How Does a Helicopter Hover?
By Ritu Asthana; Illustration by Anup Singh
Rahul couldn't sleep the night before. He had already set his alarm clock to wake him up at 4 a.m., He wanted his mother to take him to the venue well before the scheduled time.
Soon after the initial formalities of flag hoisting and the entry display of the various tableaus came the march past of troops from the armed forces.
Suddenly with an ear shattering roar flew the fighter planes, doing aerial acrobatics, amidst thunderous applause from the audience. Then came the moment Rahul was so eagerly waiting for. His father's name was announced and he could see a helicopter come chattering towards them.
The moment it reached above the dais of the President and the Prime Minister, the helicopter stood still in mid-air and showered flowers on the V.I.P guests.
"Oh my God!," thought Rahul, "What is papa doing?. . .He'll fall down! After all how can something as heavy as a helicopter stand still in mid-air?"
However, thankfully a few seconds later, the helicopter flew away without falling down from the sky. But Rahul was very angry with his father. He couldn't wait to meet his father and ask him why he did that.
Later, when his father explained why - Rahul felt very mollified and happy and proud of his father.
His father explained that a helicopter is a machine that can fly in any direction: forward, backward, upward or sideward. It can even hover over a single spot. To understand how this is done, we must understand how a helicopter flies.
A helicopter has two pairs of propellers - the larger ones at the front, above the cabin and a smaller one at the tail. The larger ones help in flying while the smaller ones stop the helicopter from spinning round when the big blades are turning.
As the propeller blades of a helicopter slice through the air, it creates a strong wind. The wind moves downward pushing the helicopter. The air beneath the blades thus, has greater pressure than the air above them. The blades are then twisted slightly so that air is forced downward. This creates a lift.
Flaps under the wings of an airplane create a lift in the same way. In fact, the rotor blades of the helicopter are really moving wings. The difference is that the whole airplane has to move forward in order to get lift, whereas the helicopter needs the propeller to fly in the air.
This is what enables a helicopter to go straight up or down or hover over one spot. In front of the pilot, is a 'cyclic stick'. He moves it in the direction he wants to go and the helicopter flies that way. The cyclic stick works by changing the pitch of one blade at a time as it passes the side of the helicopter.
This means that one side of the rotor disc has more lift than the other, and the disc tilts. When the disc is flat, the helicopter hovers because all the lift force is straight up, keeping the helicopter in the air. If the disc is tilted, most of the force is still up, keeping the helicopter in the air, but some of the force pushes it and as a result the helicopter moves in the direction it is pushed into.
Helicopters can make sharper turns than airplanes and they don't need a long runaway to take off or land - they can even land on top of a building.
In India, the armed forces use helicopters for many different jobs - because of their manoeuvrability, they are ideally used to transport people to places hard to reach easily: people trapped in jungles or mountains; patients to hospitals; or to rescue people in floods and landslides.
In certain countries, helicopters are also used to monitor traffic conditions and by the police to catch criminals!
That was it! He would also become a pilot, like his father, thought Rahul.
How Does a Helicopter Hover? [5W&H for kids]
By Ritu Asthana; Illustration by Anup Singh
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