Scale Soaring UK

The K8 build has started in earnest. Attached some pictures. the tail bits are first. First sorted the parts and checked them with the drawing.
Because it is the first build of this plan there will be little things coming out I did forget to include in the parts or on drawing. This will be rectified as I go.
The parts were not cut by my standard supplier but an other outlet. As a return favor I got it at cost. Apart from balsa everything is cut on 900x300mm ply sheets. the parts stay in the parent sheet by means of little bridges you have to cut with a sharp knife to take the parts out. The overall dimensions means that it can be posted by Australia post instead of a more expensive courier. Also it is a nice flat-pack without loose parts that could be damaged during transport.
Made the stab spar sub assembly. The stab-elevator is fitted to the fuse to scale
Two pins on the stab spar go into receiver bushes in the fuse. Because of space restrictions the pin lugs on the ply spar are not that big. I decided to epoxy a layer of 0.5mm aluminium sheet over the lugs, recessed into plywood.see pictures S2. I do not want to loose a stab-elevator in flight.
The stab is built flat on the board with support stabs on the spar and ribs they will be removed after the top planking is in place.
The elevator is built standing up. The advantage of NC cutting is that with little tabs and holes it all goes into the right place.

Great to see you start this one Jilles. Got someone over here that is going to build this one and the Blanik L13 that you are drawing for me. Have you got the 3d printed parts for the K8 yet? they print very well.

Some progress on the K8 tail bits. The rudder is completed little things to do on the stab/elevator
I prefer a rudder that can be removed when required. There are 3 Robart 3/16" hinges in the rudder. The pin was removed and a 1/16" spring steel rod will fit. The spring steel rudder hinge pin is nearly the full length of the rudder height A 3/32"x0.014 aluminium tube of K&S is located inside the balsa rudder LE between the hinges. This tube will guide the rudder pin so it enters the hinge holes . The rudder LE has a rough radius sanded to it. fine tuning will be rquired when it is fitted to the fin.
The rudder horns are made from 1 mm aluminium strip The rudder complete is 96 grams excluding cover film and paint

Started the fuselage. The fuse assembly is more or less self rigging. half of the formers have a stand/support with an arrow at the bottom indication the center-line. alu angels keeps them in place on the board on top of the drawing top view. The elevator crank and push rod is in place, The rod supported at regular intervals in the fuse. The free movement of elevator was checked.
With the laser cut files it all goes together fast. Now the little items can start and will take some more time

This model can either be towed or takeoff under its own power on a dolly
the Brushless motor will be a permanent feature. On the field I can remove the prop assembly and change the nose cone from the motor to glider configuration. The motor shaft will then simulate the dynamic pressure tube as scale details dictates.

some progress, I fitted balsa support between the front formers at the top in front of the canopy opening, this is a considerable compound curve. Instead of fitting ply strips and sanding I decided to glass the surface. Less work and actually as per original. The fin has been planked with 0.4mm ply and all the other top planking is in place. The supports on some formers for building the fuse on the building board can be removed but it is easier to leave them on while building the canopy frame
After the canopy frame is completed I will turn things around and finish the bottom planking.

Nice work jilles!!!,l was very interested to read that you have access to "aluminium angels"for the fuselage build ,a little divine assistance perhaps ,maybe you could send some to cliff ,stay safe,jack.

jack wrote: ↑29 May 2020, 17:13 Nice work jilles!!!,l was very interested to read that you have access to "aluminium angels"for the fuselage build ,a little divine assistance perhaps ,maybe you could send some to cliff ,stay safe,jack.

You can get the angles from B&Q! I know it's difficult for you as you don't get out much!

Next report, the fuse has been set aside because it is as good as complete.To finish the fuse I need wings. Started with the Air brakes. They are Sempth Hirth type, means top & bottom, they are scratch built because ready made are is available to scale . I had brass arms in mind but had them 3D printed. In the Uk they made one arm with a spline hole so they are direct mounted to a servo. I decided not to go that way. Brass bushes are super glued in the arm to make them wear proof, These are just standard K&S brass tubes.. the blade sides are 0.8mm ply NC cut with a 1/4" balsa bar between those. 0.8mm ply washers are glued inside the blades for increased bearing surface to fix the blade pins. I had these also NC cut. Needed only 16 but had 20 cut in case some got lost. Of course
when you have spares you do not need them.

The LH wing spar was pre-assembled, and secured to the building base. the webbing have little supports so the spar is at the correct height above the board.
The ribs have the same supports so all will be nice and straight.

Got to see the finished uncovered fuselage last night, very nicely built. Looking forward to seeing it covered Jilles.

