The Limit EX plan can be purchased at www.myhobbystore.com
In the end I settled for lengthening the originally stubby nose, to alleviate the necessity for so much lead, and increased the span by virtue of more shapely wingtips. As a nod to the original design she was christened Limit EX.
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Eventually a couple of pics made it across the editor’s table, and into the hallowed pages of RCM&E via Andy Ellison’s column. The die was cast. I was deluged with requests for information about a kit or a plan – even ARTFs! After building another clutch of models for various people, I realised that the only way to reclaim my building board was to get the magazine in on the act. So here we are, with a blank sheet of paper and a remit to give you, the reader, the tools to craft your own. But where to start?
Select firm but light straight grained 3/32 balsa sheet and cut two fuselage sides as marked on the plan. Nothing too hard mind you, as the fuselage is gently curved from nose to tail.
The upper and lower fuselage sheet is 3/32 balsa once again, with grain running from nose to tail.
What we have now roughly equates to the Frankenstein’s monster of fuselages! With the help of a razor plane and Perma-Grit block we can quite quickly knock all the corners off and produce a stunningly rounded body and a huge pile of shavings! Don’t be shy with the sanding, but equally, don’t go crazy. A strong light -source placed behind the fuselage will often show the thin spots if you’re not sure. Finally, add the 1/8 ply wing holding down plate and captive nut. The fuselage can now be put to one side, whilst we turn our attention to the next job.
Whilst deeply satisfying, the built-up wing takes ages to construct and is as tricky as a box of frogs to keep straight. However, if you can’t bear the sizzle of nichrome through polystyrene, the balsa version is shown on the plan. Anyway, those of us who can put up with the stigma of a foam wing will be able to use the root and tip rib as templates. This was the first time I’d tackled a foam wing, and I have to thank fellow glider nut Adrian Hopkins for cajoling me into production. He showed me how to construct a bow, and we experimented with different foams and temperature ranges. The best cores were from blue foam, being quite rigid, with pink (Polyfoam) being a close second. The pink foam tended to warp after cutting, the eventual solution being to leave the cores in their shucks and place some weight on top for a couple of minutes, until the foam’s temperature had stabilised. Any good insulation company should be able to provide a range of foam products. I purchased an 8ft x 2ft x 50mm sheet of Polyfoam for around a tenner – although I had to cut it in half to get it in the car!
ONWARD AND UPWARD
Okay, here goes: Mark out the ailerons on each panel and carefully remove them with a sharp scalpel. For a full belt and braces job, face all the exposed foam with 1/64 ply or, do as I do – leave it unfaced and cover with film later.
Locate the wing accurately on the fuselage and mark the positions of the locating dowel and single nylon screw. Add a small disc of 1/64 ply over the wing bolt hole to spread the loads and glue in the locating dowel with five-minute epoxy. An easy way to mark the position of the locating dowel hole in the fuselage is to put a dot of paint on the end of the dowel and slide the wing into position carefully. The resulting mark on F2 gives a reasonably accurate drilling guide. I tend to drill undersize and then open up carefully with a needle file to get a really accurate fit.
So, now we’re ready to cover. I’d recommend a proprietary film finish if you just want it done quick and smart. Alternatively, if you’ve more time and enjoy a little glass-work, then a 1/2oz cloth finish looks fab. If you’re going down the film route, remember that those wing skins are very thin and the foam can be easily damaged. My favoured product is Profilm, as it’s easy to stretch around the compound curves of the nose. Control surfaces, incidentally, are attached with Sellotape Diamond, which is crystal clear and, cunningly, resistant to UV light.
My prototype had a servo on each elevator, but having flown another model with a single servo driving both elevator halves, the benefits of rudder control proved minimal.
A 400mAh NiCad fits neatly in the extreme nose, reducing the need for a lump of church roof to balance, with the Rx wrapped in foam in the remaining free space just aft of F2. Add a switch if you have room, though quite honestly I never bother as it doesn’t take long to remove the wing and plug the NiCad directly into the Rx. As a point of interest all servos were 9g types, giving more than enough grunt for all eventualities.
UP, UP AND AWAY
Elevators are very critical – start with 4mm in both directions.
Model type: Aerobatic slope soarer
Designed by: Julian Beckett
Fuselage length: 191/2
All-up weight: 8oz
C of G: 55mm from root l.e.
Recd No. channels: Two
Control functions: Aileron and elevator
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