Just what is an autorotation? When the instructor rolls off the throttle, it’s either it’s the biggest presolo adrenaline rush or the most harrowing 8 seconds of sheer terror you've ever experienced! What is this thing that causes so much excitement among the rotor crowd? Very simply, autorotation is what you have when the rotor blades are being turned by the relative wind instead of engine power. 

Just like our fixed wing counterparts, rotorheads talk about relative wind, angle of attack, and chordline when describing how one stays in the air.   But we also get to play with inflow and rotational relative wind.  Inflow is that volume of air pushed down by the rotor while producing lift and rotational relative wind is that airflow that is parallel and opposite the rotor’s plane of rotation (perpendicular to the blades leading edge) which generates lift. Want more on helicopter aerodynamics? This article should do the trick.

Suffice it to say that in flight under engine power, air flows down through the rotorblades. In autorotation, the air flows up through the blades. Lift is still generated, but because inflow is up instead of down, the relative wind vector is very different in autorotation than normal flight, still resulting in lift throughout a large enough portion of the rotor disc to facilitate a controlled glide.

So why do we do 'em? For a number of reasons. My instructor used to tell me “because they are so much fun”. Yeah, right, weirdo! An autorotation is a great way to get to ground as quickly as possible. Smell smoke? Passenger looking seriously green?  Autorotate! You can be flaring and touching down within 5 minutes from 9000 ft AGL.

To perform a safe descent and landing after engine failure is the real reason we develop autorotation proficiency. So your engine stops? Contrary to popular belief, the helicopter doesn’t just fall out of the sky.  We may not have the glide ratio of a Cessna 172, but it really isn't too bad - the Robinson R44 is about 4.7 to 1. OK so it is not much better than a rock, but consider this; we need a much smaller spot to park in than our buddy in the Skyhawk!  We may not be able to glide as far, but we get a whole lot more choices in terms of places to set down.

The autorotation is an excellent energy management demonstration maneuver. There are three energy parameters controlled by the pilot - altitude, airspeed and rotor rpm. Remove altitude from the scenario (it IS an auto after all!) and you work airspeed and rotor rpm. Airspeed is controlled by pitch attitude and rpm is controlled by collective. While maintaining one, the pilot can change the other and see how it affects the helicopter's glide. Autorotative descent from altitude is an excellent way for the student become more comfortable with the aircraft’s performance, so the next time you’re down at pattern altitude doing autos and the ground is coming up at you faster than fast, you’ve already been there and done that! No sweat.

So how do you that voodoo that you do so well? There are 4 basic steps to an autorotation – entry, glide, flare, and touchdown (or power recovcery). 

Whether you are entering an auto because you have had an engine failure, or are practicing – GET THE COLLECTIVE DOWN IMMEDIATELY!  If you want to maintain energy in the rotors, the blades have got to go to flat pitch as soon as possible. How fast rotor energy becomes depleted depends on the aircraft.  The Robinson R22 has a light inertia rotor system, and the blades can stall within seconds of power loss.  Oh, and by the way, if the blades stall THERE IS NO RECOVERY.  They fail and the ship WILL fall like a bad rock.  Doesn't matter if it is an R22 or a Huey, if the blades stall, the insurance company owns the chopper and your Maker owns you.

 Let’s assume you’re planning to put one on the numbers.  You always want to plan the auto with the final glide and flare into the wind.  Enter the auto at the same altitude and airspeed every time. By keeping things as close to identical as possible, you only have to adjust your entry point to effect whatever changes you have in mind. Enter the auto and immediately establish that airspeed and rotor rpm as prescribed in your POH.

Once you have entered the auto, you adjust the glide by manipulating airspeed and/or rotor rpm, depending on how you need to adjust your glide. There are combinations of airspeed and rotor rpm that will give you desired autorotative parameters, like maximum glide or minimun rate of descent. Those numbers are given in the POH and should be committed to memory. 

