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Goldberg Sukhoi ARF w/ OS FS120 Review

David Hogue explores this lightly constructed, brightly colored, great looking and SUPERB flying scale aerobat, with an OS FS120 Surpass for power and performance.

Splash

Introduction


Wingspan:72.5"
Wing Area:949 sq. in.
Weight:10lb 7oz.
Length:67"
Wing Loading:25 oz/sq. ft.
Servos:JR Ds811/4131
Transmitter:JR 9303
Receiver:JR 549FM
Battery:World 1500NIMH 4 cell
Engine:OS FS1.20 Surpass
Manufacturer:Carl Goldberg
Available Online From:Tower Hobbies

Gentle as a lamb when it's slowed down, the Carl Goldberg Sukhoi's ultra light construction lets its pilot draw the kind of extended vertical lines, crisp corners and compact, perfectly formed figures that are essential for thrilling, pro-style aerobatic sequences. With its superb aerodynamics and double-beveled enlarged control surfaces, this aircraft is capable of performing anything you can dream up; torque rolls, knife-edges, inside and outside snaps that start and stop instantly, precision maneuvers, plus tumbling maneuvers that really tumble become every day experiences. Unlimited aerobatics!!

Ever since the first time I saw one, I have loved the powerful, sexy, radial engined aerobat that is the Sukhoi. When AnnMarie Cross, fun manager of RCGroups, emailed me and asked if I wanted to review the Goldberg Su26, I could not type the reply fast enough to say "YES". When the kit arrived, I could hardly wait to dig in and get started.

This kit features balsa and ply construction, with some sheeted foam in the fuselage, Ultracote covering and matching painted fiberglass cowl, plug in wings and stab with aluminum joiners, a hatch that opens the whole top of the fuse from behind the canopy to just under the cowl, and another hatch that covers the landing gear attachment. All of the control surfaces are double-beveled, and there are dual elevator servos for both power and precise adjustment. In many ways, the construction and design of this Sukhoi mimics the larger 25% to 40% IMAC type aircraft, but in a smaller, more manageable and affordable size.

Kit Contents

The kit came double boxed for protection, with all the parts bagged. Nothing was damaged in shipping, but the fiberglass cowl did appear misshaped, apparently from heat during storage. It was a bit warped at the rear edge; however, with some urging, it easily slipped onto the fuselage and assumed the proper shape. The covering and paint was perfect, much better than most of my own work. I also found a nicely painted aluminum gear, lightweight wheels, engine mount, spinner, and fuel tank came included. There was nothing left to buy but the radio system, engine, servo extensions, foam rubber for radio protection, pilot figure(optional), and adhesives.

Assembly

This was one of the best ARF's I have had the pleasure of assembling. It went together very quickly and easily, and was ready to fly in only a couple evenings. The instructions were very thorough, with good pictures to help the builder along the way. I won't bother to repeat the instructions, and will only cover the highlights here and point out some of the details. The joiner systems for the wing and stab virtually guaranteed alignment, a critical step in assembling any airplane, kit or ARF.

Wing

The ailerons come taped to the wings, with slots for the CA hinges already cut. I found no problems fitting the hinges and surfaces in place, and then marked and epoxied my servo mount blocks to the servo bay covers. Once this was dry, it was a simple matter of hooking the extensions up. (I recommend using heat shrink tubing, tape, or some method to prevent the extensions from coming loose), and screwing the cover to the wing. I then made up and connected the 4-40 linkage to the bolt style control horns. The linkages were high quality, and very easy to adjust, all top notch hardware I would not hesitate to use again.

Fuselage

Not much to cover here that isn't explained in other sections. The dual elevator servos were installed in the tail, and the included leaf spring tail wheel was bolted in place. Blind nuts were already preinstalled for the hatches, cowling, tail wheel, and landing gear. The firewall area was already fuel-proofed, though the manual does suggest the builder go over all high stress areas with epoxy or wood glue for extra security. The canopy was tinted and the framework perfectly painted. I attached it with some small sheet metal screws rather than the glue suggested, in case I want to add a pilot figure later.

Tail

There were two options for the horizontal stab -- either make it removable by drilling and tapping the aluminum joiner for 4-40 bolts, or permanently glue the tube and stabs to the airframe. The latter is recommended, but I chose to make them removable in case replacement ever became necessary, or in case I ever decide to sell the Sukhoi and have to ship it. I can tell you after flying it, that's not something I plan to do any time soon!!

