dinsdag 18 januari 2011

Multiplex Fox RC conversion for gliding

The Multiplex Fox is a small (500 mm wingspan) and cheap (10 EUR) foam free flight glider. By default it has no control surfaces or electronics but it is very well suited for conversion to a remote controlled sailplane or hotliner. Many did this conversion before. You can find a lot of references on the web of great MPX Fox RC conversions and designs. This is a good tutorial on minimal RC conversion for use as a glider.

The key is to keep the weight as low as possible. This is even more important if you don't want to add a motor. It comes at around 50 gram as is with a ballast marble in front of 9 (some reported 7) grams.

Required Electronics

-> 1x < 10 gram micro receiver. I used a Pichler MASTER 4 channel micro synthesized receiver @ 5-6 gram. This is in fact a rebranded corona RP4S1 receiver. A lot of problems reported with version 1. This version 2 works just fine for me. Some glitches so don't use it on expensive models!

-> 2x 3-9g servo's. The cheapest solution are these Turnigy 9g servo's. Still affordable and a bit lighter are the HobbyKing S0361 servo's at 3,6g.

-> 1x Nokia li poly battery providing 3,7v (which is too low according to specs but it works), 860mAh @ 19-20 gram. You could get a low mah 1s cell to power everything like this Turnigy 138mah 1s 10C lipo.

Organizing electronics for balance

One of the most importance steps to get your plane up is balance. You need to have the center of gravity (CG) at the right spot or your airplane will be very hard to control or even uncontrollable. A good starting point is having the CG at 27% of mean aerodynamic chord (% of MAC).

I have the servo's and receiver up front and the battery at CG location. This way the biggest weight is almost neutralized. The weight of receiver and servo's counterbalance the tail weight. All together it comes to 84 gram in total.

Van Drop Box

More pictures and details

As control surfaces I just adde balsa crafted parts to the existing tail surfaces. 

About 25% of the original surface is fine for most planes.

Here you can see the lipo I recovered from an old nokia cellphone.

It's placed in a larger slot so I can move it around to find the correct balance point.

This is the content of the canopy. You'll have to carve it out to fit everything in.

The servo's up front.


I don't have any suitable motor yet so I began with a glider. I used elevator/rudder configuration with these 2 servo's but it seems to be hard to control (=keep level) with this high wing loading at low speed without ailerons. So I'm considering an aileron/elevator to fly it more as a combat slope glider.

Next step is to add some micro motor on top. You can cut the nose and add some wood on the front to mount the motor on (=firewall). You'll need a larger, 2s lipo for decent flight time. These are the parts I would go for (from HobbyKing):

ZIPPY Flightmax 350mAh 2S 20C
18-11 2000kv Micro Brushless Outrunner (10g) (Make sure to read about a common micro motor failure problem I described in this post: Micro motor broken wire.)

In the end I never got a goot motorless flight out of it. You need to launch it up high or find a slope in order to have a good start. And once up it's hard to control since it's so fast.

I got better results once I powered this airplane. It's still a fast and agile thing but at least you can keep it up without the need of high altitude launch techniques or a slope.

I would not at all recommend this as a plane for beginners. A far better option if you're just starting with this hobby is the BluBaby made from foam sheets.

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