The heavy-lift industry is in desperate need of a modern aerial lift solution. The current heavy lift industry relies almost exclusively on old, outdated, and largely obsolete airframes developed in the 1950s. No new generation of heavy-lift rotorcraft has been developed since. We believe there exists a tremendous market potential to develop a modern heavy-lift rotorcraft incorporating technological innovations that have taken place during this stagnant development history. Pochari Technologies has incorporated a number of important and differentiating features that enable the crane to stand out from the current heavy-lift fleet. The key features that differentiate this modern aerial crane are its unmanned flight control system, modular configuration to enable vehicle-based transport, and most importantly, a unique fuselage-less design that saves considerable weight as well as minimizing footprint. In addition, this design incorporates significantly higher disc loading than previous heavy-lift hovercraft, which at first glance may seem to be a disadvantage due to the increased power required, but this decision is carefully weighed to enable significantly reduced rotor diameter. Conventional rotorcraft are designed to maximize range for long-distance missions, heavy-lift rotorcraft in comparison require only short endurance for short radius operation, refueling can be performed periodically, thus higher fuel burn does not compromise the performance and is well worth the reduction in rotor diameter to enable landing in confined areas. One of the key advantages of the aerial crane design is the substantially reduce empty weight fraction. Since our design eliminates the fuselage, tail rotor boom, and landing gear, the empty weight fraction is reduced to 30-35% depending on the exact model, compared to 50% for traditional rotorcraft, this increase in payload makes the machine much more competitive as it reduces the hourly cost per pound lifted.
The Aerial crane is designed to shine in lifting applications that require significantly greater operating radius, unlimited mobility, greater operating flexibility, quick setup and turnaround time, and where ground-based cranes simply cannot perform. Prime applications include pre-fabricated modular construction, installing offshore wind turbines, installing wind turbines in mountainous terrain, moving air conditioning units atop a building, pouring concrete in mountainous regions, transporting an excavator atop a high rise building for demolition, transporting shipping containers from ports, installing solar farms, bridge construction, moving large stones from a quarry, mining operations, offshore oil and gas rig construction, or moving large stationary power generators or transformers from rural areas. The aerial crane shines in virtually any situation where heavy objects, building materials, or construction equipment needed to be moved fast, and most importantly, anywhere regardless of terrain conditions. Currently, conventional helicopters are prohibitively expensive to purchase and operate: Enter the Aerial crane. Designed solely as a heavy lift craft, not as a manned helicopter, we bypass all of the costly requirements that make helicopters so expensive. By eliminating the pilot, we can remove the entire cockpit section, reducing insurance and personnel costs. In addition, all of the necessary instruments and flight control systems are replaced with a simple remote-control system. The elimination of a crash-worthy fuselage and cabin section saves considerable weight, adding to the lift capacity. By designing the aerial crane to be moved and transported by truck, instead of ferrying over by flying, we can avoid operating over populated areas, enabling less stringent certification and insurance requirements. Even if ferrying over non-populated areas is feasible, the cost and time can be significant as job sites are often located far removed from remote locations all around the globe. The specialized nature of the aerial crane means the number of units worldwide is small relative to the number of jobs conterminously being performed at any given time, resulting in a constant need to transport the crane long distances. The nature of aerial crane missions is generally short-term, resulting in low utilization rates unless the crane can be immediately transported to another jobsite. Once the rotor blades are removed, all that remains is the compact drive module and shaft, once the shaft is disconnected at the base, the module can be placed inside a small box truck. The benefit of the coaxial design is the minimal mainframe footprint, the powerplant and gearbox occupy minimal volume, the shaft extends a considerable distance, but once it is disconnected, the entire unit occupies very minimal space, enabling convenient transport.
The aerial crane’s operation is strictly limited to job sites with a defined radius of operation, which is only occupied by trained personnel, if any time the aerial-crane is going to operate over populated areas, all occupants are evacuated. Ferrying or flying over populated areas is made redundant by the inherent modularity of the system which permits easy ground transport. By eliminating the need for more stringent traditional manned aviation certification, the cost is reduced by a significant margin. By eliminating the extremely high safety and performance standards required for passenger-carrying aircraft, manufacturing costs are dramatically reduced, additionally, the reduced accident rate attributable to the unmanned and partially autonomous flight control reduces the perceived hazard of rotorcraft operating in heavy-lift settings. The aerial crane will be sold for only $1,000,000, only twice the cost of the equivalent capacity tower crane. The capacity of the aerial crane is 10 tons, or 20,000 lbs, 9000 kg. The range without aerial refueling is 50 miles or one hour of operation. That means our aerial crane can carry 10 tons, over 50 miles! The crane can operate for up to 24 hours at a time with aerial refueling provides by a ducted fan drone. Conventional cranes are nearly made obsolete in the face of the aerial crane.
