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JART


Having watched a Modelling video “Lift Ticket” by Reese productions, I was particularly taken with the opening scene where a slope model was being put through its paces on the hills adjacent to the Golden Gate Bridge in the USA. The model in question is, as I later found out, a tiger shark PSS style model, with Smoke canisters fastened to the wing tips, the loops were very big and the whole flight extremely impressive.


Wanting a model like that, I embarked on a quest to find out what the model was. Some research later, I was convinced that the model was a “Jart” of Australian design and available in plan format, which left the builder to interpret and decide on the best form of construction, the plan is just a line drawing with dimensions the necessary wing section drawn to actual size. The forums showing a mix of built up construction, foam and epoxy glass. Not once did I find confirmation that this was the model design from the video, but it seemed very close in appearance and I suppose was a good enough likeness to have me convinced.
 

Having ordered my personalised plan through the now defunct website Jartworld.com, a day later I received the plan by email in pdf format.
 

Without wasting too much time, I worked out the medium and materials to use. Epoxy glass fuselage and foam veneered wings.


The fuselage which from the side elevation resembles, in my mind at least, the F20 Tiger Shark but without the engine intakes was initially fabricated in blue foam, but I soon became convinced that this was not good enough to make a proper mould from. Initially I was going to produce a lost foam model, by wrapping the fuselage with glass cloth then removing the foam to reveal a fibre glass model much like I produced the SmArt slope model. However, I felt that such a nice looking model would require a more accurate moulding and one that could be used to produce a second model.
This was to be the first mdf fuselage plug from which to make a mould I had ever made, but one that was easy to produce and obtain a good finish. Having produced the plug I passed this to my good friend Neil to produce the mould as I had never m
ade a fibreglass fuselage before either. The results were very encouraging and such a nice jet-like appearance.
 

The 60” wing and tailplane foam cores were cut by hand using templates and a hot wire cutter and then veneered and finished in 80g bidirectional glass cloth.
The whole model was assembled and fitted out with radio gear with plenty of space to arrange the electronics within the
fuselage; the aileron servos being installed in the wings.
 

On the allotted day on Parlick with a reasonable breeze, the model flew straight off the drawing board so to speak, very smooth although it did have a tendency to tip stall aggressively in the sometimes marginal conditions due to over use of elevator control. In higher wind speeds, this was not so much of a problem but could be provoked to bite – living up to it’s possible origin - Tiger Shark……or as it was stated to me during a diving experience with sharks in the Singapore Sea Life Centre many years ago, from which I lived to tell the tale… “Crazy Shark”!
 

However, on a flying session in the Peak District, Neil was flying his own version of the Jart when whilst fairly close in to the slope the model departed from its intended flight path and tip stalled into the ground. There was minimum damage due to the strong construction, but it left some serious questions to be asked.


Having got a number of flying hours under my belt with this model, trying different control set up, temporary changes to the elevator shape and after lengthy discussions with Neil over a few beers, we decided to try using an old Control line trick to couple flap with elevator, where a pull-up command on the elevator would also result in down going flap and conversely, up flap with down going elevator. This actually did the trick and removed the unpredictability of the model and it no longer bites hard enough to draw blood…. much like taking the tiger shark to the dentist, no teeth.
 

Over time is has become apparent that this model likes “Big Air” conditions, really being at home in wind speeds in excess of 20mph. It just eats up the sky and likes to perform Big manoeuvres. Flown on many hills over the years, non, having been so memorable as a visit to the Bwlch, overlooking Treorchy in South Wales on the way back from a Modelling holiday to Rhossili a couple of years ago. Given conditions of plus 30mph winds straight onto a sheer cliff face of about 400ft height called “The Wrecker” aptly named because of the curl over turbulence at the top resulting in crashed models during landing for the unwary. Indeed, such is the turbulence that whilst stood fairly close to edge pointing in the direction of the actual wind ready to launch, the wind turbulence is actually hitting the back of your head – scary stuff.
With both Neil and I having a Jart in our model collection we stood close to the edge in readiness full of trepidation, but we have flown these hills before so we knew what to expect…… A good heave of the models into the abyss of “The Wrecker” with a slight tail wind until the models hit the actual wind and mega lift as it flew over the edge gaining height rapidly. A few circuits to get a feel for the lift conditions which was particularly smooth out from the cliff face resulted face wide smiles as the model just ate up the sky. With no sign of tip stalls and fantastically big inside and outside manoeuvres being performed, much like the model on the video. Such was the lift and performance I executed horizon to horizon knife edge flights and a number of vertical eight manoeuvre starting from the bottom.


 

To explain this manoeuvre, it starts with a dive to gain speed and inertia, pull up to half a loop, followed by a full outside loop entered from inverted followed by the remaining half loop to finish back at the bottom. An impressive manoeuvre with a powered model, but remember this is a glider, no additional ballast just pure inertia and aerodynamics, this model proving its worth and performance in extreme conditions. An hour or so flying had us feeling the buzz of adrenalin and a fitting end to a fantastic week of flying and one that we often reminisce.
 

These type of models have earned the nick name of “lead sleds” heavy models that are used to fly in extreme conditions. Similar to the conditions found on the Great Orme, North Wales in extreme +40mph Atlantic winds. However, whilst the Jart could be termed as a lead sled, it isn’t true, weighing similar to any normal 60“ glider and with no additional ballast performs impressively in these high winds and in my view performs as well as a highly loaded model. Anyone that I have let play with the sticks, have said that the model just gets in the groove and feels so “locked in”... Yes, exactly. I believe any powered model flyer having had a clutch of one of these machines in the right conditions will be hooked and what’s more, the only sound is the whoosh of air as it passes at seemingly Mach speeds.
It performs very well in less extreme conditions as well and is always in the car when I go to the slope if the wind is promising to pick up. In fact, the models of choice if the wind is any more than 15mph is the Jart and Dude.
 

On my travels and having spoken to many people regarding the Jart and the model in the Lift Ticket video, I can confirm that this is not the model used in the video, but I secretly knew that anyway. A little while ago, Andy Ellison appeared in one of his RCM&E magazine articles clutching one of the afore said Lift Ticket models, yes more like a Tiger Shark than the Jart and confirmation that there is another model I now want, but whilst I would still like a model from the video, I am quite happy with the Jart.

Currently between us, we have 4 Jarts having recently completed a couple of new models for best, so to speak. My original model, has a slight twist in the wing, but over the years it does not appear to have effected its performance but I am making a new set of wings for it and giving it a bit of a well deserve renovation.

 

Colin


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