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Learning to Fly - Autorotations

Auto's are one of the most satisfying model helicopter manoeuvers. Especially once you've started to extend them, fly 180's or even do inverted tricks.

Simple Rules
Break it down into 4 simple stages; entry, glide, flair, landing
Always practise into wind, with the landing never being downwind
The flair can take a third of your inertia, so slide it if needs be (emergency downwind)

Keep the glide gentle, -2 to +2 can be more than enough if the elevator's right

Introduction
The worst thing simulators do is autorotations, they just aren't real enough. I think a 30 is great for learning auto's, but first check what size blades are on it, and how much the model weighs all up. Also what weight is each blade (grams). I was lucky, my first auto was a forced emergency one, the high speed fuel mixture needle unscrewed in flight causing the engine to stop, luckly the forced auto was a peach, and I felt real pleased with myself. That made me go out and try some more . . . it's real easy when you get into it.

The Shuttle ZXX, 55cm blades, 100g blades, all up approx 3kg - autos brilliantly - for a 30. On a windy day there's bags of reserve, but on a zero wind day there isn't much left at the end if you judge it wrong. But then that's 30's for you. Lighter or shorter blades have a tremendous effect on auto performance. 110 grams blades make it much better, but then they slow the aerobatics so it's always a compromise. So make sure you learn on a day with a good steady head wind, and it goes without saying you must fly into that headwind, never do an auto downwind unless you have to.

Another usefull thing is to have a wet patch of grass to land on, that way you don't have to stop the model moving forwards, provided you land level and not to fast - you can slide it in. You still gently let the heli transfer its weight onto the ground, but many an auto that may fail can be saved this way, but only on wet grass and at medium to low speed. Now there are a few things which will surprise you about autos: 1. You can do them with about +2 degrees pitch all the way till landing, 2. You can come down much more slowly than you think, almost hovering on a windy day, 3. The elevator control has a tremendous effect on head speed and therefore the required collective pitch setting - generally holding a bit of forward elevator during the auto descent is a very good thing as the more forward speed the heli has (within reason) the more energey is being loaded into the rotor disc .

There are two kinds of energy: the first and most important is the speed you've managed to get into the blades, number two is the forward momentum of the helicopter, downward momentum is not good, but forward is very benficial. Now for your attempt the pitch should be about -2 to -4, not too much, not to little, your best setting the neg, then just using the elevator to keep the nose down and the model moving forward. To enter the auto, fly along medium speed, then lower the collective to -2 to -4 then hit hold, do not lower the collective abruptly, it must be done smoothly and gently or it can rob you a few hundred rpm. In auto your blades may only do 1100 to 1400 rpm, and there comes a point where too much negative slows them down. On the way down be smooth on the controls, no sudden movement.

Now there is not a point where you change from -3 to +5, there is just one long smooth gradual transition. Also the collective comes last, the elevator is used first, to slow the forward speed, but it also causes the models descent to slow and can even gain you height.

At about 15 to 25 foot, you start gently pulling the elevator back to slow forward speed, when the model is tiltled back about 30 to 50 degrees off horizantal that is enough, then you can gently add collective if the descent is too fast. Hopefully this will continue until close to the ground when if all was done and adjusted well the model is 3 foot off the ground, tail down 30 degrees and the forward speed below walking pace.

At this point you level the heli with forward elevator, and use the collective to cushion the landing/slow the descent. The collective is important here, your not using it to land the model, you just keep feeding it in to gradually slow the models descent during that 3 foot, typically the collective might be at +3 and is then increased to +8 at which points she lands. A real peach of a landing is where the weight of the helicopter seems to be gently transferred to the ground - if you've watched Curtis you know what I mean.

Easy way to practise without using Throttle Hold
Now you first attempts can be done nicely with the aid of a modified throttle curve. I don't know what radio you have, but if you can setup a flight mode as in the picture graph it would be usefull. The collective is going from -7ish to +12ish, learn where on the tranny -3/4 is, learn to find it by pretending to fly at home, and checking the pitch of the blade, ideally all you pitch curves should have -3, 0, +5 in the same place. But that's another story. The throttle should be low from 0%bottam stick to 50%mid stick, perhaps going from 15/20% up to 20/25%, then it climbs dramatically from mid stick to top of box. The idea here is, forgetting the throttle hold switch, fly the model around just leaving it in this flight mode, so above half stick the model feels much as before, but when you come below half stick you can simulate a good auto, all the way down to the 3ft hover above the ground, but can still easily feed the power back in so the the auto stops at the 3ft hover point. Here your getting to practise the collective and elevator positions, and where in the sky to start the moneuver so it lands close to you. If the auto is going off just increase the throttle stick and fly round again. You do not want the clutch to disengae at the lowest throttle setting here - and you want normal collective/trottle relationship above 4 degree pitch, but then having maybe a ltittle more pitch on top, just in case the engine goes for real.

Once comfortable, you'll still use the above flight mode, but will also set up the throttle hold switch to give strong idle which may actually still turn the tail feathers, once you get better you can reduce this so the clutch disengages properly, but to start with a bit of extra engine speed and an engaged clutch can help. For the real one, you fly into it as above, reduce collective to -3 slowly, hit hold, then if all is going well and its positioned nicely you fly it down to the 3ft hover and land. If it goes wrong keep on the sticks as if you were doing the full auto, but take throttle hold off, and continue down to the 3ft, then gently increase the collective so as to hover at 3ft then flyoff - and you can go round for another try ;-)

The problems with abandoning an auto is the trottle may have actually cut, so by following the attempt through to the 3ft hover if the motor has really cut things won't be so bad, but if your at the 25ft stage, and you turn off throttle hold and bring the motor back is with an aggreessive addition of cyclic/throttle, then if the engine had cut, you've lost any chance of a safe landing.

Simulator's can help
If you can set your simulator up to do an auto in the way I have described then it will be an excellent guide as to how you feed in back elevator to slow descent and reduce forward speed, that's the big secret, the collective is obvious, but a safe auto may actually look like the green throttle curve on the graph, with an intially steep descent which gets shallower as the elevator is fed in until it actually flys horiazantaly with the ground for a bit. When your good that horizantal flight along the ground can go for 60 to 90 foot!!!

You can also slow the blades at altidude till they look like there stopping, then feed in -8 very gradually with forward elevator to start them up again. The heavier the baldes the more hieight you need to start them, we were getting 3 stops in one descent.

Now go learn the above bits, and good luck with your first auto's.

 

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