Helicopters kinda look like fat bugs lyingon their backs flailing their legs around…
so how exactly can they fly with more precisionthan an airplane?
Airplanes fly because their wings are curvedon the top and flat on the bottom, allowing
them to harness the Bernoulli Principle.
With speed, the air passing over the wingis less dense than the air under it, creating lift.
Helicopters have rotor blades that also createlift.
As the blades spin they move the air.
Less dense air passes over the blades withdenser air passing underneath it.
Put that way it sounds simple, but it’sfar more complicated, because while airplanes
get lift naturally by moving through the airhelicopters have to constantly generate it themselves.
所以它们能起飞 垂直降落 倒飞 转弯和原地盘旋
This is how they can takeoff and land vertically,and also fly backwards, sideways, and hover in place.
But they can’t glide if something goes wrong;they aren’t aerodynamic like planes.
Helicopters fly by sheer brute force, whichis really incredible, but gives them some limits.
Planes can fly upside-down — the fixed wingmeans that as long as air is moving over the
wing, usually by tilting the nose upwardsslightly, it still has lift.
As a helicopter’s rotor spins, the generatedthrust moves upwards with the direction of
lift, so flying upside-down would demand redirectingthe blades so the thrust is the opposite way,
supporting an upside-down vehicle.
That said, a helicopter could fly a barrelroll if it was moving fast enough, but that’s
a stunt you’re more likely to see at anairshow than from a news helicopter over a city.
Speaking of helicopters over cities, you alwaysknow when one is out there.
Because they’re loud.
They’re loud not because of the engine,but because the blades are running into turbulence
from each other, properly called the blade–vortexinteraction: the tips of the rotor blades
vibrate against the air as they whip around.
Airplane wings have changed overtime to haveflaps and malleable shapes that react to flight conditions.
Helicopters have done this too; differentblade shapes, tip shapes, and even materials
have shown to decrease the noise of a helicopter.
One kind of blade has flaps on edge of thatmove 15 to 40 times a second to reduce the
noisey blade-vortex interaction.
Even NASA is looking into developing betterblades for a quieter helicopter, looking to
a future where larger, versions can carrya sizable passenger load between cities.
Without runways, commuter chopper flightscould limit air traffic congestion.
But helicopters with one rotor can only liftso much.
Which is why bigger choppers like the Chinookhave two.
More blades can provide more lift, but italso adds weight and complexity.
For a heavier helicopter the extra lift fromthe added blades is sometimes vital.
Not only do those look cool, but they’reuseful.
Just like a helicopter should be.
For more epic stories of innovation that shapedour future, check out TheAgeOfAerospace.com
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