An MD-80 and a 727 both flew with an installation one side.

As mentioned above it was more efficient in many way but annoyingly noisy.

Not just in a decibel sense, the type and pitch of the noise was very irritating.

The Optica used a ducted fan and had an irritating buzz and an Islander flew with a pair of ducted fans. Again, like the open ‘Propfan’ the ducted fan was irritatingly noisy.