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Darran a Dawn Flyer (A first ever build)


Darran
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To do a full check you need to do the following. First fit the wing and bolt on, then;

1. pick up the model, look straight on to the nose. The wing should be lined up parallel to the tailplane - edge on. And the fin should make a vertical line exactly at right angles to the wing and the tailplane. This checks that the wing is level with the tailplane.

2. Turn it round and look from the back - same should apply - wing parallel to tailplane, fin at right angles.

3. Take a piece of string measure the distance from the wing tip to the point of the tail on one side. Then transfer the string (holding on to the point of measurement with your fingers) to the opposite wing tip to tail point distance. It should be the same. This checks that the wing is square to the fuselage.

4. Take a piece of string. Measure with the string from the tip of the wing to the tip of the tailplane. Transfer the string (holding on to the point of measurement with your fingers) to the opposite wing tip to tailplane tip distance. It should be the same. This checks that the tailplane and wing are square to each other.

If all these measurements work - then you have a square aeroplane!

BEB

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  • 4 weeks later...

Ok it's time to tackle sorting out the wing and tail sections and getting them correct. Firstly given BEB's instructions above lining up the wing to the tail is key. However I am yet to fit the tail to the fus, so I guess that's the first job. How do I ensure I get the tail mounted correctly and straight to give the correct reference for the wing.

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It may seem daft Darren - but its not absolutely critical to get it level. What is critical is that the tailplane and the wing are parallel and that the fin is at right angles to them. Where all that is relative to the fuselage in terms of slope is less important. But we do want to get it square.

So, place the tailplane on its seating and fix it down - a bit of tape is fine. Use the "mark one eyeball" to check its level. If not, try to fix with a bit of extra pressure on one side. If that's not enough use a shim beneath the tailplane. You shouldn't need to shim it if you built the tail reasonably accurately.

Then use the string method I mentioned above between the tailplane tips and the centre of the nose (if you look at my buildblog you will see that I marked a datuum point on the nose when I was gluing on the tail, I used that point). Carefully measure to each tailplane tip to check it was square.

Assuming it will sit in the right place, then use some slow epoxy. Fit it in place, check for level again by eye, then check with your string to the nose centre. Gradually tape/clamp the joint as you become more and more confident that it is right.

Leave over night to really set.

BEB

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TailRight tail is fitted and wing lined up. Using the string method all seems to be lined up ok. May need to build up the wing seat a little in places but in the main all is looking good. Wing now seems to have levelled out and there's only a couple of millimetres difference in it now

one thing I wanted to ask is do I need to round off the leading edge of the wing or leave it square if so how do I go about that.

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Looking good Darren.

The leading edge does need to be rounded off to give a streamlined frond edge.

I use firstly a razor plane and then finish off with a long perma grit tool. You can carefully use glass paper to get the same effect. Just be careful and not take to much of the front wing skin. Take it slowly to get the best results.

Kev

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Yes you need to round it off. Except for the central bit that butts up against the fuselage nose of course.

Some folks go to a lot of trouble here making cardboard templates etc. Personally I just take a sanding block and work away with it along the length until it looks right! Remember the golden rule here is you can always take a bit more off, but its very difficult to put it back on again! So slowly does it, a bit of sanding along the whole length of half the wing leading edge, top then bottom, and then a good squint at it.

Don't let one area get further advanced than another - work along the whole half wing, both sides, and try to bring it to a nice natural "D" shape that blends well with the wing. The exact profile isn't critical - but getting it more or less the same all the way along (and the same on both wings) is more important. This isn't a stressful job - its actually usually quite an easy and relaxing task!

BEB

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A bit of advice please on staining my model. I am sure I have already read the general idea is to rub down - clean - apply stain coat and then repeat until required finish is achieved. However how fine a grade sandpaper is best to use for the sanding between coats and what's best to use to clean the surface prior to applying the coats of varnish

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Hi Darran,

I'm sure others will have ideas too, but this is what I did and (putting aside the CA drama!) I'm pretty pleased with the final result.

First a good all over rub down with 400 grit. Don't be too aggresive, its only balsa and will dissapear under sanding quicker than you can "knife"! Just get it smooth with no lumps and bumps.

Then a good going over with a soft old paint brush - get's 90% of the balsa dust off it. I then use something called a "tack cloth" - its a horrible feeling sticky cloth - you can get them at Halfords car painters use them. Finally I have quick wipe over with a pad with some acetone or IPA on.

