Carf-Models Composite-ARF Yak-55 SP User manual

[email protected]
Composite-ARF Yak-55 SP (2.6m span)
Instruction Manual
Composite-ARF Yak-55 SP, 2.6m
TAVS Technology version 1.0

Composite-ARF Yak-55 SP (2.6m span) Sheet 1
P15P14P13
P9 P12P10 P11
P8P7P6P5 P4P3P2P1
P16
VERSION 1.0 Mike C (16 July 2004) Mac

Composite-ARF Yak-55 SP (2.6m span) Sheet 2
P31P30P29
P25 P28P26 P27
P24P23P22P21 P20P19P18P17 P32
VERSION 1.0 Mike C (16 July 2004) Mac

Composite-ARF Yak-55 SP (2.6m span) Sheet 3
P41 P43
P38
P42
P40P39P37 P36P35P34P33
VERSION 1.0 Mike C (16 July 2004) Mac
C of G: At the back edge of
the wing spar tube.
CENTRE of GRAVITY ELEVATOR THROWS
high rate: maximum
low rate: 40mm
low rate: 40mm
high rate: maximum
RUDDER THROWS
high rate: maximum
low rate: 125mm
low rate: 125mm
high rate: maximum
AILERON THROWS
low rate: 45mm down
high rate: maximum
high rate: maximum
low rate: 40mm up

Instructions for Yak-55 SP IMAC-Airplane
Thank you very much for purchasing our Composite-ARF Yak-55SP all composite aircraft, made
with the revolutionary Total Area Vacuum Sandwich (TAVS) technology
Before you get started building and setting-up your aircraft, please make sure you have read this
instruction manual several times, and understood it. If you have any questions, please don’t
hesitate to contact us. Below are the contact details:
Email: [email protected]
or [email protected]
Telephone: Phone your C-ARF Rep!!! He will be there for you.
Website: http://www.composite-arf.com
This instruction manual aims to do 3 things:
1) Show you how to build your aircraft accurately and properly.
2) To explain about your fully-composite aircraft, and how to handle and maintain it.
3) How to set up and trim your finished IMAC type aircraft perfectly to give you the most enjoy-
ment from it.
The new Composite-ARF 2.6m Yak-55 SP is based on our very successful 3.3m Yak-55SP (seen
below in our limited edition ’Honeycomb’ design), which is one of the most revered planes in the
IMAC and aerobatic scene, and uses the latest moulding technology and techniques to make it
easy for you to get this plane in the air quickly, and on a very reasonable budget. We have taken
advice from many of the top TOC and IMAC pilots to improve our original design even further,
and wish to thank all those experts for their assistance.
Composite-ARF Yak-55 SP (2.6m span) [email protected]
2

Liability Exclusion and Damages
You have acquired a kit, which can be assembled into a fully working R/C model when fitted out
with suitable accessories, as described in the instruction manual with the kit.
However, as manufacturers, we at Composite-ARF are not in a position to influence the way you
build and operate your model, and we have no control over the methods you use to install,
operate and maintain the radio control system components. For this reason we are obliged to
deny all liability for loss, damage or costs which are incurred due to the incompetent or incorrect
application and operation of our products, or which are connected with such operation in any
way. Unless otherwise prescribed by binding law, the obligation of the Composite-ARF compa-
ny to pay compensation is excluded, regardless of the legal argument employed.
This applies to personal injury, death, damage to buildings, loss of turnover and business,
interruption of business or other direct and indirect consequent damages. In all circumstances
our total liability is limited to the amount which you actually paid for this model.
BY OPERATING THIS MODEL YOU ASSUME FULL RESPONSIBILITY FOR YOUR ACTIONS.
It is important to understand that Composite-ARF Co., Ltd, is unable to monitor whether you
follow the instructions contained in this instruction manual regarding the construction, operation
and maintenance of the aircraft, nor whether you install and use the radio control system
correctly. For this reason we at Composite-ARF are unable to guarantee or provide a
contractual agreement with any individual or company that the model you have made will
function correctly and safely. You, as operator of the model, must rely upon your own expertise
and judgement in acquiring and operating this model.
Supplementary Safety Notes
Pre-flight checking:
Before every session check that all the model’s working systems function correctly, and be sure
to carry out a range check.
The first time you fly any new model aircraft we strongly recommend that you enlist the help of
an experienced modeller to help you check the model and offer advice while you are flying. He
should be capable of detecting potential weak points and errors.
Be certain to keep to the recommended CG position and control surface travels. If adjustments
are required, carry them out before operating the model.
Be aware of any instructions and warnings of other manufacturers, whose product(s) you use to
fly this particular aircraft, especially engines and radio equipment.
Please don’t ignore our warnings, or those provided by other manufacturers. They refer to things
and processes which, if ignored, could result in permanent damage or fatal injury.
Composite-ARF Yak-55 SP (2.6m span) [email protected]
3

