The Eagle Freya is Hirobo's newest addition to their already very good and comprehensive lineup. It is designed by Mr. Manabu Hashimoto, two consecutive F3C World Champion. The Freya's main frame design is based on the skeleton of the Eagle II 99 WC, but with most of the "bells and whistles" like graphite frames and aluminum parts replaced by molded plastic parts. However, what makes the Freya special and different from the run of the mill Eagle are two items: a completely new design rotor head, and a dual main gear transmission system.
The FFZ-II rotor head is a molded plastic rotor head with low flybar design. Some parts of the FFZ-II head, like the main blade grips and the flybar control brackets have the same dimension of their aluminum counterparts used in the SSR-V rotor head of the Eagle 99 WC, which is Hirobo's top of the line rotor head. With the FFZ-II head, Hirobo also introduced a new set of flybar paddles. The new paddles resembles the design of the GPH346 paddles, where weight of the paddles could be adjusted by adding or taking out lead strips from inside the paddles. The airfoil of the new paddles is more aggressive than the WC paddles, and even with all the weights on (totaled 40 grams per paddle), the new paddles should provide more powerful cyclic feelings than the WC paddles. In addition, the new paddles are mounted onto the flybar through the use of two set screws, which provided better mounting security than the WC paddles.
The dual main gears of the Freya is the single feature that attracted me the most. (Hirobo call that DTDS system) Hirobo designed the DTDS system specifically for the new FAI Schedule B auto-rotation maneuver (Effective from 2002), which the helicopter has to pirouette two 90 degree angles during auto-rotation. The requirement of this new maneuver requires the helicopter to have constant driven tail during auto-rotation. Usual design that uses a limited slip clutch (LSD) to drive the tail during autorotation could not provide enough power the tail. Also LSD robs precious power reserve during auto-rotation, because both the main gear and the clutch pinion would also be driven and drag from these parts consumes power that should be provided to the tail. The core design of the DTDS system is that it provide constant driven tail power through the use of a secondary gear that locate just under the main gear secured directly onto the main shaft. Power from the engine is transferred from the clutch bell pinion to the upper main gear, and through the main shaft drives the secondary gear that was connected to a pinion which drives a belt gear. During auto-rotation, the whole power reserve would be available to the tail and would not be transferred to the main gear and the clutch pinion cause the one-way bearing inside the main gear hub would not engage. Other manufacturers (e.g. Robbe) already has the same constant tail driven mechanism, through the use of a planetary gear secured onto the main shaft. However, one nasty thing about planetary gear design is that they have to take great care onto setting the gear mesh, or they would be stripped easily. Hirobo elect to use regular straight gears to drive the tail, rather than slant planetary gears as seen in other applications, and this does away the bad of the planetary gears.
Let's take a look at the assembly of the Freya.
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| The first view after open the box | Close-up of the dual main gear DTDS system |
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| FFZ-II rotor head | Flybar paddles |
Upon opening the box, I noticed that the package of the Freya is different from other Hirobo machines. Gone are the "Jewel Cases" that displayed various metal parts, and are replaced by bags of different sizes. All parts are packed nicely into different bags, but not according to the steps of instructions. With other Hirobo machines, bags are packaged in a way that when I arrived to a step of instruction I open one bag that is tagged with the step number in relation to the instruction and all the parts and screws required for that step of assembly would be included inside that bag. However, with the Freya, all bags are not tagged, and Hirobo packaged similar parts together in different bags to ease identification, e.g. screws in one bag, shims and washers in one, tail parts in one and so on. I had to look into the contents of different bags to gather for parts and screws required for each step, and this use up a bit of the construction time. In my opinion, the Freya's packaging is good in a way that it uses less packaging materials, and in return save more cost (hopefully make the price down...) and make less waste. I remembered the packaging of my Kyosho Caliber 60, it glittered my eyes with all the "Jewel Case" and nice boxes at the first glance, but at the second glance I thought how much of my money went into these packaging materials which would end up as waste? Sensible packaging is practiced by Hirobo with the Freya, and this should be praised. I don't mind using up some of my time to save money and be environmental friendlier.
