The Multiplex Fox is a very cheap free flight model which makes it ideal for converting to RC for slope soaring as if it breaks you've lost very little money. However breaking this model is difficult given its made with EPP foam which is extremely durable, doesn't snap easy at all, doesn't dent easy and can be super glued back together. All gluing in this project is using regular CA super glue as the foam does not melt - so you do not need special foam glue at all.
Before seeing how it is built check out the video below flying in storm Frank in North East England on the cliff side in high winds!
The stock Multiplex Fox is a free flight model designed for nothing more than being thrown around a field or park. Funnier still the piece of paper that comes in the pack shows not for use in strong winds... LOL.
The elevator and rudder and cut to 2cm deep by the full length available. I'm using hinge tape in 3 places on the elevator and 2 places on the rudder.
I have cut out a notch for the elevator to freely move up and down by a good 1cm each way.
When using elevator tape (especially for use in strong winds) remember to score (make scratches) on the tape where you plan to glue. This will give the glue something to bond on instead of gloss flat surface.
The tail horizontal stabiliser gets glue in place and you can see the notch where the elevator will be able to move up and down, remember to keep all the pieces you cut out until you know what you need to re-use.
The notch cut out early gets trimmed a bit and then stuck back in place to create a rigid tail end again.
The rudder gets hinged back in place with a small gap between so it can move more freely. A tidier way is obviously to have it right against the vertical stabiliser however with such thin foam it may cause bending over time.
Time for the ailerons, each aileron is 12cm long by 1.5cm deep. I am using Turnigy 1440 5g servos directly connected to the ailerons so no control lines at all are required. So the ailerons are placed where the servo horn lines up, its that simple.
First cut out the ailerons and remember to mark them to know later where each belongs.
Now the slot for each aileron servo gets cut out. Note how I'm only cutting out the exact amount required so there is lots of surface to glue the servos on.
Using regular CA glue (super glue) the servos go in place. At this stage its a good idea to make sure that each servo is centered!
Using a sharp knife make 2 channels down each side of the fuselage and force the cables in, the foam is so stiff it almost reseals itself, however I do also run a bit of CA glue over the top.
Now the receiver needs a home, so I cut out a nice cut out in the fuselage deep enough that when the servo plugs are plugged in place its still flush with the inner top surface.
The elevator and rudder are going to be subject to harsh forces so I'm using proper control horns screwed in place and CA glued afterwards. Note how they are on opposite sides to each other so during movement there is no collision.
The servos that control the rudder and elevator go just forward of the aileron servos in the top, while you may think this causes a lot of drag the truth is during slope soaring it makes very little difference at all. Using 1.5mm fiberglass rod as control line and full metal crimping clips which are adjustable. You want zero free play in the lines as that will lead to the model becoming unstable in flight.
The fuselage foam cover has been gutted out on the inside and has Velcro patches on the sides as well as being hinged on the front, this means the cover open outward and can never fly off during flight even if it does pop open.
The finished model is ready to fly being a full 3 channel slope soaring model. Additional modifications include using clear tape over each side of the wings and tail to re-enforce it as well as some tape ran along the bottom of the fuselage to protect the foam when landing. Past that the model is a little nose heavy which is exactly what I'm looking for, if the COG is in its standard place (1/3rd back from leading edge) then it'll simply blow away or you'll be forever holding down elevator or trimming it as such which causes excessive drag and takes away from actual pitch down authority.