Letov S-28
Designed as a replacement for the Letov S-16 two-seat biplane bomber, the Letov S-28 first flew in 1929. Powered by a Walter Castor 1 engine of 176 kW, it was found to be underpowered. After flight testing, it was modified to accommodate a Walter Jupiter VI of 330 kW. Letov found that the modification for the Jupiter engine were extensive and the new model number S-128 was applied to the new aircraft.
