by Chris Berardi
three steps to setting up your helicopter
This article is a work in progress. The graphics, and final additions should be posted in approximately 2 weeks. Down load this article, try it, and let me know if I am on the money. Please stay with me while the additions are made. I apologize for not completing this sooner.
Often, I am asked if helicopters are any harder to fly than aircraft. Initially, my response was always a firm yes, but in retrospect, the answer is not so concrete. A helicopter does demand a certain hand to eye coordination, but no more than say, feeding yourself, or shifting from park to drive with your foot on the brake. In my experience, the obstacle is not a lack of physical talent, but a lack of skill in preparing the helicopter for flight.
In most circumstances, the kit is purchased and built without the assistance of an experienced modeler. The first hurdle is to build the kit correctly. This is a challenge because there are several issues that are not discussed in any manual that I have read; for example, the removal of the preservative lubricant from fasteners before they are bonded to a nut with thread locking compound. The next hurdle encountered is the mechanical setup of the helicopter, which is then followed by the radio programming. And finally, after all that work, the terrified novice has to fly his handy craft not knowing what or how he is supposed to trim it. Every step is a hurdle, each of which is higher and subtler than the last.
What I have presented here, is a "method" of preparing a helicopter for its first flight. This method is reproducible from model to model and consistent in its result: A basic setup that guarantees success.
What is this method? Well firstly, it is totally different from a fixed wing aircraft. Most aircraft will fly if they have at least some of the following: 1) enough power 2) reasonable CG 3) free and correct controls 4) charged batteries. We have all seen them briefly fly with less than three of the above four. You could say that flying a fixed wing aircraft is 90% pilot and 10% machine.
On the other hand, the complex helicopter has a propensity to separate itself into its elements. It is unable to tolerate poor mechanical integrity due to the stresses imposed by its rotating parts. Therefore, my observations (and unscheduled empirical testing) conclude without exaggeration, that learning to hover is 90% machine and 10% pilot.
Most people are capable of supplying the 10%; however, the machine side of the equation demands more than just a casual range and control check before flight. Since the machine accounts for 90% of the equation, I would like to present my methodology in the hope that it could be of value to you in claiming as much of that 90% for yourself.
The Three Steps to Helicopter Heaven
There are three key areas in preparing a well "setup" helicopter. Starting with a carefully assembled model, the method comprises of the following:
This article will cover the three areas with systematic instructions. After following these instructions, you will understand how to setup any helicopter in a consistent and repeatable manner.
Assembly
There is more to building the helicopter than dumping out the parts bags and feverishly bolting things together. In order to prevent the machine from disassembling itself while in a 3 foot hover, there are certain things you should be prepared to do; but first, the golden rule of helicopter assembly. Never leave a part partially built. Always complete the sequence so that when you return you are starting at the beginning of another module.
The reason is that when you return to a partially complete task, you never quite pick up where you left off. As a result, you may not properly assemble some part and all you need is one loose nut, or one screw without thread locking compound to cause the destruction of your model. In case you were wondering whether I was speaking from experience, the answer is, "yes:" the telephone rang, and in my haste to answer, I temporarily attached the swash plate anti-rotation bolt. It was temporary until my next 3-second hover.
Do yourself a favor and buy some decent hardened Allen wrenches. These are the ones made from drill blanks and mounted in fist sized handles. Do not buy the Wiha drivers or the black colored "L" shaped keys. These do not allow you to torque the screws down and because they are not hardened they round off damaging both screw and knuckles. These tools can usually be found wherever model cars are sold, one brand being "Dirt Burner." You will need the 1.5mm, 2.0mm and 2.5mm drivers. The 3.0mm driver is optional because it is only generally used to tighten the blade and engine mount bolts.
Of absolute necessity is some tool to aid you in balancing parts, specifically the main blades; assuming of course that you conserve your financial resources rather than running off and buying a set of NHP Carbon Pros, or a set of Miniature Aircraft’s 3D symmetricals. I have had great success with the High Point balancer with the addition of a Tech Specialties rotor blade adapter. For reasons detailed later in this article, it is not necessary to buy anything more expensive than these two pieces of equipment. There is also the option of purchasing the Koll balancer, but it costs around $80 and is much more complicated to use. If you just need to balance your main blades, then skip ahead to the section, "Main Blade Balancing."
