Saturday, August 13, 2011

Helicopters: Why Flybarless

Why Flybarless?

By Lood Birk

Ermelo Radio Flyers

RC helicopters has come a long way since the first production heli came on the market. Many changes has been made to the original design which was basically just a fixed pitch main rotor aircraft and did not even have throttle control or a tail rotor. The newest main change to RC helicopter, of course, is the invention of the flybarless rotor system.

Even though Igor Sikorsky invented the first helicopter, it was Arthur M. Young that invented the first remote controlled heli. He originally experimented on refining Sikorsky’s designs and to do that he had to develop a small helicopter that would react like the real thing but did not cost an arm and a leg to build and rebuild. It was also Mr Young that invented the stabilizer bar, or later called the flybar in RC helis. It’s main purpose was to counter unwanted rotor and fuselage tilt and increase overall stability. This, of course, is the main purpose of the flybar.

Using a flybar on your heli has it’s drawbacks. The biggest drawback being the amount of power it steals from the motor of the heli. A flybar can steal up to 25% of the motor’s power output. This is mainly caused by the extra drag the flybar system creates while spinning as well as the extra mechanical components that is required to make it work. For normal flight, this is all fine, but we all know everybody aspires to do the ultimate, 3D flight.

During 3D flight, you want the main rotor to get as much power as to be able to generate the extreme lift changes needed for 3D flight without dropping rotor speed or bogging the motor.

So, as you can deduct by now, a flybarless rotor is a rotor setup where the flybar has been mechanically removed. And here is where the problem starts. Because you remove the part that stabilizes the heli, you now have to compensate in another way. Being quick on the sticks is one, but I have not heard of anybody that could fly a flybarless heli without stabilization.

The idea of a flybarless system is not new. In fact, there has been pilots that has been experimenting since the early eighties and to make it sort of work all types of funny stabilizations systems were invented and tested. None of them very successful and all of them required very skilled pilots, so the flybarless system never really took off.

Enter the electronic age. During the nineties electronic gyros were rapidly developed and refined to an affordable way of stabilization. Some of the pilots saw the advantage of a small and lightweight electronic device that would replace the old mechanical stabilization systems. It is not until about 2008 that the electronic systems were developed to the extent that flybarless systems could become affordable to all. So, here we are.

Below is a picture of a heli head with a flybar.

As you can see that there are a lot of mechanical parts in the setup of a flybar rotorhead. So let us look at the picture below of a flybarless rotorhead.

As you can see there are a lot less parts in the rotor head.

So what are the advantages in flying flybarless. Well, as we discussed earlier, one of the advantages are that you will have more power to the main rotor. In short you can do harder maneuvers without bogging the motor. The other advantage is that there are a lot less parts that can be damaged during a crash. It is also a lot more stable in flight due to the gyro stabilization to the main rotor head. The other nice thing is that with flybarless you have the opportunity to ad extra main rotor blades for a better scale look.

Are there any disadvantages. Well, I would not really call them disadvantages as the flybarless system is just so much better, but you have to remember that, at this stage, flybarless systems are still pretty expensive compared to the standard choppers because you need extra electronics and a special rotor head. Furthermore it can be a finicky to set up as the flybarless controller sometimes require quite a bit of setup.

So, what do you need to go flybarless? Well, firstly you need the flybarless head. Below is a picture of a typical flybarless head that you would get.

And then you require the 3-axis gyro control box. Below is a picture of a typical 3-axis control box.

You called it a 3-axis gyro. What is it and why not just use 3 gyros. Well, it is basically a box that contains 3 gyros. These gyros controls the aileron, elevator and rudder. What makes this box different is that it has mixes programmed into processor that counters adverse movements (movements caused by the secondary effect of controls). This is not something you can easily do by building your own 3-axis “black box” with three separate gyros as the three gyros do not talk to each other.

To install a flybarless system, you typically remove the rotor head and all the mechanics above the swash plate and install the flybarless head. You then install the “black box”, which has leads to receiver and the servos plugs into the “black box”. You do the setups and fly. Oh, I have to mention that with the flybarless system, you don’t need the conventional tail gyro. The “black box” replaces that.

Well, I hope you understand the flybarless system better now. It really is an interesting development that will still have us raving about in 10 years time.

Happy landings

Helicopters: Where to fit your ESC

Where to fit your ESC.

By Lood Birk

Ermelo Radio Flyers

Ok, so the title is slightly a bit misleading. This article is going to be about where to fit your ESC in relation to your receiver. This is kind of a strange subject to talk about. Not really. Let me try to explain.

To understand why we are talking about the position relationship between your ESC and your receiver, you need to know a little bit as to how an ESC operates. The ESC does not provide a constant current to the motor. That would make the electronics of your ESC big and heavy. Instead, it pulses the motor at a very high frequency. This electronic technique is called pulse width modulation or PWM in short. The frequency in which you pulse the motor is so high that you can even hear it as that high pitch electric whine you hear from the engine. In high current ESC modules, you can even hear it on the ESC’s PC board. Now the thing is this. In any conductor that carries current, a magnetic field develops around it. That is fine, but should the current pulse, or change polarity frequently it starts do develop the ability to induce a current into a conductor close by. The more current is drawn in the conductor that is pulsing, the more voltage is induced in the conductor close by. A transformer operates in that way.

