SG Models Mitchell B-25 for 20cc engines-95 User manual

1
Specications:
Wingspan--------------- 95.0 in (241.2 cm).
Wing area--------------- 1191.0 sq.ins (76.8 sq.dm).
Weight------------------- 24.2 lbs (11.0 kg).
Length------------------- 75.7 in (192.3 cm).
Engine/Motor size----- 20cc gasoline engine.
Radio--------------------- 11 channels with 14 servos.
ASSEMBLY MANUAL
Code : SEA 330

Mitchell B-25 -for 20cc engines-95” Instruction Manual.
2
INTRODUCTION
WARNING
KIT CONTENTS
ank you for choosing the Mitchell B-25 -for 20cc engines-95” ARTF by SG MOD-
ELS .e Mitchell B-25 -for 20cc engines-95” was designed with the intermediate/advanced
sport yer in mind. It is a semi scale airplane which is easy to y and quick to assem-
ble. e airframe is conventionally built using balsa, plywood to make it stronger than
the average ARTF, yet the design allows the aeroplane to be kept light. You will nd that
most of the work has been done for you already. e motor mount has been tted and
the hinges are pre-installed. Flying the Mitchell B-25 -for 20cc engines-95” is simply a joy.
is instruction manual is designed to help you build a great ying aeroplane. Please read
this manual throughly before starting assembly of your Mitchell B-25 -for 20cc engines-95” Use
the parts listing below to indentify all parts.
If you are inexperienced with basic R/C ight we strongly recommend you contact your
R/C supplier and join your local R/C model Flying Club. R/C Model Flying Clubs oer a
variety of training procedures designed to help the new pilot on his way to successful R/C
ight. ey will also be able to advise on any insurance and safety regulations that may ap-
ply.
Please be aware that this aeroplane is not a toy and if assembled or used incorrectly it is
capable of causing injury to people or property. WHEN YOU FLY THIS AEROPLANE
YOU ASSUME ALL RISK & REPONSIBILITY.
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KIT CONTENTS
SEA330 Mitchell B-25 -for 20cc engines-95”
1. Fuselage
2. Wing set (2)
3. Tail set (2)
4. Canopy
5. Cowling (2)
6. landing gear
7. Pilot
8. Fuel tank
9. Aluminum wing tube
10. Ep Motor box
ADDITIONAL ITEMS REQUIRED
TOOLS & SUPPLIES NEEDED
in cyanoacrylate glue.
Medium cyanoacrylate glue.
30 minute epoxy.
5 minute epoxy.
Hand or electric drill.
Assorted drill bits.
Modelling knife.
Straight edge ruler.
2mm ball driver.
Phillips head screwdriver.
220 grit sandpaper.
90° square or builder’s triangle.
Wire cutters.
Masking tape & T-pins.
read-lock.
Paper towels.
�20cc gasoline engine.
�Computer radio 11 channel with
14 servos.
�Glow plug to suit engine.
�Propeller to suit engine.
�Protective foam rubber for radio
system.
1.
2.
HINGING THE AILERON
Note : e control surfaces, including the ai-
lerons, elevators, and rudder, are prehinged
with hinges installed, but the hinges are not
glued in place. It is imperative that you prop-
erly adhere the hinges in place per the steps
that follow using a high-quality thin C/A glue.
Carefully remove the aileron from one of
the wing panels. Note the position of the
hinges.
Remove each hinge from the wing panel
and aileron and place a T-pin in the center
of each hinge. Slide each hinge into the wing
panel until the T-pin is snug against the wing
panel. is will help ensure an equal amount
of hinge is on either side of the hinge line
when the aileron is mounted to the aileron.
T-pin
Slide the wing panel on the aileron until
there is only a slight gap. e hinge is now
centered on the wing panel and aileron. Re-
move the T-pins and snug the aileron against
the wing panel. A gap of 1/64” or less should
be maintained between the wing panel and
aileron.
Hinge

