Seagull Models Super Decathlon ARF 120 User manual

RCU Review: Seagull Decathlon ARF 120
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Contributed by: Mike Buzzeo | Published: October 2009 | Views: 68486 | Email this Article | PDF
Mike
Buzzeo
(MinnFlyer)
Email Me
Introduction
Specifications
First Look
Assembly
Photo Shoot
Flight Report
Video
Summary
Contact Information
I love Decathlons! There is something about that classic
"High-Wing" look combined with the awesome aerobatic
capabilities that really gets my blood stirring. A few years back I
reviewed the Seagull 40-size Decathlon and it quickly
became one of my favorite planes, so I jumped at the chance to
review their new Decathlon 120.
Although this is listed as an intermediate plane, many people can
attest to the fact that a Decathlon (ANY Decathlon) is not for a
pilot with only a few planes under his (or her) belt. It is a very
deceiving airframe - They LOOK like a trainer, but these are
highly aerobatic airplanes, and their short tail moment trades
stability for agility. Generally, as long as you get a good speed
before lifting off, and always keep in mind that they can bite you
if you're not careful, you'll love them!

Seagull Models
Distributed through
Horizon Hobby
4105 Fieldstone Rd.
Champaign, IL 61822
Phone: [phone]
www.seagullmodels.com
www.horizonhobby.com
Ultracote Covering
Excellent
Construction
Excellent Aerobatic
Capabilities
Fiberglass Cowl and
Wheel Pants
Pre-Installed
Windows and
Pushrods
Manual (See text)
Rudder Thinner Than
Fin
Struts Not Rounded
Skill Level:
Time Required to Build:
Frustration Level:
What do these ratings mean?
This new offering from Seagull Models sports a 78.5 inch
wingspan and takes a 120 - 150 2 or 4 stroke engine. I have had
a Zenoah G-20ei sitting in the shelf for about 2 years that has
been begging for a home and since it is one of the recommended
engines, that's what I plan to use.
But that's enough talk, let's dig in!
Name: Decathlon ARF 120 by Seagull
Price: $319.99
Wingspan: 78.5 in (2000mm)
Wing Area: 1032.5 in² (66.6dm²)
Length: 53.0 in (1344mm)
Flying Weight: 10.0 - 11.5 lb (4.5 - 5.2 kg)
Wing Loading: 22.3 - 25.6 oz/ft²
Airfoil: Semi symmetrical
Center of Gravity: 2.75 - 3.5" (70 - 90mm) from the leading
edge of the wing
Radio Used:Spektrum DX7
Servos Used:JR DS821 (5) - JR 537(1)
Engine Used:Zenoah g-20
Channels Used: 4 total - Elevator, Aileron, Rudder, Throttle
Prop Used: Evolution 16x6
Control Throws:
Items Needed To Complete
4 Channel Radio (Minimum) w/ 6 servos (5 with EP Power)
Aileron Servo Extensions: Four 6" (152mm), One 12"
(305mm) Three dual servo connectors
Elevator and Rudder Servo Extensions: Three 24"
(609mm)
Engine: 1.20 - 1.50 cu in (2- and 4-stroke)
Motor Size: Power 110
Speed Control : CSEPHX85HV required
Recommended Battery: 1 - 4350mAh 4-Cell/4S 14.8V or 1
- 4350mAh 5-Cell/5S 18.5V (9S setup)
Thin and Medium CA Glue
30-min Epoxy
Various Standard Shop Tools

