Sig Four Star 40 ARF

 

 VIDEO FILES

 

The Four-Star series of airplanes has been one of the best all-around sport and “second”-model airframes for sometime. Thousands of model pilots who have just graduated from their basic trainers have learned the intricacies of aerobatics and sport-flying from the Four-Stars without having to sweat every landing and snap roll.

            The Four-Star wood kits have been a mainstay of RC flying because they offer good aerobatic performance, economy, and attractive looks, combined with easy handling and honest flight characteristics. Sig continues the tradition by introducing updated ARF versions of this popular airframe. The first Four-Star ARF was sized for 40 engines and was featured on MA’s Sport Aviator Web site: www.masportaviator.com.

The usual ARF parts were included, except all fit perfectly without modifications. Total assembly time was approximately 40 hours.

 

             However, this review aircraft is 10 inches longer, with 11 more inches of wingspan and 300 square inches of extra lifting area. It is meant for the popular 60-size engines.

            There are two color offerings: red and yellow. The yellow version is easier for my old eyes to see because it really stands out in the sky. The covering material is Cadmium Yellow AeroKote. (Newer versions of this ARF will be finished with Sig’s proprietary covering called AeroKote.)  If repairs are ever necessary, this color is available at any hobby shop.

Assembly: There was not a large amount of work required to get the Four-Star 60 ready for the leap skyward. Almost all the work was done, but a few parts needed attention.

            The fuselage had straight sides and the cockpit floor was level, making it easy to align the flying surfaces during assembly. You’ll want to get everything straight since this aircraft is capable of some nice aerobatics. Since it can be flown by pilots who are graduating from trainers, this review will be more detailed than those for the usual ARF.

            The Four-Star unpacked easily; all the parts were neatly bagged and separated. Even foam packing for the receiver and onboard battery was included.

Sig puts nylon string inside wing to pull aileron servo lead through to center-section. Routing servo lead wire would be a hassle without it.

 

Locate mounting holes for control horn, noting correct side of servo. Linkage holes must be exactly over center of hinge.

 

 

Wing: My usual practice is to assemble the wing first. Once this large assembly is hanging around cluttering up my workplace, I have a lot of incentive to finish building the airplane just to get the wing out of the way. The photo-illustrated direction booklet helped speed this model’s construction as well.

            Before I went crazy building, I had to tighten the covering, especially over the wing’s servo cutouts. I made sure to seal all edges of the covering too. I cut the covering over the wing’s servo mounts and sealed the edges into the openings.

            Sig installed nylon string inside the wing to pull the servo lead through into the center opening. I needed a 6-inch lead extension for each aileron servo. I made sure to tie the plugs of the extension leads together with strong thread. If they were to vibrate loose during flight, one aileron would go on vacation.

            Hinge slots were precut for the laminated plastic, cyanoacrylate-style hinges. These hinges have become standard for most airplanes—even Precision Aerobatics (Pattern) competition airframes. They last for a long time while easily minimizing control-surface gaps along the hinge lines.

            The instructions illustrated how easy these hinges were to install. For added security I made a 3/16-inch hole in the middle of all hinge slots. I positioned the aileron tightly against the wing, flexed the aileron to full travel, and applied thin cyanoacrylate. The hole ensured that the adhesive reached all hinge contact areas.

            Once the ailerons were installed I hooked up one of the 4-40-size aileron control rods to the servo. I placed a control horn square with the aileron’s LE and directly in line with the control rod, and then I marked and drilled the mounting holes. I was sure to position the control horns on the correct side of the servo for proper flaperon use.

Remove the overlapping plastic covering from each center. This allows full contact of center ribs for maximum strength.

 

Low-tack tape holds wing halves together while drying. Even with all that tape, it’s important to continually check alignment while epoxy sets.

 

            JR computer-radio systems are easiest to set up when the control rods are mounted on the outboard side of the servo. Futaba systems prefer the control rod coming off the inboard side of the servo.

            The last step was to join the wing halves. It was a good idea to remove the servos and control horns to make alignment easier. It was also a good idea to remove the covering overlapping the wing’s center root rib. Adhesive does not stick to the covering, and the extra thickness keeps the center ribs slightly apart, weakening the joint.

            I trial-fit and installed the two plywood wing spars into both spar pockets using 30-minute epoxy. At a quick but calm pace I brushed 12-minute epoxy onto the center ribs and joined the wing using low-tack tape. The quicker-setting grade of epoxy holds the alignment of the wing root securely, while the stronger 30-minute grade locks the spars in place.

            After the wing was dry I reinstalled all the equipment and connected the ailerons. A nice feature was that Sig included a handy aileron gauge used to center the ailerons in the neutral position. I covered the exposed center joint using the supplied adhesive trim strip that matched the wing color.

