Hamilton Area Wireless Kontrol Society

“Ready for Autorotations”

All flights begin and end in a hover –

This article presumes that you are far enough along in flying your helicopter that you are ready to learn how to save it if the engine suddenly dies or worse, if your tail control is lost due to a faulty gyro, control rod or servo.

You may have already crashed because of a failure not under your control and were not aware that a helicopter can safely land with no power provided there is sufficient altitude. Using the simulator can let you experiment on autorotation practice and as always, its cheap insurance becoming familiar with moves before trying them on the real aircraft.

Airplanes are able to glide large distances after a power outage; however the helicopter is not so forgiving. Helicopters rely on reverse air flow through the rotor to drive the system and maintain lift. This is accomplished by adding negative pitch. If engine failure occurs and the collective is not brought down to neutral and then a negative value quickly the rotor rpm will spool down rapidly, resulting in loss of lift and cyclic control. The sooner one reacts to an engine out condition by reducing collective to a negative value the better off the rotor speed will be. This does not mean that a loss in rpm cannot be recovered if the prevailing conditions are in your favor. Altitude and air speed will all play a role in the emergency or a practiced autorotation. Altitude can be equated to an "rpm recovery insurance policy" and forward airspeed as "money in the bank". Forward airspeed inertia can be traded off immediately for a quick increase in rotor rpm through aggressive flaring of the rotor disk where as altitude will give a slower recovery time.

The rate of descent in an autorotation can vary according to the weight of the machine, rotor rpm and airspeed. A purely vertical descent will yield a rapid loss of altitude. As air speed increases this rate of descent will be reduced until a point is reached where it will start to increase.

As observed in the graphic above, the best approach is with airspeed and a controlled descent.  Let’s go though an emergency recovery autorotation first.  Let’s say you have a helicopter that for whatever reasons the engine stops in flight.  As long as you react quickly, the helicopter can be safely brought down from fairly fast and low altitudes. Don’t panic!  Drop the collective and rotate the cyclic back as safely as possible and concentrate on maintaining head speed and landing.  Do not try and stretch your landing unless altitude is in your favor.  Let’s say you are flying some circuits fairly high 300 – 400 feet back and forth, loops and rolls etc and you have a problem.  This is where practice really pays off in case you are going left to right or face in, you will be able to calmly transition from powered flight to autorotation.

A practiced art of autorotations:

To learn this valued maneuver start with doing a throttle hold 6 – 12 inches off the ground and get used to the feel of the loss of lift and adding collective to cushion the landing.  I would do these until there are NO butterflies and the landings are spot on smooth, and then take it eye level and then 12 – 15 feet.  So, 12 – 15 feet hit throttle hold and whets going to change from 6 – 12 inches; here is where some valuable training comes into play.  When you chop the throttle at 12 inches there is a lot of ground effect cushioning, plenty of head speed and not much altitude, with 15 feet, you HAVE to preserve head speed and get the helicopter down close to the ground much quicker and then apply collective in a smooth fashion, bleeding off rotor rpm as you softly land.

Now …

From the direction of landing decent that you feel the most comfortable with to start.  Take you helicopter up about 300 feet and do some practice approaches with power on or power in throttle hold if you are comfortable.  I suggest practicing the right comfortable height and distance with power on, dropping into the area you intend to land and then pulling away.  Remember; you can always go into throttle hold and then bail out by flipping the switch and going around if the auto looks bad.

Here goes the first real one …

300 feet up and 300 feet out to the left or right and the runway is clear of traffic so you can concentrate.  Turn the nose in the correct direction and as you come down on the collective hit the hold switch and keep the nose pointed slightly downward to maintain the 45 degree approach angle.  As you fly in towards the landing spot you might need to adjust the amount of negative pitch (2 – 3) and pull the nose to a close to level position.  As you adjust the attitude and collective you will hear and distinctive blade sound as the air going through the rotor maintains a safe decent speed and rpm level.  As you approach the desired landing zone you will need to start flaring the aircraft, pull back on the elevator as need to start safely slowing the forward air speed and at the same time adding enough collective to assist with the transition from forward to a hover.  Many pilots fly the helicopter to a flared stationary position and then land straight down, while others like to turn the tail towards them at the last moments of flight and set the ship down.  The second approach takes a little more practice however; it greatly reduces the chances of striking the tail blades on landing.

Practice transitions and watch other pilots as they do autorotations and soon you will have another maneuver that is not only fun to do but, may save an expensive unnecessary repair.

Be patient – have fun – ask for help :-)

Next article will talk about what helicopter may be right for you.

Ron Keith