Wednesday, March 12, 2008

Lessons : Autorotations

Here I got Flying Lesson From, i'm sure this lesson will help you Guys.....

Lesson objectives:
1. Autorotation setup
2. Mini Autos
3. Full autos
4. Points to remember

Autorotations are yet another one of those skills that you know you should learn, but seem to put off through fear of crashing while practising. I know this was true for me. I learned nose in, fast forward flight, stall turns, loops, rolls even became fairly skilled at inverted before deciding that it really was time to learn autorotations for real.
Ironically though, when I had to auto either by mechanical problems or running out of gas (don't ask), I was able to land the heli successfully.
I knew I was kidding myself if I thought of myself as a competent flier if I couldn't auto properly, so it was time to fire up the 46 for another one of it's 'sacrificial lamb' sessions.

Do as I say, not as I do
One day I'd had a great days flying doing all sorts of inverted stuff and decided to give this auto thing a go. I brought the machine to a 3 ft hover and flicked the switch and the little Ergo settled down with a bit of a bounce. Tried a couple more of these then took it to about 7 or 8 ft with a little bit of forward speed and tried the same thing. The first two were mildly ok. The next one had too much forward speed that resulted in a boom strike and a tumble on the ground. Another boom, feathering spindle and a set of blades later and I was back in action.
A couple of weeks later and I decide it's time to attack autos again. So what do I do? Yet again I try some forward flight ones from about 8 or 10 feet which results in the boomstrike to end all boom strikes. I knew what I'd done wrong as soon as I did it. I was in too much of a hurry to get the machine on the ground and didn't have anywhere near enough positive pitch on at the bottom of the auto, plus I had a bit of back elevator on to arrest the forward motion. That combined with too much headspeed meant the blades came down and smacked the boom so hard that the blades were torn off at the root!
What was I doing wrong? A number of things, I wasn't high enough to start with, I panicked when I flicked the switch, I didn't have enough pitch on when I landed and I had some back elevator on. This is not the way to do autos.

You'll need to ensure that you have the correct ptich range in throttle hold mode on your radio. My helis are set up with -7 through to +10 pitch range in throttle hold. There are many different opinions about suitable hold pitch curves, but this is what works for me.
If you've got a driven tail (ie the tail rotor continues to rotate when the engine is off either via a slipper clutch or split gear mechanism), then you'll still continue to have rudder control during the auto, if your heli has a non-driven tail, you won't. When you're learning, it's not a bad idea to have the engine idling high enough so that the tail rotor is still slightly driven. This will mean that you've got a degree of yaw control as the machine is in the auto.
Ensure that your blades are securely fastened in your blade grips. Not too tight that it will cause vibration though. Curtis Youngblood recommends that they're tight enough that if you hold the helicopter on it's side, the blades will not move in the grips. If you have the blades too loose and an auto has gone wrong and you've lost a lot of head speed, there's a higher chance of having a boom strike when you hit the ground than if you've got tight blades.

Make sure the engine will light back up again!
The last thing you want to happen is for the engine to die when you've flicked the switch to abort a bad auto. What I do to check this on both helicopters is fly them around for a couple of minutes to get the engines up to operating temperature then land and let them idle for about 10 seconds, then quickly stab the collective and make sure they spark up without any hesitation. Be careful how you do this. For a hi-torque machine like the Z230 or high powered 60, stabbing the collective like this on the ground could cause the machine to suddenly rotate slightly so be ready for it.
If your engine doesn't immediately respond (ie it bogs and dies, or even hesitates), then tune it properly before trying an auto.

Mini Autos
Now it's time to get used to the feel of your machine under zero power situations. I recommend flying around for a bit first to get your engine up to operating temperature, then bring your machine into a low hover at about 3 feet. Get yourself comfortable and when you're ready, flip the hold switch and let the machine settle to the ground adding collective as it does so.
If the helicopter 'jumps' or 'dives' when you flip the switch, your hold pitch curve needs a bit of refinement. Ideally, you want the helicopter to smoothly settle to the ground.
Once you're used to the feel of flipping the switch and letting the heli settle to the ground, it's time to move on!

