What was the reasoning for the early Cobras tail rotor swapping position over from port side to starboard?
Better range of authority throughout the performance envelope. In easy words, it worked better.
Chief Snake
They tended to “run out of right pedal” in certain conditions. Swapping it over to the right side improved the aerodynamics considerably and greatly reduced the Loss of Tail Rotor Effectiveness ranges.
Jon
pls be gentle on me if I’m wrong…but…didn’t the moving of the tail gear box to the starboard side provide a second and equally important improvement—stress reduction of the tail (rotary rudder) gearbox mount bolts. Initially (port mounted) the tail rotor would have to pull on the fuselage for anti-torque/heading hold while starboard mounted gearboxes pushed against the fuselage during anti-torque. I thought I remembered something about that from the 70s.
Brian
Brian,
I do believe you’re right! Hopefully Snakedriver will chime in on this conversation. He was there when the change happened!
Jon
does this mean that the main rotor changed rotation direction?
No, the main rotor stays the same. The gears in the drive box for the tail rotor were changed to reflect the repositioning of the gearbox.
Chief Snake
A little bit more detail - The cause of the loss of antitorque control under some conditions was the tail rotor blades rotating in the same direction as the vortex created by the interaction between main rotor downwash and the ground. (You can see that vortex flow at the back of the aircraft any time a helo lands in dusty conditions.) That meant lower airflow speed over the blade, leading to lower lift and lower total antitorque force. To fix this, the tail rotor gearbox was rotated 180 degrees, with attendant relocation of fill openings, etc. This caused the tail rotor to rotate in the opposite direction. Flipping the whole mechanism over to the other side placed the TR blade rotating against the direction of the main rotor/ground vortex, thus retaining lift when engulfed by the vortex. It was the simplest solution, allowing the retention of all the existing driveshafts and the tail rotor blades.
Dan H.
So basically it got the tail rotor out of vortex ring state at high power settings! Very cool
Got to sit in your old project a couple weeks ago, Dan. Man that Comanche’s cool! I would love to have flown it!
Jon
Hottest ship ever built - there are faster helicopters, but none of them have Comanche’s maneuverability. There are more maneuverable ships, but none of them are as fast as Comanche. We used to start demo flights with a 200 knot pass, then come down the runway at 80 knots and do a 90 degree pedal turn and keep going at 80 knots sidewards. Ah, the old days…
Dan H.
200kts!
[bow]
160 in the Apache is… interesting… but fun!
I can only imagine what the Comanche can do…
Jon
Interesting fact I just realized: the tailrotor for the AH-1Z / UH-1Y drivetrain is back on the port side.
Insights?
–Andy
I just noticed that. Apparently it is still rotating up and away from the front of the helicopter, same as the right side tail rotor, but as far as the tractor/pusher issue, I’m baffled.
Bears some looking into, I think!
Jon
It may have to do with the new 4 bladed MR System on the Zullu and Yankee, the aerodynamics changed.
Note too, the airfoil camber on the Cobra tailfin that adds to the tailrotor authority at speed and reduces the pitch level and subsequent drag it induces.
I saw that video. Coooool stuff. I wished the Blackhawk could do that without jerking around, it would make gunnery so much more fun. Our pilots used to try to replicate it, but it ended up being easier to come in and move towards the target at a 45 degree so we could light them up, nowhere near as fast of course.