The Eagle Freya EX is a top of the line version of their Freya line of helicopter. The Freya EX is supposed to replace the Eagle II line that helped Mr. Manabu Hashimoto to achieved two consecutive F3C World Championships. The Freya EX would be the machine of choice for World Champion Mr. Hashimoto to complete in the upcoming World Championship in Muncie, Indiana.
I actually tried the prototype Freya EX at Hirobo factory last year when I was in Hirobo Cup Finals 2000, and longed to have one in my fleet. Basically the difference between the Freya and the EX are as follows:
The list price of the Freya EX is 260,000yen (street price of about US$1,800). Actually, the biggest difference of the EX to the ordinary Freya is its main frame, and I always longed for the carbon frames to shave some weight off the Freya. Although up today both my Freya have all the upgrade parts and the SSR-V rotor head installed, but with the carbon frame of the EX it completes the package.
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Freya EX |
Freya EX main frame |
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Another side of Freya EX main frame |
Note all the hollows frame, weight being shaved! |
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Close-up of beefy pitch support |
FRP tail fins and carbon tail blades comes standard |
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Beefed up tail boom clamp |
Another look at tail boom clamp |
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Close-up of DTDS drive train |
Revised tail pitch change geometry |
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FRP canopy with carbon insert |
FRP canopy with decals on |
The Freya EX's main frame design is based on the geometry of the plastic Freya in graphite frames and aluminum parts. Aside from the main frame and the tail gear box, all other parts of the Freya EX are actually from the Eagle II parts bin. The rotor head of the Freya EX is the SSR-V rotor head which first see its light in 99 Poland WC, drive train, mixers and most other parts are inherited from the Eagle II WC/DTDS. Actually, if you are the fortune one to own one of the 500 pieces limited production Eagle II WC/DTDS, all you need to upgrade is just to buy the upper main frame parts. Like the other Eagle helicopters, owners of Eagle IIs could upgrade their helicopters to Freya EXs easily. This path makes the Eagle line very popular because owners of Eagle knows their investment are better protected, and when new model comes they just need to buy some parts to upgrade to a new model.
Let's take a look at the assembly of the Freya EX.
Upon opening the box, I noticed that inside the package of the Freya consists of several small boxes. One box contained the canopy, another had long parts like main blades, tail boom and tail carbon drive, one had the SSR-V rotor head, and the rest had all other parts. All parts are packed nicely into different bags, with each bag according to steps of instructions. 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.
According to my previous experience in assembling the Eagle, the instruction steps did not follow a logical flow of assembly, and this time the Freya EX's instruction was better. Assembly started with the EX elevator lever assembly and the fuel tank, which poses no problem for me. Engine assembly came next. I use YS80ST as power plant for my Freya EX. This time, I would like to praise YS because in the past while using their YS61ST2 I need to use a 12mm cross member to extend the throttle arm because the stock throttle arm did not stick far enough for the throttle linkage to reach, but the YS80ST fixed this problem. A clutch hub, mounted with a cooling fan, was slotted onto the engine's crankshaft, lock onto position by the engine's woodruff key, and secured by the prop nut. Once again YS80ST did not include the woodruff key, so one had to be ordered (YS part # F1265). With the Eagle's clutch design, there was absolutely no need to dial indicate the fan hub. The stock cooling fan was a plastic molded item, but I changed that to a machined aluminum part made by Correct. The clutch was to be secured onto the clutch hub, fastened by two 4mm screws. The whole engine sat onto the blue T-shaped engine mount, secured by 4mm screws. A two piece fan shroud was to be installed to cover the engine's heatsink. Trimming on the fan shroud was required for it to fit, and Hirobo had included a diagram in the manual showing what to cut and trim on the shroud. The whole engine assembly was to wait until later stages of assembly after fitting the fan shroud.