Now comes the part I generally have trouble to explain to guys in general.

Your ESC has got a lot of conductors on the PC board. The same goes for your receiver. It has got a lot of conductors on the PC Board. No imagine that most of those conductors on the PC board of the ESC is pulsing. Some of them are high current conductors like the output wires to the engine. Now imagine if you put your receiver close to that ESC what voltages are induced into the circuit of your receiver. To ram the nail home, I want to bring to your attention that on the receiving end of your receiver we are talking about voltages as low as 30uV (0.000 030V) and it is not uncommon that a voltage of 50mV (0.050V) can be induced into a conductor in our case study. Let us put it another way. It will be like trying to see when looking directly into the sun. The effects of the induced voltages are especially noticeable wit the 35MHz system as twitches and even the receiver going into failsafe. On the 2.4G systems, the effects are not as noticeable as the signal is of a digital nature with error checking and correcting protocols as part of your signal, BUT the 2.4G radio systems are NOT immune to the induced voltage effects.

I must say, though, that designers of the ESCs and receivers try their best to shield the electronics and conductors and also employ clever design techniques to counter effects of induced voltages. Yet, no electronic device is fail safe from induced interference.

So, how do we try and prevent the two devices from interfering with each other? Well, you could put the ESC in a lead box but I assure you that your plane or heli won’t go anywhere, so it’s probably not advised. The other way is to space your ESC and you receiver as far apart as possible. I know this is difficult, especially in smaller planes and choppers.

I normally space my ESC and receiver apart about 7 to 10cm. In the case of high powered ESC, I tend to make that distance a bit longer. Another little trick is to ad a ferrite ring on the lead going from your ESC to your receiver. The ring dampen any induced voltages, in the lead at least. Below is a picture of a typical ferrite ring and a ESC lead wrapped around it.

For those that are not sure where to place your ESC and receiver, below is a picture taken from a typical heli manual to help you along. Mostly on the instructions of your receiver as well as the ESC it has ideas and tips on how to space your ESC or receiver. So it’s always a good idea to check the instructions.

As you can see, they try and space the ESC and receiver far apart in any of the setup configurations. Personally, I prefer the receiver at the back away from the motor in this particular Chopper.

I hope that this article helps you to understand the interaction between the ESC and receiver and in future you know to space the two for better reliability.

Happy Landings

Helicopters: Swash plate types

Swash plate types

By Lood Birk

Ermelo Radio Flyers

When I first started flying helis, I had no idea what a swash plate is, let alone that there are many different types of swash plates. So, in this article, I would like to take a closer look at the different types there is and maybe try and lift out the pros and cons for each.

A swash plate on a helicopter has the function of converting static control input to a dynamic control input. The servos being the static part and the spinning rotor being the dynamic part of the control. In the time that helis have been around, there has been many advances in swash plate design and today there are basically six types of swash plates on the market. They are single pitch servo, 120deg forward or backward pointing, 120deg left or right pointing, 140deg, 90deg three servos and 90 deg 4 servos.

Single pitch servo swash plate

Many of us started off with the good old raptor 30 and 50. The swash plate system on the Raptor was a typical single pitch servo swash plate setup. It had one servo that solely controlled the pitch, another that controlled the elevator control and one servo that controlled the Aileron servo. Control action was a complicated interacting set of levers that made the swash plate move up/down, forward/backward and left/right. In the picture below, you can see the long lever that moves up and down to change the pitch.

The swash plate of this system has the balls spaced at 90deg intervals with the elevator balls on the sides and the aileron balls set at the front and back of the swash plate. As you can see in the picture below.

The good thing of this setup is that it was very easy to set up and no real swash mixing was required on the radio other than the throttle/pitch mixing. This system could be used with basic radios. Also there as not a lot of servo interaction where the one servo’s movement effected the other. Also, because the system worked with levers on the pitch, weaker servos could be used to control the pitch.

The bad part of this system was that due to the complicated leverage system, slop on any link was amplified so that control issues were noticed quicker. Also the extra leverage booms for the pitch made the heli heavier.

120deg forward/backward pointing

These days, this type of swash plate is the preferred system for most helis on the market. The system consists of three servos connected directly to the swash plate in a 120 deg orientation. The forward/backward pointing just indicates that one point of the swash plate’s 120deg point will be located in the center of the chopper either pointing forward, or pointing towards the back of the heli. Below is a picture of a 120deg swash plate.

In the picture above, A=B=C.

The good thing of this swash setup is that the servos are normally connected directly to the swash plate, though, there might be a simple lever system in place to increase the amount of power the servo can put on the swash plate. This decreases the chances of slop and the effect slop has on the control of the heli. Also, because your servos are directly connected to the swash, the control input becomes immediate and crisp.

The bad part about this setup is that it is not easy to set up. Special tools are required to make sure the swash is level and travels level up and down the main shaft. Servos must be of a higher torque rating than the single pitch servo swash setup. Another big problem experienced with CCPM 120deg is that servo interaction is very notable. Servo interaction happens when the change of one servos position directly impacts with the other two servos in the setup. This can happen on cheaper servos where the one servo runs faster than the other, or when setup was done wrong. In this case the heli will, for instance, veer left when pitch is given.

