sentences:  Flight trials were carried out on a Yak-28N, but by then the Yak-28 had ceased production and was perceived as obsolete, and the K-28P system was cancelled.Instead the Kh-28 was adapted for use by standard attack aircraft, in particular the Su-24 'Fencer-A' and Su-17M 'Fitter-C'.The KH-28 was the first liquid fueled Russian anti-radiation missile and was quickly replaced by the solid fuel KH-58 missile, according to research from Dr. Carlo Kopp, the editor in chief of Air Power Australia.