Composite-ARF Yak-55 SP (2.6m span) [email protected]
4
Attention !
This IMAC-Aircraft is a high-end product and can create an enormous risk for both pilot and
spectators, if not handled with care, and used according to the instructions. Make sure that you
operate your Extra according to the AMA rules, or those laws and regulations governing the
model flying in the country of use.
The engine, servos and control surfaces have to be attached properly. Please use only the
recommended engines, servos, propellers, and the accessories supplied in the kit.
Make sure that the ‘Centre of Gravity’ is located in the recommended place. Use the nose heavy
end of the CG range for your first flights, before you start moving the CG back to a more critical
position for 3D-maneouvres. If you find that you need to relocate your batteries or even add
weight in the aircraft to move the CG to the recommended position, please do so and don’t try
to save weight or hassle. A tail heavy plane, in a first flight, can be an enormous danger for you
and all spectators. Fix any weights, and heavy items like batteries, very securely to the plane.
Make sure that the plane is secured properly
when you start up the engine. Have at least 2
helpers hold your plane from the tail end or
from behind the wing tips before you start the
engine. Make sure that all spectators are
behind, or far in front, of the aircraft when run-
ning up the engine.
Make sure that you range check your R/C
system thoroughly before the first flight. It is
absolutely necessary to range check your
complete R/C installation first WITHOUT the
engine running. Leave the transmitter antenna
retracted, and check the distance you can walk
before ‘fail-safe’ occurs. Then start up the engine, run it at about half throttle and repeat this
range check with the engine running. Make sure that there is no range reduction before ‘fail-safe’
occurs. Only then make the 1st flight. If you feel that the range with engine running is less then
with the engine off, please contact the radio supplier and the engine manufacturer and DON’T
FLY at that time.
Check for vibrations through the whole throttle range. The engine should run smoothly with no
unusual vibration. If you think that there are any excessive vibrations at any engine rpm’s, DON’T
FLY at this time and check your engine, spinner and propeller for proper balancing. The light-
weight sandwich composite parts don’t like too much vibration and they can suffer damage. The
low mass of all the parts results in a low physical inertia, so that any excess vibrations can affect
the servos and linkages.
Make sure that your main spar tube and sleeve are not damaged. Check that the front and rear
anti-rotation pins for the wings and horizontal stabiliser are located correctly in their holes, and
are not loose. Check that the 4 plastic wing retaining nuts are tight, that the M3 bolts retaining
the horizontal stablisers on to the aluminium tube are installed and tight, and that the hinge tubes
for the rudder and elevators cannot come out.
If you carefully checked all the points above and followed our advice exactly, you will have a safe
and successful first flight - and many hours of pleasure with your Composite-ARF Yak-55SP.
NO !!!
Secure the plane
before starting the engine.
DANGER ZONES
NO NO

General information about
fully-composite aircraft structure and design
All the parts are produced in negative molds, manufactured using vacuum-bagged sandwich
construction technology. All parts are painted in the moulds, either single colour or designer
colour schemes. A new production method, called TAVS (Total Area Vacuum Sandwich), enables
us to present this aircraft with incredible built-in strength, while still being lightweight, and for a
price that nobody could even consider some years ago. This production process has huge
advantages, but a few disadvantages as well. These facts need to be explained in advance for
your better understanding.
Description of Parts
The Wings:
Both wing halves are made in negative moulds, and fully
vacuum bagged, using only 2 layers of 2 oz. cloth in com-
bination with a very hard 2 mm foam sandwich form a hard
and durable outer skin. Because of this TAVS technology
no additional structural parts are needed except for main
spar, which is a large anodized 40mm Ø Aluminium (6061
alloy) tube with a 1.4mm wall thickness.
The ailerons are hinged already for you. They are laminat-
ed in the wing mould and are attached to the main wing
with a special nylon hinge-cloth, sandwiched between the
outer skin and the foam. This nylon hinge is 100% safe and
durable. You will never have to worry about breaking it, or
wearing it out. There is no gap at all on the top wing sur-
face, and there is a very narrow slot in the bottom surface,
where the aileron slides under the main wing skin during
down throw. This hinge setup is the cleanest you can ever
obtain, but you have to take some care during assembly for
proper installation and servo set up.
First, the hinge line is on the top surface of the wing, not in the centre. This is NOT a disadvan-
tage, if you set in about 10% NEGATIVE aileron differential in your transmitter program. This
means that the ‘down’ throw needs to be about 10% more than the up throw.
Why? Because the axis of the hinge is not at the centreline of the aileron, so it moves slightly
in and out when it travels, and the aileron gets a little "bigger" in surface area when moving up,
and "smaller" when moving down. This is why you have to set the negative differential in your
transmitter to compensate for the size changing. 10% is a good starting point, and you will find
out the exact setting during the first flights, doing fast vertical rolls and watching the fuselage
rolling in a perfect line. You can set it perfectly, this is guaranteed.
The bottom hinge slot needs some explanation, too. The cut line is exactly in the correct posi-
tion so that the aileron slides under the wing skin smoothly. If the cut was a few mm forward or
back, it wouldn't work properly. So, make sure that the lip is not damaged, and that the aileron
slides under this lip perfectly. It will NOT lock at any time, as long as the lip is not damaged. If
damage occurs to the lip, you can cut off 2-3 mm, but you should NEVER need to cut off more
Composite-ARF Yak-55 SP (2.6m span) [email protected]
5
Centreline of hinge axis
Phenolic control horn
(above) Super-Xtra wings shown
with minimal internal structure.

