Sensitivity
Partial changes show which variables have the largest effect on the objective.
AE481 · Lesson 8
Optimization and Trade Studies
Use sensitivities, structured searches, and guided iterations to improve an aircraft design.
Sensitivities reveal the trade space
A trade study changes one or more design variables, measures the response, and exposes where the design is most sensitive.
Optimization
Search for a better feasible design while respecting constraints and model limits.
Trade study
Compare alternatives directly instead of optimizing a single variable in isolation.
Optimization strategies
Different strategies spend computation and engineering judgment in different ways.
Shotgun
Try many combinations, plot the results, and select the best feasible candidate.
- Simple and transparent
- Can be computationally expensive
Genetic algorithm
Keep the strongest performers, then introduce mutations and cross-breeding over generations.
- Explores broad spaces
- May settle in a local minimum
Marching / guided
Use sensitivities and diagnostics to choose the next variable change toward a viable objective.
- Usually converges faster
- Requires engineering judgment
Optimization loop
Choose a design → evaluate constraints and objective → diagnose sensitivities → change a variable → repeat until the design is both feasible and good.Presenting results
A table preserves the exact trade-study values; a grouped chart makes the sensitivity pattern immediately visible.
Gross-weight trade-study data
| Sweep | Aspect ratio | WTO (lb) | TSL (lbf) |
|---|---|---|---|
| 40° | 2.11 | 66,000 | 86,000 |
| 3.04 | 42,400 | 49,000 | |
| 4.75 | 41,600 | 45,000 | |
| 5.86 | 42,400 | 46,000 | |
| 50° | 2.11 | 58,000 | 66,700 |
| 3.04 | 43,400 | 47,800 | |
| 4.75 | 50,000 | 52,300 | |
| 5.86 | 54,500 | 57,300 | |
| 60° | 2.11 | 96,000 | 107,500 |
| 3.04 | 70,300 | 76,000 | |
| 4.75 | 83,000 | 85,600 | |
| 5.86 | 124,000 | 124,000 |
Genetic Algorithm – 5GAT
A real design program evolves concepts through modeling, trade studies, wind-tunnel testing, and detailed structural analysis—carrying the strongest feasible configuration forward at every stage.
1 · Phase 1 conceptsModeling and analysis establish the first population.
2 · S&C studyRetain strong designs; introduce crossbreeds and mutations.
3 · Wing sweepCompare sweep alternatives and refine the survivors.
4 · Wing/tail variationExplore coupled planform and empennage changes.
5 · Large-scale testValidate the leading concepts in the wind tunnel.
6 · Final survivorAdvance the selected aircraft to structural analysis.
