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Related to this question.

My instructor described an auto-rotation as:

  1. Entry. Lever down, stick back, pedal in.
  2. Fly normally, with a little tweaking of RRPM to keep it in the green, until about 50 feet above the ground.
  3. Perform a quick stop.
  4. Perform an engine failure in the hover.

I can see the logic in this but, all of the autos that I have done have been far too busy to think about it like this and all the ones I've done to the ground have been run-ons so step 4 was not an option. Without significant extra training and experience I would not even contemplate a zero-zero landing so in practice, I will probably never get to test the theory.

Is this a valid way of thinking about the manoeuvre? I'm not suggesting that anyone does anything other than what they were taught, just thinking about how these four manoeuvres roll into one.

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  • $\begingroup$ Don't forget step 0: look down. $\endgroup$
    – Tyler Durden
    Mar 4, 2015 at 18:37
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    $\begingroup$ @TylerDurden In many lights, step 0 before step 1 will kill you ;) $\endgroup$
    – Simon
    Mar 4, 2015 at 18:40
  • $\begingroup$ What will kill you is autorotating into a high tension power line pylon. $\endgroup$
    – Tyler Durden
    Mar 4, 2015 at 18:42
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    $\begingroup$ @TylerDurden If you are in a position where auto entry will put you into the line, a Darwin Award is probably in order :) $\endgroup$
    – Simon
    Mar 4, 2015 at 19:03
  • $\begingroup$ The way I like to think about it is 1) power the rotor using airspeed, 2) use power in rotor to slow down before impact. $\endgroup$
    – casey
    Jun 10, 2015 at 13:31

4 Answers 4

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First off, auto-rotation is a general term for all helicopters and the process varies between different air-crafts and the cause of the auto-rotation. For example, in auto-rotation due to loss of tail rotor thrust you can (and should) descend with some collective power and reduce descent rate. Also, in such auto-rotation there is also a mandatory step 2.5 - cut the power. Otherwise, the craft will rotate out of control in the quick stop.

Also various helicopter types behave differently while auto-rotating such as bigger helicopters start flaring at least 125 feet above ground.

As for the steps described - I'll agree that they break down nicely the process into other familiar processes, even though obviously not entirely accurate. I think the main difference is that flaring from altitude in a 1500-3000 ft/second descend and approaching a quick stop usually with speed forward rather than downward - require significantly different flight technique and practice.

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    $\begingroup$ downvoted b/c autorotation is autorotation. if you have any power in, its not an auto. $\endgroup$
    – rbp
    Jun 11, 2015 at 13:34
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    $\begingroup$ @rbp if the engines deliver no torque and the blades are being driven by the air going through them, you are actually in autorotation. Sprite's answer is valid $\endgroup$
    – Chris V
    Jun 11, 2015 at 17:07
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And you won't land in a hover with larger helicopters at maximum weight. You will have some forward speed (unless you have wind in excess of 30-40 knots on the nose).

But that sequence sounds a bit basic, but not unreasonable.

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  • $\begingroup$ downvoted b/c he never said he would "land in a hover". the flare is to use the kinetic energy of the copter's airspeed to arrest the descent of the heli, then to pull up on the collective to expend the kinetic energy in the turning blades to cushion landing. $\endgroup$
    – rbp
    Jun 11, 2015 at 13:37
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    $\begingroup$ @rbp: '4. Perform an engine failure in the hover' $\endgroup$
    – Chris V
    Jun 11, 2015 at 15:54
  • $\begingroup$ "perform an engine failure in the hover" (Task VIII A "Power Failure at a Hover" in the PTS) is a completely separate skill from "land in a hover" (Task IV A "Hovering Maneuvers: Vertical Takeoff and Landing " in the PTS) $\endgroup$
    – rbp
    Jun 11, 2015 at 16:50
  • $\begingroup$ Dude, when you land from an autorotation, you land. Whether from a hover or not. The initial question mentioned performing an engine failure in the hover right after a quickstop.I wanted to clarify that it is highly unlikely that you can come to a hover first before landing from an autorotation. Especially for large helicopters at high all-up-mass. And yes there are(/were) helicopters that can(/could) hover shortly after an autorotation $\endgroup$
    – Chris V
    Jun 11, 2015 at 16:58
  • $\begingroup$ That erroneous concept exactly demonstrates why your answer deserved a down vote $\endgroup$
    – rbp
    Jun 11, 2015 at 17:02
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The devil is in the details. Flight configuration prior to engine failure is the first element. The second major factor will be reaction time and entry. The actual auto, assuming all went well with the initial entry is relatively benign. The next key factor is what was required for you to make 'the spot'. Did you maintain airspeed and RPM? Did you flare too early, or too late? No matter, almost all is forgivable if you at least maintained enough airspeed to stop a 1500-2000fpm rate of descent with a reduction in airspeed ("flare"). The final zen moment is timing in the flare.

At the final moments of the flare, you need as near zero ground speed as possible before settling your tail into terra firma with a nose high attitude. You see...the flare eventually 'wears off' with the airspeed and the aircraft settles. The key here is to use that final rpm 'cushion' to get as near zero forward ground speed as possible while also cushioning ground contact and avoiding a tail strike. Nose forward too much and you will slide on like an olympic speed skier. If you are in a Costco parking lot and avoid the light stanchions, this might work for you. Short of that, expect a roll or substantial collision. On the other hand, If one fails to nose forward enough, then a tail strike should be expected with a subsequent violent ... over end swap that will likely ruin your otherwise perfectly good auto.

As you can see, the entire procedure gets you to this final moment where it all counts. Assuming you entered appropriately with a manageable flight profile (airspeed and altitude), your next Come to Jesus moment will be when you A) made a survivable spot, and B) executed a well timed flare, pitch pull, and attitude that minimizes ground run while preventing a tail strike. Other than that....nothin to it.

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Those are exactly the 4 phases:

  1. entry -- lower the collective to keep the RPMs up
  2. auto-rotation flight -- keep the needle at the required RPM. 90% will give you a longer glide, but the horn will be blaring
  3. flare -- use the kinetic energy in the airspeed to arrest the descent near the ground. 50 feet is pretty high. Watch some youtube videos of full-down autos in your type of copter to get a sense of the height
  4. hover auto -- just above the ground, expend the energy in the rotating blades by pulling all the way up on the collective to cushion the landing. you will need a lot of pedal here too, otherwise you will yaw
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