Preliminary design

This 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. A link to 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.

 

Downloadable Spreadsheet Worked Spreadsheet Example
 
Aircraft Basic Data Aircraft Basic Data Example
Stall Speed Calculator
Performance Estimate Performance Estimate Example
Appendix A Flight Envelopes and Check Loads Appendix A Flight Envelopes and Check Loads Example
Weight & Balance Calculator (metric) Weight & Balance Calculator (metric) Example
Weight & Balance Calculator (imperial) Weight & Balance Calculator (imperial) Example
 

 

Design Tutorials
 
Derivation of aircraft symmetric flight envelope
Static load testing of composite wing structures