Letov Š-4

The Letov Š‑4 was a Czechoslovakian single‑engine biplane designed and built by Letov Kbely in the early 1920s. Developed as a successor to the earlier Š‑3 trainer, the Š‑4 first flew in 1924 and entered service with the Czechoslovak Air Force the following year. Its wooden fuselage was covered with fabric, while the wings featured a conventional two‑bay biplane arrangement with slight sweep and ailerons on both upper and lower planes. Powered by a 120‑horsepower Walter NZ‑85 radial engine, the aircraft could reach a maximum speed of about 165 km/h and possessed a service ceiling of 5 500 m, making it suitable for basic pilot instruction and liaison duties. The Š‑4’s simple construction, low operating cost, and forgiving handling earned it a reputation as an excellent training platform, and it remained in use until the early 1930s when more advanced monoplanes replaced it. Although only a few dozen were built, the Letov Š‑4 demonstrated Letov Kbely’s growing competence in aircraft design and contributed to the modernization of Czechoslovakia’s post‑World‑War I air arm, laying groundwork for later, more sophisticated types. Its operational reliability also influenced neighboring countries, which showed interest in acquiring similar trainers.