07/31/2011. Remarks by Johan Visschedijk: "Registered in May 1971, this one-off version of the RF-5 Sperber (Sparrowhawk) was built to a German Ministry of Defense "no success, no payment" contract to provide an aircraft that produced less than 50dBA when overflying at full power at only 600 ft (183 m) and 80 mph (129 kmh). By May, 1974 Sportavia-Pützer had reached 45dBA with the S-5, using an 115 hp Lycoming engine with a special cowling and silencer, and a special-designed three-bladed wooden Hoffmann propeller."