Preliminary Design is the stage where the design is sized and developed in outline, leading to a three view drawing, performance and weight predictions. To help with this, LAA has developed a number of spreadsheets.
Spreadsheet 1 is used to develop the basic geometry of the proposed aircraft, size the wing, fuselage and tail surfaces and work out some of the key parameters used later.
Spreadsheet 2 is used to estimate the performance of the aircraft based on the geometry, initial weight estimates, engine power and guestimates of the drag coefficient and prop efficiency, allowing you to see how the performance is affected by changing each parameter in turn.
Spreadsheet 3 is used to work out the critical structural speeds, develop the flight envelope and predict the aerodynamic loads on the main surfaces which can be used to size the structure, and as the basis for a load test program. The weight and balance spreadsheet elsewhere on our website allows the designer to quickly evaluate the implications on weight and cg of different positions for the crew, fuel tanks and baggage bay, and work out what empty aircraft weight and cg he must aim for.
Thanks to the simplicity of these programs it takes only minutes to study the implications of changing the aircraft’s specification, for example the effect of changing the wing aspect-ratio, the trade-off between extra weight and cleaning up the airframe drag, extra power etc.