The issue with the «chopping» is noise level. Counter rotating propellers are more efficient than a single propeller. «Contra-rotating propellers have been foun

The issue with the «chopping» is noise level. Counter rotating propellers are more efficient than a single propeller. «Contra-rotating propellers have been found to be between 6% and 16% more efficient than normal propellers.» https://en.m.wikipedia.org/wiki/Contra-rotating_propellers https://en.m.wikipedia.org/wiki/Contra-rotating_propellers