# How long is the life of passenger planes like Boeing-747 (Jumbo Jet) and Airbus?

There are three ways of ascertaining the life of an aircraft based on about a dozen factors like its frame construction, weight, engine strength, average flight time, etc. The first unit of measuring longevity of an aircraft is year. A passenger aircraft like Boeing-747 or Airbus 300 is normally considered “aged” after 20 years of service. However, it is inadequate to ascertain the age of an airplane in years alone. It is also important to take into account the number of take-offs and landings by an aircraft within a span of time, which is called usage cycle.
At the time of landing an aircraft endures a mild collision vertically, whereas during take-off the entire frame endures a horizontal pull. Aircraft’s metal then “tires” just like human muscles after physical hard work, and gradually becomes weak. To talk in the language of engineering, an aircraft experiences metal fatigue. The most memorable example for this is of Boeing-737 of Aloha Airlines in Hawaii. Flying between various islands this plane took off from the runway for a similar flight on April 1988, and when it was at the height of thousands of feet all of a sudden its roof went off. One air-hostess and a passenger were thrown out with the wind, while the other passengers had their seat-belts on, hence they remained safe with minor injuries. Eventually the plane landed on the airport, but in the below picture you can see the condition it is in. After this accident Boeing declared the life of Boeing-737 to be 75000 cycles. It means once the aircraft completes 75000 take-offs and landings its life is over.

 Aloha Airlines’ Boeing-737 Accident

The third unit of measuring an aircraft’s life is hours of flight. At the latitude of 32000-33000 feet the air temperature is about minus 48° Celsius. Plane’s metal is contracted at that low temperature. After beginning to land, within 15 minutes as the plane hits the ground the air temperature is much higher, possibly around 30° Celsius. Such a difference in temperature within 15 minutes is no small matter. As a result of this an aircraft experiences another kind of metal fatigue which diminishes its strength. By this measure, the life of Boeing-737 is 51000 hours of flight. Whereas the life of the supersonic Concord is 45000 hours of flight. For more information about different planes refer to the table below. As shown in the table there are three parameters of longevity. A take-off and landing equals one cycle. Boeing-747 (Jumbo Jet) is meant for International travel, hence it does fewer take-offs and landings and has higher hours of flight compared to the planes used for domestic flights.

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# Why do air travelers experience jet lag after a long-haul flight? And how to prevent or remedy it?

Jet lag affects travelers flying east-west or west-east journey, crossing the time zone and finding themselves in a place where the local time differs from the home time. The rising and setting of the Sun is out of sync with their body clock, which is still on time due to 24-hour biological rhythms. So jet lag is the failure of the body to adjust its own routine to a clock that may, for instance, bring darkness (and bedtime) ten hours earlier or later than usual. In such conditions, the long-haul passengers feel like going to sleep just as darkness turns to light with the rising of the Sun, and just as everyone else is waking up ready to start the new day. Eating and exercising are also uncomfortably affected and mental reactions may slow down considerably. The result could be headaches, poor sleep, constipation, poor mental performance, giddiness and even slight depression.
The effects of jet lag seem to be greater on eastbound flights than on westbound. This is because traveling westwards you are traveling with the Sun, and the hours of daylight you experience will be longer than normal. The day will appear to be longer than 24 hours. This goes well with the biological clock, because many of the body rhythms have a period of 25 hours and they show a natural tendency to move towards the new time zone at the rate of about one hour a day. Conversely, when traveling eastwards, the day is shortened. So, body rhythms have to be pulled back to less than 24 hours, against their natural tendency to lengthen.
There is no way one can prevent jet lag and it is not possible to bring all the body rhythms back in sync immediately. Experience shows that one full day of natural recovery is needed for each five-hour time change. However, travelers should try to go to bed as near as possible to their usual bedtime on the first night after arriving. This helps, though not much.

Jet lag (Wikipedia)

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# How does petrol-electric hybrid car that uses regenerative braking work?

Two major problems with petrol/diesel cars are their inefficiency and emission of harmful of pollutants. In a bid to create environment-friendly cars that give better mileage, hybrid cars have been developed in recent years, the best known example being Toyota Prius. (See photo below.)

