Phase 3 - Wing to boom mounting and alignment
1. The first thing that needs to be done is to mark up the boom and joint it to the pod. I took a slight swerve from the norm here and used my own technique for drilling, as I've found it very difficult to get an accurate centre line drilled with a pilot drill on a carbon boom before (the drill tends to wander even in a pillar and it's hard to get the exact centre line).
The method I've used for many years is shown in the pic, you basically pre-drill the pilot in boom (no need to centre it), dry fit pod and boom, whack on some masking tape and then replace the drill bit in the hole to act as a sight line. Now mark the center of the pod opening at one end of the masking tape and then sight down the pod/boom using the sticking up drill bit as a guide. Rotate the boom until the mark/drill bit and boom end all align. Then put it down and draw a lign between the mark and the hole in the boom. Disassemble, epoxy, refit and align the lines you drew on the pod & boom. Remove the tape and clean any excess epoxy off with acetone before it sets. That's it - quick and easy instant pilot hole starter dead on centre and your drill won't wander.
2. Once your pod/boom is dry, you need to drill out the pilot hole with a 5.5mm drill for the wing mounts.
3. This step is very important! Temporarily push the rear wing mount post into the wing and then take some scrap 3mm balsa or ply and push it up against it at the back to provide an temporary incidence block. Tape this block in place securely and then remove the rear wing mount post.
4. You now need to test fit everything before permanently mounting the front post in the hole you drilled. The method I use is a metal bolt (that fits the mount), a cooks (big) match stick, and split CF rod. You could use a piece of string, but this usually takes ages if you've got a nice tight fit planned! The method is this: Put the metal mount in the split rod (see pic) this will allow you to position it easily under the boom hole. Once in position, pull it through the boom hole by screwing in the metal bolt. Now remove the bolt and make a shim out of a folded piece of parcel tape (yellow in my pic) that will go between the wing and the boom to stop any stray epoxy gluing them together - fit this as per the photo. Next pull the mount through the wing by screwing in the cooks match which seems a perfect size. Finally refit the metal bolt and snug everything up tight (but not tight enough to crush the wing). This will hold everything in place and under pressure whilst the epoxy sets. However do the test fit first, and you'll find the balsa incidence block will angle your post exactly the right amount and that you can make final tweaks to the canopy alignment.
5. Now you know everything fits and you've done a dry run - make up some epoxy/balloons to a stiff mix (whipped cream) and coat the bottom of the metal mount. Insert the mount into the split stick and re-run the procedure in Step 6 above. Once complete leave the DLG to dry upside down so that epoxy runs into the mount's underside.
6. Once dry you need to make up an incidence block if you don't want to use the ply one supplied. This is easy, just make a small square mold in a tea light candle or bar of soap about 15x15x6mm deep. Insert a stiff mix of epoxy/balloons into the mold and when 50% set flatten the top off by pressing against glass. Remove the block from the mold and shape to fit - it should be 3mm high and you can shape it by wrapping sand paper around the boom and then wing seat and using them to sand the block to the correct profile. It'll be tiny once done, but don't lose it!
6. Now you need to mark up the rear post/mount position. First fit 2 x layers of masking tape (no more!) on the boom at the point where the rear mount will go. Don't remove your temporary balsa incidence block on your wing yet, you'll need it! Insert the rear metal mount into the wing from above and wrap some masking tape around a sharpened nail so that it will screw snugly into the mount. This nail will mark the centre for your rear mount when drilling the boom. Now refit the wing and screw down to the front mount but leave it slightly lose to allow adjustment movement.
7. You now need to set the wing/boom decalage. The easiest way to do this is to use fishing line attached to the centre rear of the boom with tape and then ensure that the distance to each wing tip is the same by measuring against this line. Once you are happy, tighten the screw in the front mount to prevent any further movement and then screw/push in the nail to mark the boom at the rear post point. This is what the 2 x layers of masking tape were for - the nail bites into them and marks the position.
8. Disassemble and drill the boom for the rear mount - start with a pilot (1mm) and work up to the 5.5mm drill bit.
9. Remove you temporary balsa incidence block from the wing. Now you need to set the rear mount into the boom in the same way as you did for the front mount in step 5 and 6. This time push you real incidence block under the wing and into position behind the rear mount. Remember to do the test run, and remember to clean the mounts after epoxying and use the shims.
10. Once everything has set, dissassemble and check the strength of the boom mounts. Now prep the boom for gluing the incidence block in place by sanding it a little and cleaning both block and boom with acetone. Reassemble one last time without any shims or masking tape, screw down the wing but don't tighten it fully and then position the incidence block in it's correct location. Grab some cyno and wick it under the edges of the incidence block before screwing down the wing fully and letting it set. Once dry you can do the final shaping of the block (and colour it black if you like!).
That's it, once done you'll have a perfectly aligned wing/boom/pod that's a very tight fit on the mounts - so you can disassemble the FF DLG later on and still have no "trim wander" issues
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