The L.H. wing is well underway a support for the TE was setup. ribs in place and top spar fitted. Between the main ribs in the D-box is just foam for the 1.5mm balsa planking support. This works form better than half ribs. Foam blocks are cut into shape with a foam cutter with the ribs as guide. Weight is not an issue compared to balsa half ribs
The TE cross section is a sandwich or 1.5mm balsa at the bottom. a chamfer 10 mm at the rear edge. a 10x0.5mm carbon strip at the rear edge, an ex 3mm balsa core and 1.5mm balsa top..Cost a bit of time but compared to the total build time not an issue
In my view it has the following advantages, the TE stay straight, it is stiff and dent proof.
pictures and TE cross section attached

it has been a while but the l.h wing is now complete. After fitting the top balsa planking the wing was removed from the board and building tabs cut of from the bottom. In the NC laser kit are 9 mm balsa supports to supports the wing upside down on the building board. These are shaped to the wing top surface with 1.5mm balsa planking included There are 5 in total and they are numbered to the rib position they need to be located. These supports help to keep the wing straight when fitting the bottom balsa planking. Some weights are placed on top of the wing to keep the wing in place, These supports add a bit to the cost of the NC kit but saves a lot of time in setting up
3D printed tips sections are used. the rear edge is twisted upwards to make thing to scale.
Next is the Rh wing I will not bother you with a story on that one. All the same, just have to make sure I do built a RH wing. I heard a story that some modeler built two LH wings by mistake.
I will continue the thread when the second wing is complete. it will take a while.

Jiles, lovely glider but I do wonder why you foam fill the D box between the ribs ? The rippling between the nose riblets and the ribs is a feature on the full-size. The rippling on my quarter scale Charlesworth K8 0.4mm wing skins looks scale to me. Regards John.

John Vella wrote: ↑20 Jul 2020, 09:17 Jiles, lovely glider but I do wonder why you foam fill the D box between the ribs ? The rippling between the nose riblets and the ribs is a feature on the full-size. The rippling on my quarter scale Charlesworth K8 0.4mm wing skins looks scale to me. Regards John.

Mainly to stop you putting your fingers through!!

On that subject be very careful who you have launching (handling) your glider. Regards John.

Nothing to do with that John! Just putting it together!

Cliff is right on the money. Because the planking is 1.5mm balsa and the distance between ribs to scale (wide) the foam is to prevent damage by pushing fingers through and by transport. The foam is not fitted over the full length. From root to start of aileron and the last three rib bays near the tip. The balsa is not glued to the foam, only to the ribs, the foam is only for support when pressure is applied from outside. You will still see the ribs when painted.
The rippling effect is a feature of the full size but only when they get older. Schleicher made high quality gliders with a nice near perfect finish.
Over the years the rippling effect appears due to handling and varying stresses during flying.

Jilles, now that makes it clear that the foam is just for support and not bonded to the skin, clever idea. I have done many hours in the K8 and have great regard for the glider. Regards John.

Just something to keep you up to date. The last wing is nearly completed than the construction of major parts is done. I made a plug to vacuum the canopy. As mentioned earlier I do built the K8 with the smaller canopy that was later replaced with a full canopy with the K8B. Reason was that most model around have the larger canopy so it is a kind of novelty. Also the smaller will fit my vacuum forming machine. I started the plug with some 5mm craft wood formers as a guide, Filled the spaces in between with pine blocks and started shaping the thing. When happy with the result a layer of 80gr/m2 glass with epoxy resin was added, and after that on other layer of epoxy resin. This was sanded smooth with 240 grid wet sand paper. an other layer of epoxy resin was applied and then final sanded with 240-800-1200 grid sand paper and lots of water. Got it very smooth.
In the coming days I will try to form a canopy or two. I do use 1mm clear PETG, Vivac is the brand name. It is only available in 2.4x1.2m sheets at $50 Australian. Got already lots of interest to buy parts of left overs from me.

managed to get the canopy vacuum formed but was only successful on the third attempt. The first two had lots of folds everywhere so I was a bit disappointed. On these attempts I had the vacuum cleaner on before I dropped the frame with heated clear Vivac on the plug.
the third time I dropped the frame over the plug without the vacuum on The plug was formed for say 80% by its own weight without folds, then the vacuum was switched on and it all came good. Maybe this is how it is supposed to go but I do not have much experience with this
With the vacuum switched on before dropping the plastic it may go all to fast and the plastic does not get time to stretch were required.
Maybe somebody in the know can give us some light on this

When at Sarik hobbies and watching them pulling canopies, the vacuum pump comes on after the plastic is pulled over the mould so, yes get the plastic down over the mould as far as you can before turning on the vacuum. Perhaps Barry from Sarik could advise.

Jilles,
How do you heat the PETG?

the PETG is heated by an old Oven grill. on attached picture you see the top structure of my vacuum machine, the grill is housed in the timber structure.
The knob shown is the on/off and thermostat. The aluminum window frame with PETG is hooked to the top. It forms then a closed box. With the thermostat the heating is controlled by increasing the heat slowly. This way the PETG sheet is evenly heated.
When the PETG comes down from the frame half way the plug during heating I lower the frame. With the K8 canopy it was the first time the frame was lowered completely to the foam seal on the bottom before applying vacuum.
It was the first time I made a canopy this big and using PETG. Previous material I used for smaller canopies was not satisfactory. During heating it formed small air bubbles inside the plastic regardless of slow or fast heating. These bubbles stayed visible in the finished product.
This PETG is perfect. I use 1mm sheet.
Before I get any smart comments, the picture of the frame shows the PETG with cover film still attached. This is to prevent damage to the surface when fitting the PETG to the frame, And yes it was removed before the heating process.