The first part of the assembly dealt with assembly of the upper main frame, that also houses the elevator arms and the front tail drive transmission. The top main frame assembly comes in two pieces of molded plastic frames, with an addition piece that goes to the front for receiver tray. The moldings are of high quality, and everything fit without the use of saw and file. Special attention must be paid to the orientation of the elevator arms, cause if you get them wrong you have to disassemble the frames again. (I learned it the hard way...) Stock Freya uses metal philips screws to secure the parts, I change them to stainless steel hex screws for more strength. Since it is a plastic frame, I could secure all screws with Loctite in one shot, without the need to loose them again for alignment. The bearings that comes stock are inferior Thailand made ones, I changed all the high speed rotation point ones (e.g. main shaft, tail shaft) to better quality ones from SKF. Thailand made bearings are known to be wear out easily and wear out bearings cause glitches. Even though the fitting of the bearings to the frames are tight fit, I applied some Loctite on the side of the bearings to prevent them from turning loose inside the frame. Finishing up the upper main frame is to put on the canopy mounting posts. These mounting posts are exact copy of the limited edition WC canopy mounting post, without the blue anodize.
After the upper main frame was standing in front of me, I found that stock Freya uses two bearing blocks to support the tail pinion shaft which is located under and over the tail drive pinion, with the top of the belt drive gear unsupported. After some fiddling, I found that I could fit in a plastic Shuttle lower tail bearing block (Hirobo part #0402-523) on the top of the belt drive gear to strengthen the support of the whole front tail drive mechanism. Now, the front tail drive mechanism is being supported with three bearing blocks, instead of just two. The extra bearing block not only reinforces the whole tail drive, but also act as a cover to prevent the belt from jumping out of the tail belt gear if belt tension is lose during flight.
Joining of the upper with lower mainframes comes next. The lower main frame comes in two pieces of molded plastic, with the fan shroud incorporated into the frames. Before joining the lower main frame to the upper, the fuel tank has to be assembled first. The fuel tank is the exact replica of the Eagle II, with different plastic material used. The fuel tank is housed in between the lower main frames, and is hold onto position with six rubber grommets. These grommets have to be glued onto the lower mainframes before fitting the fuel tank, cause they would came loose easily when fitting the tank. Assembly of the whole main frame was so easy that it take me less than one hour to have it standing in front of me. According to the instructions, fitting the landing gear comes next, but I intentionally skip that and wait until all the mechanics have been fitted onto the main frame.
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| Upper mainframe | Assembled main frame |
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| Frontal view of the whole main frame | Note the additional bearing block on the tail drive |
Next comes the fitting of the main shaft with the DTDS gear onto the main frame. The main shaft of the Freya is in fact the same dimension of the Eagle 99 WC, without the harden treatment. Like the 99 WC main shaft, the Freya item also provided two mounting length adjustments (185mm and 195mm respectively). Although the instruction said to use the 185mm hole, it is still possible to use the 195mm hole just by changing four push rods that connects the rotor head to the swashplate. The longer length main shaft setting is said to provide better hovering characteristics. The dual main gear DTDS system comes completely assembled. I could not resist to play with it for a while, appreciating how smooth the whole thing work. After some fiddling, I found that the upper main gear of the DTDS system is just the same design as the Eagle II, with a one-way bearing being fitted inside a hub that drives the main gear. The difference between the Eagle II and Freya is that the aluminum one-way bearing hub and the main gear of the Eagle II changed from machined items to molded plastic parts of the Freya. I disassembled the whole DTDS system, inspected the plastic one-way bearing hub, and conclude that it might not take much abuse. Hirobo Eagle owners know that one of the weak points of the Eagle lies with its one-way bearing assembly. In fact, the same one-way bearing is being used by Hirobo from their basic Shuttle to the top of the line Eagle WC. While the same one-way bearing might be "bullet-proof" using on Shuttle or GPH346, it could not take much abuse with 60 class machine. The usual way that the one-way bearing went "Kaput!" on the Eagle is that metal fatigue from prolong use would crack the side of the bearing, and when this happen the helicopter would suddenly loose power because power from the engine could not be transferred to the main shaft. When the one-way bearing crack during flight the aluminum hub of the Eagle II would still hold the bearing in one piece, giving some time for the pilot to notice the problem and hopefully land the helicopter safely. However, if the same case happen with a Freya, its plastic hub might not have enough strength to hold the cracked one-way bearing in one piece and even worst, the cracked bearing might explode out of the plastic hub. As a result, I fit the aluminum one-way bearing hub of the Eagle II onto the Freya to prevent the above mentioned from happening. (I happened to have several of these aluminum hubs in my parts bin). After re-assemble of the DTDS system with the aluminum hub, I found that the lower part of the hub rubs on the inner side of the lower main gear. To remedy that, I use a file to trim the bottom part of the aluminum hub. Further, I replace the stock molded plastic main gear with a machined Delrin main gear of the Eagle II (Further parts from my parts bin...). The modified DTDS main gear gives me more peace of mind. Finally, I replaced the stock collar with a "clamp on" style one from Correct to prevent denting on the main shaft.
