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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

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

First I have to finish the construction of the wings, then all the pull-pull wires for the controls, than the canopy mold and then all the bits of ply. First I separated the ailerons from the wings.Image
I wanted to build the round nose of the aileron from 0.6mm ply, so it should form a small ply "D "box to add torsion stiffness to the aileron. I prebended ply with boiling water, dried it and glued on the ailerons
pre drilled ribs, hinge is glued  on the reversed side
pre drilled ribs, hinge is glued on the reversed side
cut the rib, not the hinge
cut the rib, not the hinge
taken apart
taken apart
wing side; sanded with a powerfile
wing side; sanded with a powerfile
aileron side; sanded with a long sanding block
aileron side; sanded with a long sanding block
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The aileron stays demountable, sliding outward.
Vincent

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

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

The wingjoiner tubes need some glassingImage This because I wanted to fly the Gull also without struts, as a Gull III.
The CNC holes had to be opened a bit, because of the angle of the ribs
The CNC holes had to be opened a bit, because of the angle of the ribs
There is 2mm room between the brass tube and the webbing, so the glass tape can go round the tube
First glass tape, than epoxy with filler and the glass tape folded back, so it form a loop
First glass tape, than epoxy with filler and the glass tape folded back, so it form a loop
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cutting of the partial cured epoxy/glass
cutting of the partial cured epoxy/glass
finished
finished
Made the canopy mould from multiple layers of 20mm balsa
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enlarging the block to make it fit for vacuum foming
enlarging the block to make it fit for vacuum foming
finished mould with canopy
finished mould with canopy

I an a bit sorry that I didn't glass the mould, the balsa with a lot of layers dope deforms a bit under the heat and the vacuum, so the canopy material itself is a bit distorted.
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 »

I was a bit puzzled about the seat of the pilot, the drawing was also not very clear about it ( I thought :? ). A couple of days ago I found the first photo of the Gull with the pilot in the cockpit
cockpit gull.jpg
I my mind the head of the pilot is mostly more or less flush with the rear of the canopy, but not on this picture. So I had to change quite a lot of things :shock: The servo's needed to go back quite a bit....
I put the servo for the tow release on the bottom
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I later decided to put full lenght brass tube in the centre section, all filled up with slow epoxy with filler
The pilots seat in its place
The pilots seat in its place
I started to put the ply on the fuselage, Because I made the middle section of the wing separate, I had some problems to solve
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First I glued 0.6mm ply strips on the frames, functioning as butt plates.
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Vincent
Last edited by Bovin on 05 May 2020, 08:55, edited 1 time in total.

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

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

Now I could do the topside of the tailboom. After making a panel fit, I put in two pins to put the panel at the proper place.
Image
Now I glue the panel with thick cyano only at the stringerand after a minute I put on glue on the frames and other stringer and wrap the panel in place. To make the horizontal stabilizer fit to the fuselage, I had to make a balsa filler.
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The ply is glued with epoxy/filler to the centre section
The ply is glued with epoxy/filler to the centre section
IMG_1433.JPG
Between the root ribs and the fuselage are ply fillers, hopefully it will be rugged .
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 »

I went on with the vertical fin, first some photo's about the retaining wire for the rudder, so it can be easily taken off
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covered with ply

the rear of the fuselage made fit to the horizontal stabilizer
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boven aanzicht.png
boven aanzicht.png (130.08 KiB) Viewed 272 times
On this photo it seems likely that the ply was in vertical strips at the fixed lower part of the rudder
IMG_1536.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 »

