Since I bought this Titan Trex 450 from China, I can’t solve the unstable tail problem of this beast. I even used a tripod stand and made a wooden platform to fasten the helicopter by it’s skids using plastic clamps and screws. The platform is screwed to a wooden pole so the heli’s body with it’s tail can rotate. Then I test the heli by giving it at least half throttle and adjust the gyro’s sensitivity until I think the heli is stable enough. I followed the setting given by some heli pilots on the web like forums and Youtube. And most of them recommend 50% delay (for analog servos)  and 100% limit of the gyro. Of the two settings, the delay has the most effect on the stability. When I reduce the setting to less than 50%, lets say 25%, the tail is still unstable.  But so far 50% seems satisfactory. By the way I’m using a low cost TowerPro SG90 mini servo for the tail control after the titan digital servo burned out.

I never deviate from that 50% delay setting of the gyro until what I discovered yesterday when I’m trying to figure out why the tail rotor linkages are sloppy and today when I’m practicing hovering. The tail rotor pitch is moving when I try to move it with my fingers and seems there is something loose. I found out that the metal ball attached to the bell crank is smaller than the hole where it fits. So I have to make the hole smaller to fix it. I used a 1/8″ heat shrink tube and cut it to 1/8″ length then insert the metal ball to make it bigger then insert it to the bell crank hole. Well it seems that the remedy is effective. I applied a little silicon spray lubricant to make the linkages move smoothly. And even before that, I sprayed a lot of silicon spray lubricant on the rubber belt hoping the tail rotor effectiveness will improve and remove the squeaky sound.

Then I made a test flight again in the morning and I’m expecting that the tail control will be more stable because of it. Yes it did reduce my rudder stick control movement while hovering. Unlike before that I can’t feel the use of the gyro because I keep counter acting the tail movement just to point the helicopter in one direction. But I’m still unsatisfied because I still can’t make hands-off on the tail control even for a second. I was made to believe that the reason is because I’m hovering in a windy condition. I tried to adjust the gyros delay fro 50% to 25% to see if there is some improvement. But it seems there is no effect so I changed it to 50% again.

In the afternoon, after I charged the battery, I decided to play again with the gyro setting. And after a few minutes of hovering and flying, I changed the setting to 0% hoping it will improve or my fear that the tail will wag back and fort. But to my amazement the tail becomes stable and I can hands-off for a few seconds and the tail controls became solid. So I think the lesson is don’t be afraid to experiment. I thought only digital servos can be set to 0% and analog servos should be set to 50% delay. Maybe generally it applies to majority specially to other versions of titan trex clones using metal rotor head and tail assembly. Mine were only made of plastic. Anyway if you think you’ve done everything and nothing happens, this might be the solution.

If you came to this page looking for a Trex 450 FMS model, I guess you tried all your best finding that hard to find FMS model. I also search the internet for weeks and gave up. All I can see in the Google search cache are forums talking about how to get that Trex 450 FMS model and there is a post in a forum posted by the creator himself Sekiai that he is giving a free Trex 450 model but the link is nowhere to be found. So here it is, just download it for free!

Download it here: TREX 450 FMS model

Well, if you want to own a cheap 6 channel collective pitch RC helicopter, I guess buying a titan trex 450 clone is one of the best choices. You can order direct from China sellers and you can buy a cheap RC heli but the only problem is the custom taxes that will be imposed to it. In the Philippines, specially if you use EMS, be prepared for the heavy taxes and out of nowhere they will guess the amount of your item even if the declared amount is stated on your package so they can impose more taxes. So far I’m happy that I got mt new heli and I’m ready to play with it. But since I was so excited I forgot to set it up properly and didn’t purchase a training gear for it even though I have experience flying a collective pitch 6 channel RC helicopter many years ago. I once have a Kalt Baron 50 powered with .50 cu. in. glow engine but I’m not very familiar with CCPM (Cyclic Collective Pitch Mixing).So I have to research on programming the transmitter and configuring the helicopter controls.

I ended up with a tailboom strike, burned tail servo, burned ESC and tip overs damaging the tips of the rotor blades all because of negligence and haste.  So the lesson I’ve learned is treat your Trex 450 helicopter with respect. I was thinking that since it is only small and battery powered, unlike the glow engines, I thought it is chicken feed setting up this 6 channel heli. But I was wrong. This size is comparable to it’s big brothers in set up and damage it can cause to people and property. This is not a toy like those micro coaxial rc helicopters sold in toy stores. This is a toy for the big boys.

So after those painstaking  moments I now restored it. See the photos below:

Chapter 5 : Helicopter Powerplant

Model radio controlled helicopter is often powered by a two cycle internal combustion engines but there are other types like four-cycle internal combustion engine. Most of the internal combustion engine for models are fueled by methyl alcohol called the “glow engines” and the other one is unleaded gas which his usually a four cycle or four stroke engines. ( see also Airplane Powerplant Fig. 19 , Fig. 20a ) These engines are powerful which can supply the demand for the needed power to fly the helicopter. But because of continuous development of lighter and stronger materials, powerful electric motors and light but powerful batteries, it is possible now to fly a helicopter using electric motors.

