Multiplex Fox RC conversion
to 3 channel glider

These pages document the stages of a little project I recently undertook, the conversion of a Multiplex Fox kiddie's chuck glider to a 3 channel rc glider. It may not be the best conversion around, but it worked for me! If your modeling skills are up to scratch, you should be able to do something similar.

I've always liked the idea of having a small rc glider to keep in the car, and the Fox is the ideal candidate for a conversion. It's a 20" wingspan EPP foam kid's chuck glider manufactured by rc giants Multiplex. The glider is a nice design and being of EPP is extremely robust.
The photo below shows the Fox as purchased and assembled...

The ingredients

The number one priority of the Multiplex Fox RC conversion is to take your time in the thinking and planning process! Decide which components you want to use, and stick to them. My basic ingredients were...

1 Multiplex Fox
1 Spektrum AR6300 nano receiver
1 300mAh 4.8V 4-cell battery pack
1 Tower Pro 9g micro servo for ailerons
2 3.7g ultra-micro servos for rudder & elevator
Fine gauge piano wire for control rods
Micro size control horns
Mylar hinge strip
2mm carbon rod
3M cross-weave reinforced tape

I can say right away that not all these items are perfectly suited to the job, but this was my first attempt at such a conversion and we live and learn, so they say. I'll indicate where I would improve things (marked with a *) as I go through the various stages...

The conversion process

Multiplex Fox overview
As already said, the glider is sold as a kid's chuck glider. Out the packet it weighs in at around 35 grams or so, depending on the accuracy of those cheap n' nasty kitchen scales! A large ball bearing planted inside the canopy gives it some ballast. The wings and tailplane slide into slots in the fuselage and sit snugly in place. As a chuck glider, it can be vaguely trimmed by bending the rear half of the fuse, as per the instructions!

The test glide
Assemble the glider as is and do a few test glides. I was quite surprised just how 'floaty' it is, even a gentle glide lasted the whole length of our back garden! The glide was even and straight, indicating no need for trimming or CG adjustment.

Find the CG
If your initial test glides are good, find the Fox's Center of Gravity and mark it on the underside of the wing. As the photo below illustrates, the CG on my Fox fell around the halfway mark of the wing. Needless to say, it's very important to work out carefully what needs to go where, in the planning stage, in order to keep the CG correct without having to add any dead weight ballast afterwards (OK, so mine needed a small woodscrew in the tail, but hey)...

Remove the canopy
Carefully prize off the canopy. It's held on by a large foam lug but there is nothing physically attaching it to the fuselage. It is very secure though and you'll need a strong, non-flexible knife blade or similar to do the job...

Remove the steel ball
Planted firmly inside the canopy is the Fox's ballast, a marble-size steel ball. Carefully prize this out, and while you're at it you can cut off the lug that holds the canopy in place...

Make battery pack compartment
Given the heavy weight of my battery pack* (a 'GP' 2/3AAA 4 cell 300mAH pack, 32g) I decided to place it on the CG and rely on all the other electrical stuff in the nose for ballast. So the compartment was made in the belly of the fuse, directly below the wing midway point. I found that making lots of cuts (slicing) in the foam and pulling out the squares with thin-nose pliers worked well, and left a nice neat hole. Make the hole slightly smaller than the pack, this way the foam will hold it in place nicely.
Be warned that a very sharp blade is required, otherwise the foam just bends around the blade and you won't get a neat cut...

* NB - with hindsight I would try and use a lighter pack, probably a single cell Li-Po although this would fall below the minimum servo operation voltage. Contact me with suggestions!

Prepare the nose for the rc gear
Again, using a very sharp knife cut away the foam neatly to make the appropriate size holes for servos and receiver. In the photo below, the main slot is for the rudder and elevator servos and the one I'm cutting is for the Spektrum AR6300 rx. The aileron servo hole is yet to be cut, but will be on the upward rear face of the 'cockpit'...