Guy Norris/LOSANGELES Andrew Doyle/LONDON
ROLLS-ROYCE IS preparing to test a production RB.211-524 turbofan fitted with the high-pressure system of the Trent 700, in an experiment aimed at extending engine-component life and reducing fuel consumption.
The hybrid is being evaluated as a potential upgrade for the -524G/H family which powers some Boeing 747-400s and 767-300s, but will be offered only "-if it offers a demonstrable benefit", according to RB.211 project executive Neil Ansell.
The tests come as British Airways begins to evaluate engine options for its imminent order for at least ten Boeing 747-400s (Flight International, 5-11 June, P4). The airline is not committed to the RB.211 for these aircraft as its existing agreement with R-R, which powers all of its 747-400s, expires at the start of 1998, before the new batch of aircraft are due to be delivered to British Airways.
The UK flag carrier is telling engine manufacturers that it wants higher-performance engines for future 747-400 deliveries, although it is thought unlikely to switch to an alternative supplier.
R-R's -524 upgrade would effectively supersede modifications encapsulated in an earlier "Package 3" improvement plan, which was subsequently dropped.
The hybrid demonstrator will integrate the 0-4 module of the Trent 700 with an otherwise standard -524 production engine. The 0-4 module forms the high-pressure (HP) core of the engine and consists of the HP compressor, combustor and turbine. "The Trent 700 is about the same size, so the 0-4 module fits neatly," says Ansell. Potential benefits include extended life for the turbine and other HP-core components, greater turbine exhaust-temperature margin and better specific fuel consumption.
The more advanced combustor in an upgraded -524 would also alleviate the need for inspections and modifications imposed after a late-1994 incident when a core fairing just aft of the chamber burned through on a 747-400 engine shortly after take-off.
Meanwhile, the RB.211-524Hs which power BA's 767s are still subject to a 1,500-cycle turbine-life limit following a HP turbine failure on 31 January, 1993. This limit, is expected to be lifted, as single-crystal turbine blades are gradually retrofitted in place of the original directionally solidified nickel alloy blades. The airline is having to flow higher-cycle -524s from 767s on to 747-400s, to maintain an inventory of younger engines for 767 extended-range twin-engine operations.
BA is also being briefed on the engines under development for proposed growth derivatives of the 747, the -500X and 600X. These include a Trent derivative, almost certain to be designated the Trent 900, and a new design from a GE/Pratt & Whitney joint venture.
Source: Flight International
