RCU Review: Great Planes ElectriFly SU-31 Sukhoi EP ARF

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    Contributed by: Andrew Griffith | Published: August 2009 | Views: 51737 | email icon Email this Article | PDFpdf icon
    Electri-Fly SU-31 Sukhoi ARF

    Review by: Andrew Griffith

    Distributed in the US by:
    Great Planes Model Distributers
    PO BOX 9021
    Champaign, IL 61826-9021
    Phone:(800) 338-4639

    Website: www.greatplanes.com

    SU-31 Sukhoi Video
    Broad Band

    Ease of build.
    Looks and quality of covering.
    Great flight performance.
    Easy battery access.
    Carbon wing tube is sturdy and very light.
    Good contrast between top and bottom of the model.

    Cowl ring installation was somewhat frustrating

    Click HERE for explanation

    Skill level required: Low

    Time to complete:4-5 hrs

    Frustration level: Low

    The Sukhoi SU-31 was designed in Russia by the Sukhoi Design Bureau. While Sukhoi is probably better known in aviation circles for their military fighter planes, they also produce a line of high performance aerobatic aircraft that includes the SU-26, SU-29, and SU-31. While outwardly similar to the SU-26, the SU-31 replaces the tubular steel construction with an all composite airframe and an available 400hp engine that swings a 100" composite 3 blade prop.

    So capable are the Sukhoi aerobatic aircraft that during the FAI Aerobatic World Championships in 2007 that took place in Spain, the SU-31 was flown to first place in two of the three categories (men's and overall) and took 4 of the top 9 spots. It may also be interesting to note that the SU-26 took 3 more of those spots, including the women's championship.

    So what does all that mean to us? The Great Planes ElectriFly SU-31 Sukhoi is a small model that has big shoes to fill. Read on and we will see how it compares to it's full scale counterpart.

    Kit Name: ElectriFly SU-31 Sukhoi EP ARF
    Price: $109.98
    Wing Span: 41" (1040mm)
    Flying Weight as tested: 2 lbs 0 oz (907g)
    Propeller Used: APC 10x7e
    Motor Used: RimFire 35-30-1250
    Battery used: ElectriFly Power Series 20C 2100mAh Speed Controller Used: ElectriFly Silver Series 35Amp
    Radio equipment: Futaba 9C with FAAST module, R617FS FAAST reciever, S3154 digital servos

    • 4 Channel (minimum) radio, receiver and 4 servos
    • Brushless Motor and Speed Controller (35A)
    • 3 cell LiPo battery (1250 minimum, 2100 recommended)
    • Small Phillips screwdriver
    • Thin CA
    • 6-Minute epoxy
    • T-Pins
    • Clear tape or canopy glue
    • Medium strength (blue) thread locker
    • Propeller

    Park Flyer program legal
    Well packaged ARF

    After inspecting the contents of the box, the first order of business is always to examine the instruction manual. Great Planes aircraft usually have excellent instructions and the manual that came with the SU-31 ARF is no exception. Spanning 28 pages, it includes a full inventory, precise building directions, clear photographs, and even a section on doing some advanced aerobatic maneuvers.

    I put the Sukhoi together over the span of three evenings, keeping in mind that a review model needs to be photographed and documented along the way. If you have everything ready to go when you start, the average modeler with a few airplanes under his or her belt could easily assemble the SU-31 in two evenings or a rainy day.

    I'll be using ZAP adhesives throughout this project as I have had excellent results with them in the past. As with the use of any chemicals, ensure you have adequate ventilation while using them.

    Full inventory
    Wings ready for servos
    Futaba's TINY digital servos

    As I unpacked the kit a few things stood out at me. The covering job was excellent and the airplane is covered in real Top Flight MonoKote. After making sure the parts in the kit matched the inventory I heated up the sealing iron and put a fresh blade in my hobby knife. This is one of those areas that reading the manual will let you consolidate a little bit of work. It will also save you time waiting for your covering tools to heat up each time if you do them all at once.

    Using your hobby knife and a sealing iron, cut out and seal the edges of the following areas.

    Wings: Aileron servo bays and aileron control horn slots (watch you don't do lightening holes by accident!)

