What's your favorite yaw control?

[Kyrilian]

While it may be (relatively) simple to calculate the expected best case noise and performance of a given design, there are many complex factors that are better understood through experience...

Considering control, performance, noise, maintenance, weight (and whatever is important to you), what's your favorite anti-torque design (conventional, 'fenestron', NOTAR, coaxial, tandem, etc)?

[HOGE]

One that works all the time!!

[Thomas coupling]

Fan in Fin, to be fair...nistron

http://www.gograph.com/Images-7298/AnimatedGif/black_helicopter.gif

:)

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TC

[Dangrenade]

Nice one Hoge...have to agree.

[The Nr Fairy]

Having played with it the other day, and it's my only experience other than a Robbie, got to say tandem a la Chinook. Only moved my feet to spot(ish) turn the beast - sim only, of course.

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I got bored with "WhoNeedsRunways"

[Grisoni]

Fenestron is nice but it eats power at a hover like it's going out of style. Not having flown notar or coax I'd have to say tandem (as long as the SAS is working)

[whatsarunway]

out of notar conventional and fenestron which i have flown id have to go for the fenestron , didnt notice the power demand in the hover though

[Grey Area]

Notar is great until you enter autorotation when you lose the coanda effect and need to pedal like a cyclist.

Tandem is pretty good because you don't need a tail boom (but is best flying sideways!), but not very precise.

Fenestron is a good all-rounder. Not to good if you lose tail rotor control.

But I would have to plump for the good old tail rotor because it is cheap, predictable and in my experience gives you the most options if you get a control malfunction especially when varying NR to offset torque in a fail safe fixed pitch setting.

Sorry to be boring but I always think malfunctions first!

[Kyrilian]

Thanks for everyone's reply!
Unfortunately, I have no experience with unconventional yaw control devices. I've only flown 2-seat single-engine piston training helicopters (also got the chance to handle a twin turbine once :) but nothing with NOTAR, fan-in-fin, or multiple main rotors. As an engineering student I have calculated some of the benefits in terms of performance of the NOTAR, and noise considerations for the new unevenly spaced 'fenestrons'. However, I've also heard of complaints regarding yaw control (by the border patrol?) of the MD600.

I also like to consider malfunctions first, but I've got to questions (for Grey Area):
1. In a NOTAR, it would seem that as you enter an autorotation the additional countertorque provided by the Coanda effect (slot) wouldn't be necessary... things would balance out as torque necessary and torque available was reduced. Is there a large transient initially until you get into a stabilized descent or do you need to kick in a lot of (right?) pedal all the way down?

2. I guess it depends on the failure, but why is a TR failure with fan-in-fin worse than conventional TR (neglecting the benefit of not having to worry so much about FOD to the fan than a TR)? It would seem that if you lost control actuation, both would be designed to go flat pitch, at which point you've got a decent area in both cases. If things stop rotating do most fan-in-fin designs present less of a horizontal (vertical fin) area?

[212man]

I think you'll find that most fan in fin (fenestron) a/c have larger vertical stabilisor areas than conventional t/r types.

This is because the fenestron does not provide the disc effect, which contributes a large proportion of yaw stability, that the conventional t/r does in forward flight. Hence the practical size of such types being limited to the 76/Dauphin category (though I believe there was a Supe Puma demonstrator with one).

PS Thomas Coupling, is that lump under the fenestron on you picture, a Tucano absorbtion device?

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Another day in paradise

[This message has been edited by 212man (edited 17 December 2000).]

[Grey Area]

Kyrilian,

With the NOTAR system a large percentage of the anti-torque force is created by the coanda effect; the slots in the tail boom rely on a variable pitch fan in the boom; however in autorotation the coanda effect is lost due to the descent airflow so the “bucket” at the end of the tail boom is doing just about all the work. Even though there is little requirement for anti-torque one still needs to control heading, because you get less anti-torque effect per inch of pedal movement the control regime is quite different and large applications of pedal can be needed. This can be a shock to the pilot as the helicopter seems to have become much harder to control in yaw.
(Good diagram here: <A HREF="http://www.scienceweb.org/movies/speed8.jpg" TARGET="_blank">http://www.scienceweb.org/movies/speed8.jpg)</A>

I am not saying that a TR control failure with a fenestron is worse, only that the variables one can use to effect control, such as crosswind component, sideslip and especially forward speed have a much greater effect on the anti-torque generated in a normal tailrotor. A total drive failure will be a different kettle of onions!




[This message has been edited by Grey Area (edited 18 December 2000).]

[RW-1]

Me personally? I like the string :)

It tells me when I need an input if I haven't felt it thru my butt.

OTT, tail rotor, effective and I know how to keep it fed, so it doesn't go looking for things to chew while I'm flying.

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Marc



[This message has been edited by RW-1 (edited 17 December 2000).]

[whatsarunway]

grey area
having recently had a stuck pedal in an ec120 id have to say the fenestron is the best , the big fin really helps , my pedals were stuck about 1 and a half inches to the left and completed a successfull runninglanding, i dont think i could have done that in a ranger, I could be wrong though.

[Thomas coupling]

The rumour over here whatsarunway, is that your mobile phone jammed the pedals....did it???

http://www.gograph.com/Images-7298/AnimatedGif/redstar.gif

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TC

[Grey Area]

Whatsarunway,

You could well be right, I've not flown a fenestron cab for quite a while; and that was a gazelle.

[MightyGem]

Thomas, were you off flying for a few months this year after crashing you m/c?

[whatsarunway]

Mobile phone left on the back seat fell onto the floor of the cabin and proceeded foward to the front of the cockpit then fell through a gap between the perspex and floor and ended up under the floor (where i couldnt see it) jamming the control linkages