Gliding

1. Gliding

2. 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

3. 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

4. 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.

5. 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!

8. 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.

9. 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.

10. Questions

11. Questions

12. Answers • 1. c) • 2. b) • 3. c)