than this. Make sure that the control horns are glued into the ailerons properly. The hole in the
phenolic horn for the quick-link needs to be exactly perpendicular to the hinge axis line, and in
this manual we show you a simple way to ensure that the horns in all pairs of control surfaces
will be identical, making it easy to set up your R/C for accurate flying manoeuvres.
The wings are already set-up with servo covers and hatches for 2 servos per aileron, and we rec-
ommend a pair of high-torque servos, like the JR D8411, in each wing. Our servo covers and
milled plywood mounts make both installation, and exchange if necessary, very quick and easy
and provide a rock solid servo mounting and linkage system.
The wings are attached to the fuselage with the 4 threaded
aluminium dowel anti-rotation pins, with 4 plastic nuts
inside the fuselage. If the aluminium dowels come loose in
the wing, the wing will slide outwards, away from the fuse-
lage, and the main spar will definitely break. So take great
care to inspect the glue joints of these anti-rotation dowels
in the wing REGULARLY. Excessive vibrations or hard
shocks can cause the glue joints to weaken or break.
Monitor these joints whenever you set up your plane. Never
forget to tighten the nuts inside the fuselage. Your flight will
end after 100 ft and you will have to fix a hole in your club’s
runway. Please DO NOT modify these attachment dowels in
any way, their perfect function is proven for many years.
The Fuselage:
The fuselage is also made in negative moulds, and it is all constructed using TAVS technology.
All the loadbearing internal parts are glued in during manufacture, to ensure accurate location
and reduce the assembly time for you. The sleeve in the fuselage that takes the main wing spar
tube, the stab spar tubes, and the holes and reinforcement plates for the anti-rotation dowels,
are already installed. There is no need to even check the incidences - you can be assured that
these are already set in the moulds so that no adjustment is necessary.
The landing gear mount is strong and doesn’t need any extra reinforcement. You have an
extremely light weight fuselage, and the gear loads need to be led into the structure gently. No
glue joint needs to be stronger than the materials that it is attached to, as it would just result in
increased weight for no advantage. The landing gear is a fairly flexible design, which works very
much like shock absorbers. This plane is not made for crashing, but the landing gear will take
some hard landings without problems. Do not change or modify it, as the results would only be
negative. We had plenty of time and experience to engineer the strength needed in this area -
and we did !
The motordome and firewall are preinstalled,
and provide plenty of strength for any
engines up to 100cc on the market today.
See the Engine Installation section for details
of engine and setting thrust angles.
The engine cowling and canopy frame
should be attached using the method shown.
It is only a little work and this mounting has
been tested and proven for many years.
Composite-ARF Yak-55 SP (2.6m span) [email protected]
6
(above) Yak-55SP full-composite
wings and 40mm Ø 6061 alloy
main spar tube.

