The Piper PA-32-3M was basically a PA-32 Cherokee based prototype modified as a Trimotor aircraft with two 115-hp Lycoming O-235 engines fitted to the wings, for development of the PA-34 Seneca at Vero Beach FL. in the early ’70s. This prototype significantly helped many other development projects at Piper.
It was an early attempt to convert the PA-32-260 Cherokee 6 into a simple, low-cost trimotor, retaining the fixed gear and using fixed-pitch props. This was actually tested by adding two 115 hp engines to the wings and throttling the Cherokee 6’s 260 hp engine back to simulate a third O-235 for a total of 345 hp.
Performance on all three engines was fine, but engine out performance was not. Switching the 115 hp engines for 150 hp units solved that problem, but speed was now so high on 450 hp that controllable-pitch props were needed, defeating the original purpose. That model eventually became the Seneca, but with two larger engines, variable-pitch props and retractable gear.
All Aero 