120deg forward/backward pointing

This swash setup is basically the same as the one found on the 120deg swash plate with forward or backward pointing. In this case though, the one point of the swash plate points to the sede of the heli and the other two points are situated on the other side of the heli. In my research for this article, I could not find any reason why this is so and I have myself never seen a swash setup like that, but I wanted you just to be aware of this swash type.

140 deg Swash.

This swash plate looks like the 120deg swash except that two corners of the triangle are closer together than to the other. Using the same picture as above you will see that C=B, but A < than C or B. Below is a picture of a typical 140deg swash plate.

This swash plate is in essence the same as the 120deg swash, which is better known as the CCPM system. It suffers the same positive and negative issues. Though, there has been discussions about the available travel being less than on the 120deg swash. Another concern is that servo loadings may become unequal due to the unequal spacing of the points on the swash plate.

90 deg 3 servo (Also known as the HE3 setup)

This is also a CCPM setup like the 120deg swash setup, but the points on the swash plate is set at 90 deg to each other. Belo is an example of such a setup.

The advantage of this swash plate is that the interaction between the servos are a bit less, but proper setup is still required for proper flight.

90 deg 4 servo (Also known as the H4 setup)

This is a derivative of the 90deg 3 servo swash and is considered as probably the best setup for helis. Below is the swash layout of this layout. The other picture is basically the same, but the 90 deg cross is just turned sideways.

This setup has been considered to probably be the best setup for helis still. The main reason is because you are using four servos in a 90 deg configuration, the force you can assert on the swash plate is so much more. This means that you can do harder maneuvers without the danger of stripping a servo.

Well, not you know more about the types of swash plates out there.

Happy Landings.

Helicopters: Radio Setup

Setting up your radio for heli flight

By Lood Birk

Ermelo Radio Flyers

There has been some questions as to go about setting up your radio so that it’s ready for hover, normal and 3d flight. In this article, I want to touch on just the radio setup. I will try not to be radio specific, but rather just touch on the basics like the pitch and throttle curves. What idleup1 means and so forth.

Setting up your heli on the radio is but one part of the entire exercise to get your heli in the air. What precedes the radio setup is the hardware setup. If the hardware setup has not been done correctly, no amount of fiddling with the transmitter is going to sort out your problems. Having said that, the reverse is also true. No amount of fiddling with the hardware will sort out a wrongly set up radio. So what are the setups that has to be done to get your heli airborne? Well, there is not really a lot to do. All you have to do is set up the swash plate type, the servo directions ,the sub trims, the swash plate travel, the pitch curves and the throttle curves. It all sounds like a mouth full, but not really all that complicated. So lets get cracking.

Before you start, make sure that all trims are centered and that there is no throttle or pitch curves programmed on the model when setting up a new model. Sometimes I reset the programming for that specific model and start all over again just to be sure.

The first step is to set the sub trims. This should actually have been part of the hardware setup, but I am going to just discuss this in short again. A chopper’s setup rests on one fundamental rule. This rule states that all controls must be at a right angle to the next. So, if you have a control rod that hooks onto a servo arm, the have to be at a right angle to each other (90deg). Now on servos, you never get the servo arm to correctly fit at a 90deg or 180deg angle to the servo, so we have to compensate for that by using the sub trim. All heli radios has got a sub trim function in the menu of the radio. Using this feature trim each of your servos so that it is at the desired angle. If you find you have to sub trim too much then rather see if you can find a servo horn that fits better.

The next step is to program in the swash plate type. Your radio should have a menu entry that lets you choose the swash plate types. Some radios the menu can only be accessed by pressing certain buttons on the radio while switching on. Currently there are one servo, 90deg, 120deg and 140deg are the most common ones. There are more, but they tend to be less common. Some radios tells you which servo will be elevator, aileron or pitch, but if it does not, consult either the heli instruction manual, or the instruction book for your radio.

Once you have selected the correct swash plate type, you have to select the servo directions. This sometimes is not easy as the swash mixing can interfere here. Especially when you are setting up a CCPM system. Let me try and see if I can easy the confusion a bit though. Let’s start with the tail servo. That is the easies to set the direction of. Firstly plug the tail servo directly into the receiver. Rotate the tail rotor till you have a blade pointing down. Now look at the leading edge of the rotor blade pointing down. If the leading edge of the blade moves to the left (seen from behind of the heli), the nose of the heli will move to the right. If the leading edge of the bottom rotor moves to the right, the nose of the heli will move to the left. So no you must set your servo direction in such a way that id you give left rudder input, the leading edge of the bottom rotor blade must move to the right and vise versa. As easy as that.

As to the gyro direction, it is just as easy. Connect the gyro into your system and make sure it is set to headlock mode. Center your rudder and move the helis nose to the left. The leading edge of the bottom rotor blade should move towards the left as well and vise versa. As simple as that. Do not forget to set your end points on the gyro.

