Europa #435 G-RODO Build Journal - 2008 04

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2 Phone factory to see if they have any opinions on the skin misalignment problem. Roger offers the same advice as Neville.
3 Mark extent of port wingtip flange problem on wing skin and cut off the inner layer of glass. Chisel out the majority of the brown foam and use the Perma-Grit spar slotter to clean off the rest. Need to be quite careful as the outer skin appears to be no thicker than the inner. The impression of considerable thickness in the outer flanges appears to be thanks to an extra layer that is not carried in to the main body. Turn skin over and try fit - a considerable improvement but not quite enough. File down the LE end of the flox corner at an angle and extend the slot a bit further aft. Now seems to fit well, requiring only minimal pressure to get good conformity between skin and tip across full width. 977.8
4 Chamfer LE of skin for better fit against rounded corner of LE skin. Position on wing, hold with spring clamps and drill 1/8" at root and tip for locating clecos. The tip one goes just aft of the slot in the brown foam and close to the flox corner to avoid crushing the foam. Fit clecos and apply masking tape along skin LE to form a hinge. Notice as I do this that there's a slight gap between the skin edges at mid-span. Could have re-profiled the LE of the rear skin to reduce the gap but it's a bit late now that the cleco holes have been drilled. trim off the vertical piece of the bottom skin that protrudes above the aileron closeout on the line between aileron and flap, to allow the skin to adopt a better profile there. Mark rib positions on underside of skin. Cut and apply pieces of polyethylene sheet to underside of skin to cover all marked rib positions, with a large single piece from BL39 rib to root. Tape down all edges of sheets to prevent the flop-over problems experienced on the starboard wing. Cut away the vertical piece at the aileron-flap junction preventing movement of the TE to conform to the flap. Remove both pushrods. Start to apply polyethylene sheet masking around ribs and horn boxes to catch drips. 980.5
5 Finish masking off around ribs and horn boxes. Fit aileron (quite tricky without the aileron pushrod) and flaps (quite tricky with wing right-way-up). Notice that aileron drive bolt is just catching outboard end of flap at extreme angles, so shorten by about 2 threads (leaving 2 threads visible beyond nut), clean up cut end and apply grey zinc primer. Find 48mm piece of mahogany to wedge up TE and wedges for root and outrigger positions. Cut strips of vinyl to act as spacers on aileron and flap. Stick down to flap using masking tape at front edge and cover contact area with parcel tape for better release from Redux. At full down-aileron, slide edge of vinyl sheet between aileron & closeout with some difficulty and apply parcel tape to cover exposed part. Bring aileron to neutral, lifting closeout in places with old steel rule to stop it peeling the tape off again. Clamp up flap hinge. Find piece of ply to hook bungees onto at wing LE. Put adjustable stand at tip with shaped piece of wood against underside of tip. Although using same piece of wood as last time, it needs a slight wedge under it for best contact. 15C, 52% RH. Turn on fan heaters at thermostat 4. Top up the flox drum from the big bag. Degrease all bonding areas with acetone-soaked tissue and abrade with fine Perma-Grit flexible sheet. Degrease again. Mix 100g + 40g fresh Redux and add 3 and a half doses of flox. Spread onto inboard ribs (except root). Mix another 100g + 40g batch. This needs about 4 doses flox to get non-slump consistency. Spread on remaining ribs and horn boxes. Lower skin, press down by hand, lift to check contact area. Some squeezed out and some thin places. Scrape off the excess areas and transfer to the thin places. Lower skin, fit clecos, position square tubes and tape down with masking tape. Position wood bridges. Tension bungees on flaps and insert 3mm spacers (pairs of mixing sticks) at flap LE. Pile on sandbags and lead weights and leave to cure. 24C, 36% RH. 986.7
7 26C, 23% RH. Wind heater thermostats down to 3. Remove weights, wooden bridges and load spreader tubes. Lift skin and all areas are well covered with good conformance to masked-off skin areas. As no more pre-bonding needed, remove masking from inside skin and protective sheets from around ribs and horn-boxes. Close down skin again to remove stress on masking tape hinge. 987.2
8 File the squeezed-out bits of Redux off the edges of the ribs and horn-boxes. Fortunately much less excess this time (maybe another example of the more I practice, the luckier I get), so no need to break off big chunks as I did last time. Not happy about the fact that in the slot I've cut in the foam at the tip (to allow the skin to lie flush despite the misalignment of the tip flange), there will only be a bond to the outer skin. Consider applying a BID patch and working it into position with a long thin spatula from the tip-light hole, but then the obvious answer dawns - make another flox corner at the inboard side of the slot to provide a bond between inner and outer glass layers. File away the brown foam on the inboard edge of the slot with the Perma-Grit spar slotter. Wrap a piece of sandpaper round a small piece of aluminium angle to clean up inside surface of inner skin as I can't get at that properly with the spar slotter. No need to make an epoxy flox corner - will just fill it with the Redux-flox mix. Degrease all bonding areas with acetone-soaked paper tissue. Abrade all bonding areas - glass with fine Perma-Grit flexible sheet and Redux pre-bonded areas with coarse Perma-Grit block and file. Not enough time left before Gloster Strut meeting to complete the job, so fold the skin back into position. All the abrading has seriously loosened the tape hinge so cleco the skin into position, strip off tape and apply fresh. One fan heater appears to have blown a fuse - will need to fix that before proceeding. 991.2
