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Mirage IIIO 1/32, Scratchbuild


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  • 2 weeks later...

A tail with a happy ending

 

As @Biggles87 pointed out earlier on in this thread, the wings on this thing are likely to prove 'challenging'.  The tail too as it turns out.

 

I've never been entirely comfortable with how to make wings and tails. At first glance they look much simpler to make than the fuselage but that's not really the case.  The tail of the Mirage is a good example of why.  Here the tail must be absolutely straight and vertical when viewed from the front and even though it starts as a thin structure must get even thinner towards the top. In addition the trailing edge must be razor sharp and the true outline of the tail preserved.  My first attempt at representing this tail was using my usual plywood and thin sheets of laminate - the exact same method I used on the Mig-15 a few years back, and I wasn't sure about it back then either... 🤔

 

Cut out the tail in the usual manner and use scissors to cut out a series of templates using wood laminate.

1dOFqdN.jpg

 

Glue all the bits together like a sandwich

832mR0I.jpg

 

Now fill and file and fill and file until you have something like this. it's not too bad at first sight but note that the first problem has already appeared.  The central slither of a sheet plywood has a grain and hence will tend to break along certain directions. In this case the central bit of plywood's grain is running up and down the tail and so a couple of mm of the tip of the tail have already broken off (at the point indicated by the red arrow) leaving something other than the nice angular sharp bit that we want there.  I wouldn't have been so concerned about this except that exactly the same thing happened with my Kfir C2 model 40 years ago and this was proof that I had not learned my lessons properly.

Ts1srhu.jpg

 

Much worse was that the tail appeared too thick and that the central sheet of plywood had either developed a warp or had one all along that I had not noticed.  Plywood is great to work with if its well supported, but standing alone like this it seems prone to have warps in it.  I needed a method that would essentially guarantee a straight and tapered tail regardless of how thin it needs to be.  I stuck that thought in the back of my mind and let it rattle around in there for a few days.

LyrYaSp.jpg

 

Meanwhile I marked out the rebate that the tail will fit in...

p3xpjiT.jpg

 

and then merrily chopped it out with a bandsaw and a flat chisel.  That bit was easy.

ZwrVNww.jpg

 

After a few days I thought 'why not do what the RC modelling guys do and build the tail from a series of thin stringers and longerons and then fill the gaps between them'.  Here I've made a start. Essentially the idea is to reduce the problem to a series of 2D blocks individually thinned and tapered 'to perfection',  glue them into place and fill the gaps between them with balsa.  Once that's done I could then file and sand the balsa to shape and 'viola'. 

Suffice to say the theory was good but the actual experience was less gratifying. This soon proved to be a slow and somewhat frustrating process.  it turns out there's a reason I don't build flying models!

zRieUj4.jpg

 

So then I thought long and hard about what materials can be essentially guaranteed to be thin but also flat and free of warpage.  There are surprisingly few, but I thought back to the methods and materials my dad uses to build his models. His preferred material is MDF  (medium density fibreboard) 'Customwood' as its sometimes called in New Zealand.  In the past I have generally shied away from the stuff because it typically leaves a slightly 'furry' surface that must be dealt with - but dad loves it.  In particular he likes the fact that it has no grain, is generally warp free and has a layered structure that allows it to be split into very fine wafers. He reckons that it combines the best features of both wood and cardboard.

 

I didn't really think this would work, but decided to give it a try anyway.  This is 6mm thick MDF being cut with a scroll-saw to into the shape of the tail.  That's 'Frankie Goes to Hollywood' in the background by the way.

ndYTUB2.jpg

 

Here is some detailed shaping going on. I only include this picture to remind everyone not to breathe MDF dust. I had my P2 dust protector on at the time and had used the scoll-saw to cut as close to the line as possible to minimize sanding.

5ogpHPg.jpg

 

Now use an 'incra rule' 'T-Square' to put two marks at exactly 2mm from the edge of the panel, leaving a defined 2mm central section.

boUYiUb.jpg

 

Now cut a 'stop line' at the root of the tail. This is the line below which you want to leave the MDF at it's full 6mm thickness.

