Fighting Falcon

I’ve always liked F-16s. Full-size or model, in the air or on the screen, it doesn’t matter – I’ve always liked ’em, and always fancied a model of one, too. So, as I mainly fly electric these days, I was rather pleased to be asked to review Ultrafly’s version, which is made for pusher props and hand-launching.

CUTTING TO THE CHASE
I’m going to break with tradition here and skip the pedestrian business of describing box contents and what have you, and just get on with the build, which begins with the canopy. As this is a foam model, of course, the canopy’s a solid piece of polystyrene covered with a plastic screen, and the whole thing’s held in position by a small magnet. This is a system that I’ve used before and one I’ve known to let go at the most inopportune of moments, although we’ll talk more of that later.

To the wings, then, which are supplied as a single moulding from which the ailerons must be cut, before being mounted using the hinges provided. Control of the ailerons is achieved by means of simple torque rods, which are quite straightforward to assemble. The elevator control rod, on the other hand, requires a lot of tricky bending to achieve the right fit – tricky enough, in fact, for Ultrafly to devote a whole page of the instruction book to a full-size drawing of the finished article in both plan and side views.

The HS55 servos that I’d decided to use fitted very snugly into their cut-outs, but even so I glued them in place just to be sure.

ALL-MOVING TAIL
When it came to assembling the all-moving tailplane, I was faced with a flat piece of wire protruding from either side of the fuselage, and four pieces of flat Depron foam, which had to be attached to the wire somehow. Now, as this was the first tailplane of this type that I’d built, a little more guidance from the manufacturer would have been useful here. The instructions – which are long on detailed pictures but short on words – don’t make it clear whether the wires should be recessed into the Depron, or simply sandwiched between it. I thought that the former would be the strongest option and set about pressing some spare wire onto the Depron in an effort to form a channel for the drive wire. Of course, the Depron, resilient stuff that it is, just kept springing back. I then tried cutting a groove, but found it very difficult indeed to avoid going right through the thin material.
In the end, I held a soldering iron close enough to the Depron to cause it to heat and shrink away from the tip, forming the groove I needed, but without weakening the Depron at all. In this way, I was able to let the wires into the material so that they could be glued together without any gaps – just the job.

Once the glue had set, it was time to get the sandpaper out and chamfer the edges, top and bottom of the tailplane to create an aerofoil section. With hindsight, I’d have to say that this is a task best done with the tail halves off the model.

MOTOR AND PROP
A square stick attached to the rear of the fuselage provides the mounting for a well-built 2.38:1 gearbox, which is suitable for both brushed and brushless motors. While this mount incorporates a neat little slot in which you can route the wires from the motor, the mounting holes themselves didn’t line up with those on the brushless outrunner with which the F-16 is supplied. A little work with a small needle file was all that was needed to marry them up, though, and with the model’s fin glued to the motor mounting stick, the back end was complete.

BELLY PAN & JET NOZZLE
Fitting the fuselage belly pan presented me with another little self-help exercise. Ultrafly, you see, provides a plastic plate with a captive nut that’s supposed to be stuck to the bottom of the fuselage, and a second, drilled plate, that needs to be glued to the top of the belly pan; the fixing screw is then supposed to run through the belly and into the captive nut. The first problem, however, is that there’s nothing to tell you where the two plates should be mounted. When you’ve worked that out, you then find that the supplied fixing screw isn’t long enough to do the job! With this sorted, there’s also a clear Lexan belly pan cover to fit, which provides some protection from the wear and tear of landing.

The motor cowl – jet nozzle, or whatever you like to call it – is made from clear plastic, which I chose to smoke with model car body paint before screwing it into place. Incidentally, once in position you’ll note that it also helps to secure the rear edge of the belly pan.

With the construction largely complete, it was time to finish off the confounded electrickery.

RADIO FIT
As luck would have it, my chosen servo leads were more than long enough to reach the top canopy, which meant that I could squeeze the JR77S PCM receiver in behind the retaining magnet. The fit, in fact, proved a little too much of a squeeze, so I removed a small amount of foam to give me enough freedom to plug in the leads. Having then fed the aerial forward to the front of the canopy, I made a small hole for an exit and taped the end to the top of the fin, making sure that it was taut enough to stay clear of the propeller.