Other optional equipment that makes life a little easier but is not totally necessary: the RVB ball link duplicator, and a gram scale accurate to at least 0.1 gram.
As you open the individual bags to assemble the kit step by step extra time must be taken to ensure the cleanliness of every screw. A light coating of a cosmoline type preservative oil is present on most screws and control rods. If you try to use a thread locking compound on an oiled screw it will not bond and will inevitably loosen. Personally, I use M.E.K. to clean the screws, but isopropyl alcohol would probably not shorten your life by so much. Cleaning screws is a job that you could be doing while watching TV as is it just as moronic as some of the prime time line-ups.
Thread-lock everything except where a bolt is screwed into plastic. To enhance vibration resistance in these areas use Polyzap cyanoacrylate adhesive. Additionally, ball bearings and shafts should be secured together with a bearing fit compound. I have found that low rpm shafts, the main shaft for example, do not require it, but the engine start shaft and tail rotor gearbox shafts certainly do.
Loctite manufactures a green colored thread-locking compound, #290, for just this purpose. Be warned, use it a pin drop at a time or you will not be able to remove the bearing from the shaft. It goes without saying that both the bearing and the shaft be cleaned with solvent prior to assembly. The bearing fit compound is designed to secure already assembled components, provided they are degreased.
Incidentally, you may use a cyanoacrylate desolver to remove thread-locking compound from bearings or fasteners.
Main Blade Balancing
More to come when I get the time!
The prelude to a truly great performing helicopter begins with the mechanical setup. Too often the electronic wizardry of the modern radio is used to offset or correct for poor mechanical setup. However, there is only so much the electronics can do, and what the radio is unable to do is restore proper geometry. Wayne Mann (1997 U.S. team member for the World Games in Turkey) follows the current Japanese philosophy in this regard.
The Japanese believe that in order to fully utilize the electronic mixing and compensation programs, that the mechanical setup be as particular and precise as possible. The idea being that the electronic setup merely fine-tunes the mechanical setup. Where does this start? To begin with, a decision must be made on what type of flying you expect to do. There are two basic styles: Freestyle/3D and F.A.I. Freestyle flying displays the almost unlimited attitude capabilities of the model helicopter in equal amounts of upright and inverted flight. The flying ballet of F.A.I. is a demonstration of hovering and pattern flying ability with only limited inverted flight segments.
If you decide on 3D flying, your mechanical setup is predicated by the need to have symmetry about the 0° point. For F.A.I. style flying where the emphasis is on hovering maneuvers, a setup point around hovering pitch (5°-6°) should be established. In my experience in helping others, the concept of setting 0° as the starting point seems better comprehended. Later, when the helicopter is flying well and the pilot is aware of how a correctly setup helicopter should behave, the setup method can be changed.
The symmetrical setup starts by identifying the 0° point. On the head this is the point where the blade holders and their mixing levers are level. On the mast, this is the point where the swash plate is in the middle of its travel and the washout arms are level. Servo mid points are those points that position the servo output arm perpendicular to the control rod when the transmitter sticks are centered.
The radio only needs to be turned on when you are ready to connect the mechanical linkages to the servo. There are some radio adjustments that go hand-in-hand with the mechanical adjustments, and these are covered as we get to that point.
To start the mechanical setup you begin in the most unlikely of places. You would think that you should start at the servo and work your way to the head, but it is much easier to work from the head finally ending up at the. The first mechanical alignment is that from the blade holder to the Bell/Hiller mixing levers. Just to refresh your memory, the mixing levers combine the swash plate input with that of the flybar. They mix the direct Bell input, from the swashplate, with the indirect Hiller, from the flybar.
Adjust the linkage from the blade holder to the mixing lever so that the blade holder is at 0° while the mixing lever is perpendicular to the main shaft. Once you have adjusted one linkage simply copy the length to the opposite blade holder. It may be useful to invest in a ball link duplicator like that made by RVB in Dallas. Occasionally, some trimming of the shank of the plastic link may be necessary to allow the two ball links on the control rod to be screwed closer together. Usually this control rod is short (about 12mm) so the shank of the ball links may interfere with each other.
