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US Army ponders CH-47F engine alternative after T55 delays

The US Army is thinking about alternative engine manufacturers for the CH-47F Chinook helicopter amid recurring delivery delays of the T55 turboshaft from Honeywell.

The service disclosed its concerns at the US Army Association exposition on 16 October.

“Our only concern with the Chinook engine right now is it is an old design and the OEM that is manufacturing it is, quite frankly, struggling to keep up with demand,” says Major General Thomas Todd, programme executive officer for US Army aviation. “The only thing that we would be interested is if the supply base cannot keep up with the demand. Who do we turn to? Where do we turn? We're not there yet.”

The US Army says Honeywell is currently on schedule with its deliveries of its T55, but the service is concerned because the manufacturer has fallen behind previously. The service did not elaborate on the nature of the problem, instead it referred questions to Honeywell.

Honeywell did not address the US Army’s delivery concerns, but issued a statement.

"Our dedication in continually improving the T55 is a testament to more than five successful decades working alongside the US Army to protect and serve its soldiers,” says Dave Marinick, vice-president of engines at Honeywell. “We are on contract to the US Army on T55, and we expect to stay there.”

Boeing declines to comment on the T55 and the US Army’s comments, but says it has delivered the CH-47F an average of 50 days ahead of schedule since 2012.

Introduced in 1955 by its original manufacturer Lycoming, more than 6,000 T55 engines have been produced, logging about 12 million hours of operation on the CH-47 Chinook and MH-47 helicopters, according to Honeywell. The T55 produces 4,800shp (3,580kW).

Discussion of replacing the CH-47F Block I’s engine comes as Boeing, the US Army and GE Aviation are testing the more powerful GE T408 turboshaft engine on a CH-47, with the intention of possibly folding the turboshaft into the aircraft’s already underway Block II upgrade prototype programme.

The GE408 produces 7,500shp. The Block II is an upgraded version of the cargo helicopter, which is currently in the prototyping and testing phase. It would add new rotor blades, a redesigned fuel tank and improved drivetrain.

A more powerful engine was originally considered as part of the Block II upgrade to the Chinook but wasn’t pursued because of lack of US Army funds. Nonetheless, GE Aviation invested its own money in the effort in order to show the feasibility of the idea and reduce technical risk should the service decide to pursue the re-engining idea.

The GE T408 is also the powerplant for the US Navy’s forthcoming heavy lift CH-53K King Stallion helicopter.

Ground testing of the GE T408-equipped Chinook is scheduled to begin this October and run for six weeks with 25h of flight tests planned soon after, says GE Aviation.

Not to be outdone, Honeywell announced its own proposal for a Chinook engine upgrade. The company says it has created an improved version of the T55 that has 20% more power at sea level, nearly 10% more power at high and hot altitudes, and 9% less fuel burn. The turboshaft would be offered as a new engine or a kit to upgrade engines during overhauls, says Honeywell.

Despite the GE T408 testing effort and Honeywell’s T55 upgrade pitch, there is no programme of record for re-engining any of the US Army’s Chinook fleet.

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