“Lower the lever or things are going to get interesting” – An introduction to Auto-Rotations
“Lower the lever or things are going to get interesting” - An introduction to Auto-Rotations
Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, rather than engine power driving the rotor. In layman’s terms other words, gliding!
The classic is, when in conversation with a non-flyer they often say “The problem with helicopters is when the engine stops, they just fall out of the sky!” My usual reply is ‘they don’t if you do the right thing i.e. lower the lever, they then glide and not just forward, we can even glide sideways or backwards!’
The basics of an autorotation can be explained using principles of flight. Air strikes the rotor blade from below is known as the induced flow, strikes the blade in such a manner that it pushes the blade round (much like the wind hitting a sail of a boat at the correct angle drives the sail and boat forward). There’s obviously more to it than that but you get gist.
Over 23 years ago, when I was first taught how to auto-rotate, my instructor explained its nothing to worry about as its part of the normal flight envelope of a helicopter. This helped put me at ease and I still use the same words today with my students.
A basic autorotation is relatively simple. Just enter into a descent (Power Attitude Trim) but instead of only lowering the collective lever enough to create a standard 500 fpm (feet per minute) ROD (rate of descent), you keep lowering it until the engine is no longer powering the rotors round, instead, the autorotative force being created is driving the rotors round. That’s it really. An advanced autorotation however has a little more to it (more of that later).
Before entering into auto-rotation there’s a bit of house keeping to be done namely a HASELL check:
HEIGHT Is it suitable to perform an autorotation and recover by 500’ agl (above ground level) to keep things safe and legal. Don’t forget you are probably flying around on the QNH so you need to take the ground elevation into consideration and subtract that off your current altitude reading i.e. if you are at 2000’ QNH AMSL (above mean sea level) you need to subtract the ground elevation say 300’ then subtract 500’ agl then subtract approx. 200’ for the recovery and you are left with approx. 1000’ of height to use for autorotation. Bearing in mind a helicopter usually comes down at a rate of 1750 fpm you have approx. 40 seconds of useful autorotative time so 2000’ should be a minimum to start with.
AREA Is it a suitable area to perform this manoeuvre away from any built up area and not too close to any airfields etc with a suitable landing site should anything not quite go to plan.
SECURITY Is everything secure in the cockpit, seatbelts, charts, kneeboards, doors etc.
ENGINE Are all the warning lights out? Are the temperatures and pressures in the green? What about carb heat? If you are in the R66 heater needs to be off otherwise the engine is likely to flame out and you’ll be doing your first real engine off landing!
LOOKOUT All around and below for other traffic.
LOCATION If you are responsible for the navigation, it’s worth making a note of where you are as its easier to orientate yourself at altitude.
Once completed, your instructor will say something along the lines of “Practice autorotation go!” and then down you go 😉 If you are performing an advanced autorotation then you may be altering the airspeed, NR (rotor rpm) and direction in order to achieve a suitable landing site before recovering to the climb again.
Eventually, you’ll be using your basic and advanced autorotative techniques to simulate an engine failure almost in your sleep and become confident in your ability to safely ‘glide’ your helicopter down to a suitable landing spot.
If you would like to learn more about auto-rotation or feel like you need a refresher before your next self fly hire please give us a call.