The Stabilisers:
The stab parts are also vacuum bagged sandwiched. The
rudder and elevator control surfaces are hinged with 4mm
ø aluminium tubes, fitted through phenolic hinge bearing
plates which are installed during manufacture for perfect
alignment.
The rudder and elevator design allows for at least 50
degrees throw. All the structural parts are preinstalled. The
horizontal stabs are mounted with one 20mm tube and one
aluminium anti-rotation pin each. Please remember during
assembly of the plane that every gram of weight should be
saved in the tail area.
Take Care:
Composite sandwich parts are extremely strong, but fragile
at the same time. Always keep in mind that these contest air-
planes are designed for minimum weight and maximum
strength in flight. Please take care of it, especially when it
is being transported, to make sure that none of the critical
parts and linkages are damaged. Always handle your air-
plane with great care, especially on the ground and during
transport, so you will have many hours of pleasure with it.
Composite-ARF Yak-55 SP (2.6m span) [email protected]
7
(above) A general view of the
Yak-55SP stabilisers.
(below) The lightweight fin-post
has the phenolic rudder hinges
already installed at the factory
ensuring perfect alignment.
A couple of views inside the new
factory, showing the a small part of the
Finishing area, and the Quality
Control/Assembly areas with the 2.6m
Yak-55SP, 2.6m Extra 330L, 2.3m Extra
and Rookie production lines.

The ‘Paint Job’
Occasionally customers notice certain problem areas with composite parts.
But the question is: Are these real problems, or are they just a misunderstood sign of high-tech
construction, proving the high-end composite technology?
Seams:
ALL composite parts have seams.
They are there today, and they will
be there forever. You will have to get
used to them ... or you’ll have to
touch up the paint yourself !
But what is a seam? A seam on the
fuselage, especially already painted
in the mould, proves that this is a
vacuum-bagged high-tech part,
made in negative moulds. Our
seams are fine and straight, no neg-
ative impression at all ... but they are
there. When possible we include
5mm wide strips of self-adhesive
vinyl, painted in exactly the same
colour as the plane for you to cover
the seams if you want.
Paint flaws:
If the aircraft is painted in the
moulds, you can save a lot of
weight. At least 2 lbs ... and that is
definitely worth saving !
A negative paint job is very compli-
cated to make. The painter never
sees the result of his job. He cannot
see the design growing and devel-
oping - he is painting ‘blind’. He
even cannot see little mistakes and
flaws, and even if he COULD, he
could not correct them. The maxi-
mum time to apply a designer paint
scheme in the mould is no more
than 20 minutes. It is a big rush
against time, because even if it is
just few minutes too slow then the
masking cannot be removed without
pulling off the paint itself ! This is a
BIG challenge, but the result is
extraordinarily impressive. Even
with slight flaws the general appear-
ance of these one-of-a-kind paint
jobs is unique.
Composite-ARF Yak-55 SP (2.6m span) [email protected]
8
(above) An example of one of our big Yak-55’s in the
honeycomb ‘limited’ edition’ scheme ... all painted in the
moulds !
(below) One of our customers with the 3.3m Yak-55SP
practising his tail-in hovering on a very windy day !

In a ‘positive’ paint job some effects can never
be done. Just think about the shadows, peel
backs, highlights, and 3D effects - and all with
a perfectly flat and uniform surface for opti-
mum airflow and aerodynamics.
Truly hard to do, but still possible, are the
paint jobs which seem to be so simple at first
glance: Schemes with straight lines and
stripes. Quite easy with positive painting, but
it’s very hard masking the lines in the negative
moulds, because we cannot assemble the
parts before masking. To get the stripes lining
up exactly at the rudder, wing and cowling
joints is therefore almost impossible. This is
why we suggest using thin vinyl trim to make
sure that these stripes line up perfectly.
Sometimes it is necessary to do that, and it is
definitely not a quality problem or a "flaw". It
comes back to what is possible, and what is
impossible.
If you want to have a really
perfect paint job, then you
might decide to have a sin-
gle colour version and have
it painted by yourself or
your friend.
But don’t forget: Consider
the additional cost, consid-
er the additional weight,
consider that even if it is
painted ‘positive’ there will
be areas you won’t be
happy with.
Of course you won’t com-
plain, because you created
these flaws yourself… !
Composite-ARF Yak-55 SP (2.6m span) [email protected]
9
This is the FiberClassics (now ‘Composite-ARF’) force at the TOC
2000, with all models painted in the moulds.
(above) A general view of the tail-feathers of the
new ‘Shulman 2000’ paint scheme on the 2.6m
Yak-55 SP.

