Above: AeroVelo's Winning Flight (AeroVelo)
Human-powered flight has been a longstanding challenge. Back in the fifteenth century, Da Vinci sketched several human-powered aircraft, and some of his contraptions required pilots to flap their arms. By contrast, modern aeronautical engineers and enthusiasts have usually designed craft that fly using leg power. One of these recently allowed a group of Toronto engineers to win the prestigious Igor I. Sikorsky Human Powered Helicopter Competition.
The Sikorsky Prize, first announced in 1980, was introduced to encourage human-powered flight in helicopter form. The prize was initially set at $25,000. After many years, the American Helicopter Society (AHS) got involved and increased the award to $250,000. This made it the third-largest prize in aviation history. It is named after Igor I. Sikorsky, a Russian-American pilot who designed and flew the world's first multi-engine airplane. He also designed the first workable American helicopter.
While many tried, the prize remained unclaimed for 33 years. Eventually, it was awarded to a team from the University of Toronto led by pilot and chief engineer Todd Reichert. This occurred on June 13, 2013, when the AeroVelo team and their Atlas aircraft set a world record for human-powered flight.
Finding the necessary parts, and then designing a device a person can both power and fly, is no easy feat. Powering a helicopter to hover over a fixed spot is even more difficult. This is because of the complex engineering and physics needed to power and maintain flight. Most designs rely on pulleys to turn rotors (rotating propeller blades), which provide lift. Like airplanes, helicopters use airfoils (curved rotors) to get off the ground.
This is where Bernoulli's Principle comes into play. It states that air flowing over the curved upper surface of an airfoil must travel faster than the air underneath it. This creates a difference in pressure and pulls the airfoil upward.
The design of a human-powered helicopter has to be light enough to ensure a favourable power-to-weight ratio. In other words, in order to hover, a helicopter needs to have more power lifting it upward than weight from gravity pulling it downward. Rotors with a larger surface area can help provide more power. Strong, lightweight materials are used to provide a stable structure with less weight.
Both large rotors and lightweight materials were the key to the success of AeroVelo. Atlas’s frame was built using mostly carbon fibre tubes and lightweight but strong balsa wood. Four large rotors (each one measured 20.4 m) were attached to the frame. The entire craft weighed in at 55 kg. That’s not counting the engine or the pilot, Todd Reichert, who sat on the seat of a heavily modified bicycle.
Did you know? Bernoulli's Principle explains why a curveball "curves". Air flows over the stitches of the baseball faster than the rest of the ball, causing the pitch to swerve.
By hovering 3.3 m above the ground for over a minute (64.11 seconds to be exact), Reichert set a world record for the longest duration of hover and met two of the major requirements of the Sikorsky prize. (The other major requirement was that the helicopter could not drift outside of a 10m x 10m area during the flight.) The team’s achievement was officially recognized by the AHS on July 11, 2013—about a month after the historic flight. The achievement surprised many who thought it was impossible.
The AHS has promised to issue a new challenge to further test the limits of human-powered flight. Meanwhile, Reichert and his team hope to continue pursuing their dreams while inspiring others to push the limits of what the human mind and body can do. What other technological achievements that are currently considered impossible do you think will one day become reality?
This article was updated by Let's Talk Science staff on 2016-10-31 to improve readability by reducing the reading grade level.