Stir the stain well and apply it to whole areas pretty quickly. Don't dawdle over this brushing in small features or you'll get a patchy finish. Just apply to the whole top surface quickly then brush in long strokes the length of the surface.

Once dry I use a soft sponge-based sanding pad (I think its about 600 grit equivalent) to just raise the texture a little for the next coat. In all I did 4 coats I think then finished with a coat of a water based clear PU varnish for a bit of extra protection.

Watch out when doing balsa end grain - like round the cowl rim, its very absorbent and difficult to get even. Probably the best strategy here is to use an almost dry brush and gradually build it up. But it very hard to get that bit really right.

BEB

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What stain/varnish are you using Darren?

If you're using a separate stain/varnish then you need to apply the stain with a rubber made from a folded pad of lint free cloth. Apply a reasonable amount of stain to get the balsa wet then wipe off with the rubber immediately, rubbing it into the wood and blending it to get a even colour. Apply another coat if required then finish with 2-3 coats of polyurethane varnish, lightly sanding with fine wet & dry (used dry) between coats

More work than a combined stain/varnish but being a carpenter I feel it gives a much better finish and control of the colour and finish.

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  • 4 months later...

Hi Darran,

sorry to hear that - but don't fret too much, I think just about everyone has broken the lattice work somewhere along its length at some time on this model. Its a nice attractive feature - but its not strong!

As long as its a really good fit back together - ie no missing bits - then just push it back together and dribble a little CA into the joint - let it wick in. For this to work as I say there must be a perfect fit between the two broken parts. I repaired mine this way and its been fine ever since. I suspect the CA joint is probably stronger than the wood!

If there are gaps you will need a little bracing added. Some thin ply on the inner face as a splint would be fine. Once that is fixed in place you can fill the gap.

Obvioulsy you have to take care that the tail goes back on straight!

BEB

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Posted by Biggles' Elder Brother - Moderator on 27/12/2014 20:51:38:

Hi Darran,

sorry to hear that - but don't fret too much, I think just about everyone has broken the lattice work somewhere along its length at some time on this model. Its a nice attractive feature - but its not strong!

As long as its a really good fit back together - ie no missing bits - then just push it back together and dribble a little CA into the joint - let it wick in. For this to work as I say there must be a perfect fit between the two broken parts. I repaired mine this way and its been fine ever since. I suspect the CA joint is probably stronger than the wood!

If there are gaps you will need a little bracing added. Some thin ply on the inner face as a splint would be fine. Once that is fixed in place you can fill the gap.

Obvioulsy you have to take care that the tail goes back on straight!

BEB

It's not quite come totally apart and there appears to be no bits missing if I offer it back up. I will try ca and see how we go. Was just worried as it's the tail I might have to start again.

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Sounds like its broken at the same place - and in a similar manner - to how I broke mine! The CA repair, carefully done, should be fine. It is a well known weak spot, some folks have reinforced the bottom plate and the sides with ply - but TBH I suspect that would just shift the fracture point backwards along the tail which would probably be a more difficult repair.

BEB

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Posted by Biggles' Elder Brother - Moderator on 27/12/2014 21:07:47:

Sounds like its broken at the same place - and in a similar manner - to how I broke mine! The CA repair, carefully done, should be fine. It is a well known weak spot, some folks have reinforced the bottom plate and the sides with ply - but TBH I suspect that would just shift the fracture point backwards along the tail which would probably be a more difficult repair.

BEB

One side has broken but has nothing missing. The other has split but not quite broken not sure what to do with this side. I guess just feed some ca in an see if it takes

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Yes - its the best plan. Use the thinnest CA you have and apply it drop by drop. Its not quantity we want here - its getting the glue in exactly the right place so that it wicks into the crack that's left once you push everything back together again.

How did it fly? I'm really pleased you got it finished. You never told us you'd maidened it!

BEB

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BEB

It's not quite finished. I was testing the wheel struts I had made and overdid it and the tail caught a wall. Not so good at ground movement as I am in the air. Once fixed I'm going to wait for a summers day to maiden it. The instructor at the club who taught me to fly will help me with my first maiden.

Will have it repaired and finished hopefully in the next week. Will post some pictures when done.

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Yes some pictures would be nice.

The DF can be a bit of a minx on the ground - well mine can anyway. The main U/C track is a bit narrow really, the rudder isn't large and of course there is a skid rather than a wheel at the back. All these join together to make the ground handling a bit of a challenge!

BEB

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