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R/C Helicopters – Blade Pitch Setup In-Depth

July 13, 2010 Leave a comment

Setting up the pitch curve on your helicopter is one of the most crucial parts of setup.

First of all, lets define ‘pitch’. Pitch describes the angular movement of the rotor blades in relation to the horizontal plane. For example, when the angle of the blades is upward, the blades are described as having ‘positive pitch’. Likewise, when the angle of the blades is downward, the blades are described as having ‘negative pitch’.

Rotor Blade in Positive Pitch

Rotor Blade in Positive Pitch

Rotor Blade in Negative Pitch

Rotor Blade in Negative Pitch

Setting up the pitch curve

Once you have read this article, read the tutorial on Helicopter Setup then the tutorial on Radio Setup.

Setting up the pitch curve on your helicopter is one of the most crucial parts of setup. What is a pitch curve you ask? OK…

First up, I’m no aerospace engineer, so I’m not going to give you the physics behind everything. I’m gonna give you the story from my point of view.

First of all, lets define ‘pitch’. Pitch describes the angular movement of the rotor blades in relation to the horizontal plane. For example, when the angle of the blades is upward, the blades are described as having ‘positive pitch’. Likewise, when the angle of the blades is downward, the blades are described as having ‘negative pitch’.

The amount of pitch is measured in degrees above or below the horizontal plane. A normal pitch range for many helicopters is about 22 degrees in total, that’s positive and negative pitch combined.

When the rotor blades get more positive pitch, the helicopter will ascend (climb), likewise, the more negative pitch, the faster it will descend (fall). Unless of course it’s upside down, but we’ll get to that later :).

Now, back to the pitch curve situation. The amount of pitch on the blades is dictated by the position of the collective stick on your transmitter. If your transmitter didn’t have pitch curve point adjustment, you’d have a pitch curve that looks like this:

The graph on the left illustrates a ‘linear’ pitch curve. This means that moving the collective stick along will represent an equal change in the amount of pitch on the blades.

If it weren’t for the provision of pitch curve point adjustment, the amount of change of pitch in the rotor blades would be linear. Meaning that movement of the collective stick would yield equal movement of the pitch on the rotor blades. In some cases, this is fine, but what about if you want to set up different modes of flying? A pitch curve that enables you to hover nicely is probably not going to let you do inverted flying very well. For this you need to be able to adjust your pitch curves.

Most good radios have points on their pitch curves that can be adjustable. The cheaper radios have about three points, good radios have five, while the top-of-the-line radios can have about thirteen. The more points that are adjustable on your radio, the more you will be able to tune your pitch curve.

Most radios also have multiple flight modes. This means, at the flick of a switch, you can change the flight characteristics (pitch curve, throttle curve etc) of your helicopter. So for each flight mode, you can set up different pitch curves that suit different types of flying, hovering, fast forward flight, inverted etc. Flight modes are often called ‘Idle Ups’. Not sure why! Some radios have one idle up mode, others have two, some more advanced can have even more.

You need to set your helicopter’s pitch curves up as well. Make sure you use a pitch gauge to set up your curves. Doing it by eye is just useless.

Linear Pitch Curve

The graph illustrates a 'linear' pitch curve. This means that moving the collective stick along will represent an equal change in the amount of pitch on the blades.

I’ll come back to this later to show you in more detail the type of curves you can create and in what situations they are typically used. For now, that’s it! 🙂

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R/C Helicopters – Blade Tracking In-Depth

June 15, 2010 Leave a comment

Hi all,

It’s been a while since my last post, as i had a well deserved holidays period. Now back on track, i will try to recover the time and keep coming to you all with the best and most accurate information i can provide.

This time, i will focus on how to correctly execute the blade tracking setup on a heli. This could be described in just a few lines of text, but i want to fully cover this subject, as this is a key setup action to ensure your heli will be stable and smooth. This is also forgotten or ignored by many practitioners, either by lack of knowledge or by improperly doing it, leading to many flight difficulties that are usually related with incorrect blade tracking and, as a consequence, a very unstable heli.

