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Design & Build Sport Twin


Nigel R
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20190304_225210.jpg

 

Started to get the wing structures together. I drew out the rib and spar locations on paper so do actually have something that approaches a physical plan!

Card template has been cut at 88 deg to use for the root rob dihedral.

All very standard stuff here. Carefully line it all up. Ali blocks are used for getting things at 90 deg to the boas. Pinned down and weighted in a few key places. Then a drop or two of cyano on every joint.

Edited By Nigel R on 05/03/2019 06:23:44

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  • 3 weeks later...

Must confess I've been rather distracted from this of late, getting some foamboard airframes up together. Anwyay...

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...there are some U/C doublers are being stuck in - 1/32" ply running between the two pairs of spars.

Which brought me to...

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...getting the lower wing sheeting being applied, with contact adhesive. I pin down some blocks to hold the spars straight and in the right place, and use jig strips at the TE to keep everything straight. Two cocktail sticks get poked through the sheet into the spar to keep the sheeting aligned during the whole operation. Takes me about 20 minutes to get a surface done by the time the glue is on and dried and it is all pressed down and stuck.

Next job is to install the 1/4" ply U/C blocks, before the the upper sheeting goes on. I'll be using a torque rod U/C so the inboard end gets a second ply block.

Next time I don't think I would bother with two spars, it took a fair old while to double up on the bits and put them all in. I think I'd just make the main spar a bit more solid, maybe use 1/4" square spruce or basswood.

I'm still wondering whether it is worth putting in some flaps. Might be a bit tricky at this stage. But I could still chop the ailerons in half and add extra servos. Hmm.

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Second post seemed to go missing there...

 

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I cut a groove with the razor saw. Next time I will probably build up these blocks from 4mm pieces. Anyway. They're ready to go in with epoxy. Then it is time to close up the wing with the top sheeting.

Edited By Nigel R on 30/03/2019 06:48:36

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  • 4 weeks later...

Been a bit lax about updating this log lately. Nevertheless some slow but useful progress. Top sheeting is now on and leading and talking edges attached and I've got the ailerons shaped.

All very conventional so far. Next jobs are to sort the torque rods and then join the panels.

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I feel like I've reached a bit if a milestone

Only tips and joining to go really then it's on to the fuselage. Three if them, kind of.

Weight of wing in total so far is almost exactly 1lb. Both panels with the same to within a couple of grams. Very happy with that.

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Mooching steadily forward. Like Abraham Lincoln. As long as I don't go backwards, all is well. 

 

Panels joined and rough cut tips in place.

 

Wing is starting to outgrow the workspace! I have to be extra careful with it now to avoid the dreaded hangar rash.

A wiser man might have shaped the tips first. Never mind. 

Edited By Nigel R on 08/05/2019 23:12:00

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20190510_223706.jpg

Tips knocked back to airfoil shape.

Three layers of lightweight glass on the wing join, 2", 6" and 12" all stuck down with high tech PVA.

The glass still needs one or two more thin costs of PVA to fill the weave properly and make a nice smooth surface.

Also realised that I have cut the ailerons slightly short. So will have to stick on a 1/2" block to disguise this and give enough material to blend into the shape of the tips. Whoops.

It's definitely feeling quite large now. I nearly trod on a wingtip while moving it from one place to another and the wind caught it. That would certainly have made the aileron gaffe look inconsequential.

I need a bigger workshop!

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Thanks DD much appreciated!

Time to put the wing aside for a little while now.

Got a bit of the tailplane done today:

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My usual method of 1/8 framework and 1/16 sheet. All cyano for this bit but the next sheet will be contact adhesive.

When I've finished the sheeting I'll add a hard 1/4 at front and rear which act a bit like spars and stiffen it up a bit.

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Inching along. Main tailplane sheeted, sheeting trimmed back, and some med/hard strips going on at LE and TE:

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Tricky to see above, but the edges now look like:

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...and it has stiffened up nicely with the med/hard material around the edges.

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Time for the elevator to be put together.

Start with some 1/2 x 1/4 spruce and med/hard balsa. They have had a taper put on them using a disc sander:

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The taper is about 30 deg. Total length of spruce joiner, about 5". I like spruce joiners, they do double duty as a good hard point for the control horn. Less vague than a wire joiner, too.

Next up, stick them together...

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And I will also need a 1-12" wide strip of med or med/light balsa:

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...and then they both needs sticking together...

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and presto - I have an oversized blank... which is then cut down to length, and hinged:

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I shall probably leave the tailplane there. That all went quite well, I've managed for once to get the hinge line in the right place (i.e. the middle)!

Only problem encountered was that the 1/4 med sheet I had is a bit heavier than I'd like. Not a massive deal in the grand scheme of things, but unwanted weight at the tail end is always worse than anywhere else.

I'm going to do the rest of the tailplane jobs later on in the build - the rudder cutout, any shaping needed for the LE and tips, and the taper on the elevator. I think I have enough done now to use when building the fuselage.

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Made a start on the fuselage by cutting the sides and doublers. I've not shaped the wing saddle yet, that's the next job.

The ply was scrubbed with some 180 grit before doing anything with it.

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The doublers were glued on with contact adhesive. I find a big syringe, 10ml or 20ml size, is very useful to evenly spread the stuff around. It dries very very quickly in this warm weather.

I use a couple of toothpicks to peg everything in the right place as I'm pushing everything together:

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After that, they were laid flat on the board and weighted down overnight, while the contact adhesive dries out.

The bond is of course very strong right from the get go (hence the pegs to align things and avoid misalignment) but I believe it takes a good few hours for all the solvent to evaporate and for the joint to achieve full strength.

Edited By Nigel R on 22/05/2019 10:44:35

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