Where is the datum located on a single-engine rotorcraft under 14 CFR Part 27?

The datum on a single-engine rotorcraft under 14 CFR Part 27 is defined as a reference point determined by the manufacturer, making the choice that indicates it can be located anywhere the manufacturer sees fit the correct response. This flexibility in determining the datum allows manufacturers to establish a point that optimally facilitates the design and performance characteristics specific to that rotorcraft model.

The datum serves as a baseline for measuring moment arms and calculating weight and balance, which are crucial for safe operation. Each rotorcraft may have unique design considerations, so allowing manufacturers to select this reference point is practical and essential for the aircraft's specifications and performance metrics.

In contrast, locations like the tip of the rotor or the plane of rotor are specific and do not necessarily represent the optimal or most useful reference for each type of rotorcraft. Center of gravity is also a critical reference point but does not serve as the datum itself, as it's based on the aircraft's mass distribution rather than a fixed measurement reference.