Master Airscrew (Windsor Propeller) 3MR Series 3-Blade 7x3.7 Carbon Fiber Reinforced Propeller

The 3MR 7x3.7 is a carbon-fibre-reinforced three-blade propeller of the 3MR series from Master Airscrew (Windsor Propeller, USA) for small-class 7 in FPV drones and for small cinelifter multicopters. The designation gives diameter and pitch: 7 in, 3.7 in.

The diameter is 7 in, and 177.8 is given as the figure in millimetres. The 3.7 in pitch is flat for this size: it keeps the current draw per unit of thrust low and suits builds with a camera load that need plenty of thrust at moderate speed. Three blades raise thrust at a limited diameter at the cost of efficiency. The weight is 6.2 g, the bore 5 mm, and the hub is 8 mm thick. The propeller does not fold and is offered in the counter-clockwise version (CCW).

Legally the finished aircraft counts. Whether a 7 in build exceeds 250 g take-off mass depends on battery and camera; from that limit operator registration is mandatory. In the open category visual contact with the aircraft applies, with an observer when video goggles are used, and a maximum altitude of 120 m. The propeller carries no class.

Carbon-fibre-reinforced composite is stiffer than plain plastic and deforms less under load, but breaks less forgivingly on ground contact. A quadcopter needs two left- and two right-rotating propellers; the CCW version needs a counterpart with the opposite direction. After impacts the blade tips and hub are checked; even a single nick causes imbalance at 7 in that passes into the picture and the sensors as vibration.