Buying a model helicopter can be a hard enough decision in itself. Prices, durability and availability of parts should all be a part of the equation. In addition a modeler might want to consider which machine has the most alternate sources of parts supply from other upgrade manufacturers. The question might have crossed your mind about the costs of required upgrading with the alternate source question put aside. Who wants to buy a low priced heli only to have to spend a fortune in upgrades to make it into a well flying durable machine? Upgrades come in various forms relating to cosmetics, durability, convenience, precision enhancing and cyclic control modifying. Some are good and some simply add nothing more than extra weight/cost to a model helicopter. You have to ask yourself what am I going to get out of this upgrade and is the current part doing the job it was designed for. I am going to give you some basic tips to help the unknowing make a more informed purchasing decision. If on the other hand you are interested in having the prettiest heli, the information contained herein may be of little use to you. This article is not meant to bash after market parts but simply to help average people get the best bang for the buck through intelligent purchasing decisions.
The big durability question with any metal part is: “By the shear fact of being metal will this be beneficial to me”. Plastic or composites as they are sometimes called, are lighter than metal but will not stand up as well in certain applications. Some manufacturers have taken the best of both worlds and combined the two to yield a part which is as durable as a full metal counterpart and lighter. This of course excludes crashes since anyone can make a strong heavy machine. Ideally what we want as advanced pilots with our helis, is components that will stand up to the maximum flying stresses with long wearing qualities. From this we can conclude that what might be good for the beginner may not exactly be right for the more advanced. Before you decide to replace a plastic control system part have a look at it and see if it is flexing under maximum servo loads or if it is simply in need of better bearings. A good ball bearing type plastic washout assembly with a brass bushing to slide on the mast will preform the same as a metal copy, plus it will be lighter and cheaper. A plastic washout guide with metal guide pins will more than cope with applied stresses. If you have a plastic swashplate expect the center plastic ball and ball ends to wear out quickly. If you have a plastic swashplate with a metal inner pivot ball and outer race with metal ball ends don’t bother going to metal until it succumbs to crash damage. This is because it will perform / wear just as well as the all metal unit while being lighter. Plastic clutches and clutch bells do not generally stand up as well as metal units because of the heat and friction involved. When these wear out I would recommend going to the machined metal counterparts. For the most part plastic rotor heads fly exactly the same as the metal copies, are lighter, cheaper to repair and more than tough enough for the job at hand. The smart designer mixes plastic and metal rotor head pieces to end up with a cheaper, lighter and properly stressed component. Composite side frames are better than metal in my mind. Metal over time is more prone to cracking from vibration. Although metal sideframes are heavier, they sometimes can be bent back into shape after a mishap, where as broken composite frames are normally toasted. Plastic frames will take a lot of abuse and are not affected by high cycle stress as is metal. (metal fatigue). One of the biggest disadvantages of plastic is its ability to allow for easier thread stripping when things are cross threaded or over tightened. With sideframes this can be eliminated through the use of aluminum spacers/bearing blocks or metal threaded inserts embodied in the plastic. Poorer grades of plastic can stretch or split as can highly stressed parts. Metal bushings moulded / pressed into or around the plastic will contain and distribute the load over a wider area to alleviate this problem should it be present. An example might be to have the blade bolt holes in the plastic grips bushed with aluminum or brass to prevent plastic creep. A metal ring around the damper area of a main rotor head block would seem prudent in certain designs. As I hope you can see, material selection mixing for various parts should save weight while achieving adequate stress factors. Plastic has in some cases received a bad rap due to poor designs and chemical composition. But as time goes on and manufacturers adapt better one can expect the model helicopter of the future to be lighter, stronger and preform better. The type of plastic and manufacturing technique can have a large influence on the durability factor. Plastic which is similar to what is currently used in the more popular fixed wing motor mounts is very tough as is carbon fibre or graphite. Plastic parts can be cheaply cast in a mold and then have the required accuracy machined in where needed. As an example lets say a plastic washout hub is cast to a tolerance of about .008″. We then accurately machine the hole in it for the a brass bushing (mast). The surface for the washout arms is now centered to the mast, the holes for the screws to thread into are then accurately drilled. Functionally the part is probably more than accurate enough in its cast form but we have added durability and tighter tolerances if so desired. Why waste time and money on extreme casting or machining precision where it is not required? A similarity could be said of a rotor head. Close accuracy matters with the rotor head grips at the centering and depth of the inner bores for the bearings, blade bolt centering in the grip and the grip slot location. The hub and grips could care less if its outside width is off several thousands of an inch if the inner centering , width and length are accurately machined. Composites and metal should and can be our companions by coexisting for the maximum benefit.
