Electric Aircraft Are No Longer a Fantasy
As an industry, we hear about various experiments with differing approaches to electric aircraft. Some of these announcements have been in regards to solar-powered aircraft staying aloft for long periods of time, and others have concentrated replacing legacy propulsion (namely gas-powered engines) and control systems with electronics by getting rid of heavy pneumatic/hydraulic systems. The first set of seemingly true aircraft breakthroughs are now emerging due to essentially copying the Toyota Prius approach — namely, a hybrid approach.
The two major issues facing electric aircraft (including those that will use a hybrid approach of utilizing both gasoline-powered engines with electric motors) are weight and battery limitations. Due to the current state of technology for each of these limitations, it is doubtful that breakthroughs in either issue would allow the industry to launch a non-gasoline power flying machine. Instead we must refine both areas and find a way to take lessons from the automotive world. We must take an evolutionary step with hybrid aircraft where engines are driven by a set of gas and electrical power sources. Basically, we must put wings on a Prius.
First, the Easy Part: Improving What We Already Know
Advancements in engine technologies have moved along on an evolutionary scale since the early days of aviation. This slow advancement has allowed aircraft and engine manufacturers to constantly upgrade the power, reliability and efficiency of gas-powered engines. Other evolutionary advancements were improvements in materials with not only aluminum and steel alloys, but also with plastics, titanium, composites and ceramics being used to develop lighter and more fuel-efficient aircraft. This allowed aircraft to get larger, fly farther and higher, and provide the aviation industry with an economical means to operate aircraft anywhere in the world.
More recently we have seen a movement into bio-fuel mixtures, which have primarily been aimed at providing less-ecologically-damaging aircraft, but also to help alleviate supply chain issues for certain use cases (military and regions where most or all oil is imported). Before the recent expansion in shale oil and fracking, which has expanded the oil industry in the U.S. and Canada greatly, there were many concerns about the ready supply of oil in a world where the demand was growing, and fears of running out of oil seemed quite valid. For at least a few years, these concerns seem to have diminished due to not only an expansion of global oil production, but due to conservation efforts and economic slowdown in key parts of the world. These have now resulted in an oversupply of oil.
Each of these three sets of advancements (better engine technology, lighter aircraft materials and less-polluting fuel) has extended the life of the current state of the art in gas-powered aircraft, and will probably allow the world’s aviation industry to maintain the current fleet of legacy aircraft for a few more decades.
However, with each new technological development, the fate of purely gas-powered aircraft nears its end that much sooner.
The End of the Era of Gas-Guzzling Aircraft
The entire fate of electric and hybrid aircraft will essentially be driven by one technology — namely, batteries.
In fact, because of the lack of novel commercially-viable battery technologies, the industry is forced to move in an evolutionary manner from pure gas-powered aircraft to hybrid aircraft, rather a pure electric aircraft for wide-scale commercial use. This change will happen over the next 20 years, paralleling the experience of the automotive industry, which has only recently been able to provide commercially-viable hybrids (and some electric vehicles) after many decades of research and development.
Another pertinent example of this industry-wide evolutionary approach is the lighting industry, and pointedly the replacement of light bulbs. Incandescent bulbs have been around for decades with only slight improvements to their efficiency (or lack of) and reliability over time. Compact fluorescents (CFLs) were launched with great fanfare despite their many drawbacks since they were designed to be an exact replacement for existing bulbs, and were several times more efficient. But, the ultimate goal in lighting is the move to LED technology — that is, until some other solution emerges — since it promises even better reliability, greatly reduced operational costs and new use cases (i.e., new types of designs, new implementations, and eventually reduced-cost fixtures once we transition society away from legacy bulbs and related fixtures).
Aviation will need to do the same, and slowly move toward a hybrid aircraft that can be supported easily with existing industry infrastructure, and move toward operating and maintaining electronic power on aircraft over time. Think of how each airport and MRO facility will need to be upgraded to support electrically-powered aircraft, not to mention handling much more secured aircraft data which will be bi-directionally communicated to e-Enabled aircraft. (If you think your wireless connections for your smartphone are not adequate today, just imagine when we have many more devices sending and receiving critical data loads and status updates.) This goes far beyond installing a few more Wi-Fi routers around each terminal or maintenance facility.
With more airports going green to reduce their carbon footprint and use less energy for their operations, such facilities will need to re-think how they will need to support electrically-powered aircraft and their ancillary equipment. New staff who understand power and communications-related issues will need to be hired and trained as well. New facilities with greater capabilities will undoubtedly need to be built.
