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Scratch built Slingsby King Kite 1/4**

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Bovin
Posts: 107
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Scratch built Slingsby King Kite 1/4**

Post by Bovin »

Hello everyone,

To start with, English is a foreign language for me,sorry for the mistakes!
Its almost winter again and it started to itch, what should I build? Whilst building the Slingsby Gull I had the possibility to read the book “ Slingsby Sailplanes ” by Martin Simons, writing about the development of all their gliders. There was a wonderful story about the Slingsby King Kite T- 9. This was a innovative design from 1936/37 with the aim of participating in a major international competition at the Wasserkuppe in July 1937. It was said that gliding would become Olympic. This glider was equipped with flaps and built to be able to fly fast. Because there was little time 3 prototypes were built simultaneously. During the test flights , the aircraft unfortunately turned out to be extremely sensitive to spins . As an emergency measure, all kinds of enlarged vertical stabilizers were built and with such an enlarged vertical stabilizer he finally flew and did reasonably well. Afterwards it turned out that there was a mistake in the building of the wings. Which mistake has never become completely clear, but what I understand is that the wing twisting was not well built (in all 3!) And that the center of gravity was quite far back. It is a wonderful story , it can also be found on this website : articles / rise and fall ., wonderful to read!
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Because this glider was covered with plywood (I like that) was innovative and had good flying possibilities, I decided to build it in 1: 4 scale. The wingspan will then be 3875mm and I hope to keep the weight below 4.4 KG
Scan2020-11-06_143028.jpg
Now the making, a different story. I grew up with pencil and drawing board and now I wanted to draw this glider digitally. I bought the drawing programs Devwing and Devfus4, just affordable . It took me quite some time to learn to work with it, but gradually I managed to do useful things sometimes with frustration, but in the end gave me a lot of satisfaction.
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I also had a problem what to use as wingjoiner. After breaking the carbon 8mm round wingjoiner (it was designed for a steel rod, which is has it now) of my Nemere 1/6, 330cm wingspan and with some warnings on the Retroplane forum, I had my reservations about carbon wing joiners . A steel wing pin is quite heavy and I really wanted to keep the weight down. Due to the gull wing there is quite a bit of dihedral in the middle part of the wing , which did not make it any easier.
On the Dutch modelbouw forum and on the Retroplane forum I stumbled in an excel sheet with wing spar and wing joiner calculations. That was nice, I'm educated in Kilogrammes , later Newtons and finally Mpa's , and I was afraid to make a mistake by a factor of 10 or something. With this program I could calculate the wing spar and also a wingjoiner.
http://voiletech.free.fr/Modelismeplane ... ngeron.htm
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I realized that if I made a wing joiner of UD glass/epoxy myself I could make it with dihedral built in . This means , moreover, that the wing joiner could only be held in place by the (reinforced) skin of the fuselage, a tube is not possible because of the built-in V . I bought 20 X 20mm square aluminum tube which will fit nicely between the 20 X 4 mm upper and lower girder of the main spar . Now I had to make a 17 X 17mm square glass rod so it would fit into this square tube . I thought let's try to make that. From spruce battens and a board (covered with packing tape to get a non sticking surface) glued together with hotglue, I made a simple mold.
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I took four pieces of UD glass tape, 7.5cm wide (600gr / m). Impregnated that with epoxy resin and folded lengthwise twice double (4 thick) , placed on the bottom of the mold, and after that the two upright sides in a similar way. In between those upright impregnated glass tapes,I first put 2mm balsa strips of 11mm, each against one side and then I put 1mm balsa strips between the other balsa strips to get the impregnated glass in place without touching it. Thereafter, the last layer of glass on it, and closed it with a batten with the tape to get a flat surface. Now I got a square glass / epoxy tube with a balsa core.
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The wall thickness turned out to be more than 4mm, making the joiner much stronger than the wing spar , it should stand 27G according to the above calculation program
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The weight of this joiner is 168 g, 60 cm long. I was glad with this experiment, now I could start the building of glider itself.
There is very little info of this glider, all info is very welcome!
To be continued.