    Fuselage: Wing tube hole, wing mounting hook area, aileron servo lead holes, wing anti rotation pin holes, horizontal and vertical stabilizer slots, elevator and rudder servo bays (again, watch the lightening holes), and the landing gear slots.

    Tail surfaces: Rudder control horn slot, and the elevator control horn slot.

    After all of the holes were cut and sealed I went ahead and gently used my my heat gun to shrink down any areas of loose covering. A poor covering job will look shabby fairly quickly in the Florida sun but the Sukhoi didn't need much work with the heat gun and iron to get things tight. I would rate the covering job above average in workmanship and outstanding in looks.

    Aileron servo installation
    Wings held in with rubber bands.
    Wings are done, time to move on to the tail.

    The ailerons come pre-hinged so there's not much work to do here. Several trees of plastic parts are provided with the Sukhoi that appear to be generic and contain parts for several kits so don't be alarmed at the quantity of left over parts at the end of the build.

    Locate all of the plastic parts you will need for the two pushrods and control horns. Install the servos in the wing and fish the wires through to the center. You can either glue the servos into the wing or use small self tapping screws. I used small screws so I marked the holes and then moved the servos off to the side while I threaded the hole and hardened it with thin CA.

    I would go ahead and start setting up your transmitter and receiver at this point. Hook up the ailerons using a Y harness or using transmitter mixing and make sure the servos are centered. Locate the appropriate control arm provided with the kit for the servos you are using. If you are using servos that the provided servo arms do not fit perfectly on the output shaft, obtain the correct servo arms from your servo manufacturer. I am using Futaba micro digital servos, so it was no surprise that the provided arms fit perfectly.

    When you get the servos secure, build the pushrods and install the control horn. Note that you have to trim the control horn, if you skip this step it will pop out of the top of the aileron. Trim the ends of the pushrods and the wings are ready for the installation step.

    Rough up about half of the anti-rotation pin with 80 grit sand paper and glue it into the wing root rib using either medium CA or epoxy. Install the very nice carbon fiber wing tube and slide the wings into the fuselage sides. The carbon wing tube was a perfect fit and didn't need any sanding or tape to get things to fit together nicely. The wings are held in place by two large rubber bands that pull them together by attaching to hooks that are pre-installed in the wing root. I was a little skeptical of this arrangement but as of this writing the plane has been flown for three weekends without any problems. I'll keep a close eye on these and replace them often.

    Horizontal stab installation
    Elevator with pins to ensure CA hinges are centered
    Notice the large control surfaces, this should be fun

    The secret to good flying ARF planes is to make sure to assemble them straight. With that in mind, pay careful attention to the steps outlined in the manual to make sure the wing and stabilizer alignment are correct. Test fit the elevator joiner rod and make sure everything is straight before you glue anything. Rough up the ends of the elevator joiner for maximum glue adhesion and coat the center section with petroleum jelly or WD-40 so you don't get any inadvertent adhesion to the stabilizer. The wing and stabilizer alignment on my kit was right on and it was a good tight fit so I used thin ZAP CA to secure it in to place.

    The hinges are small so be sure to center them using pins. This will ensure you get a good grip on both sides of the hinge. You can get a lot of control throw and do some pretty wild stuff with this plane so make sure the hinges are glued properly.

    The rudder is pre-hinged to the vertical stabilizer but you still need to install a hinge between the rudder and the fuselage. Be sure to center and pin this hinge as well. I dry fit the rudder and made sure it was straight and used thin CA to secure it and the lower hinge into place.

    Once all the glue has dried it's time to install the servos. Again, you want to make sure the servos are centered and the servo arms fit the servos properly. I've seen servo arms slip a spline or two in flight, the results are either humorous or scary (depending on if you own the plane in question). Mount the servos the same way you mounted your aileron servos by either gluing them in place or using small wood screws.

    Locate all of the plastic parts you will need for the push rods and install the pushrods and control horns. I also made sure I glued the control horn keeper to the control horn with thin CA and then trimmed it flush. Once you have all the servos and control surfaces centered go ahead and trim off the ends of the pushrods. I used a high speed rotary tool with a cutting wheel. If you wrap the rods with Scotch tape it will make a nice clean cut with no splintering. I put a SMALL drop of thin CA on the end of each rod when I was done.

