Cleveland Model Helicopter Club Autorotation Page

Autorotations

It goes without saying that once you have learnt circuits you should start to think about learning how to do autorotations as your next step forward. An autorotation is a way of bringing the model down to the ground safely and in once piece (or at least minimising any damage to it!) having had an engine failure whilst in flight. This is can be practiced by using the 'Throttle Hold' function on your transmitter to simulate an engine stopping.

Setting Up

Firstly, you must set up the throttle hold function on your transmitter to give you a suitable pitch curve. Initially you will need a pitch curve ranging from -4° to at least +10° (Fig 2). On some models you may be able to stretch the positive pitch to say, +13° (Fig 3), if this is the case you can set this extra pitch on your throttle hold function so as to give you some extra lift at the end of your auto. Once set up check that there are no noticeable pitch changes when switching from normal mode to throttle hold that may upset the model during flight.
Secondly, the throttle should be set to send the engine to a smooth idle when switch to throttle hold mode.

Fig 1: Normal Pitch Curve
(-10° to +10°)

Fig 2: Throttle Hold Pitch Curve
(-4° to +10°)

Fig 3: Ideal Throttle Hold Pitch Curve
(-4° to +13°)

Driven or Non-Driven Tail?

You need to determine whether or not your model has a driven tail or not. Most 30 size engine models are non-driven such as the Raptor 30 or Century Hawk but there are exceptions such as the Caliber 30. Models of 50 size engine or over such as the Raptor 50 & 60, JR Voyager, Fury, Vigor have a driven tail.
Having a driven tail means you will have tail control throughout the auto, whereas a non-driven tail will tend to weather cock into the wind or the direction of forward flight and rudder inputs will have no effect. With a non-driven tail the model will tend to turn due to a torque reaction as positive pitch is applied when you flair so be aware of this and if you are uncomfortable landing nose in approach from the right direction so the model will turn tail in to you!
The only other thing of note is that a drive tail saps power from the head in an auto unlike a non-driven system which is the main reason for the smaller models being non-driven.

Your First Hops

Your first steps into autos should be taken at a only a couple of feet from the ground whilst still in ground effect. Get used to activating the throttle hold switch and 'floating' the model down to the ground under no power. This will give you an initial feel for the model and also flicking the throttle hold switch on and off again. Continue to practice this increasing the height of the model up to around eye level and become comfortable with this before proceeding any further. It is also useful to learn this side on as well as tail in but not totally necessary if you are not confident at landing side on to yourself.

Your First Hops Using Throttle Hold

The 45° Approach

The next step is to become confident at taking the model up to a reasonable height and bringing it back down at a steady 45° descent and into the hover in front of yourself whilst still under power. Get yourself comfortable with this and pay particular attention to the positioning for the start of the manoeuvre so as to make the descent smooth and aim to bring the model into the hover directly in front of you. The descent should always be flown into wind as this will help when practicing the actual auto. This is a similar manoeuvre that is required for the BMFA 'B' Certificate as shown in the diagram opposite:

The 45° Descent Under Power

Aborted Autorotation

Before attempting this step make sure you are confident at turning the throttle hold switch to the on and off position. At this point it is also worth asking an experienced pilot to stand by you and talk you through it. Fly the model as before to a suitable height for your 45° descent. As you begin the descent turn on the throttle hold which will send the engine to idle and lower the collective stick to achieve a steady descent rate using negative pitch. Use the cyclic stick to maintain a very slightly nose down attitude and keep some forward momentum - this will help the airflow through the rotor disc as well as producing some transitional lift. Continue down and as the model passes through the horizon turn the throttle hold switch back off and raise the collective stick to regain power and fly the model off or bring it into the hover as before. If at any point through the descent you are not happy simply turn off throttle hold and fly the model as normal. Continue to practice this manoeuvre until you are comfortable with it as aborting an autorotation is something you will always need to how to do when practicing them.

The Full Autorotation

Once you are comfortable with all of the manoeuvres mentioned above it is time to complete your first full auto. Fly as before but as the model descends through the horizon start to apply some back cyclic to stop the forward momentum and also start to progressively apply positive pitch to arrest the descent. Aim to slow the model just above the ground and then gently touch down as you level the model out so as not to let the tail touch the ground first. Try not to apply too much positive collective too soon as you will use up unnecessary blade energy too high and this may result in a heavy landing and possible boom strike.
It is worth noting that once the model passes below the horizon it will be too low to abort the descent by turning throttle hold off again and you must commit yourself to landing the model under no power.

After successfully completing the autorotation it's just a case of 'practice makes perfect' and you will quickly get a feel for the model and it's characteristics. After each flight as the tank is getting empty try a couple of autorotations and you will soon get more confident at them and then when the inevitable happens you should be able to pick the model up in one piece with a big smile rather than in pieces with a grimace!!

Now, onwards to inverted aerobatic autos...........