Tools and Adhesives
Tools etc:
This is a very quick and easy plane to build, not requiring difficult techniques or special equip-
ment, but even the building of Composite-ARF aircraft requires some suitable tools! You will
probably have all these tools in your workshop anyway, but if not, they are available in all good
hobby shops, or hardware stores like "Home Depot" or similar.
1. Sharp knife (X-Acto or similar)
2. Allen key set (metric) 2.5mm, 3mm, 4mm & 5mm.
3. Sharp scissors
4. Pliers (various types)
5. Wrenches (metric)
6. Slotted and Phillips screwdrivers (various sizes)
7. M3 tapping tool (metric)
8. Drills of various sizes
9. Small spirit level, or incidence meter.
10. Dremel tool (or Proxxon, or similar) with cutting discs, sanding tools and mills.
11. Sandpaper (various grits), or Permagrit sanding tools (high quality).
12. Carpet, bubble wrap or soft cloth to cover your work bench (most important !)
13. Car wax polish (clear)
14. Paper masking tape
15. Denaturised alcohol, or similar (for cleaning joints before gluing)
Adhesives:
Not all types of glues are suited to working with composite parts. Here is a selection of what we
normally use, and what we can truly recommend. Please don’t use inferior quality glues - you will
end up with an inferior quality plane, that is not so strong or safe.
1. CA-Glue ‘Thin’ and ‘Thick’ types. We recommend ZAP, as this is a very high quality.
2. ZAP-O or PlastiZAP, odourless (for gluing on the clear canopy)
3. 5 minute-epoxy (highest quality seems to be Z-Poxy)
4. 30 minute epoxy (stressed joints must be glued with 30 min and NOT 5 min epoxy).
5. Epoxy laminating resin (12 - 24 hr cure) with hardener.
6. Milled glass fibre, for adding to slow epoxy for stronger joints.
7. Microballoons, for adding to slow epoxy for lightweight filling.
At Composite-ARF we try our best to offer you a high quality kit, with outstanding value-for-
money, and as complete as possible. However, if you feel that some additional or different
hardware should be included, please feel free to let us know. Email us: feedback@composite-
arf.com. We know that even good things can be made better !
Composite-ARF Yak-55 SP (2.6m span) [email protected]
10

Composite-ARF Yak-55 SP (2.6m span) [email protected]
Accessories
Here is a list of the things you may need to get your Composite-ARF Yak-55SP in the air. Some
of them are mandatory, some of them can be chosen by you. What we list here are highly
recommended parts, and have been thoroughly tested.
1. Power servos (min. 8 required). We highly recommend JR 8411’s for the ailerons and
elevators, and either 8411 or 8511/8611’s for the rudder.
2. Throttle servo (1) Any standard servo will do (eg: JR/Graupner 4041)
3. Aluminium Spinner 125 - 140mm dia (5 - 5.75”). eg: Tru-Turn.
4. Main wheels 125 mm ( 5"). Dubro wheels are recommended.
5. Engine DA-100. This is the recommended engine for your Yak-55SP. The instructions
refer to that engine throughout, but you could use any other 80 - 100cc engine.
6. Mini-Pipe or Tuned-pipe set. (Incls: 2 canisters/pipes, 2 aluminium or stainless-steel
headers, 2 Teflon couplers, 4 spring clamps, & mounting hardware. Available from C-ARF)
7. Standard exhaust muffler. (optional, if noise is not a problem at your field)
8. High quality heavy-duty servo extension cables, with gold connectors. High quality
receiver and ignition switches, ‘Y’ leads, ceramic/ferrite chokes etc.
9. Receiver battery. Either one 2800 mAH pack, or 2 x 1800 mAH packs if preferred.
10. Powerbox 40/24 or Professional and dual powerswitches for dual batteries if preferred.
11. Fuel tank (900 - 1000 ml) with gasoline stopper. We use Dubro.
12. Cable ties in various lengths.
13. Propeller. 2-blade Carbon Meijzlik or Menz 28” x10” for DA-100.
Did you read the hints and warnings above and the instructions carefully?
Did you understand everything in this manual completely?
Then, and only then, let’s start assembling your Composite-ARF Yak-55 SP.
If not, please read it again before you start the assembly.
11

