I‘ve been flying the smaller Raptor helicopter for several seasons now and for the price it has exceeded my expectations. When you look at its place in the market, the over all manufacturing quality of the raptor 30 is certainly up to modern standards and is astonishing value for money. The well priced spares do the product no harm either adding extra value after the initial outlay. One can see why it is so popular with beginners and the more experienced alike. It is however not without mechanical problems based on severe usage. Some may go the upgrade route and install many metal parts, but when compounded this actually exceeds the price of a high-end kit. Due to wider manufacturing tolerances and differing building techniques one machine may show problems before another identical ship. After weeding out the areas prone to long term wear without resorting to fancy upgrades, I thought it only fair to share my experiences with you. I am extremely pleased with the machine in its present state. The first area to deviate from the normal factory assembly process concerns the clutch. TT now includes a shim to raise the clutch shoes above the fan hub surface to extend service life. While this is a good idea to subscribe, it is still not enough. The clutch liner is marginal in thickness and minor wear will cause the clutch to shoe clearance to exceed limitations. A space of .005″-.008″ between the shoe and liner is an ideal starting place. This means the outside diameter of the clutch will be smaller by about .010″- .016″ when compared to the inside of the installed clutch bell liner. Unfortunately the factory tolerances are higher causing the shoes to stretch and fatigue. The easiest way to rectify this situation is to use a thicker liner or somehow make the stock liner thicker. A TSK liner works very well if you can find one. Easier still is a method of fattening up the TT liner with a strip of paper glued to the liner full length prior to installation. The paper will face the clutch bell when the liner is glued in place. Paper comes in different thickness approaching that of a thin business card. I have found that a .005’ – .007″ paper thickness meets my requirements. The clutch will engage at an rpm just above idle and may even drag a tiny bit until broken in. This is the ideal starting point for the longest service life. Be warned that if the clearance is set too tight engine starting will be difficult.
TSK clutch liner fits the task requiring no shimming.
The most convenient tool you have for setting the clearance is the clutch. Glue thickness application can alter clearance and a liner cut too long can cause a local high spot. A strip of paper or a few strips of tape rapped around the shoe to a material thickness of .005″ will be best. It must have no overlap upon itself. The correct thickness liner and clutch bell are coated with a very thin layer of epoxy glue and placed into position. The liner length must be exact or even a tiny bit short. A long liner will develop a hump or high spot even when clamped correctly. By inserting the taped clutch into the bell will aid in the establishment of an ideal clearance. A large socket built up to the correct dimension with non overlapped tape can be substituted for the clutch since it will not compress locally as the clutch shoes do and alter internal clamping pressure. Alternately the clutch can be removed and rotated several times to different clamping positions as the glue dries. A little oil on the tool will make this job easier, just remember to clean it off the liner with thinners after the glue cures.
Fan hub offers four fitting positions, clutch shim raises the flexture area off the fan hub and the DTI ensures accurate low run-out operation.
The clutch can bolt on to the fan hub in four positions so select the best one with the lowest runout using a dial test indicator (DTI). Removing the glow plug gives better readings. Be warned that all this technical care is in vain if the engine has loose bearings. This will result in early clutch failure. Matters can be easily checked with the DTI while loading the crankshaft lightly side to side. I find that .001″ runout is fairly easy to accomplish in most cases by using the tester. Do not take readings on the shoes since they may be sprung as most all clutches are by a few thousandths of an inch. Use the inner one way bearing flange.
On rare occasions with other machines, which have had less than perfect runout after selectively fitment of various parts at all possible positions, I have had to resort to stronger measures. The bolt holes in a clutch can be elongated and the big central hole in the fan hub can be reworked to allow the clutch to shift to a best position. Care is needed when removing metal with a dremel tool, a tiny round file and sandpaper. You should first make sure the problem is not in the engine crankshaft trueness before attempting a correction.
Manufactures intent on extending service life sometimes recommend loctiting certain shafts to specific bearing inner races. One such company is Miniature Aircraft. I tend to apply this advice to the Raptor clutch start shaft by bonding it into the clutch bell inner race and also into the top start shaft bearing inner race. This prevents the shafts from wearing out as the softer shaft will eventually spin and chatter inside the bearing inner race. Disassembly for clutch liner replacement will require that the sideframes be split. Heat needs to be applied to the shaft in order to remove and replace the bearings when conditions dictate. In my mind this is well worth the trade off for an extended running time.
It is very easy to site the lateral engine alignment with the servo tray removed. The start shaft must be free running in the over ride direction with no roughness.