The vertical stab was designed to have it's flat sheet base glued to a flat area on the top of the fuse, and then the joint was covered by a plastic fairing. My stab did not sit flush on the fuse because the fuse sides protruded up slightly past the flat plate. I didn't want to trim the sides down or cut into the fin to make clearance because this meant cutting into the covering, so I decided to add a 3/32 balsa shim to the bottom of the stab. This seemed like a great idea at the time, and I could see no reason why this would not work. However, when I tried to fit the fairing I realized I had not thought ahead as well as I first imagined, and now the fairing didn't fit quite right. I worked with it as best I could, and kicked myself for the mistake. I may order a new fairing and cut the fin off and fix it later, because it bothers me, but it's a minor cosmetic flaw and totally my fault. Had I trimmed the fin slightly, the fairing would have covered it up, and everything would look perfect.

Radio Installation

All of the servos I used are standard size, and fit in their precut locations perfectly. I had the option of locating the rudder servo in the rear with a short push rod, or using the location by the throttle servo and hooking it to the surface with pull-pull controls. I chose the forward location as I knew I could add a little weight to the tail if needed, but if I came out tail heavy with the servo in the rear, it would take quite a bit of nose weight to offset the condition. As it turned out, my balance point was perfect for my flying style with the battery just in front of the rudder and throttle servos, accessible via the bottom hatch/landing gear cover. The receiver was wrapped in foam, placed in a plastic bag, and held in place just behind the servo tray area with a Velcro strap.

Engine Installation

The instructions suggested using #10 sheet metal screws to retain the engine to the mount. I have used sheet metal screws on small engines and never had one come loose, but I didn't trust them on this large an engine, so I tapped the mount for 8-32 bolts, and added lock nuts on the back side for extra security. Once the engine was fastened to the furnished mount, it was just a matter of lining it up on the pre-marked firewall and drilling for the blind nuts.

I marked the cowl and made cutouts for the engine's head, muffler, and glow plug access using the provided clear plastic template method that was explained in the manual. I taped the plastic to the fuse, used a sharpie to mark clearance openings on the plastic as if I was drawing on a transparent cowl, and also marked the exact location of the plastic where it was taped to the fuse. The openings were then cut in the clear material. Next the engine was removed, the cowl installed, plastic taped back in its original place and it became a simple matter to transfer the exact locations of the openings to the cowling. This worked beautifully, and was easier to do than explain. I did add a Dubro remote fuel button on the third line going into the tank, to ease the job of filling and emptying the tank after a days flying.

Completion

I was done so fast I had to look over everything several times to make sure I hadn't forgotten anything. I sat down and setup the low rates on my transmitter to just a bit more than the instructions suggested, and set the high rate well above that, with plenty of expo on both to smooth things out. I checked the CG and found I could hit the recommended 5" from the LE with the battery beside the tank, so I was very happy with the choice of rudder servo location. I then took the Sukhoi apart, loaded it up and made sure the batteries were on charge and ready for the upcoming flying day. My co-pilot wanted to take it up right then, but I told her she wasn't ready for this kind of flying yet.

Flying

Basics

This is a well designed and sweet flying airplane. Honest flying aircraft have few bad habits, very little control coupling, and are generally very easy to fly because they don't do anything the pilot doesn't tell them to. I found the Sukhoi to be a very honest aircraft. It flies fantastic, and I cannot wait to get more air time on it. The new OS 1.20 started on the first application of the starter, and has run perfectly so far.

Taking Off and Landing

The Sukhoi tracks perfectly straight on take-off without any conscious rudder input, and I found it just as easy to land. Even balanced at 6" back from the LE (again, the manual recommends starting at 5"), I found no tendency to drop a wing at comfortable landing speeds. I simply set up a descent, controlled the sink with power, and she came down on the mains or all three every time.

Aerobatics/Special Flight Performance

The Surpass is brand new, and still breaking in, and I have not spent that much time in the air as of yet, but so far I can find nothing this combination will not do. Balanced at the suggested CG, the Sukhoi requires just a little down pressure to maintain inverted flight, and it will fly inverted hands off with the balance a little further back. Rolls are very axial and fast -- blistering fast on high rates; loops can be flown nice and round, huge or small. Snaps are crisp and easy to stop at just the right time, although my feeble piloting skills need more practice to get them right.