Building Instructions
Please note that this Instruction manual shows photos of both the original Red/Blue/Yellow
scheme, and also the new-for-2004 ‘Shulman 2000’ paint scheme.
Some of the photos of the original scheme show the prototype fuselage, which had our ‘diagon-
technique’ carbonfibre reinforcing on the inside surface of the fuselage moulding - but this was
found to be completely un-necessary. The ‘production’ Yak 2.6m fuselage is extremely torsional-
ly strong and rigid, and does not need any further reinforcement.
With experience of the prototype we also redesigned some of the internal wood parts for the fuel
tank tray and rudder servo mounting plates, etc, to save overall weight, make it quicker and
easier to assemble, and also move the weight of these items backwards as the prototype was a
bit nose-heavy.
If you have any questions during assembly of the Yak-55SP, or can suggest any information or
details that should be included in these instructions, please don’t hesitate to email us at:
[email protected] or [email protected]
We know that even a great product can be made better !
General Tips:
We recommend that you follow the order of construction shown in this manual for the fuselage,
as it makes access to everything easier and saves time in the end. The wings and stabs can be
done at almost any point, and only need servos and control horns installing anyway.
The first thing to do is protect the finished paint on the outside of the model from scratches and
dents during building - so cover your work table with a piece of soft carpet, cloth or bubble-plas-
tic. The best way to stop small spots of glue getting stuck to the outside of the fuselage is to give
the whole model 2 good coats of clear car wax first, but of course you must be sure to remove
this 100% properly before adding any decals or markings. Additionally you can cover the major-
ity of the fuselage with the bubble-plastic used to pack your model for shipping, fixed with paper
masking tape, which also protects it very well.
When sanding any areas of the inside of the fuselage to prepare the surface for gluing some-
thing onto it, do NOT sand right through the layer of glasscloth on the inside foam sandwich !
It is only necessary to rough up the surface, with 60/80 grit or equivalent, and wipe off any dust
with alcohol (or similar) before gluing to make a perfect joint.
Before starting construction it is a good idea to check inside the fuselage for any loose glass
fibres that could cut your hands, and a quick scuff over any of these with a coarse Scotchbrite
pad will remove them.
Important Note: Preparation of all mating surfaces for gluing all parts and components is
extremely important. Scuff both surfaces properly, with 80/120 grit sandpaper or a Permagrit tool,
and then clean off the dust with alcohol, or similar. Sanding and then gluing without cleaning the
surfaces gives nearly as poor joints as not sanding at all !
Composite-ARF Yak-55 SP (2.6m span) [email protected]
12

Landing Gear Finished in 2 hours
The 1st job is to fit the landing gear legs (wheel pants can
be done later) - and you can leave these in place, as they
will protect the bottom of the fuselage during assembly.
Composite-ARF developed a new carbon fibre landing gear
for the Yak 2.6m. It consists of 45 deg laminated carbon
fibre cloth and a huge number of carbon tows inside, all
made under vacuum and heat-cured. However it is still light
weight, and retains enough flexibility to take the shock out
of any landings that are less-than-perfect!
The legs are fitted through the glassfibre sleeves that are
installed at the factory, and bolted to the plywood bulk-
heads and plates shown here with M6 x 20mm bolts and
13mm Ø washers. Both main legs are identical, and can be
used either side.
Fit the wheelpants to the legs as follows: Set the fuselage
on a level surface with the tailwheel (optional tailwheel
assembly available from C-ARF) in place. Fit the wheel-
pants over the M6 x 70mm axle bolts, and also temporarily
fit the wheels, and screw the bolts into the threaded inserts
that are moulded into the legs during manufacture.
Adjust the angle of the wheel pants so that the tops of both
are parallel with each other, and the bottom edges angle
upwards a little, as shown in the photo at the top of page
14. When satisfied with the angle, temporarily tack the
wheelpants to the carbon landing gear legs with a small
drop of thin CA. Remove the wheels and axle bolts and
then secure the wheelpants to the legs with 2 small sheet-
metal screws (2.2 x 10mm), into 1.8mm Ø holes drilled into
the ends of the carbon legs.
You can use any 5" main wheels of your choice. Kavan
wheels are very lightweight, but not very durable on asphalt
runways, and Dubro wheels are a little heavier but much
more solid, and this is what we use at C-ARF. The head of
the axle bolt goes on the outside of the wheel. The order of
the items on the bolt is: Bolthead, washer, wheel hub, 2 or
3 washers, M6 nut, washer, fibreglass wheelpant, carbon
landing gear leg. You may need to adjust the number of
washers, or add a 6mm wheel collar behind the wheel to
maintain free wheel movement and centre the wheel
against the wheelpant, depending on the actual wheels
used. A drop of loctite on the M6 axle bolt where it goes into
the threaded insert in the leg is good insurance.
Any standard tailwheel assembly from a good hobby store
is suitable for your Extra. The tail wheel setup shown in
Composite-ARF Yak-55 SP (2.6m span) [email protected]
13
(above and below) The wheel
pant is held to the main leg with 2
2.2 x 10mm sheet-metal screws as
shown here.
(above) The main landing gear legs
are bolted to plywood bulkheads
that are factory-installed.
(below) Wheel axles are M6 bolts,
which fit into threaded inserts in
the moulded carbon legs.