The next step is to do your servo directions on the swash plate. The description on how to do this will vary from heli to heli, but the basics still apply. When you press the down elevator, the swash plate must tilt forward and when you pull up elevator, the swash plate must tilt backwards. I turn, if you give left aileron, the swash plate must tilt to the left and if you give right aileron the swash plate must tilt to the right. On a singe pith servo system, this is very easy to achieve, but on a CCPM system you will have to fiddle with the swash mixing as well as the servo reverse. Let us assume your CCPM system has one servo in the middle rear (call it the middle servo) and one on the 120deg left side of the swash plate (call it the left servo) and one on the 120deg right side of the servo (call it the right hand servo). The important thing you need to know is that with CCPM when you give down elevator, the middle servo moves upwards and the left and right servo moves down. When you pull back on the elevator, the left and right servos needs to move upwards and the middle servo needs to move down. When you give left aileron, the left servo moves down, the right servo moves up and the middle servo stays static. Should you move the ailerons right, the left servo moves up, the right servo moves down and the middle servo stays static. If you stick to these rules, it becomes a matter of setting your radio correctly. Not always and easy task though. So now you know which direction the swash plate must move on your corresponding stick movements and we need to change the settings on the radio so that we can get the swash plate moving in the correct direction. I suggest you use the swash mixing feature in your radio to do this. Before we do this, make sure that there is no EPA (End Point Adjustments) or trims on your radio. This will just make your life difficult. The Swash mixing is your EPA for the heli. The other thing you must remember is that your hardware setup HAS to be correct for this to turn out OK in the end. Right. You will notice that the swash mixing has three values. These are Aileron, Elevator and Pitch. You will notice that all three of them has got the same value for instance 60%. When you set these values you must keep them the same otherwise you can get unexpected swash movements which will make your life difficult whilst you fly. No say you wish to change the direction of the aileron servo, all you do is move the aileron value to -60%. This will reverse the operation. To increase the swash plate’s movement, increase the values, but be careful not to se it so much that it binds or presses somewhere when you give cyclic input.

So now you know your controls are going in the correct direction. The next thing that has to be done is the setup of the pitch and throttle curves. So, let us start with the pitch curves. In essence most radios has two settings, hover and 3D. My radio has provision for three so I normally set it up as hover, flight and 3D. I will do the flight mode as well to show you what it looks like. When setting up the pitch curves, always make sure that you work from the 50% pitch mark on your radio. At the 50% pitch mark, your rotor blade pitch has to be 0deg. The reason for this is that when you switch between flight modes and you did not set you radio and hardware to be 0 pitch at 50% input, you will get that the heli will unexpectedly climb or fall when switching modes

Let’s Start with hover. Just a quick note, the pitches I give might be different from your chopper model. Reference your chopper’s manual for the correct pitches.

In hover, you want little negative pitch to prevent the heli from slamming into the ground on landing, but enough to get you down if the wind is blowing. Mostly I use about -3 deg till about +9 deg pitch on my chopper. So the curve will look something like this…

Notice that my pitch lines always are in a straight line.

For the flight mode, I want more negative pitch because as the chopper picks up speed the rotor starts acting more like a wing and generates more lift. To be able to descend, you need more negative pitch to be able to bring the chopper down. You also want a bit more positive pitch because with practice you can do simple aerobatics in your flight mode. So the curve looks something like this …

Notice again that the lines are straight.

During 3D flight, you normally want the same amount of negative as positive pitch for that crazy upside down maneuver. So you will probably will be needing a pitch range of about -11deg to about +11deg depending on your chopper model. Thus the pitch curve looks something like this …

Notice that the 3D Pitch line is straight. No bends.

Lastly, we want to set up the throttle curves. Now the throttle curve is different to a heli with a governor that to one without. I am going to be doing the curves without the governor because you should know the principle of operation. I can tell you this though, your governor throttle curves normally runs in a straight line.

The basis to which you setup your throttle curves is to try and give you heli a constant rotor speed, so you might have to fiddle with the curves once you start flying. I am going to give you the basics though to try and help you understand the curves.

Let’s do hover first. In hover you want to have zero throttle on startup, spool it up till it’s ready for hover, but you might need that little push if you should open the throttle fully. The curve looks something like this…

This is a sample curve. You have to fine tune the engine by moving the flat part up or down to increase motor speed and tilt the flat part if you see the motor over speeding on the lower pitches but no having enough power at full throttle.

In your flight mode, you never want the throttle to close completely, so your throttle setting at 0% is going to be of such a nature that the rotor keeps its speed, but does not over speed as the chopper descends. So it will look something like this…

On your 3D throttle curve, you want your engine to produce proper thrust toward the full negative and the full positive, so your throttle setting will look like this...

As you can see, you have 100% throttle when the stick is at 0% as well as 100%. Needless to say, NEVER EVER start your chopper in this mode.

As stated before, you might have to fine tune the curves, but the basic principle stays the same.

I hope that you now understand the cyclic and rudder setup on your radio.

Happy Landings

Helicopters: Controls

Know your heli controls

By Lood Birk

Ermelo Radio Flyers

This is quite a strange article to write about and I know that most of you will probably laugh to think that I am writing an article about what happens on the heli when you give certain control inputs on the transmitter. Yet, many of the new guys that buy their first heli either don’t read the manual of the heli or they don’t understand what they read, so I still end up having to explain just what happens when you move the stick forward. A couple of years ago, I wrote something similar for a kid who lived far from “heli help” and it aided him to no end, so I decided to do this for everybody else out there.