Vincent.
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Bovin
Posts: 107
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Scratch built Slingsby King Kite 1/4

Post by Bovin »

Hello everyone,

I thought it would be most convenient to start with the tail surfaces, I wanted to make the plans digitally, for me completely new. I had already played around with the drawing program Devwing last summer and I started to understand a bit how that worked
3D view of the vertical stabilizer
3D view of the vertical stabilizer
Schermopname (136).png (117.97 KiB) Viewed 3606 times
. In addition, I had to try to understand how the real glider was constructed. Unfortunately, things went wrong in those two learning processes, it turned out that the horizontal stabilizer of the King Kite was more complex than I had realized. I also managed to make entire drawings disappear. Finally I managed to send the files as DXF. A good friend,Adri CNC'd the ribs and I started to build the horizontal stabilizer. Because I had misinterpreted a few construction details the result were unsatisfactory. Adri suggested it was better to CNC a new set of horizontal stabilizer ribs. In the meantime, I started on the vertical stabilizer. I wanted the rudder itself to be easily detachable, which is convenient for storage and transport.
The fin in construction, the laminated edge arch is already in place, as are the hinges
The fin in construction, the laminated edge arch is already in place, as are the hinges
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.
The top and TE of the rudder are completely curved, so I laminated the top of 3x1 spruce, bent after being poured over with boiling water and glued with thin CA. The rear of the TE is made up 3 pieces of 0.4mm plywood, scarfed joined, on both sides, filled with balsa, forming a sandwich.
right half of the py TE glued on and holes already drilled where rudder must be detached
right half of the py TE glued on and holes already drilled where rudder must be detached
TE rudder under construction
TE rudder under construction
The two hinge pins are made 1mm steel in 1mm epoxy/glass, so I can slide the rudder from above over these pins. It is secured with a sliding steel wire at the lowest rib
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I covered the front of the rudder with curved 0.4mm plywood, together with the main spar of the rudder this becomes a light and stiff plywood tube.
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basic structure of the rudder finished
basic structure of the rudder finished
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With the rest of the plywood covering I wait until a later stage of the construction, first I will built the horizontal stabilizer.

to be contimued,

Vincent.
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Max Wright
Posts: 168
Joined: 10 Mar 2020, 19:57
Location: Clayton Bay South Australia

Re: Scratch built Slingsby King Kite 1/4

Post by Max Wright »

Hi Vincent

Not to worry. Your English is fine and easy to understand.

Thank you for posting. It is a very interesting thread.

Cheers
Max
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Bovin
Posts: 107
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Scratch built Slingsby King Kite 1/4

Post by Bovin »

Hi Max,

Thanks a lot, glad you find it interesting :). The real glider was quite ahead of its time, hopefully I get the model flying well.

Cheers,
Vincent
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BrianF
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Joined: 19 Mar 2018, 09:36
Location: Brisbane AU
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Re: Scratch built Slingsby King Kite 1/4

Post by BrianF »

Very nice, and you make more sense than some native speakers.
I have the same experience with DevFuse/Wing, a bit frustrating initially, gets better as you get used to it and figure out workarounds.
Der Himmel ist blau und die Luft ist gut!
www.seqsa.net
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Bovin
Posts: 107
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Scratch built Slingsby King Kite 1/4

Post by Bovin »

Thanks Brian, I looked at your pics from Devwing, its helps me to learn what is possible with it.
In the meantime Thomas (on Retroplane forum) found a wunderfull photo of the Wasserkuppe event he wrote the following
"I found the list of participants, aircraft of the international competition of 1937 and the result in the book by Peter Riedel "Über sonnige Weiten" - Experienced Rhön history 1933-1939"
teil1_191.jpeg
P M Watt, placed 12th with a towel? on his head and a sigarette, cries out to be modelled!
He also has the participents
Teiln_569.jpeg
and the results
Wett_127.jpeg
Vincent
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Bovin
Posts: 107
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Scratch built Slingsby King Kite 1/4

Post by Bovin »

