相关题目
Unlike landplane operations at airports, seaplane operations are often conducted on water areas at which other activities are permitted. Therefore, the seaplane pilot is constantly confronted with floating, objects, some of which are almost submerged and difficult to see - swimmers, skiers, and a variety of wa tercraft. Before beginning the takeoff, it is advisable to taxi along the intended takeoff path to check for the presence of any hazardous objects or obstructions. Thorough scrutiny should be given to the area to assure not only that it is clear, but that it will remain clear throughout the takeoff. Operators of motorboats and sailboats often do not realize the hazard resulting from moving their vessels into the takeoff path of a seaplane.To accelerate during takeoff in a landplane, propeller thrust must overcome only the surface friction of the wheels and the increasing aerodynamic drag. During a seaplane take off, however, hydrodynamic or water drag becomes the major part of the forces resisting ac celeration. This resistance reaches its peak at a speed of about 27 knots, and just before the floats or hull are placed into a planning attitude.Several factors greatly increase the water drag or resistance: heavy loading of the air craft, or glassy water conditions in which no air bubbles slide under the floats or hull, as they do during a choppy water condition. In extreme cases, the drag may exceed the available thrust and prevent the seaplane from becoming airborne. This is particularly true when oper ating in areas with high density altitudes (high elevations/high temperatures) where the en gine cannot develop full rated power. For this reason the pilot should also practice takeoffs using only partial power to simulate the long takeoff run usually needed when operating at water areas where the density altitude is high and/or the seaplane is heavily loaded.1.Before beginning to take off, it＇s advisable to （ ） ．
Before the airplane begins to move, thrust must be exerted. It continues to move and gain speed until thrust and drag are equal. In order to maintain a constant airspeed, thrust and drag must remain equal, just as lift and weight must be equal to maintain a constant altitude. If in level, the engine power is reduced, the thrust is lessened, and the airplane slows down. As long as the thrust is less than the drag, the airplane continues to decelerate until its airspeed is insufficient to support it in the air.5.If the airplane is to be held in level flight, （ ）.
Before the airplane begins to move, thrust must be exerted. It continues to move and gain speed until thrust and drag are equal. In order to maintain a constant airspeed, thrust and drag must remain equal, just as lift and weight must be equal to maintain a constant altitude. If in level, the engine power is reduced, the thrust is lessened, and the airplane slows down. As long as the thrust is less than the drag, the airplane continues to decelerate until its airspeed is insufficient to support it in the air.4.How many speed regimes are mentioned in the passage?
Before the airplane begins to move, thrust must be exerted. It continues to move and gain speed until thrust and drag are equal. In order to maintain a constant airspeed, thrust and drag must remain equal, just as lift and weight must be equal to maintain a constant altitude. If in level, the engine power is reduced, the thrust is lessened, and the airplane slows down. As long as the thrust is less than the drag, the airplane continues to decelerate until its airspeed is insufficient to support it in the air.3.When an aircraft descends, （ ）.
Before the airplane begins to move, thrust must be exerted. It continues to move and gain speed until thrust and drag are equal. In order to maintain a constant airspeed, thrust and drag must remain equal, just as lift and weight must be equal to maintain a constant altitude. If in level, the engine power is reduced, the thrust is lessened, and the airplane slows down. As long as the thrust is less than the drag, the airplane continues to decelerate until its airspeed is insufficient to support it in the air.2.If the air is to accelerate, （ ）.
Before the airplane begins to move, thrust must be exerted. It continues to move and gain speed until thrust and drag are equal. In order to maintain a constant airspeed, thrust and drag must remain equal, just as lift and weight must be equal to maintain a constant altitude. If in level, the engine power is reduced, the thrust is lessened, and the airplane slows down. As long as the thrust is less than the drag, the airplane continues to decelerate until its airspeed is insufficient to support it in the air.1.In order to maintain a constant airspeed, （ ）.
