In 1968, Cavalier Aircraft owner/founder David Lindsay began developing a highly modified version of the Cavalier Mustang for use as a counter-insurgency aircraft. Cavalier initially mated a Rolls-Royce Dart 510turboprop to a Mustang II airframe. This privately funded prototype was also intended for the same CAS/COIN mission that the Mustang II was built for. The Turbo Mustang III had radically increased performance, along with an associated increase in payload and decrease in cost of maintenance, and was equipped with Bristol ceramic armor to protect the engine, airframe, and pilot. Despite numerous sales attempts to the United StatesAir Force, neither the U.S. military nor any foreign operators purchased the Turbo Mustang III. Seeking a company with mass production capability, the Turbo Mustang III, renamed the "Enforcer", was sold to Piper Aircraft in late 1970. Cavalier Aircraft Corp. was closed in 1971 so the founder/owner, David Lindsay, could help continue develop the Enforcer concept with Piper. Piper was able to lease a Lycoming T-55L-9 engine from the USAF and flew the aircraft some 200+ hours. In 1971, Piper built two Enforcers by heavily modifying two existing Mustang airframes, fitting them with Lycoming YT55-L-9A turboprop engines along with numerous other significant modifications. One airframe was a single seat, the other a dual-control aircraft. Prior to the Pave COIN evaluation, N202PE was lost in a crash off the Florida coast on 12 July 1971 due to flutter caused by a Piper-modified elevator trim tab. Although the Enforcer performed well in the 1971–1972 Pave COIN test flown by USAF pilots, Piper failed to secure a USAF contract. In 1984, with a $US12 million appropriation from Congress, Piper built two new Enforcers, giving the new prototypes the designation PA-48. These aircraft were evaluated by the USAF, but flown only by Piper test pilots.
Flight testing and evaluation
For another eight years, Piper and Lindsay lobbied Congress to force the Air Force to officially re-evaluate the Enforcer. Eventually in the 1979 defense bill $11.9 million was allocated for Piper to build two new prototypes and for the Air Force to perform another flight evaluation. Since the Enforcer was never in the Air Force inventory, it was not given an official military designation and did not receive a serial number. Instead, it carried the Piper designation PA-48 and the FAA registration numbers N481PE and N482PE. By the time the PA-48s were completed, they shared less than 10 percent of their structure with the P-51, and were longer and larger. Essentially, the PA-48 Enforcer was a completely new aircraft. The two PA-48s were tested during 1983 and 1984 at Eglin Air Force Base, Florida and Edwards Air Force Base, California. As in the Pave COIN tests of 1971, the PA-48s were found to perform well in their intended role, but the Air Force again decided not to purchase the aircraft.
