Bertrand U1

Aeronautical engineers have known for many years that the efficiency of a propeller can be improved by placing it in an annular channel. At the same time, the additional mass and aerodynamic resistance of the channel can often negate the achieved increase in the efficiency of the power plant. Some designers sought to solve this problem by turning part of the fuselage into an annular channel.

One of these aircraft was the monoplane Bertrand U1 (Bertrand Unic 1). This French “tunnel” aircraft built in 1909 had a number of unique features. One 30 hp Unic engine. (22 kW) set in motion two propellers, each of which was installed at opposite ends of the tunnel (diameter 2 meters). According to the aerodynamic scheme, the aircraft was a “duck” equipped with an additional tail unit. The ailerons were not installed on the wing (span 13.40 m), but on the ends of the PGO.