KlhOrxv.jpg

 

Take a razor blade and carefully start splitting and peeling off each of the 2mm surplus wafers of MDF until only the central 2mm slice remains. Use the stop-line to ensure that the splitting stops at the tail root and you don't keep peeling further than intended. The process is surprisingly simple and quick.

scLMdLT.jpg

 

Now use a razor to cut the limits of where you want the central panel to be still thinner. Mark out the edges again and repeat the peeling process. Here the front cm of the tail is getting thinned down to a little more than 1mm thick. 

jsqijjY.jpg

 

Soon you should have something like this.  Here I'm cleaning up with a nice sharp flat chisel. (Beware MDF blunts tools very quickly).

wixOKrz.jpg

 

From here you can probably guess the rest.  Use a combination of filler and files and rasps and sandpaper to get the streamlined profile of the tail just how you want it.

8OAhRRz.jpg

 

 

It turns out that the furriness of MDF is not a problem. Just spray some automotive filler / primer on the surface and sand normally.  After a couple of cycles the MDF is as smooth as injected molded plastic. if you look closely you can see some subtle dents in this piece but that's not a problem - I have a cunning plan for them... 🧐

aiD7vLN.jpg

 

So now we have a very poor blurry photo of a nice thin, straight, bolt-upright and properly tapered Mirage III tail.  

0LaeZyJ.jpg

 

And here it is in place.

0TqvYP2.jpg

I'm very happy with this outcome!
Just as I used to not be keen on using balsa but have started to find more and more uses for it, MDF is now firmly in my 'happy to use when required' category of materials.

So far this is the best method I've found for making a slim tapered tail (or wings I guess).  I've learned something here and this method will definitely be used again.  

 

So it really is a tail with a happy ending.

 

Bandsaw Steve

 

 

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A terrific outcome Steve. Fascinating to watch this come together.

I thought Frankie Goes To Hollywood was one of the best bands to come out of the 80’s. I listened to Welcome to the Pleasuredome just the other day while I was working in my shed.

Cheers

 

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Nice recovery with the fin. Another idea wound to have used some fruit e wood , apple or pear, they have very close grain even box wood if you can find it.

I've just passed your thread link to aa friend here near George, South Africa. He build a 32nd Buccaneer a few years back. Made a fine job of it for a pilot!

 

Colin

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That looking a bit good mate, not bad stuff that MDF, I just spent the last 3 days making it, 'cept ours is Golden Edge, Customwood is just another tradename but to be fair it was the first made in the country so lent its name as a generic for a long time. Its handy stuff, very good for making fibre glassing moulds. :)

Steve.

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1 hour ago, stevehnz said:

That looking a bit good mate, not bad stuff that MDF, I just spent the last 3 days making it, 'cept ours is Golden Edge.

I just googled ‘Golden Edge MDF’ and think that’s a pretty impressive business you are working in. Important work too;  I foresee a lot more MDF in my future.

 

By coincidence, one of my earliest childhood memories of Nelson was being taken for a joy-ride in a logging truck around the port.  I have no idea how such a sight-seeing trip was organised for a five year old kid, but it was certainly memorable.

 

Bet it couldn’t happen these days! 🤔

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44 minutes ago, Bandsaw Steve said:

Bet it couldn’t happen these days! 🤔

Bet you're right. ;) :D

Riding our bikes around the port was common weekend entertainment as a kid, can't get near it now, it works pretty much 24/7. Playing on the chip heap was fine, as long as you didn't get chased away but no physical security, nothing.  Kids today, don't know what they're missing. :lol:

Steve.

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Air Intakes

 

Rather than leave it another couple of weeks before a further update I might as well press on and write about the air intakes.

