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Voltij. Click to see larger.

The market for slope aerobats is a strange one. Every slope flyer indulges in a few aerobatic gyrations once in a while, yet over the last few years there have been very few models specifically designed for the job.

Of the airframes that are available the only one that most UK readers will be familiar with is the ubiquitous Phase 6 from Chris Foss and, as one would expect, design and materials have moved on since that design was first kitted getting on for 20 years ago (blimey, I feel old!).

Later models such as the Jedi and Storm have provided their owners with ample reward for their perseverance in obtaining models that are not overtly imported or advertised in the UK. As you can imagine when the chance came to review a modern purpose designed slope aerobat that is available in the UK it was too good to miss.



Your 180 investment will furnish you with two ready finished glass on foam wing panels, one glass fibre fuselage complete with more side-area than an aircraft carrier and two ready finished glass on foam tailplane halves. You'll also find two carbon pushrods, one bag of bits and some excellent instructions, which unfortunately (for me) happen to be in French. You need to source the limited wooden items yourself; it's strictly scrap box stuff though, so it's not a problem.



Building time is swift, indeed it would be possible to build the Voltij in one weekend if you put your mind to it. Having said that, I didn't find it a particularly pleasant experience, there's a lot of epoxy and microballoons and plenty of scope to go wrong for the inexperienced or unwary. Although the instructions are in French the diagrams are good and even this Anglophile could glean enough information to take most of the guesswork away. I'll do my best to write this review so that anyone could complete the build, although I'll steer clear of the obvious stuff.

I started with the wings. The flaperons have already been separated from the wing, which saves a potentially difficult chore. What is left to do is face and hinge them. The first job is to sand away a few millimetres from the underside wing skin so that the flaperon can travel downwards; this is marked clearly in the instructions. I marked out the amount to be removed using a marker (the permanent overhead projector type are excellent for things like this) and set about it with a long Permagrit sanding block. Work slowly and keep checking to ensure that you don't remove too much material. Half an hour later and both ailerons are sanded and it's time to remove some foam from both the trailing edge of the wing and the leading edge of the aileron. This is easily accomplished using an old soldering iron or even a heated screwdriver. Remove extra foam where the horn will go, as this will need to be reinforced with epoxy and microballoons. Watch out for the fumes; if they don't make your head hurt your better-half will! So make sure you've adequate ventilation. If you're worried about overheating the glass and causing ripples use a mini-drill to remove the foam, it works just as well.

Once you've done this it's time to face the flaperons with a mix of epoxy and microballoons. This is essential to add torsional rigidity to the surface, so don't skip it. It will save a lot of heartache and time later on if you mask the top and bottom surfaces of the flaperon to avoid epoxy smears and fingerprints.

The diagrams show that it's only necessary to face the flaperons in this way, and indeed twisting the wing shows that it's already rigid enough for the intended purpose.

Once the flaperon facings have dried do a quick check to make sure you can get enough downward travel and then it's onto the hinging. This will be a revelation to anyone who's never tried silicone hinging before. Do not be tempted to use tape hinging; silicone is quicker, neater and altogether groovier!

Hold the flaperon to the wing leaving a gap of around 1 mm, and temporarily hinge with masking tape. Bend the flaperon back on itself and run a thin bead of silicone along the hinge-line. I found it easiest to put some silicone into a plastic syringe with the end snipped off. Do a test run and check the bead is around 2-3 mm wide. The best silicone is that used for sticking the sides of fish tanks together; it has a high silicone content, is immensely strong and is stocked in many garden centres (I knew there was a reason such places exist!). Once you've applied the bead use your finger and gently run it along the bead to ensure it's pushed right into the hinge-line and touching the masking tape. You are looking for a minimal bead that leaves no gaps. If you inadvertently apply too much silicone be sure to remove it with a tissue or your final hinge won't be free enough. Sounds a hundred times harder than it is, trust me!

Return the flaperon back to the neutral position and leave for 24 hours before removing the tape. You are left with a splendid hinge that returns automatically to neutral, is very strong yet free and looks as neat as a living hinge.

