SIG MFG. Four-Star 40

Model Airplane News, Nov 2004 by Jensen, Bill

A favorite sportster is reborn in ARF form

The Sig Four-Star Series of sport planes includes the 40 and 60 sizes In kit and ARF versions and a 120-size available only as a kit. In the decade or so since the Four-Star 40 kit was introduced, It has developed a reputation for being a tough, easy to build and fly sport aerobatic airplane. Many have been flown as first low-wingers and many more as backup sport planes for seasoned RC'ers. I've owned my kit-built Four-Star 40 for a number of years, and I use it as an engine test-bed and as a winter mule with skis! The plane has proven to be rugged and easy to repair, and it fits in my full-size wagon with the wing on! When the chance came along to review the ARF version and compare it with my veteran kit, how could I refuse?

ASSEMBLY

This ARF comes very complete, and for the most part, I used the hardware items that came with it. Things fit together well, and I had no assembly problems. The plane's design is quite basic with no undue complexity. One extra step I take with all my planes is to fiberglass the wing's center section for added protection during violent aerobatics. The manufacturer's wing-joint design on this bird is probably strong enough as is, but this extra step is a carryover from the days before ARFs were popular, and we built most planes from kits or scratch and always fiberglassed the wing's center joint.

* Engine installation. Installing the engine is a breeze, since the nose area is mostly open (only a cheek plate on each side), and the holes are predrilled in the firewall. No fussy cowl fitting required here! I cut a relief in the right cheek plate for the muffler and sealed the edge with thin CA and color-matched fuelproof paint. I selected the Norvel 40 for this project, but any engine in the suggested size range would be easy to mount. In fact, my kit-built Four-Star 40 has been used to flight-test six different powerplants over the years!

I used the predrilled holes in the firewall to mount the engine for this review. If you plan to do extensive inverted flying with the Four-Star (or any other plane), however, it's a good idea to mount the engine so that the needle valve is at the same height as the tank's centerline. If you do that, the fuel-head pressure is the same whether flying upright or inverted and provides more constant rpm. On this model, that means lowering the engine about 5/6 inch, but the tradeoff is less prop ground clearance. You can start with the standard engine location, but if you notice that the engine runs rich when you fly inverted, you can use this trick. Another trick I use is to adjust engine downthrust to regulate approach speed; more downthrust gives a slower approach, and less up-elevator is required.

* Radio installation. Sig has made this step easy by providing a built-in servo tray that accepts standard-size servos and by preinstalling the pushrod tubes. What a timesaver! I found that I could stiffen the nylon inner pushrod tubes for the elevator and rudder by installing 2-inch 2-56 rods and clevises at the control horns. I fitted a soft-foam block to retain the receiver and battery and used the control throws specified in the manual. Little trim input was needed on the first flight-a testament to the straightness of the jig-built airframe!

* Finishing details. All that was left to do was to install the landing gear and trim and apply the decals. The decals are really the only place where Sig doesn't do the hard work for you; the decals must be handtrimmed, and this can take some time. Of course, you'll have plenty to spare because of all the time you'll save on the rest of the assembly, but precut decals would have been nice.

CONCLUSION

The quality and workmanship of the FourStar 40 are topnotch, and much of the detail work has been done for you. Having flown the kit version for years, I was pleasedbut hardly surprised-that the ARF version exhibited the same familiar flight experience. The Norvel 40 is a great match for this bird; it offers brisk performance and plenty of power for any maneuver that the Four-Star is up for. I like the ARF concept, especially when the quality is this good, and I can have one of my favorite planes without going through the trouble of building or covering it myself!

APC; distributed by Landing Products (530) 661-0399; apcprop.com.

Futaba; distributed by Great Planes Model Distributors (217) 398-6300; (800) 682-8948; futaba-rc.com.

Master Airscrew; distributed by Windsor Propeller Co. (957) 41-0250; (916) 631-8385; masterairscrew.com.

Norvel (800) 665-9575; (805) 547-8360; norvel.com.

Oracover; distributed by Hobby Lobby (615) 373-1444; hobby-lobby.com.

Sig Mfg. (800) 247-5008; (641) 623-5154; sigmfg.com.

Norvel's new-age power

One look at Norvel's AX-40 engine, and you can see that it is not just another 40-size 2-stroke. The cylinder head is an unusual 3-piece design; the head button and head shim are held in place by an aluminum ring that screws into the one-piece cooling fin/cylinder sleeve. The distinctive color of the fin/sleeve piece is due to the second novel feature-an oxide-based ceramic coating. The sleeve's interior is lined with Sliktek~a Teflon-like substance that reduces friction and increases durability but is much lighter than traditional chrome or nickel plating. The result is a 40-size powerplant that weighs just 13.2 ounces! It isn't light on power, though; the AX-40 is rated at 1.4hp at 16,000rpm. Not bad for a suggested retail price of $110!