3D LabPrint North American B-25J Mitchell User manual

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Fully 3d printable
North American B-25J Mitchell
12:1 ~ wingspan 1.72m/68in
User Guide rev. 2019/12

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North American B-25J Mitchell– fully printable R/C
plane for your desktop 3Dprinter
Future of flying - Print your own plane. flight video
The really first 3d printable bomber plane. This even bigger evolution including some revo-
lutionary features. For the second time this model uses new method of joining parts, really,
now on most of parts - stronger, easier to assemble and more precise.
This plane can be recommended to medium skilled pilots. We hope you enjoy printing,
building and flying it, although this build will truly test your abilities and quality of your
printer.
Welcome to the thin wall printing!
The first fully printable airplanes with files prepared for your 3Dprinter, with
flight characteristics, comparable or even supperior to classic build model airplane.
This is not a dream, now you can print this HI-TECH at home. Simply download and print
the whole plane or spare parts anytime you need just for a cost of filament only about $40
Extensive hi-tech 3d structural reinforcement making the model very
rigid while maintaining a lightweight airframe and exact airfoil even it’s just a plastic. This
perfect and exact 3d structure is possible only thanks to additive 3dprinting technology. So
welcome to the 21st century of model flying and be the first at your airfield.
Easy to assemble, you don’t need any extra tools or hardware. Just glue the printed
parts together. The most complicated operation is probably shaping the landing gear legs,
the rest of the assembly is very easy. Simply add brushless motor, ESC, servos and radio sys-
tem. Detailed step by step PDF/VIDEO is included. You will get a superb performing precise
and detailed legendary plane.

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General specifications:
Wingspan: 1720 mm / 68 inch
Length: 1360 mm / 53,6 inch
Height: 400 mm / 15,7 inch
Wing area: 43 dm2 / 4.7 sq ft
Wing loading: 83.2 g/dm2 / 27.3 oz at sq ft
Center of gravity: 83mm / 3.27 in from LE
Airfoil: 3DLabPrint semi 04
Weight of printed parts (w/o wheels): 1980 g / 72.7 oz
Takeo weight (4s 5000mAh Li-Pol): 3600 g / 160.5 oz
Max takeo weight: 4200 g / 194 oz
Never exceed speed, Vne: 120 km/h / 93 mph
Design max maneuvering speed, Va: 75 km/h / 46 mph
Stall speed Vs: 32 km/h / 17mph
Performance measurement:
Max speed VH (level flight): 110 km/h – 75.6kn – 87.0mph
Rate of climb: 21 m/s (6 500 ft/min)
Flight time (4s 5000mAh): 7:00 min (+20% reserve)

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North American B-25J Mitchell, History
The North American B-25 Mitchell is a medium bomber that was introduced in 1941 and
named in honor of Major General William „Billy“ Mitchell, a pioneer of U.S. military aviation.
Used by many Allied air forces, the B-25 served in every theater of World War II, and after the
war ended, many remained in service, operating across four decades. Produced in numerous
variants, nearly 10,000 B-25s were built. These included a few limited models such as the
F-10 reconnaissance aircraft, the AT-24 crew trainers, and the United States Marine Corps‘
PBJ-1 patrol bomber.
The Air Corps issued a circular (number 38-385) in March 1938 describing the performance
they required from the next bombers — a payload of 1,200 lb (540 kg) with a range of 1,200 mi
(1,900 km) at more than 200 mph (320 km/h). Those performance specifications led NAA[4]
to submit their NA-40 design. The NA-40 had benefited from the North American XB-21 (NA-
39) of 1936, which was the company‘s partly successful design for an earlier medium bomber
that had been initially accepted and ordered, but then cancelled. However, the company‘s
experience from the XB-21 contributed to the design and development of the NA-40. The
single NA-40 built flew first at the end of January 1939. It went through several modifications
to correct problems. These improvements included fitting 1,600 hp (1,193 kW) Wright R-2600
„Twin Cyclone“ radial engines, in March 1939, which solved the lack of power.
In March 1939, North American delivered the substantially redesigned and improved NA-
40 (as NA-40B) to the United States Army Air Corps for evaluation. It was in competition
with other manufacturers‘ designs (Douglas 7B, Stearman X-100, and the Martin Model 167F)
[5] but failed to win orders. The aircraft was originally intended to be an attack bomber for
export to the United Kingdom and France, both of which had a pressing requirement for
such aircraft in the early stages of World War II. However, the French had already opted for
a revised Douglas 7B (as the DB-7). Unfortunately, the NA-40B was destroyed in a crash on
11 April 1939 while undergoing testing. Although the crash was not considered due to a fault
with the aircraft design, the Army ordered the DB-7 as the A-20.
The Air Corps issued a specification for a medium bomber in March 1939 that was capable of
carrying a payload of 2,400 lb (1,100 kg) over 1,200 mi (1,900 km) at 300 mph (480 km/h) NAA
used the NA-40B design to develop the NA-62, which competed for the medium bomber
contract. No YB-25 was available for prototype service tests. In September 1939, the Air Corps
ordered the NA-62 into production as the B-25, along with the other new Air Corps medium
bomber, the Martin B-26 Marauder „o the drawing board“.
Interior of huge aircraft factory where rows of bombers are being assembled
North American B-25 Mitchell production in Kansas City in 1942
More...