Next it's time to mount the wings onto the fuselage. Hold paper over the wing-root and do a rubbing with a pencil to locate the joiner tube holes in relation to the aerofoil. Hold this to the wing-root area of the fuselage and mark where the joiner holes should be drilled. Carefully drill the holes and mount the wing. Check that all is square (i.e. fin is perpendicular and the incidence of the wing marries up with the fuselage wing-root moulding) and if it isn't open up the holes until it is true. Once happy epoxy the aluminium tubes that receive the carbon wing joiners into the fuselage.

Next fiddly job is to mount the all-moving tailplane crank. The instructions do show a separate elevator option but almost all builders plump for the all-moving version, so that's what I did.

Have a look at the photograph to see roughly where the crank should go. It's not too critical, just be sure it's not too high on the fin as it will be too narrow, or too low where there will not be enough room for the pushrod. Mark the pivot point and carefully drill through the fin as perpendicular as you can. Once done you can offer up the crank on the outside of the fin and using a marker pen follow the arc of the crank and remove material from both walls of the fin to allow the rear tailplane joiner to move.

Cut some blocks of ply to reinforce the pivot point. The blocks I used were thicker than those recommended in the instructions as they were what I had lying around, mine have worked fine as I'm sure would those recommended.

With the wings on mount the tailplane and check that it is true in all three axes. It should be perpendicular with the fin and parallel with the wing both in planform and front view. If you're anything like me it'll take more than one attempt. I ended up opening out the holes, gluing and re-gluing several times. If you exercise a little patience you will get it right and once done you've guaranteed yourself a true and accurate flyer. If you lose patience and accept a less than accurate result you'll spend your whole time flying the model on one foot as you'll be kicking yourself with the other.

The rest of the build is straightforward enough, just a few minor points merit a mention.

The fin post is attached with cyano but be sure not to build any stresses into the rear end otherwise it'll put the tail out of whack - not ideal considering you've just spent an age lining up. It's not difficult, just make sure the fin post is a good fit and don't twist it while you're gluing.

The rudder is hinged in the same way as the flaperons, no worries there.

The servo tray (you'll have to supply your own ply, but the dimensions are clearly given in the instructions) was attached using silicone. I've seen one or two Voltij’s crack off their epoxied in trays in less than subtle landings thanks to the slab sided fuselage flexing. My theory is that the silicone will flex with the fuselage, we'll see.

When building my model I set the servo tray fairly low in the fuselage in case there was a need to fit a ballast tube at a later date. The theory was it could sit on top of the wing joiner tubes in the fuselage. Sit tight and you'll see if it was needed.

There's bags of room for the radio; standard servos for elevator and rudder and, with a bit of a squeeze, for the flaperons too. As you can see from the photographs I chose Multiplex Micro MC V2s as they were too good to be left in my spares box doing nothing, and despite the micro tag (15 mm thick) they are more than powerful enough for the task. A standard receiver fits without problem and the battery can be up to sub C size and beyond if you should wish. I used a 4 cell, AA sized 1500 mAh NiMH square pack leaving only a few grams of lead required to balance.

Finally, comes the canopy. I tried fixing it using the suggested wires at the front and back but found that it could still slide from side to side. Eventually I used diamond tape to side hinge it and another length of tape to secure the other side. The side hinging actually works really well and is accurate enough for at least one owner that I know of to simply use a magnet as the latch on the other side!



The first flight with any model using an all-moving tail is always a bit of a clencher but my guesswork was good, or more likely my luck was in, and it didn't need a single click of trim. A quick check to see if the CG was there and thereabouts, which it was (the recommended 95 mm from the leading edge works fine), and it was time to play in the buffety off-the-slope wind.

I started having a stab at precision aerobatics. Whilst I can accomplish all the manoeuvres I simply haven't the time or patience to practise them to millimetric precision. This is where the Voltij will help you out as it makes aerobatics real fun, so practise isn't dull anymore.

Not dull maybe but it was only a matter of a few minutes before the hot-dogging temptation was too much to overcome. The thing that amazed was quite how slippery the Voltij is. It's not heavy yet without ballast the energy retention is simply amazing. In a bizarre way it seems to have all the benefits of a lot of inertia yet none of the drawbacks. Square manoeuvres are incredibly crisp, yet complex '8 Balls' that really test energy retention are a doddle.

