Propulsive anti-torque system could lead market fightback
In a revealing market-strategy clue to its next-generation commercial product line, Bell Helicopter executives say the proposed new family of aircraft may benefit from a breakthrough technology called a propulsive anti-torque system (PATS).
Developed as Bell's piece of a Lockheed Martin bid for the now-cancelled Unmanned Combat Armed Rotorcraft (UCAR), PATS replaces conventional tailrotors and tailfans with high-bypass engine power, adding perhaps 40kt (75km/h) dash speed while simultaneously serving anti-torque needs.
Bell's proposed new commercial offering - the Modular Affordable Product Line (MAPL) - has suspended development work on the new tailfan in favour of the PATS technology, says Dan McIlroy, senior vice-president of Bell's XWORX, a rapid prototyping and concept engineering team.
Bell's shift toward the breakthrough PATS technology is driven by recent feedback from a customer advisory panel, which warned Bell to avoid pursuing a "me-too" tailfan system and recommended the UCAR-derived system, says McIlroy.
The move also may reflect a seismic shift in Bell's market strategy over the past two years, which is now focused on recapturing a commercial market lead lost in the late 1990s to European competitors and doubling revenues within five years.
It helps that early development work on PATS has boosted the company's confidence in the technology. Analytical and scale-model testing during the UCAR programme "answered many of the physics and feasibility questions", says McIlroy, adding: "I think one of the challenges we're going to face is answering the question 'what are all the [market] possibilities?'"
PATS works by diverting heated air emitted by the turboshaft engine into one of three ducts - pro-torque, anti-torque or propulsive. A flow diverter manages the escaping air, channelling it into either left-and-right ducts in normal flight, or, in dash speed mode, closes the pro-torque duct and ejects the air out the back for propulsion.
The system is intended to overcome aerodynamic speed barriers for all conventional helicopter designs, which now limit light, single-engined helicopters to about 135-140kt top speed.
But McIlroy is quick to acknowledge several potential roadblocks ahead. "You have to slow the rotor down if you're going to be approaching these kinds of speeds," he says. "There's a whole set of control law and thermal dynamic law issues we have not discovered yet. We have to control this whole suite of systems."
STEPHEN TRIMBLE / FORT WORTH
Source: Flight International
