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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

Re: Scratch built Slingsby King Kite 1/4

Post by Bovin »

Before continuing with the cockpit, I got some doubts about the size of the stringers in the fuselage. They have about the same (scale) size as the example, but my landings are a bit rougher than the real ones. On the other hand, a light tail boom provides much less ballast and so on. I decided to put a single glass roving with epoxy on the inside of the left and right stringer, the stiffness of glass is closer to that of wood than that of carbon. I hope it works out well.
I drilled 2mm holes next to the beam and with a double folded 0.2mm steel wire
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I pulled the dry roving wire through the holes and impregnated it with epoxy. After curing, the girders feel much stiffer and not much weight is added.
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To get the cockpit right I first fitted the pilot (borrowed from my Gull) and after some fiddling he was neatly in place .
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Made a backrest, seat and floor from plywood / balsa sandwich, they are fixed with screws in plywood supports
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Enough space over the servos.
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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 »

The planned receiver battery box had a conflict with the pilot's feet, so I changed it and now the pilot has room for his feet and there is space for a 2s 1700Mah LiFe and 4s 2000Mah eneloop, they will be connected with a Schottky diode. If all goes well I can read the voltage on my transmitter.
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Now I could start making the cockpit canopy. In that period it was not possible to make a bubble canopy , so this canopy is made of curved panels, nice characteristic, beautiful (thanks to Thomas for the photo)
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To make the supporting structure I laminated three frames
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and glued them together on the fuselage
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The canopy is secured at the front two pins (yellow arrow) and in the back with strong magnets, both in the hood as in the fuselage. The magnets are glued between layers 0.6 triplex (Black arrow). From 0.6mm plywood I laminated the longerons?
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The canopy was quite a time consuming job, but now the frame is ready for varnishing and glazing.

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 »

Before I was able to sheet the fuselage with ply, I had to do some preparatory work; the topside of the fuselage ahead of the cockpit will be sheeted with narrow strips (like the real one) so I had to fill it with thick balsa
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, and sand it smooth
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. I built the nose itself from 20mm balsa, sanded the side view first, then the top view
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and then roughly into shape
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. I hollowed out the inside further (I had already partially done the gluing of the balsa together) and glued a plastic jar in it. That jar can hold 170 grams of lead.
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What I'm planning is this; when the plane is ready I put the 170gr lead in the jar, I measure how much ballast is needed and then fill the nose with lead snippets and epoxy resin. Then I have the option of removing ballast without cutting it out.
I glued in plywood reinforcements for the rear of the wing mount and 10mm balsa at the bottom of the fuselage where you grab it when you handtoss it.
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Now I could sheet the fuselage with 0.6mm plywood. Until now I glued the plywood with thick cyano, but this time I wanted to try the white glue and iron technique, which I picked up at this forum :) I had already made a few test pieces and it turned out to work.
Because the fuselage at this stage is still very flexible I put it back in the construction frame. I started with a tricky piece, first chamfer the edges with this set-up
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], then smear the glue surface with PVA and let it dry
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. I could now place the piece exactly in place, fix it with clamps and iron it on
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. To be sure, I later applied extra glue on the inside, you never know, this technique is new for me.....

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 »

After that tricky first piece of sheeting, I went on with the top of the fuselage, which was still temporarily attached to the building jig. Scarfing the thin plywood is a time-consuming job, especially if the panels are not straight. I made up a few sanding tools in the hope that I would make fewer mistakes
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By the way, the self-adhesive sandpaper “easy-touch” is really great!
Some pictures of the glueing of the panels, using the "iron" method, which I dared to do, thanks to this website.
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The fit with the scarfed joints, which are also curved, is critical and I don't know if I can work accurately enough. Another problem was that the horizontal (longitudinal) seam was difficult to straighten, I found it difficult to get each panel exactly in place. I temporarily fixed with it clamps
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and glued it with a iron (middle position, 150gr). I decided to make the remaining panels a bit too long and later sand them to the correct length, with another sanding tool
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On the same picture the connection horizontal stabiler / fin is done.
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A picture of the top of the fuselage,
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The fuselage is now stiff enough to remove it from the building jig.

Vincent
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SedB
Posts: 95
Joined: 14 Nov 2019, 09:17
Location: Netherlands

Re: Scratch built Slingsby King Kite 1/4

Post by SedB »

Hi Vincent, what a piece of art you are building here!
Maybe a stupid question, but I was wondering why you will be using different voltages on your batteries? What is the gain or bennefit?

I'm looking forward to the varnishing process (and am curious what materials you'll be using), must be a rewarding part in the build to see all the wood come alive!

Dan
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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 Dan,

Thanks for your nice words!
Surely its not a stupid question, I planned to put two big Lipo's in the nose, useful ballast! But, there wasn't enough space for the pilots feet, so I changed it. I put a 1700 2s Life and 4x 1.5 AA eneloop Nimh in the nose. They are going to be connected with a shottky diode (that knowledge is of a friend), so when the Life is really low, it wil switch to the Nimh cells. In this setup I don't need a voltage regulator, so it should be possible to read the voltage on my transmitter. Hope you like the idea....

