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R/C Glider

Slope Soarer

During one of my many Slope Soaring outings to Parlick, my local model flying sites near Preston, I met Ron Ovenden on the Southerly face of the hill. I turned up with a Wannabee Flying wing (EPP design by Pheonix Models) and my SmArt model glider. I hadn’t met Ron before, but we soon got talking and my ego was stroked with the many questions and positive comments about my model aircraft, especially the SmArt.

That flies really well……..

Where did you get it from? How much did it cost, What’s it made from?............

We’ve all heard these sort of questions before. However, the answers were not that straight forward but Ron was still really interested and wanted to buy the model off me…… Sorry not for sale!

And Here’s why – a little blood and tears……….

The "SmArt" is a scratch built model, made from a pair of damaged wings from a Discus Launch Glider (DLG) with a one-off epoxy glass fuselage made by using the "lost foam" construction technique. What? I hear you ask, well read on.

The Wings:

Some years ago I came across a youtube video of a DLG model being put through its paces, called the “Blaster”  – what an amazing performance. The Blaster is of a fully moulded model designed and manufactured by Vladimirs Models in the Czech republic, but I couldn’t get hold of one. The distributor at the time did not have any stock. However, a year or so later a friend of mine said that he had just purchased one from Hyperflight UK. Not to be outdone, I contacted the new distributor and a few days later I took receipt of an updated Blaster, a  "Blaster 2" in fact. I was so impressed with this excellent moulded model, I went right ahead and order the Electric Version. They float around really well, and are quite aerobatic - Brilliant models!!!!!

However, during a few DLG practise flights at a RAF Model Aircraft Association (RAFMAA) gliding event. Disaster! My wing failed during a launch………. I had the other wing from the Electric version of the model, so I was able to compete and eventually win the event.

A quick call to Hyperflight, a few photos and emails later, my damaged wing was replaced. I didn’t have to send back the damaged wing and having left it in the workshop for a few months I saw the potential of the undamaged wingtips to make a new smaller aerobatic slope soarer. A model based on the dimensions of the “Gnott” a free RM plan of the early 80’s, and a fuselage shape influenced by the “JART” another aerobatic model that I had just finished making. For the record, this is where the name came from (Small Jart – SmArt)

Wings:
The wings are moulded construction – a glass / foam / glass composite sandwich with some carbon for strength. Separating the wingtips from the damaged part of the wing with the bandsaw resulted in a set of wing panels similar in size to the Gnott model. The installation of a couple of 5mm brass tubes to take a wing joiner and ¼” ply wing root profiles resulted in a wing that could be plugged into a fuselage.

Fuselage:
I had just finished building a Jart Slope soarer and its fuselage shape -a streamlined version of the F20 Tiger Shark seemed very attractive, so having sketched a similar shape to scale, I set about cutting and sanding a solid blue foam mock-up fuselage. Once that was done I offered the wings to the fuselage, made up a couple of cardboard cut-outs of a tail plane in keeping with the shape of the main wings and it looked good.

Standing back to admire the shape of my handiwork, I looked around to find a huge mess. If you have ever cut and sanded foam, you will know what I mean. statically charged foam dust sticks to absolutely everything. Indeed, I was covered from head to foot in the stuff.

The next day, having cleaned up the workshop I set about the next stage of creating the fuselage. I had read about and attempted a “lost foam” technique moulding before with encouraging results. So with no time to waste, I cut 2 layers of 80g glass cloth and mixed up some epoxy resin and set about covering the foam fuselage, finishing with a layer of 25g cloth for a finer / smoother finish. Once the epoxy had fully set, 2 days later, I finished the exterior of the fuselage with wet and dry.

Now for the tricky / sticky bit:

Gaining access through the canopy hatch that I had cut before covering with Epoxy, I excavated as much of the foam that I could. This was followed by liberal use of cellulose thinners to melt the rest of the foam. The resultant sticky sludge was poured from the fuselage. More thinners progressively cleaned up the inside.

Hey Presto - a fibreglass fuselage is born.

Tail Feathers:

A balsa tail plane and fin was cut and sanded to shape and covered in epoxy glass cloth (25g). Incidentally, I also made the tail plane plug-in, so that the whole model can be packed into a small box / case. Totally unnecessary, but I did it anyway; an experiment you might say.

Back to the Fuselage

After the installation of a brass tube across the fuselage to hold the carbon wing joiner, assembly of the fin was straight forward with the main plane, tail and fin lining up really well. A small sprung loaded canopy hatch finalised the building.

A coat of Halford’s primer and car paint resulted in think is quite a good finish.

Radio Installation:

The radio gear installation was fairly straight forward. Aileron servos were installed into each wing and the elevator and rudder servos installed in the fuselage. These were trialled in different positions to try and get the best C of G position and resulted in the servos being laid down in the bottom of the fuselage behind the wing joiner, not to interfere with the rubber band holding the wings onto the fuselage. This allowed for everything else to go up front. A standard 4 cell 1500mAh NiMh battery and a Spektrum AR500 receiver in the nose. A little nose weight was required to get the C of G in the right place.

Flying:

A lot of moulded gliders use “Crow Braking” by mixing the flaps and aileron, which is a very effective way of reducing height and slowing the model down significantly. This technique involves the aileron being set to go up to about 45 degrees and the flaps being drooped down to about 60 degrees by moving the throttle lever. Roll control is maintained by electronic mixing which drives the appropriate “up” aileron back down.

However, my model has no flaps, just ailerons; on other models I’ve tried using just up going ailerons as Spoilers which should kill the lift and slow the model down, but this just seems to have the opposite effect, yes the model looses lift but has a tendency to speeds up - no good for landings on a slope in good lift.


This time, encouraged by a conversation with another fellow modeller, I configured the ailerons as flaperons to be drooped on landing to give more lift / drag. Mindful that this may also cause the model to tip stall, I was a little cautious, but it worked well; some differential in the aileron mix allowed for about 45 degree of flap, which preserved some aileron authority when the flaps (now flaperons) deployed. This also results in pitch trim change when the flaperons are drooped - easily sorted with a little coupled elevator mixing. Again, all activated varying the position of the throttle lever to give the required drag / lift.

The first flights on the slope did not disappoint, although it became apparent that I had made a slight mistake with the wing, the model was a little unstable in roll. I had planned to build in a slight amount of dihedral (flat on top) but realized my mistake when on closer inspection I had assembled the wing joiners the wrong way resulting in a small amount of undesirable anhedral (flat on the bottom). Not a major problem, but I will be correcting this in the future.

A week before meeting up with Ron and Tom on Parlick, I attended the RAFMAA slope event and flew the "Smart" into second place in the Pylon Race. She is quite fast if you let her fly properly,  reflexing the flaperons (up) slightly really gets her moving. (oh, did I forget to mention that I can mix in a little negative flap.....Oops). In light conditions a couple of degrees of down flaperon also helps, which is how I managed to keep flying while others were running out of lift on the day I met Ron.

Sorry Ron, its still not forsale!

Will I be making any more?

Well I am not going to cut up any more Blaster wings, so any future model will not be quite the same, but I am considering making a proper mould and laying up a few fuselages and creating some vac bagged foam wings......   However, not just yet, as I am currently busy developing the “Dude”. Another own design: 60” and 72” flying wings (Epoxy glass / Carbon fus and foam wing) to try my hand at Dynamic Soaring. Early results of the three prototypes I’ve made so far are very encouraging. But this is a story for another day.

Colin Waite

 

Seen in the RCM&E Jan 2012 as part of the "Hey Dude" article (Andy Ellison)

 

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