Principles of Flight Leading Cadet Training Resources

Principles of Flight Learning Outcome 4: Be able to apply the principles of flight and control to gliders

REVISION

Questions What happens to Lift when a Wing is Stalled? Lift Increases as Angle of Attack Decreases. Lift Decreases as Angle of Attack Increases. Lift is Greatly Reduced. Lift Remains unchanged.

Questions The Critical Angle of Attack is Generally about? 5o. 15o.

Questions Which of the following will NOT REDUCE the Stalling Speed? Extra Weight. Larger Wing Area. Flaps Lowered. Flaps Raised.

GLIDING

Gliding Objectives: List and describe the Forces acting on Glider during balanced flight. State the effect of Wind on the distance travelled over the ground. Explain the effects of Airbrakes on Glide Performance. Understand the ‘Gliding Angle’ (Angle of Attack).

The Glider Previously we looked at the balance of forces acting on a powered aircraft (Chapter 1 & 2) Now we will be looking at a glider, which only has three forces acting, LIFT, WEIGHT and DRAG. The only way to maintain airspeed in a glider is to remain slightly “nose-down”. This uses the pull of gravity to drag the glider forwards. The forces on a glider can be balanced also, just like in a powered aircraft, and the glider can maintain its straight and level flight this way.

The Balance of Forces As has been mentioned, the glider has only three forces acting: LIFT, WEIGHT & DRAG They balance as shown: As you can see, the glide is slightly nose down to maintain airspeed. The speed is generated by the pull of gravity downwards on the weight of the aircraft

Speed Just as a bike can “coast” down a hill without being peddled, a glider can “glide” forwards without an engine. In order to keep going (and avoid the stall) the pilot puts the nose of the glider slightly down. To increase speed, the nose is reduced further, and vice versa for decreasing the speed. Since there is no engine, and the glider is always nose down, it is continually descending, hence most gliders cannot stay airborne all day.

How Far Can It Go? The distance a glider can travel is related to its height and gliding angle. The higher the glider is, and the shallower the angle, the longer it can stay aloft for. A high glider with a deep angle may not be able to glide as far as a low glider with a very shallow angle. The “Lift/Drag” ratio also affects the distance a glider can travel. This will be optimum at a particular angle, which will differ from glider to glider by design differences. This information will be available in the Pilot’s Notes.

How Far Can It Go? Most modern gliders are quite efficient, and hence have a very good “Lift:Drag” ratio and optimum gliding angle. The ATC’s Gliders, the Viking has a gliding angle of 1 in 35, so for every 1metre up, it can glide 35 metres in still air. Example: if the glider was 1km (1000metres) up, it could glide for 35km before landing.

Gliding Angle

Effect of the Wind The wind direction relative to the glider flight path will have an effect. If travelling downwind (i.e. in the same direction as the wind) the glider will travel further than id it is travelling upwind (towards the wind). The wind slows down the aircraft going upwind, hence more nose down angle is required to maintain airspeed, hence the glide angle is increased, and the glider will be able to cover less ground before it touches down.

Effect of the Wind Example: A glider travelling at 35kts into a head wind also of 35kts will appear not to move forwards, but instead stay in one place and descend.

Air Brakes Gliders do not have flaps as powered aircraft do. Instead they make use of air brakes to have the same effect. These are deployed from the upper and lower of the wings to interrupt the airflow over the wing surfaces. The airbrakes are deployed by the pilot on landing, and cause a huge increase in the drag on the glider.

Air Brakes This means a deeper angle is needed to being the glider in, hence it looses more height faster. This allows the glider to land in a much smaller space, as we have said, a Viking at 1m would require 35m of runway in order to land, and that’s without the distance to slow down!

Any Questions?

Gliding Objectives: List and describe the Forces acting on Glider during balanced flight. State the effect of Wind on the distance travelled over the ground. Explain the effects of Airbrakes on Glide Performance. Understand the ‘Gliding Angle’ (Angle of Attack).

Questions Name the Forces Acting on a Glider in Normal Flight. a. Force, Weight and Lift. b. Drag, Weight and Thrust. Drag, Weight and Lift. Drag, Thrust and Lift.

Questions How does a Glider Pilot Increase the Airspeed? a. Operate the Airbrakes. b. Lower the Nose by pushing the Stick Forward. Raise the Nose by pulling the Stick Back. Lower the Nose by pulling the Stick Back.

Questions A Viking Glider with a glide ratio of 1:35 descends from 1640 ft (0.5 km). How far over the ground does it Travel (in still air)? a. 17.5 kms. b. 35 kms. 70 kms. 8.75 kms.

Questions When flying into a Headwind, the distance covered over the ground will: a. Be the same. b. Decrease. Increase. Take you to Burger King.