One thing to note is the gear ratio to be used. The Freya EX comes standard with a 10T pinion clutch bell and 95T main gear, that gives a 9.5:1 ratio. This setting is for a 61 engine, but if you are going to use a YS80 or OS91, you would need to change the clutch bell to one with a 12T pinion (Hirobo parts # 0414-187) that would give a 7.92:1 ratio that suits better to the power curves of the bigger displacement engines. I know that for some Freya EX package they comes with both the 10T and the 12T pinion clutch bells, but these packages only exist for the first batch of production for promotion purposes. if yours does not include the 12T pinion clutch bell, and you want to use a bigger than 61 engine, you have to get the 12T clutch bell, or risk over-reving and destroying your engine. One way easy way to differentiate between the 10T and 12T pinion is that the 12T pinion have gears that looks like small blocks, while the 10T pinion have triangular shaped gears. Due to the design of the Eagle series, there is no adjustment of gear mesh allowed, so for Hirobo to fit a 12T pinion on a 10T pinion circumference they "cheated" and used smaller size pinion teeth on the 12T pinion. While Hirobo's way is workable, I feel the small block shaped teeth of the 12T pinion would "bite" on the Delrin main gear very much and increase its wear, due to the fact that the corners of the small blocks would always touch on the flat surface of the teeth of the Delrin main gear. As a result, I changed the Hirobo 12T pinion to one from CMPS that has the same pitch as the original 10T pinion. Now I have a pinion that would retain the gear ratio while minimizing wear and tear on the main gear, but then I am faced with another problem....Since the gear mesh is not adjustable, how am I going to fit the now bigger circumference pinion into the drive train and retain smooth operation? More on that later.....
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| YS 80 ST engine | CMPS and Hirobo 12T pinion |
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| Correct and original cooling fan |
Engine installed with clutch parts¡@ |
After the engine assembly, now it comes to the upper main frames. The upper main frames housed the several main shaft bearing blocks, elevator arm assembly, collective pitch assembly support, and the tail transmission assembly. The elevator arm assembly should be finished in previous steps and was sandwiched by the two carbon frames together with the collective pitch assembly support. Of note is the collective pitch assembly support that was very hefty in construction and should beef up the strength of the main frame very much.
The main shaft and the tail drive bearing blocks once again came pre-installed with inferior Thailand bearings, and I changed all high speed rotation point ones (e.g. main shaft, tail shaft) to better quality ones from SKF. I kept on saying bad things about Thailand made bearings, but I was sad to see them again and again in premier kits..... Anyway, I took the Thailand bearings from the bearing blocks by using a torch to heat up the bearing block, and after heat the bearing would drop off easily from the bearing block, then I would put in the better bearings with loctite to held them into position. While fitting these bearing blocks onto the main frame, be careful of their orientation. These main bearing blocks each had a 1mm offset for adjustment of gear mesh, and each of them would have a notch on one end of the block to identify the side with more offset. With the Freya EX's stock gear mesh setting, the notch on the two main shaft bearing blocks should face to the rear of the helicopter, and the dual bearings clutch bearing block should have its notch facing to the front. The upper main frame was erected on a flat piece of marble to ensure square ness, and temporary set with hex screws. Once again I used stainless steel hex screws and machined aluminum screw spacers on the frame assembly for better strength.
The tail transmission assembly consisted of two separate set of gears and bearing blocks that was set at 90 degree to transfer power from the engine to the tail via pipe, and were being mounted onto the upper main frame. There were a lot of holes on the Freya EX's upper frames for the user to either use the stock style transmission system or to use the optional DTDS counter gear assembly for pipe (Hirobo part number 0414-155). Since the optional part was out of stock at the moment when I assembled the Freya EX, so I used the stock transmission component for the time being. While fitting the stock tail transmission to the carbon frame, to my astonishment the holes on one of the bearing block could not line up to the holes on the carbon frames! After some fiddling, I need to use a needle file to elongate holes in the carbon frames for the bearing block to mount, but there were a total of eight holes for the bearing block mounting and I need to modify four to fit, which ones I should modify? The answer was very important because power to the tail was transferred from the lower DTDS main gear first to the Delrin pinion, then to a slant gear that set 90 degrees to another slant gear that connected to the tail pipe. I had to make sure that after the modifications the gear mesh of the slant gear were right on, or risked stripping them during flight. I then came to conclusion that I had to modify the top four holes that would give the best gear mesh. I did just that, checked the gear mesh on the slant gears again and found them to be smooth. I communicated this problem to Hirobo, and they addressed the problem promptly. According to Hirobo this problem was due to an error on the CNC data, and this should only be present in the first batch of productions. Later batches should not have this problem. While Hirobo kindly sent me a replacement set of frames, I felt that errors like this should not even be surfaced in the customer's hands. So if you are one of the "lucky bunch" that had the same problem as I had with the tail transmission, contact your seller for a replacement.
