The Douheret helicopter of 1919 was the first helicopter with the engine placed between its two coaxial rotors.

Thanks to Joel Lowers from Belgium for the photos and information

Fatal error: Uncaught mysqli_sql_exception: Connection refused in /data03/virt15346/domeenid/www.aviastar.org/htdocs/helicopters_eng/douheret.php:56 Stack trace: #0 /data03/virt15346/domeenid/www.aviastar.org/htdocs/helicopters_eng/douheret.php(56): mysqli_connect('mysql5.zone.ee', 'd14657sa18989', Object(SensitiveParameterValue)) #1 {main} thrown in /data03/virt15346/domeenid/www.aviastar.org/htdocs/helicopters_eng/douheret.php on line 56