Next comes knife-edge and it's this that will make you never want to leave the Voltij at home. Give it a bit of speed and the knife-edge is easily sustained, enter with more speed and you can climb, do a wave, dive then climb, all knife-edge. Flying in a big slope in big air is such a blast. You can knife-edge on and on until eventually you'll start to sink at around 25 degrees. At that point you can steer around on the elevator and fly (albeit inefficiently) in the knife-edge position. OK, so sinking at 25 degrees, even on a big slope, means you'll run out of space eventually, but the precision you can fly around at knife-edge in the interim is just breathtaking. The only limitation is thumbs and imagination. Did I mention the control line turns?

Earlier I made reference to making provision to retrofit a ballast tube should it be needed. It isn't. The Voltij is remarkably slippery and winds of beyond 50 m.p.h. haven't caused her a problem without ballast.

Once you've flown your Voltij it'll just seem to migrate to you're car at the merest hint of a trip to the slope and so it's been that mine has had a thorough workout in a variety of conditions.

Light conditions are great fun. Drop a little flap and the Voltij becomes a slightly grumpy thermal soarer. Very efficient and actually reasonably easy to thermal turn, but try and squeeze that little bit too much out of her and she'll bite. To put it in context though the fully aerobatic Voltij with its symmetrical section will out soar a lightweight foamy and in tight bubbles of lift will give an F3B/F model a run for its money. What's real fun to do when there are Voltij virgins on the slope is to dial in some reflex and thermal her inverted. It takes a little practise if you want to use the rudder properly but it's worth it to see the look of disbelief on the faces of those who 'know' it can't happen.

The flying is simply a revelation and the construction of the wings and tail is accurate and truly very, very strong, there is however a small chink in the armour. That deep, knife-edge enabling fuselage has proven a little prone to damage at the hands of one or two Voltij owners. The depth of the fuselage that is so essential for knife-edge flight makes it very strong in one direction but less so when it comes to a side load.

There are two things worth pointing out here. If you land properly you wont damage the fuselage and if you do inflict any damage there's a good chance it would have smashed the wing and the tail on any other model!

Having heard mention of a potential 'weakness' I felt it my duty to explore further. Whilst enjoying a little thermal soaring followed by aerobatics on a frozen hillside the numb thumbs set in meaning a landing was required. As it was virtually Alpine soaring conditions (almost nil wind but smooth cyclic thermals) there was no headwind to slow the approach speed, and a few overshoots only served to emphasise the efficiency of the airframe. A pass or two later saw the Voltij as slow as she was going to get, but tufty, frozen solid ground grabbed a tip and caused the fuselage to hit another tuft whilst it was yawing along the ground at 45 degrees. The result was a bit of gelcoat cracked off the fuselage where it had flexed just aft of the wing.

There was no apparent loss of strength and flying again didn't reveal a problem so I'm currently cogitating on the best way to deal with it. In an ideal world I think I'd cut a plywood tray (not dissimilar to the servo tray and again attach it with silicone so it didn't crack off) and insert it approximately halfway along the wing chord to an equal distance down the fuselage towards the tail, to stop any side to side flexing. In my world, where time is a serious issue, I'll either ignore it entirely, settle for a drop of cyano or wrap a few layers of grass cloth and epoxy around the area.

On future days when I'm flying the Voltij in little or no wind I'll probably experiment with dropping the flaperons for landing rather than raising them. Not advisable for windier days as raised flaperons effectively give you a lot of washout and allow you to lift the nose without the risk of a tip stall and nestle her in at catching speed. Take away the headwind and with nothing to bite into it's harder to lose ground speed. Dropping some flap will help here but the risk of a tip stall increases, so caution is advised. Strikes me it's a bizarre problem to have; I never thought I'd fret over the best way to land a fully symmetrical aerobatic model in no wind before, not at the top of the hill anyway!



The Voltij is quick but a bit fiddly and messy to build. The flight performance is simply fantastic. It's been the kind of performance leap that getting your first moulded model is. Words or still images simply can't do the flight performance justice.

The appearance of the Voltij has matured nicely the more I've flown it. When the bits came out of the box I remember being quite astounded at how it was possible for a model aircraft to be so unattractive, but having had several hours behind the wheel I've almost grown to admire its piscine appearance. Maybe she's still not the prettiest but she's got a sparkling personality!

