If the ECO 8/16 is built strictly by the manual, you will create a helicopter which has extremely tight linkages and will have severe vibration problems and will be difficult to hover. Please follow these tips so your ECO 8/16 will fly well.
It is possible make the ECO more durable and crash-resistant by "doubling up" the sideframes. To do this, buy another set of sideframes, and epoxy each set together - don't forget to rough up the mating surfaces of the sideframes with 200 grit sandpaper first for better epoxy adhesion. You will need to replace the M2x8 with M2x10 screws, and also replace the M2x30 screws with two extra-long M2 bolts or two M2 threaded rods because the M2x30s will be too short to reach through the tail boom mounts. The double frames will add about 41 grams to your AUW and reduce your flight times by about 30 seconds, but the frame will be much stiffer for better control and also survive most crashes.
The stock ECO 8 landing gear is a bit narrow and makes landing difficult for beginners. You may want to replace it with the ECO 16 landing gear (67916 + 67917) or the ECO 8/16 extra wide landing gear (67822).
The ECO 16 landing gear is about 1 inch longer and two inches wider than the stock ECO 8 landing gear. This landing gear will need slight modifications to work on the ECO 8 because it is designed to hold two battery packs.
The ECO 8/16 training gear is about 1 inch longer and 3.25 inches wider than the stock ECO 8 landing gear. This can hold either one or two battery packs and requires no modification.
Both the ECO 16 landing gear and the ECO 8/16 training gear use the ECO 16 skids (67917) which are wider in diameter.
The control balls on the plastic swashplate (67701) have been known to break off on extremely hard crashes. You may want to upgrade to the aluminum swashplate (67707) immediately. Also, the aluminum swashplate can be configured to support 120 CCPM which offers better control than 90 CCPM.
The stock main rotor shaft (67535), the stock feathering shaft (67509), and the stock tail rotor shaft (67550) are very soft and bend easily in minor crashes.
If this happens, I highly recommend replacing them with the hardened versions: 67940, 67942, and 67941 respectively.
I don't recommend using the mechanical mixer, because electronic mixing works much better than the mechanical mixer. If you do choose to use the mechanical mixer anyway, you will need fairly strong servos because the mechanical mixer needs a lot of force to move it around. Probably HS-81s are not adequate for mechanical mixing - you need at least HS-85BBs.
The stock wooden main rotor blades are fairly durable and are very good for beginners because they will survive minor crashes. I would recommend using the stock wooden main rotor blades for as long as possible - definitely while learning hovering in all orientations.
Pg 6: The tail drive belt pulley (67702) may wobble because the hole is not drilled exactly in the center of the pulley. This usually does not cause problems, but in some cases the hole is very out of center, and the tail belt may slap against the tail boom as it spins up or while it's flying. In this case, it is advisable to replace the tail belt pulley with a new one that is hopefully better, or replace both pulleys with the Voyager E rear belt pulleys (060860), or replace both with aftermarket aluminum pulleys ( PMP ATPS).
Pg 6 and 13: It is best to prethread the setscrews (67574) into the plastic pulleys (67702) before mounting the pulley onto the shaft. This will reduce the chance of stripping the setscrew hole. You should use a small nutdriver (Wiha #263 or similar) to tighten the setscrews.
If you accidentally strip the hole, you can repair the hole by using the CA trick mentioned in the general construction tips section.
Pg 8: If the aluminum skids (67563) are difficult to fit into the undercarriage cross member (67562) try using a hairdryer to heat the cross member until it softens slightly, then slide in the aluminum skids.
Pg 9: When building the pitch compensator, the manual does not mention the arm (67591) has a TAPERED hole for the pin. If you try to force the pin through the narrow hole instead of the wide one, this may cause damage to the arm.
Pg 9: The two collective pitch compensator arms (67591) will rub against each other on a stock ECO, which is bad. You should put an M2 washer between each arm (67591) and the hub (67590) to increase the spacing between the arms.
Pg 10: The flybar seesaw (67610) usually does not seesaw smoothly on the rotor center unit (67639). This flybar seesaw needs to move very smoothly on its pivots otherwise this will cause vibrations when hovering.
To fix this problem, take some extra-fine steel wool (#000) and spread it with your fingers to make a very thin mesh. This mesh should be about 1 inch by 1 inch and be mostly air with about 50 or 60 strands of steel wool running through it.
Remove the flybar seesaw, then put the steel wool mesh on top of the pivot, then mash the seesaw on top of it so the steel wool is trapped between the pivot and the seesaw. The seesaw should snap on with moderate pressure; if you need too much pressure then your steel wool mesh is too thick.
Now wiggle the seesaw up and down about 10 times, then remove the steel wool and check if the seesaw pivots smoothly. If it still does not pivot smoothly, then repeat this process. Do not repeat more than twice because this will wear out the pivot. For the final finish, apply some powdered graphite onto the pivot. After this, the seesaw should move very smoothly.
