Originally Posted by
soarbum
Another interesting bird! I see that it has 2 rotors on the tail rather than the ducted system on the speedhawk.
Does anyone know of a compound helicopter where the tail rotor itself articulates?
Yes, Sikorsky flew a modified S-61 called the S-61F that could add wings, jet pods, and a rotating tail rotor along with some aerodynamic cleanup. Sort of a precursor to the S-72 RSRA. They called the swiveling tail rotor “Rotoprop” and demonstrated the possibilities on the S-61F. Downside of shoving a draggy helicopter through the air with a propeller is that it takes a lot of power, far more than a tail rotor normally consumes if you want to get well over 200 knots. On the X-2 aircraft, the propellor requires more horsepower than the main rotors do. So this swiveling prop adds a lot of weight to the very aft of the aircraft which hurts yaw inertia and moves your CG back. If it’s part of a new design, this is all manageable.
I think the main issue is that a pusher propeller on a helicopter can’t give you tiltrotor speeds and is a significant weight and cost penalty. Since a simpler winged helicopter can cruise near 200 knots and a tiltrotor rules at 250+ knots, there is only a narrow window where a thrust compound might be competitive. So far, that window doesn’t appear to have been wide enough to result in a production aircraft.
Oh, Karem proposed a rotating prop/tail rotor solution for their FARA.