Graham Warwick/WASHINGTON DC
Pratt &Whitney resumed testing of the F119 fighter engine on 19 March to clear a near term solution to a compressor seal failure which led to the halt of all development testing. P&W hopes that the cure will allow flight testing of the F119 powered Lockheed Martin/Boeing F-22 to restart as planned in April.
F119 development testing was halted on 6 March when the knife-edge seal on the first compressor stage failed during altitude testing of the engine at the US Air Force's Arnold Engineering Development Center in Tennessee. Examination of the failed seal revealed high-cycle fatigue, says F119/F-22 programme manager Tom Farmer.
The problem has not occurred before in over 6,000h of F119 testing, but the affected engine has aerodynamic improvements which increase performance, he says. As a near term solution, while the root cause is being determined, clearance between the seal and its honeycomb rubstrip has been opened up. Testing at Arnold will measure the effect of this repair, Farmer says.
P&W has until the end of March to determine whether flight test engines, which are of an earlier configuration, are affected and require modification, he says. If they do, the new tests will determine whether opening up the seal clearance will be sufficient to allow flight testing to restart.
Boeing, meanwhile, is tackling manufacturing problems which will delay F-22 deliveries beginning with the third development aircraft. Titanium castings which form the wing to fuselage attachments have been contaminated by a ceramic protective coating used on the moulds, requiring exhaustive X-ray inspection, machining out the ceramic chips and weld repairing.
Delivery of the wings for the third flight test F-22 will be five months late. Boeing expects to be back on schedule by the seventh of the nine development aircraft. A problem with the titanium tailbooms has been overcome by revising design and assembly and will not delay the programme, Boeing says.
Source: Flight International