Pg 10: The flybar (67609) usually does not rotate smoothly in the flybar seesaw (67610). You MUST make the flybar seesaw rotate smoothly in the flybar seesaw otherwise the heli will be very difficult to hover. You will need to push the flybar through the flybar seesaw repeatedly (like playing a violin) for about 5 minutes until the rod slides smoothly through the flybar seesaw. This will make the heli much more stable and easier to hover.
Pg 11/update: (Advanced) You can give make a free tail pitch slider upgrade by installing a brass ball on the outer slide ring (67643). You must do this modification BEFORE the needle bearing (67644) is installed inside the outer slide ring. Cut off the plastic ball from the outer slide ring, then drill a 1.5 mm hole where it was. Take an M2x8 screw and a brass ball, and screw it into the 1.5 mm hole. Look inside the outer slide ring and check how much of the screw protrudes inside. Remove the screw and trim it to size, then CA the screw and brass ball into the outer slide ring.
Pg 12: The diagram does not show this, but you will need to bend the top of the 93mm ball link very slightly (maybe 5-10 degrees) to ensure it does not rub against the flybar when the swashplate is at the bottom of its travel. Check to make sure the ball link does not rub against the flybar seesaw (67610) when the swashplate is moved up and down. If the ball link rubs against the flybar seesaw, then reduce the angle of the bend. This bend slightly increases the usable negative pitch range.
Pg 13: The tail rotor shaft (67550) is asymmetrical and one notch is closer to one end than the other. The shaft end with the notch FARTHER from the end should slide into the pulley (67702), not the blade grip hub (67549).
Pg 13: The tail blade grips (67542) should controlled by the leading edge of the blade, and not the trailing edge. If the tail blade pitch is controlled by the trailing edge, the tail may wag. Double-check and make sure the Ikarus logo on the tail blades is visible from the right side of the heli, and the control ball for the tail blade grips is on the leading edge of the blade.
Pg 13: There is a serious problem on this page. In some versions of the English manual, the instructions do not mention using threadlock on the screw holding the tail blade grip (67603) to the tail hub (67549). The German version of the manual correctly tells you to use threadlock on this screw. If you fail to do this your tail rotor grip may fall apart in flight causing the heli to pirouette out of control. Do not skip the threadlock on this screw! Also, if you disassemble and reassemble the tail rotor later, don't forget to reapply fresh threadlock on this screw!!
Also, be sure the screw tail blade grip is left slightly loose so it can rotate freely on the ball bearing and screw. If the tail blade grip is screwed too tightly to the tail rotor hub, then the tail may "wag" because the mechanics may bind and gyro will have trouble controlling the tail blade pitch.
You should check the play in the tail blade after installing the tail blades. There should be approximately 12 mm (half inch) of play in the tail blades. If you have significantly less or more play, then you should remove the tail blade and readjust this screw.
Pg 13: The M2x6 screw (67561) should not be screwed too tightly into the short ballend (67564) on the tail. If the screws are too tight,then the tail pitch lever will not move smoothly around the middle of its range because the ballends will not be free to flex outwards. To adjust this screw properly, screw it in completely, then reverse it approximately one-eighth turn. This should be about right but you should check the pitch lever movement to verify it moves smoothly.
Pg 13: The pitch lever (67541) must move VERY freely on the tail housing (67548). On an unmodified ECO this is very sticky, which will make the tail "wag" with a heading hold gyro!
To fix the stickiness problem, rub the post where the pitch lever mounts with some extra fine steel wool to remove the grooves left from the molding process. Next, apply some powdered graphite to the post and to the inside of the pitch lever and mount the pitch lever. Wiggle the pitch lever a few dozen times to spread the graphite. The pitch lever should now move very smoothly.
Pp 16-21: Don't use servo grommets to mount the servos to the frame. Instead, cut a 4mm length of very small fuel tubing and slide this onto the M2 screw. When this tubing is compressed, it will fatten out and fill the gap between the servo and screw.
Pp 16-21: If you are using the aluminum swashplate with 120 CCPM, mount one servo in front and two in the back at the 12 o'clock, 4 o'clock, and 8 o'clock positions. This is easier to mount than two servos in front and one in back. You will need to fiddle with the transmitter swashplate setting to swap the front and back with this servo configuration (SWASH AFR on the Futaba 9C).
Note: This servo arrangement will not work with a frame brace (because the front servo will hit the frame brace) nor will it work with a stock Hacker B50 heatsink (because the heatsink will hit the frame brace). The Hacker B50 heatsink will require about a 1.25" section of it removed so it doesn't interfere with the front servo.
Pg 22: The suggested component placement will work if your gyro requires mounting on a vertical surface but does not work well if using a gyro which requires mounting on a horizontal surface such as a Futaba GY240 or GY401. If using these gyros, then mount the gyro on top of the tail boom support behind the shaft (instead of the receiver) and mount the receiver upside down under the tail boom support (where the frame is angled). This component placement keeps the ESC far away from the receiver and gyro and prevents radio glitching problems.