The Evolution of Electrically-Powered Flight
The development of rechargeable nickel-cadmium batteries opened a door for model airplane builders to experiment with small electrically powered aircraft. Nickel-cadmium batteries have the advantage of being extremely light despite their relatively low power density. Model aircraft could stay aloft for durations of a timespan of some 3-minutes. New developments in small battery technology enable model aircraft to remain aloft for longer durations.
The appearance of rechargeable nickel metal hydride batteries and lithium-ion batteries now allow the same types of electrically powered model aircraft to remain aloft for durations of 20-minutes and more. Researchers at Brown University (Rhode Island) are testing lightweight plastic-polymer batteries that are scheduled to become commercially available over the next several years. A rechargeable variant is also likely in the future and would help keep model aircraft aloft for an hour and more.
New developments in solar photovoltaic technology have seen the conversion efficiency increase from around 9-percent to some 27-percent. A variety of solar aircraft have been built over the past twenty years and include pilot controlled and radio controlled versions. New developments are planned in solar photovoltaic flight including flying craft that would remain aloft for prolonged durations when flown at extreme altitudes or during summer months at the north of south pole (24-hours of sun). The latter solar electric aircraft may likely carry several vertically mounted solar panels to capture sunlight.
Ongoing developments in the field of electrical energy storage technology have encouraged research and development into various electrically powered single-seat aircraft. One such concept being development in Spain and uses hydrogen fuel cells to produce the electricity needed to drive the propeller. Several kit plane builders are also exploring possibilities in electrically powered flight. Their objective is to build a pilot controlled craft capable of covering a distance of 250-miles.
Advanced Battery Technology: There is ongoing research in battery technology that holds the promise of greatly increase storage density and usable life expectanty while reducing the time required for a recharge. A research team at Massachusetts Institute of Technology (MIT) is developing a nanotube super capacitor (http://www.ultracapacitor.org) that could operate as a high-density storage battery. It is intended to become commercially available within the next 5-years.
A competiting group in Texas (EEStor) is researching an energy storage ceramic ultracapacitor technology that can function as a high-density storage battery. The A123 systems group (http://www.a123systems.com) has plans to develope large versions of their rechargeable lithium-ion batteries. These energy storage technologies are intended to power vehicles. The possibility of high-energy storage density (per unit volume and per unit mass) of these technologies could make them attractive to store propulsive energy aboard small aircraft.
The combination of energy storage density, rapid recharge duration and long usable life expectancy could enhance the longterm cost competitiveness of these energy storage technologies. They may likely become cost competitive against fossil fuel in small aircraft within the next decade. The longterm maintenance and repair costs of electric propulsion motors would likely be lower than the costs of maintaining aeronautical piston engines and small turbine engines (for turboprops). These factors could lead to the possible development of electrically powered short-haul commuter aircraft and their introduction to service on some high-density routes within 20-years.
Wireless Power Transmission: There are technologies that could be developed to enable electrically powered aircraft to be flown over extended distances. Nikola Tesla theorised that it may be possible to transmit large amounts of electric power using wireless technology. He was among several people who have researched and tested such technology. An electrically powered aircraft was kept aloft for an extended duration several years ago by transmitting power to it from ground level using microwave technology.
There may be scope to enhance wireless power transmission technology to enable it to provide power to electrically powered aircraft that fly on selected (high-density) routes. The military has a targeting or "lock-on" technology that can keep an aircraft in the focus of advanced (and automated) optical technology. There may be scope to modify that technology to keep aircraft "locked-on" so as to transmit a focused energy beam to it from series of ground-based installations.
One or more aircraft (on different flight paths) that operate on high-density routes may receive a proportion of their propulsive energy by such means. The potential use of such technology would likely evoke concern from environmental groups. It may however be within the scope of future research to address and resolve such concerns. Most of the contemporary research in wireless power transmission is currently focused on the transmitting low levels of power over short distances at low cost.
Possible Future Developments: Flow batteries are cumbersome units that have traditionally been used in a variety of stationary applications to store energy inside buildings. New developments that are on the horizon for flow batteries could result in them becoming lighter while the energy storage density increases. Some variants could be adapted for some types of vehicular application in the future.
Hydrogen as been touted as a possible fuel in small aircraft that are powered by fuel cells. The hydrogen fuel cell is actually a very old technology that is facing competition in terms of overall conversion efficiency. The main competitors are the new storage battery technologies that are currently under development. Storage batteries would return a higher percentage of the recharge power and be more efficient in terms of energy usage over the long term.
The American Defence department considered building a small fleet of nuclear powered aircraft during the Eisenhower years in the White House. There were several drawbacks to using such technology during that time period. However, new developments in nuclear technology and other power conversion technologies could again form the basis of nuclear powered flight. Such technology may resolve the issues that relate to the concepts that were examined during an earlier era.
New developments in pebble bed modular reactor (PBMR) technology allow for the use of small spherical nuclear fuel pellets. The technology can be adapted to operate on thorium (instead of uranium) and operate without need for water. A micro version of such a pebble bed nuclear reactor could provide heat to energise a series of thermoacoustic engines that convert heat to standing sound waves that in turn will activate linear alternators that generate electric power. The electric power may be used to drive propellers, propulsion fans or compressors.
There is the likelihood that other types of energy storage technologies will be discovered or developed in the future. Some of these storage technologies may be compact, lightweight and have high energy density. Storage technologies that are as yet unknown could appear during a future time and form the basis of some form of future electrically powered commercial flight. Technology that is currently under development could form the basis of electrically powered passenger flight within the next decade. Electrical aeronautical energy storage and propulsion technology could appear because such technology would likely be cost competitive.
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