The two accident airplanes were part of a three-airplane formation flight comprised of an RV-8 airplane in the lead position, an RV-8 in the second position, and an RV-4 in the third position. The group performed a formation flight briefing prior to flight. Three uneventful formation maneuvers were performed after departure; for the fourth maneuver, the lead pilot made a radio call commanding the group to begin a climbing left turn. All members of the group responded in the affirmative, and the lead pilot pitched his airplane up and began the turn. After a 2-second interval, the second RV-8 pilot began the maneuver, following the first airplane. The RV-4 pilot then began the maneuver and momentarily lost visual contact with the second RV-8. He then made visual contact with the lead airplane but misidentified it as the second RV-8. He then realized he was in error, but, just as he was about to perform evasive maneuvers, his airplane struck the second RV-8. The RV-4 sustained substantial damage to the aft fuselage, and the left wing tip and aileron partially separated from the airplane after making contact with the propeller of the RV-8. The pilot reported that the airplane began a 4,000-foot-per-minute spiraling descent and did not respond to aileron control inputs. He regained control of the airplane utilizing rudder, elevator, and throttle control, and subsequently performed a forced landing into a field. The RV-8 sustained substantial damage to the outboard section of the right wing leading edge and returned to the departure airport uneventfully. Both pilots reported no preimpact mechanical malfunctions or failures with the airframe or engine that would have precluded normal operation.