Tools of the Trade
This particular article is meant to introduce people to specialized tools common to model helicopter up keep and includes alternative methods. The intention is to familiarize the new comer and make his life easier. Several articles are contained on this site with reference to specialized tooling, being more task specific with detailed application including.
Model helicopters are wonderful mechanisms meant to be flown and tinkered with. This also helps to maintain a user friendly personality. Our job as model aviation technicians is to keep our machines well oiled, finely tuned and in top physical condition. Due to the modern nature of this toy, we will not be using stone knives and chisels for tools. Compared to the fixed wing, four wheeled, and marine modelers we require much more dedication, caution and experience to become proficient and safe.
The most important instrument you have at your disposal is inside your skull and without it any precision tool is a wasted effort. Often several modellers through of the use of the “old noodle” will go co-op on tool purchases by pooling resources. The most expensive tools are not a requirement since many offer convenience rather than improved accuracy over their counterparts. Various tools in the same category do an identical job but in a different manner. Some ultra precision tools offer a higher accuracy level unnecessary for model helicopters. Quite a few add nothing more than complexity, but this is often considered entertainment or play value when viewed by seasoned flyers. Being a practical and economical type I shall keep to the basics with the odd stick thrown towards my over indulging friends. The bottom line is to obtain acceptable results.
One tool we need to know about is the pitch gage since this will help us get airborne. Most helicopter manuals usually recommend collective pitch settings for the beginner of about zero degrees at low stick, five at half stick and eight or nine at top stick position. This is fine, but a tool is required to do the measuring. Two different versions are on the market, one with lots of pieces to be installed before use and the other which simply clamps on to the airfoil to be quickly and easily viewed. Both read within 1/4 of a degree to each other so accuracy is not really a deciding factor. Besides, who wants to lug a bunch of smaller parts to the field only to go searching for them later in the grass! Since this tool is intended to get one into the ball park, I recommend the simple rugged one piece unit. The main benefit of the unit with the jeweled movement is that once setup it is slightly easier to view with more consistant results. With the one piece clamp on unit it is often possible for two people to have small differences in tool interpation. This bacially makes the jeweled unit better as a bench tool. To put the whole thing in prospective, wood blades usually need tracking adjustment even if the gage shows equal measurements. Final but small rpm adjustments are going to change the static collective settings carried out on the bench. This is due to slight building and manufacturing variances as well as different airfoil types.
After we start flying the inevitable happens and things don’t exactly fit together as originally intended. Often the small discrepancies are not easily viewed with the naked eye. Such would be the case of a slightly bent mast or the new control rods that were quickly threaded together. The dial indicator and vernier caliper come in handy during these situations. Inexpensive units with more than enough accuracy can be had for less than $40.00each, from local tool suppliers. Most helicopters require a dial indicator to precisely build the drive train, as is the case of clutch, fan hub, and/or start shaft alignment. This device is nothing more than a clock with a gear train connected and moved by a sliding shaft. The biggest difficulty in using this tool is in its mounting method. Often a magnetic base can be used but this limits the applications. A better mounting method would be to use a clamping device to hold the dial indicator. This will allow direct mounting to the helicopter or engine and be unaffected by landing gear flex or external movements.
Vernier are designed to measure inside and outside dimensions. The better ones use a clock face to indicate the small precision portion of a measurement. They can be used to accurately set control rod lengths, measure clutch liner clearance, bearing fits to a shaft or bore, only to name a few. These can be purchased for $25.00. Acquire one with a clock face since the small slide rule like scale types (vernier scale) are hard to read. You can upgrade and purchase a digital battery powered unit with a PC interface if you like for under $100. I have often found these units to have dead batteries when they are needed most, so I don’t bother with them if I have a choice.
Broken blades need to be replaced either by ARF versions or blades supplied in a kit form. In the ARF situation it is wise to check and balance the blades if required. You don’t need to spend a lot on balancing tools but better results can be had if you have access to a precision scale for measuring weight. With the precision scale and using any rotor or blade balancer, very good results can be expected. Balancing main rotor blades in themselves can be easily done with a scale and common household items. The spanwise blade C of G can be located using a round object like a pen or better yet a small triangular shaped ruler. Proper adjustments can be made to blade mass and c of g location using these two items. Later, the completed rotor assembly can be balanced span wise by the flybar on common household drinking glasses. The flybar can be teeter balanced using its own pivot point with the controls carefully disconnected.
The tail rotor assembly may be balanced using an inexpensive airplane prop balancer. The same individual main rotor blade balancing techniques may be employed on the smaller blades but due to the small size it is often a tedious job. This kind of thing is a waste of effort as a T/R hub and blade assembly balanced as a unit will run very smooth. If you pick the right balancer it may also be used on the main rotor hub and blade assembly, fans, and hubs. Another option is to select a shaft the same diameter as the hole in the tail rotor hub and use two drink glasses as balance pivot points.
