相关题目
An aircraft stall results from a rapid decrease in lift caused by the separation of airflow from the wing’s surface brought on by exceeding the critical angle of attack. A stall can occur at any pitch attitude or airspeed. Stalls are one of the most misunderstood areas of aerodynamics because pilots often believe an airfoil stops producing lift when it stalls. In a stall, the wing does not totally stop producing lift. Rather, it cannot generate adequate lift to sustain level flight. Since lift increases with an increase in angle of attack, at some point the lift peaks and then begins to drop off. The amount of lift the wing produces drops dramatically after the critical angle of attack is exceeded, but as stated above, it does not completely stop producing lift. In most straight-wing aircraft, the wing is designed to stall the wing root first. The wing root reaches its critical angle of attack first, making the stall progress outward toward the wingtip. By having the wing root stall first, aileron effectiveness is maintained at the wingtips, maintaining controllability of the aircraft. Various design methods are used to achieve the stalling of the wing root first. In one design, the wing is twisted to a higher angle of attack at the wing root. Installing stall strips on the first 20–25 percent of the wing’s leading edge is another method to introduce a stall prematurely.4. What can be regarded as good stalling characteristic for an aircraft?
An aircraft stall results from a rapid decrease in lift caused by the separation of airflow from the wing’s surface brought on by exceeding the critical angle of attack. A stall can occur at any pitch attitude or airspeed. Stalls are one of the most misunderstood areas of aerodynamics because pilots often believe an airfoil stops producing lift when it stalls. In a stall, the wing does not totally stop producing lift. Rather, it cannot generate adequate lift to sustain level flight. Since lift increases with an increase in angle of attack, at some point the lift peaks and then begins to drop off. The amount of lift the wing produces drops dramatically after the critical angle of attack is exceeded, but as stated above, it does not completely stop producing lift. In most straight-wing aircraft, the wing is designed to stall the wing root first. The wing root reaches its critical angle of attack first, making the stall progress outward toward the wingtip. By having the wing root stall first, aileron effectiveness is maintained at the wingtips, maintaining controllability of the aircraft. Various design methods are used to achieve the stalling of the wing root first. In one design, the wing is twisted to a higher angle of attack at the wing root. Installing stall strips on the first 20–25 percent of the wing’s leading edge is another method to introduce a stall prematurely.3. What is the relationship between lift and angle of attack?
An aircraft stall results from a rapid decrease in lift caused by the separation of airflow from the wing’s surface brought on by exceeding the critical angle of attack. A stall can occur at any pitch attitude or airspeed. Stalls are one of the most misunderstood areas of aerodynamics because pilots often believe an airfoil stops producing lift when it stalls. In a stall, the wing does not totally stop producing lift. Rather, it cannot generate adequate lift to sustain level flight. Since lift increases with an increase in angle of attack, at some point the lift peaks and then begins to drop off. The amount of lift the wing produces drops dramatically after the critical angle of attack is exceeded, but as stated above, it does not completely stop producing lift. In most straight-wing aircraft, the wing is designed to stall the wing root first. The wing root reaches its critical angle of attack first, making the stall progress outward toward the wingtip. By having the wing root stall first, aileron effectiveness is maintained at the wingtips, maintaining controllability of the aircraft. Various design methods are used to achieve the stalling of the wing root first. In one design, the wing is twisted to a higher angle of attack at the wing root. Installing stall strips on the first 20–25 percent of the wing’s leading edge is another method to introduce a stall prematurely.2. When an aircraft stalls, （ ）.
