OA Composites NRJ Handbuch
NRJ – Assembly and settings manual
Thank you for the purchase of our glider, we hope that you will enjoy flying it!
Please pay close attention to the following assembly instructions, to have the most reliable machine
the NRJ can be.
Servo tray preparation.
The servo tray is 3D printed and requires some fine-tuning to sit perfectly in place in the fuselage. Small thickness
variations in the fuselage are expected, and as such it is necessary to lightly sand the tray for a perfect mating. The tray
should maintain accurate dimensions in the corners and along the length of its contact with the fuselage. It should also
let servo wires through freely. Run multiple dry fittings and check that the external nose cone slides without forcing or
deformation. An improper placement of the tray may prevent the nose cone from fitting when the servos and servo
horns are mounted.
To leave the possibility of ballasting the glider correctly, a distance of around 23 mm between the end of the tray and the
central lip of the fuselage opening is necessary.
The tray can be glued with fast (less than 90 minutes) epoxy, whose different properties from the long-curing fuselage
epoxy allow an easier removal of the servo tray if required. Glue with 4 mating points on the top and bottom sides of the
tray. Be careful to not fill in the cable channels of the tray with glue, meant to allow the servo wires to reach the nose.
Check the neutral position of servos with a servo tester An exemple of servo mounting on the tray
Servo mounting: It is imperative to do so only once the tray has been glued in right place. Two screws per servo. Check
the screw diameter against the tray’s pre-drilled hole, the plastic is hard and fragile screws may break while screwing in,
which would obviously complicate assembly. (if needed, drill it again with a 1.2mm bit)
3 types of servo trays available:
4 x KST 08 ‘ , 4 x MKS DS75K ‘ and 2 x KST 08 + 2 x MKS DS75K ‘.
You can replace KST08 by Dymond D47 for tails (light versions).In this case, glue a little piece of 4x4mm (pine wood)
under the D47 leg , to have the right horn’s height position. D47 works in 1S, but it’s better to supply it with a 5 to 6 V
voltage booster.
Ailerons servos and linkage system mounting:
Mount the ailerons servos close to the wing and the tails servos on the front of the tray. Ailerons linkages must be as
short as possible.
Here, sleeves are only dry mounted to check their possible length.
To insert the servo wires in place, disassemble the servo leads from the plugs while being careful with the order of those
leads in the plug. Then use a thin string attached to one or all three leads and pull them through the channel towards the
front of the fuselage. If necessary, gently separate the joined wires from each other by pulling the leads apart to have
more play to pass the leads one at a time through the channel. The NRJ’s fuselage is very thin and space is thus at a
premium, however this is the price of having a significant decrease in drag!
Aileron horn installation
To minimize the “accessory” drag of the ship, the aileron horns must be installed as close as possible to the fuselage. Be
careful to keep the installation of horns symmetric and respect the given distances for the best range of motion. Cut a
notch of 1.5 mm wide and 25 mm long on the side of aileron root, as close as possible to the hinge. Put a tiny drop of oil
on the Kevlar hinge, to prevent CA to enter in it. Glue your horn precisely with CA, adding a 25mm joint between
aileron and horn on the bottom side of aileron.
Vertically, the horn’s hole is backward offset from hinge to prevent the command rod from bending excessively during
full flap extension.
Aileron linkage installation
In order to have as little play and as rigid a control rod as possible, it is preferable to use the elements provided in the kit,
such as the plastic sleeves and 1mm control rods or TFLE (Teflon) tubes and 1.2mm rods.
Check the hole diameter of the horns both the servo and control horns for a tight fit. If one of the holes is just a bit loose,
using a slightly oblique elbow joint or a CA drop should help remove the residual slop.
Kinematic requirements for ailerons:
For the optimal range of motion on the ailerons (+35mm of down for full flap, -13mm up) we need a linear range of
(+6.5mm, -2.5mm) of the control rod at the aileron horn linkage, with a matching range of motion on the servo horn. The
aileron servo horn should normally be a 2 holes horn for KST servo (Axle to 2nd hole: 6.5mm) and 1 hole for MKS servos...