As to the long-term ownership aspect, I would definitely recommend using silicone to adhere the servo tray; it's worked splendidly. I would also recommend inserting a plywood plate (again using silicone) to try and contain the sideways loads on the oval fuselage just aft of the wing. I certainly wouldn't let the observations that have been raised about the fuselage put you off. As I mentioned earlier it's more of a reflection on the strength of the rest of the model. Try as I might I haven't found a single Voltij owner who isn't prepared to wax lyrical about what a great plane it is, and that speaks volumes.

Value for money is an interesting issue. At 180 the Voltij is not a casual purchase (well not for me anyway) but as you've probably gathered already I do not begrudge a penny of it. Indeed I cannot remember a plane that has endeared itself to me quite as much as the Voltij.



Get yourself to a hill where someone has a Voltij, watch them and if possible blag yourself a go, but only if you have 180 to spare as otherwise you're likely to make yourself decidedly grumpy!



Span: 2.02 m
Length: 1.25 m
Area: 36 dm2
Weight: 1600 to 1800 g
Loading: 44 to 50 g/dm2
Aerofoil: MG05 9% (Symmetrical, double reflex)
Price: 180 in the UK


Voltij - A few years on...

It's only fair to say right from the start that I love my Voltij. If I could, I would bear it's ugly little fish shaped children, raise them as my own and give them all the benefits other Voltijs never had.

Alas, the cruel hand of Copyright law means I can never bear my own Voltij but sure as eggs is binding, I can foster another one and give it the start in life my first born Voltij never had.

What benefits would I bestow upon the fortunate little critter? There are one or two tricks that can be used to help develop your Voltij from being a gifted little feller to the complete package that would be David Beckham, Ronaldo, Zidane and Figo all rolled into one.

Fuselage first. I have never been a great fan of silicone but for a big slab sided, flexible fuselage like the Voltij it is perfect for adhering things, far better than epoxy, which tends to crack off. The servo tray and fin post are prime candidates for the silicone treatment. Whilst on the subject of the fin post, take a few minutes longer to craft it from horizontal grain balsa (with the ends of the grain being at the join) rather than vertical grain. This will stop it tearing and allow you to use lighter balsa whilst imparting more strength.

A couple of siliconed in place glass fibre (printed circuit board) cheeks to support the elevator bell crank pivot will allow you the benefit of landing like a berk and not worrying about the loose bell crank death rattle that is the signature tune of so many all moving tails.

The fuselage tends to suffer most of its stress towards the trailing edge on the wing junction. I resolved the issue by crashing hard into dense rock and performing an almost invisible repair using a carbon bandage I'd swiped from the workshop where the Caracho is built.

A more forward thinking approach is to make a horizontal crutch from ply or glass and silicone it at half-depth level spanning a 3 or 4 inches either side of the line of the trailing edge. Those who've tried this have survived the mandatory follow-up crash test.

Next the wing. Nothing much to do here, just add some colour to the underside and reverse the mounting of the servos so that they live in the wing and not the fuselage. Just for good measure you can make the servo wiring connect automatically when the wing is plugged on and use those neat Multiplex press-stud type affairs to hold the wing in place.

If I ever get time to replace my much abused (surely that's the real sign of a good plane) Voltij I'll build it along these lines and end up with a fantastically tough model that rigs just by plugging the wing and tail on, and whose flying capabilities are only limited by the pilots thumbs and imagination. Splendid.

Finally a quick word about silicone. There is the cheap stuff you get from DIY shops and then there is the good stuff you get for sticking fish tanks together. The difference, other than the price, is that the DIY silicone is packed full of dyes and various other things that compromise what we want it for. The fish tank stuff (stocked by most pet shops) and the silicone good glaziers use is pretty much pure silicone. I can assure you that you'll not regret paying that little extra for the good stuff.


UK: Europa/Soarhigh Models 01261 818404

France: Pyrenees Modeles, 16 Avenue Larrieu Thibaud, 31100 Toulouse, France. 05 61 43 85 24 Fax: 05 61 43 85 25.

USA: Composite Specialities, 2195 Canyon Dr #D, Costa Mesa, CA 92627, USA 949-645-7032


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