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| Carbon main frames | Alignment of upper main frame on glass |
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| Bearing blocks | Replacement of better bearings |
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| The tail transmission assembly | Bearing blocks could not align to holes |
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| Close-up of tail transmission assembly installed | Assembled upper main frame |
Its time for assembling the lower main frames. The completed engine assembly, fuel tank, and other cross members would be sandwiched by two carbon lower frames, and temporary secured by hex screws on a flat piece of marble to ensure square ness of the frames. Of notice is that the lower main frame of the Freya EX was exactly like the Eagle WC/DTDS. Stock Freya EX comes with landing gear brackets made by pressed metal, but I changed those to the optional EX landing gear brackets for more strength. (Hirobo part number 0404-820) Also, under the engine I used a Correct reinforcement bracket to further strengthen the lower frame.
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| Assembled lower frame | Correct reinforcement bracket |
Joining of the upper with lower main frame comes next. At this stage, another pair of helping hands would be best to help ensure the whole main frame was squared. Once the frame was set squared, I would unscrew each screw again, put on loctite, and secured them again to lock on the frame. Joining the frames looked easy, but if you absolutely want your helicopter to have a right mechanical foundation, you had to use much care and attention at this stage.
After erecting the whole main frame, various parts were being fixed to the main frame. The Freya EX used the collective pitch design of the Freya, where two pieces of carbon and some cross members would made the collective pitch control assembly. The elevator arms would be held onto the collective pitch assembly, which fit together without any problem. Works on the various mixing arms would be to put on joint balls, and those were easy. When fitting the X shaped mixers, note their orientation. Both X shaped mixers either have a dot on one side to mark their upper and lower side. I use a special aileron control arm with revised geometry that prevent differential aileron control that is present with the standard item. The battery tray was the same plastic piece of the Freya. Two pieces of tail boom mounts were fitted into the main frame.
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| Assembled main frame | Close-up of drive train |
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| Plastic front battery tray | Massive collective pitch assembly support |
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| Special aileron control arm | Optional EX landing gear brackets |
Next comes to the fitting of the drive train onto the main frame. The main shaft of the Freya EX, which was the same as the Eagle, provided two mounting length adjustments (185mm and 195mm respectively). I followed the instruction manual to use the 195mm hole for the longer length main shaft setting would provide better hovering characteristics. Make sure the main shaft could "drop" easily onto the two bearing blocks, cause that meant your main frame was squared. The stock DTDS main gears came pre-assembled. However, remember that I used a bigger size pinion? With my pinion I could not fit in the stock 95T Delrin main gears. What I did was to use a 93T main gear from Correct. The Correct 93T main gear had a small size than the Hirobo main gears, and it just fit into my Freya with very good gear mesh. One thing that you might not know is that Hirobo used some "magic" and made their 93T main gear in the exact size as their 95T main gear to fit into their Eagle which did not allow any adjustment of gear mesh. The Correct 93T main gear was made in correct size, which was a bit smaller than the 95T main gear, and fitted into my Freya with ease. According to my experience, Correct main gears were proven for better precision and smoothness compared to the Hirobo Delrin main gear.
