Electric aircraft have significant advantages over fossil-fuel powered conventional aircraft. For example, electric aircraft can achieve the same horsepower at any altitude, whereas fossil-fuel powered aircraft lose substantial power at higher altitudes due to low oxygen levels. Electric aircraft are capable of generating instantaneous torque at low RPM. Still further, electric aircraft have zero emissions, a low noise output, and low heat generation, all of which are particularly advantageous in military applications, where low noise and heat levels in particular enhance the stealthy characteristics of the aircraft, thus allowing the aircraft to more effectively avoid enemy detection and attack.
Civilian and commercial operators also benefit from the advantages associated with electric aircraft. For example, electric aircraft are upwards of 90 percent efficient, compared to fossil-fuel powered aircraft which are roughly 35 percent efficient. Thus, electric aircraft may be less expensive to operate than fossil-fuel powered aircraft, especially in light of the ever increasing cost of fossil fuels. As stated above, electric aircraft have zero emissions and a low noise output. Electric aircraft are, therefore, environmentally friendly. This alone has the potential of opening up new flight operation opportunities in noise abatement zones and environmentally protected areas as well as complying with future pollution and emissions mandates.
Of course, there are drawbacks associated with electric aircraft, particularly electric aircraft that operate on battery power. The primary drawback is range. An electric aircraft operating on battery power is severely limited in range, that is, the distance an aircraft can travel without having to land and refuel, or recharge in the case of electric aircraft. This problem is primarily due to limitations associated with the current state of battery technology.
Current state of the art batteries have very low energy densities compared to, for example, gasoline. Indeed, the large energy density gap between fossil fuels and batteries is impeding the widespread adoption of electric vehicles, including electric aircraft. Present state of the art electric aircraft are barely able to achieve ranges of 200-300 miles before having to land for a long period of time to recharge the onboard battery.
Mid-air refueling of gasoline powered airplanes is known in the art but requires high precision flight and typically involves the pilot of a plane to be refueled to carefully maneuver into position behind a tanker refueling plane in order to perform the high precision operation of inserting a small, round probe into a moving basket drogue chute “probe-and-drogue” or through the similarly difficult method known as “flying boom”. Disturbances in the air from turbulence and wake vortices from the tanker plane make the accurate connection of the probe and drogue a difficult, time-consuming and potentially dangerous operation that has proven impossible to automate. Despite being reduced to practice in the 1940's, mid-air refueling operations of today still require highly skilled pilots and recharging operators for these operations which are still more “art” than “science”.
From 2010 to 2012, DARPA spent $33M in project KQ-X awarded to Northrop Grumman in an unsuccessful attempt to have one NASA Global Hawk refuel a second NASA Global Hawk flying at high altitude in close formation. The two UAVs flew within 100 feet of each other but were unable to connect and transfer fuel and the program was cancelled.
Companies such as Amazon, Google, FedEx, UPS and DHL are expressing interest in utilizing fleets of drones to deliver packages to consumers as well as for agricultural, law enforcement, film and television and many other applications that would benefit from a substantial increase in flight duration and payload. The U.S. Military is interested in persistent aerial platforms to carry sensors and other payloads in hostile environments where electric aircraft more easily avoid enemy detection due to reduced noise and heat signatures. Companies providing internet services including stakeholders such as Facebook and Google are interested in persistent aerial platforms to provide internet services over regions currently without such services.
Efforts have been made to extend the range of electric aircraft without returning them to their base of operations such as through inductive recharging on static power lines as found in U.S. Pat. No. 7,714,536, which is hereby incorporated by reference. This is not a desirable option for extending the range of electric aircraft because the permanent location of existing power lines severely restricts the operational area of the aircraft, permissions are required from the owners and operators of such power lines, and the extremely high voltage and proximity to neighborhoods creates a safety risk of trying to land remotely piloted aircraft on them. Additionally, since the power lines are fixed and the electric aircraft requiring recharge are moving, complicated latching mechanisms are needed, which add weight and complexity, especially for fixed wing aircraft, which cannot slow down or hover like rotorcraft to effect a consistently reliable attachment to the high-power utility lines.
To increase the flight duration of electric airplanes, the inventors of the present invention created a mid-air recharging technology for electric airplanes based on an improved probe-and-drogue as well as flying boom recharging apparatus entitled “LONG RANGE ELECTRIC AIRPLANE AND METHOD OF OPERATING SAME”, filed as PCT/US2013/034420 and published as WO 2014/011255 A2, which is hereby incorporated by reference. One embodiment of this invention is for a UAV to act as the recharging plane and/or the plane receiving the recharge, thereby removing human pilots and/or recharging operators from the process. To accomplish this level of automation, a new approach is needed to establish and maintain the electrical connection between two or more aircraft flying in close formation.
Accordingly, what is needed is a method and apparatus of establishing and maintaining a mid-air connection between one or more manned or unmanned electric airplanes requiring a recharge or supplementation of the on-board energy source from a manned or unmanned recharging airplane that is easier, faster, safer and precisely repeatable with automation than current probe and drogue and boom connection techniques known in the art.