For this article, I am going to use a standard variable pitch chopper. If you are starting with a coaxial chopper, don’t worry, the principles are exactly the same except that instead of pitch you will talk about rotor speed to make your heli rise. I am also using a mode 2 radio as example as most heli pilots flies mode two. To understand what is meant by mode, read my article on transmitter modes.

On your transmitter you will find two control sticks, also sometimes called gimbals. There is a left hand one and a right hand one. By moving each stick in either a horizontal or a vertical direction, something specific will move on your heli’s control surfaces. It is these interactions that you need to know before you attempt to fly your heli. If you don’t know them your road to flying your heli is going to be a bumpy one.

First let’s look at the different controls that is required to make a heli fly. You need cyclic, pitch and throttle and lastly rudder control. Cyclic is the control that makes your heli tilt forward and backward as well as rolling it from left to right.

Pitch and throttle control is based in two places. Throttle is either on your engine’s carburetor or the ESC in the case of an electric heli.

Pitch is the tilting of the main rotor blades to produce more or less lift as you move the stick.

Rudder control is when you move the tail of your heli left and right and is better known as yaw.

I am now going to look at them individually, starting with the cyclic. As I said the cyclic controls the forward backward and roll of the heli. Take your transmitter and look at the right hand stick. You will notice that the stick can move in a forward/backwards movement as well as a left/right movement. If you move the stick forward, you will notice the swash plate move forward and the heli’s nose will tilt down. Move the stick backwards and the swash plate moves backwards and your heli’s nose will move upwards.

Move your stick to the left. Here you will notice that the swash plate tilts to the left and the heli will roll to the left. Move the stick to the right and the swash plate will tilt right and the heli will roll to the right. Moving your cyclic does not cause the heli to climb or descend. Below is a snapshot I took from a heli manual.

Moving over to the left hand stick. This stick controls two different parts of the heli, so a bit more thought has to go into what you do there.

Let us look at the forward backward motion of the left hand stick first. The forward backward motion of the stick makes the swash plate move up (when pressed forward) and down (when pulled backwards). This will increase the pitch (stick forward) and decrease the pitch (stick backwards) of the main rotor blade. Increasing the pitch will make the heli climb and decreasing the pitch will make the heli descend. Blow is a picture I took from a heli manual as a visual reference.

Coupled with the pitch is your throttle. Now on the throttle side you do not have to worry to much, because it is directly linked to the pitch of the chopper and it will increase or decrease as you increase or decrease the pitch on the main rotor blade. It does require some fancy setup on your radio, but you don’t have to worry about it at this stage.

Lastly we look at the left/right movement of the left stick. The left/right movement does not move anything in the heli’s rotor head. Instead you have to look towards the back of the heli at the rudder. The rudder controls the yaw of the heli. Yaw is when the tail of the heli moves from side to side. When you fly, however, you DON’T look at the tail, you look at the nose of the chopper. It is just easier this way. So, if you move the left hand stick to the left, the nose of the chopper will yaw left. If you move the left hand stick to the right, the chopper’s nose will yaw right. Once again, I include the picture from my heli manual for you.

Flying your heli is an action of continuously giving input on both sticks and in all four directions per stick. You can probably see now that knowing which stick input controls what helps you to understand the control inputs necessary to keep your chopper airborne.

Happy Landings.

Friday, August 12, 2011

Pics from Sunday 7 August

Helicopters: Night Flying

Here is a challenge for all those heli pilots who think they have done it all. You'll need a couple of extra channels for those fire works at the end. And maybe keep a fire extinguisher handy if you fly a nitro... Let me know when you try this, I want to watch.

Helicopters: Forward Flight Transition

Heli Forward Flight Transition.

By Lood Birk

Ermelo Radio Flyers

I have been flying helis for some time and when I was asked how to move from a hover into forward flight I had to sit down and think about it quite deeply. You see, I have been doing that quite a bit and it has become second nature. None the less, it is a very good question. I am going to try and explain to you the type of stick movements that could expect when you transition from a hover into forward flight and vice versa.

You might think that there is nothing to it, but you are mistaking. To explain why I am going to give a very simple aerodynamic lesson. When a heli hovers, or flies, it generates a downdraft of air. For the sake of simple understanding, call it an air bubble. It is this air bubble that makes the difference when you transit between flight modes (hover and forward flight). During hover the air bubble generates lift for the chopper (keeping it very simple). Because the chopper is stationary, the lift is more or less equal on all sides of the rotor blade. To put it another way, the heli is balancing on the air bubble. When you fly, the heli is always trying to get away from the bubble and the lift forces becomes different and the heli starts reacting a bit differently. Making the move from the one to the other is called flight transition. Geesh, I make it sound so complicated, but it’s not really that bad. If you have mastered the controls on your heli, the corrective inputs normally comes quite naturally and you don’t even think about it. Coming to think about it, on a properly set up heli the inputs are quite small.

Ok, onward ho. You are hovering your heli and the mood strikes you to try some forward flight. No problem. Just push the stick forward. Right. Partly yes, but don’t forget that you are now moving away from your air bubble, so two things are going to happen. Firstly the heli’s nose will keep tilting forward as your air bubble suddenly gives more lift at the rear of your rotor than the back and it will lose height because the lift balance changed. So, as your heli starts moving forward you will give some back stick and some pitch. Now comes the fun part. As the heli speeds up the rotor becomes a like a Frisbee and start to generate lift like an aircraft wing. Because the rotor is nw generating more lift, your heli will start to climb, so you can bring back the pitch a bit to keep it at one altitude. Once you are in forward flight, your heli will more or less become balanced and you have transitioned into forward flight.

