Studio Ingegneria Aeronautica

dott. ing. Filippo Grotti

Advanced Aircraft Design

From AIR PRESS – May 1986

Italian idea for more efficient jet aircraft

In the "Inventions and Applied Science" section of the 1987 "Rolex Awards for Enterprise" competition was an interesting Italian project proposed by an aeronautical engineer, Filippo Grotti.

It involved a new idea which allows a jet plane to take off and land at low speed by drastically changing the wing loading in the different phases of flight . The variation of the wing loading has always been the dream of aeronautical designers because it avoids to compromise between the needs of high wing loading for flight at cruise speed and that of slow flight which requires the lowest possible wing loading.

In the past, some designers tried to vary the wing area and experimented with a telescopic wing or transforming a monoplane into a biplane with little success. In the end the only solution found to be efficient for a wing area variation and subsequently for a wing loading change, is a variable-geometry wing, normally obtained by changing the sweep-back angle of the wing itself.

This solution though, rather than changing the wing loading in a meaningful way, enables suitable aerodynamic configurations to the different phases of flight (take off and landing, normal cruise, supersonic flight).

Grotti's proposal actually allows to double or halve the wing loading, depending on the phase of flight, by adopting a biplane type architecture, but with one mobile and one fixed wing. The mobile wing is regularly positioned perpendicularly to the longitudinal axis of the aircraft during take off and landing or when flying at low speed, while it is positioned along fuselage during high speed flight.

The plan presented at the competition refers to a military subsonic flight trainer, with a fixed upper wing and a lower wing, where the main landing gear retracts, pivoting 90° around its center, to align with the fuselage underside.

The documentation includes a computer simulation of two solutions to allow a comparison of performances: one referring to the new experimental design and one to a conventional jet, with one fixed wing, but with the same wing loading in the take off and landing configuration.

These preliminary results show an 11.6% increase in maximum speed and an 18.3% decrease in fuel consumption in favour of the "rotating-wing-biplane". Better results would be expected for a bigger and faster airplane.

Such a solution, observed designer Grotti, involves notable research, construction and maintenance costs. It also implies weight increase and possible malfunctions. Considering though that variable geometry aircraft, which seem to offer less advantages compared to the new project, are regularly produced today, it should follow that the proposed solution would be of great interest and convenient in its realization.