Aircraft Industry Consultant Reduces Week Long Job to One Hour Using Computerized Engineering Handbook

Leonard Marchinski, President of Leonard Associates, Mt. Carmel, Pennsylvania is a consulting structures engineer whose specialty is performing design and analysis for large aircraft manufacturers. Marchinski has recently achieved dramatic time-savings in the structural analysis of a variety of aircraft components by switching from manual calculations and finite element analysis to the use of The Desktop Engineer, a computerized engineering handbook marketed by the Desktop Engineering, Woodcliff Lake, New Jersey. The Desktop Engineer, according to Marchinski, is especially valuable for problems with multiple loading and boundary conditions because it allows a wide Variety of alternate conditions to be quickly analyzed thus allowing the designer to easily determine the worst case scenario.

Marchinski cited the example of a structural optimization study on a composite panel used as an access door. The manufacturer wanted to select from a variety of materials the one that would provide the lowest weight and cost while offering the capability of withstanding all flight loads. One difficulty involved in the analysis is that the edge fixity conditions of the panel are very complex -- somewhere between simple and clamped support. Another complicating factor was that the aerodynamic loads were not known to a high level of accuracy. This type of problem, Marchinski said, cannot be efficiently handled by either finite element analysis or manual calculation. The uncertainties involved made it necessary to analyze a wide variety of conditions to determine the worst case scenario. Manual calculation would, Marchinski said, require about half a day to analyze each set of conditions thus meaning that a comprehensive analysis would require at least a week. And, finite element analysis would require up to a week just to build the initial model.

The Desktop Engineer, on the other hand, allows the analyst to evaluate alternate load cases and boundary conditions in minutes, Marchinski said. "This makes the program ideal for this type of analysis." Marchinski selected the "plates and shells" module of The Desktop Engineer which requires only a few simple input parameters: the length, width and thickness of the panel, material properties, boundary conditions and loads. Marchinski started by analyzing a honeycomb panel. He performed about a dozen different cases involving simple and clamped support and a range of loads and based on the results made a judgment of the most applicable case. This entire process took less than an hour. The results of the optimization showed that the honeycomb material provided the lowest weight and cost of the alternatives that provided adequate strength for the application.

The Desktop Engineer is basically a computerized handbook of solutions to structural/mechanical engineering equations. It uses these equations to calculate deflection forces and stresses in loaded structures. It is divided into categories such as beams, plates, columns, frames, etc. In each category, the program prompts the user to provide information that is needed to solve the defined problem. The information requested is related to the geometry, material, support and loading conditions of the structure. This is the same information that would be needed should the user do the problem by hand.

Once the problem is defined, the program will quickly perform the necessary calculations and provide the associated numerical and graphical output. In most cases it will do the equation substitutions, integration, boundary condition analysis, exactly like one would do if the problem was done by hand. In some of the more complicated analyses, the program uses finite elements to get a solution (even though the input and output format remains similar to the other modules and the user is not required to know finite element techniques). Once a problem is accurately set up and modeled, it can be quickly changed and rerun to allow the designer to look at various design options or modifications.

Several utility modules are included to assist the designer with complex problems. A superposition module allows the designer to fool< at the effects of several concurrent loads on the same structure. A module is included to produce Mohr's circle analysis for multi-axial states of stress and strain. Modules are also included to assist the user with calculating section properties. The program also has a convenient material property database and several modules that look at complex geometries and dynamic conditions.

In conclusion, Marchinski said The Desktop Engineer turned out to be a considerable time-saver on this project. By quickly solving for a variety of load cases, boundary conditions and materials, the program solved in a hour a problem that would have taken at least a week with either manual calculations or a conventional finite element analysis program. Marchinski also said that The Desktop Engineer provides another-advantage which is particularly important to anyone like himself whose use of the program is sporadic rather than regular. He said the program is virtually self-explanatory to use so that he can pick it up after a long absence without even looking at the manual.