 

Before we start, here's a view of the project at the point I left it at the end of the last post.  Don't worry too much about the wings as they are somewhat rudimentary and are likely to be re-done.  This is really just here to show off the tail from a better angle. 

TGz5ciG.jpg

 

Anyway this thing needs some air intakes, so let's see how we go.   It's the usual deal with the mark-up.  The wood here is sassafras - more very fine carving wood from Tasmania. I think that Liquid Ambar and Kahikatea are slightly better as this seems a little bit fibrous by comparison. It's no problem though, this is easily good enough for this work.

yd6QjdM.jpg

 

You know the deal - cut it out with a bandsaw...

xYiW3hF.jpg

 

Mark out the topside...

lwalJsP.jpg

 

Cut out the plan view shape and draw up a series of cross-sectional profiles.

7cnC7IP.jpg

 

Start carving. Note how there is plenty of surplus wood both in front of and after the part that we are working on.  This makes holding the job in the vice much easier and helps prevent damage on the final surfaces.

NPanJFn.jpg

 

Get stuck in with a rasp. I bought this one brand-new a few months ago and must say that a new rasp with nice sharp teeth makes a huge difference.

gZyMrRY.jpg

 

Soon after the photo above I cut off the block of wood ahead of the intakes to expose the front of the block. This allowed me to take a spade-bit and start drilling out the intake. 

SlSzslR.jpg

 

A top tip with a spade bit is that when starting a new hole run the drill backwards to gently scribe a perimeter around the future drill hole. This prevents the drilling process 'chipping out' wood from the mouth of the drill-hole. That's important in this case.

TM328Lh.jpg

 

Now drill out two holes side by side and overlapping as shown.

TOp7DqJ.jpg

 

As you can see in the photo below, the entire intake structure is still a bit 'chunky' compared with the cross-sectional profiles, so continue carving and rasping and sanding until the piece matches the required sectional shape.  Note the red pen-lines. They are there to mark the positions of surfaces that were cut by the bandsaw and therefore define the correct shape in plan or profile view. If you avoid removing the red marks while carving you have preserved the correct 2D outlines. 

WmQ0JeA.jpg

 

Once the piece has been fined down a bit, then cut it in half...

lNqEk0F.jpg

 

leaving two air intake trunks - albeit with large surplus block of wood behind each one.

5SwvfY5.jpg

 

Not looking too bad against the plans, but the leading edges are still very blunt.

G2Zwbml.jpg

 

So get the scoop chisels out and do some of this.

m9U2mWJ.jpg

 

Then get out an abrasive grinding head and fit it to a Dremmel tool (or some cheap equivalent as in this case) and very carefully grind the inside of the intake down until the leading edge is suitably fine.

NBzv0e4.jpg

 

Finally sand out the interior until you have this...

wfo9fMd.jpg

 

Which - when fitted into position on the model - looks a bit like this...

3AbfQ7Y.jpg

 

Note that the large block of wood still stuck on the rear of each intake interferes with the main fuselage component, which is why the rest of the fuselage is not present in the photo above. The best I can do to show the whole thing together is this;  A super stretch Mirage! Let's say a 'Mirage 3000' for argument's sake. :think:

ikETbkO.jpg

 

That's it for now folks.  Thanks for all the interest shown. 👍

 

Wings next...

 

Best Regards,

Bandsaw Steve

 

 

 

 

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Gidday Steve, that's neat work you've done. I wonder how MDF (I have trouble spelling it 🙂) would go for ship hulls?

And you think your Mirage is stretched? How about this Corsair?

DSCN5527

It has the experimental 900 cylinder engine. Actually, the nose was so long simply to give me something to hold onto. It was later trimmed about 2.5mm in front of the wing.

     And back to your Mirage, what's next on the build agenda?     Regards, Jeff.

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Wings next Jeff,

 

but really I should be getting back to the PZH 2000 soon. The poor thing is feeling a bit neglected. With some concentrated effort I reckon I could have the PZH finished by the end of the coming winter.