RC helicopter blade tracking has been a mystery to many new RC helicopter owners, but I’m going to demystify the whole concept for you right now so that you’ll have a complete understanding of blade tracking by the time you finish reading this post.

First, we need to answer this important question: What is blade tracking?

Essentially, blade tracking is when one rotor blade rotates in a circular motion and the following blade follows exactly behind it. Both rotor blades spin on the same plane without one blade being higher or lower than the blade it’s following. Another way to look at it is that both blades travel through the same airspace created by their spinning. If the rear blade is following the front blade on a higher or lower plane, then it can cause a lot of unwanted vibrations for the RC helicopter.

How To Track Your Blades

If you’re flying your RC helicopter for the first time, you need to see if the blades are tracking properly and you may need some help from an experienced RC helicopter pilot. You can check the blade tracking by simply hovering the helicopter in place at eye level and looking at the blades as it hovers. If you see a lot of shaking and vibrating, your RC helicopter is more than likely not tracking properly. If you’re not sure if it’s tracking properly, here are a few simple steps to check it:

  1. get two different colors of tape and apply a small strip of one color to one blade. Put a red strip on one blade and a blue strip on the other blade. By using a different color on each blade, it makes it a lot easier to see which blade might be out of track.
  2. Now that you’ve applied the colored tape, have an experienced RC helicopter pilot hover the helicopter in place so that you can see the blades as they spin. As you watch the blades spin, you’ll know if they’re in track if you only see a single circle or both blades spinning on one line. If you see two circles or two lines, (red above blue or vice versa) then you’ll know that one of the blades is off and needs to be aligned.

Blade Tracking
Blade Tracking

You should always make sure that your blades are balanced before you look at the tracking, as unbalanced blades will effect how they track. I will come back to this subject (blade balancing) in a different post later).

To properly track your rotor blades, you need to land the hovering RC helicopter first. After the blades have stopped spinning, you can adjust the blade that is out of alignment. You’ll need to have your RC helicopter manual handy so that you can look up the proper blade tracking information in it. Be sure that you adjust the correct linkages in what the manual says and not what someone says. This is the best way to be sure that you’ve done it correctly. Usually it involves lengthening the linkage to the blade grip of the rotor that was spinning lower, by removing the ball links and unscrewing them one turn at a time until the tracking is dead on.

If you need to unscrew one blade grip linkage by more than a couple of turns, you might want to tighten the other by a turn or two and alternate until the tracking is perfect.

Once you’ve tightened or loosened the correct linkage or linkages, you need to have someone fly the helicopter again so that you can look at the blades. You’ll repeat this process as often as needed until your blades are tracked properly and they spin on the same plane. Once you’ve completed proper blade tracking, your RC helicopter will handle a lot smoother than it did before and be much easier to fly.

Remember to always use the blade that you did not use to set the pitch with. If you did not use a pitch gauge or do not remember which blade it was, then it depends on how you want to affect the head speed. If you want more head speed, lower the high blade, if you want less head speed, raise the low blade. If you want to maintain the head speed, you have to raise the low blade and lower the high blade by the same amount.

One thing you might want to keep in mind, is that anytime you remove the main rotor blades, you’ll want to keep note of which one goes where to avoid having to readjust the tracking in the future. Also, every time you replace the main rotors, you should check the tracking. I keep a small roll of red tracking tape with me, so I can check the tracking anytime I’m at the field.

Getting Started on RC Helicopters – Part 6 (Learning to fly)

May 10, 2010 Leave a comment

In this (very long) post, i will go through the several stages of learning to pilot a RC helicopter. I can tell you it will not happen without practice and time, so keep your anxiety controlled. But, if you follow these guidelines, you should be able to progress in your skills and soon will be flying like Tareq Al Saadi!

Level 1 – The hover

This first step into flying model helis is probably the hardest part to learn, mainly because you have to do it yourself. Of course an instructor can hover your model and show you the basic controls, he will make it look very easy but at least you know that if he can do it, the model must be okay. On your first attempt at hovering you might wonder what you have got yourself into as it seems almost impossible, don’t worry, its like riding a bike and once you can hover there is no going back.

