Thursday, May 31, 2007

Automated UAV Operations from Ships

Tenix-Navantia Landing Helicopter Dock Ship Cross Section DiagramAustralia is planning to purchase two "Landing Helicopter Dock" (LHD) ships for its Amphibious Ships Project. These looks like small aircraft carriers, but are intended to operate helicopters, not fixed wing aircraft. However, they would be able to operate some types of small UAVs (Robot Aircraft). The mix of UAVs and helicopters could be made safe and efficient with automation.

In his April talk in Canberra, Systems Safety Engineering expert,
Dr Mark Nicholson, mentioned the safety analysis needed to allow to fly in the same airspace with piloted aircraft. This problem is particularly acute for military ship borne operations, due to the limited space and high tempo of military operations.

The traditional method of achieving separation of parked, landing and departing aircraft on an aircraft carrier is to use an angled flight deck . Neither of the ships on the Australian short list has an angled flight deck, but a small Virtual Angled Deck (VAD) could be created for UAVs. The VAD would be a painted area on the fore deck of the ship. Helicopters, personnel and equipment would be prohibited from this area during UAV operations.

UAVs would approach the ship from one side to land and take off over the other side on the VAD. Aircraft could "go around" after a missed landing. A malfunction during landing or takeoff would result in the aircraft going over the side of the ship into the sea, clear of equipment and personnel. One of the ship designs, the Navantia LHD has a ski-jump ramp area which could be used for the VAD. The ski jump would assist with shorter takeoff and landing, as well as making use of an area of the deck not suited to other purposes.

Very small UAVs could use a conventional rolling takeoff and landing from the VAD, without the use of catapults or arrestor wires. Larger suitably equipped UAVs could us a Shipboard Rolling Vertical Landing (SRVL) and takeoff. This would allow much larger UAVs with higher payloads, than could otherwise be used. Apart from painting the deck, no other modifications to the ship would be required.

Even with a separate deck area, UAVs could impede other ship operations and be a risk to the crew. To minimize this, the UAVs could be set up for remote deck operations. The UAVs would be serviced below decks in a hangar and then transported by a robot tractor to the deck and launched without any crew present. The tractor would recover landed aircraft from the deck and return them to the hangar. The tractor would also be equipped with firefighting equipment and a bull bar to be able to push crashed aircraft over the side of the ship in an emergency.

This would reduce the risk of injuries to crew and increase the efficiency of operations. Aircraft could be launched and recovered far faster than with a conventional aircraft carrier. Only two crew would be needed on duty to maintain continuous flight operations.

Bell Eagle Eye, Model 918, is a tiltrotor unmanned aerial vehicleThe smaller UAVs already in service and planned for the ADF could be used for shipboard operation. However, VSTOL units would be particularly suitable. Like their larger counterparts, UAV helicopters suffer from speed and payload penalties. One option is to use a tiltrotor design, with the craft able to take off and land vertically, then travel as a conventional aircraft. The Bell Eagle Eye, Model 918 tilt rotor uses this approach. However, like the Bell-Boeing V-22 it requires complex mechanical couplings between the engine and the tilting rotors.

MW54 miniature turboprop engine from Wren Turbines Ltd
An alternative would be to use one engine for each rotor, with electrical coupling. An engine would be mounted at the wing tip directly connected to one rotor. A lightweight electrical motor/generator would be integrated with the rotor, similar to the design of the Serafina Miniature Robot Submarine.

Serafina Mark-II Robot SubmarineThe speed, or lift of the craft would be controlled by throttling the engines. The balance of the craft would be controlled electrically, by generating electrical power at one wing tip and transferring it to the electric motor at others. The aircraft would be able to fly and land conventionally with two engines stopped.

As an example four 6 kw MW54 miniature turboprop engines from Wren Turbines Ltd, plus four .5 kw electric motor/generators would weigh approximately 12 kg and produce 26 kw. The UAV could have a launch weight of 80 kilograms and have a speed of 300 kph and a length of 3m. Endurance of 8 hours and range of 2,000 kilometers.

On a runway the aircraft would take off conventionally, with the rotors in the horizontal position, allowing an increased payload. Neither the Eagle Eye nor Osprey can take off or land vertically, due to the diameter of the rotors. Vertical takeoff and landing would use the rotors in the vertical position, with a reduced payload.

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