Kraga Roa II User manual
Roa II build guide 1.0
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Development of a new plane and support of the old ones is very time consuming. Only with your help I can
focus fully on this project and spend some quality time with my family.
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Printing
You need to use two printing methods to print all parts:
1. Solid parts (fuse and accessories). Use dense infill. This is common
way of printing objects and these parts should be printable on every
printer.
2. Shell parts (wings). Use 0% infill and no horizontal
surfaces (thickness of the shell is one layer). Only this
way you can achieve required weight of the plane.
You can check what method to use on what part in bill of
materials table.
Other recommended printing settings:
•Nozzle size: 0.4 mm
•Layer thickness: 0.19 mm
•Rafts: yes
You can use any material you like, only limitation is high temperature from ironing when covering
assembled parts. Heat from the iron can deform the parts. Although I was not able to damage any
part and I tried to cover many materials (ABS, PLA...), please test film covering on your testing
part.
One of the goals when designing KRAGA models was to use minimal or no support during printing.
Removing support after printing is big pain and you can easily destroy your part. That is the reason
why you should use default orientation of all parts during printing. There are only a few parts from
whole plane which require support, the rest of the plane should be support-free.
I strongly recommend to mark every printed part with it's name (I'm using masking tape for that).
There are many parts in this plane and from each part there is also mirror side which can easily
cause confusion during assembly.
I also recommend to print parts in bulks, especially smaller parts like ailerons or moving section on
the plane tail. Otherwise there is not enough time for material cooling in each layer and you might
end up with rough layers, ugly edges or print fail.
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Preparation for assembly
KRAGA Roa II plane consists of parts that are printed and parts that you need to buy separately
(they are not included in sold product) – carbon tubes and pinned hinges.
List of required parts:
dimensions count
carbon tube ⌀ 2x1 mm 1 m10
carbon tube ⌀ 3x2 mm 1 m5*
carbon tube ⌀ 4x3 mm 1 m4
carbon tube ⌀ 6x4 mm 1 m2
carbon tube ⌀ 8x6 mm 1 m3
carbon tube ⌀ 10x8 mm 1 m4
carbon tube (woven) ⌀ 14x12 mm 800 mm1
covering film 4 m1
pinned hinge ↕ 16x28x1.2mm 26
folding propeller 13 x 8 in 1
spinner ⌀ 45 mm 1
screw M2 8mm22
⌀2x1 mm – means tube with outer diameter of 2mm and inner diameter of 1mm
* 2 pieces of 3x2 mm carbon tube are meant to be used for tail linkage with threaded couplers and metal clevises
And of course you need all the common accessories like clevises, push rods (horns are printed so
you don't need those) and servo extension cables (2 pieces of 90 cm cable for aileron servos). One
way how to make custom pushrods is using 2x1 mm (or 3x2 mm) carbon tube glued into threaded
couplers and screwed into metal clevises (picture below).
Next step is to cut carbon tubes and rods into smaller pieces, which will be used as spars, joiners or
boom of the plane. Don't forget to mark every piece to avoid confusion during the assembly.
