Prop separation

I’m running some numbers through ecalc to get an idea of the motor/prop combo that would suit my needs (duration and stability over speed and manoeuvrability), and as we know the larger the prop the better [citation needed]

Anyway, my quad airframe has a separation of 15.55 inches between motors, but I’m not sure that if I put 15" props on, a half inch separation would be sufficient. I read a paper saying that there’s some evidence of vortex interference which might decrease efficiency, but what I’m interested in is if there are any practical problems having such a small gap.

Any thoughts or advice welcome.

There’s definitely air coming out horizontally from the tip of the prop. But would an extra inch help for the benefit of a larger prop running slower? Be interesting to see your results if you experiment

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