Gnatty

When I first started flying in the 1980s, with my father, most models of the time, at least in our club, were quite traditional. However, Leicester Model Centre (LMC) changed all that with the release of several fibreglass fuselage and foam wing 'jet' designs that were prop driven and became rather popular. As a beginner, models such as their Hawk or Phantom were a bit beyond me in complexity and price, but there was a design called the Gnatty that caught my eye. Yes, you guessed it, it was very loosely based on the Folland Gnat, albeit at a very great distance, but it had a modern look to it that made it stand out. 

Having a shoulder wing layout, Gnatty was available in different versions for all levels of pilot: the Gnatty Trainer had a dihedral wing, whilst Gnatty Sport had a straight wing. And then there was the Super Gnatty, which featured a swept anhedral wing.

Gnatty Owners Club

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From every angle, Gnatty is a stylised jet airframe and full of character.

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I still like the look of this model, even 30 plus years on!

The famous Woodvale Rally was still in its prime as one of the premier model events of the summer. Living only an hour away my wallet was duly primed with funds and I became a member of the Gnatty owners' club later the same day.

I spent a happy time with my original Gnatty Sport. It was a bit heavy with its fibreglass fuselage and foam wing, but I loved it. It was a sad loss when it finally went to meet its maker, which I think was just down to wear and tear as I don't remember a specific incident laying claim to the model. But then it was thirty plus years ago. I never replaced it, Leicester Model Centre changed to Peterborough Models and I moved onto other things, but it left a fond memory and a lasting impression. I always thought, and still do, that they got something right with the styling.

Roll forward many years and an online auction site advert for an unbuilt original Super Gnatty and spare parts. I watched and waited with interest and ended securing the deal for just £20. Clearly, I am one of the few that desired this style icon of the 1980s.

Slow Start
Having succumbed, and now with my prize at home, it was some time before I was able to start to assess and put together this classic airframe. Whilst my previous version had a white fuselage, this was the red version for the pseudo Red Arrow livery in the pre-BAE Hawk years when the famous display team flew the Folland Gnat. And so, this was the obvious scheme to go with. 

The acquired parts included two sets of wings, a GRP moulded fuselage that incorporates the fin, the canopy moulding and a few bits and pieces. The balsa tail was missing but an elevator was present, so a few measurements and photos aided in establishing the correct shape and size of the tail, which is simply cut from 1/4" sheet balsa. The main undercarriage leg assembly was present, but the nose leg was not.

Over the following months, which turned into year and a few months, I collected a range of bits and pieces, including a fuel tank, engine mounts and a suitable engine. I even found one of the original sprung oleos that LMC used to offer for their jet style models, although it is rather a weighty item.

Of course, these days it might have been an option to fit an electric set up. Certainly, the model could have accommodated such a change, but I am afraid the call of a classic two stroke won through.

When it finally came to construction, I commenced with the fuselage and the somewhat painful task of fitting a ply bulkhead down the front end. Why so difficult, I hear you ask? Well, the fuselage has no cowl, so the ply bulkhead needs to be shaped and fitted inside the fuselage at just the right place and angle. I took me several attempts before I realised I was missing a trick and that if I mounted the engine onto the mount, then measured the distance from the front of the bulkhead to the face of the propeller boss, then I could cut a timber block, plus a couple of mm, and screw this to the ply bulkhead and use it as a means to locate and set the alignment. Still a tricky operation but measuring with shims and using a belt sander on the ply bulkhead, after 30 or 40 attempts I had a good fit. I then tacked the bulkhead in place with thick cyano before fixing it permanently with strips of fibreglass bandage and resin. It was a technique that called for a cheap brush taped onto a stick and a plastic bag taped loosely over my right hand and arm to avoid having to pick drips of resin out of the hairs on my arm later. I must have looked like a vet about to get up close and personal with a cow's backside, but it worked.

I also fixed the main 6mm ply undercarriage plate with glass cloth and when dry I attached the main U/C, a rather nice pre-welded assembly, which is screwed in place with the use of saddle clamps.

Engine Fit

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The OS46LA two stroke was side mounted, with a cowl created for ease of maintenance.

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A 4mm diameter piano wire nose leg was made with the ever useful SLEC wire bender.

The engine, an OS 46L two stroke, is set such that the exhaust can run down the side and also give reasonable access to the needle valve. I decided that sooner or later some maintenance would be required so I would need better access. Using a razor saw, I cut free the front of the fuselage a few millimetres beyond the location of the bulkhead. This effectively created a cowl that was easier to trim for fit around the engine and gave access for fuel lines and the throttle linkage. Had I thought of this earlier, I would have done this first and fitted the engine bulkhead second - and saved myself an awful lot of frustration!