9 Fan heater fuse is OK. Take heater apart and find that the element has drooped as a result of an earlier mishap and had touched the internal frame and blown at that point. Twist the ends together and crimp as tightly as possible with pliers. Straighten frame to prevent recurrence & reassemble. Now works fine. Open skin, abrade some areas that still look in need of attention (was obviously getting tired of sanding yesterday). Degrease with acetone on paper tissue. Run around with vacuum cleaner again and double-check that there is nothing left inside the wing. Mix last of the 1st drum of fresh Redux (79.8g + 32g - not enough hardener so had to open next pack) and add about 3 doses of flox. Spread on all bonding areas of the wing, starting at root. That covers to about the rib inboard of the double one. Open 2nd new drum of Redux and mix 100g + 40g. Add 4 doses flox and spread onto remaining bonding areas. Work into the hollow at the inboard side of the slot in the foam at the tip. Lower skin onto wing, press down by hand and raise again to check coverage. Pretty good except for a few areas. Move some Redux around and spread a bit more to cover thin places. Lower skin, fit clecos and root-rib spring clamps. Place and tape down the square tubes, add wooden bridges and weights. Add extra support with adjustable stand and a wedge under wing TE at mid-aileron point. 25C, 31% RH. Enough Redux-flox left for a sample. 993.9
14 26C, 24% RH; 5 days since wing skin bonding started so turn off heaters.
15 Remove sandbags and wheelbarrow them back to the shed. Remove lead weights, spreader boards and square tubes. Remove adjustable supports and wedges. Insert normal chordwise support blocks. Peel off masking tape at joint. Slightly disappointing lack of conformity between front and rear skins, despite apparently good fit before. I had noticed that the square tube at the joint was sitting parallel to the spreader boards rather than the skin and so there was not direct pressure on the LE edge of the skin, only about an inch in from the edge. This may have contributed to the problem. Remove flap hinge clamp and aileron tip clamp. Aileron moves a bit, but vinyl stays stuck to wing. Remove flap and aileron. Parcel tape pulls off Redux much more easily and cleanly than the vinyl itself did last time, so that was obviously a good idea. The TE joint looks good apart from the fact that the Redux appears not to have squeezed quite to the edge of the joint in some parts of the aileron area. The skin and flange are not quite parallel and the contact line appears to have been in a bit from the edge. May have been a similar problem with the square tube as at the front edge. Remove inspection plate and with Wilma's help, insert the lateral pushrod and screw onto rod-end on outer bellcrank. Fit outer rod-end to quick-connect bellcrank. Tighten pushrod locknuts at 4 threads out from fully home, both ends. Raise wing off table and lower onto LE at east side of table for better access to TE. Stuff pushrod hole with a rag to stop anything falling into it, and replace inspection plate. Cut off top skin flush with aileron closeout flange. Hack out poorly-bonded areas with fine hacksaw blade and then abrade both inner surfaces with fine Perma-Grit flexible sheet. The unbonded area goes right across the flange in a couple of areas. Clearly I should have used a bit more Redux. I only used 252g this time, but the starboard wing took 304g. A look at the starboard wing shows that the bond in the aileron area was very thin - the Redux line is almost invisible in places - so I would have actually needed more for the port wing, not less. Looking again at the clamping arrangements, the square tube at the aileron should have been shortened a bit more so as to keep the ends clear of both the tip moulding and the slight rise at the flap junction. That would have given a more even pressure all along. Try out various clamping arrangements and settle on using pieces of aluminium angle within the aileron closeout, with the square tube outside. Short it by about 10mm. Check the flap area for bond quality. It had been generally better clamped than the aileron area, but there is one small area slightly gappy. Abrade that. Mask off both sides of bonding areas with masking tape and polyethylene sheet to catch drips. Find a suitable small syringe for applying the Redux. 998.1
17 Do some more cleaning up and abrading of the unbonded wing skin TE areas, this time with the fine Perma-Grit file which allows pressure to be applied all the way in rather than just at the edge as with the flexible sheet. Connect up the new airline to the filtered outlet of the compressor and get ready to clean the bonding areas with the small air duster. However, find that the Clarke brand hose (already exchanged once at Machine Mart because of faulty connectors) is leaking at both ends. Undo to check and find that the internal noses of both connectors are poorly machined, making the tapers too big to fit. I've had enough of taking faulty stuff back to Machine Mart in Gloucester and getting rather unsympathetic treatment so just cut off the bad ends and fit a couple of decent 1/4" BSP connectors. Re-fit air duster and blow out bonding areas. 998.7
18 12C, 48% RH. Turn on one fan heater. The second one is too close to the wing on the floor so leave it off for now. Try raising wing onto a couple of stools to keep it out of the direct blast of the heater. That's fine but a bit too high for convenient working on the TE so lower again. Soak a piece of thin cloth in acetone and wrap it around the rounded end of a steel rule to degrease the bonding areas. Blow them dry with the air duster. Degrease a small screwdriver so I can use it to lever the bonding flanges apart slightly if the syringe nozzle won't go in. Mark up positions of clamping pieces to avoid confusion. 17C, 41% RH. Mix 25g + 10g of the fresh Redux and suck some into the syringe. Apply to bonding areas, using screwdriver to wedge open as needed. Repeat with more fills of syringe until almost all the mix is used. Seems barely enough at first, but when flange faces squeezed together it is obviously plenty. Apply polyethylene sheet to both sides of joint to contain overspill and to stop clamping pieces sticking. Clamp up and raise onto stools. Turn on 2nd fan heater. Check that Redux fills all bonding areas - in fact it's welling up quite a bit between the sheets of polyethylene so no question that I have used enough this time! 21C, 36% RH. 1000.5
23 5 days curing, so turn off heaters.