So now you are flying around and as your fuel becomes less and less you make the decision that maybe it’s time to bring your heli back into a hover and ultimately land. By this time you are shaking because you know you have to do that transition thing again. Once again, it is no real biggie. If you had the skill to move into forward flight, going back to hover should be no problem. Lets look at the procedure. Firstly you will have to slow your heli down. You do this by pulling back on the stick. Now because you are pushing your rotor disk into the wind (remember to thing of your rotor as a Frisbee) it will start to generate a lot of lift, so you will need to reduce the pitch a bit. As your heli slow down, the lift will become less and you will have to give a bit more pitch. Remember now that you are almost stationary and you will be riding on top of your air bubble now, so the chopper will tend to fall backwards on it’s tail. Here you must give it some forward cyclic to bring the heli nose down again and there you go. Nicely established in a hover again.

I just want to emphasize that it all sounds so complicated, but it’s really not all that bad. It is something you should be aware of, but if you are proficient at hovering your heli, the control inputs to counter the transitions will come naturally. So, don’t be scared.

Hope this helps a bit. (for those who asked)

Happy Landings

Helicopters: Nose-in hover

Heli Nose-in Hover

By Lood Bik

Ermelo Radio Flyers

Ahh, the age old subject of the infamous nose-in hover. I know of guys that spend a lot of time and money to get that right, but if you think about it, the principle is pretty easy. In this article I want to give you a couple of pointers to help you along.

For a heli pilot the nose hover is kind of important as it is the most difficult maneuver you will learn after the hover. It also is the last step in being able to control your heli on all four points (tail, left side, right side and nose in). In all fairness, it is not the easiest of moves to master at first, but hang in there.

Firstly, simulator, simulator, simulator. A simulator is a great place to start learning any funny maneuvers on a heli. Not to mention a whole lot cheaper. But we have to be honest and say that flying on a simulator and controlling your chopper out at the field are two different things altogether. I suggest the following to get your heli to nose hover.

Firstly you probably will not start by taking off, swinging the tail 180deg and try to nose hover the chopper. Well, you can, but I don’t advise that course of action. I suggest the following.

Make sure that you are able to hover your chopper on both sides properly. Then start to fly figure of eights and make the heli turn away from you at each turn (left and right). In the beginning have the chopper fly past you so that you fly the chopper while seeing the side. In time, make the circuit look more like an eight. Once again, in time make the chopper fly directly towards you before turning it out towards the outer side of the eight. Now comes the tricky part. Once you can fly a proper figure of eight with the heli flying directly towards you on the section where the flight path crosses, begin to fly the figure of eight slower and slower.

What must be remembered now is that the controls are now reversed. Yes. That is what makes hovering in the nose so difficult. Just remember this little tip. If the heli to the left, your instinct is going to be to move your stick to the right. Fatal. Your chopper is actually banking right, so left input needs to be given. Or easier to remember. If the heli banks left, push the stick under the side that is dipping. Almost like putting a pillar under the rotor to stop it from tilting.

If the heli’s tail starts dipping, move the stick in the same direction of the tail movement, so you will have to push forward. Like putting a pilar under the tail to stop it from dipping. And vice versa.

The tail is easy. Normally when you hover, you reference the nose to determine which direction to push the stick to counter the rotation. During nose in hover, use the tail as reference and the control input will stay the same.

One big thing that people normally forget during the first couple of nose hover attempts is the pitch. Guys, please don’t forget to control the pitch during that moment of intense concentration.

It takes a lot of practice to get it right, but it is not impossible. It just feels like it in the beginning.

Now, if things start to go pear shaped during the hover, don’t panic. Just flip the tail around 180deg and bring your heli in a stable normal hover, you might also want to open the throttle and climb to give you some time to think. It might be a good idea to land your chopper and take a breather before the next attempt. To steady the nerves so to speak. BUT, you must keep trying till you get it right.

Lastly, I would just like to add that it is advisable to try this at a fair height in the beginning(say 10 - 20feet) so that you have time to recover in case things go really pear shaped.

Happy Landings

Helicopters: How to get rid of those shakes

How to get rid of those shakes.

By Lood Birk

Ermelo Radio Flyers

RC Helicopters are probably THE most amazing piece of engineering available to the man in the street. The mechanics and aerodynamics of the heli is truly amazing and at the same time mind boggling. In this also lies the problem. The heli has so many moving parts that interact with one another that finding something as simple as a vibration or a shake can be a monstrous task. Well, my aim today is to give a rough guide at how to go about getting rid of the shakes.

Well, let us start by talking about why vibrations are present in your heli. There are three main reasons why a heli can give you the shakes. The first is quite simply that something is out of balance. The second is that something is loose and the third is that something is bent. The trick is to find the offending part or problem.