The position of the pilot had surprised me, half his head behind the canopy, in fact between the leading edge of the wing. I also didn't like the missing of this support. When I am using carbon joiners, the wing can damage the fuselage with a hard landing
Then I discovered small triangular reinforcements in the real thing
rugleuning.png
rugleuning.png (116.29 KiB) Viewed 238 times
and I made a reinforcement
outside the fuselage
outside the fuselage
and fitted in
and fitted in
finishing off
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Next was the fuselage/wing fairing, difficult to find pictures :(
There is no fairing at the underside and front topside
but the rear top is hard to find out. On the above photo of the prototype, there seems to be a quite big fairing, but on the other photo's
Schermopname (121).png
Schermopname (122).png
Schermopname (122).png (105.66 KiB) Viewed 238 times
Schermopname (120).png
Schermopname (120).png (139.81 KiB) Viewed 238 times
This funny part is a kind of lid, fitting on top of the fuselage, between the two wings, practically no fairing
Maybe (in hindsight) it had been better if I made the prototypical wing/fuselage fittings, always a difficult choice with scale models.......
I decided to make the best of it and after a false start I made balsa fill-inns and covered it with pieces of pre bent ply. The tape on the ply is to prevent glue coming on the surface of the ply, which gives colour differences with staining
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I had to start over a few times to get it acceptable.
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 »

Finished the fairing, it is in plain sight...
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The prebend ply (learned that on Retroplane, as lot of other tricks) works as
follows; take a strip of ply with the grain at right angles over an aluminium angle, put a round thing on top, pour over boiling water and put on clamps(with springs)
IMG_0536.JPG
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after drying its stays inform, I use this technique quite often it makes fairings in ply easier.
Vincent.

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

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

Now it was time to get the cockpit done. I couldn't find a proper drawing, so I thought to make the pilot first. Scaled a drawing of a man down to the proper size
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sawed the basic form out of 20 and 10mm balsa sheet
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and after some cutting got the basic pilot
IMG_1577.JPG
the knee and elbow hinges are fron Robart, the shoulder and hip joints are from 4mm shockcord. A few tricks, make a knot first, stretch it and cut it then, melt it, so the knot stays put.
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Hold it under a bit of tension
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This pilot is quite flexible and also rugged
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The hands and head will be made later, I needed this basis body first to get a matching interior.
The seat and floor, made from 0.6mm ply 3mm balsa and ply again
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with a mockup instrument panel
IMG_1557.JPG
Vincent.

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

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

It was time to make the struts. Now I like to fly it as a Gull I, with struts and also as a Gull III (also known as Cantilever Gull) without struts.
So the brackets should be completely demountable. I made the brackets from 0.5 mm mild steel (a side panel of an old computer :D), cut roughly and drilled the holes
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IMG_1590.JPG (59.85 KiB) Viewed 236 times
Fold it twice, so it became a "U
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soldered with 145 degr solder a M3 nut on it
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and cut, file and sanded it into shape
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I drilled holes in the main frame
reinforced the frame and glued the plate with nuts with slow epoxy at the inside
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Vincent.

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

Re: Slingsby Kirby Gull scale 1/4

Post by Bovin »

The original struts were made of metal tube and with a wooden fairing. I had some 4mm stainless tube steel left. Hard soldered a piece of tube as an attachment with silver
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and after the soldering I cut it of.
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It appeared that left and right were just as long, that was a good thing for my mood
It had to be streamlined and also a bit stiffened
IMG_1614.JPG
with balsa, LE spruce and carbon strips of 0.8mm, 3mm wide
on 0.4mm ply (unfortunately I had quite a bad spot in these sheet, it was not good glued at some spots :( )
IMG_1618.JPG
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Fitting the brackets at the wing, a similar as the fuselage. Earlier I had filled up the space between upper and lower spar to fix two plates for the strut, but I could not make that demountable :(
Now I also had to reinforce the lower spar to compensate for the holes
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The rear of the spar is in sight, so I used glass/epoxy as reinforcement
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When the brackets are screwed off I can have a clean wing and can fly it as a Gull III
IMG_1605.JPG
When I fly it with struts, I can use carbon wingjoiners, without I need steel wingjoiners
The struts are 52gr a piece, carbon wingjoiners are 120 the two, total weight is about 230 gr. The steel rod joiners are 600gr
I am curious ho it will affect the flying characteristics....
Vincent,

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