Back in 2002,
Blackhawk accident was NOT settling with Power thread elicited a lot of knowledgeable discussion over in Rotorheads.
Nick Lappos' contributions are well worth reading, particularly
Post #9:
Blenderpilot,
I have to agree with squirrel. You and sultan are mixing up the fundamental problem of having too little power with the other aerodynamic condition specifically related to reingestion of the downwash known as Vortex Ring State or settling with power.
What I think you are concerned about is a true issue for pilots - the behavior of the machine when you are severely performance limited. That causes most helicopter accidents that occur on landing, is especially a problem at altitude and high temperature, and has nothing at all to do with settling with power.
It is a very common mistake for pilots to lump these things together, and it is passed from instructor to student as gospel, but it is still wrong.
In the case you describe, the engine power available is very little more than the hover power required, so there is almost nothing left to maneuver. Any disturbance, or any downdraft can absorb all the extra power that you have, and you will descend. That is because you don't have the power to climb, since there is no more power left. Most landing accidents at altitude are caused by this. You are right to be concerned if it is glossed over.
However, that is NOT Vortex Ring State, and it is NOT settling with power. To get into VRS, the rotor must descend fast enough to catch up with its downwash. That speed DOES depend on the disk loading, and that rate of descent IS around 2500 feet per minute for a Black Hawk. The downwash speed of an H-60 is about 45 knots, which is about 4500 feet per minute. At about half that rate of descent, the inboard sections of the rotor are eating up wash, and not producing any down wash. No downwash, no lift. THAT is settling with power. For a Huey, with half the disk loading of a Hawk, you get the first nibbles of VRS at about 1200 fpm rate of descent.
The reason why this is important is that you can't go around teaching folks that some mysterious stuff happens to the rotor at altitude, with moderate rates of descent. You must teach them that at altitude with moderate rates of descent, if you don't have enough power, you will get painted into a corner you can't climb out of, and the earth will smite you.
If you think a downdraft can cause VRS or settling with power, you are on the wrong page! That downdraft is dangerous, I agree, if you are in a heavy helo with little excess power, but that has nothing to do with settling with power.
I can mail you some charts and pictures and stuff, or post them on the web to discuss this more fully, if you'd like.
For the non rotary peeps, Nick Lappos was then a very senior test pilot with Sikorsky, and is now a Director of Bell Helicopters' 'skunk works'.
He knows what he's talking about