Whichever engines you use, the drive mechanism to rotate the blades are basically the same design. Main gear, pinion gear, clutch assembly and the engine or motor ( see Fig. 24 ). The only difference between the internal combustion engine powered versus the electric type is the clutch. Electric powered type doesn’t use clutch. The motor is directly connected to the pinion gear without the clutch unlike the I.C.E. ( Internal Combustion Engine ). ( See Fig. 25 )

A feature, which is called auto rotation, the main gear connected to the main shaft is free wheeling so in an event the engine malfunctions or stopped, the main rotor will continue to rotate.

Fig. 24 RC Helicopter Powerplant

Fig. 25 RC Electric Model Helicopter Exploded View

In a model radio controlled helicopter, two type of internal combustion engines are usually employed with regards the fuel they use. There are other types like two stroke and four stroke engines but we will tackle only on the most common types.

1) Glow engine – engine that uses methanol for fuel and castor oil for lubricant. The igniter is called the glow plug, shaped like a miniature spark plug but uses coil for burning the fuel and air mixture ( see Fig.26 ). Power source for the glow plug is 1.5volts NiCad (Nickel Cadmium) battery or dry cell with high ampere. Usually 75% methanol and 25% castor oil
is the fuel mixture. Castor oil readily mixes with methanol unlike the petroleum based motor oil. But for more speed, nitro methane is added depending on the type of aircraft flyer desire (e.g. pylon racing, sport flying or pattern flyer).

Figure 26: Typical two cycle glow engine

2) Gas engine – Gas engines are commonly used by larger RC helicopters because this type has larger displacement. It uses ordinary unleaded gasoline and petroleum based motor oil. You can compare its size with an ordinary handheld chainsaw.

Electric powerplant used by model helicopters are straight forward. The electric motor wires are connected to a speed controller. The speed controller is connected to the rechargeable batteries and radio control receiver. ( See Fig. 27 )

Figure 27: Electric Heli Powerplant Components

 [ Previous Chapter(4) => Helicopter Weight and Balance ]

[  Next Chapter(6) => Choosing My First Model Helicopter ]

Producing Fiberglass Components ( The In-place Technique )

Construction:

Photo 1: The fuselage is completed and sanded to its final contours. The working centerlines are well defined and that portion of the extended fuselage, onto which the finished fiberglass cowl will actually overlap (back almost to the cabane
struts), is protected with strips of masking tape. The strips of masking tape are butted together, rather than overlapped, on installing. The masking tape used here became almost totally transparent due to its color match with the balsa wood,
and does not show up too well in this photo.

Photo 1

Photo 2: Polyurethane foam blocks are tack cemented to the firewall. Working centerlines are extended onto the foam blocks with a felt tip pen.

Photo 2

Photo 3: Paper templates (part of the actual plans) are used to mark out the general outlines of the cowl.

Photo 3

Photos 4, 5, & 6: The foam blocks are worked and shaped toward the ultimate contours. The foam is easily sawn. cut with a sharp knife, or sanded to shape. The Stanley brand Sure-form Files work well also. If an area is undercut, dented, or nicked, etc., a bit of spackling compound can be applied to correct the condition.

Photos 4

Photos 5

Photos 6

Photo 7: As this cowl requires a returned lip at the front air intake opening, the foam block is carved to produce a recess, so as to receive the laminating material. The final sanding of the foam is done with fine grit sandpaper to bring the foam flush with the masking tape which is protecting the wood fuselage. With the sanding completed and all the particles of foam removed with a vacuum cleaner, the masking tape is given two coats of P.V.A. No P.V.A is applied to the foam.

Photo 7

Photos 8 & 9: The glass cloth is then resined into place. For this cowl, three layers of 1-1/4 ounce cloth will be applied. The number of overlapped joints is kept to a minimum. After the second layer of cloth was applied and cured, the entire cowl was rough sanded to reduce the bulge of the overlapped fabric and any other lumps and bumps which may have developed. In the actual application of the glass cloth, avoid any excess use of resin. The fabric need only be thoroughly wetted. Excess resin only adds weight, not strength. The strips of butted masking tape applied to the fuselage are now quite visible.

Photos 8

Photos 9

Photo 10: The laminating is completed and allowed to cure for an hour or so. It is then sanded again to a smooth finish. When sanding (wet sanding works best) the completed component, do not worry about sanding through a layer of cloth.
Before removal, the entire component be given a coating of resin only to seal any fabric which may have been exposed by sanding. I have found that if any areas are left where the glass cloth has been exposed, in time, these areas will actually
show right through the primer paint and finished paint job as well. The cowl is now ready for removal. To make removal of the polyurethane foam easy, I use a stiff piece of music wire with a small ninety degree hook bent onto one end. Used
in an electric drill, the revolving wire hook digs out the foam with ease. Had this foam been of the polystyrene type, a bit of acetone would make its removal even quicker.

