Tail Rotor Position/Orientation (vs. Huey)

[Bearfoot]

On the Huey, the main rotors turn counterclockwise (to the left), and the anti-torque rotor is on the left side of the tail boom, with its thrust toward the right to counter-act the torque. This is the same orientation as the following diagram:

 

 

On the DCS Mi-8, however, the main rotors turn clockwise (to the right). So I would expect the anti-torque rotor to be on the other side of the tail boom. But I see that it is not --- it is on the same side as the Huey.

 

So I looked up images of the MI-8, and see that while many have the anti-torque rotor on the left,

 

• 
   
  
• 
   
   
  
• 
   
  
• http://www.russianhelicopters.aero/en/helicopters/military/mi-817/photo.html
   
  

 

many others have it on the right

 

• 
   
  
• 
   
  
• 
   
  
• http://www.aircharterservice.com/aircraft-guide/cargo/milhelicopters-cis/milmi-8
   
  

 

 

What gives? Is the tail rotor placement arbitrary? Is there a design/engineering principle? Is the direction of the main rotors the same in all these cases (i.e., to the right/clockwise, opposite of Huey)?

 

At the same time, I found images of the Huey with the tail rotor on the other side as well

 

Edited October 17, 2017 by Bearfoot

[Holton181]

Without specific knowledge in this specific cace, tail rotors may be of either "blowing" or "sucking" type depending on what side of the tail it is placed relative to the main rotor direction. The "free" side (without things in the way of the airflow) dictating the type.

In the top diagram it's a "blowing". If it was located to the right it would have been a "sucking". Airflow direction will be the same.

I'm pretty sure the main rotor for a given helicopter type always rotate the same direction.

I don't know why the designers choose one or the other tail rotor confirmation thought. Interesting question, I didn't know same models could have different configurations.

[Jester986]

The two concerns at play are rotor downwash and whether you want the vertical stabilizer blocking the tail rotor inflow or outflow. You can design a tailrotor on either side to be a pusher or puller and to turn either way you want. If you look at the R44 and R22 tailrotors though you'll notice they're both on the left side but turn opposite directions. This is because the newer designed R44 has its blades ascending into the rotor wash for a higher relative airspeed. But the main rotor turns the same way? Yea, but the t/r blades then pitch the opposite direction so you still have a pusher. They flipped it to the right side on the Huey because it was easier then reengineering it to spin the other way and they picked up some benefits from it being a puller as well. My Huey is a Franken copter with a Bell 212 tail rotor, and a cobra engine, transmission and tail boom. We have one in the hangar That's a UH-1H with a PT6 engine(never put in a Bell Factory Huey) and UH-1B tail rotor. The hodge podge of parts you get on these can be pretty impressive... It's funny though on the MD-500/ OH-6 variants they still do it the "wrong" way because they said screw it it works well enough as is.

Edited October 17, 2017 by Jester986
trying to be less obnoxious

[AlphaOneSix]

For the MI-8, switching the tail rotor from the right side to the left side increased its efficiency. It's all the exact same parts, they just flipped the gearbox around 180 degrees starting with the Mi-8MT, the same version that also got the TV3-117 engines instead of the older TV2-117 engines. Previously, the tail rotor rotated "with" the airflow from the main rotor, and when flipped, it rotates "against" the airflow from the main rotor, which increased its efficiency.

 

Basically the same thing happened with the Huey.

 

EDIT: Should have said effectiveness instead of efficiency, but probably both reasons really.

[Jester986]

Alpha I think we were typing at the same time lol.

[Bearfoot]

Thanks for clearing this up! It was really bugging my OCD buttons!

[AlphaOneSix]

I type slow. :D