Favorable and unfavorable forces, to act on the airplane, an engine-driven fixed-wing air-craft, heavier than air, when in flight, changes in magnitude, to apply pressure, to be consi-dered as, to maintain altitude, to enter a climb, shape of airfoil, speed of the air passing
over the wing, a twisting or rotating motion of an airplane, to increase the performance of the air-plane, by increasing the efficiency of the desira-ble forces of lift and thrust, to satisfy the func-tion and desired performance of the airplane.
© НИЛ НОТ НИО УВАУ ГА(и), 2009 г
Aviation English Fundamentals | 8
Reading
Text. FORCES ACTING ON THE AIRPLANE IN FLIGHT
Figure 1-1. Forces acting on the airplane in flight
When in flight, there are certain favorable and unfavorable forces acting on the airplane. It is the primary task of a pilot to control these forces so as to direct the airplane's speed and flightpath in a safe and efficient manner. To do this the pilot must understand these forces and their effects (Figure 1-1).
Airplane is an engine-driven fixed-wing air-craft heavier than air, that is supported in flight by the dynamic reaction of the air against its wings. Among the aerodynamic forces acting on an airplane during flight, four are considered to be basic be-cause they act upon the airplane during all ma-neuvers. These basic forces are lift, the upward acting force; weight (or gravity), the downward acting force; thrust, the forward acting force; and drag, the rearward acting, or retarding, force.
While in steady flight the attitude, direc-tion, and speed of the airplane remain constant until one or more of the basic forces changes in magnitude. In unaccelerated flight (steady flight) the opposing forces are in equilibrium. Lift and thrust are considered as positive forces (+), while weight and drag are considered as negative forces (-), and the sum of the opposing forces is zero. In other words, lift equals weight and thrust equals drag.
When pressure is applied to the airplane controls, one or more of the basic forces change in magnitude and become greater than the oppos-ing force, causing the airplane to accelerate or move in the direction of the applied force. For example, if power is applied (increasing thrust) and altitude is maintained, the airplane accelerates. As speed increases, drag increases, until a
point is reached where drag again equals thrust, and the airplane will continue in steady flight at a higher speed.
In straight-and-level flight (constant alti-tude) lift counterbalances the airplane weight. When lift and weight are in equilibrium, the airplane neither gains nor loses altitude. If lift becomes less than weight, the airplane will en-ter a descent; if lift becomes greater than weight, the airplane will enter a climb.
A number of the factors that influence lift and drag include: wing area, shape of the airfoil, angle of attack, speed of the air passing over the wing (airspeed), and density of the air moving over the wing. A change in any of these factors affects the relationship between lift and drag. When lift is increased, drag is increased, or when lift is decreased, drag is decreased.
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© НИЛ НОТ НИО УВАУ ГА(и), 2009 г
Aviation English Fundamentals | 9
Airplanes are designed in such a manner that the torque effect is not noticeable to the pilot when the airplane is in straight-and-level flight with a cruise power setting.
By definition, "torque" is a force, or combination of forces, that produces or tends to produce a twisting or rotating motion of an airplane.
Airplane designers make an effort to in-crease the performance of the airplane by in-creasing the efficiency of the desirable forces of lift and thrust while reducing, as much as possi-ble, the undesirable forces of weight and drag. Nevertheless, compromise must be made to satisfy the function and desired performance of the airplane.
Ex. 5. Comprehension check.
1. What is the primary task of a pilot? 2. How can you define an airplane?
3. Name the aerodynamic forces acting on an airplane during flight. 4. What does lift counterbalance in straight- and-level flight?
5. Specify the number of the factors that influence lift and drag. 6. What is “torque moment”?
Vocabulary practice
Ex. 6. Five of these words can not be used in combination with force. Which ones are they?
Favourable, pressure, unfavourable, basic, forma-tion, upward acting, retarding, forward acting, factor, opposing, applied, forcing, negative, posi-tive, desirable, angle, undesirable.
Ex. 7. Cross odd one out.
1. Aircraft, vehicle, airship, glider, air balloon, spacecraft 2. Lift, drag, weight, pressure, thrust.
3. Negative, positive, neutral, additional.
4. Climb, magnitude, straight-and-level flight, descent. 5. Twist, rotation, torque, stability.
6. To reduce, to drop, to decrease, to fall, to increase. 7. To tend, tendency, tending, thrust.
Ex 8 ∗. A: Match the words in column A with those in column B. Example: h – 2.