An aircraft stall results from a rapid decrease in lift caused by the separation of airflow from the wing’s surface brought on by exceeding the critical angle of attack. A stall can occur at any pitch attitude or airspeed. Stalls are one of the most misunderstood areas of aerodynamics because pilots often believe an airfoil stops producing lift when it stalls. In a stall, the wing does not totally stop producing lift. Rather, it cannot generate adequate lift to sustain level flight. Since lift increases with an increase in angle of attack, at some point the lift peaks and then begins to drop off. The amount of lift the wing produces drops dramatically after the critical angle of attack is exceeded, but as stated above, it does not completely stop producing lift. In most straight-wing aircraft, the wing is designed to stall the wing root first. The wing root reaches its critical angle of attack first, making the stall progress outward toward the wingtip. By having the wing root stall first, aileron effectiveness is maintained at the wingtips, maintaining controllability of the aircraft. Various design methods are used to achieve the stalling of the wing root first. In one design, the wing is twisted to a higher angle of attack at the wing root. Installing stall strips on the first 20–25 percent of the wing’s leading edge is another method to introduce a stall prematurely.1. An aircraft may stall （ ）.
When I boarded the aircraft, it could be seen from the jetty that there was quite a deposit of snow and ice on the entire span of the wing upper surface. The temperature was probably around freezing, and light snow was falling from time to time. Although on-stand de-icing is the normal procedure at the airport, the engines were started and the aircraft taxied towards the runway holding point. I became more and more worried as it became clear that we are not going to be de-iced before takeoff. We stopped near the runway in queue for departure. I was just about to say something to the cabin crew when the first officer came out of the flight deck and had a look at the wings. I had a quick word with him and said we need to de-ice. Soon after he returned to the flight deck, the captain announced that the aircraft was returning to the stand as he was not happy with the ice on the wing. We departed later after de-icing had been carried out, much to my relief. I think it was very likely that the need to de-ice was made apparent by radio from following aircraft, which prompted the appearance of the co-pilot in the cabin for inspection. I cannot imagine what else would have facilitated this check at this late stage. Whatever it was, I am glad that the last link in the safety chain held on this occasion. 5. How did the author feel when the captain announced the aircraft would return to the stand?
When I boarded the aircraft, it could be seen from the jetty that there was quite a deposit of snow and ice on the entire span of the wing upper surface. The temperature was probably around freezing, and light snow was falling from time to time. Although on-stand de-icing is the normal procedure at the airport, the engines were started and the aircraft taxied towards the runway holding point. I became more and more worried as it became clear that we are not going to be de-iced before takeoff. We stopped near the runway in queue for departure. I was just about to say something to the cabin crew when the first officer came out of the flight deck and had a look at the wings. I had a quick word with him and said we need to de-ice. Soon after he returned to the flight deck, the captain announced that the aircraft was returning to the stand as he was not happy with the ice on the wing. We departed later after de-icing had been carried out, much to my relief. I think it was very likely that the need to de-ice was made apparent by radio from following aircraft, which prompted the appearance of the co-pilot in the cabin for inspection. I cannot imagine what else would have facilitated this check at this late stage. Whatever it was, I am glad that the last link in the safety chain held on this occasion. 4. Why did the captain announce that the aircraft was returning to the stand?
When I boarded the aircraft, it could be seen from the jetty that there was quite a deposit of snow and ice on the entire span of the wing upper surface. The temperature was probably around freezing, and light snow was falling from time to time. Although on-stand de-icing is the normal procedure at the airport, the engines were started and the aircraft taxied towards the runway holding point. I became more and more worried as it became clear that we are not going to be de-iced before takeoff. We stopped near the runway in queue for departure. I was just about to say something to the cabin crew when the first officer came out of the flight deck and had a look at the wings. I had a quick word with him and said we need to de-ice. Soon after he returned to the flight deck, the captain announced that the aircraft was returning to the stand as he was not happy with the ice on the wing. We departed later after de-icing had been carried out, much to my relief. I think it was very likely that the need to de-ice was made apparent by radio from following aircraft, which prompted the appearance of the co-pilot in the cabin for inspection. I cannot imagine what else would have facilitated this check at this late stage. Whatever it was, I am glad that the last link in the safety chain held on this occasion. 3. According to the passage, what may have promoted the first officer’s appearance in the cabin?
