Did you know…
Was there a turboprop Mustang?
Short answer
Yes: in 1968 Cavalier fitted a Rolls-Royce Dart 510 turboprop to a Mustang II airframe. Lindsay sold the project, by then renamed "The Enforcer," to Piper Aircraft in 1971 for series production, and the two resulting PA-48s were tested in 1983 and 1984 without the Air Force ever buying them.

Cavalier fits a turbine to a Mustang
In 1968 the Cavalier firm fitted a Rolls-Royce Dart 510 turboprop to a Mustang II airframe. The idea was simple to state and unusual to see: where the fighter had carried a piston engine, the new installation placed a turbine driving the propeller, not starting from a new design but from an existing airframe of the Mustang family. The result was named the Turbo Mustang.
From Turbo Mustang to The Enforcer
The project did not stay in the workshop where it was born. Turning that aircraft into a mass-produced type required a company with serial production capacity, and that search decided its fate: in 1971 Lindsay sold the Turbo Mustang to Piper Aircraft. In the deal, the program already carried another name, "The Enforcer," by which it would be known from then on.
Two PA-48s before the Air Force
With Piper, the development ultimately resulted in two aircraft designated PA-48, which underwent trials during 1983 and 1984 at two sites: Eglin Air Force Base in Florida and Edwards Air Force Base in California. The technical outcome was favorable, since the PA-48s performed well in the role for which they had been designed, just as had happened earlier in the 1971 Pave COIN trials. The decision also repeated that earlier one: the Air Force again chose not to acquire the aircraft. Thus, the path of the turboprop Mustang runs from Cavalier's 1968 conversion to those 1984 trials at Eglin and Edwards, closing without production examples.
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