3D

I haven't explored the SU26's 3D capabilities as of yet, because the OS is still new and needs a few more tanks through it before I will be able to lean the carb and extract the engine's full potential. I do know that at present, and running very rich, the plane will hang on the prop, and that is with a Top Flite 15x8, obviously not the optimum prop for 3d flying. I will experiment with props and get some video with more aerobatics and some 3d flying at a later date. More to come on that!

Is This For a Beginner?

Absolutely not!!! While very easy for the experienced pilot, this plane is not the place to start flying. I would venture that anyone with low wing sport plane experience would find the Sukhoi very easy to fly, as it is lightly loaded and has no vices. I would recommend a less experienced aerobatic pilot begin at the manufacturer's recommended CG and throws, then experiment from there to suit his own needs and style.

Flight Video/Photo Gallery

Downloads

Conclusion

I was extremely pleased with both the looks and the fit and finish of the Carl Goldberg Sukhoi SU26MX, and the flight performance has certainly lived up to the full size aircraft's sparkling record. If you have been looking at the big IMAC types but don't have the room or pocketbook for one, take a look at this kit, I don't think you will be disappointed!

PRO's:

Complete, over 90% built and beautiful covering and paint work. If I pushed myself, I could have had it ready overnight, I am sure. Flight performance is outstanding, and I really like the "neat factor" of the plug in wings and stab.

Con's:

The cowl was a bit out of shape, and the vertical stab base needed trimming to fit correctly. One elevator and the rudder had slight warps, which were removed with a heat gun. These were very minor points, and hardly worth mentioning.

Discussion

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Old Jan 09, 2005, 01:12 PM
Registered User
burr ridge illinois
Joined Oct 2003
1,450 Posts
Nice review overall, but one criticism:

I had one of the original kits for years and loved it. It was capable of mild 3D with a YS120 at 9.5 lbs, and I've thought about replacing it with the ARF.

The ARF includes mods which make the plane more sophisticated but also probably heavier. The first thing I looked for in the article was the 3D flight assessment.

Instead I found the now ubiquitous "I didn't do it" paragraph, which in this case sounded a little like "it hangs on the prop, but barely".

If the 15x8 is not the right prop, get the right prop. If the motor isn't broken in, break it in. We want to know what this baby is capable of!

I would love to see an update to the review soon: Vertical punchout form a hover, torque rolls, waterfalls, harriers, rolling harriers, knife edge loop, etc...

Thanks,

Eric
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Old Jan 09, 2005, 09:52 PM
I broke it
David Hogue's Avatar
USA, NC, Clayton
Joined Feb 2001
5,709 Posts
Eric,

I appologize for the lack of 3D flight exploration in the article and video. The article was published as you see it to have it online for Christmas shoppers, with intentions of adding more video once I get the engine fully broke in, experiment with props, throws, etc. Stay tuned for more video, and in the meantime, I can tell you for sure, Goldberg makes some very nice ARFS. I just got a used Decathlon, and its every bit as nice as the Sukhoi. They both fly very, very well. Your YS should be more powerful than my OS, I plan to try a 16x6APC on mine the next time out. I would have flown it today, but I spent too much time on the Decathlon getting the engine running right, and flying and shooting some video for another review. It will be up as soon as I can get it done, I promise you that

Thanks,
David
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Old Jul 01, 2005, 08:18 AM
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Joined Oct 2004
8 Posts
You Promised,But I still dont see it

Still waiting !
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Old Jul 01, 2005, 12:09 PM
I broke it
David Hogue's Avatar
USA, NC, Clayton
Joined Feb 2001
5,709 Posts
Whoops,

Sorry, should have added an additional video or at least comments by now. I have been flying the Sukhoi on a 16x6 apc and 15% 4s fuel. I think I could go to a 17x6 and get a little more grunt out of it, but it really could use a bigger engine for all out 3D performance. It's definitely not underpowered, but dont expect it to pull verticaly out of a hover with the 1.20. Takes between 3/4 and just short of WOT to hover on my tx, but it will hold it. Snaps, knife edge, walls, harrier, and elevators are all taken in stride...the plane has no problem with any of that, and is still a joy to fly every time I get it out of the trailer. I just looked, and the other video I have shot isnt very good.. I will try and get some more done

thanks,
David
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Old Jul 03, 2005, 09:12 PM
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burr ridge illinois
Joined Oct 2003
1,450 Posts
Yeah, I suspected it wouldn't pull away from a hover. For me that's the kiss of death for a plane advertized as 3D.

Breaking in and tweaking props can only do so much.

Thanks for the update,

Eric
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