S2B OR NOT S2B - CML Distribution

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S2B OR NOT S2B - CML Distribution
test pilot
] 60’ span Pitts S2B ARTF
- part 1
]
Reviewed by Jason Robinson
S2B OR NOT S2B
A 120 SIZE PITTS - YUM, YUM...
W
hen Curtis Pitts
introduced his
little biplane to the
competition aerobatic
scene, it was clear that a revolution
was about to take place. Legendary,
exhilarating, responsive and perfectly
balanced are just a few of the words
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used to describe one of the most
highly regarded aerobats of all time.
For some time I have been looking
for an ARTF model of the Pitts to
suit the biggest engine that I have,
a 120 four stroke. The Great Planes
Pitts is too large, the Jamara Pitts
too small. I had all but given up,
but recently while flicking through
a recent American modelling mag, I
saw an advert for the Cermark Pitts
S2B, which with its S2B cowl, looked
a bit different - and it was designed
around a 120 4-stroke! It was
confirmed to be fate that I should
have one, for when at the NEC show
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11/1/05, 5:28 pm
(Model Expo) a couple of weeks later,
I saw the very same Cermark Pitts on
the CML Distribution stand. They had
just become UK distributors for the
Cermark range, so I made an order
then and there for one of the first
batches, due in a matter of weeks.
The Cermark version of the
control surfaces will be high, so
decent servos are required on
ailerons (4), elevator (1) and rudder
(1) - the instructions recommend
servos with a minimum torque
capability of 42oz.in. on the ailerons
and 75oz.in on each tail surface.
A standard servo is fine for the
throttle, however! With this size of
servo, I would recommend fitting a
6v Rx battery of at least 1000mAh,
a heavyduty switch, fit a visible
battery level indicator - and fit a
throttle failsafe! OK, let’s go...
ASSEMBLY
legendary Pitts is a big, beautiful
ARF - designed and developed by
America’s Dave Patrick. It’s claimed
to be capable of huge knife edge
loops, tumbles, etc - anything you
can handle, in fact. The kit features
single servo controls on rudder
and elevator, mounted at the rear
for a solid and precise control. The
interplane struts are very quick and
positive to fit with neat ‘thumblock’
connectors that make assembly at
the field fast and accurate. A look
into that cavernous fuselage reveals
a laser cut, top quality balsa and
plywood structure, with veneered
foam top decks, painted fibreglass
cowl and wheel pants, complete
good quality hardware including
wheels, fuel tank - even a custom
Pitts shaped, Spin-Right metal
spinner! The standard of finish and
covering is first class in a choice of
two AVIAT Team colour scheme,
either blue on white, or traditional
red and white.
A sheet of vinyl decals registration, Pitts logo and a variety
of ‘stars’ completes the kit, together
with a nine page instruction booklet.
As this is a highly aerobatic
model aircraft, the loads on the
Now if you’ve got the skill and
ability to fly the Pitts, you’ve
probably built a few aircraft getting
there, so you shouldn’t have any
difficulties putting it together. I
say that because the instructions
aren’t the best I’ve seen - just about
adequate, I’d say was an accurate
assessment - they would certainly
fox a beginner, but then again, a
beginner wouldn’t be looking to fly
the Pitts, would he, or she...
Having said that, the steps are
logical, well illustrated and the
standard of English is very good!
One of the very first steps is
to fit the ailerons (each designed
to be operated by an individual
servo) to the wing panels. Here, I
must say, I don’t understand the
design philosophy employed here.
The ailerons are round nosed and
the wing panel cut outs, are semi
shrouded, so the fit should be nice
and aerodynamic. The hinges are
large diameter, metal-pinned, plug
in type and the holes are accurately
produced in the aileron leading
edge and in the wing TE sub spar
- but then they go and spoil it! To
get the benefit of the round nose
and shrouding, the hinge pin should
be at the centre of the nose radius,
however, the indication is that the
hinge pin should end up at the
aileron leading edge! This means
that the top edge of the aileron
moves upwards when the aileron is
deflected up, fouls the shrouding
and limits the amount of throw. The
perfect answer would be to inset
the hinge into the aileron nose and
slot the aileron leading edge to
allow full movement of the aileron
- I’ve drawn a sketch to show what
I mean. As it happens, I checked
the throw with the hinge pin at
the aileron leading edge and it just
allowed the high rate throw advised
in the instructions (7/8” up and
down) before fouling the shroud,
so I left it as is. A photo shows the
aileron fully up, showing how the
aileron top surface rises above the
top of the wing. It is interesting to
note that in this position, the aileron
trailing edge is out of step with
the wing panel TE, indicating that
the aileron should be positioned
further forward i.e. hinge pins inset.
