Originally Posted by LOMCEVAK
My previous post was made somewhat hastily, and I had made an invalid oversimplification. I had just considered the mechanics of a propeller connected directly to the turbine by a single shaft. In that arrangement, there would be no more torque reaction causing the aircraft to roll than in a turbofan...
I have to disagree with you here too, because of the essential difference between a turboprop and turbofan. No, not the shroud, but the fan stator vanes just downstream of the rotor.
Turboprop: The accelerated airflow leaving the prop blades does not travel straight aft, but is rather is a swirl or vortex centered on the prop axis. The rotation of this airflow means some of its energy does not contribute to thrust. But it's an acceptable compromise for the usual turboprop (or piston) application. The corollary Newtonian reaction in the engine mounts equals the torque
on the prop shaft. PS - it makes no difference if the gearbox is planetary or offset spur gears; It's the output torque that counts.
Turbofan: The accelerated airflow leaving the fan rotor blades does not travel straight aft, but is rather is a swirl or vortex centered on the fan axis.
BUT just downstream is the fan stator row, which a) stops the vortex rotation, and b) is a diffuser to lower the velocity and raise static pressure. In stopping the vortex, it is the Newtonian reactive torque that otherwise would show up in the engine mounts. So, if the fan stators are properly designed,
there is no torque resolved in the engine mounts in normal operation.
OK?
