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)