Gehlbach Leads Big Air Derby(International News Service)HOUSTON, Texas, July 25—With Lieut. Lee Gehlback of Little Rock, Ark., still leading by a wide margin, the eleven airplanes still in the all-American air de: *)y today prepared to take off from municipal airport for San Angelo, Tex., the next controlpoint.Lieutenant Gehlbach, flying a small monoplane, had an elapsed time of 3:01.34 on his arival here from Little Rock late . yesterday. His total unofficial elapsed time was 15:22.32.