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Cermarks .90-1.4 size Sukhoi SU31 ARF Review

AnnMarie Cross ("AMC") explores this sharp, capable, well built, fast assembly, scale aerobatic ARF, including fun flying video such as a huuuuge knife edge loop!

Splash

Introduction

Ready to go!
Ready to go!
Wingspan:68"
Wing Area:816 sq. in.
Weight:10 lbs.
Length:60"
Wing Loading:28 oz/sq. ft.
Servos:Futaba S3151 digital servos
Transmitter:Futaba 7C
Receiver:R148DP
Rx Batt:Futaba 4C 1000mAh
Recommended Engine:.90 2-stroke
120-140 4-stroke
Tested Engine:YS140
Tested Prop:16x10
Manufacturer:Cermark
Available From:Your Local Hobby Shop, or online at Cermark

For those of you who know me, or who have competed at IMAC contests with me, you might already know that I'm a scale aerobatic plane fanatic. I could write pages on the history and my passion about these airplanes, and especially the Sukhoi. For those who don't know me, I literally "cut my teeth" on a Goldberg Extra as my first airplane, and competed in an IMAC contest before I could consistently land on my own. Suffice it to say, I LOVE these scale aerobatic airplanes. So, when I saw Cermark had released a Sukhoi the perfect size for my YS 140, and in a more feminine "pearl red" color, I just had to have it....

Introduced by the Soviet Team at Békéscsaba, Hungary during the 1984 World Championships, the SU-26 was one of the first of the composite material, monoplane design aerobatic aircraft of the modern era. After a slow start (26th in 1984) the Sukhoi as become the mainstay of team Russia. Imported in America by Pompano Air Center, the Sukhoi SU-26 and its two seat variation the SU-29 are familiar sights at aerobatic contests around the world. The latest refinement is the Sukhoi SU-31, which is a single seat version of the SU-29 which makes greater use of lighter composite materials. (Courtesy of Air And Space World Championship Coverage.) For more of the Sukhoi aerobatic family history, visit this Russian Aerobatic site!

Kit Contents

Assembly

The Sukhoi’s manual was well written (although a little light in instruction in a few places) and a modeler building an aircraft of this type should have several quality ARF builds under his or her belt, so I will try my best not to bore you with every step as written in the manual. What I will try to point out is anything that I thought might be a concern or was just really cool.

One other neat touch was that the tank cap protruded through the front of the firewall, so by simply removing the cowling, the tank could be serviced. (Sorry, the photo didn't turn out well.)

Decal Application

The most time-consuming portion of the process was decal application. However, although Cermark forgot to mention it in the manual, they DID provide a WONDERFUL tool to make decal application easier. A product known as 'frisket paper', or decal transfer paper, was included in the box, but without instructions for its use, so I'll provide that here.

Power, Radio Gear and More

The engine range on this aircraft was quite large, but the selection was easy. I just so happened to have a YS140 that was truly a trusted old friend. Like all YS's, it required a bit more finesse, a gentler hand than some of the less powerful engines in this range, but the performance it provided was sooo worth it! If I were to buy this aircraft again, and needed to select an engine for it, my YS was honestly more than the airplane needed. I would likely buy something a little less powerful and a little less pricey.

I chose to use my new Futaba 7C for this aircraft, which I recently reviewed for RCPower, including the provided digital servos. Boy those babies were nice! So crisp, so responsive. I do love the feel of a digital servo.

As far as throws and CG, I used the stock CG. I'd like to tell you I had the throws dialed in carefully to exactly match the manual -- and it would be the truth!! Except that while working on my aftermarket book for the 7C, I apparently wiped the Sukhoi's settings by accident. OOPS! So the maiden and several additional flights were at 100% of the available travel, with a low rate of about 40%, no exponential. I have no doubt that for future flying time, I will take the time to play with the throws, trying the manufacturer's recommendations, and adding some exponential. Even on low rate, the aileron response around center was too snappy for my personal tastes. Don't misunderstand, it was VERY controllable, just not competition precision soft.

Flying!

Downloads

I worked in the RC industry for about 5 years, full time and then some. It takes A LOT for me to get excited about an airplane these days....but, I have to tell you, am I excited to fly this girl again! I could spend the next 2 hours writing to you about flying this airplane. The video is flown by my husband, Mike Cross, 2 time US National Freestyle IMAC champion, and an unlimited class IMAC competitor for many years. Hope you enjoy it!

Take-Offs and Landings

The videotaped takeoffs have a bit of tailwag in them, but that was due to breezy conditions and less than flat "runways" (aka country roads). On smoother surroundings and less gusty days, take offs are dead on straight, with just a touch of rudder needed. The landings were smooth as glass, as the end of the video shows so well.

Pilot Skill Level

The Sukhoi is no trainer, but it definitely follows my favorite philosophy regarding aerobatic aircraft -- to be a good aerobat, the model must first be easy to fly! I would gladly recommend this as a first scale aerobatic plane to a pilot with some aileron trainer experience, and someone to help him/her get used to these larger glow engines and the visual differences of flying a larger bird.