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DTDS with Correct main gear |
Correct main gear besides stock main gear |
One of the gems of the Freya EX is the SSR-V rotor head, which in the past is only packaged in limited edition Eagle WCs. This rotor head was fitted to Hashimoto's machine when he won the World Championship in Poland in 1999. The SSR-V head came pre-assembled, and it was packed by itself in a small box. There was not much to do for assembling the rotor head other than fixing the flybar paddles, and linkages. The flybar paddles that came with the Freya EX was the same plastic WC paddles as with the other Eagle WC. Two pieces of 7gram flybar weights were also included for pilots to tune cyclic response. After I assembled the rotor head, I balanced the whole rotor head on a high point before putting it onto the main shaft
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SSR-V rotor head |
SSR-V rotor head |
Next came to the assembly of the tail unit. Tail gear box came pre-assembled. Preliminary inspection of the tail gear box revealed that it was much the same as the Eagle tail gear box for pipe, but the Freya EX's tail gear box had less parts count than the Eagle one. Tail rotor had two bearings and a thrust bearing on each blade grip for smooth operation. The tail boom of the Freya EX was made in aluminum. The whole tail gear box was secured onto the tail boom through screws and the metal vertical fin mount that was equipped with dampers for vertical tail fin mounting. Power was transferred to the tail through a carbon pipe drive that operated inside of the carbon tail boom. While the Hirobo carbon pipe was very nicely made, but very delicate and could not take much abuse. The tail servo mount was made by two metal mounts and a piece of graphite. Stock tail pitch change linkage was a piece of carbon wire with metal rod ends. The whole tail assembly was to be mounted onto the main frame through the two metal clamps on the main frame. To prevent the boom from slipping, used tapes on the boom that was to be clamped on for better security. Two aluminum tail boom support was installed from the lower main frame to a plastic horizontal fin mount to support the tail. The fins were the same ones as with the Eagle WC, which were made in FRP. Later, I found that the tail drive mechanism of the Freya EX was in fact works the opposite direction of the Eagle. Due to this, I could not use the upgrade DTDS counter gear assembly on the Freya EX because that would make the tail rotor became clockwise rotation, which was not an effective way of using tail thrust.
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Close-up of tail boom mount |
Tail gear box |
Servo installation comes next. I used Futaba 9Z WC II radio with Futaba 9252 digital servos on cyclic, 9201 on throttle, a GY601 gyro and a 9251 on tail. I made all pushrods according to the instructions, but instead of the flimsy 2mm metal rods and stock Hirobo links, I used 2.3mm hardened stainless steel CMPS push rods and Pioneer oil filled ball links for better strength and smooth operation. While making the ball links, I used a JR ball link sizer to prep the links. 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, but they are more suited for Futaba servos. For the aileron and elevator servo disc, make sure that both balls are not in line, but set back a bit from the center to prevent binding on the extreme position. After all servos and pushrods were mounted, I set up the radio for the correct movements and ATV. I mount the GY601 gyro on the front main frame.
One thing that I didn't like about the original Freya EX design was its collective pitch control, that used only one ball link for pitch control, while other collective control points were in push-pull configuration. The collective pitch, in my opinion, was the part that take most stress, and I see only a single pushrod would not provide a solid foundation for precision control. After much fiddling, I found that in the front main frame, near the pitch servo position was a 3mm hole drilled for no purpose. After some more fiddling, I found that using a EX aileron lever, adding some push rods, I could convert the pitch control to push-pull. With this bell-crank style push-pull system, I could still achieve a 22 degrees pitch window, while providing more precision to pitch control. If you are interested into this conversion, you would need these parts:
First, locate a 3mm hole that is situated in front of the pitch servo opening, near the middle of the whole opening. Then, use a drill to make that hole into 4mm. Next, slot the 4X25mm screw from the middle of the main frame to stick out of the main frame. Slot the aileron lever onto the 4mm screw and fasten with 4mm locknut, you would need some 4mm spacers to adjust the aileron lever so that the arms would be in line with the pitch arm above. Then connect the pitch linkage to the aileron lever, and use two pushrods to connect the lever to the pitch servo, I found that putting the servo linkages on the inside, and the linkage to the pitch control arm outside achieve the best position without binding. Make sure you check to see if there is any binding after your conversion, and uses shims to further adjust the position of the aileron lever to prevent any bindings.
