The MiG-15, which could not safely exceed Mach 0.92, served as the basis for the MiG-17, which was designed to be controllable at higher Mach numbers.[74] Its wing sweep, 45° near the fuselage ( the same as the F-100 Super Sabre), changed to 42° for the outboard part of the wing.[75] A further derivative of the design, designated MiG-19, featured a relatively thin wing suited to supersonic flight that was designed at TsAGI, the Soviet Central Aerohydrodynamic Institute; swept back at an angle of 55 degrees, this wing featured a single wing fence on each side.[76] A specialist high-altitude variant, the Mig-19SV, featured, amongst other changes, an adjustable flap to generate greater lift at higher altitudes, helping to increase the aircraft's ceiling from 17,500 m (57,400 ft) to 18,500 m (60,700 ft).[77][78]