these photos is an optional part available from C-ARF, and
is mounted with 4 sheet metal screws and 2 plastic ‘U’
brackets under the fuselage, screwed into the plywood
reinforcement installed in the fuselage at the factory.
You do not need to make the tailwheel steerable, a simple
castoring action is fine. However, for asphalt runways you
may prefer to connect it to the rudder horn with 2 springs as
shown. It’s easy to make these by winding some 0.8mm or
1.0mm Ø piano wire around a 5mm drill bit, turned slowly in
a battery-drill, with a small hook in each end to connect to
the tailwheel steering arms and the rudder horn.
Remember - keep it lightweight at the tail end!
Cowling and Grilles Finished in 2 hours
Attaching the 1 piece cowling is quite easy, as it is already
cut and trimmed at the factory, and should need almost no
adjustment for a perfect fit. With the fuselage set on it’s
main undercarriage legs, on a level table, trial fit the
cowling on the fuselage, checking that the moulded lip on
the cowl sits properly into the groove moulded into the front
edge of the fuselage. If necessary, sand the inside back
edge of the cowl slightly, and the moulded-in groove in the
fuselage, to get a perfectly flush fit.
Mark a centreline on the top of the cowl and the fuselage,
on small pieces of masking tape. File a small slot in the top
centre of the fuselage lip, as shown here, to take the loca-
tion tab on the milled plywood part that will be glued inside
the cowling to locate it. Tape the cowling firmly in place on
the fuselage, and glued the milled plywood tab onto the
inside of the cowl with 30 minute epoxy and milled fibre. Be
careful not to glue the cowling on permanently! This tab
makes it easy to locate the cowling, so that the bolts in the
bottom line up with the securing M3 blind nuts etc.
Composite-ARF Yak-55 SP (2.6m span) [email protected]
14
(above) The completed wheel
pant and wheel (5” Dubro shown)
(below) Optional tailwheel assem-
bly from Composite-ARF. It is simply
fixed to the bottom of the fuselage
with the clamps supplied, and 4
small screws into the plywood
plate that is installed at the factory.
(above) Milled plywood tab glued
to inside of cowling to locate it
(above) A small notch must be
filed in the front lip of the fuselage
to take the milled plywood tab.

Composite-ARF Yak-55 SP (2.6m span) [email protected]
The split joint at the bottom of the cowling is reinforced with
the CNC milled plywood parts supplied. Prepare all the
mating surfaces carefully with some rough sandpaper and
clean off the dust with alcohol. Tack glue the plywood parts
in place with CA as shown, and add the small triangular
pieces at the front and back to hold them at 90° to the cowl-
ing. Wax the threads of two M3 bolts and fit through the
holes in one side and CA the bolt heads in place.
Remove the cowling and secure the plywood parts with
some fibreglass cloth and slow epoxy on both sides, mak-
ing sure that the glue goes into the milled slots in the ply-
wood parts. Also secure the heads of the 2 bolts with some
epoxy thickened with microballoons at the same time.
When cured refit the cowling and check for a perfect joint
line at the bottom. Then drill two 3 mm Ø holes from the
underside through the cowl and fuselage - about 8mm from
the back edge of the cowling. Wax two M3 bolts and fit into
the holes with two M3 blind nuts on the inside of the fuse-
lage. Secure the blind nuts to the inside of the fuselage with
a drop of thick CA, then remove the M3 bolts and secure
the blind nuts properly with 30 min epoxy and microbal-
loons. Note that the Blind nuts are fitted inverted, with the
spikes pointing upwards !
For flying the cowling is held together using the 2 strong
steel paper clamps (supplied) as shown in the photo. This
system makes it very quick and easy to remove the cowl-
ing for motor or exhaust system access if needed, and has
been proven with many hundreds of our Yak 55’s.
The 6 vacuum-formed grilles (louvres) for the cowling come
pre-painted in a single colour and trimmed approx. to size
from the factory. However you need to cut out the vertical
face behind each angled blade on the louvres - easily done
with a very sharp X-Acto knife in a couple of hours. It is
important not to forget this as it allows the cooling air to
escape from the cowl.
Mask each of the 6 pre-cut openings in the fuselage
about 5mm (1/4”) outside the cut-out, with tape as
shown, and scuff up the exposed surface with coarse
sandpaper. Prepare the bottom surface of the grilles in
the same way and glue them in place with slow CA.
The last photo below shows the completed cowling
and grilles, and you can also see the position of the dual Rx
battery switches. The Ignition battery switch is on the other
side of the fuselage in a similar position. ‘Powerswitches’
were used for both Rx batteries and ignition switches, and
are available as an optional items from C-ARF., and highly
recommended.
15
(above) Finally the cowling is
retained with two M3 bolts from
the underside, into Blind nuts
glued onto the inside of the fuse-
lage with epoxy & micro-balloons.
(above) Parts for the cowling joint.
(below) The milled plywood parts
are glued into the cowling, and the
two M3 bolts are glued into one
side only. Secure the plywood
parts with small pieces of glassfibre
cloth and epoxy. The spring clamps
hold the parts together for flying.

