Tele-everything and the advances of technologies such as renewable energies open a myriad of alternatives for transportation.
By Dennis Bushnell Chief Scientist
NASA Langley Research Center
The prospective future of civilian air transportation is changing rapidly, responding to serious issues with solutions that carry major societal, commercial, and industrial implications.
The overarching issues to be addressed include emissions, climate and energy production/harvesting, road and infrastructure costs, the shift to doing everything remotely, possible of on-site printing versus air cargo for some commodities, the shift to automation on the way to autonomy, electron ubiquity and vulnerabilities, the limited capacity of existing airports, acoustic strictures, safety, the need for increasingly capable air traffic control (ATC), security, and hub/spoke efficiency. To this litany is now added recovery from the aeronautical downturn left by the Covid-19 pandemic.
A potential change is the scale of the future effects on civilian air transportation as a result of virtual/digital reality, immersive presence, and tele-travel, as was made apparent in the major Covid-19 effects on air travel.
Tele-travel through immersive virtual presence has long been forecast and in development. The technology, especially regarding bandwidth and 5-senses virtual reality, is at the point where it’s a serious alternative to physical travel given the current challenging times. But tele-travel is just one aspect of the rapidly developing virtual age of tele-everything.
Work, education, medicine, shopping, commerce, politics, entertainment, and socialization have been happening remotely for a while now. And with the help of on-site printers, tele-manufacturing also exists.
The benefits of tele-everything include lower costs, reductions in climate impacts and travel time, minimal time away from family, more engagement opportunities, and the possibility to be anywhere at any time.
New era of air transportation
A civilian air transportation renaissance will be enabled by a plethora of revolutionary technologies, including increasingly inexpensive renewable energy, electric propulsion, nano materials and materials processing, printing manufacture, artificial intelligence (AI) and autonomy, an emerging global sensor grid, safety and reliability attainment, resilient navigation and communications, and, eventually, autonomous personal aircraft and ATC.
Cost reductions in large air transport is also necessary, along with improved metrics for all speed ranges, from personal air vehicles to supersonic transports. The buildout of the personal aircraft markets could approach $1 trillion/year eventually, with millions of flying things in controlled airspace.
The benefits of such personal air transportation include reduced costs for current auto infrastructures, and shortened travel time, with electric systems charged with renewable energy, and with autonomous operations hopefully saving lives.
The functionalities for small/personal class aircraft include an extensive number of service, business, and government applications that could yield better range along with easier and faster commutes. And because these personal air vehicles are autonomous, they could be readily used by the young and the infirm.
For long-haul air transport, especially intercontinental, at transonic and supersonic speeds, the outlook includes emissionless electrics recharged with renewable energy approaches slated to provide 80% of electricity in ~2 decades.
The same inexpensive energy source is increasingly producing “green” hydrogen and hydrocarbons from CO2 captured from the atmosphere. Then there are biofuels, with a potential huge capacity enabled by halophytes, which are salt plants grown on wastelands using saline or sea water.
Another enabling factor would be improved aerodynamic performance via drag and weight reduction, which would double the range for a given battery energy density. In addition, advanced nano composites and nano scale metal printing with superb microstructures promise major drag/weight reductions, consequently increasing range.
Renewable energy is now at or below cost parity with fossil carbon generation. Renewables are 90% of new generation capacity, and produce 28% of electricity worldwide. The ongoing cost reductions for both renewables and energy storage, which dropped 70% over just the past 3 years, appears to guarantee minimal emissions for electric- or green-fueled aircraft going forward.
Mod-sim. In the 1960s, as computational machines and algorithms improved, numerical solutions of differential equations joined theory and experiment for aero design. Over these past decades, mod-sim and the computing machines have become excellent for experiments in simulated situations.
There’s ongoing research to develop “certification by computation,” and “numerical wind tunnels.” Historically, we have built what we can compute, and as computational capabilities have allowed ever more complex approaches/designs, we have morphed from linear thinking and designs to ever more complexity, including multi-disciplinary optimization.
We are now entering the age of exaflop machines and serious research devoted to quantum computing. If successful, the latter offers possibilities for computing complex turbulence flows configuration-wise in a design mode, which would be seriously revolutionary.
Combining such mod-sim capabilities with developing AI-based optimization approaches that work with data from the emerging global sensor grid should produce ever more efficient and lower-cost aero transportation capabilities.
Materials. There are 2 disparate approaches being pursued to produce much improved materials that are both stronger and lighter. The first of these efforts has been ongoing for 2 decades, and focuses on nanotube composites.
The second devolves from observations over the years that the performance of metals is seriously degraded because of the approaches to processing materials. The recent “get well approach” for metals is printing at the nano scale, producing improved microstructure and properties of materials.
These much-improved metals would constitute competition for composite materials because they could be produced at lower costs, with equal or better properties, improved repairability, and innate lightning protection.
Safety and reliability. Current commercial aviation and, to a lesser extent, general aviation, have established an excellent safety record, with 80% or so of the remaining safety concerns attributed to human factors.
The expected growth in numbers of aircraft will require much improved safety statistics due to the fact that most of the additional aircraft operations will take place over populated or developed areas, not over wastelands or water as with scheduled airlines.
In order to achieve better safety records, aircraft need to be autonomous. Additional safety improvement arenas include inspections, vehicle health management, crashproofing, recovery approaches, obviation of single points of failure and redundancy, zero-defect manufacturing, and flow control.
