Gliding
Balance of Forces
• A glider in steady glide has 3 forces acting
on it.
• Note the angle the glider is to the horizontal.
• Lift acts 90º to the flight path
• Drag acts along the flight path
• Weight acts vertically downwards
Speed
• A glider falls in a controlled way from a set
height.
• As the glider descends, air flows over its
wings producing lift.
• The lift reduces the rate of descent.
• To raise the airspeed, the nose of the
glider is lowered and the aircraft descends
faster
• Rising the nose reduces the rate of
descent and hence the airspeed.
• Reducing the airspeed too much could
result in losing so much lift that the aircraft
will stall.
• Since a glider has no engine to propel it
through the air, in order to maintain steady
flight the aircraft must be continually
descending.
How far will a glider travel?
Glide angle
• The flatter the angle, the further the glider
will travel over the ground
• The glide angle is least when the ratio of
lift to drag is at its highest.
• Viking and Vigilants have flat gliding
angles so that they can go a long way
whilst coming down slowly. (Viking 1 in 35)
– From height of 1km it will travel 35 km before
touching down!
Effect of wind
• A glider travelling downwind will cover a
greater distance over ground than a glider
travelling into wind.
• The airspeed, glider’s angle of attack and
gliding angel relative to the air will be the
same in both cases.
Air brakes increase the glide angle
• Most gliders do not have flaps.
• They are fitted with airbrakes which are panels
which normally lie within the wings and lie with
their edges flush with the surface.
• The pilot makes them pop out of the upper and
lower wings at 90º to the surfaces, where they
interfere with the smooth airflow, increasing the
drag considerably.
• To maintain air speed the pilot now lowers the
nose-which increases the gliding angle, and
allows the pilot to land in a smaller space.
Questions
Questions
Answers
• 1. c)
• 2. b)
• 3. c)