Precision Aerobatics

Precision aerobatics -- pattern and scale aerobatic pattern competition -- are where this airplane EXCELS. The Sukhoi stayed right where I pointed it at all times, trimmed with no bad habits, had just the slightest of balloons on power application (meaning a mild thrust angle adjustment might be needed), and, beautifully, took ZERO rudder-to-aileron mixing for both flat turns and knife edge! It had just the slightest of rudder-to-elevator coupling, which would vary with minor changes in CG. The tank position was a bit further forward than I would've liked, as the bird gets slightly more tailheavy as the fuel is burnt off, but this wasn't a significant change and was barely noticable in flight.

I can't wait to find the time to get the factory rates set and fly the Sukhoi again. The only thing we struggled with was snaps, and particularly avalanches, which required significantly less aileron input even than my 'guestimate' low rates.

This bird LOVES to spin! It entered instantly, exited with just the slightest time needed to recover airspeed, and entered again on command. Even the toughest of judges would have a hard time claiming this model didn't break into a proper spin, as it clearly fell around the wingtip, without the slightest indication of wingover.

Like all good precision aerobatic planes, the Sukhoi is as happy inverted as upright. Dead center on the stock CG, the Sukhoi took the slightest of push to maintain inverted flight.

That large rudder was perfect for knife edge and stall turns -- and even the huge knife edge loop shown on the video. While the surfaces were not enough for the level of 3D that is 'all the rage' with smaller, non-scale aircraft, they were more than sufficient for the maneuvers for which she was designed, and at which her full-size counterpart excel.

The YS provided more than enough power for any maneuver asked; at just 10 lbs, I suspect on a less pricey, less powerful engine the Sukhoi would still handle vertical 8s, figure Ms, and nearly anything else asked of her.

Sport Aerobatics

Don't let my passion for scale aerobatics scare you into thinking this is a 'pattern bird' that wouldn't make the average sport pilot happy! Like all great aerobats, this aircraft is first a joy to fly, whether just lazily cruising the field, or practicing for the Nationals. It looks great on the ground and in the air, and has a nice large presence without being so big it requires gasoline power and all that goes with that. It is smooth flying and forgiving, and quickly recovers from those minor blunders we all make now and then.

Conclusions

Cermark has a real winner on their hands with this Sukhoi. It looks great, builds easily, balances without an ounce of lead, and has a real presence on the flightline. In the air it is a pure joy to fly, with absolutely NO roll coupling, minimal pitch coupling, and not a bad habit I could fine. It's been a long time since I've had an airplane I'm excited to call my own and anxious to get in the air, but I think the Sukhoi and I might just have to hit the tarmac again tomorrow.

Hits:

  • Hardware packed with the parts that use them. For example, the cowl had the cowl mounting screws in a bag taped inside the cowl.
  • Included graphics transfer paper.
  • Fuel tank access via the cowling.
  • No weight needed to balance.
  • SUPERB flight performance!
  • ABSOLUTELY ZERO rudder-to-aileron coupling, and nearly no rudder-to-elevator coupling.

Misses:

  • The instructions stated to glue the aileron hinges in both the wing and the aileron at the same time. I did this on the first wing and found it difficult. On the other wing panel I glued the hinges in the aileron first and then into the wing. It was easier to get everything aligned and moving smoothly.
  • The wing joiner caused the TE of the wing to have a gap of about ¼”. Although this looked hairy, there was not problem in pulling it together with tape after coating the joiner and wing center ribs.
  • The instructions were vague about how the axles and wheels mounted to the landing gear.
  • There was not enough throw available to allow more than very basic 3D aerobatics.
  • The quality of the screws provided, particularly the cowl screws, was lacking. They stripped a little too easily.

Discussion

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Old Mar 24, 2008, 10:06 AM
Balsa is my friend
infinitemass's Avatar
Jersey shore
Joined Feb 2005
517 Posts
Just a bit of a warning for those interested in this plane. It`s now version two.
Aside from increasing the cost, the other "Updates" include:

The bottom of the entire airframe is grey. Almost impossible to see unless it`s a very clear sky.

The spinner is no longer included.

Gone are the aileron sockets and pin hinges. It now sports Cya type hinges with huge,draggy, park flyer type bevels.

The covering is no longer cut at the factory for the servos or stabs.

The hardware is subpar to say the least. The wing bolts were so poorly molded, they were square. At least three pieces were missing from my herware package all together.

Unfortunately, the manual is still for the first version so I`m not even sure if the missing parts are supposed to be in v.2 or not.

I know you get what you pay for but they increased the price to the point where it`s no longer a bargain and nowhere on the web site do they inform you of the changes.
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Old Apr 23, 2008, 06:39 PM
Registered User
Joined Nov 2004
26 Posts
Other Version 2 or 3? differences

The propwasher distance is now 5-18" from the firewall.
The Cermark tech reps plane balances at 4-1/4 from the leading edge which is at the rear of the previous versions xeroxed manual.
There are no wing bolt guides.
The fuel tank needs a front support.
The belly pan is no longer pre-drilled.
The firewall should be re-inforced with tri stock and epoxy -or- fiberglass and resin.
This is still a pretty good plane for the 169.00.
Flight reports have been very positive as of 4/08.
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Old Jun 17, 2014, 12:09 PM
Registered User
Joined Oct 2013
6 Posts
Can anyone sell me a cowl for this bird. (Or post a link for where i can find one??)
infinitcircus@gmail.com


Mark
Grizlore is offline Find More Posts by Grizlore
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Old Sep 08, 2014, 02:40 PM
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Joined Mar 2004
5 Posts
I'm in need of a cowl also! Mark, did you find a source?
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