Mejzlik Propellers s.r.o. 40x13.3 2B MC

The Mejzlik 40x13.3 2B MC is a two-blade composite propeller from Mejzlik Propellers s.r.o. (Czech Republic) for heavy-lift platforms. The designation gives diameter and pitch, 40 in and 13.3 in, and the blade count as 2B. It is made by wet layup.

The 13.3 in pitch is a third of the diameter: a flat layout for hovering and efficiency at low rotational speed, as is necessary at a 40 in diameter. The weight is 191 g with a tolerance of 5 per cent, and the propeller does not fold. The core diameter of the hub measures 35.6 mm. The maximum speed of 4,500 rpm is, according to the datasheet, the hover limit, bounded by blade-tip speed; in forward flight the limit drops. The maximum thrust of 62.6 kgf is simulated. Both values hold only with a given motor, voltage and operating state.

At this size blade-tip speed governs noise and losses: it grows with diameter and rotational speed, so the speed can only be low. Thrust values of this order usually belong to platforms beyond the 25 kg limit of the open category; there the specific category applies, in which operation rests on a risk assessment. A spinning 40 in blade demands distance from people and a de-energised drive before any work at the propeller.

On selection: the hub has a core diameter instead of a standardised bore; the mounting must match the motor. On long composite blades delamination starts at the trailing and leading edges; frayed edges and dull-sounding areas are reasons to replace. Clockwise and counter-clockwise versions are fitted in pairs. At 40 in imbalance loads the motor bearings and the structure particularly, so replacement is made only with balanced propellers.