For aesthetics alone, I would have
carried out the mod, but as this is a
review...
You need some six extension
leads to fit out the model, plus a
couple of Y leads for the ailerons.
The instructions say to fit a Y lead
on the Rx - one leg for the top wing
and the other for the lower wing,
so needing three Y leads. I opted to
be able to use the computer aileron
differential function, if I needed it,
so linked the left hand servos with
a Y lead in channel 1 and the right
hand servos with a second Y lead
into channel 7 (Futaba FF9 Tx).
The level of ARTF is such that
the model can be literally taken
out of the box and the wings and
struts fitted, bolts tightened - in
about two minutes - the design of
the interplane strut attachment is
very novel and one of those “why
haven’t I thought of that, before?”
solutions - very neat and very quick.
This biggest job in the whole
assembly is fitting and gluing the
tail surfaces in place, making sure
that they are perfectly aligned.
Hard points in the tailplane and
fin have to be drilled for the bracing
wire fittings (all supplied). The
bracing wires being cut from nylon
covered fishing trace and crimped
around brass plate fittings bolted in
place. Again, the high loads during
flight mean that this bracing is
absolutely necessary - they don’t
need to be ‘guitar string’ tight - just
ensure there is no slack. The tail
hinges are of the ‘furry Mylar’ type
- perfectly adequate, as long as they
are well-glued in, with plenty of thin
cyano ‘wicked’ in to the joint.
The rudder and elevator servos
are mounted at the back, on
opposite sides of the fuselage exactly opposite! Using the larger
torque servos (bigger cases) as
advised, I found that the bottoms
cases touched each other before the
mounting lugs touched the fuselage
sides - the only solution for a
totally firm mount is to fit 1/8” play
packing plates under each servo
(remove the film from the fuselage
sides in way of the packers before
gluing them in position - a minor
niggle, but something perhaps that
the pre-production models should
have shown up.
The undercarriage is a substantial,
pre-bent, aluminium plate with
lightning holes in the belly plate
- the captive nuts are already drilled
and fitted - simply bolt on!
Model Flyer
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11/1/05, 5:28 pm
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
test pilot
] 60’ span Pitts S2B ARTF
- part 1
]
Reviewed by Jason Robinson
CONSTRUCTION
CERMARK PITTS S2B
The nifty strut attachment method
makes assembly very quick...
The bottom of the strut has a
locating peg to prevent the strut
twisting...
Just locate the strut in the hole
and finger tighten the knurled nut
- easy!
The ailerons are round nosed in
section...
As designed
Preferable

But the hinges aren’t recessed into
the aileron to give true aerodynamic
movement - note the inboard hinge
has to be trimmed...
...to clear the aileron servo, when
mounted in the wing aperture.
The effect of the hinge line in front
of a round nose is to lift the top
surface of the aileron above the
wing surface...
... and the recessed sub spar has
narrow shroud strips top and
bottom...
...which restricts the amount of
aileron throw (aileron shown in full
‘up’ position).
The top wing is fixed at the
centre with the mounting plate
sandwiched between two cabane
struts and secured by two M3 bolts
and Nylok nuts.
The tank is planned to be retained
by Velcro straps, but I preferred a
more rigid location.
The sturdy undercarriage bolts to
the fuselage bottom - blind nuts are
factory fitted.
The large cowl need minimal
trimming to fit a 120 4-stroke...
...Which is almost totally enclosed
within it.
The crimped fishing trace tail
bracing is necessary to prevent tail
stress overload, whilst...
...high torque servos are needed on
all control surfaces to prevent flutter
- the Blue Bird BMS621 servo has a
90oz torque rating.
The spat attachment method is
extremely efficient, again indicating
the high level of thought that has
been put into the design. Wooden
plates have been glued to the inside
of the spats, ready to be drilled to
match the two holes in the bottom
of each the UC legs (either side
of the axle stub hole), when the
aircraft is placed on its wheels to
ensure the spat lower edge aligns
with the ground. Drill through the
holes and the spats, remove, fit the
captive nuts and bolt them in place
- a nice and strong installation.
and I found that it crushed when
the mount bolts were tightened,
so I threw it away and made up
a tapered birch ply plate. The
danger of using too soft a packer is
that it will continue to crush with
vibration, resulting with the engine
mount becoming loose.