Mitchell B-25 -for 20cc engines-95” Instruction Manual.
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6.
7.
3.
4.
5.
NOTE : e hinge is constructed of a spe-
cial material that allows the C/A to wick
or penetrate and distribute throughout
the hinge, securely bonding it to the wood
structure of the wing panel and aileron.
Deect the aileron and completely saturate
each hinge with thin C/A glue. e ailerons
front surface should lightly contact the wing
during this procedure. Ideally, when the
hinges are glued in place, a 1/64” gap or less
will be maintained throughout the lengh of
the aileron to the wing panel hinge line.
Turn the wing panel over and deect the
aileron in the opposite direction from the
opposite side. Apply thin C/A glue to each
hinge, making sure that the C/A penetrates
into both the aileron and wing panel.
Using C/A remover/debonder and a paper
towel, remove any excess C/A glue that may
have accumulated on the wing or in the
aileron hinge area.
Repeat this process with the other wing
panel, securely hinging the aileron in place.
Aer both ailerons are securely hinged,
rmly grasp the wing panel and aileron to
make sure the hinges are securely glued and
cannot be pulled out. Do this by carefully ap-
plying medium pressure, trying to separate
the aileron from the wing panel. Use caution
not to crush the wing structure.
Work the aileron up and down sev-
eral times to “work in” the hinges
and check for proper movement.
Note :
Hinge
CA glue

5
WING TIP BULBS
Please see below pictures.
ey are designed to operate on volt-
ages 12 volts.
2.
1.
3.
4.
5.
6.
7.
CA glue
CA glue

Mitchell B-25 -for 20cc engines-95” Instruction Manual.
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INSTALL THE AILERONS
CONTROL HORN
Fiberglass control horn
Epoxy
Fiberglass control horn
8.
1.
2.
3.
Epoxy
1.
4.
2.
3.
Epoxy
Install the ap control horn using the
same method as same as the aileron con-
trol horns.
INSTALL FLAP CONTROL HORN

7
1.4.
5.
6.
7.
2.
3.
INSTALLING THE ALLERON SERVOS
Because the size of servos dier,
you may need to adjust the size of the
precut opening in the mount. e notch
in the sides of the mount allow the servo
lead to pass through.
Place the servo between the mounting
blocks and space it from the hatch. Use a
pencil to mark the mounting hole loca-
tions on the blocks.
Use drill bit in a pin vise to drill the
mouting holes in the blocks.
Apply 2-3 drops of thin C/A to each
of the mounting holes. Allow the C/A to
cure without using accelerator.
Use dental oss to secure the connec-
tion so they cannot become unplugged.
Secure the servo to the aileron hatch
using Phillips screwdriver and the screws
provided with the servo.
C/A glue
Minimum servo spec.
Torque : 194 oz-in (14 kg-cm) @ 6.0V;
236 oz-in ( 17kg-cm) @ 7.4V

Mitchell B-25 -for 20cc engines-95” Instruction Manual.
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Apply 1-2 drops of thin C/A to each
of the mounting tabs. Allow the C/A to
cure without using accelerator.
Remove the string from the wing at the
servo location and use the tape to attach
it to the servo extension lead. Pull the
lead through the wing and remove the
string.
Set the aileron hatch in place and use a
Phillips screw driver to install it with four
wood screws.
3x10mm
8.
11.
12.
13.
14.
9.
10.
C/A glue

9
AILERON PUSHROD INSTALLATION
Please see below pictures.
INSTALLING THE FLAP SERVO
Repeat the procedure for the ap servo.
INSTALLING THE FLAP PUSHROD
Repeat the procedure for the aileron
pushrod.
15.1.
2.
1.
2.
1.
2.
80mm
80mm

Mitchell B-25 -for 20cc engines-95” Instruction Manual.
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SET UP BOTTOM HATCH SYSTEM
Please see below pictures.
1.
5.
6.
7.
8.
2.
3.
4.

