Bill Galbraith wrote:
You don't 'enter auto-rotation' just because you lose power. I haven't flown or looked at this model at all, but in a helicopter with irreverisble controls, if you shut off all power, yes, you are going to lose control, because there is nothing to move the swashplates, the control surfaces per sea. If the hydraulic system isn't modeled correctly, and power to the swashplates depends only on the engiens running, then turning off engines loses hydraulic pressure, and thus control. So, don't look at how the actual aircraft is designed to see what the proper response is in the simulation. You have to look at the simulation to see if that particular malfunction is modeled correctly.
Autorotation is more a maneuver than a state. Losing engines in forward flight, as the air flows through the blades, aerodynamic drag causes the blades to spin, which creates some lift. In a hover, the first thing upon engine loss is to push the nose over and gain airspeed, and thus lift. That's why "low and slow" (hover near the ground) is so dangerous. If you lose an engine, you can't recover and get into an autorotation.
In an auto-rotation, you regulating the lift produced by controlling the rotor speed. Pulling up on the collective, you decrease your rate of descent, but you also slow ther rotors down, and therefore decrease your lift and increase your sink rate. As you approach the ground, you pull up on the collective which produces more lift, thereby cushioning the landing. You have to pull collective at the right time. Too soon, and you've bleed all the speed from the rotors and you are still off the ground. Too late, and you hit the ground too hard.
I heard it described once as "An autorotation is something to keep the pilot
busy while he is crashing".
Bill obviously knows a lot more about this than me, but let me add ...
I've seen people practice autorotations in R/C helicopters. I don't know how that scales to full size helicopters but in R/C land, if the autorotation is flown carefully it can be done very safely with a gentle touch down. As you "fall", you configure the collective so the rushing air spins your rotor. At just the right time (relative to hitting the groud) you increase the collective, the momentum of the rotors carry through a bit, and you can generate all the lift you need for a gentle touch down. You just have to time it right and you don't get any second chances. But it's the sort of thing that when done right, you never feel your life or airframe is in any kind of danger (especially if you are watching from the ground.) :-)
Curt.
-- Curtis Olson http://www.flightgear.org/~curt HumanFIRST Program http://www.humanfirst.umn.edu/ FlightGear Project http://www.flightgear.org Unique text: 2f585eeea02e2c79d7b1d8c4963bae2d
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