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Mar 15, 2007, 07:22 PM
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Build Log

Scheibe-Loravia Build Thread


Ok, guys....I've sat on this long enough and have finally made enough progress (and got to the interesting bits!) to start a build thread. I became interested in the Scheibe SF-27 some years ago when a plan was published in QFI by the late Mick Moore for a 2m version of the SF-27. I ordered the plans and started drawing, but it was waaaay down my list of things to do. A letter to Mick gave me some more info and I started gathering detail for the future. I have been globetrotting a bit and haven't had a decent workshop until recently, but finally I do, so started things going again.

The SF-27 was built under licence in France as the Scheibe-Loravia, with a few enhancements over the original SF-27, and that is the version that I have decided to build. I'll start with the three-view, and a couple of pictures of the full-size plane that I have decided to model.

Bear with me, as my building rate is pretty slow, especially with many spring house projects to make right, but my target is to be flying this one at the Skagit Aerotow in September. September 2007, I hope!

Hope you enjoy...

Dave Smith
Last edited by Seadog; Mar 15, 2007 at 07:28 PM.
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Mar 16, 2007, 01:03 PM
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That's a nice looking plane. Should gather a lot of interest due to it's uniquenesss. Looking forward to the build thread.
Mar 16, 2007, 01:06 PM
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Wings


Here are the first couple of shots of the wings coming together. All the ribs were plotted using Profili, printed, and the patterns glued to sheet stock using a glue stick. Used on balsa, the glue stick allows you to peel off the patterns without residue; on ply if you leave the patterns on too long, you may have to fight a bit to peel them off, but ultimately it can be done.

Rib stock is 3/32 balsa and the inner four ribs are 1/8 ply. Rib blanks are rough cut out of the sheets (i.e. within 1/16" of final line) with an x-acto (scroll or band saw for the plywood), and then I use my 8" sanding disc to sand down to the line. The band or scroll saw is then used to cut notches. It sounds tedious to create 60+ ribs, but in fact you can make the full set of ribs in a couple of evenings, which isn't a huge investment compared to the total project effort.

Spars are 1/8 x 3/8 spruce. You can see in the pictures that the outer half of the wing has bottom sheeting whereas the inner half is (mostly) open. For the outer half, I originally tried to shim the trailing edge to the right height, but I was unable to accurately fit the bottom sheeting to the undercambered rib bottoms. In the end, I cut mirrors of the undercamber and pinned them in place at each rib position, then set the sheeting over them and when the ribs were glued in place, the sheeting was sandwiched between the rib and the mirror, with the right curvature. Again, it sounds way more tedious than it actually is.

In the first picture, the ribs have not yet been glued in place and you can see the undercamber gap between the bottom of the ribs and the sheeting.
Mar 16, 2007, 04:33 PM
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Quote:
Originally Posted by Seadog
In the end, I cut mirrors of the undercamber and pinned them in place at each rib position, then set the sheeting over them and when the ribs were glued in place, the sheeting was sandwiched between the rib and the mirror, with the right curvature. Again, it sounds way more tedious than it actually is..

If you have a hot wire cutter you can cut a bottom building "form" from foam to match the airfoil.....place the plans over it......and build on that. I did that with my Minimoia and it worked great!
Mar 16, 2007, 04:59 PM
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Yeah, I know. I have thought of that approach....but I am just a balsa and ply guy. No hot wire cutter, and anyway the bits only took me 1/2 hour or so.

Dave Smith
Mar 16, 2007, 05:10 PM
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Dave, your wing construction method just about mirrors my own, I could have written the foregoing...!
One slight difference though: if you white-glue the bottom of the ribs, but leave a small gap, maybe two, at the point of max undercamber you can then lift up the wing, squeeze the sheeting to the first rib and use penetrating cyano to 'pin' the sheeting in place whilst the real glue dries, working your way along, of course...

cw
Mar 16, 2007, 05:16 PM
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Update


No, I don't really build this fast, but here is the next wing update. As I didn't take any pictures during the intermediate stages, there is a bit of a gap, but here's what happened between the first pictures and now.
  1. glued ribs in position, using the aforementioned cambering foils to maintain undercamber shape
  2. added shear webs
  3. added top spar
  4. filled in box around brass wing joiner box
  5. added bottom TE on the inner half of the wing
  6. added 1/4" wide .014 CF along entire TE
  7. cut ribs and added sub spar and aileron LE
  8. cut ribs and fit air brakes
  9. added 1/8" ply mount for spoiler servo and mounted servo
  10. made up extended servo leads and put the aileron servos in place. They will be covered over and then access hatches will be cut later to finish installation

Dave
Mar 17, 2007, 02:13 PM
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Details..


