Kyosho Caliber M50

Background

On October, 1999, Kyosho showed a prototype 50 version of their flagship Caliber 60, the Caliber M50.  The Caliber M50 is basically a miniature Caliber 60, targeted at Japan's F3C-M rules which is gaining popularity.  The F3C-M rules is based on the 1995 FAI F3C maneuvers, and is strictly limited to up to 50 sized engines.  As with the Caliber 60, the Caliber M50 is once again designed by Mr. Makato Kunii, a well respected helicopter designer in Japan, who also owns Correct, a Japanese helicopter parts manufacturer.  Being a happy customer of both the Caliber 60 and Correct products, I have confidence that the Caliber M50 would maintain the high precision and quality in line with Mr. Kunii's products.

The Caliber M50 inherited the main frame of its bigger brother.  It is a box consist of eight pieces of machined aluminum, instead of the usual stack frame as found on most helicopters. All metal parts are made with 2017S alloy which is lighter and harder than regular T6061 which are popular amongst other helicopters. Two pieces of 2mm plates are used on the front of the frame for servo mounting. Control is through a three servo 120 degree ECCPM mechanism. Power from the engine is transferred through a belt first to a secondary gear that drives the main gear and the tail pinion to the tail. All top helicopters said they have a CG mounted fuel tank, but the Caliber fuel tank is situated right under the main gear, which make difference of fuel level ineffective to the helicopter's CG, the best design that I've seen so far. The Caliber M50 listed for 160,000yen in Japan (about US$1,300), and once again is the most expensive 50 class mass production helicopter ever.

After seeing the M50 prototype, I waited patiently for the M50 to release officially. I asked Mr. Kunii the progress of the M50 release every time when I have a chance. Luckily, I once saw several prototypes of the M50 in Mr. Kunii's office, and did get my hands on them.  The initial impression was that the M50 flies more like a 60 class machine, with the precision and stability.  After trying the Caliber M50 of Mr. Kunii's, I wanted the M50 more. (I also have to admit that being a friend of Mr. Kunii's does give some influence to me getting the Caliber M50) The M50 was officially released on early 2000, but strictly to the Japanese market only. I got my Caliber M50 through Mr. Kunii right after its release. However, its up till late 2000 when I start assemble it.

Assembly

The box of Caliber 50M does not have any "jewel showcases" to show the parts as with the 60, but all parts are neatly packed in bags and traceable in steps. Preliminary checking of parts reveal that metal parts are being made by machining and forged. Machining of the metal parts are very popular amongst r/c helicopters, but forged parts are rare.  I remember once when I had a chat with Mr. Kunii in his office, he did mention that machining of parts is not always the best way to manufacture metal parts, and he found that for some parts it would be better to forge instead of machine.  Forged parts would yield a higher density that strengthen the part made, but forged parts are harder to make and cost more than machined parts, according to Mr. Kunii.  In the Caliber M50, forged parts are present mostly in the transmission system.  All metal parts are very high quality made.  All metal parts of the Caliber M50 are not anodized in any color.

Further inspection reveals that the bearings that comes with the M50 are once again inferior Thailand bearings. I can't say enough the bad things about these inferior bearings, and at the high price of the M50 it should come with better bearings. Once again I have to change the bearings on the high speed rotation points to better quality ones by myself, and that means more work and money wasted. For my M50, I used bearings made by SKF of Sweden, and NSK of Japan. I spent about US$170- for the better bearings.  Since most bearings that needed to be changed are pre-installed in metal parts, I have use the "heat method" to take the old bearings off without damaging the part.

Part I - Main frame and drive train

First few steps dealt with the assembly of the main frame and drive train. The main frame is constructed by bolting together eight pieces of aluminum frames and two pieces of aluminum plate as platform for servos and various mixers.  I am quite surprised that the servo frames are in aluminum, not graphite as shown in the prototype machine. At the price of the Caliber M50 I expect graphite servo frames.  Nevertheless, I have a set of graphite servo frames made by a friend who has hydraulic cutting machines.  These frames are made to the exact dimension of the aluminum frames, but due to the hydraulic cutting method, the sides of the frames are smooth and round, and does not need extra work to smooth out the side to prevent chaffing.