You will need to fit a training under carriage, there are two types, crossed sticks with balls on the end or crossed sticks with a standard hula-hoop attached, either type is okay and they are usually fitted using cable ties.

Whatever radio you use make sure you have the best gyro you can afford as this will make control of the tail a lot easier. If you can get your hands on a good simulator it will help considerably, and at around £100 if you have a PC, it will be money well spent.

Try to choose a day with little or no wind and make sure you keep the model pointing into wind as this will help to keep the tail straight, all you are trying to do at this stage is to keep the model hovering on the spot at about 1 to 6 inches (25mm to 150mm) high, if it gets any higher, lower the throttle, land and try again. Just keep practising for as long as it takes, it will probably take several visits to the flying field to perfect the tail in hover.

So you can hover tail in and land fairly smoothly. Do not remove your training under carriage; it will still be useful for the next step, which is hovering side on. You can do this by hovering diagonally and gradually turning the model side on as you progress, make sure you practise on both sides of the model, it is very easy to get handed and once you have got the habit of hovering only your favoured side it is hard to get out of.

All the above will take many hours of practise to perfect so take your time and don’t remove your training under carriage until you feel you are ready to do so, you may want to move directly on to learning the nose in hover while you have it on, or you can leave nose in hovering until you can fly circuits when you can gradually fly the model towards yourself until you can stop and hover, which way you do this is up to you as I have seen it done both ways.

Remember, the most important things you will need to become an RC Heli pilot are patience and determination.

Level 2 – First Circuits

Before we get into the flying, set your lower pitch to about minus 2 degrees with 5 to 6 degrees in the hover position and 8 to 9 degrees at the top. It is also useful to set up the radio so that the throttle trim gives you tick over in the middle, idle up at the top and engine cut at the bottom. You should be able to achieve this using the travel adjustment (not the throttle curve) on the transmitter, if not you will have to adjust the throttle servo arm as required. You should now fly the model with the throttle trim at the high position; this will keep the engine revs up when in negative pitch there-by giving more control. As with learning the hover it is a good idea at this stage to get an experienced pilot to fly the model and adjust the trims as required, this will make it much easier for you.

Start with the model tail in, facing into wind, at a height that you are happy with, then hover over to your left side, back to the middle and then to the right side, keep practising this with the tail in then gradually turn the tail to follow the direction of the model and without stopping in the middle. The turns are initiated by applying lateral cyclic (aileron) to produce a bank, together with tail rotor (rudder) to make the tail follow the turn. The amount of aileron and rudder applied will vary according to the forward speed of the model and whether you are turning upwind or downwind. With practise this will eventually become a figure eight with the turns at both ends away from you and at the same height all the way round.

Do not be tempted to fly the model in a circuit around yourself; this is bad practise as most flying sites will not permit you to do this, so all flying should be in front of the pilot and anyway, you will not learn much from this as the model is in the same situation relative to you, all the way around.

Some pilots find the transition from forward flight to the hover quite difficult and avoid this manoeuvre by stopping the model at height and lowering the model vertically to land. This looks very untidy and if you are ever going to fly in a scale like manor you will have to approach at 45 degrees, you will also need to be able to do this to learn autorotations.

To return the model to hover from forward flight reduce power and apply back cyclic, adjust the amount of each control to achieve a 45 degree approach. Ideally the approach should be into wind but make sure you practise from the left and right to avoid getting handed.

As you gain confidence with flying circuits try to gradually make them higher and faster. The height will be useful later when you attempt new manoeuvres, giving you more time to correct a mistake before the ground comes up! Also don’t be afraid to fly on a windy day, I have seen many pilots build up a fear of the wind and you can’t let the weather stop you flying, particularly if you live in the UK.

Remember, the only way to learn is stick time and lots of it.

Level 3 – Autorotation

There are many pilots who advance to quite a high level of flying yet never bother to learn autorotations (autos), a comment often heard is “why stop an engine that is going perfectly well”, fair comment I suppose but what if your engine cuts, chances are you will panic and crash the model. So there is one good reason to learn autos, the other reason being the shear satisfaction of landing your model time after time with no engine power. I having gone through many stages of learning to fly but I found the autorotation the most rewarding of all.