What Needs to Happen First
The key issue that needs to be addressed is how to store enough power on an aircraft to be able to operate it safely. Currently, petroleum-based fuels (and this includes those mixed with biofuels to a lesser degree) have the highest energy density per weight, which is difficult to match with any other power source (as shown in Figure 1).
Commonly available batteries simply cannot provide enough power for a large aircraft for takeoff (although many smaller aircraft have been able to, notably some small training aircraft) or operate for more than a few minutes. Smaller, lighter aircraft with limited use cases are a different story. One example of pure electric aircraft is the Aero Electric Aircraft Corporation two-seat Sun Flyer which will be a renewable energy, solar-electric aircraft. This company intends to bring to market the first practical all-electric airplane to serve the training and recreational markets.
Due to technological limitations of solar power and lithium batteries, this will not work for larger aircraft or those that need to fly farther and longer. The Sun Flyer is aimed at a market which only needs an hour or two of operational time per power charge.
There is hope on the horizon. As noted in an earlier article for regular readers of this column, the automotive industry has begun researching the use of lightweight supercapacitors that can essentially be formed as body panels, thus reducing much weight from a vehicle (or plane). These body panels will have the capability to hold much higher charges that will provide more power, faster charging time, and potentially reduce costs by eliminating the use of expensive rare-earth metals upon which most higher-end batteries depend today. These panels could conceivably make better use of captured energy produced by regenerative braking and extend the range of a vehicle. Early versions of these supercapacitors might need to be combined with lithium batteries to be economically feasible initially, according to recent reports. Early versions of these supercapacitors — a “sandwich” of electrolyte between two all-carbon electrodes — were made into a thin and extremely strong film with a high power density. The film is embedded in a vehicle’s body panels, doors, roof, and floor, storing enough energy to turbocharge an electric car’s battery in minutes. More research and refinement is needed but much progress has already been made.
This automotive industry innovation will undoubtedly be applied to aircraft once it matures. This could possibly be the innovation that might end the dependence upon petroleum for aircraft. By incorporating the power source into the aircraft body panels, we can solve the main issue of how enough power can be stored on an aircraft without sacrificing passenger or cargo space.
The Interim Approach: A Flying Prius
Many companies and research institutes have been experimenting with hybrid aircraft, where two power sources are used to drive a propeller. (Jet engines will apparently have to wait a bit longer.) One notable project is one wherein Boeing and the University of Cambridge collaborated to create a single-seat electric-hybrid test aircraft powered by a Honda four-stroke piston engine and a custom-made electric motor/generator. The two power sources are coupled so that either can drive the propeller. At times when a lot of power is required (such as during takeoff) the plane uses both the engine and the motor to drive the propeller.
Once at cruising height, however, the motor can continue to assist the engine to help save fuel or be switched into “generator mode” and for it to recharge the batteries while the plane is in flight. According to the University of Cambridge, this is the first time this has been achieved. A module designed by the engineering department at Cambridge is used to control electrical current to and from the lithium-polymer cell batteries, 16 of which are housed in compartments in the wings.
There are many other similar efforts, including those by NASA, Airbus and a number of startup companies, and that are moving in similar directions.
More to Come
The move towards electrically-powered aircraft is still years away from having commercially-viable products, but we should see many novel UAVs, small GA and experimental aircraft emerging on the scene. It’s coming sooner than many might think.
If aerospace firms are able to adapt technologies from the automotive and electronics markets in regards to power generation, power storage, and newer materials, the hybrid business jet cannot be that far away. It could then be followed by a hybrid regional jet. We might need to wait a bit longer for an “Airbus A380, powered by the Energizer bunny,” but who knows? All it takes is a few unpredictable research breakthroughs in nanotechnology, better solar cells and a few lighter aircraft materials.
John Pawlicki is CEO and principal of OPM Research. He also works with Information Tool Designers (ITD), where he consults to the DOT’s Volpe Center, handling various technology and cyber security projects for the FAA and DHS. He managed and deployed various products over the years, including the launch of CertiPath (with world’s first commercial PKI bridge). John has also been part of industry efforts at the ATA/A4A, AIA and other industry groups, and was involved in the effort to define and allow the use of electronic FAA 8130-3 forms, as well as in defining digital identities with PKI. His recent publication, ‘Aerospace Marketplaces Report,’ which analyzed third-party sites that support the trading of aircraft parts, is available on OPMResearch.com as a PDF download, or a printed book version is available on Amazon.com.