PAUL LEWIS / WASHINGTON DC
Manufacturer identifies series of structural changes to make required savings
Lockheed Martin is confident of being able to bring the weight of the F-35 Joint Strike Fighter (JSF) in on target after a preliminary bottom-up review of the airframe design revealed a higher-than-expected projected weight. In response, a specially created "Blue Ribbon Action Team" has identified a number of solutions, including making structural efficiency improvements.
An initial weight estimate, calculated on the basis of volume and density, revealed a 30% difference in the F-35's airframe weight com- pared with the projected estimate using parametric data from previous aircraft. The latest weight estimate factors in external-load windtunnel testing of the design and the impact this has on internal load distribution and frame sizing.
While similar reviews of the vehicle systems, mission systems and propulsion came in under the parametric weight predictions, the airframe accounts for about one-third of total weight on the short take-off vertical landing (STOVL) version.
The expectation had been for weight to be 20-25% above the parametric figure, regarded as acceptable based on past programme experience and the relatively early stage in F-35 development, with internal layout still to be finalised.
"The fact is we came in a little high and in February we convened a team to go back, take a look across everything and see if there are any issues that brought the weight up," says Tom Burbage, Lockheed Martin JSF programme manager. "We found that some of our techniques to build the aircraft introduced more weight. We are going back and making it right," adds Burbage.
The challenge is to improve airframe efficiency while trying to fit into the fighter the weapons bays, sensors, fuel tanks and, in the case of the STOVL version, a shaft-driven lift fan, as well as cater for low observability, lean manufacturing and ease of maintenance - all of which can drive up weight and make for inefficiencies (Flight International, 11-17 March).
Solutions are needed before the preliminary design review can be completed. Weight control is critical to the STOVL version meeting key performance parameters (KPP), particularly short take-offs and "bring back" payload when landing vertically. Gen Jack Hudson, JSF joint programme office director said in January that while he "expects positive margins to the KPPs", there were a "modest number of points where we do not meet or have a low confidence to meet thresholds".
Source: Flight International