During autorotation the negative pitch will control the glide angle of decent, this will be about minus 3 degrees but will vary according to wind conditions, blades, and forward speed during the auto. I always set my negative pitch to about minus 5 degrees and then adjust the pitch with the stick to get the ideal decent angle.

Before you start, you will need to set your throttle hold switch so that it gives a reliable engine tick over when operated. If your tail is driven during autos you should set the tail blades with no pitch when the hold switch is operated, as there is no torque from the rotor head during autorotation the tail does not need any counter acting pitch. You must be able to perform a 45 degree approach and landing before any attempt at autos. Also make sure you are familiar with the throttle hold switch position on the transmitter, you will need to find it quickly while practising.

To give you an idea of how much power is in the rotor head with no engine power, from the ground, raise the throttle until the model is light on the skids, switch to throttle hold and gently add pitch, the model will hover for a short time.

Start by flying your normal circuits at a safe height, when flying into wind hit the hold switch and apply negative pitch, the forward motion of the model should keep the tail straight, if the tail kicks to the left or right return the hold switch to normal and land the model, adjust the tail trim and try again. Once you are happy with the tail trim keep practising autorotation descents but only down to a height that will give you time to abort (return the hold switch to normal). After hours of practise you will be able to descend at 45 degrees, apply back cyclic to flair (stop the forward speed) and add pitch to land. The difficult part is the timing of all this, if you add to much pitch to early (to high) you will use up the inertia in the rotor head and will not have enough to land. If you add pitch to late the result is obvious.

Autorotations are easier with a 60 size model due to the extra blade power but wither it’s a 60 or 30 size model, the type and weight of the blades will have a major effect on auto performance, use glass/carbon blades like SAB or TG for best performance.

Keep practicing, but remember – it is supposed to be fun!

Level 4 – Setup for Aerobatics

Most transmitters will have three flight modes available via the flight mode switch (sometimes called the idle up switch), this will give you three pitch and throttle curves, one for normal hovering, one for aerobatics like loops and rolls, and the third one can be set for more extreme 3D type flying.

Throttle Curve 1 - Normal

Throttle Curve 1 - Normal

Throrrle Curve 2 - Stunt 1

Throrrle Curve 2 - Stunt 1

Throrrle Curve 3 - Stunt 2

Throrrle Curve 3 - Stunt 2

During aerobatic manoeuvres negative pitch is used during the inverted sections so the throttle curve is set so that it will not drop below 50%, while you have full pitch control. These high throttle curves should only be switched in when flying and not before take off as the engine will over rev in this situation.

Pitch Curve 1 - Normal

Pitch Curve 1 - Normal

Pitch Curve 2 - Stunt 1

Pitch Curve 2 - Stunt 1

Pitch Curve 3 - Stunt 2

Pitch Curve 3 - Stunt 2

The main difference in pitch curves will be in the negative section where up to minus 8% may be used for inverted flight, where as for the hovering mode minus 1 or 2% will be ideal. It is also useful, in the hovering mode, to flatten out the curve at the centre point to make the model less sensitive.

Revolution Mixing

This is available on most transmitters and is quite simply a mixer, which adds pitch to rudder to correct tail swing on adding power. However it is not always easy to set up and if you have one of the latest piezo gyros with heading hold, you probably wont need it.

Cyclic to Throttle Mixing

Some transmitters have dedicated mixers for aileron to throttle and elevator to throttle but you can use any free mixers, try about 20% throttle to start with and if possible only on flight mode 3 for more extreme manoeuvres. Be aware that if your throttle is already flat out, the mix will try to add more throttle and could overdrive the servo, some transmitters (like the JR PCM10) take account of this and therefore will not overdrive the servo.

So your model is now set up for aerobatics!

Rotor Head & Vibration

The main enemy in any model heli is vibration; this can be split into two types; high frequency and low frequency.

High frequency vibration usually stems from the engine, fan or clutch area and cannot easily be seen until cracks appear in the side frames or servos and other radio parts start to fail. All you can do is balance fan and clutch and all should be okay.

