Hangar 9: Sukhoi SU-31 ARF

FLIGHT TEST

The Russian-made Sukhoi SU-31, with its 400hp Vedeneyev M14 radial engine, has the highest power-to-weight ratio of any production piston airplane in existence. This monstrous excess of power gives it an awesome climb rate of 3,543 feet per minute and an unrivaled sustained vertical climb, while its composite airframe can sustain up to 12 positive G. The Sukhoi SU-31's responsiveness and agility also make it an outstanding aerobatic airplane. With its fully balanced controls and blazing 400-degrees-per-second roll rate, you could say it's a top fuel dragster with the handling manners of a Porsche.

Hangar 9 has captured the essence of this Russian wonder in a 1/3-scale-looking ARF that promises to be just as exciting as the full-scale version.

WHAT'S IN THE BOX?

The Sukhoi is completely built though not assembled and beautifully covered with red, yellow and blue UltraCote, with most of the graphics already applied. The craftsmanship is topnotch, and the plane's over-- all appearance is outstanding. The plug-in wings are built up of balsa and lite-ply with the servo and hinge pockets already cut out. All control surfaces are dual-beveled at the hinge line, which allows more than 45 degrees of thrown for radical freestyle maneuvers. The vacuum-formed canopy and forward turtle deck form a one-piece hatch that allows easy access to the interior of the fuselage. The Sukhoi has a painted fiberglass cowl and wheel pants as well as rugged, painted-aluminum landing gear. I thought the color match between the painted parts and the red Ultracote was pretty close, but not exact.

The fuselage is extremely light for its size and is made of lite-ply has balsasheeted foam turtle deck. The verticle fin is an integral part of the fuselage and it has an airfoil shape, as do the rudder and plug-in stabilizer and elevators. The kit does not come with any hardware, but an optional hardware package is available from Hangar 9 that includes just about everything you need to complete the Sukhoi (except engine and radio). The contents of the optional hardware package are listed in the instruction manual so you can decide whether you want to use any or all of the hardware. The 44-page instruction book is full of photos and very well written with lots of detail. It lists the equipment, parts, tools and adhesives needed for each step. And, to put icing on the cake, it also includes some great setup and flying tips by designer and Tournament-of-Champion pilot Mike McConville.

ASSEMBLY

Wing. The Sukhoi is built so that most of the assembly work involves hinging the control surfaces and installing the servos, linkages and engine. The plug-in wing is well designed and easy to install. First, make sure the alignment pin in each wing root is securely glued into place. Slide the joiner tube into a wing panel and then slide the assembly into the fuselage. Slide the other wing panel onto the tube, lining up the alignment pin with the holes in the fuselage. Then secure the wing panels to the fuselage from the inside using the 1/4-20 bolts that screw into the root ribs.

Each aileron requires two servos with a minimum torque of 60 ounces. I used four JR 8231 digital servos that have a torque of 88 ounces, and I replaced the stock servo arms with the heavy-duty metal arms included in the optional hardware package. All of the control surfaces are hinged with Robart Super Hinge Points, and the holes for the hinge points are already drilled; this makes an often difficult job very easy. To hook up the ailerons to the servos, I used the recommended Nelson Hobby control horns, ball links and the 41/2-inch-long Hangar 9 titanium Pro-links. The Pro-links have right-hand threads on one end and left-hand threads on the other, which means they can be easily and accurately readjusted without being disconnected. The Nelson Hobby ball links have left-hand threads and work well with the Pro-links.

Because the model uses two servos per aileron, special attention is required during setup to ensure that the servos do not fight each other and drain the battery. The key here is to pair up servos that have exactly the same neutrals and keep the geometry for both linkages the same; the instructions cover this procedure in great detail. I attached a 6-inch and 24-inch servo extension to the inboard and outboard servos respectively and then connected each servo to a Y-harness. You must do this for both wing panels. I then connected the two Y-harnesses into two different channels and used the flaperonmixing function on my JR XP8103 transmitter. If you don't use a computer radio, you will need an additional Y-harness to connect the aileron servos to the receiver.

The instructions state that sealing the aileron and elevator hinge gaps is mandatory, and that failure to do so may cause control surface flutter. The material required to seal the hinge gaps is included in the kit.

Tail assembly. The Sukhoi uses removable stabilizers and elevators that plug into two aluminum tubes. The stabilizer halves are attached to the longer of the two tail tubes with 4-40x3/8-inch sockethead screws that are threaded through a hole in each stabilizer half and into the tube. A shorter tube is used to prevent rotation of the stabilizer.