Prior to flare, return to the airspeed and rotor rpm for “normal autorotative glide”.  Yes, there is such a thing. The aircraft is flared about 40 feet AGL. It’s all happening so fast-how to gauge 40 feet? Got trees? 40 feet is about the height when you are no longer looking down at the tree tops! Or at the airport, it’s when you’re about even with the roofs of most aircraft hangars.  You have the flare down when you feel the energy leave the aircraft.

After flare, pitch forward to level flight.  If it is a full down auto, pull the collective to arrest your descent in the final few feet.  In the R44 you should be able to touch down just as soft as if it were a normal landing.  It takes practice to pull collective at just the right rate, so you don't pull too fast and baloon up or hit hard due to pulling too slow.  If it is a power recovery, with a piston, you can roll on throttle and recover skids level about 6” above the runway.  I can't tell you definitively when to roll on throttle in a turbine (that may vary with aircraft and engine). The only autorotations I have done in a turbine (Bell 206) have been touch downs – and there was plenty of energy at the bottom to make a soft touchdown with collective to spare.

There are a lot of variables out there when doing autos; not entering the same way each time, wind variables, air temp, humidity, just a whole host of variables– some of which you don't even have any control over. This is why no matter how many hundreds of autos you do, no two are exactly alike. You can do 6 or 7 during a lesson and you will touch hard on some, soft on others, and rarely in exactly the same spot. Especially in the lighter inertia rotor systems like the R22. I guess that’s what keeps them “fun”…

I remember one flight in particular. I did my best autorotation up to that point; it was on my commercial checkride. It was a 180 degree auto, and upon entry everything fell into place, needing very little adjustment on the way down. I rolled out on final with a couple of hundred feet and recovered with power right over the designated spot.  Whooopee! Just a little while later on the CFI portion of that checkride, a full touchdown auto was required. I did everything identical and up until touchdown, everything looked just like the one I did earlier. I could not have been happier, right up until the audible,“Tick, scraaAAAPE”. Yeah, I’d touched the tail, and on a checkride; “you scrape the tail, you fail.” Within a half hour, I had done my best auto ever and my worst!  Yet wouldn’t you know that even though I scraped the tail,that was still the smoothest auto I’d ever had in an R22. Figures.

A few months later, I was prepping a student for his commercial checkride.  We were doing autorotations to power recovery at the bottom.  He was having a good lesson and all was going well. He enters the auto, and it is a smooth ride all the way down and into the flare.  But then he rolls on throttle and...nothing. Nothing happens! Suddenly always being ready for just such a possiblity became much more than academic. From that moment on and all the way through to the touchdown, everything happened in super slow motion.  We simply turned it into a full down auto. Landing accomplished, we sat there through about 5 seconds of silence before we looked at each other and simultaneously went, “whoaooooooo”.

And he goes  “what happened?” with the widest eyes I ever did see. What happened? Exactly nothing, to be precise. The engine didn't come back to life on cue. I was told that would happen once or twice to any instructor, but life is not fair: it happened to me within my first few hours giving dual!  So, instructors, be ready for anything at the bottom. Every time.

Want a peek into another one of my lessons? I was flying with another commercial student. We were doing 180 degree autos and he got low and slow. SO what does he do? Starts lifting collective?!? Oh, no, no- that just droops the rotors, robbing you of all your energy! The stall horn comes on (yes, we have one, too) and here we sit, looking at a whole lotta trees getting closer, reaching up to snag us.  No, this one is not gonna work.  So I just rolled on throttle and we went back and talked about it. That woulda been really ugly! If the auto is so bad that it could get dangerous, just break it off and go around. Never turn your simulated emergency into a real one.

Autorotations can be fun – I guess one's mental attitude towards them makes all the difference. If you understand what is happening and why (go up to altitude and play with airspeed and rpm for a while), the fear factor will drop.  If you understand that there are no two autos alike (but you can make them real similar) and keep the aircraft within prescribed parameters, you can get real good at them.  And if you practice them regularly, you'll be your instructor's new best friend by your next BFR!

All you fixed wing pilots, go take a couple of helicopter lessons. Be sure to learn how to hover and experience some autorotations. You'll be surprised how quickly you find yourself hooked! Rotorheads, keep at it. Practice regularily and enjoy the ride...