The aerial crane is transported to the jobsite by a specialized truck which serves as a landing platform. If a road is not located nearby, the crane is set up and flown over a non-populated route to the jobsite. The crane itself cannot land on terrain, the reason is landing gear adds a significant amount of weight, therefore we decided to eliminate all onboard landing gear. The crane is required to land directly on the truck-based platform. Once landed on the truck-based platform, the rotor blades can be removed, allowing the main module (power module), consisting of the powerplant, gearbox, driveshaft, and flight control system, to be placed flat down and carried on a flatbed truck. Set-up time is less than an hour. To control the crane, a portable screen displays footage taken from a camera placed underneath the drive module aiming down towards the load, displaying the position of the suspending load, enabling the operator to precisely place the load in the required destination. Flight controls are performed with a joke stick device, with directional controls provided by tilting the joystick in the desired direction, yaw control is provided by a separate joystick, and collective or altitude control provided by sliding the yaw or cyclic joystick up and down. Flight controls are designed to remove most of the workload from the operator, freeing the operator to focus on load placement. Unlike conventional rotorcraft which are extremely difficult to control, the aerial crane is as easy to fly as a consumer quadcopter.
The core of Pochari Technologies’ aerial crane is a highly novel ground-based corded electric power supply. Rather than using expensive jet fuel burned in gas turbines onboard the aircraft, we use an ultra-lightweight composite power cable using high-frequency electricity to power onboard electric motors. This allows the operator to take advantage of grid power, which costs far less than the net per kW cost of combusting jet fuel in low-efficiency turboshaft engines.
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. This means new aircraft can be designed and operated commercial without needing to attain costly FAA certification. In 3rd world countries, this is even easier since most heavy-lift helicopters are Russian Mil designers. All over the world, Bell 205s, S-53s, and more recently, ex-Military UH-60s, perform heavy lift work installing air conditioning units on rooftops or erecting cell towers. These rotary cranes are irreplaceable, they have enjoyed no substitute or competitor.
As mentioned above, 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 Peninsula 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, or 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. The electric would be off-the-shelf axial or radial flux motors used in electric vehicles with glycol or oil cooling systems. The power density of these motors is about 5 kW/kg which is comparable to an Arriel 1D turboshaft or PT6.
In order to design a lightweight conductor, the amount of current must be reduced to an absolute minimum, the only way to facilitate this is by increasing voltage, to permit more power to be carried with the least current. But the problem with increasing voltage beyond 5 kV is that electric motors are unable to use the power, so some form of step-down transforming is required. But unfortunately, the weight of a transformer operating at 60 Hz is prohibitive, the transformer would be many times more than the weight of the aircraft operating at standard grid frequency. Silicon laminate steels used in conventional transformer cores feature very low flux density, resulting in a large area of a core required per watt as well as a high number of turns per volt. This resultant transformer has a power density of only a few watts per kilograms, several orders of magnitude too little to be used in aircraft. 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, even as high as 200 kHz, but 100 kHz is found to be optimal from the perspective of power density. 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 a miniscule $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, the flux density of these nanocrystalline cores is unparalleled.
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 with high throughput cooling systems.
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. 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 only 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. A standard conductor at 60 hertz, since the skin depth is deeper than the diameter of the conductor, will use a full solid cylindrical conductor, while we can use a very thin layer wrapped around a lightweight composite hose for structural integrity. Depending on the amount of power needed, the cable can either be cooled through ambient convection or actively using a liquid cooled internal system. For a standard rotorcraft using a 1000 hp for a 10,000 lb lifter, only 730 kW are needed, resulting in minimal Ohmic heating of the conductor. The 150 micron or less metallic conductor, which can be constructed out of aluminum, would be exposed to the air and cooled naturally.
The cabled lifter is a simple yet powerful concept. The operating cost for a 10,000 lb lifter would only be $73 an hour using electricity at 10 cents/kWh. For a heavier lifter, such as a 30,000 lb or ten ton, the operating cost would be $370/hr.
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: classic helicopter technology, with its intrinsic efficiency and high-frequency rectification paired with the skin effect.
In order to develop a low-cost aerial crane solution, a far more affordable powertrain system is called for, we have concluded electric ground based power is this solution.