Allison Engine hopes to certificate an ambitious upgrade for its Model 250-C20R Series II turboshaft engine in the third quarter of 1998, says the Rolls-Royce owned company.

Allison says that the "Super R" project will provide up to a 20% increase in power and is aimed at improving performance for existing Allison users as well as providing a re-engineing option for other helicopter types. Super R chief project engineer Sally Randall says: "We think a third quarter certification is possible, but we still have pretty good wickets to get through. When you change four turbine wheels it is not a routine certification."

The main improvements include an increased centrifugal diffuser throat area, new first and second stage gas generator nozzles and discs, and new third and fourth stage power turbine nozzles and discs. The package also includes aerodynamic changes to the compressor, which has been adapted to the 9% flow increase which results from the enlarged diffuser. Many of the component changes were originally developed for the -C20R/9 engine, which, unlike the Super R package, also includes a full authority digital engine control unit.

Allison says that it is "-working with several manufacturers on certification programmes which will lead to the installation of Super R engines on new and existing airframes", as well as "supporting aftermarket efforts to develop and certify several supplemental type certificates [STCs]". Potential applications include the Agusta A109 following "indications of interest" in the upgraded C20R, which would be known as the C20R/S with the Super R package. The upgraded C-20R2/S is aimed at the Boeing MD520N, which already uses the standard engines, while the -20R4/S would be offered under an STC for the Bell 206 JetRanger series. The engine is also being discussed with Eurocopter for the BO105, as a way of helping it meet the upcoming European Joint Aviation Requirement Ops 3, and the AS355 Ecureuil 2 as a potential re-engineing option. The AS355 is now powered by twin Turboméca TM319 Arrius 1A turboshafts.

The upgrade provides up to a 20% power increase in hot day/ high altitude conditions, as well as reducing fuel consumption (by between 8% and 12%, depending on power level). Allison also plans to increase the Super R rating to 380kW (510hp).

Source: Flight International