The packaging was pretty good. Everything was individually bagged, but not taped in place so
the wings and stab could slide around and I did have one slightly damaged wingtip.
Construction was very good. I especially liked the alignment pin on the fin. This makes aligning
the tail feathers a piece of cake. A metal frame in the cockpit adds to the scale looks and the
removable door give ample access to the radio compartment.
Manual
Tech Notes from Seagull: The center of gravity noted in the manual is too far aft. The CG
should be 2.75 - 3.5" (70 - 90mm) behind the leading edge of the wing.
As is so often the case, the manual is the weak link. My first
impressions were that it was not too bad, although it uses a
lot of pictures in place of written instructions, but as the build
went on, I noticed two things in particular that should be
noted (aside from the Tech Note above):
First and foremost, the manual instructs you to hinge the
rudder at the same time that you hinge all of the other control
surfaces. The fin has an alignment pin that goes straight
down, through a hole in the stab and into the fuse, but the
lowest hinge on the rudder (the one that goes into the aft
edge of the fuse) needs to be inserted horizontally and I had

to cut the rudder hinges off and add new ones after the fin
had been epoxied in place.
The second thing is not as big a deal, but it was enough to cause me to waste a lot of time. It
deals with installing the turnbuckles in the wing. The only written instructions are, "The hole
location of turnbuckles shown in picture below [sic]" and, "Installing the turnbuckle for the wing as
same as pictures below [sic]." (See pics below).
As you see in the first two illustrations (which are directly from the manual), the locations are
somewhat vague. When I looked at the left wing, I saw 4 pinholes in the covering so I screwed
a turnbuckle into each one, but as I screwed the last one in (inboard, rear), the turnbuckle just
popped through the balsa and there was no blind nut for it to go into. My first thought was,
"They omitted installing the turnbuckle mount".
At this point, I did a little minor surgery and placed a piece of plywood under the surface to give
the turnbuckle something substantial to grab on to. Then I covered the scar with red Ultracote
(which was a perfect color match).
However, when I did the RIGHT wing, I noticed that the inboard, rear hole was much further
forward than where the pinhole was on the left wing. A little probing with my finger found the
location of the blind nut on the left wing. It had not been marked with a pinhole, and was much
farther forward than what the illustrations show (as you can see from the picture above).
So, as I said, this was not a big problem, but had the first hole been marked correctly, it would
have prevented me from wasting a lot of time.
We start by hinging the ailerons. The manual now tells you to hinge the elevators and rudder, but
DO NOT HINGE THE RUDDER AT THIS TIME.

Now the control horns can be installed. The hole locations are marked by a pin hole in the
covering. I found that I had to clear out one of the holes with a drill bit, but the rest were clear
through.
ENGINE AND TANK

There are holes with blind nuts for
the supplied engine mount, but
since I was using the G-20, I used
its back plate as a template to drill
the new mounting holes and
installed 8-32 blind nuts.
Using two 1.4" wood blocks as
stand-offs, the engine was bolted
to the firewall and the throttle
pushrod was added. Note: Due to
the RF output of a gasoline engine,
I could not use the supplied metal
pushrod and substituted a
non-metallic pushrod instead.
I used a standard JR 537 servo for
throttle.
The electronic ignition module was
enclosed in a box and bolted to the
Zenoah G-20 Spotlight
Zenoah G-20EI
Zenoah 20cc Electronic Ignition Gas Engine
Zenoah's groundbreaking G20Ei isn't just Zenoah's first engine
with electronic ignition, it's the first gas engine from any
manufacturer that can fit .60-size planes that, until now, were
limited to glow or electric power choices. Its dimensions are
especially well suited for round cowl models like Hangar 9's
popular Corsair 60 and P-47D 60 ARFs. It has plenty of power
for many .90 to 1.20-size sport applications as well. Much of this
incredible versatility can be attributed to its lightweight
magnesium-aluminum alloy crankcase that gives it an
impressive thrust to weight ratio compared to most gas engines.
Key Features
Electronic Ignition
Small & Lightweight
Easy Operation and Mounting
Excellent Power
Lower cost Fuel
New Magnesium Case
Fuel consumption is 1/2 that of a similar glow engine
Specs
Type: Gas Electronic Ignition
Displacement: 20cc
Bore: 32mm
Stroke: 25mm
Cylinders: Single
Total Weight: 41.6oz with muffler, ignition, and mount
Engine (Only) Weight: 33 oz
Crankshaft Threads: 8x1.25mm
Benchmark Prop: APC 15 X 6 9500rpm
Prop Range: 14 x 6 through 16 x 6
RPM Range: 1400 - 10,000
Fuel: Gas Oil mix 32:1
Muffler Type: Compact Welded can (included)
HP: 1.7HP @ 8500rpm
Cylinder Type: Nikasil, ring
Download the Manual
Zenoah G-20 Instruction Manual (2.8 MB)