Photo 10

The completed cowl. To remove the cowl from over the masking tape on the fuselage, a thin section of a hack saw blade, with the teeth ground off, is slipped between the fiberglass and the masking tape to break the bond of the resin and the P.
V. A. applied over the masking tape. The excess fiberglass is trimmed away after removal.

Photo 12: A few embellishments, panel lines, screws, rivets, etc., and some pain finish the project. Now you may well ask how long did this process will take? Approximately it wil take a little over four hours in total time. One yard of glass cloth was used along with six ounces of polyester resin. The cowl, as you can understand, is a perfect fit onto the fuselage. It has to be, of course, it was produced “in-place.” The thickness of the masking tape used to protect the wood fuselage was the same thickness as the ultimate covering and finish applied to it a few days later. If a thicker finish material was planned, then another layer or two of masking tape could have been applied before shaping the expendable foam block. Removal of this foam core block was very easy on this particular cowl design because of its generous intake opening.
But, bear in mind, that it does not take a very large aperture to insert the music wire hook to chew-up the foam into small particles. The interior of the fiberglass cowl is a bit rough on completion, but a bit of sanding on that portion, where
the foam was, and a coat of paint hides all manner of sins . . .This technique, with variations, can be used on all sorts of model items. The very large wing fillets (Photo 13) for the Quarter Scale PT-19A were produced “in-place” over modeling clay and card stock on already finished surfaces. The P. V. A. release agent protected the finish from adhesion with the resin.

Photo 12

Photo 13

Photo 14: The complex stabilizer fairing made of fiberglass is from the same model and same method, only in this case, regular window putty was the expendable media over which the fiberglass was laminated.

Photo 14

Photo 15: Illustrates the cowl for the PT-19A. This cowl is the product of two techniques. The front nose bowl was layed-up in the more conventional manner of: wood plug, finished, female plaster mold, etc. A small recessed flange was left at the rear edge of the nose bowl, which later became homogenous with the “in-place technique” that produced the very large rearward section of the cowl. This cowl is over 15″ deep and it was made right over seven separate sections of foam fitted and shaped over a rather complex engine mount. This cowl also overlaps the basic fuselage by several inches.

Photo 15

Photo 16: Still another “in-place” cowl. This one ,is from the Quarter size Stinson Voyager. The nice part of having these cowls overlap the fuselage is that they are so very well supported, due to the closeness of fit. that only a small screw or two is needed to keep them in place. I have only shown here the rather large cowls. This does not indicate nor mean that this method only works on big models.

Photo 16

Photos 17 & 18: Illustrates the fiberglass fairing to secure the windscreen. The expendable materials for the mold are a section of thin aluminum sheet only taped in place right on the fuselage and a piece of styrene sheet taped onto the aluminum at the proper angle. Again, P. V. A. is the release agent used to allow easy removal. A bit of trimming, some sanding, and paint complete the project. This neat little fairing takes less time to produce than it does to describe.
You will have to admit that it add that touch of class to the model, aside frombeing very functional in holding the windscreen in place. The screws are decorative only.

Photos 17

Photos 18

The “in-place technique” not only works for our models. I can think of all sorts of fiberglass parts such as framing over a clear canopy, hatch covers, gear-leg fairings, nacelles, wheel doors and covers, antenna fairings, hinge covers, and on and on. The list is only limited by one’s imagination. These are only ideas for our models. These can be carried further into full-sized aircraft. How many more items might there be for boats, cars, and all sorts of prototype work in general? In describing/demonstrating my “in-place technique” for fiberglass, it is my hope that the next time you ponder a new model subject, the thought of having to produce an item or two in fiberglass no longer will be viewed as: too troublesome or difficult. I close with a word of caution: When working with the materials described here, please read, heed, and follow all the manufacturer’s instructions and recommendations.

 [ Go to Introduction to Producing Fiberglass Components ]

Producing Fiberglass Components ( The In-place Technique )

Introduction:

There are various methods of working with and producing fiberglass components for use in our hobby of model building. Some, of course, are very technical or complex while others are more simple or basic. There are many modelers asking just how to go about producing fiberglass components. Most avid modelers have some of the basic knowledge required to produce fiberglass parts in the conventional method of master or plug, female mold, and ultimately laminating or laying-up of the glass cloth with resins. Though this may well be the best time-proven method for producing any sort of fiberglass component with any sort of accuracy, it is too time consuming for many of the single or one-of components we may need for our models.

