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Topic: Tail rotor and lateral stability< Next Oldest | Next Newest >

Group: Member
Posts: 3
Joined: May 2016
Posted: Aug. 30 2017,10:23

I'm playing HTR for the default 206 these days,I found when Increasing the thrust of the tail rotor,the copter have  a tendency to roll right. I think It's understandable since the tail rotor of 206 is higher than the c.g. but I have no idea if It's right because I dont know the accurate c.g of a 206.

Hovering the dodo 206 however,It seems that the copter is stable when I yaw left with the cyclic steady.

I just want to know HTR or dodo which one is more realistic about the lateral stability?   :)

Edited by prime_max on Aug. 30 2017,10:25

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Group: Member
Posts: 2293
Joined: Sep. 2005
Posted: Sep. 05 2017,17:55

It's not quite as simple as that. The main rotor provides a lot of circular momentum which would dampen a rolling tendency somewhat.  Plus, tail rotor shafts aren't always perpendicular to the main rotor shaft. They are often canted to offset the rolling moment.

All I can say is our test pilots and commercial pilots who use the Dodo in certified training systems say it's about right.  But every pilot always has their own personal opinion, and they all differ! :)

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Group: Certified Pilot
Posts: 3360
Joined: Jan. 2004
Posted: Sep. 07 2017,10:27

This opens up a whole world of brain hurt - but stay with me.

The roll is coupled to the opposing mass of the aircraft and cancels out into a drift to the side.

The main thing to remember is that the roll force isn't acting on a fixed point.
Consider that you are being held up by the main rotor and gravity wants to keep the CofG directly underneath that point.
The tail rotor is above the CofG but slightly below the main rotor - it is between them.

If the CofG was fixed, yes, the aircraft would roll, but it is isn't fixed, except to the main rotor, which also isn't fixed; however, the Main rotor and CofG are coupled together by being mechanically fixed to each other and by the vertical thrust v mass relationship (gravity wants to keep the mass/CofG directly under the MR by moving either or both)

Pushing sideways with the tail rotor is pushing between these two free moving but coupled points  - so everything drifts sideways, which you will see in our 206.

Gravity, for a change, is helping out.

As Simon said it is a bit more complicated than I've described but that is the broad picture.

Mark Adams     U.K.    Hovercontrol Certified Pilot

Bluebottle: Flying insect with unsavoury habits,
incapable of flying in a straight line, often lands inverted.
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