It is not often that I get excited over a new model helicopter design but today it was different. I have seen designs come and go or one manufacturer copy and add something off another. With the Raptor this is different. This helicopter has some very original ideas, it has also not copied one but has implemented several excellent ideas from other brands. It has done so in a much improved manner. The best thing is that Thunder Tiger, the manufacturer, has kept the price extremely low. Being of a conservative nature I waited for a while after the machine hit the market and observed purchasing trends and comments by many users. When I could wait no longer I purchased the 49BB ARF to see what kind of assembly would materialize. Yes, I buy my helicopters at market price just like most everyone else. This article will convey where I found ARF assembly lacking and what I consider to be sound engineering and why.
Even though this is an ARF model I decided to disassemble and/or inspect certain areas I consider to be paramount to long term model survival. I always check the clutch runout on any model since excessive runout will cause vibration, bearing chattering and wear leading to clutch failure. Some people are having clutch shoe failures and I wanted to do my best to avoid this problem. Spinning the engine start shaft over by hand with the glow plug removed indicated clutch bell wobble with the clutch bell stationary. This is the easiest method to notice clutch runout. So out came the engine and dial test indicator which verified a problem to the extent of .006″ runout, with .002″ being the limit in my opinion. The ARF is mass produced at a very low price so the same care cannot be expected on the assembly line as what we as modelers expect of ourselves.
I was pleasantly surprised upon clutch removal to find some unique design features in the clutch/fan sub-assembly. The fan hub screws on with the addition of a locking nut for extra security. The hub has four possible mounting locations for the clutch allowing selective fitting for minor runout corrections. The runout can be from a combination of engine fan hub assembly and individual manufacturing tolerances. I found that to get the best condition that the clutch bolt torque could be used as a fine tuning. A little bit of locktite or epoxy between the clutch contact area and the fan hub where the low torque bolt pressure was applied assures a tight installation. When the epoxy hardens full bolt torque can be exercised. My clutch had a higher than normal clearance between the clutch shoes and the clutch bell liner but so far has been fine. After the first few flights the clutch stretched and engagement rpm became normal. It now has a full season with this clutch.
The starting arrangement is Ergo like in nature using a one-way bearing inside the clutch assembly
The start shaft runs inside the one way bearing with a hex adapter at the outside end. It has full bearings only unlike the Ergo which uses cheap bushings. The flybar carrier has some end play and this has been found on several raptors. Removing the bushings inside the two bearings and sanding them down equally in length rewarded free and smooth teetering. Many rotor heads suffer minor play in this area. The flybar has limited teetering angles. While there is ample for very aggressive flight there is not too much. What this means is that during a blotched auto the flybar cannot teeter extensively (from a ground contact induced impact) at low rpm causing a non commanded cyclic input to encourage a tail boom strike. The machine is very forgiving for a 30 sized helicopter. Standard are thrust bearings inside the main rotor blade grips to which many plastic and metal machines lack.
The fuel tank chafes on the side frames causing mechanical wear. Installing a foam cushion at these contact areas will prevent this from occurring. The skids should be pulled aft so that the tail does not easily make ground contact. The supports for the tail rotor pitch change control rod are a sloppy fit to the tail boom securing these with goop works very well indeed.The tail belt drive system is simple, accurate and better mechanically supported than any I have seen. The power train as a whole is free running, strongly built and well aligned. The cyclic and collective control design is the best I have seen in any 30 sized plastic model up to this point in time(1999) It has no mechanical crosscouple between the collective and cyclic controls. This is something that even the high end X-Cell and Vario products cannot lay claim to. A simple test for this interaction is to apply cyclic at stationary collective extremes and watch to see if the swashplate center ball rises and falls. Check you buddy’s machine at the club should this claim need to be proved correct!
What I did not like about the model was the lack of wiring attachment points when mounting a gyro behind the mast on the gyro mounting pad.Again goop came to the rescue.
Without going into deep details I’d have to say this model is one of the best plastic 30 sized that I have used. The TT36 engine lacks the reliability demanded by a modeler into forward flight so I’d recommend an OS32 with the ball bearing Raptor kit version. I tried the OS carb on the TT36 and still had problems. I also spent many hours trying to get the TT engine to run consistently. The OS 32 worked perfectly the first and every flight. For those animals out there, a 46 engine can be wedged into the machine with modifications to the engine mount and fan hub (or replacement there of with aftermarket parts)
The problem with the 46 engine is that the blades cannot handle the extra power properly and so engine instability occurs. This is usually noticed as two/four cycling in the hover or during low power operation. To remove this problem wider or longer blades are needed. If longer blades are used then a longer belt and tail boom are needed. Further to this some people are still having engine instability and have resorted to a new 10 tooth clutch pinion which drops the engine rpm and available power. The Raptor model works well in its original configuration and lasts a long time.
Here are some updates on the Raptor for 2001. There is now a clutch a shim available which raises the clutch shoe off the fan hub thus relieving shear loads at the flex point. Expect the clutch to last longer. Two thickness shims are available, .030 steel from Heliproz and .015″ aluminum from ECMC at www.greathobbies.com. The thinner shim means less of a chance for the top of the clutch to rub on the top inside portion of the clutch bell.
