Designing a Stronger Raptor
Before building a model helicopter its role should be considered. Deliberation to the flying skill of the modeler and to the flying style come to mind. For the beginner easy disassembly becomes an important factor. For the skillful 3-D flyer using an extreme rotor rpm a strong and more permanent build up takes precedence. The advanced or sport flyer who rarely crashes can also take advantage of a more solidly built mechanism.
The reasons I picked the Raptor V-2 for this building exercise have to do with its popularity, wide flight envelope and the fact that many beefed up areas are the result of the factory listening to the masses or to the people who actually purchase and fly the product under less than ideal conditions. The original version of the Raptor 30 worked out very well indeed, but like most things in life it was not perfected on the first attempt. Thunder Tiger has a firm hold on the 30 sized market which will not be wrestled away easily by the competition in the near future for these justifications. The techniques mentioned below may be applied to most all helicopters where the design allows. At the risk of boring some of you, some of the methods embodied are mentioned through an earlier V-1 article, but most may still be applied to the newest version.
By having a look at the history of the Raptor it can be seen that what was intended as a 30 has evolved into the 50 through the result of a grass roots movement. Individuals initially were drilling out fan hubs and adapting motor mounts to support the 46- 50 sized engines. Aftermarket companies quickly jumped upon the bandwagon with fan and engine mounting kits. It was abruptly discovered that longer blades and a longer tail boom were needed to correctly harness the larger engine power. Still some people had engine handling issues with the longer helicopter so the gear ratio was then altered by means of a clutch pinion change. Since the main gear initially remained stock the gear mesh suffered. A noticeable amount of mechanical incompatibilities like this cropped up with these hasty upgrade companies. During this time Thunder Tiger carefully and patiently watched as some blundered while others had success. After gathering accurate information from a free market data base they implemented a more accurate upgrade program then manufactured said products to the same close tolerance as the helicopter. This took the market by storm but was certainly not the end of it. I believe that by this point in time the design team had bigger fish to fry in the board room with regards to the R-30 program.
The desire for the larger engine installation actually came from the need for better 3-D performance in a rather inexpensive package both purchase and operational wise. Still, as inexpensive as the conversion is for the added fun factor, there comes penalties of increased size and weight creating a substantially higher fuel consumption, higher capital cost, and more airframe stress. In other words for some, the overall gain is not as attractive as one may think when the Apersonal big picture” is viewed. Do not get me wrong because the added 50 flight performance is definitely there, but at increased cost. These factors are reflected in the conversion. Many people do not need a massive power injection afforded by the 46 or 50 engine size to give them the edge they want for 3-D in a box. Now with this reasoning the TT39 ringed engine has been born. The average guy on a budget competently turning the machine inside and out during his flight will appreciate the slightly bigger engine in the standard 30 ship format.
As I go over important building segments, improved V-2 areas will be pointed out including the reasons why. By having a look at the 39 engine it is conceived to ideally maximize the mechanics, power train and cooling shroud. The ringed piston will stand up to abuse much better than the non-ringed version. Power is up due to added displacement while the fuel burn increase is of a very minor nature. The engine is manufactured on the latest CNC equipment so the fit of the internal parts is at the top of the ladder. This is the first 40 displacement helicopter engine I have seen offered with the external 32 dimensions. Rest assured others are going to follow this lead. We have by the way installed the TT39 into the Version 1 and found the power to be much better than the 32-36 installations. It is also a very easy to tune engine which holds its setup well during changing ambient conditions.
The first thing to do with this engine is to correctly install the fan carefully by holding the crankshaft as the retention nut is tightened. The fan does not need massive torque to screw it to the crankshaft prior to the nut installation. The big mistake some make is to hold the fan as the nut is installed which can cause the crankshaft to screw away from the fan. A toothbrush handle in the carb mounting hole is a good way to lock the crankshaft during nut tightening. The nut needs blue loctite to keep it secure or alternatively a high friction locking nut may be used.
Now comes the decision for best reliability. Do we just install the clutch to the fan hub, or do we use a dial test indicator(DTI) to perfect the situation? I recommend the DTI method for all helicopters, but if you do not have the tool then you should receive assistance from a fellow modeler who does. Many times when I install the 30 clutch the runout is fine, but often enough it is not, the same goes for most helicopters with this type of clutch system. The DTI is needed to verify the clutch runout, because TT cannot control engine bearing and crankshaft tolerances which will sometimes affect how the products fit together. The Raptor clutch has four fan mounting positions for the clutch so select the one that gives the lowest runout. If by chance the runout is still greater than .002″ I recommend very carefully working the fan hub bore and the clutch mounting bolt holes with a file or Dremel tool. Keep in mind if you need to alter the runout by .002″ indicated then only material which is half this dimension need be removed. TT now supply a special thin steel washer to raise the clutch flex area up off the fan hub to increase longevity. TT could have machined the area on the fan hub but that would reduce selective clutch positioning to two choices. A smart and wise decision in my opinion.
