Is it safe to fly? - 2
Most of us have probably seen or felt wind blowing flags or kites around. But you may ask, how is it possible that heavy airplanes (some weighing almost half a million pounds, or more than 200,000 kilograms) are able to be supported by air high above the ground?
The answer may sound strange at first, but it's actually the air that is pushing the airplane's wings and the rest of it up. The air under the wings pushes up more than the air on top of the wings pushes down. This "pushing" by the air is called air pressure. We can think of air pressure as air "press"-ing down or up against something else. On a windy day, you can actually feel the air pressure pushing against your body. The wings of an airplane "feel" a similar force, but there happens to be a bigger pressure under the wings and a smaller pressure on the top.
What's really amazing is why this happens. The unique shape of an airplane's wing makes the air moving around it behave in a certain way. If we look at an airplane's wing from the side, we can see that the wing has a shape of an airfoil(shown in the picture below).
An airfoil is curved on the top and flat on the bottom, causing some of the air to go over the top and the rest of the air to go along the bottom. This shape looks simple, but it is the main reason airplanes can fly at all. Because of the airfoil's curved shape, the air moving under the airfoil moves at a slower speed than the air going over the top. In fact, birds and airplanes have the same flight principles besides the difference in the ways they create lift(upward pushing force). Birds flap their wings to produce lift and thrust whereas airplanes uses stationary wings and engines/propellers to produce the two forces respectively. Ultimately, both birds and airplanes pushes air down to produce lift and pushes air back to produce thrust. So much on how birds and airplanes fly.
The answer may sound strange at first, but it's actually the air that is pushing the airplane's wings and the rest of it up. The air under the wings pushes up more than the air on top of the wings pushes down. This "pushing" by the air is called air pressure. We can think of air pressure as air "press"-ing down or up against something else. On a windy day, you can actually feel the air pressure pushing against your body. The wings of an airplane "feel" a similar force, but there happens to be a bigger pressure under the wings and a smaller pressure on the top.
What's really amazing is why this happens. The unique shape of an airplane's wing makes the air moving around it behave in a certain way. If we look at an airplane's wing from the side, we can see that the wing has a shape of an airfoil(shown in the picture below).
An airfoil is curved on the top and flat on the bottom, causing some of the air to go over the top and the rest of the air to go along the bottom. This shape looks simple, but it is the main reason airplanes can fly at all. Because of the airfoil's curved shape, the air moving under the airfoil moves at a slower speed than the air going over the top. In fact, birds and airplanes have the same flight principles besides the difference in the ways they create lift(upward pushing force). Birds flap their wings to produce lift and thrust whereas airplanes uses stationary wings and engines/propellers to produce the two forces respectively. Ultimately, both birds and airplanes pushes air down to produce lift and pushes air back to produce thrust. So much on how birds and airplanes fly.
Well, the next few lines may scare you off a bit but stay with me. Do you know? In fact, air accidents can also be caused by birds, commonly known as bird strike. A bird strike in aviation, is a collision between an airborne animal(often a bird) and a man made vehicle, especially airplanes. It is a common threat to airplane safety and has caused a number of air accidents.
It is believed that most potential collision are avoided because the bird is able to change it's course in time. However, the faster the airplane is moving, means reaction time given for the bird is shorter or even zero, putting the airplane at higher risk. Most bird strikes happen close to the ground where majority of the birds are found(in bird airspace). Therefore, bird strikes happen most aften during takeoffs and landings or during low altitude flights. With jet engine aircraft, the animals is frequently sucked into the engine, causing damages to the fan, the housing or the airflow ducts. Depending on the force of impact, a bird strike may damage or even destroy components of the airplanes, or even injure people in the plane.
It is believed that most potential collision are avoided because the bird is able to change it's course in time. However, the faster the airplane is moving, means reaction time given for the bird is shorter or even zero, putting the airplane at higher risk. Most bird strikes happen close to the ground where majority of the birds are found(in bird airspace). Therefore, bird strikes happen most aften during takeoffs and landings or during low altitude flights. With jet engine aircraft, the animals is frequently sucked into the engine, causing damages to the fan, the housing or the airflow ducts. Depending on the force of impact, a bird strike may damage or even destroy components of the airplanes, or even injure people in the plane. Yes, bird strikes are scary. However, it is no longer as scary flying in a mordern airplane today. Firstly, most mordern commercial jet engines include design features that ensures they can safely shut down after an impact of a bird weighing up to 1.8kg. The jet is still able to land safely after a 1.8kg strike even if one of the two engines is down. Secondly, to reduce bird strike on takeoff and landing, airport introduce bird management and control. It includes changes to terrain to reduce the attractiveness as an habitat to birds and introducting devices that produces sound and light to scare them away. There are many other ways to keep birds away from the airport. One example from an airport in New Zealand is that it uses electrified mats to reduce the number of worms that attracted large numbers of sea gulls. Finally, pilots are trained to gain awareness of birds habits and avoid migratory routes, wildlife reserve and estuaries where birds may congregate. In addition, with today's technology, birds activities can also be traced using radar. Hence, be rest assured chances of bird strike these days are very slim or appaoximately zero. In my next post about flying, I will talk about airplanes..
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