AH-1 Cobra tail rotor question.

[Tulio]

Looking at photos of Cobras, I noticed that some models have the tail rotor on the port side, while others have it in the starboard side.

Why?


Does it make a difference torque-control-wise?

Does it influence flight characteristics?

Please, educate me.


Saludos,


Tulio

[sandiego89]

You will find some Huey's and Cobras with the tail rotors on the left, some on the right.

As I understand it the earlier models had them on the left, but it was later found that there would less main and tail rotor interference if the tail rotor spun in the other direction, with the up going tail blade being closer to the main blade. With the blade on the left and spinning the less optional way the tail rotor would get washed out more easily.

The easiest remedy was to flip the tail rotor to the right side and have it spin in the other direction. Later models had this built in. Some were converted, some were not. You will see both.

[Tulio]

Thank you!!


Tulio

[JohnB]

Years ago, I notice that on a USAF UH-1N...so I asked the pilot.
He had no idea...I'm not sure he knew they were ever on the left (he was a young guy who started flying long after the change).

In addition to the reason given above, I've been told that the tail rotor is most often used to push the fuselage to the left to counteract main rotor torque...and the blades worked better "pushing" rather than "pulling".

[CoastieJohn]

In addition to the reason given above, I've been told that the tail rotor is most often used to push the fuselage to the left to counteract main rotor torque...and the blades worked better "pushing" rather than "pulling".

Can't speak for all helo's other than the ones I worked and flew on. I started out on the old H-52's then went to the H-65's, then H-60's then back to H-65's. The T/R will normally push/hold/pull the tail boom based on pedal input to counteract MRH torque. As I recall, on the H-65.....once the airspeed hits 47kts, the airframe will hold direction of flt without T/R (fenestron) input due to the vert fin canted design. I think the H-60's will too above a certain A/S. I don't think the H-52's had that aerodynamic technology in them.

The pushing vs pulling efficiency makes some sense. I'm guessing it is less stress on the airframe and components too. However all T/R's will push and pull regardless of what side they're on. Another "as I recall"....when doing T/R rigging/range checks, there was slightly more pedal authority (in degrees) in one direction vs the other based on direction of rotation of MRH. I'm pulling all of this out of the mental archives so take it for what it's worth.

[lucky52]

The "C" and "M" model Hueys had an airfoil type vertical fin that brought the nose left instead of using left pedal to keep it in trim.The Bell 206 series has the vertical fin bolted on at about 4 degrees or so(can't remember the exact amount) to do the same thing.Less left pedal reduced the amount of power the T/R was using.

[Tulio]

Thank you, Lucky52!!!


Saludos,


Tulio