iFLY Queenstown: Indoor Skydiving Engineered to Reduce Environmental Impact

I was impressed by iFLY's closed-loop airflow system, which recirculates air within the wind tunnel rather than constantly pulling in and expelling outside air. This design helps reduce energy waste and minimizes environmental impact compared to open systems. While the tunnel does require electricity to power the fans, it does not rely on jet fuel or airplanes like traditional skydiving. As a result, iFLY avoids the carbon emissions associated with aviation, making it a more environment-friendly alternative for experiencing freefall.

IFLY Queenstown is an indoor skydiving facility that is operated by iFLY Indoor Skydiving in Queenstown, New Zealand. It opened in June of 2018 as an adventure activity that is available all year round, regardless of weather conditions.

IFLY allows people to experience the free-fall experience of skydiving without having to jump from an airplane.

The main attraction is a flight chamber with a vertical column of wall-to-wall upward-moving air that is generated by a wind tunnel. The flight chamber is a cylinder-shaped container with transparent walls that allow spectators to view a flyer's "skydiving" event. The diameter of the flight chamber is 3.7 meters (12 feet), and the flying height is at least 9.6 meters (36.6 feet).

Diagram of a closed loop system by Warren Volles

The iFLY wind tunnel works by recirculating air through a closed-loop system. The airflow is created by powerful fans that are located at the top of the flight chamber. The fans generate a strong upward airflow by drawing air from the bottom to the top of the flight chamber.

The fans then drive the air within ducts toward turning vanes that are positioned in the corners of the air ducts. The turning vanes guide the air down through the return air tower in the side of the wind tunnel. They are shaped and positioned to maintain laminar airflow by managing the direction and speed of the air as it cycles back to the flight chamber.

laminar airflow:

As first described by Osborne Reynolds in 1883, laminar airflow refers to air that moves smoothly in parallel lines without disturbing or mixing with other streams of air. It reduces turbulence and drag within the air ducts, which is important for maintaining the power efficiency of the wind tunnel. Power efficiency measures how well a system converts energy input into useful output. A highly efficient system uses most of its energy input for its intended purpose, with minimal energy wasted as heat, noise, or vibration.

When the air reaches the bottom of the wind tunnel, it is directed by more turning vanes to an inlet contractor located below the flight chamber. The inlet contractor decreases the cross-sectional area of the airflow before it re-enters the flight chamber. As the air moves through the inlet contractor, its mass flow rate remains constant. A constant mass flow rate means that the mass of the air entering the inlet contractor is equal to the mass of air exiting because there is no addition or loss of air within the system. Since the air's mass remains constant, the velocity of the air must increase as the cross-section narrows to maintain a constant mass flow rate along the inlet contractor.

The air's behavior is governed by the principle of continuity of mass flow, which states that the mass flow rate of a fluid (air) flowing in a closed system must remain constant throughout its path. The principle of continuity of mass flow is an application of the conservation of mass principle in fluid dynamics.

Mass flow rate

In fluid dynamics (the study of how liquids and gases behave under various conditions), mass flow rate is defined by the equation:

where ṁ represents the mass flow rate, ρ is the air density, A is the cross-sectional area, and V is the velocity of the air.

continuity of
mass flow

According to the continuity principle, a fundamental principle of fluid dynamics, the continuity of mass flow across the inlet contractor in the wind tunnel is expressed by the equation:

where ρ1, A1, and V1 are the density, cross-sectional area, and velocity of the air, respectively, at the beginning of the contraction; and ρ2, A2, and V2 are these values at the end of the contraction. Assuming the air density ρ remains constant, which is typical in wind tunnels where temperature and pressure changes are minimal, the continuity equation is simplified to:

conservation of mass

The conservation of mass principle says that mass cannot be created or destroyed in a closed system like a wind tunnel. Therefore, changes in cross-sectional area must be balanced by changes in velocity to maintain a constant mass flow rate throughout the entire closed system.

As the high-velocity airflow exits the inlet contractor, it enters the flight chamber through a mesh floor. The airflow must be strong enough to overcome gravity and generate sufficient aerodynamic lift to counteract aerodynamic drag. Aerodynamic lift is what enables a person to become airborne and remain stable in the chamber. To achieve lift, the air velocity must exceed the terminal velocity of a free-falling human, which is approximately 193 kilometers per hour (120 miles per hour).

aerodynamic lift:

The aerodynamic lift in the wind tunnel at iFLY is the upward force, generated as air is blown from below, that lifts the flyer off the mesh floor at the bottom of the flight chamber. The lift equation is expressed by the equation:

L = ½ρV2SCL

where L is the lift force, ρ is the density of the air, V is the velocity of the air, S is the surface area of the flyer, and CL is the lift coefficient, which depends on the shape of the flyer and the angle of attack (how the body is oriented to the airflow). This equation shows how the lift and, thus, the altitude of the flyer can be changed by adjusting factors like airspeed, suit design, or body position.

aerodynamic drag:

The aerodynamic drag in the wind tunnel at iFLY is the force that acts opposite to the direction of the airflow. It resists the flyer’s upward motion by pushing against the airflow as it moves across the flyer’s body, mainly along the body’s length. The drag force on a flyer in the flight chamber is described by the equation:

D = ½ρV2SCD

where D is the drag force, ρ is the density of the air, V is the velocity of the air, S is the surface area exposed to the airflow, and CD is the drag coefficient, which depends on the flyer's shape and the orientation. Unlike lift, which supports the flyer against gravity and helps maintain altitude, drag works to slow their motion relative to the airflow. By adjusting body position, surface area, and suit design, flyers can control the amount of drag and achieve better stability, maneuverability, and control during flight.

aerodynamic lift vs. aerodynamic drag

Diagram showing the aerodynamic forces impacting the flyer in the chamber by Warren Volles

The maximum airspeed within the flight chamber at iFLY Queenstown is 263 kilometers/hour (163 miles/hour). This airspeed was sufficient to lift me off the ground and keep me suspended in the air. The technicians adjusted the airspeed based on my weight and skill level as a flyer.

In addition, I wore a helmet, goggles, and a special suit that increased drag since it was made from loose-fitting fabric. The suit increased the surface area that was exposed to the airflow so I could catch more air as I moved through the flight chamber. The increased drag slowed down any rapid movements that I made, allowing me to maintain my balance and control my maneuvers and altitude.

Additional Insights

IFLY Queenstown joined the Climate Action Initiative (CAI) in 2021 to reduce its carbon footprint and become a more sustainable business. Running a wind tunnel uses a lot of electricity so iFLY knew it needed to take action. The CAI helped them take practical steps to reduce emissions, with the bold goal of reaching carbon neutrality. iFLY’s commitment has changed how they operate and inspired other local businesses to take part in climate action. Their journey shows how small businesses can make a real impact when they’re supported by community-focused programs and a shared vision for a greener future.

References

Environmental Accounting Services. (2023, September 24). iFLY’s journey towards carbon neutrality through the Climate Action Initiative. https://enviroaccounts.com/2023/09/24/iflys-journey-towards-carbon-neutrality-through-the-climate-action-initiative-2-2/

iFLY Holdings. (2024). Experience the freedom and thrill of flying with our one-of-a-kind indoor skydiving adventure. https://www.iflyworld.com

IFLY Holdings. (2014). The Science and Engineering of iFLY. https://www.iflyworld.com/wp-content/uploads/2016/02/iFLY_presentation_HS.compressed.pdf

NASA Glenn Research Center. (2023, December 8). Conservation of Mass. https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/conservation-of-mass