Multiplex TwinStar

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Multiplex Twin Star 2

The Twin Star is a twin motor, high wing aileron model from Multiplex, made from Elapor. It is a good second model after the Multiplex EasyStar but is also a good primary trainer with an instructor. It is also popular for aerial photography and FPV flying, as there is no prop in front of the cockpit to obscure the view.

The current model is actually the Twin Star II (replacing the older Twin Star). The main improvement is the Elapor foam, replacing the older, more fragile foam. The aerodynamics and assembley have also been improved.

Specifications

  • Wingspan 56" (142 cm)
  • Length 43 " (108.5 cm)
  • Empty weight 31.89 oz (904 gr)
  • All Up weight 35.98 to 51.15 oz (1020gr to 1450gr) Depending which battery used
  • Wing Area 4.7 sq.ft (43 dm²)
  • Wing load 7.65 to 10.88 oz/sq.ft (23.72 to 33.72 gr/dm²)
  • CG location 3.35 " (8.5 cm) from wing edge
  • Controls Aileron, Elevator, Rudder, Throttle (optional flaperons)
  • Time to build 6-8 hours

Assembley

As with most Multiplex models, the TwinStar is easy to build, simply gluing large blocks of foam together with a few well made plastic parts (and installing the radio gear). No great modelling skill is required.

One area that is not quite perfect is the route of the rudder control cable. This has some tightish bends and does not line up easily with the control horn. It helps to fit the small cylindrical metal cable clamp to the underside of the rudder control horn, although some people have ignored the moulded channel for the cable, and made their own in a more direct line.

The canopy hatches are a weak point in many multipex kits, and are often replaced by a number of magnets at the front of the canopy. Dig matching holes in the canopy and fuselage, fill with glue, place a magnet in the fuselage hole, cover with polythene and place another magnet on top of the polythene, then fit the canopy. The magnets will hold themselves in place while the glue dries, and the polythene will prevent the glue sticking the canopy to the fuselage.

Flaps

The ailerons have separate servos, so it's easy to mix them as flaperons. This is not recommened as the TwinStar already has a good glide, and (because the ailerons are not full span) it adds wash-in which will lead to tip stalls. However, deflecting the ailerons upwards as spoilerons is a good way to allow steeper landing approaches without gaining speed.

Power System

The twinstar is designed for two speed400 motors (with 5x4 Gunther props) and a 8x3300 Nimh battery, but is often converted to brushless motors and lipos.

The original motors have a Kv of about 2000, but this model works better with larger props and a Kv of 1000-1500.

The new BL drive set from Multiplex contains two Permax BL-O 2830-1100 (1100 kv outrunners, weighing 52g each), two 8x5" props and two 20A ESCs with switching BEC. Battery is a 3s/3000mAh pack.

A popular choice is the A2212-10T 1400Kv, available from BRC in the UK, or BP Hobbies in the US. Some people have opted for the even more powerful A2217-6T 1500Kv, but at 250W per motor, it's at bit excessive. These motors are the same diameter as the official multiplex motor, in this case '22' is the diameter of the stator, whereas Multiplex (and HobbyKing) usually give the larger stator size.

A switch mode BEC is a good idea for this model if you are planning to use 3s batteries, as the BEC on most ESCs can only handle 2 or 3 servos at this voltage, and the TwinStar has 4.

Most people put the ESCs in the engine nacelles and lengthen the batteries wires slightly to reach into the fuselage. No one has has any problems with this but ESC manufacurers don't recommend lengthening these wires, so keep it to a minimum.

Motors with a 22mm stator will usually fit inside the engine naceles, but you can't use the standard 'X' shaped firewall mount. Here are a couple of neat adaptations of the stock engine mount:

Brushless engine mount
Brushless engine mount

Alternately, it's possible to push the shaft through most motors with a vice (usually after undoing a grub screw or two). Then the motor can be mounted behind the firewall.

The largest prop that will fit without hitting the fuselage is 9". It is possible (with enough power) to take off from the ground without undercarridge but even a 7" prop will be damaged.

See Also

Park Flyer Plastics do a lovely Seaplane conversion kit for the TwinStar2