With vague power comes vague responsibility . <| sep |> With these newer experimental designs that include ' Pusher Props ', they are slowing down the mainrotors during fast flight . While you still will experience dissymmetry of lift counteractedsolved by the opposite rotor , the problem of the advancing blades approaching the speed of sound and producing shockwaves is greatly reduced . If you tried reducing the RPM of the blades of a conventional coaxial or tandemrotor helicopter in forward flight , all that would happen would be that you slow down , as you are reducing the forward thrust as well . Since helicopters like the Sikorsky X 2 and the Eurocopter X 3 use propellers to help with forward thrust , you can reduce the rotor RPM while still maintaining fast forward airspeed .