we can’t see the thermals themselves, there are visible signs that betray their locations. Fluffy cumulus clouds often (but not always) form high up within the thermal “tower”, so clouds are our most reliable sign. Some birds such as eagles also like to circle within thermals … if birds are flying and not flapping, then they’re in a thermal ! Hard dry areas on the ground heat up faster and are more likely to create thermals. So flying over bare or rocky hills, the roofs of a town, a shopping centre, a ploughed field or the car bodies in wrecking yards and carparks will increase your chances of finding a thermal.

Q. So does that mean gliders can only fly when the sun is shining?
A. Generally, that’s true.   No sun, no thermals. However, there are other types of lift, the most common being “Ridge Lift” and “Wave”.  Ridge Lift occurs where air is being pulled upwards over a smaller obstacle such as a hill or escarpment.  Wave occurs when air is being pulled over a larger obstacle, usually a mountain.  Flights in ridge lift or wave can continue for as long as the wind keeps blowing …  sunshine or overcast … throughout the night … even for several days.

Q. Do you need clouds or wind to fly at Grafton?
A. No.  Sunshine is the most important ingredient for us.

Q.  How quickly do gliders climb?
A.  That very much depends on the weather and the skill of the pilot.  On a day with strong sunshine, a sailplane can climb more than 1,000ft per minute in a thermal.  Sailplanes flying in wave can more than double that figure.  Climb rates between 300ft per min and 500ft per min are considered normal.  By comparison, a Cessna light aircraft climbs at 700ft per minute and a Boeing 747 climbs at about 3,000ft per minute.

Q. Does a glider have to stay near the airfield?
A. No

Q. So, how far can a glider fly?
A. The world record distance for a daytime flight is just over 3,000 kilometres, set in South Africa. (That’s the distance from Perth to Sydney!)  The Australian record is a 1,300 kilometre flight from Kingaroy QLD to Benalla in VIC.  Gliding flights of 300 kilometres or more occur almost every day in Australia.

Q. How can a glider fly that far?
A. Simplest answer? …

“Circle under a cloud to gain height  … Use that height to fly to another cloud … REPEAT ”

Q. How close does the next cloud have to be?
A. Given strong sunshine and a high performance sailplane, you might fly 120 kilometres before you need to “top up” your height under another cloud.  It is common for pilots to travel between 30 and 70 kilometres between clouds.

Q. How long can gliders stay in the air?
A. Competitions for the longest flight duration were abandoned during the 1950s. It was recognised that encouraging pilot fatigue was irresponsible. The world record at that time was 56 hours. A recent flight of 2,400 kilometres in New Zealand took eleven hours to complete. Most everyday flights in Australia will be around four hours or less but flights in excess of six hours are also common.

Q. How high can a glider fly?
A. The world record altitude is 76,000 ft … set by an Australian!   Everyday flights operate between 2,000ft and 10,000ft where there is sufficient oxygen for the pilot to function normally without needing to carry special breathing equipment.

Q. How fast do gliders fly?
A. The world record average speed over a 300 kilometre triangular “track” is 225 km/h. Remember, this also includes the time that was spent circling in thermals to gain height! Modern gliders can fly up to 300 km/h. Everyday flights are generally flown in the range from 70km/h to 150km/h.

Q. How much does a glider cost?
A. How much do you want to spend? A brand-new high performance glider with flight computers and a retractable jet engine can cost upwards of $300,000! On the other hand, a second-hand modest performance aircraft will cost around $15,000 or less. Many pilots form syndicates to share the cost of buying a high performance aircraft. The cheapest option is to join a gliding club and hire your club’s aircraft.

Q. How do you measure the “performance” of a glider.
A. Now we’re getting technical … There are a number of ways to measure performance depending on what you consider to be more important. The simplest explanation is to compare glider performance to the fuel efficiency of a car. Cars that can travel furthest using one litre of fuel are often said to have a better performance. Gliders don’t burn fuel … they use up height as they travel. Gliders that can travel furthest using 1,000ft of height are said to have a higher performance.   This performance figure is normally expressed as a “glide ratio”.

Q.  Can you explain this “glide ratio” thing a bit better?
A.  Certainly!  Our two-seat training aircraft has a glide ratio of 26:1.  That is, it will travel 26 metres forward for each 1 metre of height that it descends. By doing some maths, this converts to a distance of eight kilometres forward per 1,000 ft of height used. High performance gliders can have a glide ratio of 60:1 or more and can travel over eighteen kilometres per 1,000 ft of height lost.

Q. How does the performance of a sailplane compare to other aircraft?
A. A Cessna light aircraft has a glide ratio of 9:1 … with its engine off, it will descend at 730 feet per minute.  Surprisingly, a Boeing 747 has a much better glide ratio of 17:1.  Yet, with its engines off,  a 747 will descend at nearly 1,200 feet per minute.  The glide ratios of sailplanes range from about 25:1 up to 60:1, yet all sailplanes descend at very similar rates around 140 feet per minute.  Doesn’t seem to make any sense?  We told you that the detailed answers are fascinating!

Q. Is it frightening to fly without an engine?
A.  Not at all …  In fact, some people say it’s more frightening to fly with one!  The question in their mind is …

“What’s going to happen if that noise suddenly stops?”

For example, suppose our Cessna and Boeing 747 have engine failure at 5,000ft.  The Cessna will be able to travel 13 kilometres before it lands.  Its pilot will have 6.8 minutes to find an airfield somewhere within that 13 kilometre radius.  The 747 will be able to travel 25 kilometres before it lands but its pilot will have only 4.5 minutes to line up on a mighty big airfield.  A sailplane descending from 5,000 ft will be able to travel between 42 and 90 kilometres before it lands …   That’s an available landing area between 5,500 and 25,500 square kilometres!  The sailplane pilot will have 36 minutes to identify an airfield or paddock within that area and to plan their approach.    There’s simply no reason to be frightened.

Q. Did you just say “land in a paddock”?
A.  Yes.

It’s a big country!

Sometimes you just can’t find a thermal or an airfield where you need one.   Sailplanes need very little room for a landing and they are specifically built to perform landings on rough ground.  All glider pilots are trained to land in paddocks.   We call these “outlandings”.  Landing in a paddock is exactly the same as landing on a runway … only different!  Outlandings are not frightening either, just inconvenient.

BTW … This would be a good time to ask why sailplanes have only one wheel.

Q. Okay … Why DO sailplanes have only one wheel ?
A.  Glad you asked!

There are a number of reasons.  Having one wheel means that the sailplane can be made narrower and more streamlined.  It also reduces the overall weight of the aircraft.  But two very important reasons are often overlooked.  The first is that a single-wheel, compact design is very much stronger than two and three wheel designs.  Secondly, having one wheel on the centreline of an aircraft is vastly superior when landing on rough and uneven ground.  The aircraft won’t be suddenly deviated or twisted by one off-centre wheel touching down first or getting snagged on something.  It’s is all part of that tough design that gives you confidence in your aircraft and its ability to set you down safely in a paddock without drama.