| Manufacturer | Letov |
| Model | S-21 |
| Modification | S-21 |
| Country | Czechoslovakia |
| Years | 1925 |
| Type | Other |
| Main rotor diameter | - |
| Tail rotor diameter | - |
| Wingspan | 10.10 m |
| Length | 7.53 m |
| Height | - |
| Wing area | 19.60 m2 |
| Zero fuel weight | - |
| Empty weight | 641 kg |
| Maximum takeoff weight | - |
| Normal takeoff weight | 863 kg |
| Flight duration | - |
| Engine | 1 Hispano Suiza 8Aa |
| Power | 1 x 180 HP |
| Thrust | - |
| Maximum speed | 210 km/h |
| Cruising speed | 180 km/h |
| Rate of climb | - |
| Practical range | - |
| Service ceiling | 4000 m |
| Hovering ceiling | - |
| Crew | 1 |