    Ready for servos
    Landing gear parts, note the thread lock, be sure to use it
    Completed landing gear, ready to install in fuselage
    You can build the landing gear then insert them into the fuselage. However if you need to be careful to note that the struts only mount one way and after carefully making sure I had everything right I proceeded to build them backwards. If you want to do it once just mount the struts first, then assemble the wheels and spats. Make sure you use thread locker on the nuts and let it cure ensuring that the wheels rotate freely but don't wobble. The landing gear installation is solid and you can remove the struts fairly easily if you happen to bend one or both.

    The rear wheel on the full scale airplane is replaced by a simple tail skid on the model. The skid is split and you glue a washer into the skid. It's a great theory and works fine in the grass but after the first day out on a paved runway my Sukhoi was missing both the washer and about half the skid. I glued a small carbon rod on the bottom of the skid and it's been fine since then.

    It's time to build the motor box and get the business end finished. ElectriFly has provided a clever, laser cut, interlocking firewall. If you use the recommended power system, the hard part is already done for you. If not there are some options on mounting the firewall to accomodate other motors but you will likely have to drill your own holes.

    When installing the blind nuts, rather than simply pressing them into the firewall, get them started by hand but don't press them all the way in. Use the mounting bolts to pull them down tight, this will ensure they are straight. I installed mine with medium ZAP CA. You can do this one of two ways. You can coat the bolts with WD-40 so you if you get any glue on them they don't get glued to the firewall or blind nut and let the medium CA cure. This will entail cleaning the bolts later so you can thread lock them in place. The other option, and what I did, was to pull the nuts tight and remove the bolt immediately before the medium CA set.

    Test fit and thread lock
    Tail skid and washer
    Laser cut firewall box
    Completed motor box
    RimFire electric motor

    Dry fit everything to make sure you have all the pieces in the right place. When you're satisfied, mix up some 30 minute epoxy and assemble the motor box. I wrapped blue painters tape around the box and then glued the motor box to the fuselage and set the whole thing aside to dry.

    While I was waiting on the glue to dry I installed the magnets in the cowl ring, battery hatch, and firewall. When installing the magnets, make sure to get the polarity correct. There's a simple way to do this. Separate the magnets into pairs that are stuck together. Mark the exposed sides with a felt tip marker. Install the magnets so that neither mark is visible and the polarity of each pair will be correct. I used medium CA to install all of the magnets. Also, when installing the magnets and backing plates on the cowl ring, be careful that you don't cover up the lower two holes, they are were the dowel pins slide into and hold the battery compartment hatch in place.

    When the glue on the motor box is dry you can install the motor and speed controller. The location in the manual for the speed doesn't quite work out when you try to install the cowl ring so move it forward about half an inch or so. I mounted the receiver on the bulkhead under the cockpit so I had to run a short extension on the speed controller line going to the receiver.

    The hatch battery hatch is located on the bottom of the plane right behind the cowling. It provides very easy battery access and a good bit of room to move the battery back and forth to make CG adjustments. The last plane I assembled in this size range required removing the wing bolts and wing to get to the battery; this is a much better arrangement.

    Gluing the cowl ring to the engine cowling was the only step that gave me any trouble while building the Sukhoi. Of course, now that I know how to do it, doing it again would be a snap. Tack gluing the cowl to the cowl ring like shown in the manual only made me get glue all over the place. Install the spinner back plate, install the cowl ring on to the firewall, then slip the cowl in place. Using the spinner back plate as a guide, fit the cowl to the cowl ring. I used a Sharpie marker and marked the cowl on the top and bottom, then remove both the cowl and cowl ring from the plane. With the cowl off of the plane it's easy to glue it to the cowl using CA and kicker to make a nice fillet.

    Battery hatch and magnets
    Cowl ring magnet installation
    Motor and esc mounted

    With the cowl mounting complete there's only a few quick steps left before we head to the field. The Sukhoi decal sheet has an instrument panel decal which I cut out and applied to the cockpit. The canopy I attached using strips of clear packing tape. You could also glue it on with RC-56 canopy glue but mine has held up fine with the tape and its almost impossible to see.

