THE US AIR FORCE and Lockheed Martin/Boeing have agreed to allow the F-22's empty weight to increase by 610kg, or 3%, to avoid pushing costs up. The growth comprises a 385kg weight-budget increase and a further 225kg allowance for uncertainty.

The F-22's projected empty weight has increased from 13,980kg at the preliminary design-review in 1992 to 14,365kg at the critical design-review, completed in February. Programme officials are confident that the additional 225kg allowance will not be needed.

The growth is a result of design teams requesting additional weight budgets to meet requirements such as reliability, survivability and observability. The USAF says that it is "...trying to hold the line on affordability" and wants to trade weight against cost and performance.

The F-22 does not have a weight requirement. Instead, it has performance specifications. It is missing the performance targets in some areas - none of them major, Lockheed Martin maintains - as a result of the weight growth. The company is negotiating with the USAF to reduce certain performance specifications in light of the agreed weight increase.

The USAF says that a weight increase of 450kg will reduce the F-22's subsonic range by 25km (14nm) and reduce its sustained-turn performance at Mach 0.9 and 30,000ft (9,150m) by 0.08g. The service says that it is considering reducing the subsonic-range and sustained-turn performance specifications.

The F-22's Pratt & Whitney F119 engine is about 8% above its subsonic-cruise specific-fuel-consumption (SFC) specification, although it is meeting or beating its supersonic-cruise SFC target, the USAF says. Officials believe that the subsonic-cruise SFC can be reduced to below 2% above specification.

Fuel-consumption problems are highlighted in a new US General Accounting Office (GAO) report , which questions the urgency of the USAF's need for the F-22. The Congressional watchdog recommends delaying full-scale production by four to five years, until flight-testing is complete.

"The need for the not urgent," the GAO says, recommending that production be limited to between six and eight aircraft a year until after initial operational test and evaluation (IOT&E) is completed in 2001. The report notes, that, 80 F-22s worth $12.4 billion will be on order before IOT&E is completed.

Lockheed Martin points out, that only nine of the 80 F-22s will have been completed by the end of operational testing and that approval to increase production to 36 a year, will come only shortly before the end of IOT&E, with approval for a full 48 aircraft-a-year production not planned until 2003.

Lockheed Martin's Fort Worth division has received the first titanium bulkhead for the F-22 from subcontractor Wyman-Gordon. The wing carry-through bulkhead is one of four for assembly of the centre fuselage of the first F-22, which is to begin in May.

Source: Flight International