So, with all those intimidating moving parts in your heli, how do you go about finding the offending part. Well, I normally tackle the problem from big to small. Let me explain a bit better. Firstly you determine where the vibration is coming from. Once you know if it is coming from the tail rotor or the main rotor you are halfway there. Then it just becomes a matter of following a good couple of rules and you can sort out your vibration problem chop-chop.

Right-o, so let us start at the beginning and take it down in steps. Firstly, find out where the vibrations are coming from, the main rotor or the tail rotor. To do this, start up your chopper and have a look at the oscillations you find on the chopper. If it’s a slow shake with the tail mostly moving in an up/down motion, the problem most probably lies at the main rotor blade. Beware though, a badly installed motor can also give you the same symptoms as a unbalanced rotor head. Also, a too low rotor speed can also cause a slow up and down movement of the tail, so just be aware of it. If you get a high frequency vibration and is mostly from side to side, the problem most likely lies with your tail rotor assembly. So now you know in which area you are looking at to find your fault. I am now going to break this article up into two sections. One will give a breakdown of possible problems in the rotor head and the other in the tail rotor.

Main rotor

Finding vibrations on the main rotor is generally not that difficult, but it can become quite a bit of work, so be prepared to be at it for some time.

  1. Check the blade tracking. As I described in a previous article on blade tracking, a pitch difference can cause vibration.
  2. Make sure your rotor blades are balanced.
  3. Are the main rotor blades tightened equally?
  4. Also check if your rotor head (complete unit) is out of balance. To do this, you have to use a balancer like the one on the WiFly site, Extreme accuracy Prop/Rotor balancer. In essence what you do is place the entire rotor head in the balancer and see if it balances.
  5. See if anything is bent. If anything is bent, it will most probably be the feather shaft, the main shaft or fly bar. To check these two shafts properly, you will have to remove them and I normally roll them on a piece of flat glass or of you are fortunate enough to have a clock gauge, you can use that as well. Do not forget to check all the arms and levers to be straight.
  6. While you have the feather shaft out, check the damper rubbers to be in a good condition. The damper rubbers are situated inside the main rotor head housing and the feather shaft goes through it.
  7. Are the paddles from the fly bar level and at the same distance from the center of the main shaft? As a matter of interest, I have heard of professional flyers that balances their paddles, but normally the difference of the paddles are not of such a nature that it would influence a beginner or intermediate pilot. Though, might be worth the while just to check.
  8. Check if anything is loose. Check that all the nuts and bolts are fastened properly. A loose arm flopping about can also cause vibration. At the same time look for extensive slop on the ball links.
  9. Is the feathering shaft installed to tightly or to loosely? If the nuts on the ends are turned too tight, the rotor blade grips will not be able to move and vibration will occur. Too loose and the shaft will move from side to side causing vibration.
  10. Is anything binding or tight in the head? A too loose head causes slop and a too tightly assembled head will prevent the parts from moving freely as they should and that can also cause vibration.
  11. Does the main shaft move up and down?
  12. Are the bearing and bearing blocks OK and fastened well? This is something that is generally overlooked.
  13. Is the main and autorotation gear running true? It’s not wobbling or oval in shape. Yes, I have found that. Are all the teeth present on the main gear?
  14. Is your auto bearing OK? Properly lubed and working properly? It must be run freely in one direction without sticking or grinding to the main shaft.
  15. Has the motor been mounted too tightly to the main gear? If you do this, there is no room for any play between the main gear and the motor pinion and this can also be a source of vibration.

If by now, the vibration that originates from your rotor head is still there, I would suggest you disassemble the entire head and re-assemble it from scratch. When you do this, make sure you have the manual for the chopper at hand to check if all the bits and pieces are there and assembled in the correct order. Most of the decent choppers out there have got websites where you can download the manuals.

Tail rotor

The tail rotor moves about three times faster than the main rotor. For this reason diagnosing vibration problems on the tail rotor unit can be more difficult. I have had instances where there are no vibration on the tail rotor until a certain RPM and then it would shake. All I can say is keep to the list below and go over the setup again and again till you find the problem.

  1. Are the tail rotor blades balanced?
  2. Is anything bent? To check if your tail rotor shaft is bent, you have to remove it and roll it on a piece of glass.
  3. Is the tail casing loose? This and a bent tail rotor shaft are probably the most common reasons for vibration in the tail rotor assembly.
  4. Is the tail rotor shaft moving from side to side?
  5. If your heli has a belt drive, is the belt tensioned correctly? When you turn the main rotor head, is it skipping teeth on the belt?
  6. Check to make sure that the tail pitch slider and tail pitch arms are not loose or sticky.
  7. Is your tail pitch control rod properly supported? A vibrating tail pitch control rod can be the cause of vibration and normally wrongly diagnosed as a faulty part in the tail rotor assembly.
  8. Is your tail servo loose or worn?
  9. And then lastly, is your Gyro gain set too high. This is rarely the case as mostly vibrations progressive in nature.

Now for those of you that are flying glow helis out there, there is an added section that I briefly want to touch on. Having an engine turning your heli brings added problems and is sometimes very difficult to find due to the high precision needed. A clock gauge here is, I would say, a must. So if you have done all of the above and you are still struggling, look at the following that could possibly be wrong.