    The business end then received an APC 10x7E composite propeller. I ran the motor up in my shop and it had plenty of power to fly right out of my hand so flight testing should be fun. I'll be using the Electri-Fly 2100mah 20C LiPo and this combination pulled 384 watts and about 33 amps on the bench. The plane came in at two pounds even with this battery and I can't see sacrificing flight time or performance with a smaller battery to save weight.

    I set the control throws exactly as shown in the manual using my 9C with a 3 position switch. The combination of the 3154 digital servos, along with the FAAST module in my 9C gave instantaneous control response. The servos may be small but they are very fast and precise.

    I normally cut my own vinyl markings but the decals that came with the SU-31 were very attractive so I went ahead and applied several to the airplane. The only thing left now is to see what she's got in the air.

    Cat not included.
    Completed cowl installation
    APC 10x7E propeller
    Radio installation
    Heli battery from previous review worked well
    Electri-Fly 2100mah 20C Lithium battery

    I firmly believe that the most difficult part of any review is getting a weekend, good weather, and a pilot or camera operator, to come together at the same time. Even though I didn't have either a test pilot or cameraman handy I was very excited to fly the Sukhoi so I went ahead and did a few test flights when weekend and good weather intersected.

    On low rates, with the CG in the center of its range, the Sukhoi is very docile. I don't mean to imply that it's a trainer, the Sukhoi is a high performance aircraft with large control surfaces and a high power to weight ratio. As such it's intended for pilots with some experience flying tail dragger style airplanes. On low rates however, it goes where you point it and doesn't have any alarming habits. It was obvious the instructions were written by someone who has actually flown the plane so start at the recommended throws.

    Using mid rates the Sukhoi is capable of an impressive array of aerobatics. I would say I did about 70 percent of my overall flying with the Sukhoi in mid rates. Snaps were crisp both inside and outside and stopped immediately when the sticks were centered. Spins were tight and easily entered but wouldn't flatten out. I moved the battery back in increments until it was pushed back against the wing tube. Now we are talking!

    With the CG as far back as I could get it with the battery, and switch set for high rates, it was time to get it on. This plane does the best looking blender of any plane I've ever flown. Period. When crossing the ailerons in a spin the spin would flatten out at just past neutral and with a little power the Sukhoi would come down like a leaf in a fall breeze.

    The Sukhoi will hover in high rates but lacks the power with this prop for an authoritative punch out. I may give a few more propellers a try. Harriers and rolling harriers are easy to accomplish but look better in mid rate than they do in 3D rate.

    Great Planes SU-31 Sukhoi in action

    Download and Watch in Windows Media Player here

    Broad Band | Dial Up

    Strike a pose

    The SU-31 Sukhoi ARF from ElectriFly has proven to be a very capable aircraft. Its a very light aircraft that sports an attractive covering job in real Monokote. The control surfaces are generous and the optional S3154 servos provide plenty of zip. The light wing loading makes advanced aerobatics impressive and landings easy. The carbon wing tube and rubber band and hooks stood up to some very violent flying without any issues.

    Review models always seem to get a lot of attention at the flying field and our clubs recent electric fly in provided plenty of onlookers when I took out the Sukhoi. I brought several batteries and let a variety of people have a turn flying the Sukhoi. I could sum up the impressions by the number of offers I had to buy the plane that day. No thanks, I'm keeping mine.

    ElectriFly and Futaba

    Distributed exclusively by:
    Great Planes Model Distributers

    PO BOX 9021
    Champaign, IL 61826-9021
    Phone:(800) 338-4639
    Website: www.greatplanes.com
    email: productsupport@greatplanes.com

    Comments on RCU Review: Great Planes ElectriFly SU-31 Sukhoi EP ARF

    Posted by: boex on 08/08/2009
    I know it was windy but I think the plane could fly better with a lighter battery pack. Good job on the review.
    Posted by: Eugene C. Wald on 08/09/2009
    I guess I will have to get one. Great review! rccorky@gmail.com
    Posted by: R/B-PLANES on 08/15/2009
    Posted by: 3W flyer on 08/26/2009
    in my opinion great planes should have made this thing look more like the real sukhoi.
    Posted by: Sessholvlaru on 11/01/2009
    I have the 1.60 size and love it. I wonder how they compare?
    Page: 1
    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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