why Cobra tail rotors swapped sides?

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

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!

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