The Autorotation (or auto for short)

10 hole instrument panel on N7086L. Taken over Virginia. July 2015
10 hole instrument panel on N7086L. Taken over Virginia on my trip from Florida to New Hampshire.
July 2015

 

“Laconia traffic, helicopter 7086 Lima is high final for runway 26, Laconia”. The all too familiar radio call that has now become instinct. I can see most of Winnipesaukee from here with boats scrambling across the lake. Weekenders trying to squeeze in their last few days of summer weather before pulling the boats out of the water. 70 knots, 1,300 feet. Fast and very high for already being over the runway threshold but I need all the altitude I can get. From the left seat I hear the inevitable “3,2,1, engine failure” I know it is just practice, but my heart starts to race every time. I drop the collective pitch all the way, apply right anti-torque pedal, roll of the throttle to remove the engine power, and pull back on the stick. Pit in stomach, we are falling like a rock. Heart beats faster. A warm blast of exhaust wafts through where the doors normally are, but in the 85 degree heat, we would rather have the breeze. The smell of burnt 100 low-lead coming through the vents brings me back to when I used to go to the airport diner in Lawrence as a kid to watch the planes and helicopters take off and hope that one day, I could fly one. Many years later, here I am. Dropping at a thousand feet per minute. “Airspeed, RPM, eyes outside, airspeed, RPM, eyes outside”. The ground continues to come up faster and faster, even with the vents open, it feels hotter than before. A bead of sweat runs down my forehead as I have to fight my own instinct with every bit of strength I have to not stop the descent until my heart is jumping out of my chest. 40 feet above the tarmac, flare kills descent, rpm spikes, pull collective to prevent overspeeding the rotor, roll in throttle to catch it at 20 feet. Skids touch the ground perfectly. An autorotation is a sketchy, potentially lifesaving skill that feels like eternity crammed into about 45 seconds. 

From the day I had my first ride in a helicopter, I always wondered what would happen if the motor stopped. By the time I started flight school, I knew exactly what would happen, and it scared the hell out of me. Many people will think about an engine failure in an aircraft with the idea that a plane would be safer in that situation than a helicopter. I’m here to tell you that after becoming licensed then doing hundreds of emergency procedures, I would rather be in the helicopter than the plane.

autorotation 4

You may be wondering “Well what happens when you lose an engine in a helicopter, don’t you just fall out of the sky?”. The answer is yes but no. A helicopter flies by forcing air down through the rotor system (generally speaking, but I’ll explain why that isn’t necessarily true another time). In the event that an engine fails, the blades are no longer able to force air down through them. Without the ability to do this, the helicopter begins to descend. Now air begins to move up through the rotor system but in order to take advantage of this, the pilot must remove the pitch from the blades to prevent them from slowing down. As this air moves faster and faster through the rotors, they begin to spin faster. To make sure they they don’t do what is called an overspeed, the pilot must pull pitch back in to slow them down. This pitch on the blades, being what gives the helicopter lift in the first place, slows the descent. This balance must be maintained all the way to the ground in order to land safely (unless it is practice. Practice autorotations normally terminate by the pilot bringing engine power back in so that there isn’t impact with the ground). There is, however another thing to worry about, airspeed. A pilot can manipulate the path of an autorotation in order to land in different places if he/she has to ex. to avoid landing in water, trees, or wetlands. The most common manipulation is making large, banked turns. These provide a tremendous amount of energy to the rotor system and allow the pilot to hit a spot much closer to where the engine failure occurred, rather than stretching it out in a straight line. Airspeed is a critical component of the auto. When a pilot has established a good balance in rotor rpm (revolutions per minute) and descent rate, they must control how fast they are moving forwards. This adds a third component to the mix that must be watched all the way to the ground. If airspeed gets too low, the helicopter falls too fast, if airspeed is too high, the landing will involve sliding along the ground a.k.a. a run-on. Once the helicopter is roughly forty feet above the ground, a flare is initiated by pulling back on the cyclic control. This slows the helicopter down. While still moving forward, the pilot continues to descend slightly. At about six to ten feet, a final flare is initiated to stop forward momentum and slow the decent. As this happens, the last of the rotor system’s energy is used up by increasing pitch to cushion the landing.

 

 

This may sound very complicated but, to any pilot with a license, it needs to be instinctual. Once someone has enough experience with these, they can make engine-out landings almost anywhere there is room. And trust me, there is a reason that a helicopter can land on a space the size of a picnic bench while a plane needs a runway.

For more information about the controls and parts of the helicopter in the simplest way I’ve seen it put, here is an excerpt from the book Thing Explainer By Randall Munroe.

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image source:http://www.ilmuterbang.com/images/stories/Teori/Pengetahuanumum/autorotation%204.jpg

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