Graupner Junkers 52
Kit Review by Trevor Hewson
(Written for 'Sloping Off', the newsletter of the Christchurch and District MFC - June 1995)

Why d'ya get it?
The idea of a twin engined electric model has always had a certain appeal for me. Initially I thought in terms of two 540 size motors with a 7-cell battery pack in each engine nacelle. This though would result in quite a large, heavy model (probably over 5lbs), not really suitable for flying at our local public sites.

At Sandown last year, I spotted a nice P38 Lightning. This is a twin boom model (another weakness of mine) and was powered by two Speed 400 motors. This model was light, compact and 'not yet available'. I left my name and address but either they have lost it or the model is still not available. The only drawback I could see with the Lightning was that it was a hand launch, belly landing job and, for me, the landings and take offs are quite an important part of the appeal of a scale model.

So, if two 540s result in a model that is too big and two 400s lead to one that is too small, what's the answer? Enter the Graupner Junkers 52 powered by three Speed 400s - obvious really, isn't it!

I first read about this model in the Feb/Mar 1995 edition of Silent Flight and was immediately struck by the claim that it ran off a single 7-cell, 1700mAh pack (in fact the instruction sheet that comes with the model says it can be powered by 6 or 7 cells). At nearly 5ft in span the Ju52 is quite a large model and, with lots of draggy features such as three engine cowlings, a big fat fuselage and slotted flaps & ailerons, this seemed quite a tall order. My Aerojet, in contrast, spans only 47", is aerodynamically relatively clean, is nearly a pound lighter than the Junkers and uses the same size battery.

Still, Graupner ought to know what they are doing, and the man from 'Gliders' was very reassuring - "You've got three 6.5 x 4 props whirring away" - so I took the plunge. To make sure that the model would perform as the maker intended I also ordered the special 3 motor accessory pack.

What d'ya get?
Starting with that motor pack. £35.95 sounds a lot of money when Speed 400 motors only cost £5.00 each. But you also get: 3 motor mount sets, 3 suppressor capacitors, 3 scale propellers, 3 prop drivers, 3 connectors (with gold contacts), a supply of connecting wire, a bag of mounting screws, an Allen key for the prop drivers and the usual thorough German instruction sheet. Now, you may be able to save a little by getting this lot together separately, but unless you have some of it in stock already the convenience of receiving all you need (including some bits you hadn't even realised you did need) in one box is well worth the extra.

But what about the kit? To be honest, the pictures in the Silent Flight write-up almost put me off this kit. They featured the plastic moulded cowls and nacelles, and I was a little concerned that the ARTF syndrome might have got the better of Graupner. When I saw the box was labelled "Schnellbaukasten" (translated to "Quickie Kit" on the plan), I became even more concerned. I needn't have worried - on opening the box I was greeted with wood - bundles and bundles of it! There were diecut ply and balsa panels, precut fuselage sides with slots cut in them to locate the formers and strip wood galore. The wood was all of good quality and the diecutting very clean.

The fuselage, wings, tailplane and fin are all built-up structures. The ailerons and flaps are beautifully pre-shaped from hard balsa and the elevators and rudder are laminated to provide anti-warp structures. The plastic content is confined to the engine cowlings and nacelles, with clear plastic mouldings being provided for the cockpit canopy and for the fourteen windows. To give you some feel for the complexity of the kit, the parts list runs to 148 entries and took a whole evening to check!

At first sight I was alarmed by the large amount of plywood used. All the fuselage formers, some centre section ribs, a built-up battery cradle, motor mounts, servo mounts, various doublers and reinforcing pieces are all in ply, most of it 3mm. Closer inspection, though, showed that diecut lightening holes and cut outs had been incorporated very skilfully to ensure that at least 75% of the plywood supplied never makes it into the finished model. Indeed, at one point in the construction I thought that this weight saving technique had been taken a bit too far. On pulling the fuselage sides in at the nose, one of the formers began to bow. A quick look at the instructions showed a reinforcing doubler to be fitted to the over-stressed former, which also acted as the wing attachment point, so all was well.

All in all, a high quality, well thought-out kit. It is clear that the "Quickie Kit" label comes from the amount of thought that has gone into the design, not from extensive preassembly or use of plastic.

Getting it together
The biggest problem in building this model is space. The plan consists of two A1 size sheets and the instructions occupy a further A1 sheet - in German. Don't worry though, a fourth A1 sheet contains instructions in English and French, but only the German version has the photographs, so you need to refer to all four sheets. You then have to find somewhere for the box of bits and then, if there is any bench space left, you can start building.