The engine mount has a cross groove cast into the back to trap a 4mm piano wire leg, so it was out with the wire bender and following a few basic measurements I produced something suitable to be clamped in place.

A hole was drilled for the fuel lines and throttle cable through the bulkhead and then hardwood blocks were glued in place to fix the cowl section back in place. The motor was bolted into position, followed by a quick test fit of the cowl, which was fixed with self-tapping screws.

The fuel tank, eight ounce in this case, is mounted on a 6mm balsa plate with an end stop and a hook and loop strap to hold it in position. The tank was assembled, fitted with fresh fuel lines and located in the fuselage and connected to the carb, exhaust pressure nipple and with the fill/drain line exiting by the engine. A control snake was also run through for the throttle linkage.

Back End

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I used more filler than I would have liked when fitting the tailplane.

The tailplane was referenced from photos and the original elevator, and made up from 6mm balsa. It was then slid into a slot in the rear fuselage. Due to the rather larger than required gap some wedges and scrap packing pieces were required. A few drops of thick cyano held everything in place whilst the joint was made good with more fibreglass resin and a little filler. A new elevator was made as the old one was looking a little rough, but it was a simple task to make a new part from 6mm sheet. The elevator horn is fixed on the centre line, with a small slot being required in the top of the tail pipe to allow full movement of the horn.

The fin is a moulded part of the fuselage and simply required a balsa insert at the trailing edge, sufficient to hold the hinges. The rudder is 6mm balsa sheet cut to shape and sanded to a taper. 

I then spent a happy time using bright red heat shrink film to cover the tail, elevator and rudder followed by a touch up of the filled areas with a car paint spray can of the closest match I could get, which to be fair is pretty darn perfect. 

Foam Veneer Wing

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Foam wing joined with glass bandage and fitted with the ABS moulding.

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Wing pockets were cut into the foam with a hot wire to allow independent servos to be fitted for the ailerons.

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The servo pockets were lined with balsa.

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Hitec H85MG servos were used for the ailerons, fitted to ply plates.

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Aileron servos are coupled to their respective horns with 2mm pushrods.

The wing is a foam and veneer finished item, with balsa leading and trailing edges. The panels are joined at the appropriate anhedral angle with epoxy. This is not so easy as it sounds as the instructions were missing, so a bit of a guesstimate was made on the angle. I concluded that providing it was set square, a small variation should not be too significant and there was not much I could do about it anyway. The wing joint was strengthened with a six-inch wide fibreglass bandage.

I never liked the wing tips on the original as they were just straight. So, my only major deviation is the nice curved tips from soft block that I think are more in keeping with the Gnatty's jet look.

The wing needs a dowel that locates into a ply plate fitted in the fuselage, and which was a bit of a fiddle to get everything correctly aligned. As with most jobs like this, measure twice, then again, and then cut.

The wing bolts at the rear are a little easier, using captive nuts fixed to another ply plate bonded into the fuselage. The plate can then be drilled through to fix the wing's position once all is square.

The ailerons on the original had torque rods and a single centrally mounted servo. These parts were missing and so, adopting a more modern approach, two servo pockets were cut out of the foam using a hot wire in my soldering iron and lined with balsa. Mini servos were mounted onto ply plates, which were then fixed flush onto blocks mounted in the servo pockets. A short connecting rod to the horns affixed to each strip aileron completed the task. 

Canopy Mouldings

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I made my own pilots from latex and plaster moulds, with just a simple acrylic paint finish.

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The rear canopy section sits on top of the wing. Don't forget the navigator!

Before any of the clear canopy sections were fitted, I chose to cover the wings with bright red film to match the fuselage. I found Oracover had a near perfect match.

An ABS moulded fairing forms the rear part of the canopy and this is glued onto the wing, being aligned to the rear fuselage first. It then needs to be aligned with the forward clear canopy sections. So, a bit of measuring is required before committing to the glue.

The clear canopy is in two sections; the rear is glued onto the wing and aligned with the rear ABS moulding, and the front is attached to the forward fuselage. The trick is to get both aligned so that it looks like a continuous form. In fairness, what could have been tricky proved quite straightforward and the faint moulding lines on the canopy proved to be just about right when trimmed. 