In the previous construction report I had already written something about the horizontal stabilizer. I had completely overlooked something in the plans
1 Schermopname (134).png
1 Schermopname (134).png (84.1 KiB) Viewed 3383 times
The front of the moving part is not only a semicircular plywood tube (which I was used to) but also a square box girder behind it. I think this is there to take up the bending and torsion of the balancing tips. In addition, the designers opted for a thin profile, which can be clearly seen in this photo
2 Schermopname (160).png
(Thanks to Thomas from Retroplane who found this photo on an item about W Watt, here is the link to this info. https://benitz.com/Watt/WattPercyM1906_Photos.html) This also an enlarged rudder, to prevent spinning problems, due to an very unfortunate unknown wing (construction?) problem, it was an prototype.
Because the horizontal stabilizer is also very tapered, the profile at the tips becomes very thin. I also wanted to keep the horizontal stabilizer very light, I presume that the 0.5mm plywood covering and web plates, glued with 2 X 2 mm spruce, should be strong enough.
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I had to make sure that there was enough sheeting to keep the construction stable when removing it from my buildingboard, so I filled the space between the 2x2 beams of the rudder with balsa and glued all the web plates in. I glued diagonals in the nose, which together with the top sheeting should already form a kind of D box. The bottom sheeting can only be added when the stabilizer is off the building board. Top sheeting, scarf joints
5 IMG_2243.JPG
6 IMG_2244.JPG
The TE, just like the vertical tail, is constructed from 2 layers of 0.5 plywood with balsa in between. The balsa ribs appeared to be very fragile at the TE, so I reinforced them with thin spruce battens Yet another problem caused by the balancing tips is the detachability of the rudder, it cannot be slided aside. I bent a hinge pin from 1mm steel wire, which I can later detach with a screwdriver or a similar tool from the bottom
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Nose D box bottom also sheeted, the prebent ply strips in the background are for the nose of the elevator itself. The outer ribs were to thin for the hinges, so I put them one rib to the inside.
7 IMG_2248.JPG
To be continued,

Vincent
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VinceC
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Re: Scratch built Slingsby King Kite 1/4

Post by VinceC »

Nice and considered build. Well done
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Bovin
Posts: 107
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Scratch built Slingsby King Kite 1/4

Post by Bovin »

Thanks Vince for your encouragement. The building of and reading about the King Kite makes me aware that the real thing was some project.
I hope to build a nice replica, it will take some time...

Vincent
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Bovin
Posts: 107
Joined: 30 Sep 2017, 12:43
Location: Hillegom

Re: Scratch built Slingsby King Kite 1/4

Post by Bovin »

I went on with the elevator. First I cut the rudderhorn from 1mm epoxy sheet. I had to attach that to the extra box girder of the elevator
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To get a proper bond, I filled the inside of the web plates with spruce strips. I didn't want to glue the rudderhorn in its place yet and stored it .
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On pre-bent ply strips (with boiling water) I drew the ribs on the inside to make the various gusset plates in one piece. In reality it was different, but I want to keep it as light as possible. I glued these pre-bent strips over the main spar of the rudder to form a torsionally rigid and round nose. At the location of the hinges I milled openings in this
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and now the rudder had to fit the fixed part of the horizontal stabilizer. After some fiddling it did. However, once I had glued one capstrip in place , attaching and loosening the elevator with a screwdriver (to keep the spring hinge pins unlocked) turned out to be quite inconvenient. After a night's sleep I made a kind of angled screwdriver from 1mm iron strip, which I could temporarely fix with a piece of tape. Now all hinge pins were simultaneously “unlocked” and I could slide the rudder into place.
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Then I could turn the iron strips back and I could (combined with maximum deflection of the elevator) take the strips out. Now the pivot pins sprung back in place and the rudder was secured. I was very happy with this, because I could also apply this technique to the ailerons. Besides I like to have the rudders removable, its easy with varnishing and covering.
With some clamping the tips were sheeted with ply.
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Then I sanded all the triangular gusset plates neatly into shape and the stabilizer was more or less ready.
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It feels very stiff and weighs 118 grams, I can’t get it lighter....

Vincent.
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