The second adjustment resides on the other end of the Bell/Hiller mixing lever. This is the input from the swash plate so it is essential that the swash plate be held square to the main shaft. The length of these two rods are adjusted so that the swash plate is in the middle of its travel. This ensures that you get the full range of movement on both the positive and negative pitch ranges.
If you are unsure where the mid point of travel is, look at your plans or assembly instructions. Usually, there is enough information here to determine the approximate mid-point. If you do not get the accuracy immediately, it is a simple matter to adjust these linkages when fine-tuning at the end of the mechanical setup. While adjusting the length of these two rods, ensure that the flybar is also level so that the blade holders are held parallel to the workbench (0°). After the length of one rod is determined, simply duplicate it for the other.
The result is: the swashplate will be in mid travel with washout arms and mixing levers level. The blade holders will have 0° pitch.
The last linkage on the rotor head to be adjusted is the simplest. These are the two linkages from the washout unit to the flybar. The purpose of the washout unit is to remove the collective pitch input while still allowing the cyclic input to deflect the flybar’s paddles.
On every model I have seen, the washout unit is connected to the swash plate by a pair of short molded linkages of fixed length, so no adjustment is necessary from the swashplate to the washout unit. Just place the swashplate in mid travel, level the washout units arms and adjust the rod length to fit between here and the flybar. It goes without saying, but I will say it anyway, that the flybar must be square (paddles level).
At this point, take a look at what you have achieved:
The symmetry of it all is key. When it comes time to program your pitch curves, you will find that the percentages needed at each point remain fairly constant from model to model. You can tell at a glance if there is too much pitch versus too much throttle. More of that later when we look at the first flight final setup.
Step back and relax. If you have completed the above steps and understand the mechanical and geometrical arrangement, you can successfully apply this to any other brand of helicopter and look like a wizard when you do it. Any helicopter can be set up this way, even at the field where you might not have extra tools. Its usually quite easy to determine when something is level or parallel, and there are plenty of references available on the mechanics or workbench without resorting to a pitch gage. You can use a pitch gauge later to check your work and make adjustments.
The servos must be connected to the swashplate, usually via L-levers or bell-cranks. It is not important whether you work from the swashplate to the servos or vice versa. What you are going to accomplish is to make all levers 90° to the control rod when the servo is at neutral or center.
It is at this point that some radio work must be performed, so power up the transmitter and receiver. The first thing to do is expand all the travel adjustments to their maximum. On most radios this is known as ATV. For JR radios, I usually expand these out to 150% for each of the five channels (T-throttle, A-aileron, E-elevator, R-rudder, P-pitch).
Next, select the output arms and wheels needed and fix the ball links to the arm. Many people like the aluminum output arms, and certainly, these seem easier and more secure when screwing a ball link down. A personal preference of mine is to place 2mm nut under the ball to lift it off direct contact with the servo arm. This allows more room for the shoulder of the ball link when it moves over the arm and removes the potential for interference.
Place the output arms/servo wheels on the cyclic servos. For each servo try to place the arms on the spline that most closely places the arm at 90° to the control rod. If it appears that you cannot get the arm perpendicular to the control rod perform the following:
Access the subtrim function for that channel (aileron or elevator) and adjust the subtrim so that the servo wheels rotates to the 90° position. You thought that subtrim was for recentering your trim sliders didn’t you? Well, if you use them for this purpose, you will offset your mechanical setup. To trim the helicopter in the hover, you readjust your linkages to the swashplate, this keeps the servo output arms symmetrical about their center or neutral.
Adjust the mechanical advantage of the servo arm so that the swashplate is not driven over its articulating ball. Alternatively, you can reduce the cyclic ATVs , but if using this method do not allow the ATV to fall much below 100%. Falling below 100% indicates that too much advantage exists which increases the load to the servo. Check to see that it does not bind by giving full fore-aft and left-right cyclic (place the cyclic stick in a "corner"), and rotate the head. You can feel if any binding takes place.
Technically, the best mechanical linkage arrangement exists when the arm length is at a maximum at both the servo and the control surface. The constraint is determined by the adjustment available at each of the arms which therefore affects the mechanical travel volume. In summary, try to keep the ATV adjustment to a minimum.
The throttle linkage requires a little more thought. Check that the ATV is expanded to 150% on JR radios. Place the throttle stick (transmitter) to full power and position the carburetor control arm to fully open the throttle barrel. Place ball links on the throttle control rod and roughly adjust in length to fit between the fully opened throttle and servo arm. The ball links on both the throttle and servo arms should be equidistant. I use about 12mm as reference.