Since a correctly centered clutch works within the clutch bell, attention to its interior should be given. The liner needs to be installed correctly to offer the best clutch shoe clearance and lowest internal runout. We have a large control over these two issues during the build which can reward us with extended clutch bell bearing and clutch shoe life. It may also reduce high frequency vibration. Let it be stated that a clutch with a larger clearance between the shoes and liner will not last as long as one with a minimal gap. If the gap is too large the clutch flex area will be strained and crack, if the gap is too small then the clutch will drag at engine idle. Slight clutch drag at engine idle is preferable to an overly flexed clutch shoe. The gap should be .008-.010″ which means the installed liner inside diameter (ID) is .016-.020″ larger than the clutch outside diameter(OD). It should be mentioned that the V-2 clutch flex or sprung area is now larger to offer a wider section to better distribute bending stresses. The clutch circumference is larger as is the clutch bell ID. The new clutch is thinner and so the new and old shoes have about the same contact area. The liner length needs to be cut short leaving a tiny space when installed firmly into the clutch bell. This is to prevent bulging or internal runout. This is one of the overlooked errors when installing a clutch liner. Another over looked parameter is the clutch shoe clearance dimension mentioned above. Since the clutch bell inside diameter is fixed as is the liner thickness you may wonder how we will make concessions here. This is completed or checked through a dry fit measurement prior to gluing the liner. It can be done mathematically by subtracting the liner thickness times two from the clutch bell ID and then subtracting the clutch OD. The clutch OD is measured at the non-flexed area. The other way is to measure the installed non glued liner ID and subtract it from the clutch OD dimension. Once we know the actual clearance we can reduce it by CA gluing .002″ thickness or larger paper to the back side of the liner. The liner must be cleaned with thinners before gluing the paper to the liner. In most cases this will not be required since the fits are so much better these days. When we do establish the proper fit, the liner will be glued with 5 minute epoxy into the solvent cleaned clutch bell. To accurately press the liner into the clutch bell while the glue dries and also to encourage even glue squeeze out we could use a large socket rapped with masking tape. The tape sets the socket size large enough to push equally, and firmly force all the liner bonding surface (paper side if so shimmed) into the clutch bell.
My V-2 kit came with the liner pre-glued and so I measured the liner to shoe clearance. It came to .010” per shoe which is a good fit. This is unlike the original Raptor which came with about .015” or larger clearance. I see no reason why the correct tolerance will not be standard with all V-2s and so the above techniques may be unnecessary during the initial build.
The clutch bell has two bearings, one inside and one on the top of the pinion gear. The pinion bearing needs to be a press fit to last. If you can pull it off by hand then my advice is to bond the inner race to it with loctite sleeve retainer. This will mean that the sideframes need to be split to remove the bearing or clutch bell. The benefit is the bearing will not chatter and wear the pinion end. The start shaft is larger on the V-2 and this allows the clutch bell inner bearing to be larger and the start shaft to be thicker partial length. The bottom line is that the clutch support now becomes stronger over the original design and the hex adapter set screws will hold better. The start shaft uses a clip to locate it height wise and I recommend bonding the start shaft to the clutch bell inner bearing inner race for added strength. The same goes for the top start shaft bearing. All this is best done before the sideframes are assembled. The clutch stack-up now includes a thrust washer on top of the start shaft circlip located above the one way bearing, so do not forget it. The sideframes need to be screwed together at the start shaft/clutch bearing block areas before the bonding agent cures to seat the bearings most accurately.
The V-2 clutch bell pinion has been bored out so the larger start shaft will fit and the top start shaft bearing is a different size both internally and externally for the same reason. Because of this a compatibility issue between the V-2 and the original exists. This is also reflected in the sideframe design. A V-2 clutch system cannot be easily fitted to the older version without using a home made top start bearing outer race spacer of .5mm wall thickness and a 15mm ID. The new type top bearing OD is 15mm while the older is 16mm. One minor thing I did notice is that the gear mesh is not as smooth as what I have come to expect from the Raptor and I have traced the issue to the pinion teeth. The new pinion gear will eventually break in I expect.
It is best to install the engine slightly loose to the aluminum mount and install the assembly into the helicopter with the servo tray removed. One can then sight the engine fan hub and clutch bell from the front of the helicopter to set the lateral alignment as the four bolts are tightened. Looking sideways the fore/aft alignment can be checked also. A final check of your handiwork may be done by removing the glow plug and turning the engine over by hand, if a stationary clutch bell wobble can be seen by the naked eye then the clutch run-out is too high.
The sideframes are changed in design in order to add mechanical drivetrain reliability, extended fuel tank size and offer better support to an optional 50 engine mount. The engine mounting area on the sideframes have a third lower mounting lug for this reason. This allows the lower sideframe engine mount screw not to interfere with the lower engine fixing screws when tightened in. Looking at the rear it can be seen where the added tank width is offered up by means of a minor alteration to the molding. Wire routing points are now part of the frames to keep gyro and servo wires tidy, secure and out of harms way. Also notable is the reinforcing web to the front legs which doubles as a fan shroud extension. The fuel tank outlet now uses a 90 degree fitting which gives an easier and neater fuel line routing.
