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!
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
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 firewall below the 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
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.
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.
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!
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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