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| DTDS main gear | Eagle II and Freya upper main gear |
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| Eagle II main gear hub after modification | Modified DTDS gear |
Next comes the assembly of the FFZ-II rotor head, swashplate, and the mixing sliders. I noticed that Hirobo do not go cheap with the Freya because all rotation points are equipped with bearings. During assembly of the rotor head, it is better to follow strictly with the instruction on the parts that the instruction said requires glue, specifically the flybar control bracket and the spindle shaft bushes. Although the spindle shaft bushes are tight fit onto the plastic yoke, prolong flying would make these bushes loose inside the cavities of the plastic yoke, this would wear out the cavities and causes slop. As to the flybar control bracket, it is a pair of plastic molded items with a bush that goes inside each of the plastic molded bracket to strengthen mounting onto the flybar. Once again prolong flying would make the bushes loose inside the cavity of the plastic brackets if the aluminum bushes are not secured with glue inside the cavities of the brackets, and the flybar might became uncontrollable due to this. There are three settings available for sensitivity of rotor head control to suit different needs, and I used the medium setting. Except for the gluing, the assembly of these parts are a breeze. As to the mixers and the swashplate, they assembled without any problem, but care has to be taken while setting up the timing of the washout slider. The slider and the fixer are designed to be slant at an angle, and if you aligned the washout arm not perpendicular to the rotor head, phasing would produce and there would not be positive control on the cyclic. (e.g. aileron would be introduced when just elevator commands are made, and vice versa)
Next comes fitting the engine onto the main frame. During assembly of this step, I found that the clutch, clutch bell, clutch hub and fan are items from the Eagle II, with the exception of the engine mount which is just two aluminum blocks instead of the one piece machined item of the Eagle II. I use OS61SXWC as power plant for my Freya, and once again all parts fitted without a problem. When fitting the engine with the engine mount onto the Freya, I had to first slide in six bushings onto the plastic main frames in between the frames and the engine mount. These bushings are there to prevent the mounting holes on the plastic frames to deform after securing the engine mount onto the frame with the six 4mm screws. Just by reading the instruction, I fear that lot of time might be consumed during this step because the bushings might drop off during the fitting of the engine onto the frames. However, when I put these bushings onto the designated openings on the plastic frame, they would "snap" onto the frames and not come loose. I found this curious cause there are absolutely no hooks and/or harness of any kind on the frames for the bushings to snap onto, I wonder what magic Hirobo had put into designing these bushes... Anyway, the engine go into the frames without hassles. After securing the engine onto the main frame, I found that the fan shroud do not extend to cover the engine's heatsink, and in fact, the whole heatsink is exposed. This might cause the engine to overheat. To counter this, I glued on two pieces of thin wood to extend the fan shroud to cover the heatsink. I then mounted a Hatori 666 muffler to finish engine installation.
Next comes the assembly of the tail unit. The gear box consists of two pieces of molded plastic that encase the tail gear and fit together alright. The tail pitch change mechanism is more like those used in the Shuttle RG, albeit bigger in size. The tail rotor has three bearings that make tail pitch change very smooth, and is the exact same part from the Eagle II. Tail belt is fine pitch type. The tail boom is hexagon shaped, in exact the same size as the ones used in the Eagle II, without the black anodize. The plastic molded tail servo mount is very sturdy and well made. Another good change about the Freya is that I do not need to saw a section off the boom to fit the belt tail drive as with the belt tail Eagle IIs. Eagle II owners with tail belt drive knows that in order to fit the tail boom into their belt driven Eagle II they have to cut the boom about 7cm short, or the boom will be too long for the belt. The whole tail was secured to the boom through 4 hex screws that goes through the main frames, and the tail boom seemed very secure after tightening these screws. Nevertheless, after setting the belt tension, I drilled two 3mm holes on each side of the frames, through the boom, and use two 3mm hex screws to set the boom so that it would not slip and cause the belt to loose tension.