Assembly tools are sometimes included with new kits. This might be in the form of hex wrenches or a clutch alignment tool. I would recommend a small set of jewellers screwdrivers, a small metric socket set, high quality internal hex wrenches (Allen keys) and sone tiny open end wrenches. Another clever item to have is forceps. These enable a person to reach hard to get at fasteners and fuel tubing.
Since our machines have moving parts subjected to high speeds, the use of tiny ball bearings is common place. These require periodic lubrication weather it be oil or grease. Oil applicators can be purchased at your local electronic supply shops. The included liquid lubricant often contains Teflon which is a very good lubricant. The applicator has a long needle which will most often reach those difficult locations. The other option is to grease the bearings either by hand or with a tool. I like grease since it has better staying power than oil and lubrication periods are not as often. Most bearings are supplied with grease and repeated oiling can wash out this lubricant. There are tools available for greasing shielded bearings without removing the shield.
Some times when servicing our helicopters the smaller pieces get stacked into a small pile. Some control system rod assemblies come in sets with each individual rod having been matched to a particular blade and a cyclic side of the swashplate. Since we went to the trouble to match and adjust the system to the best of our abilities we should install these pieces back in their original locations. This will certainly save setup time. A simple method to avoid any conflicts would be to match mark the rotating controls from the swashplate up to and including the blade on one half of the control system. This can also be a great help when tracking the rotor…..what control rod was it that I adjusted anyway? Thick and fast drying finger nail paint can easily be swiped from the female member of the household, otherwise expect some strange looks at the makeup counter!
Sometimes a machine has favourite parts it likes to shed. Often muffler brackets, motor mounts, bearing blocks, tail booms etc loosen off or creep over time. By using witness paint early detection of a loosening or shifting part may save further aggravation down the road. A quick visual inspection the night before may mean less embarrassment later at the flying field.
I realize some beginners are going to crash and might be on a budget. That may leave tools low on the priority list. There are ways to get around not having proper tools in certain cases. A mast can be checked for a bend by rolling it on a flat surface like a piece of plate glass or counter top then noting a wobble or hump. The single through spindle can be evaluated in-situ by removing the blades and turning the spindle with a socket wrench and watching closely to see if the grips rock. The spindle can be removed and rolled on a flat surface like the mast should you desire confirmation. Plastic parts generally break but otherwise remain serviceable after a crash, so special measuring is not required, although close visual inspection is.
Ball link pliers are very nice but not an absolute necessity. Needle nosed pliers can be used to snap the link off. Duck billed pliers can be modified into ball link pliers at a fraction of the cost plus they will be more durable than some tools presently on the market.
As the first detailed procedure, here is how I balance the T/R hub and blade assembly. In order to acquire the best accuracy the blades must be lined up to one another. This is accomplished by moving the blades fore and aft in their grips while attempting to maintain a balanced chordwise horizontal position. When you find a spot where the blade will not feather on its own, the chordwise c of g is now in line with the spindle. Pull the grips out board to insure best balancing conditions. You may find that the holes in aged plastic blades are slightly elongated, so the same prudent attention to detail should be practiced. I recommend tightening the blade bolts to hold this position.
It is now time to carry out the spanwise balance of the T/R hub and blade assembly. This can be done with a dummy shaft inserted through the hub center. The unit can be laid across two levelled drinking glasses, knife edges or rulers. An airplane prop balancer can make short order of the work. If knife edges are used in a non leveled condition the assembly will roll down the hill so to speak. Flipping the rotor assembly 180 degrees should indicate the same heavy blade as a simple calibration check. Modern plastic blades tend to be pretty accurate in composition as are hub and grip tolerances. What this means is that minimal weight adjustments are the norm. Personally, I do not adjust the T/R blade and deal with any balance compensation using washers at the blade bolts. A slightly longer bolt may be used in extreme cases. Washers and bolts can be ground or filed to a precise weight. The washers are best added equally to each side of the grip when possible, if the quantity is equal. For recessed nuts secure the washers under the bolt head. Sometimes both the nut and bolt head are recessed in the grip. In this case material can be filed or ground off the flat side of the nut, or additionally a longer bolt used/trimmed oppositely. This may sound repetitious but there is one thing that must be taken into consideration during all measurement readings: end chuck of the grips can throw off the true readings. This might be the case of one grip close to the hub while the other is further away…..again lightly pull both outward. After the assembly is levelled through careful balancing, please mark the blade, grip, hub and hardware so that future maintenance will require only re-assembly by retaining prior locations or moments. You can see from the stack of washers on the $70,000 BO-105 tail rotor that this” industry standard” method of balancing is quite acceptable. We use the same basic principals to statically balance the full size tail rotor although the tools are somewhat more expensive.
In closing I like to say there is nothing finer than having an equally smooth and reliable machine resulting from the use of basic but accurate methods which actually compare very well in results to some expensive over complicated devices. Your project may even turn out better due to the lack of extra procedures with a corresponding possibility of induced errors. There are other methods and I am simply passing on what has worked best for me through experience. No one is going to know what lies in your tool box at home after seeing your smart looking pride and joy smoothly humming along in the sky!