APC Propellers (Landing Products Inc.) 14x5.5MR Multi-Rotor

The APC 14x5.5MR comes from the MR series of APC Propellers (Landing Products Inc., USA), which was developed specifically for electric multicopters and is made in the USA. At 14 in diameter it is a propeller for mid-sized multicopters of the kind built as camera platforms and survey aircraft. MR stands for Multi-Rotor.

The diameter is 14 in and the pitch 5.5 in, clearly less than half the diameter: a value suited to hovering and to efficiency at low speed. Two fixed blades, not foldable, weigh 30.1 g together with the hub (APC lists 1.06 oz). The bore is 6.35 mm, and the hub is 0.65 in in diameter and 0.38 in thick. The maximum speed of 7,500 rpm follows the APC rule of 105,000 divided by the diameter in inches; it is a rule-of-thumb figure for the series and not a measurement on this propeller.

Legally the whole aircraft counts: from 250 g take-off mass the operator must register. Multicopters with 14 in propellers fall, depending on take-off weight, into the span of classes C2 (under 4 kg) and C3 (under 25 kg); both require direct remote ID. The propeller itself has no class, but a different type changes thrust, weight and noise compared with the configuration on which the manufacturer's classification rests.

For selection the rule is: the larger the diameter, the lower the rotational speed should be, and with it the KV rating of the motor. Adapter rings for shafts thinner than 6.35 mm are not included. Before each flight it is worth inspecting the leading edges, the hub and the blade roots; nicks, cracks and white stress lines are reasons to replace the propeller. Because imbalance on large propellers loads the sensors more strongly, propellers are replaced as a set and the correct direction of rotation is checked on each arm.