America Free Zone

To reduce energy consumption and support its overall sustainability record, the AFZ operates nearly 2,000 photovoltaic (PV) solar panels, which produce an average of 382 MWh of electricity. The facility’s contractors wanted to understand how a planned installation of additional PV panels to the roof of a building could affect – and be affected by – the operation of a helipad AFZ offers for the use of its business tenants.

There were two main issues to consider: glare and “wind” from the operation of the helicopter’s rotors during takeoff and landing. Glare from PV panels is a significant issue in aviation: after air traffic controllers at one U.S. airport were briefly blinded by such reflections in 2013, rules governing solar arrays near airports were overhauled. As for wind, solar panel racks are typically designed with ordinary wind forces in mind – not the unique loading patterns created by helicopter downwash. Preventing damage to solar arrays around a helipad requires accurate estimates of the potential forces helicopter takeoffs and landings will exert.

After working with AFZ’s helipad specialists, EnTEC Aerospace Division, to understand the facility’s context and priorities, we undertook analyses that would ensure safe operating conditions for the helipad while protecting AFZ’s commitment to renewable energy.

Glare:

To understand the potential for harmful glare in the airspace around the helipads, we applied the same methodology the American Federal Aviation Administration uses. We conducted an initial screening assessment, and found that glare originating from the PV panels would extend at most 160 m along the approach and takeoff paths. Establishing this range helped us to make an informed selection of numerous specific viewpoints for further study. We modeled glare at each viewpoint for every minute of an entire year – to capture every season and every time of day – and gathered detailed statistics on visibility. We found that, given the flight paths to and from the helipad and the positions of pilots during takeoffs and landings, the risk of significant glare impacts existed only for brief periods in the early morning and late evening hours during the shoulder seasons. The EnTEC team was able to plan the installation of the new panels with confidence that the potential for harmful glare was low.

Wind:

To predict the maximum downwashing airflow the helipad would experience, we combined the weight and dimensions of the heaviest helicopter expected to land there. Based on previous studies of helicopter downwash and outwash patterns, we were able to estimate the maximum expected mean and gust outwash speeds. Our analysis took into account the flight path, helicopter specifications and distance of rotors from the building’s roof, geometry, the location and orientation of the solar panels, and the gustiness of the airflow. Analyzing the various airflow effects from helicopters, we were able to generate a complete picture of the loads that would act on the solar panels near the helipad. This analysis let the design team understand the precise structural requirements for the PV racking system.