firewall below the engine.
A good tank is supplied, but since I was using a gasser, I couldn't use it. I switched to a DuBro
16oz tank with a gas stopper.
For the cowl, I placed strips of tape along the sides of the fuse and marked where the firewall
was. Then I put the cowl on, aligned it, held it in place with the tape and used the marks to drill
the mounting holes.
TAIL
Adding the tail section starts with the removal of the covering on the stab center section.
Alignment is a piece of cake thanks to the alignment pin in the fin. Once the epoxy on the stab
and fin has set, you can now hinge the rudder.
I was perplexed at first to see closed loops in the tail brace wires, until I realized that the sleeves
had not yet been crimped (whew!). Tabs are bent and bolted to the stab and fin, the wires are
looped through the tabs and the sleeves can be crimped with a side cutter.

The other end of the wire gets a connector similar to a pushrod connector which I may change to
a regular cable sleeve in the future.
Now the pushrods (which are pre-installed) can be connected to the control horns and the tail
wheel assembly is installed.
LANDING GEAR
You must cut the slots in the fiberglass pants for the axels. I found that I needed to go a little
higher than the 14mm stated in the manual for the plywood back plates to be fully concealed.
Assembling the pants was very easy and they are then bolted to the bottom of the fuse. There is
also a plastic cover that gets glued over the area which I decided to omit.
RADIO INSTALLATION

The Decathlon uses one servo in each wing, one for the rudder and two for the elevators (no
servo reversing necessary). I used JR DS821's for all control surfaces. I was surprised to see
that even with the weight of the G-20 and all of its components up front that the battery needed to
go under the tank to get the CG on the spar.
I also added a Du-Bro Kwik Switch & Charging Jack.
FINAL ASSEMBLY
The wing attaches to two aluminum tubes - a main tube up front and a smaller, anti-rotation tube
in the rear. Wing bolts inside the cabin secure the wings to the fuse.
The instructions tell you to drill through the wing and tube and to insert a screw through the holes,
but I skipped this step - The wings already have bolts holding them to the fuse, so bolting through
the tube also would not only be redundant, but it would greatly increase assembly/disassembly
time. Of course, if you should choose to add the bolts, I won't say not to.
The door is now secured with two small nylon thumb screws.
For the strut attachment point, a plate is installed through the fuse and secured (before closing
the door of course). The struts bolt to the fuse and have clevises on the outboard ends to attach
to the turnbuckles on the wing. The strut braces are also connected with clevises.
That's it! She's ready (and BOY, does she look good)! It's time to add a few decals and bring her
outside.

To be honest, I was slightly
concerned that the G-20 would
have the power to do justice to
this 120-size airplane, but the
first takeoff put my fears to
rest. The Decathlon lifted off in
about half of the space I had
expected it to. That brought on
another wave of anxiety -
Decathlons are notorious for
torque-rolling into the ground if
they lift off too soon. No
problem there either. The
Decathlon took to the air like it
had been waiting to get there.
Once airborne, I did the usual
"fly the box" to get her trimmed
out and after only a few minor
trim adjustments, she was
flying "hands off". Now let's
see what she can do.