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Excellent work on the nacelles, you've got a couple of good looking gouges there. You can't beat quality tools when you are doing this sort of work. I have a Paring chisel made from a 400mm planer blade. I made it in the mid seventies. Took me through my modelmaking career and I think I've only sharpened it five times. Honed it a lot, though!

 

Add Obeche to the list of woods I gave you above, used to be used in the flying model aircraft game.

 

Colin

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53 minutes ago, Bandsaw Steve said:

but really I should be getting back to the PZH 2000 soon.

Yeah, I've been periodically checking to see if there's another update on it. I rarely have more than one build on the go at any one time. I find that I lose the continuity and have trouble working out what I should be doing next. They Who Must Be Obeyed would probably call it 'Mere Male Syndrome', the inability to do more than one thing at a time. At my age senility doesn't help. 😟 Regards, Jeff.

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18 hours ago, ArnoldAmbrose said:

I rarely have more than one build on the go at any one time.

I wish I had such wisdom - three projects on the go at the moment and about 50 more in the ‘one day’ queue. 

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10 hours ago, Corsairfoxfouruncle said:

hows the research going into your coastal steam ship project ? 

Well....  ummmm.... 🤔 

 

Put it this way . The SS Xantho thread is fully up to date, even though it hasn’t been updated since around about last August. So not much happening I’m sorry to say.

 

The good news is that in July I’m returning to Albany to visit Ross Shardlow again (he’s one of Western Australia’s leading maritime historians) and I want to take a full set of drawings for his review, so I have to get that project moving again quite soon.

 

👍

 

Steve

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  • 2 weeks later...

Wings - Finally

 

No longer can I put off the dreaded moment that work must begin on the wings.

 

As the photo below shows these wings are not just big flat triangles they have a certain subtlety in their contours that I must at least attempt to reproduce.  The hardest part is going to be the wingtips where there is a truly savage amount of washout.  More about that later - much later.  For now, let's just look at the curved contour on the top surface of the wing.

HuZ1YBh.jpg

 

Fortunately the plans I'm using have a cross-section of the aerofoil.  How accurate this is I don't claim to know but I'm going to use it as 'the truth' and see if I can reproduce it reasonably faithfully.  

 

But first a disclaimer.  It is my preference when writing longer sequences of work to write as if I'm instructing you what to do.  The only I reason I do this is to prevent a boring 'and then I did X'  'and then I did Y' sort of prose. 

 

Please note that I don't really expect anyone to actually follow these instructions and I certainly don't want to paint myself as some sort of 'expert'. That's certainly not the case, in fact I'm really just making most of this up as I go along! :thumbsup:

 

Anyway let's have a go at making some wings.  First draw a line from leading to trailing edge, effectively dividing the wing into a top and bottom half.  This post will be working on the top half.

xP5B5Ag.jpg

 

Use a roller-ruler to trace on a series of parallel lines at 1mm spacing from the center-line upwards and mark the point at which each line intersects the top surface.  Here 5mm is the maximum thickness above the central plane.

gfyuc0a.jpg

 

Now take two slabs of (in this case) 6mm MDF and partially glue them together. Only partially glue them together because later on you will want to split them apart.

zPvCc1A.jpg

 

Clamp them up and let the glue set nice and firmly.

Kin0lpg.jpg

 

Now do the usual thing with a paper pattern...

0qQGrbL.jpg

 

and cut out the wing planform with a scroll saw (or a fret saw if you prefer).  I've had problems with the scroll-saw before, especially when using it on very small sheets of thin plywood which tends to wobble and bounce about as the blade cuts.  However, I have found that working on 12mm thickness MDF the saw cuts beautifully as there’s really no ‘bounce’ in the wood. Since we have glued the two sheets of MDF together, we can be certain that the cut will produce two identical shapes.

Pg6TAJN.jpg

 

Note how the two slabs are still stuck together at the front but are readily separable at the rear - this is what I mean by ‘partially glued together’.

