In the 2011 State of the Union speech, President Obama described the development of clean energy and transport technologies as the Apollo projects of our time. It was disappointing that Obama’s speech did not mention clean aviation. Electric aviation can replace our oil based transport with a system that is faster, cleaner and cheaper using existing technology. No advanced batteries are required to build this system!
In 2008, NASA funded several teams to design aircraft with 70 percent lower fuel consumption and a 71 decibel reduction below current FAA noise standards. The teams were led by General Electric, M.I.T., Northrop Grumman and The Boeing Company. The Boeing team designed a hybrid electric aircraft to reduce noise and fuel consumption. The team’s report concluded that hybrid electric engine technology “is a clear winner, because it can potentially improve performance relative to all of the NASA goals.” The major limitation of electric aircraft continues to be the weight and cost of batteries. Current electric aircraft have low payloads and speeds due to limited battery power. The Chinese company, Yuneec, demonstrated its E430 electric aircraft in 2009. The single-seat aircraft flies with lithium batteries for up to three hours with a maximum take-off weight of 1034 lb. The light sport aircraft is promising, but has a maximum speed of just 150 km/h.
In the 1950′s, the missionary pilot Nate Saint pioneered the use of circular flights for retrieving payloads from the ground using fixed wing aircraft. A bucket trailing the aircraft on a cable was lowered to the ground and kept stationary by flying in a circle. After the payload had been transferred to the bucket, the aircraft would revert to straight flight and the payload would ascend on the cable. Modern pilots have demonstrated the technique which can be viewed online.
An electric takeoff system can be built using the same principle for much greater payloads. Electric tow planes would circle a hub at an existing airport with one rotation every two minutes. Payload aircraft would attach to a winch cable at the hub using a three point harness. The winch motors in the hub would immediately tow the payload to altitude with acceleration similar to an electric elevator. The take-off would be silent and smooth for the passengers.
At the top of the winch cable, the payload aircraft would be travelling as fast as the tow planes and with an altitude of 30,000 feet or more. The harness could be detached when the aircraft is travelling in the desired direction. For higher altitudes including suborbital flights, the payload would detach from the winch and continue along the extended cable using centripetal force. As the cable travels in a circle, the payload would be accelerated towards the outside of the cable. To avoid drag, the cable would fly at high altitudes using its own lift. Centripetal force would cause longer cables to extend outside the atmosphere due to the curvature of the Earth.
Any new transportation system should be evaluated on the key criteria of economics, market and safety. Basic economic modeling shows that the electric take-off system would be cheaper than conventional aviation and trucking for freight. Electric power prices are generally lower and more stable than oil prices. For a typical aircraft, electric take-off and climb would be complete in less than three minutes compared to fifteen minutes for a conventional take-off. A Boeing 737 consumes about 5000 lb of jet fuel in an average takeoff and climb to cruise altitude. That fuel cost is $2000 at current jet fuel prices compared to a projected $650 for an electric take-off. There is a strong business case for airports and airlines to deploy the technology to reduce their consumption of jet fuel.
The global aviation industry spends approximately $200 billion on aviation fuel based on current prices. A significant fraction of that fuel is spent on taxi, take-off and climb as they are the least fuel efficient phases of any flight. By retrofitting aircraft for electric take-off assist, much of this fuel cost could be saved. In addition, cheap electric air freight would capture market share from the trucking industry thanks to lower fuel costs. The trucking industry is estimated to contribute 5% of America’s GDP. The development of electric take-off would be motivated by fuel cost savings in the aviation sector and it could potentially replace a large share of America’s freight industry with electric transport.
Take-off is the most expensive and dangerous phase of any flight. An engine failure in the first minute of flight gives the pilots little time to respond. Electric take-off has the potential to be safer than conventional aviation through the use of reliable electric motors and redundant tow planes. In the event of a power failure, the electric tow planes could be landed at the airport under battery power. The winch cable could be fitted with parachutes at regular intervals to be deployed in case of a broken cable. Residents living near airports should welcome the electric system as it will eliminate aircraft take-off noise. The tow planes will fly at high altitude and will not be audible from the ground.
The electric take-off system has the potential to be safe, economical and to capture a large share of the aviation market. The system hub would be constructed adjacent to existing airport runways. The tow planes would take-off and land under electric power in the same way as normal aircraft. The airspace around existing airports is tightly controlled by the FAA and airport authorities. Air traffic controllers should be able to schedule landings to avoid the short period when the cable will overfly the runway. Overall airport capacity will be increased as take-offs will no longer require use of the runway.
Cheap access to space and suborbital flight would be a simple extension of the infrastructure. As suborbital vehicles become available, they could be launched by extending the length of existing cables used for aviation. The cables can be constructed from commercially available HMPE fiber that is currently used in the oil and gas industry. Lift would be generated by the tow aircraft flying in circles and the cable would be shaped like a wing to generate additional lift as it travelled through the air. A 1000km cable could accelerate the payload to a speed of 8 km/s at the tip which would allow suborbital flight and the potential to reach low Earth orbit. For suborbital flights, the system would be much cleaner, safer and quieter than a rocket launch. The design is discussed in a 2009 book by Michel Van Pelt titled “Space Tethers and Space Elevators“.
President Obama has called for Apollo projects to deliver clean energy transportation to America. Electric aviation can deliver cheap, clean transport for passengers and cargo without the political controversies of high speed rail. There is a strong business case for airlines and airports to deploy the electric take-off system to reduce fuel costs. The system could reduce aviation’s dependence on expensive oil and capture freight market share from the trucking industry. The aviation industry should take the lead in developing and deploying this clean transport technology.