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Slingsby Kirby Gull scale 1/4

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Bovin
Posts: 52
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Slingsby Kirby Gull scale 1/4

Post by Bovin »

Hello everybody,
After finishing a new fuselage for my Nemere 1/8 which had crashed due to a failing wingjoiner, a carbon rod, now a steel one, I started thinking about a new glider. First I wanted to build a Fokker FG 1, but that is very similar to the FG 2 that I had already built. Besides I like the period of varnished ply gliders! A fellow modeller mentioned the beautiful Fafnir. I talked about the flying characteristics of the vintage gliders. Because I do almost all my flying on flat fields, not on a slope (not much slope in Holland..) I realised that the thermal qualities are much more important. I thought building the wonderful Petrel, almost started with the frames when I realised that it has also a thick wing profile which cannot be changed without changing the “looks” of this glider. Luckily I found the Slingsby Gull,and a much thinner wing, but with struts. A development was the “cantilever” Gull, with a stronger wing (not thicker) and without struts. Fortunatly it has also spoilers, a great help for me with landings!
If I build this glider in scale 1/4 it has a span of practically 4 metres, which suits me well, with a relatively short fuselage, luckily in varnished ply. Also I wanted to build it light, hoping it will fly better in thermals.
The real one;
gull 3 a.jpg
gull 2 a.png
gull 1a.png
gull 1a.png (114.65 KiB) Viewed 629 times
I found a great drawing in the Martin Simons book about Slingsby
tekening gull a.png
tekening gull a.png (81.62 KiB) Viewed 629 times
The scale soaring Uk has also very usefull documentation :D
Because I (still?) can’t work with digital drawing programs I enlarged his drawing
IMG_1056a.JPG
The nasty thing is that the lines are also enlarged, so the frame plans are rather crude. In this case I started without a detailed plan, I just work from the original plans, often to find solutions while working. I also plan to make the fuselage with as few girders as possible. With good butted joints the ply should take all the loads. I tried that on a new fuselage of my Nemere 1 / 8,
http://www.retroplane.net/forum/viewtopic.php?t=4632 end of page 1, which seemed to work well.So I started with the frames, I laminated them from 7 layers 1 X 5 mm spruce, dry bended, clamped and glued with thin cyano
IMG_1060a.JPG
IMG_1063a.JPG
IMG_1059a.JPG
This is a very easy way of making the frames, now I could set up the fuselage.
To be continued,
Vincent

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Bovin
Posts: 52
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

Hello everyone,
Next I made a building jig from a piece 20mm chipboard. 10 X 10 mm spruce battens screwed at a small angle on it on which later the frames are glued temporarely. So the frames are placed at that small angle, just as the plan, to achive the correct joints of the ply panels later. Because the inaccuracy of the frames it took some time to line it all up. Luckily its easy to thicken a frame with an extra 1mm batten. I sanded this setup with a long sanding block to get all the humps out. I had to remake one frame but in the end I was quite pleased with the result
IMG_1073a.JPG
IMG_1081a.JPG
IMG_1086 a.JPG
IMG_1087a.JPG
The batten on the inside of the frames will form a "sandwich " girder with the strip of the buttjoint of the skin panels (from 0.6mm ply)
IMG_1093.JPG
Hopefully this sketch explains my intention!
We went to Scotland last summer and my friend Rob found out that a Slingsby Gull was exhibited in the National Museum of Scotland, Edinburgh, what a coincidence :D. First time I could actually see the real thing before making it! Because the Gull was suspended under a glass roof, it was difficult to make good shots, but I could figure out quite some details.
CIMG9988klein.JPG
Back at home I went on, made the main spar of the fixed part of the rudder,
IMG_1097 klein.JPG
and attached it with the frame of the fuselage.
IMG_1098.JPG
Next I glued thick balsa on the inner spruce stringer, sanded it flush on the outside
IMG_1103.JPG
To align all the frames I had to sand them with a very long sanding block and on one frame I had to glue an additional batten.
On the outside of the balsa went a strip of 0.6mm ply, 12mm wide to stiffen the girder and later be a joiner plate for the skin.
IMG_1105klein.JPG
To my relief this girder appeared to be very stiff, so I thought; when I put some diagonals between the two girders it can be taken of the jig.
To be continued,
Vincent

Jolly Roger
Posts: 413
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Slingsby Kirby Gull scale 1/4

Post by Jolly Roger »

A beautiful choice of original glider.

I love your use of laminated wood. It's a great way to achieve strength and lightness from wood.

Looking forward to the next installment.

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Bovin
Posts: 52
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

Glad that you liked my choice of the Gull and yes, laminating is a very versatile way of constructing with wood :)

Regards, Vincent

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Cliff Evans
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Joined: 29 Dec 2019, 15:13
Location: Bristol
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Re: Slingsby Kirby Gull scale 1/4

Post by Cliff Evans »

Proper building! No disrespect meant to anyone!!

