I was looking for a suitable model for my local patch, which meant that it couldn’t be too big and it had to possess the ability to fly slowly to help my appalling landing technique! I also fancied a ‘profile’ or ‘slab’ fuselage kit as it seemed an interesting idea, and possibly easier to repair.
The search started and I ended up in the USA, subscribing to a forum that eats, sleeps and breathes profile planes. Here, I stumbled across a guy whose name was mentioned in almost every thread, Paul Swany. It transpired that he makes a range of profile kits that this forum raves over, so an e-mail was duly sent off. To cut a long story short, he agreed to convert the 47″ span MoJo 40 into a split wing version, re-drawing, modifying, sourcing carbon fibre tube etc… for just $12! The kit was around £35, so the overall cost was just £40 plus shipping. Such was the value that I actually bought two, one for electric Hacker power and the other for my O.S. 50SX, featured here.
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The main fuselage section went together pretty quickly, assembled on a building board cut from a piece of B&Q’s finest plasterboard (cheap and very good for building on!) The plans are very clear and all the CNC-cut parts went together very well, with only minor sanding and trimming required. Incidentally, all the parts were secured with wicked-in thin cyano’.
The fuselage is strengthened by gluing a 1/2″ carbon fibre tube along its length, from just behind the wing joiner to the stabiliser, fixed into position after the fuselage has been covered. I modified the servo mounts so that flat Hitec metal-geared wing servos could be installed, leaving one side of the fuselage unspoiled.
Once the fuselage was 90% complete I started on the two wing panels, using a bit of builder’s licence to satisfy my attention to detail. An example of this is the addition of some carbon fibre strengtheners between the first two ribs and along the leading edge. To make sure that correct alignment is maintained during the build, all the ribs have tabs that are pinned to the building board during construction and subsequently removed when the main wing structure is complete.
As for the wing sheeting, this is first applied to the leading edge, wetted to allow the necessary curving and then secured with cyano’. The servo bay is built into the wing between the first and second ribs, with hardwood rails for servo mounting. This bay also houses either the Rx or Rx battery, depending on how you decide to do the electrics.
Installing the servos in the rear of the fuselage took a fair time to plan, but it was time well spent as the final positioning proved to be about right in achieving short, straight linkages. The main carbon fibre tube serves a secondary purpose here, with the servo wires being routed along its length to the receiver.
Next on the list was the engine installation. Your chosen powerplant mounts onto beech bearers that are glued to the balsa nose section, this, in turn, sandwiched on both sides of the fuselage by ply doublers that extend back to the wing trailing edge. Now, before fitting the engine I had to decide on throttle servo placement. The original kit utilises a fixed wing which allows the throttle servo to be housed in the wing bay, with a wire throttle linkage to the carb. However, as my version was to have a removable wing this wasn’t an option, so I decided to squeeze the servo behind the engine and forward of the wing l.e. With a little jiggling, cutting and routing I was able to fix the servo in a suitable position, although quite how it will fair being so close to the heat, oil and vibration, is a mystery! The engine was installed with the suggested 2.5? of right-thrust, and no down-thrust.
With a naked airframe before me I was at a bit of a loss as to how to finish the model, and so went in search of inspiration. A quick scroll through the ‘profile forum’ I mentioned earlier shed light on some very interesting colour schemes. Being an American site, ‘stars and stripes’ ‘golden eagle’ and ‘flame’ themes run riot; not my cup of tea. One thing I did learn, though, was to make the top and bottom very different.
I eventually chose a bold but fairly simple design. To begin with, the model was covered in Profilm, this followed by vinyl stickers that I had cut by a local sign writing firm.
Just a few more things to do before committing the model skywards; fuel tank, undercarriage, Rx and battery connections, plus the connectors required to link the tail servos to the Rx when the wings are fitted.
I decided to modify the tank mounting, which in original form is simply fitted to the side of the fuselage by rubber bands, with a piece of sponge in between to reduce vibration and fuel foaming. I chose to fit two light aluminium rails to the fuselage and strapped the tank to these with Velcro, using foam to insulate the tank from the rails. This method allows the tank to be positioned further forwards than on the original model, leaving more room for fitting the undercarriage.
The u/c wire was soldered to a brass plate, this having been cut to fit in the gap forward of the wing, and flush with the tank rails. Said plate was then secured with two M3 bolts and lock nuts, fastened through the fuselage.
Two Multiplex 6-pin electrical connectors are employed; one connects the battery, throttle servo and one wing servo to the Rx, the other connects the rudder and elevator servos. This method means that just two connections are needed at the patch to complete the assembly. As a point of interest, the connectors are attached with one socket and one plug at each end, so no incorrect connections can be made.
With the Mojo now complete she certainly looked the business, and all I needed was an experienced ‘3D hand’ to give her a good workout. Enter my old pal Danny Wenham, who kindly accepted the challenge. Here’s his flying report…
TO THE FIELD!
I’ve only had a chance to fly the Mojo on two occasions, unfortunately the wind was quite strong both times and not really ideal for test flying or photo shoots. Saying that, the Mojo coped really well. The plane has been built very nicely indeed, so sweet in fact that low-level 3D seemed almost too risky. The good build quality was backed up by the fact that it needed virtually no trim for level flight. Once airborne, it soon became apparent that the safe, smooth flight condition I’d set wasn’t going to be used much, and full 3D movements with some expo’ around the centres was all that I needed.
The O.S. 50 is an absolute peach, easy to start and very reliable. We changed from APC 123/4 x 33/4″ to an APC 13 x 6″, which improved the pull-out when prop-hanging. If you like to prop-hang you’ll love Mojo, as hanging is definitely one of its strong points. Even in wind you can lock it in a hang and then go for some torque rolls. Although there’s enough power from the O.S. for such antics, there’s not much left in reserve to pull out when things start looking a bit out of shape. I can now see why the boys ‘across the pond’ are putting Saito 80s in them.
During the first flight we noticed that the servos seemed to be getting blown back, with roll rate decreasing as forward speed increased. Rather than change them Marc opted to try a 6V battery instead of the standard 4.8V pack, which seemed to do the trick. Not only are the servos now faster, they seem to be holding better in the air.
Flat spins look great – nice and tight, both upright and inverted. On a calm day I think you could probably bring the spin down very low as the pull-out is extremely predictable. Knife-edge? Well, what can I say? With all that side area it’s a must; slow or fast, the Mojo is very happy on its side. Snaps rolls look good, too! Enter with a bit of speed and they’re a blur, and at low altitude they’re certainly not for the faint hearted. Slow speed handling is good, I found no tendency for either tip to drop on finals.
If you switch into the ‘standard’ flight condition you’ll find the Mojo much softer and smoother, happy to do nice long slow rolls or really crisp 4- and 8-pointers. She tracks very nicely around loops as well, be they square, round, or even with a neat little snap at the top.
If I had more time with Mojo I would probably play with the C of G. I’m not saying that it’s wrong where it is, but it’s always good to experiment and push the limits.
If you want a good all-round sports model that will improve your 3D skills, fit in the boot of your car and still leave room for some shopping, then you won’t go wrong with one of these. Back to Marc for the epilogue…
Well my chief test pilot obviously had a ball with Mojo, and for my part it was a very rewarding build. I’ve had loads of help from members of the profile forum in America, and plenty of helpful advice from Mojo’s creator, Paul Swany. They say the Americans have mastered the art of service, and I would have to agree in this instance.
Aesthetically such a profile model isn’t to everybody’s taste, but if you’re looking to go 3D’ing and want top performance but don’t want to pay much for it, then look no further… Mojo is at your disposal and it comes heartily recommended on both sides of the pond.
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