Tail Assembly: The tail feathers were next. There were two spacers between the stabilizer fillets that I had to remove. I cut the covering over these spacers along the center of each opening. This left enough covering overlap to hide the joints once the fin and stabilizer were installed.

            I leveled the fuselage; I cut the covering away from the stabilizer’s top and bottom where it contacted the fuselage’s stabilizer mounting areas. I removed the covering from the stabilizer’s top center to allow for the fin installation.

        

    I installed the fin using 30-minute epoxy. I cut the covering overlap on the fin’s bottom, as was done for the wing halves, and glued the fin in place using 12-minute epoxy. I had to make sure the fin was pointed straight and was vertical to the stabilizer.

            The elevator halves and rudder were installed in an identical manner to the ailerons. I installed the servos in the factory-mounted plate inside the fuselage.

            This design used the tube-within-tube pushrod method to wiggle the tail surfaces. The outer tubes slid easily into the factory-cut former holes. Then I slid the inner tubing inside the black outer tube. The threaded rods were installed in the inner tube with epoxy. The rear control horns were installed like the aileron horns were, using the inner tubing as the guide. I made sure the control-horn holes were over the hinge line.

            I clamped the control surfaces in the neutral position. I connected the rear clevises to the control horns and cut the inner tube to length in the servo compartment. I centered the servos, mounted a clevis on one of the supplied threaded rods, and slid the rod inside the inner tubing with 5-minute epoxy.

            Once dry, everything was centered and slop-free. There was ample room inside this aircraft.

Extra covering over spacers can be used to seal fillet once fin and stabilizer are installed. This little trick makes for a neat installation.

 

            I tend to be prejudiced against tube-within-tube control systems. Temperature variations often cause trim changes, and sometimes one of the metal rods epoxied inside the inner tube can pull loose.

            Although the stock Four-Star 60 system worked perfectly in flight, the elevator pushrod failed on the ground when the elevator was accidentally bumped. One of the 8-inch-long metal rods came loose and had to be reglued.

            I intend to leave the outer tubing in place and replace the inner tube with a solid-steel pushrod. You might consider doing the same.

Control and Power Systems: Any brand of modern computer-radio system is so reliable, user-friendly, inexpensive, and capable that it feels like flying with magic. I happened to have a new JR XP6102 PCM six-channel system with five NES-537 ball-bearing digital servos. If you haven’t tried digital servos yet, you are missing the tightest pilot-to-airplane connection experience. So in went the JR system.

            Using a computer radio allows the ailerons to operate as flaperons. As I will go into later, flaperons made for some amazing stuff on this airplane. Proper control-surface mixing allowed the Four-Star to be trimmed for straight flight in all attitudes and conditions. If you use an analog radio system, the Four-Star still delivers amazing performance with Y-corded aileron servos.

            I used the new Irvine .61 to power the model. This amazing engine turned an APC 12 x 6 propeller at well more than 12,900 rpm running on 15% Sport fuel. Even better, the idle was a reliable 2,100 rpm from the start.

            Even the “stop engine” button on the JR transmitter had difficulty shutting down this power plant. The engine fought stopping all the way and has never quit in the air during the 46 flights I have made on the airplane.

            The Four-Star airframe has had no trouble flying a straight line. The longish fuselage, generous tail areas, and effective control surfaces are well suited to the most powerful .60 engines available.

            If flown with too lean a high-speed mixture setting, the Irvine, as will all high-performance engines, will “eat” glow plugs for breakfast, lunch, and dinner. But setting the high-speed mixture to 500 rpm on the rich side of peak—roughly 12,400 rpm—eliminates glow-plug replacement while providing outstanding performance.

 

Throttle control is via metal cable sliding inside plastic tube. Receiver is below aileron extension wires; battery pack is in fuel-tank compartment.

 

The large “Hershey’s bar” square wing excels at low speeds yet is aerobatic. The red/silver Irvine .61 engine looks great against the yellow airframe.

The Best Part: Mentioning performance brings us to the best part of any airplane review: putting the entire airborne system through its paces and testing the envelope’s limits.

            The Four-Star 60 was designed as a sport model that is suitable for a new pilot who is just out of basic training or for experienced pilots who want a capable aircraft with relaxing flying qualities. Such design criteria left me expecting an okay airplane with few aerobatic abilities. The word “wrong” does not even begin to tell you how far off the mark I was.

            The first takeoff, after approximately a 70-foot run on grass, forced me to start re-evaluating the Four-Star 60’s abilities. The usual amount of right rudder, roughly 20%, was required for a straight takeoff roll until the tail lifted. Once free of the tail wheel, the Four-Star straightened out for a takeoff that needed only slight right rudder. As airspeed increased, no rudder input was required.

            This ability translated into straight vertical climbs requiring little, if any, right rudder to remain on the line. In fact, the Four-Star didn’t need much rudder input to fly straight verticals until near the end of the climb. With the Irvine .61, the end of a vertical climb can occur near the end of visibility, so the Four-Star can be said to fly straight verticals nearly as rudder-free as a Precision Aerobatics (Pattern) airplane.

