technical question R22/R44

[mecheli]

I've noticed that the tailrotors on the R22 and the R44 turn opposite to each other (the R44 being the 'conventional' way?)

Anyhow; what’s the reason, they appear very similar to each other in other aspects with the size being the difference.

Is there any aerodynamical advantage in having the tailrotor spinning clock/anti-clockwise?

Can anyone enlighten me? :confused:

// mecheli

[CYHeli]

There's a short answer - it's weight related. Frank worked out the most weight conservative method.
And there's a longer answer which I'll let someone else give.
I believe that one of the forums already gives the answer as I believe that I have seen it before.

[Bitmonx]

At the safety course Frank answered this question. It was a while ago, so I don't know 100% exact which way it is but it has to do with the downwash of the MR producing extra airflow over the one half of the TR disc. Again, it was a long time ago......
Anybody correct me if I am wrong :)

[Graviman]

At a guess, R22 was designed and certified with top forwards pusher TR. When R44 was designed the decision was probably taken to improve TR performance using the same gearbox, so design became top backwards puller. Gearbox castings are not cheap, although in principle crownwheel could have swapped sides.

In theory top backwards pusher gives best performance, since MR downwash produces "free" TR power over climbing blade and allows unobstructed flow to wake contracted outwash. In theory also avoids any TR VRS, although i imagine you would need rediculous yaw rates to notice this.

Mart

[mecheli]

thank's for the answers guys, I guess the aerodynamical advantages of a tailrotor 'feeding' on downwash isn't big enough for Robinson to re-design the R22 to the more efficient, not that it needs a more efficient TR anyway, maybe this effect is more noticeable/needed on bigger choppers. The Hughes 300 spins the 'wrong' way around (like the R22) aswell if I'm not mistaken?

Cheers

// mecheli

[InducedDrag]

As I recall from safety school.....Frank Robinson explained that it was a weight issue.

On the 44 they had the chance to improve the T/R effectiveness. (not that the 22 is in anyway lacking)

The R44 was not as weight sensitive and allowed for the shaft to extend to the backside of the gearbox, needing additional bearing support (more weight) and it spins the other direction....

The 44 has great t/r authority. As a matter of fact, it was found to be too effective. There was an issue where a pilots foot slipped and put a full pedal displacement at cruise.... The TR blade flapped so much that there was contact with the tailboom. No major damage...just a small crease.

Frank R got wind of this and wanted to take out some of the pitch range fo the T/R. The big 44 operators and some of the engineers protested and Frank settled and only took out half of what he was going to.

[Graviman]

Interesting post, InducedDrag. So R44 is also pusher - my mistake. A crease in a Robinson tailboom generally causes the tailboom to require replacement, since it is a stressed skin. I imagine general duty TR loads would cause fatigue cracks from the stress raisers at the crease edges before compression buckling though.

Nice machine to fly (for a dumb engineer), just wish i had more cash to throw at gaining experience... :{

Mart