The pilot of N5878R, a Cessna 172G, had no previous experience in formation flying. The pilot of N2603E, an Aeronca 7AC, stated he had many hours of formation flying in the military during World War II and has made an occasional formation flight since that date. However, he apparently has very little or no recent experience in that type of flying. The two pilots had preplanned the formation flight which terminated in the subject accident, including hand signals to be used since they could not communicate by radio. The Cessna was to be the lead plane. The Aeronca was flying right wingman and gave the prearranged signal and crossed under the Cessna to come up on his left wing. The top of the Aeronca's right wing contacted the bottom of the Cessna's left wing. According to witnesses the altitude was 200 to 350 feet AGL. The Cessna pitched up, stalled, pitched steeply nose down and did not recover from the descent. The Aeronca dived, then made a climbing circle to the left and returned to the airport and made a successful landing.