PRINCIPLES OF FLIGHT

GLIDING

CHAPTER 6

PRINCIPLES OF FLIGHT

GLIDING

From previous lessons you will remember that with lift, thrust,weight and drag in balance the aircraft will fly straight and level at a constant speed.

If one of these forces is altered then the aircraft becomes unbalanced and will move.

If thrust is decreased (i.e. the engine is shut down) then the Aircraft is unbalanced.

To maintain a balanced situation the pilot can pitch the noseof the aircraft down and let the weight of the aircraft (gravity)act as the thrust. In other words gliding.

The same applies to a glider.

PRINCIPLES OF FLIGHT

GLIDING

From previous lessons you will remember that with lift, thrust,weight and drag in balance the aircraft will fly straight and level at a constant speed.

If one of these forces is altered then the aircraft becomes unbalanced and will move.

If thrust is decreased (i.e. the engine is shut down) then the Aircraft is unbalanced.

To maintain a balanced situation the pilot can pitch the noseof the aircraft down and let the weight of the aircraft (gravity)act as the thrust. In other words gliding.

The same applies to a glider.

PRINCIPLES OF FLIGHT

Balance Of Forces

The diagram shows a glider in a steady glide, with the 3 forces acting on it.

The glider can be controlled like a normal aircraft but must continue to descend to maintain speed. If the nose is pitched up too far then it will enter a stall.

PRINCIPLES OF FLIGHT

The distance a glider will travel over the ground is dependenton the glide angle.

The flatter this angle the further the glider will travel. It can be shown by Geometry that the angle is least when the Lift/Drag ratio is highest.

This happens at a certain angle of attack which varies with gliderdesign.

i.e. Lift is much greater than Drag.

PRINCIPLES OF FLIGHT

Therefore, from a height of 3,280 ft (1 kilometre),

In Still Air,

It will travel about 35 kilometres.

This information is found in a book called The Pilot’s Notes and for a Viking Glider the angle is about 1in 35.

There has to be a way of knowing when the glider is flying at This optimum angle of attack, and fortunately it is related to the airspeed.

1 km

35 kms

PRINCIPLES OF FLIGHT

PRINCIPLES OF FLIGHT

Effect Of Wind

A glider travelling downwind will cover a greater distance over the ground than a glider travelling into wind.

The pilot will fly at the same indicated airspeed in both cases, and the glider’s angle of attack and its gliding angle relative to the air will be the same in both cases.

As an extreme example, a glider with an airspeed of 35 kts, heading directly into a wind of 35 knots would make no forward progress as far as a spectator on the ground was concerned - to the spectator it would simply lose height slowly over one spot on the ground.

If the glider then turned until the wind was directly behind it, the spectator would see it covering the ground at nearly 70 knots!

Most gliders do not have flaps, but instead are generally fitted with airbrakes.

Airbrakes

They are panels which normally lie within the wings, with their edges flush with the surface. From a control in the cockpit, the pilot makes them pop out of the upper and lower wings at 90° to the surfaces, where they interfere with the smooth airflow,increasing the drag considerably and also reducing the lift.

To maintain the airspeed the pilot now lowers the nose – which increases the gliding angle, and allows the pilot to land in a smaller space than would otherwise be possible.

AIRBRAKES

PRINCIPLES OF FLIGHT

PRINCIPLES OF FLIGHT

QuestionsName the Forces Acting on a Glider in Normal Flight.

a. Force, Weight and Lift.

b. Drag, Weight and Thrust.

c. Drag, Weight and Lift.

d. Drag, Thrust and Lift.

PRINCIPLES OF FLIGHT

QuestionsHow does a Glider Pilot Increase the Airspeed?

a. Operate the Airbrakes.

b. Lower the Nose by pushing the Stick Forward.

c. Raise the Nose by pulling the Stick Back.

d. Lower the Nose by pulling the Stick Back.

QuestionsA Viking Glider 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.

c. 70 kms.

d. 8.75 kms.

PRINCIPLES OF FLIGHT

PRINCIPLES OF FLIGHT

QuestionsWhen flying into a Headwind, the distance covered

over the ground will:

a. Be the same.

b. Decrease.

c. Increase.

d. Take you to Burger King.