For all aluminum parts of the main frame, I used stainless steel cap screws to fasten them together. When bolting together these aluminum frames, make sure that the right side is facing the right direction. The manual do not clearly show the correct orientation of each frame. The two pieces of upper frames that also supports the gears are being secured by 3mm cap screws through collars to two pieces of horizontal frames. The manual said to assemble the whole frames first, then assemble the fuel tank later and bolt that to the frame.  This is illogical, which required partial disassembly of the frames again at later stage to fit the fuel tank. I disregard the manual and assemble the tank together with the main frame. The fuel clunk is made of some porous material that enables fuel to be absorbed on the whole surface of the clunk. The nipple is a aluminum item, and secured to the grommet by a nut. The fuel tubing that runs inside the fuel tank is not flexible enough, so I changed that to better ones from IM. The fuel tank have four protrude "legs" that are to fit into four rubber dampers that goes into the main frame. When fitting the tank, it is best to first press the dampers into the frames before mounting the tank, cause its a very tight fit. While assembling the frame, the great design of the Caliber frame shows, as I could fasten all screws once and for all without worrying about alignment.  I tried aligning the frame on a flat piece of glass with an angled rule, and found alignment of the frame to be true.  Putting of the two pieces of servo frames to the front of the main frames completes the assembly of the whole main frame.

The drive train is next to be installed. The drive train runs from the clutch pinion, through a belt, to a main belt pulley, then drive the tail belt pulley and the main gear pinion, then to the main gear. The main belt pulley, tail belt pulley and the main gear pinion are all fixed on to the same axle, with a one-way bearing installed inside the main belt pulley to provide autorotation. Two set screws were used to secure tail belt pulley and the main gear pinion to the axle.

Later, Kyosho introduced a 87 tooth main gear for a gear ratio to properly match the output of the OS50.  The original gear that comes stock is 89 tooth, and is molded from plastic.  This optional 87 tooth main gear is machined in Delrin, which has more precision.

The main shaft, shaft holder and main gear are installed next. The main shaft is a 10mm diameter solid steel pole. The manual do not point out clearly the orientation of the main shaft. It has one hole on either end, but the holes are not the same distance from the end.  After some measurement, I find that the one end with a 3mm hole that was farther from the end was to be mounted on to the main gear, and the other end is to be fitted to the rotor head. The shaft holder is fitted against the underside of the upper main mast bearing holder. The whole drive train has no gear mesh to set, and operate very smooth. The drive train system provided constant tail driven autorotation mechanism, with no slipper clutch for adjustment.

Close-up of the collar that slot into the frames	Close-up of the collar
The assembled main frame	Close-up of the rear main frame
Servo frames - upper: metal, lower: carbon	Close-up of the carbon servo frame
The servo frames installed	Close-up of the fuel tank. Note dampers.
	¡@
Optional 87 tooth machined Delrin main gear	¡@

Next up is engine installation. Originally, a taper collar is to be fitted first onto the crankshaft, then the clutch, clutch bell, and secure by the start shaft adapter.  The stock clutch is a forged metal unit, but later after the introduction of the OS50SXH Kyosho introduced an optional clutch that is made by spring steel, and use woodruff key instead of taper collar to seat the clutch on to the crankshaft.  I choose to use the optional clutch cause I choose to use OS50 SXH as power plant.  While fastening the start shaft adapter, its best to use the OS piston locking tool, and to put some loctite on the thread of the main shaft. The whole assembly is very clean, and does away the need to dial indicate the clutch.  The engine, with the clutch assembly, is then sit on to the engine mount.  The engine mount is two pieces of aluminum that clamp on to the main frame. Four pieces of shims are provided to adjust the tension of the belt.

The whole engine cooling mechanism is similar to that of Caliber 60, where a free rolling fan would be located on top of the engine's heatsink inside a straight fan shroud, and the fan would be powered through an O-ring that connects the fan to the clutch.  Since cooling is a problem with Caliber 60, I suspect the same problem will also be evident on the M50.  The fan of the M50 is a five blade plastic fan, not aluminum as with Caliber 60.  The fan is mount on to a piece of aluminum frame by a 4mm screw. I find that the collar that slot into the bearing of the fan have vertical play of about 0.5mm, and that might induce vibration, so I trim the collar down to eliminate the play. The whole fan assembly is secure to the main frame by six 3mm screws. The fan shroud is in two piece plastic that slips on to position with ease, and is secure by four of the screws that also secure the fan mount on the main frame. While fastening the fan shroud to the main frame, be sure not to use excessive force as this will deform the bulls eyes of the shroud.

