How To Trim Your Heli

So you can perform nose-in hover, execute a roll, and loop the loop, but is it all neat and tidy? John Parker takes us back to basics…

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Almost the start of the new season, so now’s the time to start learning those new moves. How do you consider your own style of flying? Maybe you’re a sportsman, who just enjoys gliding around the sky throwing the occasional aerobatic manoeuvre in now and again – on the other hand, you might be the more ambitious type, i.e. an aspiring 3D hot-dog pilot. Whatever, we’re still in the early stages of teaching you manoeuvres, and so our tutorials should cater for all.

In the last two issues, we’ve covered the actual technical performance of loops and rolls in some depth. This time, I’d like to take the time out to discuss what is expected of both the helicopter and pilot. This is a very important part of the process, and the reasons why shall become clearer below.

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Good Sport

About two-and-a-half years ago, I would have classed myself as a typical sports flier, with loops, rolls, nose-in hover and the odd hairy auto in my bag of tricks – but not much else. Still, I thought I was an okay flier, and the last thing I thought I would ever have to do was go back over the basics of model heli flying, i.e. the building blocks that make up manoeuvres, again.

One weekend, I decided to give some FAI manoeuvres a go at an organised AHA (Aerobatic Helicopter Association) event. To me, the hovering manoeuvres look straightforward enough – and I’ve been flying for several years now, so I could not see too many problems with that. Nevertheless, I soon discovered it’s not straightforward at all; we’re talking about a highly disciplined style of flying which requires a lot of concentration. In the end, after just a couple of months of AHA competition flying, I could feel that the FAI style was not for me.

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However, this experience did make me realise that, in order to make real progress, I would need to structure my practice. In truth, those competitions had shown that large parts of the basic skills needed for a high standard of  flying were missing – despite my experience, I hadn’t been able to perform what looked like a bunch of simple manoeuvres.

Okay, let’s be honest here: practice can get a little boring, even for the keenest of fliers. But, if you want to achieve a better level of control over you helicopter, you’re going to have to force yourself to fly with a higher degree of precision, To that end, I promise you, concentration on those most basics of manoeuvres will pay dividends. Remember, this is a foundation stone for good, controlled 3D.

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Two years ago, then, I found it almost impossible to hover side-on at head height over one spot for any length of time, even though I’d mastered nose-in hover long before. I’m not saying you should go and burn 20 tanks of fuel learning side-on precision hovering, but do think about the benefits of higher skill levels in this area, and give it some time in your schedule.

You can start by flying some very smooth circuits at head height, and at walking pace. (N.B: As you do this, think about the amount of stick movement you’re applying with the transmitter). Start the flight with a side-on take-off, and finish with a side-on landing, right in front of you. Next, take this on to some figure-of-eights – you know you can perform these at your faster flying speed, but bring the pace down to a controlled and steady rate. It’s a lot harder than it looks, eh? The better you perform these manoeuvres, the easier it looks on the eye, so stick with it.

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How well your helicopter is trimmed for flight will become more evident with precision hovering. Incidentally, how should you trim your model? Personally, I like to mechanically calibrate the helicopter rather than use the transmitter buttons during initial flights with a new machine – adjusting the lengths of your control rods will do this. Hover the helicopter in a very steady fashion, right in front of you; notice what corrections you’re applying to maintain the status quo. I face my helicopter into wind when I’m trimming, which can mean it’s either nose or side-on to me at the time.

In the perfect world, we would only need to trim the model to account for aerodynamic forces that act against it due to its design. Most radio controlled helicopters will have a tendency to lean to one side in the hover; normally, you would only trim this out with some opposite aileron. However, when down at my local field, I often find myself attempting to trim out a machine for someone who does not realise their inability to do it themselves is down to the model having poor balance. Yes, the latter is a factor in the whole trimming process.

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With a half tank of fuel (to represent an average weight) and the canopy on ready to fly, take hold of the main blade grips and rotate your helicopter, so that the main shaft is horizontal. I would imagine that a lot of you now have a helicopter that’s pointing at the ground. Ideally, your model should be free to swing on the main shaft axis, and able to balance horizontal to your body.

If you can imagine a nose-heavy helicopter, you would need to trim this out with back-cyclic (otherwise known as back-elevator). “What’s the problem with using electronic or mechanical trim to correct that?” I hear you ask. Well, we need to know which type of flying you’re after. For general hovering and a scale-style performance, there is nothing wrong in having an out-of-balance helicopter; in actual fact, it can make some scale models look more realistic, since you achieve the correct fuselage attitude. However, with a basic aerobatic set-up on a nose-heavy machine that’s been trimmed in the hover, things will change when you go inverted. Suddenly, that back-trim you applied to make it steady when upright will have turned into forward-trim – now, not only are you nose-heavy, you’re also finding yourself coping with a higher workload in order to maintain inverted hover or flight.

Hopefully, you now realise that your helicopter can unwittingly work against you, and how important it is to try and stop it from doing so. Balancing your helicopter may require the removal of items such as the battery, receiver or gyro – I’ve even seen top pilots fixing a lead weight to the tail in order to achieve a more perfect balance.

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Taking Stick

There are to two distinct routes that you can follow with helicopter flying. First we have the sports style, which lends itself to FAI; this generally requires your helicopter to be set-up with an emphasis on positive pitch management, and you’ll need plenty of collective stick. Then there is 3D, with equal amounts of emphasis on upright and inverted flight, meaning that you are ultimately aiming for a mirror effect with the collective controls, i.e. zero degrees of blade pitch at middle stick.

With either type of set-up, you can still perform a lot of aerobatic manoeuvres. Just remember that the sports route will give you more positive collective control, whereas 3D takes some of that away, moving it to the negative side of the set-up for an equal amount of positive and negative stick.

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Problem and Cure

So, where advancing into aerobatics is concerned, we have now talked about a lot of issues that the experienced pilot probably takes for granted. With bad advice or the lack of good information, it can be very difficult to identify exactly what the potential problems are, and indeed how to cure them. It only takes the application of one or two modifications to radically change the behaviour of your model, changing it from a basic, easy handling trainer to a fast reacting 3D animal. For instance, this could be achieved by replacing the flybar paddles for lighter ones, and refitting some light carbon main blades; even the adjustment of mixing ratios on the head will change the way your heli feels. You need to decide which set-up works for you.

Having read the above, you should be thinking about your own set-up, and any problems you have. With a well-balanced and correctly trimmed helicopter, learning becomes a lot easier. Don’t blame your model for shortcomings – it CAN be trimmed, whereupon the key to success becomes your own flying skills.

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Finally, remember to monitor exactly what your fingers are doing when you fly, because I find that most people learning aerobatics tend to over-correct the control movements. Think of a perfectly performed manoeuvre – let’s say, for example, a hovering backwards circuit, i.e. slow and at head height. The pilot would need to correct with only very slight, but almost anticipated, movements. Personally, I think this is the key to high-class flying.

Think about your style, and step back a few paces to consolidate those basics. Set your helicopter up so that it’s more user friendly, and try not to over control, because your machine should work a lot better once it’s been trimmed.

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