The model goes together very well. The fit of the parts is excellent and the instructions are generally clear, with fewer errors than average. The material quantities are a little mean in places. The wing tip blocks are a shade too thin - aren't they always? - and I ran out of 1/16" (sorry 1.5mm) sheet. Also if you cut one of the two snakes in half to do the aileron runs you will later find that cutting the second one in half leaves you with two pieces each just not quite long enough for the elevator and rudder. If, though, you cut one aileron outer from each piece, the remaining pieces are long enough to install in the fuz - just!

The construction methods are generally conventional, but there were three areas that were, for me a bit different.

The first of these is the top of the fuselage that is made from curved 1.5mm balsa sheet. I wet the sheet and wrapped it round a cardboard tube with rubber bands. When it was almost dry but still flexible the sheet was released from the tube and glued in place using Aliphatic resin with spots of Zap to hold it in place while everything dried. This seemed to work quite well and I took care to pull the sheet taut across the grain to ensure it made good contact with the formers. With hindsight, it seems that I overdid this bit since, as the sheeting dried out, it shrunk and pulled even tighter, giving the fuz a stretched, slightly underfed look!

The second unusual feature was the wing construction. The narrow centre section and the two outer panels are built separately. For each panel, the ribs slot, egg box fashion, onto a full depth, diecut balsa spar web. The 1.5mm balsa sheeting is then glued edge to edge with the 7mm x 1.5mm spruce spar and, when dry, this is glued onto the ribs and spar webs with the spruce strip positioned over the spar web to form a ']' section main spar. Once all three panels are complete you are asked to cut a hole in each end rib behind the spar web and insert a ply dihedral brace 'using plenty of epoxy'. Since the centre section is fully sheeted by this time, this is a totally 'blind' operation. I must admit I chickened out and left the top sheeting off the centre section until I had joined the panels. I then had to trim the sheeting very carefully to get a good fit with the already sheeted outer panels, but at least I knew the dihedral braces were secure.

The third area of complication is the tail end. I can't really describe this, but suffice it to say that it seems that everything slots into or threads through everything else. Working out what order to build, cover and assemble the various parts taxed the old grey matter more than somewhat - and I was left feeling that there was probably a much simpler way!

The finish
I am normally a determined non-painter. It's not just that I lack anything remotely resembling artistic technique, it's that paints and similar fluids in my hands undergo chemically impossible transformations. If you don't believe me, two very respected suppliers of model products have been so shocked on analysing the samples of their products that I returned to them, that they have been moved to send me boxes of their wares in an effort to convince me that I was just unlucky!

This time though, some painting was inevitable - even I would not attempt to film cover an ABS moulded motor cowling. In the event the spray painting was uneventful and quite successful, thanks largely to my discovery of the Hycote range of acrylic car paints. They smell foul but they go on beautifully. I did though draw the line at trying to paint the 1/20th scale pilots. The Chairman's son, David, did a great job for me here, and if you are thinking of asking him to do the same for you, the established rate of pay is one Belgian chocolate egg - but he may be persuaded to take harder currencies.

The model is covered in grey Solarfilm (I couldn't find Profilm in the right colour). I must say that this Solarfilm didn't seem to suffer from many of the problems I remember from previous encounters. There were no problems with the pigment separating from the film or with the film sticking to itself spontaneously. The covering on the fuselage sides did though wrinkle up after a few days, and had to be ironed down three times at three day intervals before it became stable. It will be interesting to see how it fares in the sun.

I also found that the silver grey finish seemed very sensitive to excess pressure from the iron. It seemed almost to bruise, bringing about what the motor trade calls 'flip tones'. This, coupled with some rather intricate shapes such as the tail, all those windows and the aileron flap hinges, made this probably the most fiddly film job I've ever undertaken.

What goes in it?
Three Hitec HS80 micro servos, a Futaba receiver and a Robbe RSC630 speed controller, along with the aforementioned three Speed 400 motors and 1700mAh seven cell battery pack. There's plenty of space if you want to use bigger servos, but the battery cradle is set at an angle so that the battery can be inserted through (and can eject itself out of) the cockpit aperture, and takes up quite a lot of the space in that otherwise cavernous fuselage.

With all this gear on board and the battery moved forward as far as possible, the cg was duly installed in the correct place and the model put on the scales. I was delighted to find it came out exactly at the specified weight of 1.6kg (3lb 6oz in real money).

