The retractable landing gear is completely ordinary in aviation, and now the retractable float is coming too, by the innovation of an Australian company, Tigerfish Aviation.
The hydroplanes’ floats increase the air resistance during cruise, thats the reason why floatplanes can only be economical on short distances (few hundred kilometers).
By retracting, the problem of the landing gears’ extra drag was solved quite early. The first aircraft with retractable landing gears appeared in 1917, and such aircraft became common in the early 1930s.
The flying boats are better in this area, but they also need stabilizing under-wing floats (or wing-like projections from the fuselage) for stabilization.
The RAPT (Retractable Amphibious Pontoon Technology) is practically the adaptation of the idea of retractable landing gear to floats.
Since the floats are too big to be retracted to the fuselage, they are retracted to a streamline pannier, so the extra drag during the cruise can be reduced. As you can see it in the second picture, or in the video, its rather a “packing” than retracting.
During the retracting process the floats are turning inside, so the boat-like shapes aren’t exposed to the air stream. In this way the floats’ extra drag can be reduced to 10% from 45%.
The reduced drag affects the performance in different ways. According to the statements of Tigerfish Aviation the RAPT system can generate up to 20% fuel saving, increased speed and productivity, significant reduction in emissions and decreased operating costs.
Maybe the fuel saving is the most important in these days’ when the fuel price is constantly rising. But besides the features mentioned above, it would have all the advantages of an ordinary floatplane.
The pannier contains its own undercarriage for landing at airports and for beaching. The disadvantage of RAPT can be it’s weight, which is more than simple fixed floats cause of the retracting mechanism.
Of course this conception has predecessors. The stabilization floats of the PBY Catalina, a WW2 era flying boat, were retractable too.
A less known experimental plane, the Blackburn B20 had a deployable hull, in order to combine the best features of both flying boats and floatplanes.
The RAPT system theoretically can be fitted to a wide range of aircraft from the small Cessna planes to the C-130 Hercules. The pannier is retrofitted, and has got a different design for each aircraft, which adapts aerodynamically to the fuselage, and contains a fitting undercarriage.
The project is on its best way to realization. In 2007 an 1:6 scale Cessna Caravan model was built in order to test the concept.
Do-28 aircrafts in Manila on the lawn of Iren Dornier’s factory
Recently Quasar Aerospace Industries invested 5 million $ to the project, the next phase of the development will be the modification of a Dornier 228 NG.