When I boarded the aircraft, it could be seen from the jetty that there was quite a deposit of snow and ice on the entire span of the wing upper surface. The temperature was probably around freezing, and light snow was falling from time to time. Although on-stand de-icing is the normal procedure at the airport, the engines were started and the aircraft taxied towards the runway holding point. I became more and more worried as it became clear that we are not going to be de-iced before takeoff. We stopped near the runway in queue for departure. I was just about to say something to the cabin crew when the first officer came out of the flight deck and had a look at the wings. I had a quick word with him and said we need to de-ice. Soon after he returned to the flight deck, the captain announced that the aircraft was returning to the stand as he was not happy with the ice on the wing. We departed later after de-icing had been carried out, much to my relief. I think it was very likely that the need to de-ice was made apparent by radio from following aircraft, which prompted the appearance of the co-pilot in the cabin for inspection. I cannot imagine what else would have facilitated this check at this late stage. Whatever it was, I am glad that the last link in the safety chain held on this occasion. 2. What does the author complain about?
When I boarded the aircraft, it could be seen from the jetty that there was quite a deposit of snow and ice on the entire span of the wing upper surface. The temperature was probably around freezing, and light snow was falling from time to time. Although on-stand de-icing is the normal procedure at the airport, the engines were started and the aircraft taxied towards the runway holding point. I became more and more worried as it became clear that we are not going to be de-iced before takeoff. We stopped near the runway in queue for departure. I was just about to say something to the cabin crew when the first officer came out of the flight deck and had a look at the wings. I had a quick word with him and said we need to de-ice. Soon after he returned to the flight deck, the captain announced that the aircraft was returning to the stand as he was not happy with the ice on the wing. We departed later after de-icing had been carried out, much to my relief. I think it was very likely that the need to de-ice was made apparent by radio from following aircraft, which prompted the appearance of the co-pilot in the cabin for inspection. I cannot imagine what else would have facilitated this check at this late stage. Whatever it was, I am glad that the last link in the safety chain held on this occasion. 1. What was the author doing on the aircraft?
Surface obscuration caused by fog has troubled navigators on land, sea and in the air ever since travel began – and it is still a serious cause of aircraft accidents. Fog appears to be a non-threatening form of cloud, without turbulence or precipitation (usually), but because it is in contact with the ground surface it seals off ground facilities and mountain passes with little or no warning. Fog dense enough to restrict visibility to a mile or less can form quite rapidly. All fog tends to look alike to pilots, but it is formed and dissipated under a variety of conditions with which airmen should be familiar. Radiation Fog More commonly called ground fog, radiation fog is the result of ground cooling on clear, calm nights. The ground cools the air to the dew point temperature. It is restricted to land areas because water areas do not have much daily variation in temperature. It forms almost exclusively late at night or in the early morning, and usually disappears or burns off within a few hours. Ground fog favors flat land areas – such as airports. Advection Fog This type of fog forms when moist air moves over colder ground or water. Very common along coastal areas, it is called sea fog when occurring at sea. It frequently forms offshore as a result of very cold water from the ocean depths rising to the surface. The fog is then carried inland by the wind. Advection fog results from moist air moving over a cold area. Therefore, in most areas it is more common in the winter than in the summer. Upslope Fog This fog results from moist, stable air being cooled by being moved up a sloping land surface. An upslope wind is necessary for its creation and its continued existence. Steam Fog The movement of cold air over much warmer water causes intense evaporation. This usually adds enough water vapor to the cold air to saturate it, forming steam fog. Steam fog rises from the water surface like smoke, and it is sometimes referred to as sea smoke. Since there is heating from below, turbulence often occurs in this type of fog. Structural icing is also a potential hazard. Precipitation-Induced Fog The addition of moisture to the air through evaporation of rain causes this type of fog. Evaporation can occur while the precipitation is falling through the air, or after it reaches the ground. It is frequently associated with warm fronts.5. Which of the following is true according to the passage?