Now slowly close the throttle. The ATV for low throttle is set at 150%, so change this in the transmitter as you fully close the throttle. The throttle trim should be all the way down in the cutoff position.
You are trying to adjust the throttle for the following:
Why adjust full throttle ATV to 150%? Would 100% work well? The answer is yes, 100% works well until you program a mix to add throttle. On JR radios, the master to slave relationship will add a certain percentage of mix all the way to 150%; therefore, if your mechanical limit is set at 100% throttle, the servo will be stalled as the master channel attempts to drive the throttle. By adjusting the mechanical linkage so that full throttle is reached at 150% ATV, no master channel can overdrive the servo. This has to be compensated by adjusting the lower ATV range.
The throttle servo generally does not require that subtrim be adjusted. Of most importance being the equal arm lengths, and that the arms follow each other in parallel fashion. The end result being that 50% barrel open on the carburetor corresponds to 50% servo arm arc.
Collective pitch mechanical adjustment to the servo is similar to the aileron and elevator servos; however, the transmitter setup is more complicated.
The method to use on the transmitter starts with placing the flight mode switch to flight mode 2. I am using flight mode 2 in this example, but it could easily be flight mode 1, or whatever flight mode you would like to use for 3D. As 3D essentially means that the helicopter will behave similarly whether inverted or upright, we use whatever flight mode prepares the helicopter for that style of flying.
This is extremely convenient because it provides the template with which to prepare any other flight mode. To continue, adjust the ATV out to maximum and call up the pitch-curve programming screen. Use the pitch curve display to place the pitch stick at 50% input (which equates to 50% output).
Next, attach the arm to the servo and reposition the arm on the servo output splines to get it as close as possible to center (perpendicular to the control rod or rods). Without touching the pitch stick on the transmitter, go to the subtrim screen and adjust until the servo and arm are precisely centered.
Connect the pitch control rods and adjust the length as necessary. In the previous steps, the head was set so that swashplate mid travel was 0° . All that is needed now is to adjust the collective pitch control rods so that the swashplate is again in mid travel.
When finished, attach a blade or an old blade root from a broken blade. The short blade makes it easy to adjust pitch curves on the bench without swinging a blade into the wall. Use a pitch gage and check to see that the blade indicates 0° with the collective stick centered on the radio. Lower the collective to the bottom (full negative) and measure the angle with the pitch gauge. Raise the collective to maximum and again take a measurement. Hopefully, you will have approximately ±10° . If you have something less than this then adjust the mechanical advantage either at the servo or control arms to obtain this figure. The final setup for the pitch curve occurs during the radio setup portion of this article.
Torque compensation is provided by the tail rotor. The tail is also used to provide yaw control, and, with the use of a gyro to dampen motion in the yaw axis. As the tail is not readily understood by beginners, it is quite often the most poorly adjusted. If the tail is improperly adjusted and does not function to control torque or dampen motion, it seriously affects the confidence level of a novice pilot and increases the learning period.
The tail differs from the rest of the setups because there are several factors that need to be considered. Probably the single greatest affect on how the tail is set up is determined by the gyro type, whether it is a standard yaw damper or heading hold type. To keep it basic, I will discuss the standard yaw-damping gyro, then later in advanced topics, the heading hold gyro.
In order for the transmitter software to properly calculate the amount of torque compensation required, it must know where the stick is when in the hover. Normally, tail blade pitch is increased above this point and subtracted below it. The mechanical setup then needs to be adjusted so that when the collective is in the hover position the servo arm is centered and square to the control rod. Also, the tail blades will be at hovering pitch of around 5° .
Essentially, the tail rotor zero point centers on the amount of tail blade pitch needed to counter torque at hovering power. To accomplish this, turn the radio on and insure that tail compensation mixing is off. Now, place the servo arm on the splined output shaft of the servo adjusting its position to 90° to the control rod (this rod travels all the way to the tail). Use the subtrim function to square it exactly. Note that this is a completely different method of setting up the tail when compared with a heading hold gyro. The heading hold gyro will be covered later.
Connect the control rod to the servo output arm, the distance should be between 12mm and 18mm out from the center. Read the instructions that came with the gyro as several manufacturers have suggested lever lengths.
