X8 Upper/Lower Propeller Pairing

Hey All,

I am deciding between an X8 and Hexacopter for my next project and wanted to see what the current outlook on propulsion redundancy was. In my mind both systems allow for a controlled landing in the event of a singular motor/ESC/prop failure - assuming there is enough thrust to do so. However, my upcoming project will require the aircraft to fly at high speeds (40MPH+) with a near 30 degree tip angle during flight - so I am wondering if a Hexacopter has enough stability after motor loss to return to level flight during a motor/ESC/prop failure at such high speeds. Loss of yaw control is completely fine for me. I think an X8 would handle fine - but I would ideally like to end up with a hexacopter due to its lower expense and higher flight efficiency. T:W for the Hexacopter would be around 2.6:1 at low (near dead) battery. So what do you guys think? Would a Hexacopter with this amount of T:W be able to handle motor loss at such high speeds.

Consider an Octoquad too - a little bit worse efficiency than a basic quad, but it’s got the redundancy of an Octocopter. You can use bigger props than the same wheelbase hex, and so on…
You might be able to find some examples here:
and here:

Hey! Thanks for the links. I am really trying to stay with a hexacopter layout (due to cost and the flat layout). However, if I can’t get the motor redundancy - then I guess I might have to go the X8 route. Really just hoping a high T:W hex can handle a motor failure at high speeds. Theoretically I think it should be able to - but as always theory != real world.

Hey All,

I am still fighting with myself regarding a decision - but that’s not the question I have today. I am in the process of designing an X8 propulsion system and had a question about the upper/lower prop pairing. From what I have found, it is recommended that the lower propeller by slightly lower in diameter and higher in pitch - but I don’t know how much this should vary by. If anyone has experiences with lower/upper prop pairing - that would be very helpful!

For now I am thinking 1960 on the top and 1865 on the bottom - both running a 360kv motor on 6s.

I have both X8 and Y6 configuration with 15" propellers. It is easier to set same propellers top and bottom. There are too much variables (diameter, pitch, rotation speed, distance between top and bottom propellers,…) to set a rule.

You can find academic studies but my experience show no significant delta (5% on the X8, none on the Y6) to justify the headache.