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Included:
1. STL 3d files
Universal STL files designed for use with desktop FDM 3D printers and slicer software such
as Simplify3D (recommended) CURA or MatterControl (these STLs are not compatible with
Slic3r/PrusaSlicer or Makerware slicers).
2. Factory files for Simplify3D slicer
With all our settings, these Factory files include all you need. Note: we use PRUSA i3 ORIGINAL
printers so you may need to adjust the basic printing parameters to match your printer or use
it as a starting point for you. Please look at Simplify3D
3. Step By Step PDF/VIDEO userguides
Please use this user guide along with the Printing Guide where you can find Tips and Advice
for airplane printing (Thin Wall Printing).

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4. Gcodes
Basic Gcodes prepared for direct use. We made it as universal as possible, 100% compatible
with PRUSA i3 ORIGINAL and most i3 style printers. Feel free to try it out, but we‘re not able
to guarantee it‘s gonna work with your printer.
5. Prepared settings for CURA and MatterControl slicers
If you can‘t use Simplify3D for any reason, we provide our basic configuration files for free
slicers CURA and MatterControl. Use these as a start point and amend as needed.
6. Scale markings and masking patern in PDF
Print this PDF on self adhesive foil, cut it and put it on the model according to your preferences.
Martin Sonka marking or alternatively Hannes Arch marking.

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Lenght: 1360 mm / 53.6 inch
Wing area: 43 dm2 / 4.7 sq ft / CoG is 83mm /3.27 in from LE
Centre of Gravity

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Wing span: 1720mm / 68 inch

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Step By Step PDF/VIDEO userguide (please go through all videos)
Choose airplane at www.3Dlabprint.com. Our Facebook for live information.
BasicrequirementsforourB-25Jare:atleast200/200/200mm
build volume. Nozzle 0.4mm recommended. Heated bed
highly recommended.
PLA filament (or PETG, APLA, htPLA, PC-max.... not ABS) and
some flex for tires...
If you‘re unsure your printer can handle this project, download
the test part from our FORUM (usually the largest part)
1. Create account, download
You‘ll get the download link for all zipped files to your email, or log in to your account and
download directly from our website. If you don‘t receive the link right on checkout, please
contact us on [email protected] mentioning the order number. (WC-XXXXX on PayPal
receipt)
2. Gcodes preparing
option A Gcodes:
If your printer is i3 compatible you can directly use the prepared gcodes. Simply save each to
an SD card and let 3d printer do his job. The HE temperature is set to 225°C for the best layer
bonding. You can edit speed and temperature on your printer LCD only. If prepared gcodes
doesn‘t work for you, please proceed to the next options...

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option B FACTORY files for Simplify3D (recommended)
We prepared all you need in the factory files (basic FFF profiles, parts arranged on the bed,
etc.) Use our settings as a starting point and edit according to your needs (adapt it for your
printer), choose the parts to print etc. Most 3d printers should be ok with files as they are,
however if you need some customization, please do so. We are not liable for any damage
resulting from the use of our settings. If you still encounter any dificulties, please proceed to
the next option.
option C Simplify3D manual setting (watch and learn)
Use our VIDEOGUIDE and how-to to find explanation of proper settings. This is great option
to learn a lot about Simplify3D and become a 3D expert. Of course you spend a lot of time
and the youtube pause button will become your friend. For simplification we explain only
our basic settings for wings and fuselage, please consult our prepared Factory files for the
right settings of other parts like motor mounts, landing gears etc.
AND... please watch the VideoGuides:
video 2 Simplify3D setting
2.1 video about Thin Wall Printing

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option D CURA or MatterControl (considered as the last resort, we recommend Simplify3D)
MatterControl and CURA are free and provide good results. The airframe is still strong
enough, but don‘t expect the best quality. Both slicers lacks some very useful features, and
finer settings, like multiple processes according to Z height, retraction options, layer start,
etc. Please try to find the best extrusion multiplier and temperature for good weight and best
possible layer bonding. Check the suggested parts weight list for proper multiplier settings.
Please check the Cura setup guide in the Help section.
As a starting point you can use our predefined CURA profile. Always adapt the settings for
your printer, change build volume, filament diameter, etc. according to your printer. Please
be aware some parts require dierent settings of perimeters, top/bottom layers and infill. For
some thick part you‘ll need to use support structure. Check our gcodes in printing simulation
for more details about how the result should look like. NOTE: some parts (nose, canopies,
engine covers,...) require top layers to cover the steeper overhangs, but only for a certain
spot. This is not possible to be set in Cura, however you can use the text editor gcode merge
procedure described in the Cura setup guide article.

