While performing a climbing turn to the left, at about 400 feet above the ground, there was a violent thud, a loud bang and the aircraft bank increased rapidly to the left. The pilot reduced power to reduce the level of engine vibration and levelled the aircraft. He noticed that a large portion of the left wing had been damaged before carrying out a successful, engine-off landing into a nearby paddock. An inspection of the aircraft discovered that the perforated, steel muffler core had been ejected into the propeller which flung the core into the left wing. The propeller, the aileron, two ribs and sections of the wing coverings were damaged. The above information was obtained from a report submitted by the pilot to the Australian Ultralight Federation. The report did not give the reasons for the failure of the muffler.