The length of the control arm at the tail is usually dictated by the manufacturer. There may be only one hole to screw in the ball or several. Choose the middle length for starters. Adjust the length of the control rod, by screwing the ball link in or out to provide approximately 5° of tail blade pitch. This 5° is close to what will be needed when the heli is being hovered. Any changes to hovering pitch will be adjusted mechanically by adjusting the length of the control rod.
Install the gyro according to the manufacturer’s instructions. If the gyro has upset the neutral point of the servo, either adjust it using the neutral adjust on the gyro or via the transmitter’s subtrim function. Be sure that the gyro polarity is correct.
There are several important areas to check at this point if your first takeoff is not to be an overly exhilarating one.
Leave all tail rotor mixing and compensation off until after the first flight. It is essential that several parameters are adjusted during first flight, prior to using the radio’s built-in programming.
Radio Setup
Now that the manual labor part of the hard work is done, you can utilize all the bells and whistles of your radio without resorting to getting your hands dirty.
Nobody should be flying without using exponential on the cyclic controls. On a JR radio, I enter a value of +30% to both my left/right and forward/aft cyclic. The net effect is to permit more stick deflection for a given swashplate movement around center. It feels as though the sticks are "soft" or "indirect" around their neutral positions.
The result of adding exponential is easy to observe while hovering. Without exponential, you can almost see the helicopter fuselage move about the rotor disk with every cyclic input. The model appears jerk in response to control input, which advances the misconception that it is more maneuverable. Incidentally, there is a delay between input and response in model helicopters as there is in the full size. This delay is usually quite constant for a given head speed and blade weight. The large initial control input does not result in a faster response because of this delay; however, the result of a large control input is simply a large response. The pilot reacts with a correction and the pattern repeats. The model then "feels" less stable and becomes intimidating for the novice.
A model flown with exponential appears much more solid in the hover. Control inputs are washed out due to the exponential, thereby softening most pilots’ tendency to over control. The helicopter is then perceived as being docile and forgiving. Remember that exponential softens the command around neutral but does not affect the total swashplate deflection at extreme stick positions. There is no loss of authority (you have it, when you need it).
The amount of exponential to add to the tail command is usually dependent on the operation of the gyro. On piezo gyros that support yaw rate demand, it may be necessary to add some exponential. Consult the instructions packaged with the gyro and abide by their recommendations as a starting point.
To program the pitch curves we work backwards from the 3D or "V" Curve. This is simply because we set the mechanical portion of our helicopter to symmetric about the 0° point. If we start with the "V" Curve, all we need are the programmed numbers for 3 points and we can generate everything needed to program any other curve.
Turn everything on and place a pitch gauge on 1 blade (make sure you have one blade marked so that the other blade can be tracked to it during the first flight). Place the collective at center stick and move the flight mode switch to the position that will correspond to your "V" Curve.
For this 5 point setup, center stick collective corresponds to point 3, or 50%. Blade angle should read 0° . If not use the data keys on the transmitter to be sure it is and make a note of the percentage output.
Place the collective to the ¾ stick position, or point 4 or 75%. Point 4 is the upright hovering point and should read approximately 5.5° . Again, make any adjustment and make note of the percentage output.
Finally, move the collective to full positive pitch, point 5 or 75% and adjust for +9° . One important item here is compression. If points 4 and 5 are close to each other in percentage output, for example 78% and 86% respectively, then adjust either the travel adjustment or mechanical advantage to spread them apart. Personally, I adjust my point 5 so that it requires 100% of output. Extra pitch is not made available for autorotations because 11° of pitch has no benefit at low rpm. Make a note of the reading.
To program the negative portion of the "V" Curve on JR radios, simply subtract the value from 100 and use that for the opposite point. For example, 78% for point 4 becomes 22% for point 2 and 95% at point 5 becomes 5% for point 1.
Normal Curve is easy to prepare now that the critical programming percentages are known. Flip the flight mode switch to "normal" and place the collective stick at ¼ stick, or point 2, or 25%. In Normal the ¼ stick position corresponds to the 0° point. Use the figures generated for point 3 in the "V" Curve setup and enter it.