see what she can do.
The G-20 easily pulled it
through all of the typical
maneuvers, loops, hammer
heads, a split-S, etc. Spins
were really nice - the
Decathlon both entered and
exited them easily. I think the
G-20 is an excellent power
option for scale flight. It flies
the Decathlon very well
without over-powering it - of
course, if you prefer to
over-power your planes,
there's plenty of space in front
of the firewall to go bigger!
Landings were also very nice.
She glides in well without
being a "floater", and she
touches down as pretty as you
please.
Since the maiden flight I have
flown the Decathlon several
times in a variety of weather
and wind conditions (including
once, when I flew it in an
exhibition for full-scale pilots
on a day that I would have
normally considered to be
"way too windy") and it
handled every situation like a
veteran.
The video includes some
bonus footage which was shot
using the Fly Cam One2
on-board video system!
Seagull Decathlon 120
ARF
Or, Download the Video
(35meg)
CLICK HERE

If you can overlook the faux pas in the manual, this plane definitely gets high marks.
Construction is excellent, as is the covering job and it's a great flying plane!
One of the things I am most pleased with is that there seems to be no tendency to ground loop
or torque-roll on takeoffs (which are characteristic of Decathlons). And once she's airborne,
she'll do anything you'll see a full-scale Decathlon do (I'm really thinking Smoke System at this
point!)
Even with the nice ground handling, I would discourage a beginner from trying ANY form of
Decathlon, but if you're well into the intermediate stage or an advanced pilot, the Seagull
Decathlon 120 is a definite keeper!
Seagull Models
Distributed through
Horizon Hobby
4105 Fieldstone Rd.
Champaign, IL 61822
Phone: [phone]

www.seagullmodels.com www.horizonhobby.com
JR Radios
4105 Fieldstone Road, Champaign, IL 61822
Website: www.jrradios.com
Product: JR 6102 Transmitter
Support Phone: [phone]
Sales Phone: [phone]
Zenoah Engines
Distributed through Horizon Hobby
4105 Fieldstone Rd.
Champaign, IL 61822
Phone: [phone]
Zenoah Engines
FlyCamOne2:
Hobby Lobby International, Inc.
5614 Franklin Pike Circle Brentwood, TN 37027
Website: www.hobby-lobby.com
Phone: 1-866-WE-FLY-RC (1-866-933-5972)
Fax: [phone]
Evolution Propellers
Distributed through Horizon Hobby
4105 Fieldstone Rd.
Champaign, IL 61822
Phone: [phone]
Evolution Propellers
Du-Bro
Everything For The R/C Hobbyist
Phone: [phone]
Website: www.dubro.com
Comments on RCU Review: Seagull Decathlon ARF 120
Profile
Nice review, nice plane, excellent video.
Profile
I watched the video and it looked to have plenty of power to fly scale. Does it have enough power to fly straight up?
Profile
No, but you can always squeeze a 30ish gasser in it :-)
Profile
I have a nice 30cc in mind, thanks!!
Profile
Excellent review and great video!
Profile
I have one with an RCS 140 (22cc)gas. Good flier, a little overpowered. Forget the 30cc. Good review.
Profile
Thanks for the good review, Mike. I was wondering, is there enough room inside the cowl for my Saito 130TD twin,
which is 7.5 inches wide?
Profile
Nope, the cowl is only 6.5 inches wide
Profile
Mike, Would a OS FS-120S III 4 Stroke engine fly this airplane. And would it go into the cowl. Thanks
Profile
Nice video Mike! Have you tried FPV using the FlyCamOne3? Put on the goggles and fly with the pilot eye view.
Page: 1 2 >
Posted by: daveamt on 10/17/2009
Posted by: AJsToyz on 10/19/2009
Posted by: MinnFlyer on 10/19/2009
Posted by: AJsToyz on 10/20/2009
Posted by: tailskid on 10/27/2009
Posted by: rcnutstoo on 10/27/2009
Posted by: Daniel-EL on 12/05/2009
Posted by: MinnFlyer on 12/05/2009
Posted by: egg20 on 12/11/2009
Posted by: Fly2XS on 01/15/2010
The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply
generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in
products like the one featured in the review.

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RCU4 | 10.19.111.254 | 0 | 1 | 11:53:47 PM EST | NC