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Rolls-Royce studies two new stall fixes for V-22 engines

Rolls-Royce is exploring two new avenues for reducing the susceptibility of Bell Boeing V-22 engines to in-flight stall and surge events.

The US Naval Air Systems Command plans to award the maker of the AE1107C turboshaft engines a contract to complete two studies that would validate the company’s ideas for making the propulsion system safer to operate.

One study will prove whether rescheduling movement schedules in the full authority digital engine control (FADEC) computer for compressor guide vanes will improve surge margins. R-R’s internal testing suggests the software tweak could improve surge margin by 0.8% at sea level and up to 3% at altitude.

Another study is focused on the temperature sensor located at the inlet to the compressor. R-R’s engineers have determined the T2 sensor sends inaccurate measurements to the FADEC, contributing 2.5 percentage points of a 4% steady-state power shortfall at the compressor’s corrected rotational speed limit. By tweaking the software to provide an accurate temperature measurement at the compressor inlet, R-R believes the engine safety will improve.

The AE1107C’s vulnerability to stalls and surges has been a focus of the programme for more than a decade. NAVAIR released a statement of work for the two study contracts saying the AE1107C has experienced at least 68 stalls and surge events from 2003 to October 2016.

But only about 10% of those reported events caused in-flight disruptions, says Tom Hartmann, R-R North America’s senior vice-president of customer business. Most of the events were detected quickly by the engine monitoring system, allowing the computer to avoid a compressor stall by briefly slowing the fuel flow into the combustor, he adds.

Moreover, most of the in-flight disruptions occurred on early configurations of the engine, he adds. The arrival of the Block 3 version of the engine five years ago has led to a reduction in reports of in-flight disruptions. Bell Boeing also is developing an inlet barrier system, which is aimed at preventing surges caused by ingesting dust and sand. The AE1107Cs are already equipped with air particle separators, but that technology based on centrifugal force is less effective than installing a filter on the inlet, Hartmann says.

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