Brief introduction to urban air mobility

• A Urban air mobility (UAM) refers to short range passenger air transport in urban and suburban areas. Urban air mobility is a subset of advanced air mobility, which encompasses a broad spectrum of novel aircraft technologies used in local and regional transportation, emergency services, package delivery, cargo transport and more.

  UAM aircraft are compact, low altitude and highly automated. To minimize runway requirements in densely populated urban areas, the vast majority are vertical takeoff and landing (VTOL) aircraft. Power sources include batteries, conventional and synthetic fuels, hydrogen fuel cells and more.

  Following recent advancements in electrification technologies, electric vertical takeoff and landing (eVTOL) aircraft have taken centerstage in the UAM segment thanks to their versatility and low noise levels.

  Small eVTOL aircraft equipped for 2-5 passenger flights will be integral to the development and commercialization of urban air mobility in the next decade. This includes air metro — public air transport modeled after bus and rail services — and air taxis — the long-awaited “flying cars,” eVTOL aircraft providing short, on-demand flights.

  As of this writing, air taxis are likely years from commercial viability. However, NASA estimates (PDF, 3.31 MB) that air metro could become profitably by 2028, with 740 million annual trips across 23,000 aircraft by 2030. There are currently over 700 entrants in the advanced air mobility market, developing a wide array of eVTOL designs and components that will drive innovation in urban air mobility aircraft design now and into the future.

Due to their compact, battery-powered designs and slim margins of cost effectiveness, UAM aircraft pose distinct bonding challenges. Though such challenges are felt across all aerospace segments, customer feedback received by 3M has indicated two that are particularly acute in UAM eVTOL aircraft design and manufacture: lightweighting and out-of-autoclave curing

Lightweighting

Air metro aircraft must complete dozens of flights daily with little downtime for battery recharging. This makes minimizing weight and maximizing battery range essential. However, most classical aerospace adhesives are engineered for far larger aircraft running on conventional fuels. They are frequently too heavy for the compact, lightweight eVTOLs that will be the workhorses of urban air mobility.

Low density aerospace adhesives that can be readily incorporated into existing processes will be key to optimizing performance-to-weight ratios and achieving long term commercial viability. Promising opportunities for adhesive lightweighting include structural bonding adhesives, sealants, void fillers, composite surfacing films, honeycomb core splice films and more. Given the compact designs of most eVTOL aircraft, even minor weight reductions will add up fast.

Out-of-autoclave curing

Most classical aerospace adhesives are designed for autoclave curing. While autoclaves have long been the industry standard, they are also notoriously expensive to operate due to their high energy costs, long cycle times and propensity for bottlenecks. This renders autoclave curing unfeasible for the majority of eVTOL aircraft manufacturers in the UAM segment.

Numerous air taxi manufacturers are currently exploring out-of-autoclave (OOA) curing alternatives. The broader aerospace industry has found success reducing cycle times and controlling energy costs with OOA curing. Such benefits would be especially significant in eVTOL production, where every process improvement counts.

Aerospace adhesives compatible with OOA curing have great potential to expedite mass production, reduce energy usage and save considerable production costs, ultimately paving the way for UAM aircraft commercial viability.