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Home > Forums > Aeronautic Engineers > Activities > Rotorcraft engineering Forum

Entry into autorotation on a helicopter with twin rotors

thread6-199396
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Intermesher (Aeronautics)
8 Oct 07 17:51
Does anyone have any information related to a non-simultaneous rotor passage through the vortex ring state?

Of specific concern is the possibility of roll in a helicopter with side-by-side rotors.


Thanks
Dave J
drozovs (Aerospace)
10 Dec 07 20:17
I have heard discussion that one of the V-22s during its testing phase suffered VRS in one of the two rotors though I have not been able to confirm this. In the event that you did suffer VRS in a tandem side by side rotorcraft the roll initiated by the event would most likely not be long in duration since the roll would initiate movement away from the column essentially pushing you into clean air.

-David
drozovs (Aerospace)
10 Dec 07 21:58
In response to my first post, you would experience roll if the rotors were side by side configuration and only one was in VRS. This is because when in VRS you are not creating lift, in fact attempting to increase angle of attack will only further aggravate the condition.
Intermesher (Aeronautics)
16 Dec 07 1:44
drozove,

Thanks for the information. The comment in your second post is the one that is of concern.

I suspect that if one rotor entered VRS the roll would happen so quickly that there would be no time to aquire sufficient airspeed to escape.

Dave
drozovs (Aerospace)
16 Dec 07 17:48
Dave,

    Its an interesting question. Essentially during VRS you are descending in a down flowing vertical column of air. Rolling and changing the angle the blade disc is interacting with that column might allow it to enter clean air. From an operational perspective, when the pilot enters VRS, the procedure is to accelerate in any direction, VRS should cease at one ~1 rotor diameter from your initial position during entry. This small distance might occur by itself once the vehicle begins its roll. Hope this helps.

Best,

David
Intermesher (Aeronautics)
16 Dec 07 18:46
David,

Thanks again for your input.

Dave
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