Opinions on lower-KV motor options for FT-style planes

[MiniacRC]

Hey Y'all.

Summary: I want to move away from the FliteTest A and F power packs (and comparable setups) to lower-KV options such as the Emax LS2205 1900KV, which can produce comparable max thrust but with greater efficiency using a larger propeller. I understand that I will sacrifice some acceleration but that may not be as consequential for my intended application of fixed wing general sport planes as opposed to racing/freestyle multicopters. Any insights, suggestions or lower-KV motor+prop options in the 1806-ish and 2205-ish class are welcomed. Thank you!

I have always loved the Emax RS2205 2300KV on 3-cell (and recently also the similar FT2205 2300KV), both of which are quite efficient for my desired application of miniature sport fixed-wing airplanes. I would like to try a lower KV motor option with larger propellers for greater electrical efficiency. For example, using a King Kong 6x4 propeller, the 2205 2300KV can produce around 999 grams of static thrust drawing 25.5 amps (12.0 V measured, ≈ 3.3 g/W efficiency). In comparison, using an HQ 7045 prop, the Emax LS2207 1900KV can pull 1046g drawing 24.7A (≈ 3.5 g/W). A small disadvantage is that the latter motor is about 6 grams heavier.

Analogously, the Emax or Flitetest 1806 ≈2300KV motors do well for smaller builds, but I'd like to explore lower (maybe 1400) KV options with larger propellers, sacrificing burst acceleration for longer flight times and less stress on my batteries.

Any insights, criticisms and suggestions are welcomed. I'd particulary like recommendations for well-reviewed motors in the 1806-ish and 2205-ish classes that have lower KV. Thanks FT community!

 

[Merv]

...Any insights, criticisms and suggestions are welcomed...

There is no doubt that lower kv motors swinging larger props are more efficient. In my humble opinion, if you want efficiency, you need to go much lower kv, something near or below 1,000 kv. And a much larger diameter motor, something in the 30-40 mm range.

Here is an example of an endurance plane.

 

[quorneng]

Also remember for the same motor weight a lower kV version is also a bit less powerful. Whether the improved efficiency of the larger prop cancels out the lower power is open to question but the thrust is does create is done so slightly more efficiently.

 

[MiniacRC]

Thanks @Merv and @quorneng!

I'm trying to shoot for the sub-250gram class of fixed wing-aircraft, so I'd like to stick with the ≤20-ish mm stator size. I will have to strike a balance between (i) the superior net T:W ratio afforded by the 2300KV motors and (ii) the high efficiency a <1000KV motor would yield. I'm thinking of something along the lines of the DYS BE1806 1400KV, which I've seen perform pretty well on a small foamy.

 

[LitterBug]

Would add weight and complexity, but gearing down a motor would allow use of a bigger prop too.