Low frequency vibration stems from the rotor head and normally shows as vibration of the tail boom and sometimes on the landing gear. Blade tracking is the first thing to check. Stick a strip of tape to the end of each blade, a different colour each end is required, as you bring the head speed up and looking at one side of the rotor disc you will be able to see if one of the blades is higher than the other (out of track) the different colour tape will tell you which one is high or low so it can be raised or lowered by adjusting the pitch control link.

The blades that came with your heli are probably wooden and will need balancing, how to do this is normally explained in the manual, however, I would try to use quality carbon/glass blades, I know they are more expensive but they do come ready balanced and their performance is far beyond that of wooden blades. I have used SAB, TG and NHP blades and have never had a set out of balance. I have not used any other make so I can’t comment.

Other sources of vibration can be the flybar, paddles and feathering spindle. Damper rubbers should be lubricated with silicone grease when fitting and the flybar must be centered with paddles of equal weight.

If your model has been crashed then the main shaft, feathering spindle and sometimes the tail rotor shaft will probably be bent and must be replaced. The feathering spindle can sometimes be straightened but for how much it costs it’s just not worth it. The main shaft must always be replaced as it could be weakened if straightened.

The rotor head speed on a model heli can vary from 1100 rpm to 2000 rpm at the extremes. Generally speaking the higher head speeds help stability, but things will wear more quickly, on the other hand if your head speed is to low the model will be unstable and sometimes the nose will nod up and down. The manufacturer should be able to tell you the maximum head speed permitted but good quality blades are recommended at higher head speeds. In my experience head speeds tend to vary from club to club as everyone sets up their model to sound like other models in the club, resulting in every member having a similar head speed wither its high or low. I run my Raptor 30 at about 1450 rpm in the hover, 1650 rpm in flight mode one, and 1800 in 3D mode.

So run a head speed no higher than you need to and don’t fly with any vibration and your model should perform well for a many hours.

Scale Helicopters

After several years flying model helis I was getting a little bored with throwing it around the sky at great speed and wanted something different. So scale was the way to go with so many skills required it was bound to be interesting.

There are three main ways into scale helis :

1.Buy a complete kit, which includes all scale parts as well as the mechanics. (i.e.Hirobo Lama or JR Ergo Robinson R22).

2. Buy a pod and boom model, which is also designed for use in scale fuselages (i.e. Vario or Graupner/Heim).

3.Buy a fuselage and fit your chosen heli into it.

Option 1 is the simpler and cheaper one although there will be less choice of models. Option 3 will require a higher degree of design and skill to build. Option 2 is I think the best option as once you have the pod and boom model you can fly it for some time to test and get used to it before putting it into a fuselage also there are plenty of scale fuselages to choose from.

Your choice of subject for scale might be your local police helicopter or a military helicopter or maybe one that you have seen on film, like the Airwolf, or it could be one that you just like the shape of. Whatever you choose remember that a full fuselage will always restrict access to the mechanics where as models like the Robinson R22 or Hughes 300 will be more accessible. This may not be a problem to you, but worth bearing in mind.

Three, four and five blade rotor heads can be fitted for more realism though they are expensive and have different flying characteristics to the standard two blade and flybar.

Also available from Vario are models like the EC 135, which has an enclosed (Fenestron) type tail rotor and the Notar which has no tail rotor but uses vectored air instead.

Flying a scale model is quite challenging and requires a great deal of accuracy to make it look realistic. Smooth hovering, slow climb outs and circuits, and nice 45 degree approaches are all part of scale flying. I prefer a model which flies well and looks realistic in the air rather than one which is accurate in every detail but is not flown due to the pilot being afraid of a possible crash, maybe the pilot lacks the confidence or has spent to long on all that detail!

RC Helicopters – Getting Started (Part 4)

We’re back to this series of posts related with helicopters and most of the beginners questions. So, i’ll continue to go through some of the common issues people have.

When adjusting the blade tracking, which blade do I adjust?

Use the blade that you did not use to set the pitch with. If you did not use a pitch gauge or do not remember which blade it was, then it depends on how you want to affect the head speed. If you want more head speed, lower the high blade, if you want less head speed, raise the low blade. If you want to maintain the head speed, you have to raise the low blade and lower the high blade by the same amount.