Certain laws of nature are utilized in flight. The first requirement is the appropriate fly ing shape, or airfoil, which is commonly called the wing. This is shaped like a flattened teardrop. The rounded rear edge is called the trailing edge. The aircraft is supported by the earth’s atmosphere. What we think of as air is really a mixture of gases that have mass and weight but no shape.The forces that act on the airplane in flight are weight, lift, thrust and drag. Weight refers to the force of gravity that acts on the plane and everything in it at anytime. In order to fly, the plane must create a force stronger than the forces of its own weight. This is called lift. The lift is produced by the movement of the air around the wing as the plane moves through it. When the wing moves through the air quickly, a low pressure area vacuum is created on top of the wing, and a high pressure area is created under the wing. It is like a cushion of air on which the plane rests and stays during flight. An airplane propelled by the thrust of its jet engines can be thought of as flying on this cushion of air. Drag is the total resistance of the air to the aircraft passing through it. It may occur when the wing moves through the air to create lift, or it may occur when the landing gear is lowered.The pilot has controls that enable him to operate the plane as it moves through the air. He can cause it to ascend, descend, or remain level. He can also make turns in the air. This is called banking. The controls utilize the forces of the air by making slight adjustments or changes in the wings or the tails. When the flaps-the hinged sections of the wing are raised or lowered by the pilot, they can cause the aircraft to increase lift, decrease landing speed, and so forth. Similarly, changes in the tail of the aircraft cause the plane to turn to the right or to the left.Weather and atmospheric factors also affect flight. A headwind, or wind blowing a gainst the nose of the plane, will decrease speed. A tailwind will have the opposite effect. Altitude also affects flight. There is a huge river of wind that circles the globe generally from west to east at anywhere from 2500-50000ft above the surface of the earth. This is called the jet stream. As much as two hundred miles an hour may be added to the speed of a plane flying west to east within the jet stream. 5.The airplane flying west to east within jet stream will （ ） ．
Certain laws of nature are utilized in flight. The first requirement is the appropriate fly ing shape, or airfoil, which is commonly called the wing. This is shaped like a flattened teardrop. The rounded rear edge is called the trailing edge. The aircraft is supported by the earth’s atmosphere. What we think of as air is really a mixture of gases that have mass and weight but no shape.The forces that act on the airplane in flight are weight, lift, thrust and drag. Weight refers to the force of gravity that acts on the plane and everything in it at anytime. In order to fly, the plane must create a force stronger than the forces of its own weight. This is called lift. The lift is produced by the movement of the air around the wing as the plane moves through it. When the wing moves through the air quickly, a low pressure area vacuum is created on top of the wing, and a high pressure area is created under the wing. It is like a cushion of air on which the plane rests and stays during flight. An airplane propelled by the thrust of its jet engines can be thought of as flying on this cushion of air. Drag is the total resistance of the air to the aircraft passing through it. It may occur when the wing moves through the air to create lift, or it may occur when the landing gear is lowered.The pilot has controls that enable him to operate the plane as it moves through the air. He can cause it to ascend, descend, or remain level. He can also make turns in the air. This is called banking. The controls utilize the forces of the air by making slight adjustments or changes in the wings or the tails. When the flaps-the hinged sections of the wing are raised or lowered by the pilot, they can cause the aircraft to increase lift, decrease landing speed, and so forth. Similarly, changes in the tail of the aircraft cause the plane to turn to the right or to the left.Weather and atmospheric factors also affect flight. A headwind, or wind blowing a gainst the nose of the plane, will decrease speed. A tailwind will have the opposite effect. Altitude also affects flight. There is a huge river of wind that circles the globe generally from west to east at anywhere from 2500-50000ft above the surface of the earth. This is called the jet stream. As much as two hundred miles an hour may be added to the speed of a plane flying west to east within the jet stream. 4.When we lower or raise the flap, the airplane will （ ） ．
