The term Progressive Trainer System or PTS applies to a new type of R/C trainer aircraft developed by Hanger 9, a division of Horizon Hobby. Unlike most trainers which tend to be boxy, high-winged and slow, Hanger 9's initial offering is a .40 P-51 Mustang, a low-winged warbird. The result of this additional engineering is a low-wing aircraft with the slow flight characteristics and recovery capabilities of a high-wing trainer. Removal of the training equipment results in a high-performance, fully aerobatic model.