There are no doubts that components layed-up in a female mold, more often than not, produce the best-finished products. Let’s consider an engine cowl for an example. Basically it is the outer shape or dimensions that we are interested in obtaining. Working with a female type mold to produce an engine cowl insures these outer dimensions, providing the original plug is properly sized and shaped. The interior of the cowl, so far as smoothness is concerned, is of
little or no importance in most cases. That is, until the need arises to have the interior size or shape correspond to the fuselage so it may fit over or slide onto the fuselage. It then becomes very important that both the interior and exterior
dimensions be held to a close tolerance and this then becomes another “bag of worms,” which sends most modelers back to the hobby shops in search of another kitted model rather than trying his/her hand at scratch building.

If the model subject we select to do requires the engine cowl to overlap the fuselage by several inches, if you want the cowl separation line to be in a scale-like location at the firewall of the full-sized subject. Nothing, I think, can be more
distractive on a model, than having a non-scale, additional panel or seam running around an engine cowl. Our engines, be it a small glow-engine or even a large chain-saw conversion engine, are nowhere near the scale length of any real aircraft
engine and mount. So, it is a really rare occasion, on most models, to have our engines mounted on the scale-location firewall. Aside from being able to utilize some of the excess space forward of the scale-location firewall for radio equipment and fuel tank etc. it is much easier and stronger to just extend the model’s fuselage to a point more convenient, under the cowl to secure our engine.

So as not to add any additional seams in the engine-cowl, it is best to just have the cowl overlap this lengthened fuselage. I hope to demonstrate just how simple and quickly the methods to produce all sorts of form fitting fiberglass components. I aptly named it the in-place technique. To simply describe the technique is that basically it’s a method whereby some sort of expendable material is affixed in place, then shaped as required and. over this expendable material, resin impregnated glass-cloth is laminated to produce a removable fiberglass component. A release agent is employed to prevent the resin from adhering to the subject, over which the fiberglass part(s) are being fabricated. There is no guesswork involved as to how well the component will fit upon completion, since being made directly in-place (in-place), insures an exacting fit. The expendable material, in this case, the mold over which the laminating is accomplished can be, for example: wood, paper, and clay, wax, or most of the foam products like polystyrene (normally
white and beaded) or polyurethane foam.

Basically, there are two types of resins mainly associated with the RC hobby industry. Most of the commercially
produced RC items today employ the epoxy type resin as it is a more stable product for the most part. The other resin, and one more generally available to the modeler, is polyester resin. Of the two resins, polyester offers the lowest cost and the widest range of working latitudes as it applies to working temperatures and mixing ration with its catalyst, etc. The polyester-type resin is available in most hobby shops, packaged under many popular brand names. Most hobby dealers stock two types of this resin. One is labeled finishing resin, and the other is laminating resin. It is this laminating resin which is used for laying-up the fiberglass components. You can also use the finishing type with complete success. Before actually delving into the “How to . . . of ” in-place fiberglass techniques. I would like to just touch a few bases on the materials themselves. First, as many of you know, polyester resins do not work well with polystyrene foam this is the white, beaded foam material most often employed for foam wing cores. The polyester resin will attack and literally melt this foam away unless it is somehow protected from contact by the resin. You can use beaded foam to make all sorts of fiberglass components over, but after shaping the foam, and to protect it from the resin attack, protect all the exposed foam with a thin coating of 5-minute epoxy adhesive. Epoxy resins or adhesives have no effect on the polystyrene foam.

The other foam product is polyurethane. This is a light tan colored foam and has a sandy, gritty feel to it. This material is immune to attack by either polyester or epoxy resins. Though polyurethane foam is somewhat easier to shape and sand, it must be cut or chipped away for removal. Polystyrene foam, on the other hand, can be almost melted away with a small amount of dope thinner, acetone. etc. Either type of foam boards or blocks are available at most local insulation distributors. Fall-offs, damaged or broken pieces, can be purchased very economically. Modeling clay or even common window putty, makes a very fine expendable material over which fiberglass components can be laminated. The side benefit here is that it is easy to remove after the required component is completed, plus being very easy to mold or shape. Stiff paper or card stock may also be used in conjunction with other expendables as you will learn later on. In working with any method of fiberglass lay-up, a most important item has to be the release agent.

The resins employed in fiberglass work are, in themselves, a very fine adhesive, and it is this quality which most modeler s find objective in creating fiberglass components! Many modelers have ruined the female type molds because the release agent failed. There are many sorts of products at least 5 or 6 brands of wax for protecting molds. For those not familiar with P.V.A. (Polyvinyl Alcohol), about the best description of the product is like liquid Saran Wrap. The liquid is either brushed or sprayed over whatever area is to be protected from contact by the resin. When it dries, the P.V.A. produces a very thin protective coating. P.V.A. dries reasonably fast and generally one or two coats are sufficient. The P.V.A., is water soluble and therefore, is easy to clean up or remove. It can be applied over the best of finishes without worry. Though not a hobby shop item, it can be purchased from chemical supply houses. The smallest quantity I know of is in gallon lots, which would last a lifetime, or you may choose to split it up between a few fellow modelers
and share the cost.

