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Dereck Woodward Bigga Bit

Scrap box build

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Nigel R19/01/2020 18:05:28
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3407 forum posts
524 photos

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Nigel R19/01/2020 18:06:48
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3407 forum posts
524 photos

This session saw the wing saddle fettled , the wing dowel fixed in place and the ply plate to spread the load from the bolts all sorted.

More to come...

Nigel R19/01/2020 23:07:31
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3407 forum posts
524 photos

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Nigel R19/01/2020 23:08:35
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3407 forum posts
524 photos

Wing bolts drilled and tapped. Reinforced the threads with thin cyano as ever after tapping.

Nigel R20/01/2020 09:13:21
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3407 forum posts
524 photos

As far as balsa builds go, this must be one of the simplest 20 size airframes I've ever been near. I've taken only three complete days at the workbench to get this far.

Major woodwork jobs left - fin/rudder, top rear sheeting, lipo tray and hatch. Then it is time for covering.

I'm going to leave the rudder servo until after covering, then I can figure where my balance is coming out and use the servo to adjust it a bit before fixing it in place. It is, like most of this build, out of the spares box, a mighty Hitec 300 - with ball bearings no less - in this case. I have an offcut of lightweight red sullivan snake, which is long enough (if needed) to get the servo right up against where the lipo will sit.

I keep thinking that one or other of the 40 (ish) two strokes I have, would go very nicely in a 48" version...

Nigel R21/01/2020 22:43:18
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3407 forum posts
524 photos

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Nigel R21/01/2020 22:51:51
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3407 forum posts
524 photos

Fin and rudder structure tonight - just a bit of foamboard with some laminations of 1/16 around the edge. Dead easy. will need reinforcement around where the control horn will go because that foamboard is, how to say, squashy.

Nigel R23/01/2020 09:25:08
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3407 forum posts
524 photos

I think I've reached the point where the major woodwork is done, and all the jobs now are 'not much to see' type stuff.

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That said, the small jobs done last night were

the fin separated from the rudder

the fin aligned with fuselage / wing

the fin stuck on

rudder bevelled

1/32 ply added to rudder to reinforce the horn area

the top rear sheeting sorted and attached (made up from a few offcuts of 3/32 scrounged from the scrapbox)

Nigel R23/01/2020 09:39:11
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3407 forum posts
524 photos

The fuselage as pictured above weighs 7oz. It is about as strong as a Challenger tank.

I think a large chunk of that weight comes from the 3mm liteply sides. If I was going with liteply again on this size fuselage, I'd go down a thickness to 2mm. One problem for the thicker stuff is that there isn't much scope to cut big holes in it, on something this size.

Not sure where else the weight could be shaved off, there isn't that much structure in something this big. All the balsa in the fuselage has already been thinned down a bit, to 3/32, from the 1/8 called out on the plan.

I've obviously added a good few oz's in the U/C. But you can't do touch and gos without a set of wheels.

On a slightly different note, I think I'm about two thirds complete now. Main (more small stuff) jobs remaining before covering - sort out the lipo mount and access hatch, the wing tips, elevon bevels, and then I am covering. Errors and omissions, etc.

Nigel R24/01/2020 16:55:36
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3407 forum posts
524 photos

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Nigel R24/01/2020 16:57:46
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3407 forum posts
524 photos

Buried in there is a length of hard 1/8 balsa for the lipo. It's almost on the floor of the fuselage. I kind of snookered myself with the attachment at the front add it was very difficult to get a good joint between lipo tray and fuselage floor. So underneath I did:

20200124_151304.jpg

Nigel R24/01/2020 16:58:54
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3407 forum posts
524 photos

Which is another bit of 1/32 ply pretending to be a biscuit joint. Should be secure enough now.

I also made the hatch

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Nigel R24/01/2020 17:00:03
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3407 forum posts
524 photos

More bits of scrap wood stuck together and cut down. Pushed the boat out and added a proper catch.

Next job was to get the tips attached.

20200124_160601.jpg

Nigel R24/01/2020 17:02:34
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3407 forum posts
524 photos

I shall add another triangulation in there before long.

Meanwhile the foamboard elevons have warped quite badly. I'm thinking of making some wood replacements. All I have in the scrap box that would do is some 1/16 sheet so I would need to make a framework and then add the 1/16 either side. Maybe I'll see if I can get the foamboard things flat using the covering fiat though.

Paul Marsh24/01/2020 17:20:45
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3816 forum posts
1102 photos

I remember looking at the plan and substituting the foamboard for balsa instead. It has lasted well, though foam board probably wouldn't have, so good call there.

Nigel R24/01/2020 18:54:24
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3407 forum posts
524 photos

I think the foamboard is ok when it is, like the ribs, internal, and edged with timber. I'm not so convinced for control surfaces. It's just not stable, the paper covering is like a sponge and when it gets wet it shrinks. It'll probably be ok under some heat shrink.

But.

Balsa is better

Nigel R25/01/2020 10:21:24
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3407 forum posts
524 photos

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Nigel R25/01/2020 10:25:38
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3407 forum posts
524 photos

Ready for covering.

Controls all bevelled, small block fairing added to wing root on the fuselage, tips completed.

Usually I'd slot the hinges before covering but I'm using CA hinges on this one so that will come after covering.

Same with the rudder pushrod, usually I'd want it in place before this point, but the fuselage is so short it can go in after covering, access is no problem.

All in weight including lipo, so far, is 2lb3oz. I expect covering to bring that up another 3oz or so.

Nigel R30/01/2020 23:37:43
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3407 forum posts
524 photos

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Nigel R30/01/2020 23:44:49
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3407 forum posts
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Late finish tonight. I stuck at it until the bulk of the covering job was done. The hatch needs to be covered but all else is now wrapped.

My regular Stik livery. Yellow on top, blue or black underneath. In this case, blue.

Iron crosses yet to come, after hinges are sorted.

Time to call it a night.

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