This is because it is raised in height due to the fact that the motor mount has no up and down adjustment. The sideframe holes for the motor mount can be slotted downward to lower the engine should this problem occur.
We have begun to see clutch problems after the models accumulated some operating hours even with the shim. After fiddling around we have what we believe is a cure based on the absence of any further failures. We now install the TSK clutch liners which are thicket than the stock units. Clutch engagement is lower being just above a medium idle, a hassle for autos but great for clutch longevity. Thunder tiger has a problem in this area that they are still unwilling to correct. The other matter we ran into after some flight hours was the woof and poof syndrome at the rotor disk. The delta values can easily be reversed by flipping the blade grips and washout hub. The washout hub is flipped to prevent the control rods from interfering with the bolt heads on the washout assembly. The washout arm links that attach to the swashplate need to be notched at the back side so they won’t bind at high cyclic angles at collective extremes.
The only other way I have found to remove this woofing problem is to heat up the rod ends on the adjustable linkages and introduce extra control system friction…not my first choice but it does work. If you flip the grips the collective mechanism will work in reverse. To get the collective setup you desire the short control link at the blade grips may need adjustment along with the long links to the opposite end of the mixer arms. These will keep the mixers level at half stick with zero degrees blade pitch at half collective travel between the sideframe slots. Some of the flutter problem is the spindle flex, swashplate slop, incorrect delta while the other is that the machine generally lacks rigidity. These matters cause minor blade variances by type, size and mass distribution to entice blade flutter. Not every machine will suffer due to a wide manufacturing tolerance of all the parts including blades, blade grip bores etc.
Various upgrades are now available from TT. The metal swashplate is not recommended even though it looks pretty. It is loose and will wear quickly at the center spherical bearing. The radial bearing is of such a poor and sloppy tolerance that it is not worthy to be part of any high grade swashplate.
The TT metal washout has a phasing error built in and will cause the machine to fly slightly out of sync with stick movements. This one will decidedly be corrected or pulled from the market place I am assured.
Our second Raptor was built from a kit because we found it better to buy the 29BBkit then add the OS engine/exhaust along with the TT 20 bearing upgrade. We immediately cut the ends off the metal tail boom supports and glued 1/4 scale rocket city ball links to the ends using threaded rod and epoxy.
All the bearing sleeves were loctited to the bearing inner races to remove any control system end play. The start shaft is also loctited to both bearings. The tail rotor rear pulley has the roll pin removed and a solid pin pressed and bonded in place with red loctite. We used the unfluted end of a numbered drill for the new pin. The two radial bearings supporting the tail rotor shaft are also loctited on at the inner races. We managed to lower the position of the header tank by making our own aluminum brackets for better runs at low fuel levels.
A remote glow connector was fabricated exercising a “L” shaped metal bracket mounted to the engine mount attachment at the sideframes. Since the bracket is grounded, only one wire needs to be run to the engine glow plug. The wire is soldered to the plug after a wire loop was rapped around it. (When the plug wears out cut the wire and reinstall.) Both the plug and wire were tinned first to assure the best joint. Your favourite connector can be used at the bracket. We decided to implement the normal hobby type glow plug connector for commonality to other aircraft. The airframe portion was manufactured from an unserviceable glow plug which was drilled out with a wire inserted and secured with solder. Make sure the wire is stripped of insulation correctly or it may short out internally with the ground side of the plug. The glow plug thread is a difficult one to find a matching nut for so I ran a die over the plug to match up to a common nut thread. Flipping the die for a second new thread cut will allow the plug thread to be bottomed correctly or to be cut deeper. You may think that a fixed or soldered connection on the engine glow plug might cause problems at the flying site if the plug burns out. Since the Raptor can be started using a normal connector with the canopy removed you certainly will not be grounded, provided you have a new plug and the tools to replace it. If the wiring job is done correctly then you’ll never have a loose electrical connector at the glow plug to fiddle fart with at the flying field.
The dimensions for the rotating control rods are ignored in favour setting everything level at half collective travel based on the collective lever assembly sideframe slot limitations. Collective pitch is adjusted to zero at half travel for 3-D employing the short rods from the mixers to the blade grip pitch horns. Varing this rod(s) length will determine the flying style. This enables you to have full mechanical resolution on the collective with the greatest setup flexibility.
The KSJ 32 competition muffler works great but it is vastly overpriced for what it is. I looked at other econo 32 mufflers and found some lacking in volume and flow. I substituted the Century 46 3033A onto the OS32 by drilling a hole to match the engine exhaust port bolt spacing. This muffler can now be fitted to either the 46 or the 32. The old lower 46 hole is filled with JB weld then the new bolt is secured with a nut. The nut is necessary because tapping new threads is not possible due to the close proximity of the new hole to the old.
We have used CMT550 carbon, SAB550 glass, Stock TT woodies and KSJ woodies. For the money and flying qualities the SAB are the way to go. We shop and recommend www.cyberheli.com for the \\$35US SAB 550 glass rotor blades.
We will be running a governor on the second machine in the future since the first liked the GV-1 so much. Did I mention the holes for the magnets are molded into the plastic fan? Great idea and thanks to some person with foresight, showing just how well thought out this machine really is.
Remember…whatever you can make or repair yourself will save money. You’ll also have personal satisfaction in that you’ve improved the machine with your own two hands, better than the orginal engineers intended.