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Carbon spars
part dimensions count
Wing section 1:
Main carbon spar ⌀ 10x8 mm 745 mm4
Secondary main carbon spar ⌀ 8x6 mm 442 mm4
Front alignment carbon spar ⌀ 4x3 mm 985 mm2
Rear alignment carbon spar ⌀ 2x1 mm 809 mm2
Wing section 2:
Tertiary main carbon spar ⌀ 6x4 mm 404 mm4
Secondary front alignment carbon spar ⌀ 3x2 mm 230 mm2
Secondary rear alignment carbon spar ⌀ 2x1 mm 660 mm2
Wing tip:
Wing tip front carbon spar ⌀ 2x1 mm 193 mm2
Wing tip middle carbon spar ⌀ 3x2 mm 266 mm2
Wing tip rear carbon spar ⌀ 2x1 mm 218 mm2
Wing surfaces:
Aileron carbon spar ⌀ 2x1 mm 587 mm2
Flap carbon spar ⌀ 3x2 mm 680 mm2
Fuselage:
Fuse top carbon spar ⌀ 2x1 mm 518 mm2
Fuse bottom carbon spar ⌀ 2x1 mm 535 mm2
Fuse pod carbon spar ⌀ 2x1 mm 68 mm2
Fuse servo plate carbon spar rear ⌀ 2x1 mm 45 mm1
Fuse servo plate carbon spar front ⌀ 2x1 mm 48 mm1
Carbon woven boom ⌀ 14x12 mm 785 mm1
Wing alignment joiner ⌀ 3x2 mm 75 mm1
Wing joiner carbon tube front ⌀ 8x6 mm 515 mm1
Wing joiner carbon tube back ⌀ 8x6 mm 485 mm1
Tail:
Tail main carbon spar ⌀ 4x3 mm 374 mm4
Tail mov carbon spar ⌀ 2x1 mm 362 mm2
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TIP: How to cut carbon spars. Wrap masking tape around
carbon spar and mark cut position. Use rotary tool or X-
ACTO fine saw to cut the spar.
Work outside or in room with good ventilation. Use
breathing mask to avoid inhaling carbon dust! After cutting
wipe out carbon dust from the spars using wet tissue.
TIP: Carbon wing joiner tubes on the fuselage
should fit into spars in the wing. Sometimes the
fit is too tight or you cannot insert joiner tubes
into wing spars at all. You can use drill and wet
sandpaper to make joiner tubes thinner. Use
breathing mask to avoid inhaling carbon dust!
Remove support legs from all parts. Also sand all sharp edges and
printing imperfections to avoid covering foil damage.
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Assembly
This assembly guide will describe always left side of the plane when it comes to symmetric parts. I
recommended to use medium viscosity CA glue. You can use CA glue accelerator for faster curing
time. Dry fit all the parts before gluing them together. Wing parts in assembly drawings have
printing support legs visible, please ignore it, these legs should be removed before plane assembly.
Wing section 1
Assembly first section of left wing as sketched above. Main spars
(10x8_745) and front alignment spar (4x3_985) should be aligned flush
with base of wing_root_endcap_L part. Rear alignment spar (2x1_809)
should protrude 1 cm from wing_root_endcap_L part.
Before adding wing_L_7, prolong main spars by inserting secondary main
spars into main spars 8 cm deep and secure the spars in place with CA
glue.
When all the parts are in their position, put glue on contact points where
carbon spars are touching printed parts.
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When assembling flap servo mounts, notice that screws are screwed in from bottom side of the
wing. It is strongly recommended to pre-drill the screw holes. Servo has to be glued to
flap_servo_mount_L_F_glue_on and flap_servo_mount_L_B_glue_on parts.
Wing section 2
Assembly second section of left wing as sketched
above. Before adding wing_L_11, prolong
secondary main spars by inserting tertiary main
spars into secondary main spars 8 cm deep and
secure the spars in place with CA glue.
On the left picture you can see detail of aileron
servo installation.
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Wing tip
Assembly left wing tip as sketched above. When all the parts are in their position, put glue on
contact points where carbon spars are touching printed parts.
Aileron
Assembly left aileron as sketched above. Don't forget to insert ail_horn_L part between ail_L_2 and
ail_L_3. Aileron horn should stick out from the top side of the wing. When all the parts are in their
position, put glue on contact points where carbon spars are touching printed parts. Put also a bit of
glue on trailing edge where all the aileron sections are touching each other.
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Flap
Assembly left flap as sketched above. Don't forget to insert flap_horn_L part between flap_L_1 and
flap_L_2. Flap horn should stick out from the bottom side of the wing. When all the parts are in
their position, put glue on contact points where carbon spars are touching printed parts. Put also a
bit of glue on trailing edge where all the flap sections are touching each other.