All your building skills will be wasted if the engine is not placed accurately into its mount. The only adjustment possible on the Raptor is the side to side engine cant. This is possible due to the engine mounting beam holes being larger than the bolts securing it to the metal mount. I prefer to check this alignment with servo tray removed so I may sight or eyeball final engine placement. The base lines I use are the clutch bell and fan hub. If the setting is excessively canted you will note that the start shaft rotation in the freewheeling direction will increase in friction. In most cases the engine may be carefully installed into the mount with a straight edge insuring ample accuracy, with the fore-mentioned procedure reaffirming a quality engine installation.
There is a hollow roll pin securing the rear cogged tail rotor pulley to the tail rotor output shaft. This pin transfers the drive from the belt pulley to the T/R shaft and if it shears you loose yaw control. I have found that over the long term the pin can distort and eventually fail. This failure is often compounded by tail rotor ground strikes! Replacing this pin with a solid one will reduce this risk substantially. The pin stolen from a washout assembly works well for a replacement but it must be secured with high strength loctite and it must be a snug fit. Numbered drills can be cut for this purpose utilizing only the non-fluted section. A little drop of thin CA at each end of the installed pin will allow extra insurance in that the integration will be positively maintained. Several flyers I know reverse the landing gear struts respectively shifting the aircraft c of g forward. This causes the helicopter weight to bear more on the forward strut and relieve the aft one. The end result is less chance of a tail strike during an uneven landing.
It should be noted that in the TT building instructions I presently have, the application of loctite is omitted for the tail rotor feathering spindles where they screw into the hub. These screws secure the hub to the shaft in addition to supporting the feathering bearings. Care is needed when removing the spindle nuts (which retain the blade grip bearings) so that the loosening torque does not break this most important bond. People have thrown tail rotors due to incorrect assembly and reassembly techniques only to blame the helicopter.
Now that we have the basic integrity of the helicopter up to the task of taking more abuse lets look at some finer points concerning the main rotor control system. The tiny ball bearings on various belcranks and levers are supported by an internal spacer bushing. While this is a very good method of ball bearing support it does introduce minor end play. Loctiting these bushings to the bearing inner races removes all play. Alternately they may be reduced in length by a few thousandths of an inch for the same purpose. I prefer and recommend the former method though. The down side is if you break a belcrank or lever disassembly will become more difficult. The beginner has no need for such construction quality and most likely would not appreciate the benefits.
Negative delta in a flipped grip configuration and also shown is the stock positive delta configuration on the left with its trailing blade grip pitch horn geometry. Shown is half collective carriage travel. The short pitch link is used for flying style adjustment, beginner, scale or 3-D.
A top view showing how the reversal compares to the stock setup on the left.
Many Raptors suffer blade flutter while an equal number seem unaffected. Two of my three Raptors had blade flutter which developed only after several gallons of fuel were burned. Numerous conditions can bring about this problem due to minor imperfections. Older machines are more prone since the control rod ends wear and loosen off, thus reducing friction, which can sometimes mechanically damp out this disturbance. The delta value on this machine is of a positive nature which tends to aggravate an out of track condition if it starts. The thin flexible spindle also contributes to the symptom in a similar fashion. If a blade pops up out of track using positive delta more positive pitch is automatically fed into this blade, thus aggravating the problem. At some point the blade will partially stall robbing energy from the engine and rotor disk. This is commonly referred to as the “woof and puff” syndrome. I’ve had it in a stabilized hover, sometimes immediately after a flare and up high while doing flips. Once it starts the only way to stop it is by landing or by substantially reducing collective pitch. My two affected Raptors use the stock control system configuration with both glass and wooden rotor blades. You will notice that on the Raptor 60 they have made the pitch horn position leading the feathering axis (in the direction of rotation) reversing the delta value to a stabilizing negative factor. The scaled up Raptor 60 to my knowledge does not suffer from tracking disturbances. This means the swashplate will now rise for negative collective and fall for positive. The delta reversal can be done economically and safely to the Raptor 30 with the cost being but one hour labor. The benefit is blade flutter removal whether using stock wood blades or the better composite types. If you don’t have flutter then you can certainly leave matters stock.
By flipping the washout hub there is the same control rod clearance and control rods need not be bent. Shown is approximately half collective carriage travel.