All of these are best addressed during design. Safety needs to be an independent variable, even in designs, where cost is a prime issue. Nearly everything in the entire aviation system is now executed by electrons, which, unfortunately, are extremely vulnerable to electromagnetic pulse (EMP), jamming, co-opting, and cyber-attacks.
Going autonomous and shifting to all-electric aircraft compounds the vulnerabilities to where the threats require serious consideration with regard to electron degradation.
Civilian aeronautics possibilities
Autonomous, affordable, quiet, and safe personal flight could be enabled by various manifestations of these technologies in the automotive industry, where autonomous replacements are being developed which offer longer range and can be powered by green renewable energy.
The technologies are essentially here. The current advanced air mobility developments include an increasing number of fly/drive versions with an eye toward the huge new aero markets for a flyable auto replacement.
An all-up-truss braced wing design is an example of what may be possible for a long-haul aircraft design. Use of an external wing truss provides major structural benefits, and allows reduced wing weight, thickness, and sweep.
This results in an enhanced low-drag laminar flow that is easily maintained and has reduced sensitivity to roughness, insect remains, and ice clouds, and also has reduced cross flow. The truss also enables doubling of the span.
This allows a reduction in wing chord, further enhancing the extent of laminar flow, as well as a reduced vortex hazard, and a major reduction in drag due to lift. The engines could be placed at the rear of the fuselage and thrust vectored for control, obviating the drag and weight of the empennage.
Pfenninger’s and Virginia Tech designs for such aircraft yielded lift/drag (L/D) values in the 40s – around twice current values. Such aerodynamic performance would increase the range of electric transports. Pfenninger also designed a supersonic transport that was strut braced with an L/D value in the 16 range.
The current limited capacity (thousands of aircraft) ATC system can be non-linear (small changes or occurrences can produce large problems and issues), has to function constantly, and is operated by humans with their associated latency and errors.
However, morphing the existing ATC system to what will be required for many millions of aircraft is essentially too far out – probably decades, compared to the rapidly developing market needs and requisite time frames.
Ongoing changes to the existing system (eg, FAA’s NextGen) are benign compared to what is required for the projected numbers of unmanned aircraft systems (UASs) and personal air vehicle (PAVs), and are taking far too long compared to the rapidly developing market requirements.
The enabling ATC system for UAS/PAVs will be a major issue impeding the development and buildout of these new aerospace markets. Vehicles, safety/reliability issues, and ATC, all require serious improvement.
One suggested approach that is a better, faster, and cheaper alternative to evolving the existing ATC system is to develop a giant simulation around the current system, taking data from, but not inputting into or interacting with, the existing system.
This simulation could be used to develop requisite software and associated software and hardware, including communications, navigation, sensors, collision avoidance, architectures, and AI. In this simulation, all the component parts and their system of interacting systems could be developed to create a new, wholly autonomous, minimal-latency, and fail-safe ATC system capable of handling millions of air vehicles.
This simulation could then be demonstrated in the desert. Once proven, it could become the next ATC system. The existing ATC system is then shut down and replaced by the simulation.
After nearly a century of attempts, technology is now capable of shifting personal transportation from the ground to the air, with many associated benefits. Current urban air mobility (UAM) efforts, with more than 500 vehicles in design, and many more in flight test, are the stalking horse for likely futures of a new capability for civilian air navigation.
Initially, UAM will be fee-for-hire, as opposed to a privately-owned means of transportation. Concurrently, there are now very sizable markets developing for applications of UASs to meet societal, service, governmental, and commercial needs.
Both the UAM and UAS developments feed directly into the small eVTOL capabilities required for the ultimate PAV future with its massive markets/scale, and personal and societal impacts.
At higher speeds (transonic and supersonic long-haul), the combination of frontier aerodynamics, materials, advanced batteries and/or fuel cells, inexpensive renewable energy and green hydrogen, and hydrocarbons should enable electrics with a lower-cost propulsive energy source.
Overall, a quieter, cleaner, less expensive, and ubiquitous personal air transportation system is developing rapidly. Driven by markets and climate, it is enabling technologies with PAV buildout, resulting eventually in a doubling of civilian air transportation markets from their current ~850 billion into the 2 trillion range.
The current auto market is ~2.7 trillion. PAVs would subsume a strong percentage of that market, producing in the process major savings in ground transportation infrastructure, and enabling a completely wireless-free life, off the roads and wires, using distributed energy generation and tele-everything.
A major issue going forward with regard to civilian air future is the concomitant societal shift to tele-everything, including tele-travel. We are already seeing decreasing physical travel because of this alternative virtual presence with its many and major benefits.
Major work required to enable the futures discussed herein includes batteries and fuel cells, certification of air vehicles many of them very different from what’s known now, weather issues, safety, vehicle cost/affordability, noise and ground interface infrastructures, autonomy, electric propulsion, ATC for many tens of millions of flying things, and printing manufacturing. To this author’s knowledge, these are all workable.
Dennis Bushnell is chief scientist at NASA Langley Research Center, where he is responsible for technical oversight and advanced program formulation. His major technical expertise includes flow physics and control, drag reduction, and advanced configuration aeronautics. Bushnell is a fellow of AIAA, ASME and the Royal Aeronautical Society and a member of the National Academy of Engineering.