Thanks Jilles, that explains it well.

Hi Gents,

The build is looking fantastic and I am pretty impressed with the PETG canopy forming doohiccie thingymabob.

We are still just about to move house here so no progress from me for a few months, damn COVID.

Have a great day everyone.

Steve

All major components are completed. Today I had the first total assembly. all fitted as was intended, not so difficult with Laser cut parts.
The elevator has a sort of working trim, it moves up or down opposite to the elevator movement like the full scale. It is not used to trim the model the TX will have to take care of that. The nose cone and wing tips are 3D printed. A decent sanding job and some detailing will have it ready for the cover film, fabric or Ikarex. Not sure yet what to use

Very nice Jilles.
You’ve made a good job of that

As usual, very nice Jilles.

The covering of the K8 has started. I use Icarex. There is 10m of red and yellow in stock so just as well use it. It is1.4m wide so plenty of area.
The fuselage sides and bottom were simultaneously covered with a one piece of Icarex. There are no formers at the surface to make overlaps so it had to be in one go. SIG Stix-it was used, the last I had . Fortunately by the end of the week I will have an other tin from the hobby shop. I did try the Deluxe Materials Cover Grip ( formerly known as balsalock)
It works fine but I think Stix-It works better with Icarex. The red is not the final color. The plane will be mainly sprayed white or off-white with a red bottom

attached some picturesof the current progress. Fuselage has been painted. The wings are covered to be prepared for painting. Canopy glued to the canopy frame
I have two 3d printed nose options
One for pure glider and one for a folding prop. Both options can be towed. With the prop I can take off from a dolly
The motor and the lipo battery stay always in the glider as part of the ballast. The pure glider nose has some ballast added to make it the same weight as the folding prop option.
The tube on the glider nose around the motor shaft is actually to scale. On the full scale it is the pickup tube for the dynamic pressure to be connected to the speedometer.
The motor is programmed so that it cannot run when the tow release is closed. When the line is released it will take 2-3 second for the motor to run. Just to make sure I do not wind the tow line around the prop. Curtesy to programming a Taranis TX

That looks B****y lovely Jilles.

Hi all, The Ka8 build project has come to an end. Today I determined the required ballast to balance it properly. I used an online COG calculator that from experience is very good. 114 mm from the L/E was the result. total weight is now 6908 grams, just a little 100gr under the 7kg inspection requirement here in Australia. This is 1 kg less then my Ka6E of the same scale. Different building techniques I adapted after the Ka6E built 4 years ago made it lighter but with the same structural strength
The wing platform is the same as the Ka6E but 10% lager so overall I expect to fly the Ka8 nice and slow. Also programmed the radio. The profile of all my vintage glider designs is HQ35%% and do not have a washout. This is a feature you can allow with this profile. Just for additional stability both ailerons have a reflex of 4mm up mix when the air brakes go open . This creates an artificial washout during landing with still full aileron control.
If it was not for my trip to Hamilton Island this weekend the maiden would have been this Saturday. It will now be sometime next month I hope
Some pictures attached. The airbrakes are left open for a while because the paint is fresh and still curing. If the airbrakes were closed they will be stuck in a couple of weeks from now. The pictures show the glider nose cone. I can fit a folding propeller on the field is a minute or so and take off under onboard power on a dolly. The brushless motor and battery are always fitted in the nose and are part of the balancing weight

Very nice Jilles.
I’m sure that all will go well with the maiden in due course

Lovely plane!
I flew the real PH 294 ...36 years ago! At EACz , Eindhovense Aero Club zweef..
There were 3 K8, the 294 indeed with the small glass canopy. I preferred the 371 and 353, better view large canopy versions...
It looks exactly like the real thing, only giveaway is the lacking grip on the fuse just before the tailplane..

Tjarko.

Jilles, the lifting handle that Tjarko mentions is very easy to model. It sits above the left hand longeron just in front of the tailplane. A halve quadrant of plastic coated wire attached to the longeron does the job. Regards John.

I know about the handle at the back of the fuse. I was a member of the EACZ as well from1961 to 1975. I did fly the 294 and other two Ka8 models that were in the club then. The color of the full size 294 was just white. I like the white and red of the model, it makes it a bit more visible at height. The logo did not exist in that time either, the came later when Schleicher started to add the prefix AS before the model type. This feature started with the ASW15 the first Schleicher glass glider ( or plastic as it was called in The Netherlands)
it is not a museum model , it has to fly . Items you do not see during flying were not added like the handle and a full cockpit layout.
Those who want to build this model can add details as they see fit. The model had originally a moving trim tab on the elevator until I discovered that the connection rod interfered with the rudder horn so that was deleted and the trim tab is fixed.

Gorgeous, I love it! The colour-scheme suits the model great!!

Just pulled the first canopy from the new mould. New system in making the mould seems to have worked!

That is a big canopy.

I hope the ASK13 has as good a finish on it!

It's not that big!

Another Jilles Smits K8, built by Allan Wales from Wakefield.