The washout hub will need to be flipped upside down as will the mixers on the flybar carrier. The flybar feathering control arms will be flipped also. As the intent is to flip the blade grips the blade retention bolts will now be inserted from below with the nut locking indents facing up. The washout arm levers that attach to the balls on the swashplate have a chamfer to allow full control travel without binding. Since this modification will move this chamfer outboard a similar one needs to be cut in the forked end using a hobby knife. It doesn’t take much so carefully remove a tiny amount in a beveled fashion. Check the washout drive pin engagement, which by the way will be reduced a tad at the maximum lower collective lever travel. Minor adjustment to the four rotating control rods will be needed. The key is to adjust the zero blade pitch near half collective travel at the sideframe slots and maintain level mixers with a level swashplate. In other words make the mixers level with the long control rods at center collective travel, then adjust the blade pitch with the short rods from the mixers to the blade grip pitch horns.
Top positioned swashplate and full cyclic is possible due to the cut out at the washout link forked end. The left picture shows ample minimum washout pin engagement and a close up of the small notch made with a hobby knige at the normally inboard chamfer. In operation most do not use such a radical swashplate tilt
I have also tightened up the fits between the blade grip bearing bores and radial bearings by applying thin CA sparingly with a tooth pick into the inboard plastic bearing bore. I then fully seat the bearing allowing it to bond in place. You do not want any of the CA to enter the bearing so use a very small amount. Next install the freshly lubricated thrust bearing and carry out the same careful CA procedure to the outboard radial bearing but with the spindle and nut installed at one end only. Pull the spindle to load the thrust bearing and outboard radial bearing into their operating positions. Do the same to the other blade grip. Remember to clean all bonding surfaces with thinner first, which includes the four radial bearing outside diameters.
The bearing outer races are glued with CA to the plastic bosses in the collective lever.
The two larger bearings which fit into the collective mechanism between the sideframes near the mast can benefit from bonding the outer races into their plastic seating positions using a tooth pic application with C/A (sparingly).
Finally for those who want perfection it can be seen when manually flapping the head by hand that the washout drive pins move off parallel with the mast. This is due to the head block rocking on the mast as the plastic flexes or becomes stretched. I use a small amount of five-minute epoxy on the lower portion of the head block during installation to the mast. This is best done upside down with the mast removed from the helicopter and then all excess wiped away. We don’t want the sliding washout hub to bind on any epoxy. Rest assured it is easy to break this bond for mast replacement with the mast/head assembly removed from the helicopter.
Reversing the V-1 landing gear struts can raise the tail rotor clearance from the ground. This is helpful when operating from rough or uneven surfaces.
Reversed strut installation with the antenna loops on the exhaust side and the stock installation on the right.
The normal strut height on the left as compared to the strut reversal on the right.
You may feel that these modifications or building techniques should not be absolutely necessary, and you’d be correct. The guy next to you hammering his machine all season never seems to have a clutch issue, mechanical failure or blade flutter might think otherwise.
In closing all machines have weak points and expect the cheaper ones to have more. Many inexpensive helicopters can be brought up a few rungs in the ladder with a bit of TLC. Another way of looking at build quality is to consider the effort that normally goes into a very expensive upper end model in order to give reliable service. Your plastic model is no different with respect to several key areas.
I ‘d like to keep modelers informed of my findings with the new Raptor gear ratio as it pertains to a 46-engine installation using 550mm rotor blades. This seems as good a time as any to report my long overdue findings. The new ratio or 50 ratio which drops the engine speed for a given rotor rpm allows the 46 engine to load better reducing a possible engine instability issue. You will hear the slang term “wa-waa’s” used to describe the phenomena. While the rate of climb for the helicopter is noticeably improved over the 32 version using similar rotor blades, full engine potential is not available. This is because the engine is not allowed to operate at the higher rpm needed to develop its horsepower potential and tha blades are too short to extract full engine performance. It does seem to be a fairly good trade off considering everything else in the model other than the engine mount and the two gears are left as is. (I partially drilled out the 32 fan to fit the 46 crankshaft. Do not drill out the aluminum threads) I went back however to the TT39 engine using the stock gear ratio since I feel it suits my 30 sized overall needs better. It just seems to have a slightly improved or a more balanced engineering recipe. If I did not have the spare engine with mount and the old gears on hand my reconfiguration decision would likely have been different. The 50 engine however works very well with the 8.5:1 ratio using 600mm rotor blades and longer tail boom.
Note: Positive or negative delta is decided by the flap-feather coupling which occurs when flapping is in the direction of rotor thrust. In other words if pitch is rolled out with up flap on an upright flying model then delta is said to be negative simply because it adds a negative component. This mechanical coupling is caused by the pitch horn on the blade grip being outboard of the teetering point. This is an aviation standard adopted by most all engineers and sometimes confused by modelers.