Then, back to the main frame, where various mixers and the pitch control arms are to be fitted onto the frames. When assembling this step, take note that the instruction is not clear with the assembly of the pitch control arm. The pitch control arm of the Freya is based on similar design like the GPH and the Shuttle RG, where two pieces of aluminum plates are to be connected to the elevator arm, and will pivot on a shaft with bearing supported points for pitch change. Two 3mm hex screws are used to secure the pitch arm plates to the pivot shaft. I first secured both pitch arm plates hand tight onto the shaft, and found that the whole pitch arm assembly have slop to enable quite a sizeable sideway movement, this does not look right. Further examination of the whole assembly reveals I have to secure the two hex screws so tight that they would squeeze the pitch arms onto the shaft for a tight fit. One thing of notice is that after the pitch control arm is installed, it occupied an opening which should have been made to house a servo. Hirobo should not be making an extra servo hole here just to get it occupied by the pitch control arms, something smells here... Might this servo hole is designed for something that is coming for the Freya? Maybe a CCPM conversion??? Looks logical to me, cause this servo hole is the best place to house a servo for the 12 o'clock position control point of a 3 servo 120 degree CCPM setup. Anyway, after the pitch control arm is installed, next comes fitting two X shaped mixers, the aileron control lever and the elevator arm knob onto the pitch control arm. When fitting the X shaped mixers, note their orientation. Both X shaped mixers either have a L or R marked on them, and they should be fitted either to the left or right side of the pitch control arm. The aileron control arm has revised geometry that prevent differential aileron control as with the same item of the Eagle II.
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| Tail gearbox | Tail servo mount, note the beefy tail pushrod |
Servo installation comes next, and it is also a no-brainer. I use JR NES8101 on the cyclic, DS8201 on throttle, a G5000T gyro and a NES 8700G on tail. I make all pushrods according to the instructions, and later found them to be on the ballpark with little adjustments required. Take note of the orientation of the X-shaped mixers while fixing the pushrods for their orientation, with the wider side on the bottom, and the narrower side on the top. The instruction clearly show the position of the linkage mounting point from the center of the servo discs/arms for both JR and Futaba servos. After all servos and pushrods are mounted, I set up the radio for the correct movements and ATVs according to the instruction. One thing to praise about the instruction is that it contained settings for Futaba, JR and Sanwa radios, and I find them to be very accurate. Beginners would be highly benefited with the Freya's instructions. Setting up the Freya is very straight forward and all I had done is to follow straightly to the recommended data supplied by the manual. I followed the instructions for the F3C setup, and found that only little adjustments here and there required.
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| Servo mount right side | Servo mount left side |
After radio setup, I put on the landing gears. Those stock landing gears are kind of high, and looks of the Freya would be more aggressive if I use a lower profile landing gear, like the metal landing gear of the Eagle II. Next I put on a dummy glow plug on the underside of the main frame so that I do not have to take off the canopy to put glow driver onto the engine during startup. A Hayes type header tank of K&S is also used. I omit the assembly of the wood blades that came with the Freya. The stock wood blades comes pre-covered, with symmetrical airfoil, but I felt they were too heavy and soft for real use. I use a pair of Hirobo 660mm FRP blades, which are proven for performance.
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| Dummy glow plug mounted | Header tank mounted |
The single task that consume most of my time is cutting the canopy and decals. The canopy is made of "plastic bottle" material, and stickers will not adhere very good to it. The shape of the canopy is sleek and good looking. Cutting the canopy into shape is not hard, but I had to improvise on cutting off part of the canopy to clear the main shaft cause that part was not marked in any way. According to the manual, it tells me to leave the glass opening of the canopy uncut, cut the "glass" part and fit it onto the canopy and mount both with screws. I found this would make the canopy look ugly, cause the white canopy part would show up under the "glass" part, and it would make the front part of the main frame completely invisible with the canopy mounted. I would want to leave the glass part clear so that I could look through the glass into the servos and to check my battery indicator. After some fiddling, I found that the best way to mount the glass part is to cut the "glass opening" on the canopy, mount the glass part inside the canopy, and secure the glass with the screws. I am very satisfied that my method makes the canopy looks very nice. Next comes to applying decals, they are very thin and sticky, but even this kind of decals they could be peeled off easily from the canopy. The scheme of the decals resembles "flames" with mostly red and orange livery, which is very eye catching. I used the "soapy water method" to apply decals on the canopy. The Freya also comes with decals to fill the openings of the tail fins, but I opt not to put them cause the fins looks nice with the holes.
