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Aviation History
2001
2001 - 0462.PDF
ZLlrJUPrZH f^Li JixJULULV/ Designing a helicopter with equal appeal for civil and military users poses a significant challenge. Sikorsky's answer is the S-92 Setting standards PAUL LEWIS/STRATFORD, CONNECTICUT CUTAWAY/GUISEPPE PICARELLA W HEN SIKORSKY set out in the early 1990s to design the S-92, it intended to develop a derivative of the highly successful S-70/H-60 military machine that would appeal to the commercial market and rival the Eurocopter Super Puma and provide a replacement for the S-61. The helicopter that eventually emerged from Sikorsky is essentially an all-new design incorporating many impor tant advances in safety, reliability and maintain ability, much of which will find its way on to future enhanced S-70s. The brief for Sikorsky's functional design team was a twin-turbine helicopter with a cabin large enough to seat 19 passengers in relative comfort and fly 740km (400nm). "Nineteen passengers provides a break in regulations and 400nm matches a lot of realistic missions pat terned on that of the North Sea," explains Bob Blauch, S-92 system requirements manager. In this respect Sikorsky has more than met its initial goals. During recent demonstrations to the Portuguese military, the S-92 was flown at an alternate take-off weight of 14,074kg (31,0001b), well in excess of its 12,835kg maxi mum take-off weight (MTOW). Furthermore, the helicopter has shown that with additional auxiliary fuel tanks, a search-and-rescue (SAR) version can reach as far as 1,480km. The adoption of Federal Aviation Require ment and Joint Aviation Requirement Pt 2 9.5 71 stipulated that the helicopter be designed to new flaw tolerant criteria, effectively ruling out a S-70 derivative approach. Sikorsky claims that the S-92 is the first to be designed to the amended requirements, ensuring there is sufficient structural strength and system redun dancy to avoid failure from fatigue or damage. ACCEPTABLE DAMAGE This includes "barely visible damage" up to 5/1000th of an inch without compromising any component's lifespan and then accepting larger damage up to 1mm deep without any crack propagation between and beyond the S-92's scheduled 1,2 50h inspection cycle. This dictat ed a new rotorhead incorporating dual-arm Option Clamshell w/airstair door Sliding upper W/airstair door SAR door Interior type Floor rating (kg/m2) Baggage shelf system Cabin storage compartment High comfort crew seats Passenger seat (belts, arm rest) Cabin windows* Floats/rafts Hoist S=standard, A=available. *doublepane, S VIP s VIP 366 S S VIP DN S/A Airline S Hard 366 S S S 3w/ DN S A Offshore S Hard 366 S A S 4w/o DJ S A =single pane, N=non jettisonable, J=jettisonable Utility S Soft 976 A troop SN A A Search and rescue S Soft 976 A SAR SN S A titanium yokes for load path redundancy and 4,000-5,OOOh minimal wear elastomeric bearings. "We started with a S-70 spindle-based rotor head, but in order to meet the new requirements we would have had to have grown it by such huge amounts that we switched to a new con cept to optimise the design," says James Williams, S-92 business development. The new rotorhead, along with other new dynamic com ponents, is now a candidate for growth versions of the Black Hawk such as the US Army's UH-60X. The S-92's composite main rotor blade was previously tested on a UH-60. The main differ ence is a 400mm (16in) extended radius, wider chord, new cuff rotorhead mounting and a swept, tapered anhedral blade tip. The latter reduces blade vortex interaction and in the process lowers drag and noise. Sikorsky says that it also improves hover efficiency equivalent to a 360-400kg load, or three passengers. Other blade wake remedial measures include increasing the spacing between the main and tail rotor to 350mm - four times that of the S-70. New airfoil technology, first tested on the S-76, has also been incorporated into the S-92 to optimise the shaping of the bearingless com posite flexbeam tail rotor blade to lower noise and RPM to 1.190RPM at 100% power and l,250RPMatl05%. The S-92's main transmission features a new 3,130kW (4,170hp) dual planetary gearbox, designed for 6,000h of flight between overhaul. Interconnecting shafts drive the aft intermedi ate and tail rotor gearboxes. Sikorsky uses tita nium diaphragm-type couplings in place of a flexible, stacked disc coupling to simplify main tenance, eliminate shimming and eliminate old- school inspection requirements. 46 FLIGHT INTERNATIONAL 6 - 12 February 2001
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