Guy Norris/LAS VEGAS

ALLIEDSIGNAL PLANS to certificate a new LT101 turboshaft power-turbine rotor-retention design this year, as part of an aggressive upgrade plan aimed at continuing the reliability-improvement strategy begun by Textron Lycoming before its take-over.

The redesign tackles a long-standing problem of shifting blades in the power turbine (PT) and the lengthy maintenance time needed for their continual inspection. The difficulty was traced to thermal differences between the blade and the disc in the insertable-bladed PT (IBPT) rotor. "This caused the blade to move slowly and led to ratcheting at the rivet," according to the company.

The redesign reduces critical angles in the component which exacerbated the thermal mismatch. "It's done more than 2,000 cycles in the test cell and things are looking very good," says AlliedSignal.

The company is also preparing a solution to a fuel-pump problem, which led to fuel starvation and some emergency landings in LT101-powered helicopters. The US Federal Aviation Administration, which issued an airworthiness directive (AD) to remove and inspect the pump's internal spline-drive on single-engined helicopters, is expected shortly to issue a similar AD for twins.

Other significant upgrades to the turboshaft include:

- a new fuel-control bearing, developed by Bendix to replace a unit which suffered distress if contaminants got into the lubricant;

- installation of new rear-bearing support-housings, to improve hot-section life;

- development of a new low-carbon combustor-liner, designed to reduce the faster- than-expected erosion of single-crystal turbine blades.

The sheer number of modifications made to the turboshaft over recent years has prompted AlliedSignal to continue Lycoming's plan to define new engine-configuration standards and reduce customer confusion.

Plus I engines have nine major improvements, while Plus II versions have 11. Eurocopter and Kawasaki Helicopter have requested that all their engines be upgraded to Plus II standard.

Source: Flight International