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vortex ring / dead mans curve

Posted: Fri Jun 27, 2008 8:13 pm
by 35 green
could anyone please explain these two conditions vortex ring / dead mans curve.
thanks
SM

Posted: Sat Jun 28, 2008 8:48 am
by The WingFlinger
Vortex Ring State, or Settling With Power, can occur when a helicopter inadvertently descends into its own vortices or "downwash." This situation disrupts the pressure differential that produces lift across the rotor blades.

It occurs when the helicopter has three things occurring at the same time.

A rate of descent greater than 300 feet per minute, an eairspeed slower than effective translational lift, and the helicopter is using more than 20% of its available power.

This condition can be corrected by moving the cyclic forward, which changes the pitch angle of the rotor 'disc', pitching the nose down, and establishing forward flight. The heli will fly into "clean air", and will be able to regain lift.

The height velocity or dead mans curve, is a chart found in the manual of each different manufacturers helicopter, which shows the combination of altitude, and airspeed, which will allow a safe autorotational landing.

Attempting to carry out an autorotation outside this combination of airspeed, and altitude, presumably means you're in the Dead Man's Curve because you are probably too low to be able to build up any kinetic energy in the main rotors to flare, and cushion, for a reasonably soft landing.

I'm sure the very experienced 'high time' fliers may correct that somewhat, but it's the 'gist' of it, in a 'very' layman's terms.