After soldering up some long leads to run between my Jeti 30A Advance speed controller and the motor, I mounted the controller to the fuselage belly pan facing the servos, and then fed the power leads up to the canopy with the rest of the wires. The battery itself – a FlightPower three-cell 1200 EVO20 Li-Po pack – was tucked into a perfectly sized cut-out at the front of the cockpit.
A quick weight and balance check showed that the centre of gravity was at the rearmost limit, but with a beautiful day forecast I threw caution to the wind, packed up, and headed for the field.

TAIL DRAGGER
Down at the patch, I sat myself at one of our picnic benches and went to work finishing off the model by applying the decals, which are based on the American Thunderbirds display team colours. Obviously, I should have re-visited the question of balance, too, but the sky was calling, and a clubmate was on hand to launch her for me.

Now, the lines of the F-16, with that underslung intake, are ideal for hand-launching, and everything went perfectly right up until the moment that the model left my mate’s hand. Immediately, the nose went all over the place, and despite having plenty of power applied, I was forced to use far too much down elevator to try and keep her flying. Alas, the flight didn’t end with a landing so much as a pancake into the long grass!

Back I went to the pits where I swapped the 1200mAh batteries for FlightPower’s 1800mAh EVO20, which is the same plan size but around 50g heavier. This brought the point of balance further forward so that, at the next launch, she went away perfectly.

OUT OF SIGHT
With the elevator rates on, the pitch control was much improved, and within one circuit I had her trimmed for straight and level flight. Bringing her round for some slow fly-bys for the camera, the handling became noticeably wallowy, and there was a slight lag between applying power at the Tx and seeing the result in real terms. So, following a premature landing caused by exploring this lag (ahem!), another launch was undertaken. This time, once airborne, I kept the speed on, and the strain on my eyes increased in direct proportion to the grin on my face because, down on the deck, the F-16 soon reaches the end of the patch, and you have to turn her around pretty sharp-ish before she becomes a dot against the sky – a dot, I might add, that’s quite tricky to spot against a white cloudy backdrop.

EIGHT MINUTES OF ACTION
For those first few flights, I hadn’t ‘enabled’ the motor brake, so the glide, though respectable, was hampered by the windmilling disc at the rear. Once I’d activated the brake, however, the glide became longer and much faster.

While we’re talking about the motor, I’ve jotted down a few figures for the techies out there. Using my trusty Whatts-Up, I measured a current draw of 14A at full throttle – and let’s face it, this isn’t the sort of model that encourages restraint on the throttle – at which point the chosen APC 7 x 5 ‘E’ prop was turning at 11,200rpm. From this, my back-of-envelope calculations tell me that the F-16 will flatten a 1800mAh battery in about seven and a half minutes. With the timer on my Tx set to eight minutes, I’ve found that the battery comes down hot but still within safe discharge limits. With no real way of getting any cooling airflow over the cells, without compromising the strength of the airframe, I wouldn’t like to use anything less than the 20C 1800mAh pack, even though I’m drawing less than 8C.

WEAR AND TEARING ABOUT
In total, I’ve racked up around four hours with the F-16, and you can’t fly low and fast for this long without paying a few penalties.
I’ve crashed the model twice, though in fairness the first episode was due to that canopy magnet, which let go during an inverted pass five feet above the strip. The change of balance, caused by the battery’s sudden departure through the open hatch, sent the model summersaulting into the deck, though quite without damage, somewhat amazingly.

The second prang was due to a small shrub that reached out and grabbed a wingtip as the model went tearing down the edge of the strip. This time, the F-16 cartwheeled into the long grass, but the only damage was to the last inch or so of the wing tip, which was soon glued and taped back into place.

Frankly, I didn’t expect a polystyrene model to be this durable, and I daresay that modellers with a little more time and patience than myself could make it even tougher by skinning the airframe with fine glass cloth and a splash of epoxy.

USING UP SKY
It would certainly be worth taking the trouble to look after your F-16, because this really is a superb model. She can be launched javelin-style with ease, and once in the air combines extreme maneuverability with high stability. She also looks good, with the prop’ and gearbox being sufficiently well disguised to avoid spoiling those clean jet-fighter lines.

On the flip side, the instructions do say that the F-16 is for advanced flyers, and I’d have to agree: if you want to use the speed to the full and fly her jet-style, you’ve got to use plenty of sky, which is when she gets very small, very quickly!