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Philkiteflyer
Posts: 77
Joined: 17 Mar 2015, 21:53
Location: Invercargill, NZ

Re: Slingsby Kirby Gull scale 1/4

Post by Philkiteflyer »

Bovin, that is some sweet building technique. Are you a boat builder by chance ? ? Very similar process.
I'll be watching for sure, especially to see what weight the gull ends up. Very light I expect.

Phillip C
Another Gull fan - with an ARF kit to build(strengthen).
"Keep it simple stupid"

john greenfield
Posts: 554
Joined: 18 Mar 2015, 07:52
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Re: Slingsby Kirby Gull scale 1/4

Post by john greenfield »

Very nice build but please do not butt join the 0.6mm ply skins. You will have a much better structural joint by making all the joints by overlapping them with "scarf joints as per the full size.
You can find information about an easy way to make scarf joints and also how to attach the ply skins with PVA glue and a hot iron here.

http://www.ghostsquadron.co.uk/construc ... _tips.html

AEB
AEB = Aeronautical Energiser Bunny (with thanks to CW)

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Bovin
Posts: 52
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

Thanks all for your nice comments!
I forgot to mention in this building report (what I did in "Introduce myself") that the Gull is already built, waiting for its maiden. Because I used a lot of information from Scale Soaring UK, I like to post the complete building here. I also mentioned that English is not my native language, so please forgive all the mistakes I make in writing.
@ Phillip, yes you are right, I build several sailing boats, starting with wooden short kits of sailing boats, later trimarans and small experimental proa's
@John, yes I had already seen the video's, very instructive! Via Retroplane I used a different technique, which will pop up in this report. About the scarf joints, yes I agree. I will try to explain (difficult in a foreign language) why I use butt joins. In building my Nemere, scale 1/6 in ply I found it very hard to get the scarfs perfectly aligned, giving not a nice joint (just for the view), spcially in double curvatures, as in the curve in the Gull wing. Scarfs are structural neater and better, but butt joints have its advantages.
I'll post the building as quick as I can shall we discus this point later?

Regards,
Vincent

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Bovin
Posts: 52
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

With caution I unscrewed the fuselage from the building jig and it was pretty stiff, so I could take away the temporary battens.
Image
IMG_1107klein.JPG
IMG_1108klein.JPG
I glued a 10mm wide 0.6mm ply strip with cyano at the "keel" and reinforced this joint with a fillet from epoxy thickened with wood dust.(used in boatbuilding)
IMG_1112.JPG
To make the connection between the stabilizer and fuselage I needed to have the stabilizer itself, so I started to build it. I hoped to make the ribs in the oldfashioned conventional way, but there appeared to much taper in this packet of ribs.
IMG_1115kl.JPG
it just was not acceptable. I didn't like to ask my friend(s) to cnc the few ribs (I already asked to do the wingribs..) so I choosed a bit more basic approach. I cut a lot of 2mm balsa at the same width, pinned them down on the drawing with my ply endribs in place and sanded the tophalf in shape with a very long sanding block.
IMG_1115kl.JPG
IMG_1117kl.JPG
IMG_1123kl.JPG
Made some sanding tools for the nodges in the ribs
IMG_1120kl.JPG
IMG_1119kl.JPG
Took both halves of the building board and sanded the other side into shape. Joined both halves and made some reinforcements in the middle
IMG_1124kl.JPG
IMG_1127.JPG
to be continued,
Vincent

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Bovin
Posts: 52
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

In the National Museum of Scotland in Edinburgh is a Gull exhibited ( My frriend Rob had found that).I had taken some photo's from the Gull, which is suspended at the ceiling, not easy photographing against the light. But it gives an idea how the horizontal stabilizer is fixed.
CIMG9984.JPG
I tried to make a similar way of attaching the stabilizer to the fuselage
IMG_1125kl.JPG
from epoxy print board and drilled 1 mm holes
IMG_1126kl.JPG
IMG_1128kl.JPG
IMG_1129kl.JPG
I now had the basic structure of the horizontal stabilizer. The nose had to be covered with 0.6mm ply. I thought prebending the ply; started pouring boiling water over one side of a strip of ply, wide enough for the nose
IMG_1145.JPG
turned the strip around and folded it a "U" shape. Poured again boiling water through this "gutter
IMG_1146.JPG
now I could easily fold it further and put some pegs on it
IMG_1157.JPG
Now I poured again boiling water through this almost closed gutter
IMG_1156.JPG
through the pressure of the clamps this gutter closes itself further. After some drying it stayes nicely in shape
IMG_1139.JPG
This is a sharp bend, for wider bends I fold he ply around a pipe or a wooden dowel with a suitable diameter.
To be continued,
Vincent

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