Multiplex Fox

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Multiplex Fox

The Fox is a small, cheap free-flight chuck glider that is a popular choice for conversion to radio control and frequently electric power. It is made from Elapor with wings and horizontal stabiliser that slide through holes in the fuselage and a removable canopy. In it's stock form, it's a great kids glider - very tough and easy to throw.

Specification

  • Span 500 mm
  • Length 475 mm
  • Weight approx. 44 g (for the free-flight version, which includes a 7g metal ballast ball nose weight)

Converting to RC

The fuselage and canopy are solid foam, so you need to carve out space for your radio gear and wires. Remove the ballast ball, and fit your own canopy latch. Some conversions have included slicing the fuselage in half, hollowing out the fuselage and re-joining to create a hollow fuselage to save weight and neatly accomodate all components internally. This isn't necessary however.

Most Fox conversions use ailerons and elevator, instead of rudder and elevator - this is because they are two or three times the original weight and fly more like a racer than a glider! Some have extended the wings with extra foam material to reduce the wing loading.


Motor position

There are a number of different motor mounting options:

Nose

This is simplest and balances easily but the motor or prop could be damaged in a crash. The 12mm diameter brushless motors have very thin shafts that can break, so the mini-outrunners are more suitable for this position.

Pylon

Multiplex Fox pylon motor mounting

Placing the motor on a pylon above the wing protects it from most crashes, but can cause trim changes with throttle - particularly at launch where full throttle at low speed can force the nose down. This setup usually needs the battery as far forward as possible to balance and a fast launch to overcome the down thurst from the high motor mount - if you throw it slowly and apply full power it can dive even though you are pulling full 'up' elevator.

Tail

A very light motor can be mounted in the tail (either as a pusher or on the fin) but this is hard to balance.

Wings

A twin motor setup has no trim problems, is easy to balance and protects the motors in a crash, but is more expensive and adds weight.

Twin boom pusher

The rear fuselage can be replaced with a couple of bamboo skewers, each about 3 inches from the center-line. The motor can then be mounted on the rear of the fuselage, between the skewers. This protects it and keeps the thrust-line low, although it's a bit more work than the other methods.

Working power systems

  • 4100Kv 12mm Hyperion inrunner with GWS 3x3" prop and 2s battery (300-500mAh) and 10A ESC
  • 2000Kv 10g outrunner, with a 4x3" prop, 2s 250mAh battery and 6A ESC
  • 5800Kv 12mm in runner with a 40mm GWS ducted fan, mounted above the wings, 3s 480mAh battery and 10A ESC
  • 5800kV 12mm Y-12 Hyperion inrunner with GWS 3x2" prop, 10A ESC and 2s battery 500mAh (requires a good throw on launch with a 125g AUW as wing loading is high)

Graupner make a folding CAM Prop 4.7X2.4" with a 26mm spinner that works well with a 2000Kv 10g motor

Servos

3.5g servos seem to be adequate though some use 5g. There are many possible ways to install them.

Ailerons

  • Dual servos in the underside of the wings, fitted flush
  • Dual servos in the fuselage immediately below the wing
  • Single servo under the canopy
  • Single servo in the fuselage above the wing

Elevator

  • Near or under the horizontal tail with a push rod (this is good if you need to bring the CG back)
  • Part way along the fuselage with a snake
  • Under the canopy with a snake. This option is more common in glider conversions for CG reasons.

See Also