How does it go?
Having run the motors in for a little while, I took the model into the garden for taxi trials. The tail wheel lifted immediately - the only problem was that the main wheels stayed rooted to the spot. It was clear that, in the absence of a properly prepared runway, a nose over was the only manoeuvre the model was capable of.

A bit of wire bending produced a replacement set of u/c legs, a little longer than the originals and raked forward an inch or so. With some judicious pulsing of the throttle, the model could now be persuaded to roll. But would it reach take-off speed?

A few static tests showed that the three Speed 400s generated about the same thrust as the 540 motor/gearbox combination that had enabled my Taylorcraft to ROG. Furthermore the wheels were the same size, so it seemed reasonable to hope that a similar ground speed could be reached, even though the Junkers was some 13oz heavier. Furthermore the wing loadings of the two models were almost identical, so the required take off speed ought to be similar too, so there was hope! There was nothing for it now but to wait for suitable weather.

Whilst waiting for the weather, I flew that maiden flight many times in my head. It usually went something like this:- Open throttle, nose-over, three bent motor shafts, go home. On occasions I got a bit further:- Roll out, veer off course, catch a wing tip in the grass, flip over, one bent shaft, one broken fin, go home.

Now I would hate you to think that I'm a total pessimist. Once I did a lot better:- Full up elevator, open throttle, gather speed, ease off the elevator, straight as a die into wind, a gentle bump at just the right moment, airborne! Then the brain switches to hyperdrive - Where's the elevator trim? is it climbing? too steeply? will those tapered wings tip stall? is it gaining airspeed? it's a long way away! dare I touch the ailerons? surely I must turn now? which way?

Meanwhile the thumbs remain motionless, politely refraining from twiddling themselves -
"We're awaiting some form of coherent direction from the management"
"Pardon?!"
Oh dear, I really must stop day dreaming at work!

Back to Reality
The fateful day arrived one Sunday in late April. I set off to the Park with Aerojet, Ju52 and pre-charged battery packs. The plan was to have one flight with the trusty Aerojet to calm the nerves and build up confidence. Having explained this cunning plan to all present, you can imagine their reactions when I put said trusty Aerojet into a tree on the landing approach!

Now it is often said that, to succeed at anything, what you need is confidence. However, it's not true for model aeroplanes - the secret of success is total paranoia! As you can well imagine, I was now pretty paranoid, and there was nothing for it but to give it a go.

Having selected my take off point, I was held at the end of the runway for what seemed an eternity whilst two dog walking families on either side swapped dogs and children. Eventually everyone decided which side they wanted to be and all eyes were turned in my direction - no turning back now. So, as rehearsed a hundred times, full up elevator, ease the throttle open - rolling. Veering slightly left, touch of rudder to correct, back on line - accelerating. Ease off the up elevator... I have to confess I didn't actually notice the moment of take off. The model just carried on rolling along - except now there was daylight between it and the ground.

Nothing quite prepares you for this moment. After months of handling the model on the bench, one becomes very familiar with it as a terrestrial object. The first sight of a new model in mid air with no visible means of support always stimulates a feeling of disbelief - how can it do that!? Fortunately the Junkers had no such hang ups - maybe it hadn't noticed the ground vanish either! It just flew on, rock steady, climbing gently.

Eventually the management got its act together and ordered a gentle left turn. The Ju52 obligingly flew a left hand circuit as if it were on rails. After a couple of minutes of left and right hand circuits on about 3/4 throttle, I prepared for an early landing. Thanks to the Aerojet incident, the approach was carefully planned and the Ju52 dutifully came in straight and level for what in my eyes was a near perfect landing.I did notice that I needed full up elevator on the flare out so I made a mental note to ease the cg back a shade. So ended the first foray, and I went home well pleased to check the 34 wood screws and 14 Allen screws that hold it all together!

PS
Just after completing this maiden flight I read the full review of the Junkers by George Stringwell in the June/July edition of Silent Flight. George's model tip stalled and crashed on climb out from a hand launch on its first flight. My Ju 52 on the other hand has subsequently survived a couple of low speed crosswind take offs without any such tip stalling tendency.

In the light of these differing experiences, perhaps now is the time to admit that I did depart from the plan just a tiny bit and built in about 1/16" of washout in the wing panels. In the light of George's mishap, I'm glad that I did!

With this notable exception, George's observations on the model largely tally with my own. I would also endorse his comment that weight could be saved at the tail end by the use of lighter balsa. This would avoid any risk of having to add lead at the front to get the balance right.