Assembling the Eric Arnaud Sharkie racer foamy swept wing

Couple years back when Eric flogged me the EPP cores for a song, I promised him a blow by blow of the assembly - got engrossed in the build but just enough pics to talk to - the aim being a clean, stiff, zero awful fiber tape finish. 😎

Eric's EPP simply perfect to work with, the coarse block sticky back sand paper from Russ and the medium bar sander worked great right through, just taking off any outer loose bits here pre commencing.

Laying the first of three spars per wing, one top and two bottom. Marked out on the masking tape then blade cut to a depth to allow the 6mm by 1mm (available from the KZN online hobby shops and other) flat carbon spar to settle just below the surface. Then dribbled in medium super glue and finished with Builders accelerator, which provides filling itself just above spar on surface.

The lightweight hobby filler definitely the way to go after reading of some spackle issues, mine was old so wetted slightly and played nicely spreading with fingers, a peach to work with. Warning 1, leave over night to dry properly or it can clog like the block in pic - when properly dry then zero clog. Pleasing was no hint whatsoever of of a spar ridge or dip after sanding.

Was warned that the very slightly wetted hobby filler can shrink slightly and distort things so both cores went back in the blanks under weight to settle for a week, total overkill but this combo really rigid if you want to fix later. Note the three spars staggered (location quite arb but make both wings exact same and rather have level with root) 5mm out out at tip easily cut with big scissors, not healthy stuff to Dremel cut. The rear spar quite close to the elevon hinge line as I intended using the original EPP as elevons instead of balsa to retain the gradual reflex curve.

Everything barring servos was then inserted from the root and spaces opened using my trusty Antex 15 watt soldering iron to carefully heat open from the root. Three throws of ball type lead sinkers (ex Basil Manning) for the balance (see further on pics), I would guesstimate about 220g. The servos, receiver and 300mah battery all aligned dead on the CG line of 159mm but I would next time move the receiver and mini battery to give room for a ballast to tube bay - Eric does comment that the section easily carries ballast. Servos on CG, again masking tape first and marked for knife cut then opening routed out so servos approximate level with the surface. Servos glued in with Pratley white epoxy and the leads run internally through foam to receiver.

Then wing joined using Pratley white epoxy because any overflow sands beautifully and is close as dammit to the core colour. I went flat bottom, I guess one could lay flat top to give some slight illusion of dihedral.

Wing turned to bottom and two short offcut pieces of 1mm by 6mm spar let in to support the join and nestle against the existing spars. Again below surface and fill and sand as before.

Finished product showing the spars slightly proud at the tips, to locate the tiplets later on, hot glued on (no damn fibre tape please ;-). I used Richard Steinbach's magic pressed light cardboard tiplets, excellent solution. I gottit wrong on the location, the tiplet rear definitely to align with elevon rear next time, for aesthetics and stability.

I am glossing over ironing on the thin laminate (thanks to Russ for donating) after spray gluing (Alcolin brand I used), similar to any iron on and lots of you tube video guides. Start in middle and work out in zebra crossing fashion like they tell you. I also added a double layer laminate about 50 mm wide first at the top hinge line, thanks to a tip from Russ. My warning number 2, prick the bubbles with a needle as you go, you may think you have crushed heated out the bubble but it will return..... Warning number 3 don't spray glue both sides one time, the underside will grab fine residue etc. Again overnight dry is best, was really impressed how it helped lock down the laminate, how nice does the finish look? 👀😋

Underside after laminate is completed, can see the servos under laminate, just need slits for the servo arms to nip out once covering on. 

Top view, pre cutting elevon from below and using the laminate as a top hinge (proved superb). Classic Zagi mm width is 40 mm, I played with calculator to approximate 20% root chord and 30% tip chord, settling on 50mm wide, seems to work fine. Length was just past the servo bay, not all the way (see bottom pic). Inverted V cut from bottom not quite through to top hinge line - then cracked up and cleaned out for the hinge line, works a treat.

The mini rent a crowd on the day of the successful maiden flight

showing the incredibly thin and clean profile of Eric's wing section. The wing covered in plain ole contact vinyl, the only black and white version I could locate and seems fine for visibility. The seamless one sheet does all for each wing plan was thwarted by Warning 3, do not spray glue on top of the laminate to lock the contact or vinyl or iron on, it grabs just when you don't need and is totally unnecessary.

Top view at maiden arvie, eventually decided on a gap in the covering along the hinge line to prevent crinkling, all edges sealed with waterproof clear tape, pretty damn clean. The 159mm (20%) CG proved perfect and the normal additional reflex not needed at all, as the first launch revealed. 😆

We were ring fenced to two out of three classes for the Toss races and an easy decision to loan Sharkie to Steve Muesel who was flying it better anyway - herewith Russ about to launch for round 3. 😂

Steve with Sharkie on landing approach after placing second in all three rounds and second overall for the event. Commented on just how smooth the aerie flew. 

The wing with full aileron deflection showing clean hinge line, distance from root and the aileron horns used to drive elevons, the servo drive, pushrods and horns all bottom but would rather do top next time - tiplets also reset further back. My thanks to Eric for the excellent base to try out my ideas on, most happy with the result. 😃👌