ATL87LA261

The stu plt discussed a cross country flt with his CFI, but did not get a sign off nor give a date for the flt. He then rented an acft and departed on the flt. During the flt, the com radio's became inop. The operator and the CFI were called from an enroute lndg point and made aware of the problem. After discussing the situation and a proposed route for the return flt, the CFI gave verbal approval. The plt arrived at the arpt early in the morning so that he could tkof prior to the twr opening. He dptd on rwy 21, turned left, and overflew rwy 15 to the end where he turned left again. A witness std that the acft did not sound right fm the start of the tkof. A turn back to the arpt was made. A 737 on final app to rwy 33 was observed. The plt attempted a 360 degree turn but ran out of alt and impacted some trees at the arpt boundry. The crew of the 737 were advised of traffic in the area and observed a small acft turn away from the arpt. Exam of the eng revealed a stuck exhaust valve in the no. 2 cyl and a crack in the head of no. 3 cyl.