Original Date: 05/08/1995
Revision Date: 01/18/2007
Best Practice : Finite Element Model Weight Estimation System
The McDonnell Douglas Aerospace (MDA)-St. Louis Finite Element Model Weight Estimation System (FEMWTS) is a set of management software tools used to track, estimate, and control airframe weight early in the design process when changes are easy and inexpensive to implement (Figure 2-9). Design parameters include structural arrangement, material properties, air loads, dynamic requirements, panel optimization, and thermodynamics.
The FEMWTS provides management with the information required to allocate resources to achieve inexpensive, lightweight airframes. This estimation process consists of three steps.
Transforming the strength model into a mass model using reduction algorithms. Estimating detail part weight using detail part algorithms and mass factors.
Estimating assembly weight through the addition of assembly mass factors for joints, splices, and fasteners.
Estimated assembly weight is computed by multiplying an assembly mass factor by the sum of detail part finite element model weight estimates. As the estimation and design processes continue to refine weight estimates, the assembly mass factor (a correction factor) approaches a value of 1 (Figure 2-10).
The FEMWTS has enabled MDA-St. Louis to generate estimates previously requiring up to several weeks, in minutes. The capability has been used on several programs with a high degree of estimation accuracy such as the F/A-18 E/F fuselage, wing, and tail sections (+0.7% error in estimate from actual weight); the Advanced Short Takeoff Vertical Landing aircraft composite fin (3.8% error), and YF-23 wing carry-thru bulkheads (-0.6% error). It has also allowed MDA-St. Louis designers to make more effective design trade-off decisions regarding weight and structural strength.
Figure 2-9. Finite Element Model Weight Estimation
Figure 2-10. Assembly Mass Factor Rapid Estimation Capability
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