APC Propellers (Landing Products Inc.) 16x5.5MR Multi-Rotor

The APC 16x5.5MR belongs to the MR series of APC Propellers (Landing Products Inc., USA), developed for electric multicopters. At 16 in diameter it sits at the upper end of what is fitted to mid-sized multicopters and targets aircraft with heavier payloads, where a few large propellers at low speed achieve more than many small ones at high speed.

The pitch is 5.5 in, a little over one third of the diameter: very flat, laid out for hovering and efficiency. Two blades save rotor mass compared with multi-blade solutions; the weight is 43.9 g (APC lists 1.55 oz), and the motor still has to accelerate this mass at every throttle change. The bore is 6.35 mm, and the hub is 0.80 in in diameter and 0.37 in thick. The maximum speed is given as 6,563 rpm; that is the APC rule of 105,000 divided by the diameter in inches, a rule-of-thumb figure for the series and not a test of this propeller.

The legal framework attaches to the whole aircraft. Multicopters of this size reach, depending on equipment, classes C2 (under 4 kg take-off mass) or C3 (under 25 kg); the open category ends at 25 kg. Remote ID and operator registration apply to the whole system. Anyone who changes the propeller changes thrust and noise emission compared with the manufacturer's assumptions and should reassess the propulsion system.

On selection: at 16 in the motor needs a low KV rating and enough torque. Adapter rings for thinner shafts are not in the box. With large blades, damage often shows first as vibration in the hover before it becomes visible; blade tips, leading edges and hub should be checked regularly. For injection-moulded blades too, propellers are replaced as a set and not mixed within a set.