1. Aviation page

Forces acting on the airplane

The airplane in straight-and-level unaccelerated flight is acted on by four forces – lift, the upward acting force; weight, or gravity, the downward acting force; thrust, the forward acting force; and drag, the backward acting force of wind resistance. Lift opposes weight and thrust opposes drag. Although these four forces are acting on the airplane in any attitude of flight, only their relationship during straight-and-level flight will be discussed. (Straight-and-level flight is flight at a constant altitude and heading).

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 the weight (or gravity).

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.

1. Read and learn the following words and expressions:

1. straight-and-level flight – прямолинейный горизонтальный полет

2. to accelerate – ускорять(ся)

3. lift – подъемная сила, поднимать

4. weight – вес

5. thrust – тяга

6. drag – лобовое сопротивление

7. resistance – сопротивление, стойкость

8. attitude – положение (в пространстве); угол, характеризующий положение в пространстве

9. altitude – высота

10. heading – направление полета; курс

11. to overcome – преодолевать

12. to enable – давать возможность

13. to equal – равняться

14. climb – подъем, набор высоты; подниматься, набирать высоту

15. descent – спуск, снижение

16. to maintain – содержать, придерживаться, поддерживать, удерживать

17. acceleration – ускорение

18. deceleration – замедление

2. Match the words with their definitions:

lift	the downward acting force
weight	moving faster
drag	moving up
thrust	the forward acting force
acceleration	moving down
deceleration	the backward acting force of wind resistance
altitude	moving slower
climb	the upward acting force
descent	height

3. Answer the questions:

1. What forces act on the plane in straight-and-level unaccelerated flight?

2. What does lift oppose?

3. What does thrust oppose?

4. What forces are artificially created ones?

5. When will acceleration or deceleration occur in straight-and-level flight?

6. When will climb or descent occur?

2. Aviation page

airfoil – аэродинамическая поверхность; профиль крыла

surface – поверхность

wing – крыло

horizontal tail surfaces – горизонтальное хвостовое оперение

vertical tail surfaces – вертикальное хвостовое оперение

cross-sectional view – поперечное сечение

leading edge – передняя кромка

trailing edge – задняя кромка

reference line – расчетная линия

chord – хорда

extremity – край

AIRFOILS

An airfoil is a device which gets a useful reaction from air moving over its surface. In other words, an airfoil is a device which, when moved through the air, is capable of producing lift. Wings, horizontal tail surfaces, vertical tail surfaces, and propellers are all examples of airfoils.

For convenience, we will use a cross-sectional view of a wing in our discussion. The forward part of an airfoil is rounded and is called the leading edge. The aft part is narrow and tapered and is called the trailing edge. A reference line often used in discussing airfoils is the chord, an imaginary straight line joining the extremities of the leading and trailing edges.