  1. Incorrectly installed clutch lining. This can cause shudders and vibrations that are mostly found during spool up. BUT, if your clutch is unbalanced due to incorrectly installed clutch lining, it will cause vibration even at high RPM.
  2. Worn or faulty clutch. A worn clutch normally causes imbalance due to the fact the one arm normally expands more than the other when worn, which unbalances the clutch
  3. Damaged clutch bell.
  4. Loose lock nuts. If your locking nuts are not tightened properly it will cause play in the assembly and in turn cause a vibration.
  5. Bent shafts. Not common but a very real possibility.
  6. Imbalance inside the motor. This is really not very common as the motors are normally balanced at the factory and I have not had a case like this myself, but I have read on forums that it is possible.

As you can see from the list, vibrations are in general caused by something that is imbalanced or loose. I hope that this gives you a basic guideline to sorting out your helis Parkinson’s disease.

Happy landings.

Helicopters: Gyro Setup

By Lood Birk

Ermelo Radio Flyers

Gyros have really come a long way since the first mechanical gyro till where it is today with the new MEMS gyros. Through the years, gyro setup has indeed become easier, but there is still some setup involved in the gyro.

Firstly, as with the rotor head, your tail setup has to be mechanically correct. On the tail rotor control rods, the same 90deg rule applies to the servos horns and control rods. The following bit is for those that missed my heli setup videos.

The above picture was taken from a typical heli setup manual. This picture tells you exactly how the mechanical setup should be. Have a closer look at the servo and the servo horn. As with the servos on the cyclic of your heli, you have to find a horn that is closest to 90deg while the servo is in the fully center position. Once you get a servo horn that is close to the 90deg mark, use your transmitter’s sub trim to make it fully 90deg. Beware though that if you use too much sub trim it is then better to rather reposition the horn, or get a different horn.

Once you got the mechanical setup correct, it is time to set up the tail servo direction. For this you will have to connect your servo (NOT through the gyro) directly to the receiver. Setting the servo direction is actually not so difficult. Rotate the tail rotor to the bottom of the rotation circle. Look at the tail rotor pointing down. If you give left rudder stick, the leading edge of the blade must move to the right. If the leading edge moves to the left, the servo needs to be reversed.

At this point, you are ready to mount and connect your gyro. Please pay close attention to the mounting orientation and mounting method of the gyro. This is especially so in the case of MEMS gyros. MEMS gyros are more susceptible to vibrations and electrical interference. Below is a typical picture of the mounting instructions of a gyro.

These pictures are just examples. Please consult your particular gyro’s manual.

Once the gyro has been mounted you need to connect the leads. Most gyros today are all heading lock gyros. Now heading lock gyros connection differs from normal rate mode gyros by the fact that heading lock gyros have a tail servo lead, a rudder signal lead and a gain signal lead. Rate gyros does not have a gain signal lead. The tail servo lead plugs into the tail servo. The rudder signal lead goes into the rudder channel of your radio and the gain signal lead goes into a spare channel set aside for gyro gain. That info you will have to get from your transmitter’s manual. For those that don’t know, the gain channel allows you to set the sensitivity of your gyro during flight.

There are a couple of things you have to set now. You have to set the gyro direction and the endpoints.

The gyro direction is the most important to set as the wrong direction will make your heli spin out of control. To set the direction connect your receiver and make sure the transmitter can talk to the receiver. Wait for your gyro to initialize. The direction test is easiest to do when the gain on your radio is set to 100%. Turn the rotor so that one tail rotor blade points downwards. Now move the tail to the left. The leading edge of the bottom tail rotor should move to the right. If it moves to the left, you have to reverse the gyro direction.

Next, you have to set the endpoints. I am not talking about the endpoint adjustments on the radio, but the endpoint setting done on the Gyro. The endpoints sets the limit to which the gyro will allow the servo to move as to prevent tail pitch assembly from pressing against the tail rotor hub or on the other side of the shaft where the bearing is. To do this, move your stick fully left or right and set the endpoint down till the servo stops buzzing. Most new gyros you can set the left and right endpoint. If your gyro only has a general endpoint setting, you set it till both left and right are clear.

At this point you thing you are done. But you are not. Next you have to spin up your chopper while your gyro is set to rate mode (gain set to 40% or below). The reason for this is that different main rotors will have different influences to the center position of your tail rotor. What you have to do now is see which way the tail moves when you hover. If the tail moves to the left, move the servo mount backwards a bit. And I do mean a bit. It will take a while to get it right. If you are not a good flyer, ask an experienced pilot to help as a gyro makes the heli more difficult to fly. After you got the servo position in that sweet spot, check the endpoints again.

Now it’s time to fly and check the gain on the gyro. I normally find that on about 85% gain is a good starting point. If the tail wags fast from side to side with out any input, the gain is normally too much. If the tail has difficulty stopping after control input was given, the gain has to be set up a bit. It takes a bit of time, but once done it is normally set.

I really hope this helps those who struggles with the gyro setups.

Happy Landings.

Thursday, August 11, 2011

Pics-Ryan Hards- DDRF_06 Aug 2011

> Hi Pilots,
> Saturday Afternoon at DDRF. Mark threatened to hunt me down if I didn't
> send
> these out.
> Again, not me behind the lens, but Ryan (6), I only toke one or two, see
> if
> you can spot them?
> Enjoy,
> Shaun Hards.