Heliport consultant and pilot Rex Alexander warns that the urban air mobility (UAM) industry needs to exercise caution with regard to building associated infrastructure, particularly rooftop helipads/vertiports. Alexander made his remarks at the CAFE Foundation’s UAM seminar on July 21 in Oshkosh. “Airspace is attached to the environment, and how you design it has a great impact on aircraft performance. Infrastructure should not try to kill you if you blink,” he said.
“We typically test aircraft at an airport in a pristine environment with lots of room. A lot of the work I do is up on buildings, and that is a whole different environment with a lot of other considerations to determine what is going to be safe. Once you go on a roof, all bets are off,” due to shear and other wind anomalies that greet aircraft flying in urban canyons, he noted. “Some aircraft handle better than others. How much performance do you have to have before you overtax the aircraft? I’ve seen bad infrastructure do this more often than not because bad infrastructure forced the pilot to ask more from his aircraft than it was capable of providing.”
Alexander looked at 30 buildings in downtown Los Angeles to determine which would be suitable for passenger eVTOL aircraft operations such as Uber Elevate. “Most were not,” he said. Elevated pads for those aircraft face the same challenges that have vexed helicopter operations for years including local-induced turbulence and a goulash of updrafts, downdrafts, and tailwinds that can send windsocks into simultaneous different directions at the same helipad. Even if these helipads can be operated without draconian wind speed restrictions, the ride quality to and from there is so poor as to make them commercially useless. “You don’t want passengers getting off your aircraft with a sick sack every time, because if that happens they are not going to come back,” he cautioned.
Building elevated helipads that provide for airflow under the pad can mitigate some of the problem when on the building, but building owners typically don’t want their architectural masterpieces defaced with what amounts to a large “top hat” that is not aesthetically pleasing, Alexander acknowledged, noting that, “'Aesthetically pleasing' is another term for what’s really dangerous in the aviation world.”
Still, operating from rooftops with all-electric aircraft can provide increased safety as opposed to turbine-powered helicopters, Alexander said, as electric aircraft do not have the same power lag. However, unlike today's helicopters, the design and physical space requirements of the various 175 and growing eVTOL designs may make constructing standard-size vertiport surfaces problematic, Alexander said. “The challenge is, what do we design to today? Infrastructure can be a huge help or a huge hindrance.”