Interesting replies.
My plan is to build an ultralight with an aspect ratio 2.5 wing.
AR 2 or 3 is very common in RC models and the aircraft have amazing performance. But not much in full scale at AR 2.5 that I know about.
I have run many simulations with X-plane and it works well. But still one wonders why others have not built planes with AR 2 or 3.
The Wright brothers found that AR 6 was much better than their early AR 3 glider. But they had increased the span. And span is the major factor for induced drag.
I think an ultralight with low span loading and wide chord would have low induced drag. With sufficient span the low aspect ratio is really not a factor.
It is just the result of adding area.
slowrotor