Discussion
Design point outcomes for four aspect ratios at the same requirements.
| Aspect ratio | Cruise \( T/W \) | Wing weight index | Design \( W/S \) |
|---|---|---|---|
| 7 | 0.235 | 1.00 | 5.4 |
| 9 | 0.221 | 1.09 | 5.4 |
| 11 | 0.213 | 1.21 | 5.4 |
| 13 | 0.209 | 1.36 | 5.4 |
What does the table suggest about choosing aspect ratio?
Answer: D
Correct answer: The thrust saving flattens while weight keeps growing
Compare the two columns. Going from aspect ratio 7 to 9 saves \( 0.014 \) in cruise \( T/W \) for a 9 per cent wing weight penalty; from 11 to 13 it saves only \( 0.004 \) for a further 15 per cent of weight. The benefit is diminishing while the cost accelerates.
This is why aspect ratio is not simply maximised, and why constraint analysis alone cannot choose it: the diagram shows the thrust saving but not the weight penalty, so the choice requires a weight and mission analysis to find where the two balance.
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