Now let’s get into the actual process itself, and follow the procedures used to produce an overlapping engine cowl for the Grande-scale model airplane

[ See Next Page For Fiberglass Construction Process=> ]

Chapter 6 : Choosing My First Model Helicopter

So far we have discussed some theories on the previous chapters which I hope I have imparted to you clearly. This chapter is now is for preparation on starting to choose the type of model helicopter suited for the beginner. The most appropriate model to choose is the non-collective type. Meaning, the main rotor blade’s pitch is fixed. It will only depend on the speed of the rotor blade and engine to gain or lose lift unlike the variable pitch type that can adjust the pitch to improve the lift performance. But in my experience, I started with the collective type and learned to fly and hover it with not much difficulty. Only the complexity in set-up hinders the learning progress because you have to align the main blade pitch and the angle of attack or main blade pitch using the blade pitch meter. The tail rotor also have to be trimmed against the main rotor torque by mixing the tail rotor’s pitch which is syncronized to the main rotor blades pitch and speed which very important before flying the heli.

Not only the collective pitch of the main rotor baldes that we should consider. The design of the main rotor head is essential on choosing our first model. Most of the design on the market has a flybar attached perpendicular to the main rotor head. This design has a built-in stability compared to a flybarless design. There are other types also like the bell-hiller system, multi-bladed system, hiller system which are quite complicated and not suitable to a beginner. A typical rotor head design with flybar is shown here in Fig.3 from chapter 1.

Now we go to the fuselage. For the beginner, it is recommended to have an open stark fuselage for simplicity of operation.
For example, in an open type, the engine is easily accessible for starting and for maintenance. It will also help the cooling system of the engine unlike in an enclosed type. And with regards to the size, a .30 cu. in. engine is also suitable because a bigger .60 cu. in. consume a lot more fuel and damage to people or properly is more than it’s smaller counter part. To see a typical model helicopter with a stark fuselage, see Fig. 1 from Chapter 1.

For far we have discussed selection and been familiarized with the model to choose. But there are some finer points to discuss with regards to pre-flight preparation.

Area selection – the most suitable is a closely mowed grass area, a putting green ,or a golf course if you can find one! Just kidding, just an average lawn grass is OK. The advantage is when the helicopter tip over, it will not be too hard on the blades.

If there are no available lawn, an aspalt or concrete is alright but the gritty dust of the deteriorating asphalt will cause wear and tear to your engine and mechanical parts. The best thing to do is to sweep it first with a broom and or wash it down with a water hose.

Training gear – this serves as a protection to the main rotor blades from hitting the ground while learning to hover. The construction is two pieces of 1/2″ dowel rods 3 feet to 4 feet long laid in an “X” pattern. The ends were attached with 4 pcs. 4″ whiffle balls. ( See Fig. 28 )

Figure 28: Model Helicopter With Training Gear Attached

Trimming the landing gear – this part is very helpful to speed up the learning process. As we have discussed before about the translating tendency, ( see Fig. 17 from Chapter 3 ) the tail rotor blows the helicopter to one side which tends to drift it. The cyclic control is not effective while the landing gear is still touching the ground. To counteract this, we need to tilt the helicopter by attaching a 3/8″ square wooden stick on one side of the skid. So the model will lift off the ground without applying a control input on the cyclic control which is difficult and might be over-controlled.

Figure 29: Wooden stick Attached to Skid to Tilt the Heli

So this wraps up the RC helicopter for Dodos and I hope you have absorbed the important topics before starting this hobby. I recommend buying the RC helicopter manual to further enhance your knowledge. So thanks and have a good day!

[ Previous Chapter(5) => Helicopter Powerplant ]

[ Heli for Dodos Index ]

Chapter 3: Rotary Wing Stability and Control

In the previous chapter I have discussed the priciples of helicopter flight. Now I will discuss how it is controlled and some control mechanisms to make it stable. But first I want to show the three dimensional axis of a helicopter.
These are:

1) “X” axis or the longitudinal axis
2) “Y” axis or vertical axis
3) “Z” axis or lateral axis

Fig. 12 The Helicopter Three Dimensional Axis of Rotation

The X-axis or longitudinal axis of a helicopter rotates the aircraft by banking left or right by the cyclic controls. This is similar to the rolling motion of a fixed-wing aircraft the only difference is that fixed-wing aircraft uses aileron while a helicopter uses the tilting of the main rotors either to the left or right. The Y-axis or vertical axis rotates the fuselage by means of the tail rotor. The tail rotors’ variable pitch blades controls the degree of thrust to compensate the torque or to steer the helicopter. In a fixed-wing aircraft, it uses rudder as means of control. The Z-axis or lateral axis rotates the helicopter by tilting the main rotor cyclic fore or aft. ( see Fig. 9 )

Now we will discuss more about the main rotors’ control mechanism. The type we will discuss is the flybar type although there are other types like the hiller system and a fixed-pitch type main rotor blades for simplicity. The flybar type is commonly used my most RC helicopters and trainer types because of stability. As we have encountered before on our last chapter about gyroscopic procession, you can see in Fig. 13 looking at the main rotor on stationary mode or what I mean to say is when the rotor is not yet moving. As the flybar paddle on side 1 goes down, flybar paddle on side 2 goes up. Similar to a seesaw that is why the mechanism that connect the flybar to the rotor head is called a seesaw.

