When I learnt in the 140, it was fullest tank for take off and landing, change tank 30 min after take off and then every hour after that. When its only using 30lph (22kg) their really isnt much point changing evey 30min, never any balance issues, and like the others have said, its less times your changing tanks in-flight and risking a problem arising. I too never saw its POH (I now know thier value
), anyone know what piper reccomend?