Part II - Rotor Head and Control Mechanism

Same as the Caliber 60, Caliber M50 uses 120degree ECCPM mechanism for cyclic control. The 12 o'clock control point consist of an arm that use a linkage to control the 12 o'clock point of the swashplate. The control arm clamps on to an axle, with one end of the axle hold in position by an e-clip and the other end is a push-pull bellcrank for servo control.  This axle is very near to the hex start adapter, so during engine starting the start shaft could hit this axle and damage it, so care must be needed during engine start. The other two swashplate control bell cranks are T-shaped arms that are mounted on both sides of the frame.

The swashplate comes pre-assembled with linkage balls. The washout arm assembly consists of two control arms that pivot on to a base, and a pair of swashplate links pivot on the arms with two ball bearings on each arm. The washout base is unusual in that there were two guiding pins that sticks from the base, and those pins go through the washout fixer. This design gives bigger pitch window without the pins hitting the swashplate.  Same as the Caliber 60, these pins on the M50 are off on the base that make pitch change "sticky". I have to bend them slightly to make them slide in and out of the fixer with lesser friction.

The rotor head comes pre-built, but I have to disassemble the whole rotor head to change for a defective spindle.  After initial release of the Caliber M50, Kyosho issued a recall and ask owners of Caliber M50 to exchange for an updated spindle shaft, due to the fact that the original one have mechanical problem and might break during flight.  Mine happens to be amongst the few that are being recalled, but gladly my friend Mr. Kunii, the designer of Caliber, send me some of these updated spindles.  Aside from changing the spindle shaft, I also change the original damper to the optional 3D dampers.  The optional 3D dampers are made by Kyosho, said to have better cyclic response, and would minimize boom strike during hard knocks  3D maneuvers.  The 3D dampers are machined Delrin spacers with two O-rings that act as damping unit, and due to limited damping is provide with these dampers I predict cyclic should be very responsive. The flybar is a 3mm black metal that goes through the seesaw unit on the top side of the rotor head, and the flybar paddles (Same item as Kyosho Concept) are then screwed on to the flybar. The standard flybar control arms are in two separate pieces, but I change that to a part made by Correct which is a one piece design to aid alignment.  After complete assembly of the rotor head, I put it on a high point balancer to make sure the head is balanced.

Next is the fitting of various pushrods to the mixers and bellcranks. These pushrods are stainless steel 2.3mm type, not the 2mm flimsy ones on the Caliber 60. I change the stock ball links to use Pioneer oil filled ones for smoother operation.  As to the flybar and paddles, I changed the stock one to Hirobo ones for their better performance.

Spindles - Upper one is the recall one	Rotor head
3D dampers (white) and stock dampers (black)	Close-up of the swashplate and mixing control
¡@Rotor head with Correct flybar control bracket	Close-up of rotor head

Part III - Tail

The tail hub was a machined aluminum part, with blade grips in plastic. The tail blade grips were supported with two ball bearing on each side. The tail pitch slider was another aluminum part, with the arms in plastic, and was supported by two ball bearings. As mentioned previously, the tail was powered by a belt, so the tail gear box was pretty simple.  The tail belt gear is once again a forged aluminum part, which is made in very high quality.  However, during assembly, I found that one 2mm hole that is used to secure the backplate of the tail gearbox was made without thread, and I have to re-thread that manually.  Where is Kyosho's quality control anyway? I am lucky enough to have the required tool to do this, but others might have a big problem with this.

Tail pitch control is through a bellcrank that controls two pieces of aluminum on both the upper side and the lower side of the pitch slider. This design provided a slop free control of the tail. The whole tail gear box assembly was then slotted into an aluminum tail boom and secured by an aluminum clamp. I was surprised that the tail boom was not in carbon though, given the M50's high price.

Before mounting the tail boom to the main frame, I have to slot the two tail servo mounts on to the boom.  Do not secure the tail servo mount yet cause later their position had o be adjusted when setting up the tail servo. The whole tail was then secured by two pieces of plastic parts to the main frame.  After fastening the tail boom to the main frame, I found that the tail boom slips easily on the grip, and even with plastic tapes wrap on the end of the boom the boom would still slip.  As a result, setup the tail boom at the required tail belt tension, drilled and thread a 3mm hole on the tail boom grip and the tail boom, and use a 3X6 hex screw to hold everything in place.

