GENERAL ELECTRIC'S newly unveiled CF34-8C turbofan for Canadair's proposed CRJ-X regional airliner may form the basis of an entirely new family of engines in the 60-80kN (13,000-18,000lb)-thrust class, says the company.
The GE general manager for small commercial turbofans, Lloyd Thompson, has revealed the first details of the CF34-8C engine. He says: "The new compressor will give us a baseline to develop engines from 13,000lb to 18,000lb thrust by adding larger fans and booster stages in the low-pressure [LP] compressor."
Thompson believes that the new generation of CF34s will be strong competitors for new regional airliners, large business aircraft and even military programmes.
The key changes enabling the CF34 to have this dramatic growth potential are the use of a new high-pressure (HP) compressor based on the military F414 turbofan, a new LP turbine, a multi-hole combustor based on that of the GE90 and F414, and a larger-diameter fan with wide-chord blades.
Referring to GE's design for the CRJ-X, Thompson says: "Our goal was to try and fit an engine with 50% more thrust into the same nacelle and thrust-reverser system using the same mounts."
Although fan diameter was increased by 40mm to 1,158mm, the exterior dimensions of the nacelle remain very similar to earlier engines.
This goal has been achieved by using the solid-metal containment-ring system developed for the GE90 in place of the deeper Kevlar containment ring used on the current CF34.
The HP compressor from the F414 (in development for the McDonnell Douglas F-18E/F) is used to boost pressure ratio from 14:1 in the CF34-3A to 19:1 and airflow from 15.4kg/s to 22.7kg/s. GE is confident of gaining up to an 8% improvement in specific fuel consumption from the new engine by reading over data from more than 3,000h of F414 core tests.
There are only 11 stages in the new compressor, compared with 14 for the current unit. "We took the seven-stage high-pressure compressor from the F414 and scaled it to 90% and then added four stages so we could match the current turbine."
In addition, the first three stages will be blisks (blade/discs) and the fourth and fifth stages "...may be tandem blisks", according to Thompson.
The two-stage HP turbine remains unaltered, with the exception of a change from directionally solidified alloy to single crystal to cope with the higher operating temperatures.
The LP turbine remains a four-stage unit, but is otherwise "all new" to match the higher pressure ratio fan. "We're actually looking at inertia welding of the LPT disc rather than bolting it together," he adds.
The core will have its first run around the end of 1995 with a first full engine run expected in 1996.
Source: Flight International