Practice your approaches
It's time now to start getting a feel of how the helicopter reacts in a unpowered descent. The idea of this exercise is to feel comfortable at the beginning of the auto so you don't panic and get used to managing the pitch on the way down so you don't lose headspeed and keep the helicopter on the intended flight path.
Fly the machine up to about 80 to 100 feet at about a 45 degree angle downwind to a spot in front of you where you wish to land. While in slow forward flight coming towards yourself, flip the hold switch and smoothly reduce collective to about -2 degrees. Try and ensure that the heli is still retaining some forward speed. You don't really want it to come straight down.
Manage your elevator and aileron controls so that the machine maintains it's flight path to the spot you picked out in front of you. As the helicopter gets to around 8 feet, begin smoothly flaring the helicopter and try to arrest it's descent, as soon as the helicopter has 'stabilised' and stopped descending, abort the auto by flicking the hold switch. Continue this exercise until you can bring the helicopter down while retaining good headspeed and maintaining control of the flight path of the helicopter.

Heading hold
If the flight mode you were in when you started the auto is programmed with heading hold and you do not have a driven tail, you might be in for a bit of a surprise when you abort if the head speed has decayed considerably. You see during the auto, the gyro may still be in heading hold and could be putting in rudder control to compensate for any yaw movement that may have occured. Because the tail rotor is not driven, the tail will not be moving as much as the gyro expected it to and so it will put in even more rudder input. It can get to the stage where the rudder might be at full lock. Now, when you restore power in an aborted auto, there's a good chance you're at full stick on the collective which ofcourse means full throttle. This means the drive train goes from no power to full power in an instant. Your rotors will spin up and so will your tail rotor, which is still at full lock. This can result in a pretty exciting piroette (or three) that you didn't expect. To avoid this, enter the auto in a flight mode that is programmed with normal gyro mode, or abort your auto before your head speed decays too much.

Full blown autos
By now, you should be ready to do a complete autorotation. They really are easier than you think. Begin in the same way you did with your approach practices. Remember to always auto into wind if possible! Manage the descent just as you did previously. You want to begin flaring the heli and slowlyg applying pitch as it gets to about 5 feet off the ground to arrest it's forward speed. As the forward speed dies off, and the helicopter is at about 2 to 3 feet off the ground start applying some forward elevator to level the helicopter off and continue apply pitch, continue to hold in forward elevator to prevent a boom strike.

1. Always auto into wind (if you can!).

2. DO NOT panic when you hit the hold switch.

3. DO NOT panic when the helicopter gets near the ground.

4. Be smooth on the controls, sudden, jerky movements will sap precious energy from the rotor disk.

5. If you're losing too much headspeed and you're above 4 or 5 feet, abort the auto by hitting the hold switch.

6. If you're losing too much headspeed and you're below 3 or 4 feet, go to full pitch, hold in some forward elevator and ride it out. Don't try and bail out by hitting the hold switch again. By the time the engine has spooled the drive train up enough to get any lift, there's a good chance that the helicopter has already touched down on the ground. If the landing has been a bad one, any damage will be instantly amplified by the sudden increase in power, ie what may have been a small boom strike will probably turn into a 'scorpion tail' boom-bending, blade smashing mess. Don't ask how I know this. Also, remember how we discussed what happens if you're in heading hold? Well throw in one of those nasty full power piroettes and things aren't looking good. Believe me, if you just ride it out, you'll probably get away with a popped off link or maybe a bent spindle shaft if at all.

Autos really are much easier than you might think. As soon as I did my first couple it clicked and instead of being scared to auto, I really enjoyed it and started to concentrate on landing accurately. I believe it's easier to land smoothly doing an auto than it is to land smoothly under power.
Autos is one of the few skills that will actually save your money. One day, you are going to have a flame out, or blow a plug or run out of fuel (it happens!) and the sky will go silent. Only your ability to auto is going to prevent your wallet from taking a hammering.

Once you get a feel for autos, you'll find they're really enjoyable!

Soon after writing this article I was out and about with the little Ergo. Flew about six or seven tanks. On the last tank of the day, I was doing a full speed roll at about 80-90 feet. As the heli rolled inverted the engine quit. I managed to roll it upright (you could just about count the blades as they slowly rotated!) and just decked the collective as much as I could to spin them back up again. I held out till the last minute then pushed in full collective at about 3 feet. The heli thumped down damn hard, but there was no damage whatsoever. If I hadn't been able to auto, this crash would have cost me upwards of NZ$300 or so. Learn to auto, it WILL save you cash.

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