A helicopter question for the tech minded...

[Army of One]

Dear all.......what is the reason for the canted rear rotor on some helicopters like the CH53 family....?? If I wanted to change a helo from an upright rear post n rotor with two small wings one either side of the tail boom to a canted one with maybe a wing at the top is there anything to consider re flight characteristics......??

The helo I want to modify is a Mi24 and I want to change the tail rotor to a sort of CH53 family style in order to aid folding......

I know this if whiff world but if it wouldn't fly because of the mod......

       Many thanks......H

[deathjester]

I think it might be to cut down on the noise mate.  IIRC, the Apaches have the tailrotor blades set at odd angles on their hub to alleviate the interaction of the main rotor wash, and the tailrotor wash, which is what makes helos so noisy.  The CH53 tailrotor angle might be a similar attempt to reduce noise.  I don't think it would stop it flying properly - you'd here it coming a mile away though...

[lenny100]

Changes on the CH-53E also include a stronger transmission and a fuselage stretched 6 feet 2 inches (1.88 m). The main rotor blades were changed to a titanium-fiberglass composite.[5] The tail configuration was also changed. The low-mounted symmetrical horizontal tail was replaced by a larger vertical tail and the tail rotor tilted from the vertical to provide some lift in hover while counteracting the main rotor torque
taken from wikipedia

[deathjester]

Ah!  I stand corrected! (Well, to be honest, I'm taking it sitting down)

[Army of One]

Great stuff.....many thanks........so other than noisy it should be ok......

[PR19_Kit]

Because of the angle there must be some vertical lift component from the tail-rotor, either upwards or downwards depending which way it goes of course.

Perhaps they use that to help trim out some CG issues or other things?

[Aircav]

Helps a bit with ground clearance too, get a bigger diameter in on an angle. 

[PR19_Kit]

But then the horizontal forces, which are what it's trying to resist, will be smaller because of the angle.

[Mossie]

Would that be offset by the larger diameter?  Kind of a win-win, tilt the rotor to provide more lift, which reduces the torque correction, but you can then increase the diameter to get some of this back.

[PR19_Kit]

Maybe.

It's difficult to say for sure what they are trying to do unless you have the 'before and after' data, such as the amount of torque they wanted to counteract originally compared with the amount they'd predicted on the newer version. Plus you'd need before and after diameters and blade speeds and pitches etc.

It's pretty darn complicated really, good thing we live in WhiffWorld......... 

[deathjester]

Wouldn't it be easier in that case to have the angle of the whole tail rotor variable in flight?

[jcf]

Wouldn't it be easier in that case to have the angle of the whole tail rotor variable in flight?

Sshhh, a Sikorsky or Eurocopter manager might overhear you and see dollar signs.
It would be doable, but both complex and expensive.

On the Ch-53E the 20° tilt is evidently to help compensate for the weight of the third engine.

As to the original question, in real world terms, a skewed hinge fold line would probably answer as
well as an angled tail rotor/vertical fin, but wouldn't look as cool. 

[Army of One]

Thanks for all the advice/help chaps......I think I'm gonna go with chanting the tail and a high fin like the CH53.....and do away with the tail boom fins on the Hind....if/when it's finished and I post it I'll put up with those that point stuff out......again,many thanks.......H