The tail boom supports are once again in aluminum, and is secured to the tail boom through a two piece grip which also is the horizontal tail fin mount and happens to be the same as the tail boom grip.  To prevent slippage, once again I drilled and tapped a 3mm hole on the grip and secure it with a 3X6 screw.  All through the assembly, the Caliber M50 gave me an impression of precise and good design, but these good impression are being wiped out with all the flaws and pitfalls with the tail assembly.

Part IV - Radio Installation and Final Bits and Pieces

I used JR PCM10X with DS8201 digital servos, and Futaba GY502 gyro with 9253 servo for tail control. The DS8201 digital servos were specially designed for ECCPM controlled helicopters cause there was no mechanical limit difference between each servo, and they were very precise, so movement linearity of the swashplate was guaranteed.

Servo installation were no bugger. Each servo, except the tail, was secured to the frames using 2.6mm cap screws. However, do note the orientation of the servos. All servos on the main frame should have their axles near the back of the helicopter, while the tail servo should have its axle near to the back the main frame.

On the first page of the instruction, there were "FOR ADVANCED FLIERS" printed in bold. While installing the radio components, I know what that meant. For radio installation, throughout the manual there was virtually no data given as to what servo should be reversed or what were the ATV settings. Also, Kyosho clearly showed their alliance with Futaba, as in the manual all servo horn shown were Futaba ones. If you use JR, like myself, you are almost on your own. As a result, I had to set up the radio based on my experience. First, I assembled all control rods according to the length illustrated in the manual. Then, I turned on the radio, set swash (mode 65) to 120degree ECCPM operation, and set everything center stick. Next, I had to decide what servo disc to use. For swashplate control servos, I used the big disc that comes with every super servos, and I used the outer holes that measured about 15mm from the axle as prescribed by the manual. I aligned the servo disc with control points 90degrees to the bellcrank control points, mark the holes to be used, installed the control balls, and snapped in the linkages. Finally, with the control center stick, I checked and adjusted all pushrods to make them level, and with a pitch of 6 degrees. The following data were what I used for swashplate control servos that give extreme controls without binding, and provided a pitch window of 20 degrees:

The throttle servo was installed next. I used the outmost hole of the regular "+" shaped servo horn, and it was about the same length as the outer hole of the throttle control arm. I carefully set up the middle position so that full throttle range can be covered with 100% throttle ATV.

The tail servo was the last servo to be installed. As with the Caliber 60, the 50M also featured the same  tail servo mounting, as the servo was suspended under the tail boom by two aluminum servo mounts. Gone are the push-pull tail control mechanism of the Caliber 60, and replace by a stainless steel pushrod.  I kind of like the push-pull system of the Caliber 60, and later I might retrofit that into the M50... 

Final bits and pieces involves installation of landing gears, mufflers, blades, canopy, fins and securing receivers and routing wires. The landing gear was mounted to the main frames through four aluminum spacer, but I replaced those with small rubber dampers used in Hirobo Eagle to adsorb shock from hard landings.

For muffler, I used a K&S HN50 Left muffler that was specially for the CaliberM50. This is the only muffler available for the Caliber M50 to use a OS50 SXH engine, others are just designed for OS46 FXH.  This muffler is a standard item for the Kyosho team.

The main rotor head accepts main blades with length up to 620mm. I used Hi Products PG 50L 600mm blades. The Hi Products PG series is FRP counterpart to the PX series.  Same as PX blades, PG blades features changing airfoil, on the root of the each blade are S-chamber airfoil, and will transform to symmetrical airfoil on the tip.  This blades are design to have the best performance for both hovering and aerobatics.  While the PG50 is not cheap (US$140- a pair), but the performance of these blades are definitely worthwhile.  I have been flying other PX and PG blades with good success, so I know how good this PG50 blade would be.  The PG50L blades were in fact the "team" blade of Kyosho for the Caliber M50.

The canopy was one piece FRP laminated in white, and comes with markings for window in black. While I found that the canopy is on average in quality with other makes, later I found that these canopies are in fact being made in China, not Japan, and in fact through my friend I bought two more of these canopies for spare.  I had a sense of dissatisfaction knowing this, cause with the price of Caliber M50, I would expect it to be completely made in Japan.  According to the manual, a hole on the left lower side of the canopy should be opened for ventilation, I did that, but also I cut a large triangular shaped hole in the lower middle part for more ventilation.  According to my experience with the Caliber 60, the cooling fan does not provide enough current to cool down the engine, so a big hole has to be cut in the low middle portion of the canopy to enhance cooling, and this is recommend by Team Kyosho.  I suspect the same problem would happen with my Caliber M50.