Certain laws of nature are utilized in flight. The first requirement is the appropriate fly ing shape, or airfoil, which is commonly called the wing. This is shaped like a flattened teardrop. The rounded rear edge is called the trailing edge. The aircraft is supported by the earth’s atmosphere. What we think of as air is really a mixture of gases that have mass and weight but no shape.The forces that act on the airplane in flight are weight, lift, thrust and drag. Weight refers to the force of gravity that acts on the plane and everything in it at anytime. In order to fly, the plane must create a force stronger than the forces of its own weight. This is called lift. The lift is produced by the movement of the air around the wing as the plane moves through it. When the wing moves through the air quickly, a low pressure area vacuum is created on top of the wing, and a high pressure area is created under the wing. It is like a cushion of air on which the plane rests and stays during flight. An airplane propelled by the thrust of its jet engines can be thought of as flying on this cushion of air. Drag is the total resistance of the air to the aircraft passing through it. It may occur when the wing moves through the air to create lift, or it may occur when the landing gear is lowered.The pilot has controls that enable him to operate the plane as it moves through the air. He can cause it to ascend, descend, or remain level. He can also make turns in the air. This is called banking. The controls utilize the forces of the air by making slight adjustments or changes in the wings or the tails. When the flaps-the hinged sections of the wing are raised or lowered by the pilot, they can cause the aircraft to increase lift, decrease landing speed, and so forth. Similarly, changes in the tail of the aircraft cause the plane to turn to the right or to the left.Weather and atmospheric factors also affect flight. A headwind, or wind blowing a gainst the nose of the plane, will decrease speed. A tailwind will have the opposite effect. Altitude also affects flight. There is a huge river of wind that circles the globe generally from west to east at anywhere from 2500-50000ft above the surface of the earth. This is called the jet stream. As much as two hundred miles an hour may be added to the speed of a plane flying west to east within the jet stream. 3.The article doesn＇t imply that the airplane can fly because （ ） ．
Certain laws of nature are utilized in flight. The first requirement is the appropriate fly ing shape, or airfoil, which is commonly called the wing. This is shaped like a flattened teardrop. The rounded rear edge is called the trailing edge. The aircraft is supported by the earth’s atmosphere. What we think of as air is really a mixture of gases that have mass and weight but no shape.The forces that act on the airplane in flight are weight, lift, thrust and drag. Weight refers to the force of gravity that acts on the plane and everything in it at anytime. In order to fly, the plane must create a force stronger than the forces of its own weight. This is called lift. The lift is produced by the movement of the air around the wing as the plane moves through it. When the wing moves through the air quickly, a low pressure area vacuum is created on top of the wing, and a high pressure area is created under the wing. It is like a cushion of air on which the plane rests and stays during flight. An airplane propelled by the thrust of its jet engines can be thought of as flying on this cushion of air. Drag is the total resistance of the air to the aircraft passing through it. It may occur when the wing moves through the air to create lift, or it may occur when the landing gear is lowered.The pilot has controls that enable him to operate the plane as it moves through the air. He can cause it to ascend, descend, or remain level. He can also make turns in the air. This is called banking. The controls utilize the forces of the air by making slight adjustments or changes in the wings or the tails. When the flaps-the hinged sections of the wing are raised or lowered by the pilot, they can cause the aircraft to increase lift, decrease landing speed, and so forth. Similarly, changes in the tail of the aircraft cause the plane to turn to the right or to the left.Weather and atmospheric factors also affect flight. A headwind, or wind blowing a gainst the nose of the plane, will decrease speed. A tailwind will have the opposite effect. Altitude also affects flight. There is a huge river of wind that circles the globe generally from west to east at anywhere from 2500-50000ft above the surface of the earth. This is called the jet stream. As much as two hundred miles an hour may be added to the speed of a plane flying west to east within the jet stream. 2.The forces that act on a parking airplane include （ ） ．
