Aircraft and some facts about the flight

A. The aircraft is able to rise into the air and to keep in the air because of the forces working on it. The motion itself maintains those forces.

B. When moving in the air, the aircraft produces an upward force which is called lift and acts at right angles to the direction of the air stream. When moving the leading edge of the wing pushes the air out of the way. Part of this air flows rapidly over the wing and part of it flows under the wing, both parts joining behind the trailing edge. The important thing is that due to the curved upper surface the air flowing over the wing travels faster than the air flowing under the more or less flat bottom surface. The air traveling across the top of the wing creates a reduced pressure on the upper surface. The air traveling along the bottom of the airfoil is slightly compressed and develops increased pressure. The difference in pressure between the air on the upper and lower surfaces of the wing produces lift.

C. To produce lift, the airplane wing must move through the air at high speed. This high speed is produced by a force of thrust which is acting in the direction of the airplane’s motion. Both a propeller and a jet engine produce thrust.

D.Drag is the resistance an airplane meets in moving through the air. The faster the airplane moves, the greater will be the drag.

E. In any position of flight the airplane is acted upon by four forces, the last being weight, or gravity, the downward acting force.

F. Lift opposes weight and thrust opposes drag. Drag and weight are forces inherent in anything lifted from the earth and moved through the air. Thrust and lift are artificially created forces used to overcome the forces of nature and enable an airplane to fly. The engine-propeller combination is designed to produce thrust to overcome drag. The wing is designed to produce lift to overcome weight.

G. In straight-and-level unaccelerated flight, lift equals weight and thrust equals drag. Any inequality between lift and weight will result in the airplane entering a climb or descent. Any inequality between thrust and drag while maintaining straight-and- level flight will result in acceleration or deceleration until the two forces become balanced.

H. The lifting power and the drag of a wing depend on the angle of attack, the shape and the size of the wing, density of the air and the speed of the flight.

Comprehension Check

Divide the text into logical parts. Think of the subtitle to each part. Highlight the key words of each part.

In the text find the definition of lifting force and air resistance.

3. Complete the following sentences with suitable words from the text:

1. The aircraft is able to keep in the air because of …….

2. It produces an upward force which ……

3. Part of the air flows over the wing and …

4. The air flowing under the bottom of the wing travels …..

5. The air moving across the top of the wing creates …

6. The difference in pressure between ….

7. To produce lift the wing must ….

8. A force of thrust acts ……

9. The resistance the aeroplane meets …

10. The aeroplane is acted upon by …

11. Drag and weight are forces ….

12. Thrust and lift are …..

13. Thrust is produced by ….

14. Inequality between lift and weight results in ….

15. Inequality between thrust and drag results in …..

These are the definitions. Guess the terms.

1. The force that tends to the airplane wing in a direction perpendicular to the air stream.

2. The resistance the airplane meets in moving through the air.

3. A force producing a high speed of the airplane.

4. A force with which a body tends toward the centre of the Earth.

5. The angle between the chord line of an airfoil and the direction of the air flow.

6. Blades fixed to a revolving shaft for driving an aircraft.

7. A device which is capable of producing lift when it is moved through the air.

8. The width of the wing from leading edge to trailing edge.

Agree or disagree with the statements. Use conventional formulae of agreement and disagreement.

Agreeing Disagreeing

-Absoluteli! - I don’t agree.

- You are right. – I don’t think so.

- That’s true. – I’m not sure …

- I quite agree. – I wouldn’t say that.

1. The distance along the bottom of the wing is greater than the distance over the top of it.

2. The air flowing over the top travels faster than the air flowing along the bottom of the wing.

3. The faster a gas flows, the more pressure it creates.

4. The pressure of the faster-flowing air on the bottom of the wing is less than that of the slower-moving air on the top.

5. The increased pressure differential results in greater lift and thrust.

6. The thrust and drag depend on the angle of attack.

7. When thrust becomes more than drag, the airspeed decreases rapidly.

8. The thrust pushes the plane forward overcoming the resistance of the air against the plane.

9. The lift of an airplane acts vertically upwards and its weight – vertically downwards.

10. The lift being equal to the weight, the airplane climbs; if the two forces are unequal the plane descends.

6. Answer the questions.

1. Why is the plane able to fly in the air?

2. What are the forces acting on it?

3. What happens in the air when an airfoil moves through it?

4. How does the air flow over and under the wing?

5. What does the air stream create on the top and bottom of the wing?

6. What does the pressure differential results in?

7. What condition is necessary for producing lift?

8. How may thrust be created?

9. What is the drag?

10. How do the four forces act? What is their nature?

11. What are the means of producing lift and thrust?

12. What does the straight-and-level flight mean?

13. What do the lift and drag depend on?

Vocabulary Focus

1. Match the word in column A with the word in column B having a similar meaning. Be careful, there are some extra words in column B.

A B

stream decrease

travel rear

airfoil support

join not curved

produce move

straight flow

maintain operate

act create

reduce connect

artificial aerodynamic surface

trailing man-made

leading

increase

Match the antonyms.

A B

lift weight

thrust slow

climb backward

bottom rear

flat natural

upper drag

fast upward

artificial descent

forward lower

front curved

downward top