Aileron and flap to wing
To complete wing assembly attach aileron and flap to the wing.
Hinge slots are not deep enough to fit whole hinge length. Shorten all
hinges as shown on the picture. It has no benefit in terms of added stiffness
of rigidity to use whole hinge arm length as only small hinge area is in
contact with the wing.
Be very careful when using glue near pinned part of the hinge. First insert the hinge into hinge hole
and then apply the glue from inner side of the wing. Do the same when gluing aileron to hinge. First
insert all hinges into hinge holes on aileron/flap and then apply glue from inner side of aileron/flap.
Make sure that aileron and flap have enough space for moving from every side. There should be a
gap of minimum 1 mm on each side of each moving surface.
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Tail main
Assembly left main tail as sketched above. Tail wing uses inverted airfoil. Carbon spars should
protrude 16 mm from base of tail_main_L_0. When all the parts are in their position, put glue on
contact points where carbon spars are touching printed parts.
Tail mov
Assembly moving part of left tail as sketched above. When all the parts are in their position, put
glue on contact points where carbon spars are touching printed parts.
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Fuselage
Start by gluing together boom and fuse_5. Boom should protrude 4 cm from the fuse_5 part. Apply
glue from the tail side of the wing. fuse_5 part has tiny channels for glue to soak in along the boom.
Second step is to attach fuse_4 part to the protruding boom. Make sure that all 4 fuse spar leading
holes are aligned correctly and secure it to the carbon boom with glue.
Then insert 2 pieces of 2x1_518 into top fuse spar channels of fuse_4 all the way in up to fuse_5
and 2 pieces of 2x1_535 into bottom spar channels of fuse_4 all the way in up to fuse_5. Apply the
glue from inner side of fuse_1 everywhere, where fuse spars are visible from the inside of the
fuselage. Let the glue leak further into places which are hard to reach.
It can happen that spar leading holes are too tight and it is difficult to insert carbon spars into them.
One option is to use ordinary bicycle steel spoke (2mm thick). Cut the head and the thread off,
make some kind of sharp edge and mount it into a drill. This way you can drill through all spar
leading holes to remove all printing imperfections. Another option is to use metal cable which you
can straighten and use in the drill.
Insert 2x1_68 spars into fuse_4 and secure them with the glue.
Continue with rest of fuselage parts. Always put each part in its position and only then apply the
glue from inner side.
When all fuse parts (fuse_5 ... fuse_0) are glued together, pre-drill screw holes on servo plate holder
and insert it into fuse_2. Lead 2x1_45 and 2x1_48 spars through side holes in fuse_2 and holes in
servo holder plate. Apply the glue from inside of the fuselage to secure servo plate holder and its
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spars in place.
Pre-drill also screw holes on servo plate. It is easier to attach servos to the servo plate before
inserting servo plate into the fuselage and screwing servo plate to the servo holder plate.
Make sure, that wing joiner carbon tubes (8x6_515 and 8x6_485) fit into main wing spars, if not,
use drill and wet sanding paper as described in the beginning of this guide to make them thinner.
You can glue the wing joiners into the fuselage pod permanently or keep them removable for easier
transport.
Tail
To complete tail assembly first shorten all hinges and then insert the hinges into hinge slots and
apply the glue from inner side of the main tail. Then insert all hinges into hinge slots on moving
part of the tail and put the glue from inner side of the moving part. Tip of the moving part should be
aligned flush with main part. Be very careful when using glue near pinned part of the hinge.
Before gluing tail surfaces to the tail_mount, dry fit protruding spars of the tail surfaces into
tail_mount. Apply the glue on the protruding spars and insert them into tail_mount.
Insert boom into tail_mount. Aline the tail correctly with rest of the fuselage (use joiner rods as
helping guide). Then you can apply the glue from the front side of tail_boom_mount. It has tiny
channels for glue to soak in along the boom.