Along with the seesaw effect you see in the flybar is also the change in main rotor blades’ pitch or angle of attack. The blades’ pitch rotates perpendicular to the flybar. So whenever the flybar on side 1 goes down there is an increase in pitch on blade #1 but a decrease in pitch on blade #2. So obviously the flybar who does the control of tilting the main rotor blades to any lateral direction, 360 degrees.

Fig. 13 The Flybar, Flybarpaddle Assembly and its’ functions

Now we will discuss the functions of the flybar, flybar paddle, main rotor blades in motion. As rotor turns, those two paddle are shaped like an airfoil. These are controlled by a universal link and rod to the swash plate. When the swash plate tilts in the front, the link rod pulls down and rotates the flybar assembly. The paddle then pushes the flybar downward because of the aerodynamic forces ( see Fig. 14 ). But, because of the law of gyroscopic precession, the flybar will not drop down or push the flybar down in THAT position, instead the application of force will react 90 degrees after the clockwise motion. Remember it is also a rotating mass so the law still applies. So the flybar will drop in front or where the swash plate is tilted.

Then as we go back to Fig. 13 as reference, the main rotor blade also change the angle of attack ( i.e. pitch, angle of incidence ). When blade #2 reaches paddle on side 1 position as the whole rotor system rotates clockwise, then it will
change the angle of incidence too like the flybar shown on Fig. 14 and will push the main rotor blade on that position. The effect will be 90 degrees after the application of force same as the flybar paddle. I hope this didn’t make your head spin. Just keep in mind the law of gyroscopic precession.

Fig. 14 The Flybar Assembly and Main Rotor in Motion

It’s not easy to understand how the main rotor blades tilt by the application of force with the gyroscopic procession at work. It is also hard to explain and make illustrations about it but for the sake of better understanding, I made a 3D model in autocad and will illustrate the functions:

1) The first drawing represents a rotating model helicopter main rotor mass. This is a fixed pitch type, meaning the blade is constant pitch, not variable. The flybar rotates by control input and hence changes the pitch of the paddle. The change in pitch created a downward force that tends to pull down the flybar. But due to the gyroscopic effect the flybay will not tilt down to that position because of the resistance of the rotating flybar.

2) Hence, the flybar will tilt 90 degrees after the application of force as you can see below. By tilting the flybar, the whole rotor is tilted also so the main rotor blade pitch is changed as you can see. The change in blade pitch creates a downward force in the that area but will not tilt because of gyroscopic effect.

3) Then the reaction will occur 90 degrees after the application of force. You can see the angle of tilt below to show the area where reaction occurs. Then the cycle continues with the paddle and flybar rotates and changes the pitch. I hope the illustrations are helpful. Honestly I was not very familiar with this function when I was just learning to fly rc helicopters. This is very important to keep in mind while learning to hover.

Now the tail rotor. Simply just to counter act the torque generated by the main rotor, shaft and engine. Without it the whole fuselage will spin opposite the direction of the main rotor blades’ rotation. So in Newton’s Third Law States that ” For every action, there is an equal an opposite reaction”. It will not be possible to control the helicopter for sure. The pitch of the tail rotor blade is variable in order to control the degree of pitch. Aside for counteracting the main rotor torque, it is also used as directional control of the helicopter in the Y-axis (vertical axis). And for stability, controlling it alone manually to stabilize the fuselage is almost impossible because the variable conditions that contributes. To mention a few, the throttle, specially during hovering you will tend to adjust the throtle to compensate for the wind conditions. Tilting the main rotors to balance the heli will affect the required power, hence constant adjustment to the throttle is necessary.

Fig. 15 How Main Rotor Torque is Counteracted by Tail Rotor

So the appearance of gyros ( not gyroscopic effect ), a small rotating disk housed in a casing becames necessary to effectively control the tail rotor. This gizmo is connected to the tail rotor servo to creates a dampening effect and stabilized the fuselages rotation. When an external force is applied to the fuselage, either a gust of wind, main rotor downwash, the tail rotors’ will counteract by applying an opposite force. Its like an autopilot. To illustrate further using an example of driving a car. The steering wheel is our means of control to steer tha car left or right. We balance the cars’ direction by constantly steering the wheel. If the car is moving to the right for example, maybe a strong wind is causing it to go to the right, we will counteract by applying an opposite force. So this is how a gyro works.

