Selecting motor and propellers for the LEMFEV flying model (FMBW1). Iteration 1 (just to kick off the model production!)

A while ago, we launched this exciting and oh, so educational process of scaling our Martian aircraft for Earth and designing and building the technology demonstrator for flight tests.

There are a variety of specific topics requiring extra exploration and a deep dive, but in this post, I will limit myself to the theme of matching the motor and props with the aircraft.

Being, so to speak, a theoretical aircraft designer, thinking most of my working hours about the 'external mold lines', the aerodynamic shape of an aircraft, I am new to aircraft systems. There is so much to learn, which is exactly what I am passionate about!

To kick off the production process, we started with selecting a motor and subsequently, the props. Definitely, a more time-efficient approach yielding an aerodynamically better aircraft would be to numerically optimize the propeller shape. This is something I am currently working on. Thank you, LEMFEV, for this wonderful opportunity to learn new design and analysis tools, expand the palette of my capabilities, and grow my expertise!

To select a motor-propeller combination for our flying model, we followed a series of steps.

1. Defined the required thrust (for a thrust-to-weight ratio of 2).

2. Selected a motor delivering the required thrust with 6 15-inch propellers (the maximum allowable size from the airframe's size standpoint).

3. Made sure the motor features a rapid response to enable the control of the aircraft by changing the motor speed.

4. Conducted propeller trade studies, varying the pitch distance.

5. Selected the motor's kv (based on the estimated required prop RPM).

6. Since the propellers are expected to operate at low (airplane mode) and high (helicopter mode) speeds, and since the variable pitch props seem to be too heavy for our application, we worked out a mixed prop configuration:
   

This a good starting point for our current prop optimization effort!