24 Remove clamps and masking from port wing TE. Lower to floor and trim off excess Redux in aileron area with padsaw and Perma-Grit blocks and files. Chamfer the underside of the upper TE/skin joint along the aileron area. Fit aileron and check for travel and binding. Only one small spot nearest root is touching at full down. Travel seems OK as measured by tip travel against tip moulding. (Difficult to use digital level as wing is not secured against movement.) Remove aileron, file TE area where rubbing. Re-fit aileron to check - all clear now. Remove aileron again and now that finished for the moment with major filing work in that area, remove rag from pushrod hole and install pushrod. Re-install aileron and check movement. 1002.1
26 Replace bellcrank inspection panel. Fit flap and check for rubbing. Only makes contact with wing TE at about 9mm out from hard against TE face. Remove flap and scrape off the weeps of Redux on the wing TE surface and abrade the underside of the upper skin to a taper. Rub along the edge with the long Perma-Grit block to make it less sharp. Re-fit flap. Still rubbing around middle. The flap has a bit of a bulge around the centre joint. Remove flap. Mark a line about 3mm in from the edge. Cut just clear of it with padsaw and rub down with long Perma-Grit block until line just disappears. Re-fit flap. Just touching at full up. Fit outrigger leg temporarily. No contact between flap and wing when outrigger contacts flap bracket. Remove flap and aileron and store in trailer. 1004.4
28 File off Redux squeezed out at root rib and bring skin flush with rib. Clean up Redux blobs at aileron-flap junction and at horn boxes with Perma-Grit cone on Dremel. Clear all accumulated tools off table and hoist wing onto it right-side-up for a good look at the bond on the LE of the skin. Afternoon sunlight just right for this and trying to probe it with a hacksaw blade where the Redux has not squeezed out shows that there are no gaps at this edge - I can see solid Redux all the way along. Looking into the wing tip hole confirms this - there is an even layer of Redux all the way across the flange and only slight amounts squeezed out at the inside edge of the bond. Still not too happy about the slight height difference between front and rear skins but don't know what to do about it. Mark position of UNI straps on top of root. 1006.0
29 Set up Dremel with end-mill tool in router attachment and run along LE of port wing upper rear skin in an attempt to smooth the step at that joint. Helps a bit and is good for feathering off Redux that spread onto the surface. 15C, 55% RH; turn on fan heaters. Mark up a UNI offcut for 2 off 50mm by 710mm, 590mm, 430mm and 290mm and cut out the first set. Degrease the bonding area at the wing root with an acetone-soaked tissue. Abrade with fine Perma-Grit flexible sheet and degrease again. 24C, 36% RH. Mix a peg-1 (30g) batch of fresh epoxy and paint it sparingly onto bonding area. Lay on layers of UNI in turn, wetting out each one with minimal amount of epoxy. Apply 70mm peel-ply tape and leave to cure. 25C, 34% RH so turn heater thermostats down from 4 to 3 as it's late now and it won't cure before bedtime anyway. Put dispenser nozzles in a small jar with acetone to clean them up, as the hardener in particular seemed a bit slow-flowing and might be a bit clogged with dried-up hardener. 1008.9
30 Morning: 21C, 39% RH, layup cured, turn off heaters. Evening: 15C, 53% RH; turn on heaters. Remove peel-ply from last night's layup. File whiskers off edge. Hoist up wing and turn upside-down. File off a blob of Redux left by factory on bottom of spar. Mark out positions of UNI strips on root. Degrease, abrade & degrease again. Mask off W18 with masking tape covered with parcel tape. Cut out the pre-marked UNI strips. Slit end of longest one for W18. (Note that when I did the starboard wing on 2007-12-18, 2 layers needed to be slit. This is a consequence of the UNI positions being defined from the spar, and the spar being further aft in the starboard wing.) 19C, 48% RH. Mix a peg-1 (30g) batch of fresh epoxy - didn't bother to clean and re-fit nozzles yet, but dispensing managed without too much dripping. Paint sparingly onto bonding area, lay on strips, wetting out in turn. Apply 70mm peel-ply tape (also slit at aft end for W18). 20C, 50% RH; leave to cure. 1010.5

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