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Pick up to four aircraft. The best value in each row is highlighted.
Helio Aircraft Company HST-550 Stallion
Military
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Northrop Corporation X-21
Military
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|---|---|---|
| Quick facts | ||
| Manufacturer | Helio Aircraft Company | Northrop Corporation |
| Type | Other military aircraft | Other military aircraft |
| Origin | — | — |
| First flight | 1964 | 1963 |
| Status | — | Retired |
| Units built | — | 2 |
| Unit cost | — | — |
| Dimensions | ||
| Length | — | 22.94 m |
| Wingspan | — | 28.51 m |
| Height | — | 7.80 m |
At a glance
Figures are compiled from public sources and may be approximate; they can vary by variant and configuration.