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,
After the fuselage was detached from the construction setup, I decided to do the rc part first. It's tempting to continue building, but now everything is much more accessible. I had already more or less made the servo tray and the battery box. To be able to get the latter one out easily I made a kind of clip from 2 layers of 0.6 plywood and a short piece of spruce, which you can unlock with one finger
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Next to the switch I placed the shottky diode, made two plugs for both receiver batteries and plugs for the lead to the receiver placed more to the rear of the fuselage.
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. I ran this wire between the inner and (not yet in place) outer skin
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Behind the backrest of the pilot I made an “holder” for the receiver, antennas and space for the vario
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I had already made the servo tray, I had to glue 2mm extra strips under the rudder servo to make enough vertical space between the actuation cables and rods.
The elevator actuation works with a 1mm steel wire pull / push rod, in a double plastic guide
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To be able to mount and dismount the horizontal stabiler, I made the last 70mm of this rod hinged. I bent a very small eye in the 1mm rod, in which the pin of the quicklink fitted tightly. Just bend a slightly too big eye and carefully make it smaller with pliers until it fits exactly.
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I can lift that moveble part and then attach the other quicklink to the rudderhorn of the elevator. Then the whole stabiler can be lowered in place and the moveble part of the actuation rod comes “in line” and operates without any slop.
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The rudder is operated with two pull / pull cables (20kg strong). They are attached to the rudderhorns of the rudder with self-locking steel wire hooks, so that the rudder can easily be disassembled for transport .
The controls are moving OK, now I can go on with sheeting the fuselage

Vincent
IanT-White
Posts: 27
Joined: 31 Jan 2020, 16:17
Location: East Yorkshire

Re: Scratch built Slingsby King Kite 1/4

Post by IanT-White »

Bovin , It may be better to simply have two Life batteries , each with a schotky diode after its own switch.
This way you have still the redundancy of having two batteries , also same charging regime for both batteries , plus both batteries will share the load.
Its also dead easy to check each battery by only switching one battery on , waggling the sticks and looking at the displayed voltage from the receiver.
You can then switch that battery off and test the other battery . This gives a sort of load test .
To have a battery as a backup and not being normally used , creates problems of its own ,batteries are best used ,also how do you know its going to be ok when you need it ?
One of the big advantages of LiFe batteries is the precise reliable charge that is obtained with a decent charger , no false peaks that you get with nimb batteries and the charge voltage can be seen , usually all the way from about 6.8volts up to fully charged at 7.2 volts displayed on your charger.
Really useful to keep track of how many flights/duration of flights on a flying session , then charge the batteries when you get home and note on the chargers display , how many milli amps were required to fully charge each battery
These values can then be used to calculate say how many milliamps are used , say for a flight or an hour of flying , which gives a good idea of how far you can push your batteries , I use a value of two thirds of the capacity of the battery to have a safety margin and also avoid over discharging the LiFe battery which is something that really needs to be avoided.
I hope the above makes sense and really impressed with your modelling skills.
Best regards Ian Turney-White
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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 Ian,

Thanks for your very good and detailed explanation. This not an easy subject, backups can indeed give someone a false feeling of safety.
I had rather a spare battery in the nose than just lead to get the CG correct. I thought that it was a good idea to choose different batteries, because I can read the voltage on my transmitter (when there is enough thermal activity..) and so to know if I am using the Eneloops or the Life. I choosed the Eneloops because they stay very good loaded ( I don't know the correct term fot that, sorry), for years. So I check them with the start of the season and it has saved me my already one model.
I agree 100% not to decharge more then 2/3. So, I think your are right, but my battery box is just finished, so I leave it like this. Surely I will consider it with another plane, first built and fly this one :)

Bets regards, Vincent
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Peter Balcombe
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Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: Scratch built Slingsby King Kite 1/4

Post by Peter Balcombe »

Vincent,
Please note that connecting multiple batteries to a regulator, or direct to a receiver, via diodes is good practice as diodes pass the higher of the available battery supplies through to the load at any point in time, until they reach the same voltage - after which you will not know which one is being used at any time as they will each switch in and out.

If you are using two different battery types or differently charged packs, then you should be able to see the highest voltage one being used first, until it has discharged to the same voltage as the other. After that, the 2nd battery will start being used more or less in parallel with the 1st, so you are likely to see a slower change as the batteries are effectively working together.

The big advantage with the diode connected supplies is that if one battery is faulty & discharges rapidly or suddenly fails completely, it doesn’t also discharge the others as it is effectively automatically switched out of circuit by its series diode.
A downside is the voltage dropped across the diode, but this can be minimised by using a Schottky type & is outweighed by the redundancy benefit.
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