            Like a Pattern airplane, the Four-Star 60 had no rudder coupling. Full rudder input in either direction resulted in a flat turn with no tendency to bank into the turn. Even flying inverted, flat circles without opposite aileron were easy for this airplane.

            Zero rudder coupling meant that it could fly knife edge, Point Rolls, Stall Turns, and Slow Rolls with ease. I did not have to input opposite aileron to prevent an unwanted roll during knife-edge flight or Stall Turns. The roll rate remained constant in a Slow Roll even as rudder input changed from against the roll’s direction to reinforcing it.

            The first flight impressed me enough that I wanted to give this aircraft a chance to show what it could do. I spent the next flights trimming for maximum aerobatic performance. This means trimming the airplane to fly a straight line in all flight regimes.

            Vertical trimming required 2% right rudder mixed with full throttle. Left knife-edge flight used 2% up-elevator for straight flight; right knife-edge needed no adjustment. The vertical down-line showed a slight “pull” toward the canopy, so I mixed 1% down-elevator to idle throttle.

            These trim settings were less than most modern Pattern airplanes use and were impressive. No, the Four-Star 60 is not a true Pattern airplane. Rolls were almost the model’s only shortcoming. The rolls were not “axial,” meaning the Four-Star couldn’t maintain a straight line while rolling. Since the wing was down on the bottom, axial rolls were hard to accomplish.

            However, the rolls were near axial, and that is more than expected for a sport aerobatic airplane. The Four-Star 60 pilot would not be at a disadvantage competing in AMA Sportsman-class RC Aerobatics or International Miniature Aerobatic Club Basic-class competitions.

            The Four-Star pilot would probably have one advantage in such competition: this airplane performs so effortlessly, flies with a constant medium top speed of approximately 70 mph, and has such outstanding slow-speed handling abilities that the pilot could relax and enjoy the entire flight.

 

 

Flaperons deployed, the model coasts to a landing at roughly 15 mph. Even at this low speed, handling is positive and airspeed control is simple.

 

            Takeoffs and landings were nonevents. This airplane slipped so well that most pilots would be seeking out heavy crosswind landings for the fun of it.

            As a test I flew the Four-Star 60 through the new AMA Masters-class pattern several times. It included Square Vertical Eights, Reverse Avalanches from the top, Vertical Rolling Stall Turns, Reverse Knife Edges, Point Rolls, and Rolling Diamond Eights, followed by Point Roll Square Loops. The Four-Star 60 did all maneuvers with style if not grace. This is not an everyday sport airplane.

            The Four-Star 60 was not designed for 3-D aerobatics, but it could fly the brief Torque Roll, Waterfall (with increased elevator movement), and Inverted Blender, with flaperons deployed. I experimented with coupling elevator and flaperon movements, as would a CL Precision Aerobatics airplane, and I found that it not only makes 20-foot Square Loops possible, but it also permits a range of strange, but attractive, maneuvers.

            Full flaperons on landing reduced touchdown speeds to less than the ridiculous. Yet control was easy to maintain, even in high-wind conditions. With or without flaps, the Four-Star 60 retained a constant approach speed that was slow enough to allow me time for a quick snack before I needed to return for the touchdown part of the landing.

            All control-surface movements were set per the instructions, and the fore-aft CG was at the manual’s 35/8-inch mark behind the wing’s LE. The aircraft was balanced laterally as well. Extra elevator input was added only for 3-D flying and Masters Pattern tests. The extra elevator movement quickened the Snap Rolls while flying the Masters maneuvers. Otherwise, all flight settings were by the book.

Dan VanNieuwland’s (of the Roxbury Area Model Airplane Club) Four-Star 60 was built from a wood kit. Its performance is versatile on skis. Could there be floats in its future for summer?

 

            This was impressive performance from an attractive but somewhat average-looking sport airplane. It was easy to fly and quick to perform without handling vices. The amazing flaperon abilities were a great deal of fun to play with.

            Sig’s Four-Star 60 ARF impressed me more than I ever would have guessed. I’ll bet the same thing would happen to you if you got one.  MA

 

SPECIFICATIONS:

Wingspan: 71 inches

Length: 57 inches

Wing area: 920 square inches

Test weight: 7.3 pounds

Wing loading: 18.3 ounces/square foot

Engine: Irvine .61 two-stroke

Propeller: APC 12 x 6

Fuel: Magnum Fuels 15% Sport

Maximum/minimum rpm: 12,900/2,100

 

PLUSES and MINUSES:
• Outstanding sport aerobatic abilities.

• Easy to flight-trim.

• Honest, gentle slow-speed flight.

• No assembly problems.

 

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• Could use more trim options to distinguish top from bottom.

• Plastic pushrods are weak and cause trim problems.

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