 Toyota Prius hybrid car

The hybrid car has a conventional internal combustion engine and also an electric motor, providing secondary propulsion. The motor can switch its roles so as to be employed as generator for recharging batteries carried on board. In city driving, when clutch A (see diagram below) engages wheels, the petrol engine is automatically shut down and electric power takes over, enabling the car to cruise at speeds up to 30 kilometers per hour. For acceleration and highway cruising, the petrol engine gets restarted and clutch B connects it with wheels.

### What is regenerative braking? And how does it work?

Most hybrid cars, including Toyota Prius, also use regenerative braking to top up the battery charge. In this system, when the driver brakes, the motor links up with wheels and becomes a generator. This causes kinetic energy of the wheels to be transferred to batteries via generator and helps the car to slow down. This in-car recharging eliminates the need for external recharging stations. Interestingly, in city driving such hybrid car gives better mileage than on a highway because in stop-and-go traffic the car’s regenerative braking recovers much of the spent energy. On average, a hybrid car is at least 60% more efficient in terms of fuel consumption than a standard model of similar size and weight.

Hybrid vehicle (Wikipedia)

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# How fast can a helicopter fly?

A helicopter gets its aerodynamic lift the same way a fixed-wing aircraft does, the only difference being that it has only rotor blades instead of fixed-wings. The angle of attack (the angle at which the leading edge meets the airstream) determines the amount of lift. As the rotor turns, it traces out the circle in the air which is known as the rotor disc. If a helicopter is just hovering, the speed of the blades through the air is constant at all points around the rotor disc. When the helicopter is moving forwards, however, the speed of the blade changes relatively as it travels around the disc. When a blade is traveling towards the front of the disc, its airspeed is its speed due to rotation plus the speed of the helicopter. When a blade is traveling towards the rear of the disc, its airspeed is reduced by the speed of the helicopter, which at that point is effectively traveling in the opposite direction to it.

 Westland Lynx

At high speeds, this effect amplifies manifold. The drag on the forward-moving blade is greatly increased and it begins to lose lift because of the break-up of the airflow over it. The backward-moving blade loses lift because of its relatively low airspeed. The helicopter can not sustain itself in the air. Therefore, no helicopter can fly at more than 400 kilometers per hour. The world record speed was achieved by a Westland Lynx helicopter (photo, above), which reached a speed of 400.87 kilometers over Somerset, England on August 11, 1986.

Westland Lynx (Wikipedia)

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# Which is the longest non-stop flight ever made by a commercial airliner?

The latest Boeing 777-200 LR, also known as Worldliner is especially made for long-haul journeys. On November 10, 2005 it flew 21,475 kilometers from Hong Kong to London, Covering the distance in 22 hours, 42 minutes without refueling. During this long flight, the passengers and crew members saw two sunrises.

Boeing 777 (Wikipedia)

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# What happens if an aircraft flying in stormy weather is struck by lighting?

In most cases, nothing – except a slight flickering of cabin lights and a few milliseconds of interference that the cockpit instruments experience.

Modern passenger aircraft’s skin is made primarily of aluminum which is a good conductor of electricity. Inside, there is adequate insulation, so most of the current flows through only the exterior framework of the aircraft. In the case of some modern small aircraft which have an outer skin made of non-conductive or less conductive composite materials there is an embedded layer of wires or mesh which allow the lightning current to pass through. Since the fuel tanks are properly sealed with a thick layer of insulation the lightning bolt having entered one extreme like nose or wing exits from another extreme such as the tip of the aircraft’s rudder.

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# How much petrol the fuel tank of an airplane carries?

