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Old Nov 11, 2012, 11:53 AM
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Schapel Sa882

I thought you might be interested in my winter project. A couple of months ago a parcel arrived with a set of milled ply ribs and spruce spars arrived from Andres Chavarria for his Schapel design that I was wanting to make for one of my small turbines. I am not sure that anyone else has made one of these small fast little Horten like planes.

The first task was to buy a 2.1m piece of white melamine board so I could follow his method of building. From the outset it was a good decision as Andres had put a lot of thought into the design making it as simple as possible. The design was for small turbines but I guess it would work just as well with a pusher electric prop.

The ribs come with strips and sub ribs attached. The white melamine is marked with pencil lines where the ribs are to be glued on. The ribs are 71mm apart and need to be set accurately in place so the sub ribs are lined up with the front of the white melamine sheet. I used hot glue in blobs to secure the ribs in place holding the set square while the glue goes hard. The hot glue will break off the white melamine quite easily and I also made a fillet of white glue between the bobs of hot glue.

The sub ribs give the accurate sweep back, provided they are spaced correctly.
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Old Nov 11, 2012, 11:56 AM
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Ribs glued on the white melamine board that has pencil lines for the rib locations.
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Old Nov 11, 2012, 12:00 PM
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Close up of the rib fixing. The centre rib is made up of a sandwich of 3 ribs glued together. The centre rib is a special dense 3mm ply sheet that is not commonly available, but is used in German plane making.
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Old Nov 11, 2012, 12:02 PM
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The rib sandwich needs weighting down while the glue sets.
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Old Nov 11, 2012, 12:02 PM
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Should be a fun project John and a screamer too. With one of your turbines, it should be a stunning model. I hope we see lots of construction photos on this one. It's always interesting to see how each modeler adds his own touch to Andres's well practiced construction method.

Kent
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Old Nov 11, 2012, 12:05 PM
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The first job is to attach the thin spruce strip to the nose of the ribs. This helps check alignment of the setting out. Andres supplied 'combs' so the ribs could be held in place at 90 degrees. A nice touch.

The ribs have 1.6mm ply fixed to the rib nose after sanding.
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Old Nov 11, 2012, 12:09 PM
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The main spar can be started now. It is a sandwich of 9 3 X 5mm spruce spars sitting on 2 layers of 2mm special dense ply. The layers of ply are glued in place first after scarfing/splicing the joints. These are cramped in pace and left to dry.
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Old Nov 11, 2012, 12:22 PM
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The spruce spars need bending round and because they are flat, they are not easy to hold in place especially when fitting them. I followed Andres suggestion and soaked them in a hot bath for 45 minutes and cramped them in place overnight. The next day they had assumed the shape and could be reasonably easily bent into place. I trimmed the ends so that joints were staggered over 2 rib positions and also scarfed. Also each layer alternated. I carefully marked the parts with location before gluing them in place.

This is the worst job of the build and is messy as glue gets on the hands while making sure all the spars get a good coating of glue.

With the whole lot in place it really looks like an archery bow. This structure is immensely strong and there is no carbon in sight! I cramped the upper spar in place and left overnight to set the glue before tackling the lower spar.
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Old Nov 11, 2012, 12:25 PM
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Kent

I am posting as I go along after getting to the main spar stage so not sure how quickly I will get it done. Yes I agree we can all learn from each other. I love the German scratch building with balsa and ply, the parts are well thought out and always use the best materials.

John
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Old Nov 11, 2012, 12:48 PM
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Today I fitted the lower spar in place. This is possible because of the way that the nose of the plane overhangs the white melamine. However it is far from easy and is messy. It is a repeat of the upper spar but everything is being done from underneath and cannot see what is happening. It took a lot longer than the upper one but eventually was wrestled into place, ignore the bobs of glue in the photos!
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Old Nov 12, 2012, 04:30 AM
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Last night I soaked the spruce rear spars and cramped them in place. I have just glued them in place. This is getting fun now.
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Old Nov 12, 2012, 05:18 AM
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Nice Work John!

Andrés
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Old Nov 13, 2012, 12:23 PM
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Not done as much as I wanted today, but most of the main spar has its shear web. The web is on both sides of the spars and is thin ply sheet with the grain vertical.
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Old Nov 15, 2012, 11:39 AM
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That's an amazing build Jon. I'm looking forward to following the rest of it and reading of the first flights.
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Old Nov 15, 2012, 12:45 PM
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I am now ready to start sheeting with the ply. I have added balsa caps to the spars and sanded them down as well as sanding the leading edge. Tomorrow I may start the sheeting.

Both spars have ply shear webs glued on both sides.
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