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3. Print it
Save generated Gcodes and insert SD card to your printer, prepare your printer and start
printing. We prefer to use SD rather than a direct connection via USB
Note: ABS filament is not suitable for this. Scaling the model will lead to unusable result!
Note: ninja flex or simmilar fillaments can stick very hard to PEI based surfaces be careful...
You will need: PLA filament - good quality (we need good layer bonding)
Strong hair spray (or your favorite adhesive bed surface)
(disregard with PEI or similar bed surface, Mk2/3...)
Razor blade
AND... please watch the VideoGuides:
video printing guide #3
North American B-25J Mitchell - parts diagram:

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Basic Tips and Advice
Please experiment with your extrusion multiplier to achieve the similar weights as in the list.
HotEnd temperature is very important for a strong result. The reason is, the plastic leav-
ing the nozzle has to melt the previous layer to create solid joint. Please print the thinwall
temperature tower to find the best hotend temperature value (215° up to 260° Celsius) to
achieve strong strong layer bonding without underextrusion on layer starts.. Turn OFF cool-
ing fan (Heatbreak fan of course has to be left ON). Thin walls easily cools down on its own
and the cooling fan worsens the layer bonding. You can use cooling fan for thick or very
small parts if needed...
Heated bed is very recommended, use 50-56° Celsius to print without warping ends.
Any standard quality PLA is suitable to print our planes, but the result depends on combina-
tion of PLA vs. Extruder vs. HotEnd.
Some colors and brands of filament has lower layer adhesion, please do experiment with it.
There are a lot of 3dprinters on the market, most of them are OK for printing our aircraft
(specific thin wall printing...) with sucient volume, heated bed, 0.4 mm nozzle.
Please look at FAQ and our Forum for further information:
Some advice for rubberlike fillament print-
ing (printable tyre): it is a good IDEA to
use some adhesive tape or foil... first layer
bonding could be too strong or on the
other hand too weak depends what fila-
ment is used... (picture:RubberJet - TPE32
245/30 print temperature)
After printed, heat up bed to 80 Celsius
and remove tape along with printed tyre,
clear the bed with isopropylalcohol...

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4. Assembling printed parts
4.1 Wing assembly (including Engine Gondola)
See video guide #4.1
wing L 1
95g/3.35oz
aileron L
20g/0.7oz
cowling
36g/1.27oz
wing L 3
56g/2oz
wing L 5
24g/0.85oz wing L 6
12g/0.42oz
you will need: CA Glue - medium or similar medium viscosity CA glue
Activator for CA Glue or similar, (gas presurized works better)
Soldering Iron or any hot tool to cut holes
1.75-2mm rod/axle for flap hinge (we use fillament or toothpick)
sound as a option (ESS-AIR Engine Sound System) + cable extension
Proceed the way shown in videoguide:
See video guide #4.1
flap2 L
19g/0.67oz
flap1 L
22g/0.78oz
wing L 2
82g/2.9oz
wing L 4
42g/1.48oz
motor mount
11g/0.39oz
eng. gondola1
68g/2.4oz
eng. gondola2
62g/2.19oz
eng. gondola4
39g/1.38oz
eng. gondola3
9g/0.32oz
The weight of parts can vary +/- 8% due to di PLA color or brand...!!!

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Start with glueing the engine gondola and wing1 parts (shown in the picture below):
If you want to use engine sound system, this is the time to install the self-adhesive vibration
speakers, use a hot tool to cut the hole for speaker cable (the smaller area marked red in the
picture). Stick the speaker to botom of the pod (use IP alcohol to degrease contact surface):
Proceed the way shown in videoguide:
See video guide #4.1
Apply CA glue to the contact surfaces (marked red in the picture) and assemble together,
then apply the activator, proceed this way with gondola parts and glue them together:

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Now apply glue (marked red in the picture) and assemble together motor mount and engine
gondola, then glue the „sure bonds“ (small triangle parts) in to the joints:
!ANNEALING!
We suggest to anneal the PLA motor mount. You can use this procedure: submerge in boiling
water for more than 30 minutes (pla is then much more heat resistant).
Because PLA shrinks when annealed (about 2%) it is good idea to use motor_mount_annealing
compensated for this eect, or you can adjust the scaling exactly for your PLA brand in
Simplify3D or any other slicer:
Continue with R and L motor mount, note: for proper function there is angle compensation
for propeller slipstream so right orientation is essential, see the pictures below):

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Test fit the parts together, apply glue (marked red in the picture) and assemble together
engine gondola and wing1 parts:
Use any hot tool to cut out the hole (marked red in the picture) for main landing gear wheel:
Now first part of wing and engine gondola is ready:

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Proceed with next step:
Now glue outer wing parts together (please don‘t glue the last wingtip part at this moment):
Apply CA glue to the contact surfaces (marked red in the picture) and assemble them together,
then apply the activator:

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Now you can slide aileron to the main wing hinges:
Apply CA glue to the contact surfaces (marked red in the picture) and align the parts together,
then apply the activator:
Use any hot tool and remove the hinge support (marked red in the picture):

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Go ahead and prepare both flaps:
Apply CA glue to the contact surface of the flaps parts (marked red in the picture) :
Apply CA glue to the contact surface of the part (marked red in the picture) and insert it to the
main wing part. Make sure, the aileron axle is in the right position and not contaminated with
CA glue , then apply activator: