Incident
According to the pilot, while passing through 6,000 feet, the engine began to knock severely and gradually lost power. The pilot adjusted the mixture but found that adjusting it either way resulted in additional power loss and did not resolve the knock. The pilot then set the mixture to what he considered the best setting. The pilot declared an emergency with Des Moines Departure Control, who recommended proceeding to Indianola Airport.
Sequence of Events
The pilot turned on heading and attempted to maintain a glide speed of 85 miles per hour. Despite receiving clock headings from Des Moines Departure Control, the pilot could not locate Indianola Airport visually. The only field the pilot believed he could reach was slightly ahead, but it had trees at the touchdown end. The pilot turned toward the field, lowered the landing gear, and lowered some flaps. While turning on course for the field, the pilot realized the rate of descent was too high and that he did not have enough airspeed to clear the trees while banking. At that point, the airplane struck a tree.
Outcome
The airplane's engine was later successfully run at Teledyne Continental Motors.