Wonky rotors

[Gingerbread Man]

Last night I was watching a film that featured a couple of BlackHawk choppers, when one of my friends turned to me and asked why the tail rotor was set angled slightly downward. I was rather embarrassed not to be able to provide him with a definite answer. Can anyone explain it for me?

Thinking it through, it seems that the tail rotor must provide some pitch force, but surely when the rotor changes speed/angle to yaw the aircraft, the pitch will change as well?

Cheers

Ginger ;)

[airborne_artist]

I'd expect the tail and main rotor to maintain a constant speed except in autorotation - as with all turbine-powered helos.

[Dimensional]

ISTR it allows some component of the TR reaction to act as lift, I'd imagine this has some effect on the CG range and the like...

not entirely certain though :O

[Shawn Coyle]

The H-60 series of helicopters has a tail rotor that is canted to provide both lift and lateral force. It does cause a change in pitching moment (and rolling moment) when the tail rotor thrust is changed. At the design weight/ cg condition, the mechanical mixing takes care of that - at other weight/cg conditions, the effects can be interesting. The automatic flight control system does mask some of the effect.
It was done to improve the cg range of the basic UH-60, which is quite far aft in most conditions.

[LuckyStrike]

Decreasing the sound level and providing extra lift.

It can have the tailrotor perpendicular but that means you will have more force to counteract rotation caused by the mainrotor so if there's more power why not use it for extra lift :8 (Of course the CG config allows you to do so too, have to mention that)

[Gingerbread Man]

Cheers chaps, that's satisfied a curiosity for me :ok: .

On the same subject, can anyone explain the reason for the apache tail rotors not to be perpendicular to each other? Photo here (http://s96920072.onlinehome.us/AWA1/001-100/walk072_Apache/images%20Gary%20Fairfull/apache06.JPG). Is it just easier to fit everything in the right place if it's at that angle?

Ginger ;)

[Capn Notarious]

Shawn.
For the unlicensed non flyers. Describe if you have the time. The big grin on you face experiance when pulling pitch in a H60

[Shawn Coyle]

Describe (if I have time) the fun one has in pulling pitch in a H-60....
It's been quite a while, but the impression from flying the UH-60A was that this was exactly the machine one would want to be in if going in harm's way. Robust, solid and proof that performance is more important than excellent handling qualities, it did win me over quite convincingly.
it literally begged to be thrown around - (not that I've known any women like this in my sheltered life) - sort of - hit me, throw me around, I love it.
Takeoff was always right wheel first, then left wheel, and that would then be accompanied by some dancing on the tailwheel. With all the magic in the AFCS working, it was pretty straightforward- but hovering at light weight was always at a pronounced nose up, left wing low attitude. From a hover, at light weight, you could pull and pull and pull up on the collective and be passing 1,000' AGL before you got to 100% torque. Rate of climb at light weight and sea level was close to 4,000 fpm if my memory fails me.
The canted tail rotor only became a bit of an issue if you looked for it in rapid yaw rates, but it was generally easily compensated for.
Hope that whets some appetites....

[AngloPepper]

Totally from memory, but I think this was done for dynamic reasons to reduce (eliminate) 4T vibration. It has a fringe benefit of reducing tail rotor noise at certain aspects as well.