However, the first task was to mark out the cockpit floor and paint it black. A suitable pilot and navigator were made; I have a couple of moulds for these and so two latex busts were made and painted. They were then glued in place, followed by the canopy sections, all done with RC Modellers glue.

Formers were made to plug the open end of each canopy section, from 3mm balsa sheet. These were trimmed and painted black before being glued in place. A thickness of balsa was added to the front face of the rear canopy section and sanded to blend the front to the rear shape, resulting in reasonably good alignment.

Radio Fit

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Main radio installation is easy enough, with plenty of space.

I thought it best to gather all the radio, including the battery, and see where they need to go to get the best fit for achieving the correct C of G. I used my maths to calculate the position, based on the sweep and median chord. This gave a reference position of 30%, on the basis that only flying the model would indicate if any further tweaks would be necessary. 

A couple of hardwood bearers were added in the fuselage for a screw mounted ply tray, onto which the servos and receiver were mounted. Traditional dowel pushrods connect to the elevator and rudder. 

With everything in place and a 2300 NiMH battery sitting just forward of the servos, the model balanced about a half inch forward of my calculated CG position, which I considered safe enough for a first flight.

Maiden Flight

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Maiden flight take-off was an anti-climax as Gnatty tracked true, with plenty of power.

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Climb out after take-off with more than adequate power from the slightly rich running OS46 engine.

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A few circuits into the flight and I am really starting to enjoy the look and feel, even if it is a little nose heavy.

By chance this was August Bank Holiday and the weather gods were in a good mood, so the Sunday afternoon saw Gnatty arrive at the strip for her maiden flight with only a light to moderate breeze, a blue sky and a few white clouds.

I am usually pretty thorough in my pre-flight checks, even before a model gets to the field. But in this case, whilst all the radio set up, C of G and control movements etc. had all been checked, the motor itself, an OS46LA, had been purchased second hand and not run for some considerable time. I had simply oiled, bagged and stored it away until it was bolted in place - even the plug was the original. That being said, the motor turned over nicely, with good compression, and all seemed good. When energised the plug had life and the first few drops of fuel had the motor running incredibly smoothly, almost immediately. 

And so, with a few ground photos out the way for posterity, I pointed the Gnatty into the breeze and committed her to aviation. With brisk acceleration, good authority from the rudder to steer, and a gentle squeeze of back pressure on the stick, Gnatty gracefully rotated and climbed away very smartly. Almost immediately she gave the impression of being very stable and locked in.

Some circuits saw a few clicks of trim, just to get her flying nicely. However, she did feel nose heavy and this was confirmed by the amount of pressure required for inverted flight. 

Gnatty has a fair turn of speed, even though I had kept the engine running on the rich side. All the basic manoeuvres were carried out on the first flight, although more advanced manoeuvres will need to wait till the forward C of G has been corrected. But the model was perfectly comfortable to fly, and I was having fun doing low passes for my wife, who was the acting camera person on the occasion.

Slow speed handling is good, and the approach and subsequent landing were about as good as you get. So, with the first flight out the way I was generally delighted. 

A further flight was just as enjoyable, apart from the landing, which was partly down to a little bit of cross-wind but, more significantly, the prat on the controls who manged to bounce her three or four... no, make that five times, doing a kangaroo impression down the runway and consequently breaking the prop, which served me right, to be honest. 

Post Flight
I like to do a thorough examination of a model after its initial flights. This time I noted a slight wrinkle in the covering film on the top surface of the wing, about 250mm out from the centreline on each side. Putting pressure on the underside of the wing there was a visible indication of this wrinkle line moving a bit; not a crack, rather a compression, but enough to cause the wrinkle in the film. The wing still felt strong, but it might have indicated a possible fracture in the future, so there was only one cause of action for total piece of mind...

Back on the workbench some surgery was required to let in a 3 x 25 x 200 mm ply spar to span the compression region, let into both panels. This has subsequently cured the problem and was relatively easy to complete. A simple film patch covered the job.

I also changed the location of the battery pack, moving it to the rear of the servo tray. I then committed to some extra finishing details, with paint work and decals.

Hooked On Classics

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Really showing off that swept wing in a classic Farnborough pass.

I am rather pleased with the result. The Gnatty is a model I have wanted to have for a very long time, so right now I am really enjoying a step back in time with this 1980s classic. It is a great shame that models like this are no longer in production, as I am sure it would still be popular. I still think it looks good, it flies really well and has bags of character and is just that little bit different to everything else. 

These things do pop up on auction sites from time to time so I shall be keeping my eyes open for other classic kits in the future.

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