Retrofit programme is delayed for tests to show if vibration affects Hawkeye's turboprop engine or avionics

The US Navy's programme to retrofit new eight-blade propellers to its Northrop Grumman E-2C Hawkeye airborne early warning and C-2A Greyhound transport aircraft has run into vibration problems and is facing delays.

The USN, meanwhile, is drawing up plans to extend procurement of the latest Hawkeye 2000 variant in order to fill a two-year production gap until work on the Advanced Hawkeye can start.

According to the navy, it will not begin fielding the new Hamilton Sundstrand NP2000 propeller before late next year - a two-year slip from the original schedule.

The delay is because of vibration in certain flight regimes. This has been made worse by a lack of test data on the E-2/C-2's current 54460 four-blade propeller to compare against and determine what is acceptable performance.

"This is not a show stopper, but rather a development issue. The 54460 was never baselined or tested to the extent that this new blade is being tested," says Capt Lee Lilly, USN E-2C/C-2programme manager.

The concern is over what impact, if any, the eight-blade propeller's vibration could have on the E-2C's Rolls-Royce T56-427 turboprop, its fuel lines or avionics.

The problem has been traced to the stiffness of the actuators and the seals on the composite propeller, which is based on the Ratier Figeac six-blade unit from the ATR 42/72. The proposed solution is to fit stiffer actuators and new seals.

Plans call for the NP2000 to be fitted to all new Hawkeye 2000s, any remaining Group 2 aircraft and all 36 C-2As.

Next year's budget contains funding for the final six of a multi-year procurement of 21 Hawkeye 2000s, which will be completed in 2006. Development work has just begun on the E-2C Radar Modernisation Programme (RMP) and low-rate production will not start before 2006 with the first aircraft being delivered in 2009.

As a result, the USN plans to order two more Hawkeye 2000s in 2004 and three in 2005 rather than upgrade older E-2Cs. Without this and some RMP development aircraft, Northrop Grumman would have started to shut down the production line next year. "Retrofitting Group 2 aircraft was not going to keep Northrop Grumman viable or keep its 200 suppliers busy," says Lilly.

Source: Flight International