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Covering
It is important to test film covering on testing part before you start. Covering of 3D printed parts is a
bit special because of thermal expansion of plastics. When heating up the plastics it expands a bit.
Covering is then actually done on slightly enlarged wing and when the wing is cooling down it
shrinks back. But the covering foil does not and that causes wrinkles.
That is why some covering materials work better than other. Some are very stretchy and have the
capacity to shrink down even more together with the printed wing as it is cooling down and
shrinking and some do not.
I tested couple of brands and in my opinion Solarfilm Lite is the best option for 3D printed planes
from Kraga. Unfortunately the company Solarfilm stopped production, so this material is very hard
to get. Other good options (which I did not test myself) should be AeroLITE rolls and Coverite 21st
Century Microlite.
If you cannot get one of the above mentioned covering materials, then in general lightweight
options of covering materials work the best. For example Oralight from Oracover or UltraCote lite.
I strongly advice everybody to use trimming iron instead of standard sized one, because with
trimming iron you don't heat up the wing that much.
Another very useful tool is covering film adhesive for example Cover grip from Deluxe materials.
When using covering adhesive the foil sticks better and one doesn't have to heat it up that much,
what again prevents expansion of the wing.
Finally the technique is also important, but that comes with practice. Covering video guide can be
found in how to section on KRAGA web page: https://3dprintedrcplanes.com/how_to/
My recommendation is to cover wings after they are fully assembled (center wing, tip wing and
aileron are glued together). It is a little bit more demanding but it is definitely worth it. Otherwise
you are risking, that when gluing aileron to hinges and hinges to wing tip, glue might leak and
spread all over hinge pin which will block the hinge and aileron would get stuck.
The same is valid for tail covering. Cover it after you glued on the moving part with hinges.
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Electronics
This is by no means the best way possible how to setup your plane. It is just a brief overview of
possible options.
Motor
Turnigy Aerodrive SK3 - 3536-1200kv Brushless Outrunner
I recommend to use motor weighting roughly 110 g, to have no problems setting the CG. You
should be able to fit inside motors with diameter up to 37 mm.
Suitable propeller sizes: 13x8.
ESC
Turnigy Plush 60A or similar.
BATTERY
Turnigy nano-tech 1000mah 3S 25~50C Lipo (with roughly 80 g of additional ballast) or Turnigy
nano-tech 1600mah 3S 25~50C Lipo
You can choose other battery but keep your size and weight similar to the examples above (up to
150 g). Using these, ESC and battery are installed as much as possible in the front of the fuselage
next to each other (parallel config). For heavier batteries you need to put ESC into the front of the
fuselage area and battery behind it closer to the servos (series config).
RECEIVER
This depends on your transmitter. Only requirement is to have 7 channels.
SERVOS
Hitec HS 85-MG
It is a reliable analog servo with metal gears for very reasonable price.
Servo mounts will fit servos with dimensions up to:
A = 2 mm, B = 29 mm, C = 40 mm, D = 13 mm, E = 20 mm
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Settings and flying
CG
92 mm – 95 mm from wing leading edge measured next to the wing root.
I strongly recommend to use 92 mm for first flight. Setting your CG exactly is very important!
Control throws
Consider these as rough starting point, the season ended before I had time to fine tune the settings
and play with flight modes.
Tail: up 12 mm, down 12 mm
Aileron: up 15 mm, down 8 mm
Landing/crow: flap full down, ail 6 mm up, elev 2 mm down
Template for tail zero position
You can print this template, cut it out of the paper and use it for setting zero position of the tail.
After printing it should measure 92 mm.
Wings to fuselage attachment
Joiner rods on the fuselage have diameter of 8 mm, carbon spars in wings have inner diameter of 10
mm. To attach wing to the fuselage slide wing on joiner rods all the way in until small fork on the
fuselage engages with pin on the wing root cap. This way of wing securing allows wing to detach
during rough landing.
Happy flying
Tomas
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