Canopy Frame and Canopy Finished in 3 hours
The canopy frame fits the fuselage already. It is important
to finish the mounts step by step as advised below. The
parts shown in the photo here are from the prototype, and
production versions may look slightly different.
Mill 6 slots (3mm wide x 20mm long) in the canopy frame in
the positions shown, with the outside edge of the slots
approx. 3 - 4 mm inside the outer edge. Then tape the
canopy frame to the fuselage in the correct position, and
mark through all 6 slots onto the fuselage with a felt pen.
Take off the canopy frame and mill the 4 front and back
only in the fuselage, making them about 4.5mm wide
(1.5mm wider towards the centre of the fuselage).
Then mill the 2 middle slots in the fuselage also, but only
3mm wide, so that the 20mm square plywood parts are a
sliding fit in the slots.
Now glue 4 of the 20mm square milled plywood pieces to
the inside of the fuselage directly below the front and back
4 slots, making sure that the inner faces are exactly verti-
cal. Because of the shape of the fuselage you will need to
thicken the epoxy (30 minute type with some milled fibre
and microballoons), especially for the front mounts. Make
sure that these are properly glued in place and that the
Composite-ARF Yak-55 SP (2.6m span) [email protected]
16
(above) Milled plywood parts for
the canopy frame fixing.
(below) One of the finished rear
mounting tongues in place.
(above) tape off about 5mm (1/4”)
around grilles and sand to ensure a
good glue bond.

space between the plywood plates and fuselage is com-
pletely filled with epoxy.
Drill a 3mm hole through the side of the fuselage in the cen-
tre of the 4 front and rear mounting plates only (not the mid-
dle 2 plates). Take the 4 plywood rectangles with the milled
holes, and glue the four M3 blind nuts in place with 30
minute epoxy. Bolt the 4 plates inside the plywood plates
that are glued inside the fuselage with M3 x 12 bolts, so
that the top of the plates stick up through the milled slots in
the fuselage by 5mm. Cut off excess length if necessary.
Put some clear tape around all 6 slots on the fuselage and
frame and wax these areas carefully, without getting wax
on the plywood plates. Sand the areas around the 6 slots
inside the canopy frame with rough sandpaper. Clamp and
tape the canopy frame in place and then glue the 4 plywood
parts to the canopy frame with 30 minute epoxy and some
milled glassfibre.
Slide in the 2 centre guides (20 x 20mm plywood squares,
no hole) and glue them to the canopy frame with 30 min
epoxy and milled-fibre also. These centre guides just make
sure the middle of the canopy frame stays aligned properly
with the edges of the fuselage. If the joint area was waxed
carefully, you can take off the canopy frame in about 1 hour.
Fitting the clear canopy into the frame is a little bit tricky, but
this is a step by step guide of how to do it successfully:
Sand the inside edges of the canopy frame carefully with
rough sandpaper, to ensure a perfect fit of the canopy
inside. Lay the canopy on top of the frame, and mark the
rough shape with a felt pen or wax crayon. Cut
the outer border of the clear canopy with
sharp scissors, about 12mm (1/2”) too big all
around. Unless you are in a very warm room,
we recommend that the canopy is slightly
warmed up with a hair dryer to prevent crack-
ing - but be careful not to melt or deform it!
When the canopy fits inside the frame rough-
ly, mark the final cut line on the clear plastic.
Then cut it to exact shape with a 6 mm over-
lap all around.
Make several hand-holds with paper masking
tape (see photo) to make holding and posi-
tioning the canopy easy. Push the canopy up
tightly inside the back of the frame and fix the
bottom 2 back corners with one drop of slow
CA each (ZAP-O or Plasti-ZAP recommend-
ed).
Composite-ARF Yak-55 SP (2.6m span) [email protected]
17
CANOPY FRAME FIXING
canopy frame
plywood plate
epoxy glue
plywood plate
M3 blind nut
fuselage side
M3 x 12 bolt
(above) The back 2 plywood
tongues bolted in place to the
fuselage, ready for gluing into the
canopy frame
(below) The position of the slots in
the canopy frame.