(Axle to single hole: 7mm). Keep these ratings for perfect range and precision.
At neutral, the aileron horn servos must be 20-30° backward tilted to the ailerons direction, to fit the servos and ailerons
linear ranges better. In total, 9mm of linear range must be managed on both aileron and servo horns. Notice that we
must choose the shortest servo horn possible to prevent any instance of flutter, which damages servos over time, caused
by the torque and vibration constraints that are transmitted by the aileron linkages. But we must keep enough length in
the lever arm to allow for enough linear range. You may be tempted to put quite longer horns to allow for easier ballast
passage in the center of the fuselage. Rest assured, the ballast system enters the fuselage perfectly as we designed if all
assembly is done per the instructions herein.
Always use the maximum angular travel possible for the servo with full radio travels. This will ensure the trims precision.
Fit the aileron and servo horns’ holes to the rods diameter with a rod piece. Start the linkage build from ailerons and finish it at the servo horn.
The sleeve must be glued only when the linkage will be entirely cut and ready (elbows and lengths). Don’t forget to insert rod in sleeve first.
Immobilize the aileron with a piece of tape and mount the wing on the fuselage.
Then prepare the aileron connexion with the right width and shape for an easy mounting/unmounting... The length will differ for your installation, so do not take this
image as a reference for length.
After the aileron bends are prepared, mark with a pen about 1.5 mm before the horn hole. (Again, aileron is secured at
neutral and servo at neutral with the definitive tilt!) The difficulty is to bend the rod at the right length, take your time
and calculate your gesture. Put your pliers just over the pen mark, edge to edge, the pliers must cover the pen mark. Fold
up the rod and cut it at the right height, to let the nosecone slide into position without friction.
On this photo, the ballast leg on the tray is centered on fuselage line. The new servo trays have this leg
brought down a few millimeters… a better ballast connection is now guaranteed. ;-)
Glue the sleeves after having slid them with enough linear range near the aileron horn for full flap extension.
Their lengths can be adjusted by cutting even if the extremities of the linkage are done.
For an optimal strength of the linkage, be sure to follow instructions for both inner and outer glue joints, as intermediate
mechanical reference points.
The greater the length between the points (horns anchorages and fuselage reference), the more likely the control rods
will bow and allow flex in the linkage. (And allow flutter to happen as a consequence…)
Do not under estimate all those said mechanical needs for perfect reliability and precision.
Tail feathers installation
Kinematic requirements:
Elevator
The necessary servo-side control range is +/- 4mm. Choose a short servo horn for this servo, which will yield higher
precision for the elevator’s motion. (In the same way as ailerons...) This will then yield a very high precision of the
elevator trim.
The original elevator horn’s height should be trimmed down to 10.5mm before being glued to avoid hitting against the
tail boom. For even motion the wire must be perpendicular to the hinge with the elevator at the neutral position.
Rudder
The servo control range is +/- 4.5mm. (Rudder control’s maximum motion range suggested of +/- 14 mm). Using the
same servo horn as for the elevator servo will yield a very rigid control, helping retain and transform as much energy as
possible during the discus launch and release of the glider
Stab pod preparation.
The stab pod’s rear is sanded and prepared in our factory to let the elevator wire through.
But the final slot must be finished with a 2mm bit drilling and a little file. Pay attention, the slot mustn’t be extended in
the boom structure, to ensure the boom stiffness in launch constraints.
Rudder installation
For a right-handed pilot, the peg installs at the tip of the left wing. The rudder has an asymmetrical profile, and in the
case of a right handed pilot, the top (domed) surface must face towards the peg. The horn must be glued on the
opposite (flatter) side. For a left-handed pilot, as the rudder is symmetrical, just mirror the installation by putting the peg
on the right wing tip, curved rudder facing right and rudder horn glued on the left side.
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