What is the radial offset distance and how to manipulate this value?

Radial offset distance, shown as e in the figure below, is the offset of two central axes in any radial direction. In most of the dual-motor or coaxial propulsion systems used on drones, designers tend to keep both motors on the same axis thus a zero radial offset.

Generally speaking, we use the term “overlapping percentage” to characterize potential aerodynamic effects of the airflow impact on the downstream propeller. When two propellers are at the same size and without any radial offset, we can say the overlapping percentage to be 100%. The smaller the overlapping percentage becomes, the smaller turbulence the downstream propeller may suffer and can potentially increase the thrust generated.

The advantage of radial offset is a decreased overlapping percentage in order to avoid direct turbulence effect towards the downstream propeller. This may potentially increase the thrust the downstream propeller can generate.

There are multiple constraints for a radial offset or a smaller overlapping percentage. One of the major disadvantages of radial offset is mainly about the complexity when designing the flight control system. The extra motor and propeller in a different position may increase significantly the complexity of the flight control design as each motor may be regarded as independent. Drone’s frame and position restrictions can also impose obstacles for a larger radial offset.

On the Flight Stands, you may be able to adjust the radial offset with certain setups. Please keep in mind that the diameter difference between two propellers, and the axial offset distance may also affect the optimum thrust.