Another unusual feature of the
Cermark Pitts is that the cowl is predrilled for the mounting bolts (small
caphead bolts). The holes in the cowl
are drilled big enough to locate over
short lengths of fuel tubing that have
been pre-fitted over the bolts - when
you tighten the bolts, the fuel tube
diameter expands to firmly grip the
holes in the cowl - clever! This does
mean, however, that you have to
measure the position of your chosen
engine on the mounting arms very
carefully, to ensure a nice 1/16” gap
between the rear of the spinner and
the face of the cowl.
The instructions show a GMS
1.20 2-stroke being fitted inverted.
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ENGINE INSTALLATION
Most ARTF kits are designed with
a firewall with built-in thrustlines
- not so the Pitts S2B. A square of
tapered wood is supplied to fit
under the engine mount to provide
the 2 degrees of right thrust and
zero downthrust (the tail is set at
+1.5 degrees). I say wood - the
tapered packer certainly isn’t ply
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11/1/05, 5:28 pm
A very pretty vbersion of the
aerobatic classic bipe - just cries out
for a pilot under that enormous
canopy, though!
The Cermark version of the legendary Pitts is a big & beautiful ARF - designed and
developed by America’s Dave Patrick ... and can do anything you can handle...
I opted for the Magnum 120 FS to
be mounted sidewinder, so that
the needle was a sensible height
to the fuel tank - this did mean
cutting a hole in the cowl to clear
the rocker cover - and give access
to the glow plug, but on the
plus side, it allowed the standard
manifold to exit at the bottom of
the cowl and the needle valve to be
accessed from the top of the cowl.
Now the fuselage structure is very
lightweight meaning that large
areas of the nose is unsupported
film - not a problem, just needs
careful handling, but also the
tapered fuselage bottom at the rear
of the cowl - the bit that is exposed
to the hot exhaust gases! I thought
it necessary to fit a silicon ‘dog leg’
exhaust deflector tube to prevent
the film surface getting the full heat
treatment!
Regarding the location of the fuel
tank, the instructions recommend
using the supplied Velcro straps to
secure it in place. I must admit, I
couldn’t work out how to do this
and found that with my ‘sausage’
fingers it was extremely difficult
to manipulate the tape inside the
tank bay - so I opted to locate the
tank using 3.4” x 1/4” balsa strip
glued to the ply structure to support
the rear of the tank, with vertical
pieces either side to prevent the
tank moving from side to side, with
a piece of the strip at the front to
support the neck of the tank.
With the engine, cowl, prop and
spinner fitted, the wings were put
on and the position of the battery
determined to get the CG sopt on
(1/4” in front of the rear cabane
strut on the bottom of the top
wing) - guess what, the Cermark
designers had got it perfect! With
the battery in line with the internal
Rx/throttle servo tray, the model
balanced as advised, so it was a
simple matter to fit the battery in
the fuse, on the tray, using rubber
bands wrapped around the ply lugs
designed for that very purpose!
However, just assume this will be
the case for all engine installations
- as the recommended range is
pretty big, there is bound to be
some variation in optimum battery
position placement.
BUILD SUMMARY
This is the first example I’ve
seen of the Cermark brand and
I have to say the build standard
is excellent - ARTFs have come
a long way in the last few years
and Cermark are certainly at the
top end of the pile. The materials
used look to be first class, as are
the choice of hardware supplied.
A few innovative design features
show that the designers have
really thought about the ease of
assembly without compromising
strength or weight. The standard
of covering is first class and the
whole model was, overall, very
pleasant to put together. With
a price tag of just under £250,
you expect quality and, from this
example, with Cermark, you get
it... q
NEXT MONTH
In part 2, we take a close look at
setting up the Pitts S2B and see
how she flies - believe me, it’ll be
worth the wait!
SPECIFICATIONS
PITTS S2B
Manufacturer:
UK Distributor;
Wing Span:
Wing Area:
Weight:
Motor range:
Radio:
Recommended servos:
RRP:
Part No:
Cermark
CML Distribution
60”
1020sq.in.
9lb 12oz.
.90-1.08 (2-Stroke)
1.20-1.40 (4-Stroke)
23cc (Petrol)
4 channel (7 servos)
CML Blue Bird BMS621 (90oz. torque)
£249.99
CER-A103B (Blue) CER-A103R (Red)
Model Flyer
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