Cable-powered short-range heavy lift technology.


Pochari Technologie’s cabled lifter technology. In March 2019, Pochari Technologies invented a highly novel aerial lift system. The invention arose out of a need to balance the low cost of terrestrial cranes and the degrees of freedom afforded by a helicopter crane. It was found that since most aerial lift jobs occur relatively close to fixed sites, the actual distance traveled by the heavy-lift helicopter was quite minimal. For many jobs that use heavy-lift helicopters, often it’s not so much range that is desired, but rather height. Another strong impetus for aerial cranes is turnaround time, a heavy-lift helicopter such as a Bell 205 can be operated in the “restricted category” which allows for-profit external load operations as long as it does not operate over populated areas. All over the world, Bell 205, S53, and more recently, ex-Military UH-60s perform heavy lift work installing air conditioning units on rooftops or erect cell towers. Classic cranes have difficulty practically attaining heights in excess of 200 meters, nor can they suspend loads further than at best a hundred meters from their center of gravity. The load capacity of a conventional crawler crane or truck crane might be impressive on paper, but this capacity drops off precipitously as the reach is extended. Moreover, the vast majority of helicopter lift jobs do not fully exploit the aircraft’s unlimited degrees of freedom, it spends most of its time hovering over the lift site and flying slowly back and forth to pick up the load from a truck or storage site nearby, rarely does the aircraft fly many miles with a load underneath. Furthermore, in the U.S it isn’t even legal for most of the restricted category heavy-lift helicopters to fly about over dense areas. The desired operational radius of the cabled lifter is not significantly restricting to its range of potential uses. The ground powerplant vehicle can be situated between 5 and ten kilometers, the width of the Pensionala of San Francisco is around 11 kilometers. To prevent the cable from sagging excessively, a small drone carries the cable mid-span. The weight of a ten-kilometer cable would be approximately 1100 kg, with half of the weight being carried by the lifter and the powerplant truck. In order to fly over obstacles, such as forested areas, the powerplant truck carries a telescoping pole that reaches a height of around 50 meters, providing the cable with enough overhead clearance. What we realized is that if electric power could be transmitted in a high power density configuration to the lift craft, then it could effectively hover all day long without the need to refuel, carry the weight of the fuel, nor use highly expensive turboshaft powerplants. The lifter itself would only need moderately high power density non-superconducting electric motors, a transformer to step down the voltage, and a rectifier to convert the unusable high- -frequency AC power to either DC or 60 HZ AC power. Upon further analysis, it was found all three options were available and light enough to be carried by the lift craft. In order to design a lightweight conductor, the amount of current must be reduced to a minimum, the only way to facilitate this is by increasing voltage. The problem with increasing voltage beyond 5 kV is that electric motors are unable to use the power, so some form of step-down transformer is required, The weight of a transformer operating at 60 Hz is prohibitive, the transformer would many times more than the weight of the aircraft is operating at standard grid frequency. To overcome this, a very high-frequency AC power supply is required, in order to achieve this, Schottky diode-based rectifiers are used to convert the AC power generated by the ground power supply into DC, which is then converted back to AC and “chopped” into the appropriate frequency. A transformer could easily be designed with weight reduced to the utmost minimum by stepping up the frequency to over 100 kHz. Nanocrystalline core material such as Hitachi FINEMET could be employed to achieve a gravimetric power density of >33 kW/kg with minimal core losses. The cost of the nanocrystalline material is around $9/kg, or about $0.30/kW. Nanocrystalline high-frequency transformer cores are constructed mainly from iron with grain sizes below 10 nanometers, the microstructure of the alloy facilities extremely high induction with low losses. Since the high-frequency AC power is unusable by an electric motor, the current has to be rectified back into DC which can be used directly by a DC motor or in an AC motor if rectified back into AC. Using the Schottky diodes, a rectifier with power densities of up to 50 kW/kg could easily be designed. Electric motors are by far the biggest weight contributor, with the current state-of-the-art axial flux electric motors having power densities of around 6 kW/kg at 10,000 rpm. rpm. To minimize the mass of the electric motors, a reduction gearbox had to be employed. Using high-frequency AC power at high voltage, a conductor cooled by the ambient air could be designed with a weight of 110 kg per kilometer. High-frequency conductors can take advantage of the skin effect, at 100 kHz, the skin depth of the current is only 150 microns, which means a large diameter hollow conductor can minimize mass while achieving the required resistance to minimize ohmic heating. The cabled lifter is a simple yet powerful concept. At the most basic level, the cabled lifter is as its name suggests, a flying crane that use generates thrust for its locomotion, but rather than carrying fuel onboard and burning it in a turbine, it draws high voltage and high-frequency AC current from an ultralightweight electric cable that unwinds from a ground vehicle. The concept draws from two fundamental technologies: ducted fan lifters and high-frequency rectification. In order to develop a low-cost aerial crane solution, a far more affordable powertrain system is called for. Existing aerial crane technologies consist almost exclusively of one airframe, the Sikorsky sky crane. The Sikorsky S-64 Skycrane is a classic jet fuel-powered turboshaft helicopter.

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