There are some more to consider in the tail rotor’s stabilizing effect. We call it translating tendency. It is the natural reaction of the helicopter to drift either left or right depending on the main rotors’ rotation and tail rotors’ thrust. When the helicopter is in a hovering mode, the tail rotor counteracts the main rotors’ torque to keep the fuselage steady. But the tail rotor is a creating a wind on the perpendicular side of the fuselage so its’ trying to drift the whole aircraft away.

Fig. 16 Helicopter in Hover Mode Tend to Side-Slip

To counteract the drifting effect, we will again apply a counteracting force using the main rotor cyclic control. We should tilt the main rotor on the opposite direction where the aircraft is drifting to balance everything ( see Fig. 17 ).

Fig. 17 Main Rotor is Tilted to Counteract Translating Tendency ( or Side-Slip )

When the helicopter is very close to the ground, the controls are very sensitive due to thephenomenon called “ground effect” ( See Fig. 18 ). The rotor downwash hits the ground which creates a dampening effect.

Fig. 18 Ground Effect Due to Main Rotor Down Wash

 [  Previous Chapter(2) => Why and How Helicopters Fly ]

[ Next Chapter(4) => Weight and Balance ]

Chapter 4 : Helicopter Weight and Balance

In this chapter, we will tackle the helicopters’ weight and balance just as we have tackled in the fixed-wing aircraft. There are differences between the fixed wing and the rotary wing on the weight and balance consideration because obviously, the helicopter can fly vertically and hover. There is designed weight on every helicopter whether it’s a full scale or an RC model depending on the engine size, main rotor blade diameter and pitch. Just don’t go beyond what is stated in the manual and you won’t go wrong. A light aircraft flies better than a heavy one.

The distribution of weight is as important as the weight consideration in a helicopter to fly it properly. A poorly balanced helicopter is difficult to fly and also dangerous because it might cause damage to people and property if it went out of control. Usually, the center of gravity is located along the main rotor shaft ( see Fig. 7 ). The reason is the main rotor head is the pivot point of the three major axis ( see Fig. 12 ). So whenever you are in a hovering flight, it will not be as hard to control the helicopter. This is very important on the first stage of learning. All the controls should be stabilized.

Looking at the illustration ( see Fig. 19 ), some RC pilots prefer to adjust the center of gravity in front of thw canopy to simulate the full scale helicopter. In this situation, the aircraft is out of trim, meaning you have to create a counter acting force to stabilize it. Since the the center gravity is ahead of the main shaft, the main rotor will tilt by itself ahead and have a tendency to fly forward instead of hovering first before transition to forward flight. So in order to offset the tendency to tilt down, we have to apply a force on the opposite side like pulling the control stick backwards which in turn will tilt the swashplate that controls the main rotor mass so it will fly in the vertical direction like hovering or vertical take-off
and landing ( see Fig. 20 ). So if you are just learning to fly an rc heli, the best choice is balancing it with the center of gravity in lined on the main shaft. Fig. 19 Center of Gravity Located Ahead of the Main Rotor Shaft

Fig. 20 Application of Opposite Force to Counteract C.G.

So then how will you balance it? unlike a full scale heli that weights tons, the helicopter model can only be balanced using your two hands with your fingers. In a real helicopter, balancing it requires calculation of weight distributed against the distance from the fulcrum or the place where we want the canter of gravity to be located. In this case main shaft is our desirable place. ( see Fig. 21 ) In this illustration, we should equalize the moments on both sides to balance the aircraft. Distance multiplied by the weight is the “moments”. Using some simple algebra we can get the result and can determine it both sides are equal.

Fig. 21 Illustration of Weights and Moments in a Helicopter

In a model RC helicopter, all we have to do is to use both fingers on both sides of the flybar. Lift it slowly approximately 2 inches from the surface and see if the skid is parallel to the surface or ground. By moving or relocating the internal components like the receiver, servos, batteries, gyro we will be able to balance it. But, in some cases where relocation of radio components is inevitable, putting some lead weights on the front or inside the canopy is effective.

Now we go on the balancing of the main rotor blades. This is one of the most important aspect of set-up. Unbalanced rotor blades results in excessive vibration, loss of power which in turn affects the flight characteristics of the heli. It also
might cause the damage of the chassis, radio equipments inside the helicopter. So before attempting to start the engines and fly your heli, make sure the main rotor blades are balanced.

Using a propeller balancer, the main rotor assembly which includes the rotor head, blades,flybar and shaft should be placed on the balancer in order for it to rotate freely. If the blades are not balanced, drilling some holes or slots on the lighter blades and putting some lead is an effective method.

