Helicopters: How They Work and How They Can Save Lives
By Nathan O’Brien
If you ever look up and see a plane flying in the air, it doesn’t seem too baffling. After all, it resembles many of the birds you see gliding around on a nature walk. However, when you hear the buzz of a helicopter, or a drone, you may wonder, how does that contraption fly? And, in addition to flying, how does it hover in place and take off vertically?
How Helicopters Work
The helicopter is driven by a large spinning device on its top called the “rotor.” The rotor on a helicopter spins, and, just like a house fan, generates airflow. This airflow, called “thrust,” lifts the helicopter. Thrust is generated from the unique shape of the rotor blades. Each rotor blade is made up of “airfoils.”
Airplane wings operate on the same principle: namely, that the wings of an airplane or the blades of a rotor have a cross-sectional shape. A cross section is the shape that results when you slice into an object. This is like looking at a slice of cake. The cross-sectional shape of a rotor blade generates low pressure at the top surface of the airfoil and high pressure at the bottom surface of the airfoil. This phenomenon is called Bernoulli’s principle.
The differences in pressure cause the airfoil to be pushed upwards, thereby generating “lift.” Put simply, the faster the airflow over the airfoil, the higher the lift. This lift provides the force that keeps airplanes and helicopters in the air. This airflow speed condition dictates the need and length of a runway. For example, an airplane needs a large runway to accelerate before it can fly. But, the rotation of a helicopter’s blades provides the necessary airflow to the airfoils to provide lift without any runway or vehicle speed. This means that a helicopter can take off vertically and hover in the air.
Curious to test the Bernoulli principle at home? Take two pieces of paper and hold them about an inch apart. Blow air in between them to create a low-pressure environment. As you are blowing air, you will see that each piece of paper comes together. This is due to the quasi-lift force that is generated. For those with more interest in the Bernoulli principle, I encourage you to investigate the Kutta-Joukowski theorem and its use of Newton’s third law of “every reaction has an equal and opposite reaction” to explain lift.
Image Credit: Nathan O’Brien
Now that we understand the basics of lift generation, and how the unique design of a helicopter generates the necessary lift to fly without a runway, it’s time to explore some final details. In addition to take-off and hover, helicopters must fly to their destination. Simply, to fly in any direction, the pilot of the helicopter must “point” the rotor disk in the direction they want to travel. The helicopter will then follow that direction. Want to go forward? Tilt the rotor forward! How about backwards? No problem, tilt the rotor backwards! There are other controls that dictate a helicopter’s flight path, called “cyclics,” but this is more complicated and will not be addressed in this article.
There is also another important device that keeps helicopters in the air – the tail rotor. This unsung hero may not be the flashy star player generating lift like the main rotor, but, without it, the helicopter would spin out of control! This is due to Newton’s Law of Angular Momentum. (This guy just always comes up. Take a break, eat an apple, why don’t you Newton!)
Before delving into the details of Newton’s Law of Angular Momentum, let’s discuss the principle using an example that many people know. Imagine an ice skater spinning around on the ice with their arms extended. As the ice skater pulls in their arms, they start to spin faster and faster. This is the Law of Angular Momentum in practice. As the rotating object effectively shrinks—the ice skater pulls their arms in—more of the momentum is transferred to the speed of the spin. This is because the total angular momentum must be conserved.
Helicopters function similarly to the spinning ice skater. Since the helicopter has a large spinning rotor at its top, the helicopter’s body wants to spin in the opposite direction so that it can conserve its angular momentum. As you can imagine, a spinning helicopter body would end in catastrophe. This is where the tail rotor comes in. The tail rotor provides lift to the side of the helicopter. This force is specially tailored to combat the helicopter’s body from spinning and keeps the helicopter stable for operation.
And there you have it! Helicopters operate like airplanes with spinning wings called rotor blades that generate lift to allow it to hover and take off; the angle of the rotor propels the helicopter in any direction we want; and the tail rotor prevents the helicopter from spinning out of control.
Image Credit: Nathan O’Brien
Image Credit: Nathan O’Brien
How Helicopters Can Save Lives and Explore New Worlds
Now that we know the basics of how helicopters operate, let’s investigate the history of helicopters and some of the unique and interesting ways they are used to save lives and explore new worlds.
The first rotorcraft design, a bamboo-copter, was created around 400 B.C. in China. However, the most famous design came from Leonardo DaVinci. DaVinci drew sketches of his flying screw in the 1480s, and these sketches are widely considered to be the spiritual ancestors of modern helicopters. As scientific advances swept across Europe during the Enlightenment, so too did preliminary rotorcraft designs.
However, it wasn’t until the Industrial Revolution that vertical flight was realized. During the Industrial Revolution, steam engines were used to achieve vertical flight via small experiments. The most famous of which was Gustave de Pontons’ steam powered flying screw. Interestingly, Gustave is attributed to coining the name “helicopter” from the Greek words for helical and wing.
Then, in the early 1900s, internal combustion engines were used in large, preliminary helicopter designs. These designs allowed for limited hover with humans as passengers. The first successful controlled helicopter flight was engineered by Henrich Focke in Germany in 1936. The first practical helicopter was flown in America in 1939 and designed by Igor Sikorsky, a Russian/Ukrainian immigrant. Sikorsky not only provided America with its strong technical foundation in vertical flight technology but also gave the world the motto of the helicopter: “Unlike the airplane, the helicopter will be used not to destroy lives, but to save them.”
The modern helicopter has come a long way from the designs created by Sikorsky in the late 1930s. Via their unique hover capabilities, modern helicopters can transport patients in critical condition to hospitals, ensuring patients can get the care they need in time. Helicopters are also vital in search and rescue operations, can deliver lifesaving aid, and can rescue people from conditions in areas where no other vehicle can reach, such as on a mountain or in the ocean. In the United Kingdom alone, 1,466 people were rescued by helicopters from March 2022 to March 2023. This is Igor Sikorsky’s motto in practice and shows the truly magnificent capabilities that helicopters have to save lives. Helicopters can also be used to store and drop thousands of pounds of water or fire retardant to combat wildfires. They can be used in volatile conditions like fast winds and in limited visibility. In the most extreme case, helicopters were used to put out the nuclear fires resulting from the explosion of the Chernobyl power plant.
Currently, electric powered, emission free, clean flight is being explored by rotorcraft engineers for inter- and intra-city travel via air taxis. Work is also being done to create hydrogen powered, emission free helicopters.
Helicopters can even be used to explore other worlds! In April 2021, a small helicopter was flown on the planet Mars. This helicopter collected data and conducted scientific research in areas where a ground-based rover could not reach. This small vehicle, the Ingenuity, successfully flew 72 flights in just under three years, giving humanity an unparalleled study of the red planet.
Over hundreds of years, the helicopter has employed the basics of flight technology and used them to save countless lives, put out fires, and explore other worlds. This machine has become vital to the modern world. Current research to further develop this field includes emission free flight, autonomous flight, minimizing noise, and faster flight speeds, so that more lives can be saved and flying becomes safer overall.
Nathan O'Brien is a PhD student at the University of Maryland majoring in Aerospace Engineering. His specialty is rotorcraft engineering, and the focus of his doctoral research is on dynamic instability mitigation for high speed tiltrotor flight. He received his Bachelor of Science in Aerospace Engineering from Penn State, and worked for two years in the aerospace industry as a structural test engineer before starting graduate school.