The FunJet was released by Multiplex in 2007 and instantly proved a hit with foam fans around the world. As you can see, the design is pure Multiplex, simple at a glance yet extremely clever and capable of producing a thoroughbred performance. A development of the hugely popular Micro-Jet, Twin-Jet and Pico-Jet it’s clear that the company has used its vast experience of the type in the development of this little delta. With a brushless motor and a 3s Li-Po (to provide the amps), running through a 20 - 40amp ESC, it’s capable of punching holes in the sky.
First impressions are that this is a vastly improved offering over the Micro-Jet, itself an awkward little model to assemble (some would say to fly, too) using plastic parts that took a fair bit of fettling to fit correctly. The FunJet airframe, on the other hand, consists of just seven parts, and even then I’m stretching the figure to include the canopy hatch and the turtle deck, which are already fitted to the fuselage section.
As we’ve come to expect, everything is beautifully moulded in white Elapor foam, a material that’s light, very durable and very easy to work with. It’s worth noting here that to glue the airframe together successfully you’ll need medium to thick cyano’ (with kicker), a point which is emphasised in the instructions. Incidentally, the instruction manual in my kit was in German, although a quick trip to the Multiplex website furnished me with the English version. Not that this was really needed - the construction is so simple that the diagrams will probably be sufficient for most. There was just one hitch (if you can call it that) in that the main spar, a GRP rod, was around 10mm too long and needed cutting with a junior hacksaw.
Cyano’ only gives the builder one attempt so a dry test-fit of parts is essential before committing the glue. The method employed here is to spray kicker on one surface and spread cyano’ on the other. Anyway, the ease with which the model goes together is testament to the thought and effort that have gone into the production and quality control process. It really is quick to build and if proof were needed my model took under two hours to assemble, from opening the box to having an airframe ready for radio installation. I know it’s a cliché, but applying the decals took longer than it did to build the entire model.
Radio installation is also a breeze with servo recesses and cable channels already moulded into the wings. The servo apertures are designed for the Multiplex nano S (a 9g unit), although I elected to fit a pair of X-power 9g jobs instead. There’s a moulded channel on the inside of the fuselage, which thoughtfully keeps all the cables neatly tucked away, and another for the receiver aerial, feeding it along the wing and away from the motor, ESC and that fast turning prop.
THE BIG PUSH
Since the FunJet has been available for some twelve months now, just about every possible motor and controller combination has been tried and tested, short of a gas turbine! Actually, trawling through the internet forums made me realise that I had to make a decision as to which way I wanted the model to fly. Would you believe that some have even built their FunJets extra light for indoor flying?
I had a general idea about the performance I was after but decided to run it past an expert first. John Emms at Puffin Models was my chosen guru for he has a truly vast working knowledge of the successful power combinations that work with particular models. Anyway, being the good chap he is, he’d already been toying around with some ideas. Thrown into the decision making process was the fact that Multiplex suggest a Himax 2825-2700 (their branded 480 class brushless motor), whilst I know of several flyers who have fitted lighter 400 class brushless units to good effect. Fine for most, but I wanted something with a little more oomph! In the end, then, we settled on the Mega 16/25-2, a 480 brushless motor which is lighter than the stock Himax whilst being slightly more efficient.
The cells were an easy choice; John markets an excellent range of Li-Pos, so a Sharkpower 2500XP 3s seemed ideal. These are lightweight cells that offer a 20c discharge rate and will handle a maximum 50amp current draw, in short bursts! Just the job, since John estimated that the motor would only actually draw around 30amps for the set-up.
Multiplex have a rather clever motor mount system in the FunJet which allows the pilot to adjust the up- and down-thrust. It sounded complicated and another quick jaunt around the internet chat forum’s revealed that most FunJet owners have left this alone and make adjustment to the flight characteristics with just trim alone.
One very important point I must make here concerns receiver placement. Testing the radio gear quickly revealed that there was a lot of interference generated by the ESC if the receiver was placed anywhere near it in the fuselage. This isn’t good and for reasons that you’ll see further on it’s important to get the receiver as far from the ESC as possible, especially if employing a high power set-up in the model. The only logical place is forward of the flight pack, right up front in the nose.
WHAT GOES UP...
The first trip to the field certainly presented a few challenges. To start with, my watt meter showed that at full throttle the set-up was pulling over 40amps, which was a little more than expected. As a result, the 6 x 4” APC-e was changed to a 5.5 x 4.5, which bought the current draw to under 34amps. Static thrust felt very good and, indeed, a healthy 340 watts was showing - most encouraging for a model weighing just over a pound.
A quick range check was the next task to perform, although this revealed a few glitches. Back in the pits I moved a few things around, added a ferrite ring to the cable running from the ESC to the throttle, and checked the range once more. All seemed well.
Launching into a gentle breeze the power was immediately apparent, the model leaving my launcher’s hand like a javelin. Holding in down elevator to stem the climb rate I had to feed in all the available trim to get her flying straight and level. She’d gained a fair amount of height by this time, some 200ft perhaps, and was a fair way downwind. With this, I did a reversal only to find that halfway through the manoeuvre I lost control. Alas, the FunJet ploughed straight into the ground, despite my best efforts to prevent it.
IF AT FIRST...
My investigation into the crash revealed that the ESC had caused yet more interference due to its proximity to the receiver. This, as mentioned earlier, was cured by moving the receiver right up into the model’s nose. But not before I’d bought a new airframe, got out the cyano’, refitted the R/C gear and applied the stickers! Anyway, I’m pleased to report that this receiver shift really did cure the problem. Back at the field some thorough range checking showed nothing untoward and a quick throw had her airborne once again.
The FunJet’s climb rate is phenomenal with an almost unlimited vertical ability, whilst the acceleration in any direction is just as impressive. She’s an incredibly smooth flier at all throttle settings and seems to get smoother the faster she goes. At slow speed the model is very easy to handle and the stall is practically a non event. In this latter respect you’ll find that she will go a little mushy but no flick is apparent.
The roll rate is very fast and very responsive at all speeds. Elevator is a little sharp but this could be softened with some exponential.
I can’t overemphasise that this is an extremely fast aeroplane - I would estimate that my power set-up is pushing the FunJet along at 60 - 80 mph, possibly a touch more, so the model would lend itself to club racing as it’ll turn on a pin. That said, the FunJet will also fly large jet-style manoeuvres with ease. Loops can be as big as you like and rolls are axial and practically limitless in number.
You’ve got to hand it to Multiplex, they’re a talented bunch, they have a string of classic, top-selling designs to their name, and, you know what? They’ve done it again with the FunJet.
Efficient and powerful brushless motors and Li-Pos now transform models like this and provide a performance that has to be seen.
To be honest I love it, it has the performance of a small turbine with all the ease and convenience of electric power. Whether you build it as a back-of-the-car speedster, or a club racer, the FunJet will deliver.
Aircraft type: ARTF pusher delta
Manufactured by: Multiplex
UK distributor: J.Perkins Distribution
Wingspan: 31.5" (795mm)
Fuselage length: 28.75" (750mm)
Wing area: 557sq. in.
All-up weight: 1 lb 6oz (640g)
Wing loading: 8 - 9oz / sq. ft.
Rec’d motor: Brushless inrunner (Mega 16/25-2 used)
Rec’d ESC: 30 - 40amp depending on motor / battery set-up (Jeti 40amp unit used)
Rec’d flight pack: 3s 2000 - 2500mAh Li-Po
Control functions: Elevons via two micro servos
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