Project F (also known as Projet AP) was to have been the definitive middle range Citroën and was conceived in four versions
base model powered by a bored out to 750cc version of the 2CV flat twin with torsion bar suspension
flat four, air-cooled one litre with torsion bar suspension
1600cc transverse mounted water cooled unit derived from the DS engine with torsion bar suspension
a top of the range model powered by a Wankel rotary engine and fitted with hydropneumatic suspension and powered disc brakes.
Design work started in the early sixties following the decision to abandon Projet C.
While the use of advanced techniques such as front wheel drive and hydropneumatics had been enough to put Citroën at the forefront of automotive technology during the preceding thirty years, it was felt that something new was required if the company were to maintain its reputation. That something was the Wankel rotary engine and a joint venture was set up with NSU to build the powerplants.
In 1963, there were three prototypes:
AP1 with torsion bar suspension and friction dampers mounted in the wheels; powered by the 602 cc Ami 6 engine; 125x14 tyres and weighing 555 kg
AP2 with hydropneumatic suspension; powered by an air-cooled flat four 1130 cc engine derived from Projet C; 135x14 tyres and weighing 610 kg
AP3 with hydropneumatic suspension; powered by a 950 cc engine sourced from Fiat; 135x14 tyres and weighing 640 kg
Flaminio Bertoni was responsible for the body design (which proved to be very unaerodynamic) but unfortunately he died in 1964 leaving newcomer Robert Opron to complete the exercise.
A number of innovations were to be found - this would have been the first hatchback (if one ignores the Traction Commerciale which was intended as a utility vehicle) , the door frames were welded to the roof in much the manner used by the yet to be released Renault 16 and the use of four headlamps behind a glass panel anticipated the SM's styling.
Unfortunately, the Wankel engine proved to be unreliable, thirsty, and very dirty (it would take another forty years until these problems were solved by Mazda), there were problems with body rigidity, the two versions (torsion bar and hydropneumatic) differed in length from one another, the conventionally sprung vehicle suffered too great a variation in ride height between unladen and laden states and there were problems with road holding and handling.
Furthermore, there was a considerable shortfall in refinement when the prototypes were pitted against the C60 prototype.