Next, move the collective to ½ stick, or point 3, or 50%. This is our hovering point while in normal curve. It is also critical for setting automatic tail rotor compensation when this becomes enabled, but more on that later. Enter the figure generated for point 4 in "V" Curve setup.
Points 5 for Normal and "V" Curve are equivalent at +9° ; therefore, use the same percentage.
Point 1 or full negative should correspond to approximately -5° or -6° . This value is not critical at this point. In fact, you could set it to 0° if you are a novice to smooth out your hovering while practicing. At 0° , it is hard to really dump your heli onto the ground in a moment of panic.
On the other hand, you might set point 1 at -6° . That would allow an entrance to an auto without a jump when the throttle hold is switched in. Either way, point 1 for normal can be set based on your style of flying when in Normal. Note that data is not programmed for point 4.
Again, start in your V Curve flight mode. The data entered for the various points is purely arbitrary at this point since we have only a rough estimate on how much engine power is going to be needed in the hover. As a general rule of thumb, the throttle barrel on the carburetor will be open approximately 50% when hovering. It may be advantages to pop the linkage off the carburetor and mark the high, low, and middle points with a laundry marker.
In V Curve, we run collective pitch from +9° to -9° with maximum engine power at both these points. That leaves 3 points to cater for: 1) inverted hover, 2) zero pitch, 3) upright hover.
Access the throttle curve function on the transmitter and move to point 2 (inverted hover). Enter a percentage that opens the throttle barrel to 50%. Typically it works out to be around 70% on JR radios with 150% ATV (with expanded ATV, 50% on the transmitter output does not equal 50% servo movement).
Use the figure determined for point 2 as the data for point 4 (upright hover).
Finally, we must use some value for V Curve point 3. At this position, the blades are at zero degrees collective pitch. As we are going to be doing aerobatics while in V Curve, it is essential that some power is available. Ideally, we want the head speed to remain constant to minimize torque changes; therefore, we need enough power available to maintain our hovering head speed, but less than that required to hover the helicopter. As a starting point, use a figure 10% less than the hover throttle settings. The term V Curve comes from what we have just accomplished. The throttle curve now resembles a "V" when graphed:
The graph also shows the Normal Curve. Remember, that in normal flight mode the helicopter hovers at the mid-stick position, point 3. Its value should be the same as point 4 when in V Curve flight mode. This is a great point to remember when fine-tuning after the first flight. Fine tune the Normal Cuve first, then transfer the numbers to V Curve.
Point 4 is shown with an average value of. In reality, most radios will compute this value for you or offer to leave the value inhibited. On my JR radio, I don’t even have a point 4 in Normal Curve. If it is not possible for you to similarly inhibit this point, simply calculate the mathematical midpoint between points 3 and 5.
No curves are programmed before the first flight! Earlier it was mentioned that even revolution mixing is turned off until all the necessary adjustments have been made. Details on how to handle the tail follow the section on first flight.
What is first flight? It is simply the most critical flight that takes place after assembly, rebuild, or reprogram of the system. If you are a beginner and have just completed your first helicopter, this is absolutely the time to receive experienced help. Do not even think about trying it yourself, its not worth the anxiety, the panic, and the cost! My own first flight lasted around seven seconds but as I watched it occur it appeared to last a lot longer. Even worse was the fact that the helicopter was an American "Super Mantis." The reason being that as I crashed so did the company, leaving me with an expensive first lesson. So, no matter how tempted you are, seek help.
Follow this section to understand what the first flight is all about. After reading it, you should understand that the significance of the fine adjustments made to the helicopter and the format for accomplishing these adjustments.
It is quite necessary to begin here because one of the most critical adjustments depends on a smooth running engine that is producing a compromise of smoothness and power. Yes, it is somewhat of a compromise in that ultimately the engine is capable of producing more power but at higher vibration levels. This is especially true if the engine is set overly lean. On the other hand, if the engine is set overly rich the smoothness disappears as the engine attempts to lean out and 2-cycle. This changes the torque output of the engine, which can in turn play havoc with the gyro.
The engine should be producing smoke in the hover with a crisp response to the collective as power is increased. This is important because as the throttle is opened the load is increased. This is simply because as the left stick is moved (For Mode 2 fliers) both throttle and collective pitch are changed...
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Copyright © 1998 Chris Berardi. All rights reserved.
Revised: November 25, 1999.