The fins were made of graphite, and decals were used to cover the openings on the fins. The fins featured optional cut-out section.  I left the optional opening intact, and covered the fins with decal, only to find out later that the CG is a bit off to the tail, and if I had cut out the openings I could have shaved some weight off the tail and enhance the CG.

Right side of the main frame with servos installed	Carbon tail fins with optional cut-away holes
Close-up of the tail fin	Close-up of the tail, note K&S tail blades
Rudder servo that "hang" underneath the boom	Tail pitch mechanism, precise and smooth
Canopy	Hirobo flybar paddles
GY 502 gyro
Close-up of cyclic control	K&S HN-50 (Left) muffler

Flight

The first few flights of my Caliber M50 was to set up the helicopter and break-in the engine.  I hovered the Caliber to set the trims, checked for tracking, and set the head speed.  I set the head speed on around 1,450rpm for hovering.  There were no apparent shakes, wobbles or vibrations.  Then I started to do some hovering maneuvers.  Hovering was rock solid with precision and control like a very refined 60 class machine.  During hovering, the Caliber M50 was very silent, mainly due to various belt driven drive train.  However, one thing that I found was that the tail of the Caliber M50 was very slow in response, and even with tail ATV cranked fully tail control was still very slow.  After several flights, I concluded that the tail did not generate enough current to provide adequate control.  In fact, the tail power was so weak that during aerobatics the tail could not hold still.  In addition, the engine ran very hot, and no matter how I adjust the mixture the engine would run hotter than normal.  According to my experience with the Caliber 60, this should due to the inadequate cooling provided by the tiny cooling fan of the Caliber M50.

Viewing the tail control and cooling problem, I further modified the Caliber M50 to target these deficiencies.  To target the cooling, I had opened a big hole on the lower front side of the canopy so that fresh current could be drawn for better engine cooling.  However, with the inadequate tail power, it was more complicated.  Judging from what I saw on the Caliber M50, I thought increasing the speed of the tail rotor would provide better control.  So, I went to my machinist to make two belt gears in smaller dimensions which should generate more RPM for the tail, and put that onto the Caliber M50.  After these two modifications, the tail control became very snappy and cooling improve.  Although I could fix these two problems by myself, I was very disappointed with Kyosho cause these problems should have been fixed before they push the Caliber M50 to the market.

After the modifications, I took the Caliber M50 to the field to setup for aerobatics.  For aerobatics, I set the head speed to around 1,850rpm.  Vertical climbing of the Caliber was second to none, and even with the engine on the rich side it seemed that it wanted to punch a hole in the sky.  Fast forward flight was fast and tracked straight.  However, the cyclic of the Caliber M50 was a bit numb, and roll rate was very slow.  I changed back to the stock paddles and flybar but still does not change much, and even using K&S paddles did not help.  Further investigation revealed that the rotor head could only provide about 10 degrees of flybar deflection, and this might be the reason why roll rate was slow.  Another trip to my machinist with the main rotor hub result modification on the hub that would enable flybar deflection of more than 20 degrees, and with this modification the roll rate became fast and snappy.  It is after all these modifications that the Caliber M50 showed its true color.  Now, I could throw whatever maneuvers at the Caliber and it will reply to me with very sharp precision.  The tail was very powerful after the modification.  However, cyclic response was adequate for F3C maneuvers, and 3D pilots would want faster response.  Acrobatically, I'd say it compares to the Hirobo Eagle Freya EX with a 91 engine, the helicopter of Mr. Hashimoto who graciously let me tried when I was in Hirobo factory.

Final Thoughts

If not for Kyosho's lack of quality control and lack of vision on some parts, I'd say the Caliber M50 is the best performance 50 class helicopter that money can buy to date, period.  It features advanced main frame design, coupled with a very light weight and a powerful 50 engine.  It has the rock solid hovering capability that is evident only in the best 60 class contest grade machine, flies very fast and with very powerful cyclic control that would enable even the wildest maneuvers that one could thought of.  However, its the nits and bits where Kyosho killed such a good helicopter design. At the price tag of the Caliber M50, I would expect more quality and more carbon, but Kyosho just decide to keep my money in their wallet without giving me what I paid for.  If you have access to Japanese shops, with a deep wallet, and don't mind the hassles to amend the pitfall, getting the Caliber M50 would be a good idea if you want the best performance 50 class helicopter that exist to date.  Kyosho had a very good design, but poor execution, I was very disappointed, to say the least....

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