To begin with, correct the word “petrol” in the question. If the engine is just an internal burning machine as in cars then only a high quality petrol is used as fuel. The planes equipped with jet engines use only aerial kerosene. Though this kerosene is of high quality, is not petrol. After being squirted into the jet engine the kerosene burns explosively. The hot air produced of it forcefully threshes backward, and hence as per Newton’s law the plane gets a push. Boeing-747 jumbo jet uses up approximately nine liters of fuel in less than two seconds. But at the time of take-off it is filled up with 1,77,000 liters of fuel, and so the supply lasts for hours. (In 1946 one of the South African jumbo jet had had a non-stop flight of 16,465kms from America-to-Africa, yet at the time of landing it had in it the fuel for two-hour-long flight)

One more interesting thing: There is no separate fuel tank in an airplane, as there is in a car. The fuel is generally filled in the hollow made in four parts in the wings. Each part thus is a separate fuel tank. Any part can pump in to any engine in the plane. As the tank on one end empties, apparently it leads to a change in the gravity centre point and causes imbalance. Hence in order to maintain balance the pilot keeps on shifting fuel to the emptying tanks from the other tanks. For more information observe the diagram above. The fuel carrying capacity of Boeing-707 is shown.

Fuel tank (Wikipedia)
Jet fuel (Wikipedia)

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# Why in traffic signals red light is always placed on the top but in railway signals it is placed below green light?

The tradition of using red color as signal for caution or danger was started years ago by ships. A ship carrying explosive material used to keep a red flag flying to signal other ships not to come very close.

In the beginning of 19th century Britain adopted red color as danger signal for railways also. Experts believe that as deep red color of blood could shock people into alertness, blood-red color was the most suitable as a signal for caution. As red being the color having the longest wavelength they believed that a danger signal of that color would draw attention promptly even from a distance.

Later on in 1886 the British parliament gave approval to a resolution favoring the adoption of red color as cautionary ‘stop’ signal for the use as read signal also. The regulatory authority of railways in Britain had found that red color being easily visible to locomotive drivers even from a considerable distance it would not matter much if it was kept on a somewhat lower level. So the green light got the first place on the top. Later on when the time came for putting signals on the roads, in view of shorter height of signal poles it became a rule to keep the red light at the top level.

Having read this explanation one brief matter should be understood also: The color which attracts the attention most is not red but reddish-yellow. That is why yellow-orange color is preferred to red color for life-jackets on the ships and planes. The cartridges of flare pistols used for signaling distress at the sea or some isolated place also produce yellow-orange smoke.

Railway signal (Wikipedia)
Traffic light (Wikipedia)

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# Which is the world’s most successful passenger aircraft so far?

It was DC-3, popularly known as Dakota, manufactured by Douglas Aircraft Company of USA. Powered by two 1,200 hp propeller engines, it had a cruising speed of 300 kilometers per hour and had accommodation for 28 passengers, with a flight crew of 2. It was introduced on commercial routes in 1936 and its first domestic flight in the USA took 13 hours, 4 minutes – a record at the time. Since then 10,655 Dakotas were built and sold to dozens of countries. No other passenger aircraft has proved to be so successful.

# Why the entire surface of the passenger planes is not painted over? Why the nose of the plane is black?

There are a number of reasons why the entire surface of a passenger plane is not painted over. Firstly, ordinary oil-paint will not serve the purpose. Sometimes the plane is on the runway of an airport in the temperature of 50◦ Celsius and after a few minutes it is flying at the altitude of 30,000 feet above the sea level where the temperature is below the freezing point. Therefore, specially made polyurethane paint is used and it is very expansive. The job of painting takes up almost two weeks and during this time the plane remains unused. The loss of revenue on this account is substantial. As a result the cost of painting only 1/3 surface of a jumbo jet is a whopping \$ 24,000 approximately. Moreover, almost 500 liters paint is necessary to paint 1/3 surface. This amounts to a permanent increase of half a ton in the payload. The engines have to work so much more and consume additional fuel. A plane traveling from Delhi to Kochi would burn up to half a ton more fuel to carry this extra load. Imagine the overall costs involved in painting the entire surface of the plane!

The reason for leaving the plane’s nose unpainted is quite different. The nose is fabricated from carbon alloy that is black in color. It houses radar scanner to capture the data regarding weather. The disc antenna for radar inside the nose can swing 30◦ to the right or left. As black colored carbon metal absorbs reflected radio waves better it is left unpainted.

However, most of the passenger planes made today are painted fully.

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