Compound interest

The preliminary design of a new US Army unmanned reconnaissance and combat helicopter has been unveiled by Bell Helicopter.

The Lockheed Martin-led Unmanned Combat Armed Rotorcraft (UCAR) design project is a multi-million dollar, two-year programme funded by DARPA.

‘The Army wanted a multi-purpose helicopter that could fight effectively as part of its Future Force concept,’ said Dan Rice, UCAR programme director. ‘The Department of Defence believes unmanned aerial vehicles (UAVs) will play an important role in future, especially in the army. UAVs will deal with the dirty, the dangerous and the dull operations where we don’t want to put humans in harm’s way,’ said Rice.

Thirteen air vehicles were considered, from conventional helicopters and tilt-rotor craft through to those using lift fan technology, examining 40 factors such as levels of autonomy, command and control and minimising lifecycle costs.

Eventually a heavy-fuel advanced compound helicopter concept was chosen. Compound helicopters contain an auxiliary propulsion system to provide additional thrust, enabling them to fly faster.

The 5,500lb aircraft is designed to meet the army’s performance requirements for a craft that can fly at 6,000ft in temperatures of 35ºC and still climb at 500ft per minute to 18,600ft.

The UCAR consists of an advanced rotor with cambered blades and uses a propulsive anti-torque system (PATS) comprising a high bypass propulsion system in the tail cone. This provides anti-torque capability comparable to modern helicopter designs with the advantage of forward thrust, providing the benefits of compounding without the additional weight often associated with compound helicopters.

‘We chose a compound helicopter because for a similar cost to other designs it offered 29-35 extra mph when coupled with a propulsion anti-torque system,’ said Rice.

The design replaces the exposed back tail rotor with a fan and thrust direction tail nozzle at the end of the boom.

As the tail rotor is covered, there is a high level of safety as well as reduced noise levels.

The UCAR can cruise at over 200mph. ‘The UAV must move around the battlefield very quickly and be able to complement the role of manned helicopters,’ said Rice. ‘If there is a fleeting target the UCAR must be able to get there before the manned helicopters in order to scout it out. Speed is therefore very important.’

The UCAR is very agile, enabling it to be flown autonomously at low altitude while avoiding obstacles. It also uses fuels available on the battlefield.

The team recently completed airborne and ground demonstrations of potential sensors. If all goes to schedule, the UCAR should be operative by 2012.

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