In the past, these relationships typically used aircraft component weight as the primary predictor of production costs. Weight is a powerful explanatory variable that indirectly accounts for a variety of factors, but weight-driven CERs do have significant disadvantages, particularly when applied to the JSF program. The most important disadvantage of weight-driven models is that they make it difficult to evaluate the effect of improved manufacturing techniques for advanced materials, which is a critical issue for the JSF program. The final JSF design will include a large amount of composite material, and success in meeting cost goals will depend on the ability to produce composite parts at costs well below historical values. Considerable work has been done quantifying the improvement in composite manufacturing efficiency, but applying this work to traditional CERs would distort the impact of these improvements.
Traditional models use a composite material parameter to account for two effects.
First, the materials are lighter than traditional metals, so they increase the cost per pound, even if the cost of the structure stays the same. Second, composite materials are more expensive to fabricate than traditional metallic structure. The magnitude of the second effect changes with improved production technique, while the first effect does not. Consequently, the measured production improvements cannot be applied to cost estimates without untangling these effects. The CERs being developed at IDA eliminate this problem by removing weight from the equation, thereby isolating the fabrication cost of the new materials.