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| Canopy as suggested by Hirobo | My canopy, looks better eh? |
After everything is mounted, with a 2,000 mah battery pack the CG of the helicopter is still tail heavy. About 20 grams of weight is glued onto the canopy to make the Freya balance. The dry weight of my Freya is a tad over 11lb, which is quite heavy compared to other 60 class machines. With everything ready and checked, I waited for the test flight to come. It just take me about 10 hours of work time to fully assembled the Freya, excluding the time used for the canopy.
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| Finished Freya | Finished Freya |
On one sunny, calm day I take the Freya to the field for some hovering and trimming. I intentionally set the mixture a bit rich to run-in the engine. When I increased the throttle, the Freya leave the ground, and I noticed some wobbling. I sat it down, bumped up the throttle curve, and take it up again. Wobbling is gone after the head speed is increased to around 1,550 RPM, and anything below 1,500 RPM the wobbling will be back, This might due to the hardness of the dampers. Hovering is rock stable, while cyclic controls are a bit sensitive to my taste. I adjusted the D/R and EXP to make neutral points more numb. I then do a hovering pirouette, and a big grin burst on my face. As most F3C pilots who flies with Eagle IIs know, hovering pirouettes with Eagle IIs requires more correction than with other machines. With an Eagle II during pirouette, I have to introduce lots of cyclic corrections, even in no wind condition, in order to hold it still in one point. However, with the Freya, I only give rudder command, with just a tiny bit of cyclic correction, to hold it at a point. The pirouette is so precise and easy that my Hirobo Eagle 99WC can't top it! I do numerous hovering pirouettes with the remaining first and second tank, it was fun! I even felt that my skills is upped on the pirouette with the Freya! On the third and fourth tank I do some "Hovering Triangles" and "Vertical Rectangles", and enjoy the moments when the Freya pirouette. My flying buddies could not resist and try their hands pirouetting my Freya, and they too feel the same. Autoing the Freya is another enjoyable moment. The double gears do what it was designed to do, keeping the tail powered while using very few power reserve. The tail of the Freya is very controllable and precise, while leaving lots of reserve for the main blades. I finish the day with a contest style, engine shut down auto, which is my first with a new machine on its first day of flight.
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| Entering a loop | Inverted |
A lot of people asked me the same question: Which helicopter to buy? My answers to these questions were always the same - Get the one that gives you more air time and less maintenance, and at a cost that would let you practice without the pressure of breaking it. I call these type of helicopters "Fun Helicopter". During the years of my R/C helicopter life, I have come across several of these "Fun Helicopter", and even though I owned such a variety of helicopters, every time I look back to the progression of my skills I know that its with these "Fun Helicopter" that my skills progressed the most. Its these "Fun Helicopter" that gave me most fun, not my fully-loaded, mega-bucks, top-of-the-line contest grade machine lineup.
To be a "Fun Helicopter" of mine, it has to satisfy several criteria. Parts for it must available almost everywhere, at economical cost, with average flying capability, and the design and construction have to be very easy to maintain. One special thing about my "Fun Helicopter" is that all of them have plastic frames, and have belt driven tails. Why? First, the one good thing about plastic frame is that they either break or not, they won't bend as with aluminum frame, and they won't cost "an arm and a leg" like graphite frames. In addition, changing a plastic frame would cost less time and money than changing a stack frame, where I need to align everything, and make sure they square up. The only trade-off of plastic frames are just they might be heavier than stacked frames, and might deform during hard knocks aerobatics. Second, belt driven tail have less parts count than wire or shaft driven tail, hence less parts to replace after tail damage from crashes.
I classify myself as a F3C pilot. The requirement of F3C is so harsh that you really need a good helicopter with well rounded performance to make life easier. Most 60 class machines could do just that, but I have yet to come across one that would fit into my "Fun Helicopter" classification, until the Eagle Freya. The Eagle Freya, with the proven design of the World Championship Eagle II WC, and new parts that make it even tops the Eagle II, into a package that cost just a tad over a mid range 46 class machine, Hirobo sure have a winner!