In many cases plastic casting alone will yield acceptable results as in the case of a servo trays, landing gear, tailboom clamping blocks, fin mounts etc. When your plastic fins crack from vibration a better material selection is required but this does not mean metal is answer. There is a large difference between a molded and a molded/machined plastic part. This is normally reflected in its assignment.
Convenience upgrades can take the form of pull starters or top cone conversions, if your pull starter interferes with a scale fuselage installation. It can all be related to a particular situation. A self aligning clutch can save setup time while offering nothing in the way of a performance gain. Switch mounts, adjustable (sliding) servo arms, easy off flybar weights, head buttons, remote fueler / glow drivers etc all fall in this category and generally add weight. Things like tube drives will save servicing time as compared to wire drives but can be costly in a crash or tail rotor strike. Steel tubes drives can work against you by being too strong and causing additional parts to be “taken out” in a crash. Precision enhancements we can all fall prey to, thinking that our flying skills will improve by leaps and bounds according to the dollars spent. Many refinements would only be advantaged by a very skilled individual while some others like better servos are more noticeable to the regular guy. Accurate setup will give you the biggest advantage. Things like push/pull conversions add some life to your servos and tighten up the control system slightly. Ball bearing supported rotating controls will add smoothness of control and be long wearing. Swashplate anti rotation links can fall in this category depending on the machines design. The biggest change in flying qualities comes from rotor blades, flybar paddles, and flybar weights which are all related to the setup process. I consider these to be the largest cyclic control modifiers. Different rotor head designs including damper firmness can change how your heli responds to cyclic commands and how smooth it actually looks while flying. Thrust bearings in the rotors can make for a smoother feeling heli depending on rotor rpm and blade weight / length.
I currently own and fly 4 different brands of helis with past experiences of two others. My favourites at this point in time is the Graphite Miniature Aircraft 60 size (gas) and Thunder Tiger Raptor. The machines performance relies on the use of numerous plastic parts, making it very reliable, light and durable. MA seem to have many of the plastic problems licked without actually resorting to metal reinforcing too much. The reason I say this is due to earlier difficulties with the plastic head block stretching at the lower area and thereby allowing it to rock slightly on the mast. With the addition of the lower metal static tracking adjusters this trouble seems to be gone. They have really killed to birds with one stone here. With our machines we often see patches in design flaws rather than a complete new redesign. This more often than not works out, which helps to keep manufacturing costs down. The resultant savings help to keep model prices down or profits up, depending on which side of the fence you live on. That being said, I decided to go to the horses mouth and communicated with Mr.Ted Schoonard on the matter of plastic casting. Here is what Mr. Schoonard said by pleasantly answering my questions. Carbon Fibre and/or glass fibres are used in the composition of X-Cell parts and in differing proportions. This is dependant on what is expected of a particular item. As with any good product ample testing is carried out to determine the best plastic recipe for a particular part. Currently three different resin compounds are employed to suite each parts individual “operational environment”. Here is where I had my surprise. Their mould accuracy is such that inside machining of the blade grips is not required. To be more specific any plastic/composite part containing a radial bearings outer race is molded rather than machined under size. The interference fit depends on the desired compressive holding force. As with most things of this nature there is a compression table or graph for proper reference. Any location supporting a shaft or gear is machined after casting as is the case of the auto hub, washout, and head block. I have to agree that when it comes to precision rotating plastic parts, machining will ensure runout comparable to metal. This is evidenced in machined plastic gears and auto hubs which run very true compared to cast alone units.
I foresee many new developments in composite technology filtering down to the model helicopter industry in the future. One such item available now (but not in models yet) is a composite spherical bearing which could replace the metal unit in a swashplate. These newer bearings are constructed of teflon and polyester fibres woven into a self lubricating bondable fabric supported by a filament-wound fibreglass epoxy shell. They are self aligning and capable of taking dynamic misalignment, oscillating and linear motion. I find it surprising that we are still using metal skids, auto hubs, bearing blocks, and gearbox housings to name a few. What surprises me even more is how readily some people willing replace a perfectly good plastic part with a metal one. As you can see I’m all for composite technologies.