The Nexus 46 comes as a almost
ready to fly kit based on the Nexus 30D type F
(flapping head). An extra set of instructions details
the differences to that of the 30. Apart from the OS
46FX engine the other parts that appear to differ
from the standard 30 are listed as below. A
conversion kit for the 30 is also available.
- H331A - Starter Shaft
H3340A - Starter Cone Set
H3356 - Cooling Fan
H3357 - Clutch Shoe
H3358 - Main Gear
H3365 - Main Rotor
H3371 - Engine Mount
H3372 - Muffler
H3373 - Brace Collar
H3374 - Decal
The Brace collars H3373 are
actually four 13mm round metal spacers placed between
the frames and the skids. I temporary fitted these
and couldn’t see any reason why they should be
required. Then the other half Sandhya has a quick
look and smugly points out that without the spacers
access to the glow plug, for removal or attaching a
glow driver, is difficult as the front cross brace
for the skids gets in way. This is due the 46 engine
being larger and mounting a bit further down from the
side frames. Funny how you always overlook the
obvious.
The muffler included for the
OS46FX is a large capacity type and appears to be
well made. The H3365 rotor blades are 15mm longer
than the those of the 30 and come pre-covered with
white heat shrink. These had the same CG’s but a
small amount of tape was required on one to match the
weights.
A quick check of the gear mesh revealed that the main
gear and tail drive pinion had quite a bit of
backlash with only a quarter of the teeth length
actually engaging. This was cured by adding a couple
of Concept 60 gear shims under the lower bearing
after removing the mast assembly and main gear. There
is a set of proper shims available for this. Doing
this moved the autorotation hub up which meant that
the hole in the mast now did not line up. The four
set screws on the mast collar had to be loosened, and
mast moved up a fraction to realign it with the hub.
Adjusting the main gear caused the clutch drive gear
to go slightly out of mesh so this was adjusted also.
How to adjust both of these gears is detailed in the
instructions.
The mast assembly can be
removed if required complete with head, linkages,
swashplate, mixer arms, pitch slider etc. as the top
bearing is held in a removable bearing block. This is
a great improvement over the Concept 30 series which
required the side frames to be split to do this as a
complete assembly.
The engine was also removed and
the fan/clutch assembly dismantled and checked for
balance on a high point balancer. This was found to
be okay and would hold any position on the balancer.
The tail rotor hub and blades were also removed from
the output shaft and balanced as a complete unit with
no adjustment being required. The head was balanced
using wheel collars on the fly bar as adjustable
weights. The standard paddles were replaced with the
lighter SX type H3239.
Assembly of the tail boom, head and skids is all that
remains to complete the model and is fairly straight
forward.
All the linkage balls are metal
except for those on the Hiller control lever which
are plastic. This was replaced with H3237 the
all metal version. There was some sideways play in
the fly bar which was cured by adding some brass
shim, with a hole for the flybar to pass through, on
either side of the Hiller lever.
The servo linkage rods that come with the kit use Z -
bends (yuk), were replaced with the Zeal set for the
Nexus (Z8032). The standard starter cone was
also changed for the shaft type with one way bearing
(H3401).
I couldn’t get the tail
linkage to run as freely as I would have liked so the
NHP rear tail servo mount was removed from my SRX and
fitted to the Nexus. The servo mount fits directly
without any modification but the carbon fibre rod had
to be shortened by approximately 15mm. Finding enough
room to mount the receiver and battery (Robbe
1300mAh) in the space provided was a problem. The
nose of the Nexus canopy is very narrow and hence
there is not a lot of room. The battery together with
the receiver wrapped in foam wouldn’t allow the
canopy to be refitted. I ended up mounting the
battery underneath the servo frame and the receiver
on its own up front. The JR120S gyro amplifier, was
attached on the back of the throttle servo using
double sided tape as the rudder servo which
wouldn’t normally allow this was rear mounted.
The above additions and changes
to the kit are personal preferences only and the kit
as it comes is perfectly okay without these expect
for maybe those Z-bend linkage rods (must have been
invented by a plank flyer). Ball links at both ends
is definitely the way to go for slop free control and
makes adjustments a lot easier. Though its good
practise to check anything that comes pre-assembled,
especially things like gear mesh and screws that may
not have been tightened fully at the factory.
At this stage I have only
completed three flights with the engine set at a
fairly rich mixture so I can’t comment on the
performance yet but the model does feel more powerful
than my SRX with a Enya 35 and must have a good power
to weight ratio with the 46. I haven’t had the
opportunity to fly a Nexus 30 yet. A fourth flight
was attempted but the 2mm cap screw holding the tail
rotor bellcrank snapped and caused a rather abrupt
landing, luckily no damage though. I have had my
doubts about the size of this screw before but have
never had one break. It may have been the combination
of the NHP pushrod and Zeal metal bellcrank which
doesn’t allow any give in the linkage and can be
overstressed when doing a preflight check of the
rudder control movement with the throttle stick in
the low position. This has since been replaced with a
3mm cap screw.
Having now set up the Nexus 46
properly and the engine fully run in and tuned over
the last month and a half (weather permitting during
weekends) the beast is now showing its potential.
Initially the throttle was set to be ½ at mid stick,
but this resulted in a very high rotor rpm at hover
with the standard wooden blades. A switch to some
heavier NHP carbon fibre blades helped but the
throttle had to set to approximately a third at mid
stick to obtain a acceptable hover rpm. Longer blades
would be better still but the 46 blades only just
clear the tail rotor by about 5mm. The flapping head
would likely cause contact with the tail rotor if
longer blades were used in the standard form.
Also added was a NHP carbon
tube drive to replace the standard wire in brass tube
set up. This has got to be the easiest tail drive to
fit. No tools are required, the drive ends are
pre-fitted as is the centre bearing and housing. With
a new boom or after removing the existing guides from
a standard boom its just a matter of applying some
grease to the o-rings around the centre bearing
housing and sliding the complete unit inside.
Reassemble the tail gearbox, refit the boom and its
done. The carbon fibre drive is dead straight with no
run out problems. It also eliminates any drive wire
noise and the drag encountered with the wire rotating
inside a tube. This tail drive combined with the NHP
tail pushrod and the extra power of the OS46 makes
for some gear stripping turns.
I also added a header tank as
while hovering back to the landing spot with what
looked like enough fuel the engine stopped. A quick
check with fuel pump emptying the tank showed that
not all the fuel can be picked up unless the heli is
fairly close level. So with a slight nose down or up
attitude the pick up will uncover, this may be only
peculiar to my Nexus. Maybe I should just stop flying
with more fuel left in the tank. Anyway as the header
tank remains full of fuel until the main tank starts
to empty, this always ensures a consistent supply of
fuel even if the pick up should momentarily uncover
during a manoeuvre.
The OS46FX is very easy tune
and has good throttling when coming out of a step
decent with the power on and it just drops back to
hover rpm without any run on. With the main needle
still set on the rich side power climb outs are no
problem with fast forward flight achievable at ¾
throttle. Multiple loops are easy as there’s
enough power to keep the momentum going. I still
haven’t got to grips with a roll so cannot
comment how it does those. It flies very much like a
60 powered machine but uses much less fuel and is a
lot nipper because of its size. Much easier to fit in
the car too. It also gets small very quick if you
happen to fly too far away. Now I wonder if a 60 can
be made to fit?
Northern Helicopter Modellers Club N.Z