NOISY BUT efficient and almost making its commercial debut in the 1980’s, the open rotor engine (also known as the propfan) was poised to be the revolution in engine development. Its inception accredited for by the energy crisis in the early ’70s, which brought airlines to their knees as one variable cost they could not control; fuel, forced them into the red. Twenty years later, the price of oil once again breached the $100 mark and now it’s becoming a common occurrence.
The resurgence of turboprops such as the ATR and Dash 8 family effectively killed off the 50 seat regional jet. Carriers found that operating short sectors using CRJ200s or ERJ145s could be twice as costly to run than using a turboprop counterpart. Any speed advantage is minimal, particularly on sectors less than 1.5 hours. It is on sectors of 2 hours and longer when the operating benefits become negligible, or disadvantageous compared to turbofan aircraft.
Whilst the turbofan engine remain an institution in commercial aviation, studies into open rotor viability have re-opened. Major manufacturers have identified the likelihood of a future that implements unducted fan engines, primarily in their medium-haul narrowbody fleet. The engine connects the fuel economy of a turboprop with jet-like speeds but suffers one significant drawback; an unacceptable noise profile.
To counteract this pitfall, designers are working on ways to mask the noise output. A rear-engined layout displays many benefits, such as propeller clearance. It also allows for a “pelican” tail design which encases the engines on both sides with twin vertical stabilisers.
With Pratt and Whitney’s Geared Turbofan success, and General Electric’s equally triumphant Leap-x design, the open rotor dwells on the horizon. Just like the turboprop revival, it stands a fair chance of becoming a reality once more as airlines seek to maintain control of volatile fuel prices in their aim to remain profitable.