The red idler pulleys at the rear of the sideframes may have the two shafts loctited to bearing inner races. Moving aft to the tail rotor shaft we see more improvements. It should be stated that the new attachment method for the aft toothed pulley mounted to the tail rotor gearbox shaft is now fitted in a very secure manner. The V-2 drive pin is now solid replacing the weak and hollow roll pin. It is retained by a setscrew threaded into a hollow section of the output shaft. A very good idea as the old pin could fail under adverse conditions. I tend to loctite the shaft bearings and assemble the gearbox before the compound cures. Make sure the bearings are fully seated in the case halves first. The guarantees there will be no end float in the shaft even if the case pinch fit to the bearings gets a tad loose over time.
The tail rotor hub and grips/bearings are from the 60 machine. Many have already modified the older Raptor 30 with this stronger configuration. This is one area that really needed this upgrade when exposed to the rigors of 3-D and high rpm. For the beginner the system will safely tolerate ground strikes much better. The new tail fin is longer to keep the tail rotor blades away from the ground during uneven terrain landings.
The boom supports now have plastic end fittings because after a time the old type “work hardened flattened ends” would eventually crack from normal vibrations. In the past, many have cut off the flattened ends of the older supports and then installed similar fittings. Great, now we have but another item we can fit and forget!
Basically the only part left to re-manufacture might be the rotor head. I have had no issues with the original version but apparently some have and so TT re-manufactured it by beefing up the spindle size, teetering bushing and blade grip thrust bearings. While the radial grip bearings are different and although they have the same basic load carrying abilities their location in the blade grips has been altered. The bearings are spaced further apart in the grip with the end result being a better supported assembly. This adds up to less slop and added strength. All these changes are great for safety since there is no question as to running 2000rpm/550mm blade speeds. It has the structural margin to handle heavy 600mm blades should a 50 mod kit be installed in the future. Some machines suffered blade flutter and the added strength will only improve the situation even with so many blade types available. We had one V-1 machine that was cured of flutter by flipping the blade grips to reverse the delta values to a negative one. Many others at the club never had the problem. One overlooked variable that may also contribute to the issue could be running high rpms with shrink tubing covered blades, even though the issue has at times been witnessed with glass blades. In any event the inboard covering needs to be removed to glue the plastic blade roots on for safety, so we tend to remove it completely.
We then glue the root fittings as recommended, paint the exposed wooden roots and tips to fuel proof. After that we apply fixed wing iron on covering that actually sticks to the wood blade surface. This type of covering will not lift from the airfoil surface during extreme angles of attack and airspeed. Blade flex will not affect the covering either. There is very little flex at 1800-2000 rpm though! You may be surprised that in most cases one can complete the same sweet maneuvers that composite blades allow.
With most plastic rotor hubs long term stress will stretch the fit to the mast. Eventually the hub will rock slightly on the mast during blade flapping or cyclic inputs. Some of this play or slop comes from the retention bolt squeezing the head egg shaped over many flights. The cure is to epoxy the hub to the mast and tighten the bolt before the glue cures. The machine now comes with the correct shouldered or long shank bolts both at the freewheel hub and at the main rotor hub. The shear loads at the mast are effectively dealt with in a sound engineering manner. I hope other manufactures take note of this fact and follow suite.
For the person who wants the best build possible I recommend as I have in the past, to carefully bond the control pivot bushings to the bearing inner races with loctite. This procedure may include mixers, washout arms and the flybar teetering points but not the flybar feathering bearings. You need clean parts and very little bonding agent since you do not want to contaminate the bearing. This process removes all end play. The bearing inner bushings are very accurate but there is sometimes a few thousands of an inch of play so this is the reason for the extra consideration. This will also guarantee that the bearings will rotate and not the bushing inside the bearing inner race. Remember though, since these parts are essentially glued together they will be harder to disassemble.
The collective lever which supports the roll belcranks is stiffer and is interchangeable with the original Raptor unit. While some may think this improves flight performance, I have found no difference. It will however stand up better in a crash.
Sometimes after crashes the plastic sideframes strip out where the landing gear attaches and many substitute nuts and bolts. Some will even install the V-1 landing gear struts backwards to raise the tail. With the V-2 this is not the case since the struts are specially shaped for a newer type canopy retention clip. The new canopy will fit the old helicopter but will need the newer rear canopy standoffs. The V-2 has a longer common part number vertical fin to keep the tail out of the ground. Completing some or all of the ideas as needed will add reliability and enjoyment to the hobby. This is a great little machine that deserves the building attention the bigger and more expensive machines normally receive. Thunder Tiger have also beefed up many other parts that are compatible with both the V-1 and V-2. These parts retain the same part numbers as the older ones so you can rest assured that servicing both the older and newer version will not conflict in this respect. I expect the older parts with the common part numbers will be slowly phased out as stock diminishes. Just remember the new side frames require a new clutch system and fuel tank, the tail rotor hub and blade assemblies are different plus the newer rotor head uses different parts. All the small issues I had with the V-1 have been taken care of accurately by TT in a timely manner, and I feel they should be given the pat on the back they deserve. These product updates are much better than typical bandaid fixes we sometimes see.