11
9.13.
10.
11.
12.
Epoxy
ENGINE MOUNT INSTALLATION
Locate the items necessary to install the engine
mount included with your model.
1.
2.
2mm

Mitchell B-25 -for 20cc engines-95” Instruction Manual.
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6.
7.
8.
9.
3.
4.
5.
Use four 4x30mm head bolts and four
4mm washers to attach the engine mount
rails to the rewall. Tighten the screws
. Make sure to use threadlock on the
screws to help prevent them from vibrat-
ing loose.
read locker glue
4x30mm
3x10mm

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10.
12.
11.
Position the engine with the drive washe
(140mm) forward of the rewall as
shown.
140mm
Use a drill to drill the four holes in the
engine mount rails.
4mm
13.
4x30mm
14.
15.
16.

Mitchell B-25 -for 20cc engines-95” Instruction Manual.
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Reinstall the servo horn by sliding the
connector over the pushrod wire. Cent-
er the throttle stick and trim and install
the servo horn perpendiular to the servo
center line.
Move the throttle stick to the closed po-
sition and move the carburetor to closed.
Use a 2.5mm hex wrench to tighten the
screw that secures the throttle pushrod
wire. Make sure to use threadlock on the
screw so it does not vibrate loose.
INSTALLING THE STOPPER
ASSEMBLY
Using a modeling knife, carefully cut
o the rear portion of one of the 3 nylon
tubes leaving 1/2” protruding from the
rear of the stopper. is will be the fuel
pick up tube.
Using a modeling knife, cut one length
of silicon fuel line. Connect one end of
the line to the weighted fuel pick up and
the other end to the nylon pick up tube.
Carefully bend the second nylon tube up at
a 45º angle. is tube is the vent tube.
17.
1.
2.
3.
18.

15
Test t the stopper assembly into the tank.
It may be necessary to remove some of the
ashing around the tank opening using a
modeling knife. If ashing is present, make
sure none falls into the tank.
FUEL TANK INSTALLATION
You should mark which tube is the vent
and which is the fuel pickup when you attach
fuel tubing to the tubes in the stopper. Once
the tank is installed inside the fuselage, it may
be dicult to determine which is which.
Use balsa block to hold in place the fuel
tank with C/A glue to secure the fuel tank.
When satised with the alignment of the
stopper assembly tighten the 3x20mm ma-
chine screw until the rubber stopper expands
and seals the tank opening. Do not over-
tighten the assembly as this could cause the
tank to split.
With the stopper assembly in place, the
weighted pick-up should rest away from the
rear of the tank and move freely inside the
tank. e top of the vent tube should rest just
below the top of the tank. It should not touch
the top of the tank.
Use balsa block to hold in place the fuel
tank with C/A glue to secure the fuel tank
inside the fuselage.
1.
2.
Fuel tank
3.
4.
5.

Mitchell B-25 -for 20cc engines-95” Instruction Manual.
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Set up sevor to pull the cover of the box. OPTIONAL RETRACTABLE
LANDING GEAR
Nose Gear.
If you want to use retracts in your
Michell B-25-for 20cc engines 95”, it is a
very popular add-on as optional, we rec-
ommend that you buy a good set of elec-
tric retracts as the Himark AM07 Main
Gear and Himark AM08 Nose Gear
shown as below.
8.
1.
2.
3.
6.
7.
Minimum servo spec.
Torque : 61.10 oz-in (4.4 kg-cm) @ 4.8V;
76.37 oz-in (5.5 kg-cm) @ 6.0V

17
ELECTRIC RETRACTABLE
LANDING GEAR
Electric retractable landing gear is in-
cluded in this kit shown as below.
Main Gear.
If you use the Himark Mair gear, please
cut o so that length is 170mm shown as
below.
1.
2.
5.
4.
6.
170mm
3.
Epoxy

Mitchell B-25 -for 20cc engines-95” Instruction Manual.
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4.
5.
6.
3x15mm
7.
8.
9.
10.
11.

19
15.
12.16.
13.17.
14.18.
6x25mm
read locker glue
19.

Mitchell B-25 -for 20cc engines-95” Instruction Manual.
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20.
21.
22.
23.
24.
25.
26.
80mm
2mm
27.