1F8vxZ1.jpg

 

Now measure and mark-out mm lines on the cut-out edges, working outwards from the meeting face of the two boards. Note that the paper is stuck on the underside so the whole thing is upside down in this photo.

QGWyMyg.jpg

 

Using basic geometry, careful measurement and reasonable interpolation we can now generate a series of triangles, each of which marks our best estimate of the position of the relevant thickness contour. Note that this is the thickness of the wing above that original reference plane that we drew at the start of this post. This is a bit like a topographic map with the wing's central plane as sea-level.

Lg99tKK.jpg

 

The subsequent steps will destroy this diagram so now drill a series of holes at critical intersections so that all of this careful geometric work will not be lost.

RX9FCZS.jpg

 

Pick the highest contour and scribe it to 1mm depth with a razor blade.

P1BK0CN.jpg

 

Then flip the job on its side and using the lines marked on the side of the slab insert the razor blade into the first layer of MDF and start peeling it back until it hits the contour line you just cut. The MDF splits & peels quite beautifully and consistently until it hits the pre-cut limit. The process is surprisingly quick and fun.  Repeat the process layer by layer, first by cutting the next contour on the top surface then by splitting the MDF at the relevant mm mark.    

SRCHvQD.jpg

 

Eventually you will end up with something that looks like this. It's a bit messy but do not be deterred, the underlying 3D shape is actually quite well controlled.   

OhCSeJy.jpg

 

Grab a nice wide, flat sharp chisel and smooth out the rough bits.

7eaWhDo.jpg

 

It's a bit like 3D printing in reverse! 🤣

bu9Fkih.jpg

 

After a bit of sanding you will have something like this.

TqpIYHQ.jpg

 

At this point I chose to split away the lower half, but I probably could have left it there.

xwQRTpx.jpg

 

Now run a red pen (or paint if you prefer) around the edge of each step in the contour model. In subsequent shaping, as long as you can see all of the red you know you have not removed too much material.

svs1HL8.jpg

 

Using a rasp and varying grades of sandpaper start rounding off the contours.  Remember this jet was built by the French not the Azteks! 😉

VidXkxB.jpg

 

Getting there now.  Some of the red ink is obscured by sawdust and the general fuzzyness of cut MDF but you get the idea.

j67C99u.jpg

 

Now start slopping heaps of this wood filler onto the model. This fills in the remaining steps and blocky contours.

KH9OQ8U.jpg

 

Let it dry overnight.

uajFtlN.jpg

 

And then attack it once again with some sandpaper and so-forth.

z4pl7tx.jpg

 

After a first layer of filler-primer spray paint (there will be more) we have this effect.  There is still the faintest trace of 'steps' in the wing's topside but I think a couple more rounds of filling and sanding that should see that right. 

7UzbVyB.jpg

 

I hope you can see a nice gently curved aerofoil section on that top surface. The model is definitely starting to look like something a bit Miragish now. 👍

YB1YivD.jpg

 

Next time we will flip the whole thing on it's back and try to deal with the underside in a similar fashion.

 

Till then, 

Best Regards,

Bandsaw Steve

 

 

 

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1 hour ago, Bandsaw Steve said:

Remember this jet was built by the French not the Azteks!

Gidday Steve, I think the Azteks would have needed an awful lot of filler to have done to their builds what you've done here. But it looks ingenious what you've done. I'd have settled for the triangle of MDF and simply sharpened the edges. Yeah, I know, crude! 😫 Looking forward to seeing the underside done.

     Oh, and BTW, I didn't know we had two-seat versions of the Mirage. 

Regards, Jeff.

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Meticulous planning Steve, sorry I've missed most of the action so far. My loss entirely, it's already looking very Miragey. Have hit the follow button so I don't miss any more updates! 

 

Cheers

Richie

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Lovely work Steve. This is so interesting to watch especially your use of geometry. As a retired surveyor it reminds me of producing topographic plans decades ago before we started using all the electronic equipment.

I look forward to seeing more.

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