Since a helicopter generates in own lift, in an engine failure, it cannot glide like an airplane. It will rely solely on the momentum of the rotating blades with out power. So in order to accomplish this, there is a feature called “auto rotation”. The main rotor blades will continue to rotate until it losses it’s momentum. To improve this, the blade tip is inserted with lead tip weights. ( see Fig. 23 )

Fig. 23 Lead Tip Weight for Auto Rotation

[ Previous Chapter(3) => Rotary Wing Stability and Control ]

[ Next Chapter(5) => Helicopter Powerplant ]

Chapter 2 : Why and How Helicopters Fly

Now we are familiar with the parts of a RC helicopter from our previous chapter, now lets look deeper on why and how helicopters fly. Obviously the rotating blades of a helicopter are responsible why it can defy gravity. Looking at the cross section of the airfoil shaped rotor blade, it has an angle of attack or what we call the pitch ( see Fig. 6 ). As the rotors turns and achieved the velocity needed for the aircraft to lift the ground, it generates a downward force ( see Fig. 7 ).  As we have tackled in our previous chapter, the fixed pitch type is only dependent upon the speed of the engine but the collective pitch can vary the pitch angle so even at maximum RPM it can fly or hover whatever altitude you desire ( see
Fig. 6 ).

Fig. 6: Illustration of Heli Blade Airfoil

Fig. 7: RC Helicopter in Hovering Flight

The way helicopters fly is very similar to a fixed wing aircraft on the aerodynamics side. The only difference is helicopters don’t need to move forward to gain airspeed for it’s wings to be effective. In fact it can generate it’s own lift. That’s right. Because of the rotation of it’s rotary wing, unlike a fixed wing aircraft, it can produce it’s own lift ( see Fig. 8 ) The airfoil section of the rotor blade below shows how it goes against the relative wind, the air that passes through an airfoil.

Fig. 8: Airfoil Section Along the Relative Wind

Among the heavier-than-air machine, a helicopter has a unique ability of hovering flight. It can fly suspended in the air (see Fig. 7). All the forces that acts in a helicopter during hovering are balanced: Lift = Weight & Thrust = Drag. Since there was no forward motion, Thrust & Drag is equal to Zero. So how will it move forward? In order to do that we should create an unbalanced situation for it to move forward. Provided that the C.G. ( center of gravity ) is located within the main shaft of the main rotor. Later I will discuss the reason regarding the importance of C.G. location. Again going back to the imbalance topic, if we want to move the heli forward, we should create an uneven distribution of lift. Making the lift behind cyclic rotors’ lift less than that of the front so that the main rotor mass will tilt forward (see Fig. 8). The control mechanism responsible for controling the tilting of the main rotor mass is the swash plate.

Fig. 8: RC Helicopter in Forward Flight

Theoretically the forces that acts on it will look like Fig. 9. Since the helicopter is moving thorough the air, it behaves differently from hovering since forward flight need more power. With a little analysis using using right triangles, you can see that there will be a additional lift requirement on the lift component, the resultant force: lift-thrust vector depending
on the angle of tilt. That will be the resultant of the thrust and lift vectors see Fig. 9. ( Sorry if this is quite confusing).

This explains why the helicopter needs less power while hovering that in forward flight. You will notice this when you are actually hovering a helicopter and transition to a forward flight, a slight loss of altitude will occur so you will increase power to maintain altitude until it gains momentum and climb its way up. Like wise, when you want to transition to a hovering flight again, it will suddenly gain altitude and you will decrease the power.

Fig. 9: RC Helicopter Vectors

Now we will tackle the phenomenon called gyroscopic precession. If you apply a force on a rotating disk it will not tilt on the location where you applied the force, instead it will react 90 degrees away from it on the direction of rotation. So in flight, when you are controlling the rotor blade mass, for example you want it to fly forward, you tilt the rotor forward but actually the control input is 90 degrees before the direction of rotation ( see Fig. 10 ). Again as an example, if you are looking at the top view of the helicopter, and the main rotor blades are rotating in a clockwise motion when you want to
tilt the main rotor blades in the forward direction, you are actually making the control input on the left side and then because of the law of gyroscopic procession you will notice that the main rotor is tilted forward. You can observe this when watching an RC helicopter on the ground about half throttle. And later you will know how it is controlled using the flybar mechanism.

Fig. 10: Gyroscopic Precession Phenomenon

Since we have explored the rotary wings’ some important facts, let me add some more regading the distribution of lift.
I guess this not very important just an additional knowledge. From the tip to the root blade, the thrust is not equal. The tip has the greatest thrust and decrease as you go to the root. This is because the angular velocity at the tip is much greater the root ( See Fig. 11).

Fig. 11: Angular Velocity of The Main Rotor Blades

Do you know that a real helicopter is very limited on the rotational speed of it main rotors? That’s a fact. Model or RC helicopters can be designed to rev up a very high speed rotors. The reason behind it is the length of the main rotor blades. Longer rotor blades can approach to an angular velocity to the speed of sound ( or mach 1 in other terms ). When a body, particularly an airfoil approach the speed of sound, it will behave differently than below mach 1. That is why full-size helicopters need to keep their angular velocity to a minimum ( See Fig. 11).

[  Next Chapter(1) => Helicopter Nomenclature ]

[ Next Chapter(3) => Rotary Wing Stability and Control ]