Later, in Hirobo factory, I saw Hashimoto's machine have the same conversion that I have, so that lead me to guess if Hirobo drilled that hole in front of the pitch servo for this purpose.....
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Futaba 9Z WC2 |
Futaba GY601 with 9251 servo |
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JR ball link tool used to prep ball links |
Push-pull pitch conversion |
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Push-pull pitch conversion |
Push-pull pitch conversion |
After radio setup, I put on the landing gears. The landing gears that comes with the Freya EX were the low profile type that comes with the Eagle WC99. 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. I had modified the plastic horizontal tail fin mount to fit in a Nova 3. Final details include routing of all the wires, which was the part I hated most amongst all steps of assembly. I didn't mean that routing wires with the Freya EX was hard, I just hate this step for all... Anyway, especially for the extension wire from the tail servo to the gyro, I used plastic shrink wrap to wrap the plug connection to prevent it from getting lose during flight.
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| Modified horizontal tail fin for Nova 3 | Shrink wrap used on the plug connection |
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| Gyro mounting platform | Hatori muffler for YS80 |
The canopy was another nice item, in that the "glass part" was a piece of carbon. The whole canopy was silky smooth, and looked very cool. However, since I had a custom made Nova 3 fuselage laid around my house, I opt to use the Nova 3 fuselage instead of the stock one.
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Custom painted canopy |
Custom painted fins |
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Nova 3 canopy |
Vertical tail fins with dampers |
After everything was mounted, the CG of the helicopter was tail heavy. I had to balance the CG using weights inside the front canopy.
Being the owner of several Eagle EXs, I wanted to find out the difference in flying characteristics between the Freya EX and Eagle EX. Hovering was the usual rock solid, but now the Freya EX seems to be more sensitive in control than the Eagle. Maybe I should not use more "sensitive", but more "direct" should be a better description. During pirouettes a lot of correction has to be made on the cyclic to hold the Freya EX in position even in calm winds, which was normal for SSR-V rotor heads. All in all, not a lot of difference.
Once the Freya EX was in aerobatics, then the true colors of this Freya EX would show. On aerobatics, Freya EX control feels more direct and solid compare to Eagles. Especially during rolls, the Freya EX would response by a much faster roll rate, while the Eagle would just enter gracefully with a little bit of softness in control. With the Freya EX, I felt confident to do 3D stuffs with its very powerful cyclic, but not with the Eagle. In general, I could describe that the flight performance of the Freya EX to be tuned more to aerobatics, which in the past the Eagle WC lacks a bit.
The YS 80 worked liked magic, with very good torque, and a smooth performance. The one thing that I noted for the YS80 is that its mid range was very torquey, and I have to flatten the hovering mid range throttle curve very much to prevent it from jumping up and down during hovering. However, aerobatics performance was monstrous, and the engine seemed that at full power it wanted to tear the whole helicopter apart! Compared to the OS91, I liked the YS80 more for its overall smoothness, while power between the two was much the same, with the YS liked to rev higher.
During autorotation, the DTDS system did provide much better tail control, while saving power reserves. Autos could be executed with more precision and grace with the DTDS system installed when compared to the older model Eagles. Compared to the old LSD design, I'd say the DTDS system was much simpler to adjust (in fact, there was nothing to set) and provided much better power reserves.
Hirobo Freya EX provide a very good solution for F3C pilots as their contest helicopters. It could perform very well right out of the box, and it included most of the upgrade parts that Hirobo made for it, so there was not a need to spend more on upgrade parts as needed with other helicopters in the same price range. Aside from the bearings, most of the upgrades that I put in mine were not necessary to have good performance. However, the Freya EX does have some rough edges. I would like to see if the upcoming Hirobo Freya WC would fix these rough edges and further refine the Freya line to the standards of Hirobo's very successful Eagle line.