Close ups of the airbrake servo, airbrake, and aileron servo location with aileron leading edge and sub spar.
Mar 17, 2007, 02:21 PM
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Leading Edge Sheeting


Leading edge sheeting was applied by first gluing it down to the main spar with carpenters glue, holding it firmly in place with my colourful clamps and a couple of meter sticks to provide the pressure. Once the glue dried, I painted the rib tops and underside mating surface on the sheeting with 50/50 mix of water and white glue. Then, ran a bead of full-strength glue along the false leading edge, and lashed down the sheeting with masking tape in between each rib location. Then, heated up my covering iron to hot and ran slowly over each rib location to kick and seal the glue on the ribs. Works like a charm!

(Note that the little grippers on the clamps have been flipped open, which gives a narrow, sharp pressure point to allow them to grab skinny little spots. If the clamps had their pads flat, they kept slipping off.)

Dave
Mar 17, 2007, 02:28 PM
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End Results


Jumping ahead a bit, the wings now have the sheeting applied behind the spar on the tips, and the leading edge attached.

Final shot show the two wings in their current state: additional sheeting applied at the airbrake position and capstrips completed. Remaining to be done: tips, cut out ailerons, bevel and hinge, and open up the servo position, mount servo and cover.

I didn't mention previously, but before sheeting the tops, I mounted two tow hook positions just ahead of the spars near the root ribs, just in case I want to winch. Also didn't mention that this build is at 1/4 scale of a 15m sailplane, so will yield a 3.75m (147") model.

Dave
Last edited by Seadog; Oct 25, 2016 at 03:01 PM.
Mar 17, 2007, 05:16 PM
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nice work seadog good to see the traditional art of balsa bashing is still alive and well in the times of arf plastic.
Mar 23, 2007, 12:01 PM
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More Progress


A few more progress pictures attached. First the ply parts cut out and on display. In fact, although the pictures I am going to add show a nice orderly series of building steps, reality was different. I have drawn up my own plans and as you will see shortly, documentation from different sources was significantly different. The result is that I had a number of cuts and recuts on the formers to get the shape and the lofting looking right. I may not be quite there even yet!

Also, all the "building" shown in the following pictures has been done without glue; just clamps here and there. I like to design with interlocking pieces where I can as it gives me some extra strength (I think) and also allows the trial fitting that is shown here. Just a big jigsaw puzzle. If it were ever laser cut, it would lend itself to easy assembly as well.

Dave
Mar 23, 2007, 12:09 PM
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Fuselage work continued....


The wheel fits between a half-former and the main wing-mount former. A couple of sides are made out of 1/8" ply, locked into the two formers. 1/32" ply will go around this and mate with the keel, to enclose the wheel and keep the inside of the fuselage from filling with either bits of grass, or water.

Dave
Mar 23, 2007, 12:19 PM
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Discrepancies...


Here is where the drawing/redrawing and cutting/recutting comes in. The blue outline is the cross-section of the fuselage at the back of the cockpit from Martin Simons' three-view. The green outline is from the plans that were developed by Mick Moore from measuring a full-size plane. Probably neither are exactly right, but it looks like Mick's may be close based on a lot of photographs I have of 1:1 aircraft. The problem is that Mick's plans were for a lightweight 2m version, and don't translate into 1/4 scale very neatly, particularly with respect to former positions, so I have basically had to reloft things, making some assumptions about the cross-sections. Most of it turned out OK, but I did have to redo the center 3 formers to get a smooth flow, especially on the bottom half.
Mar 23, 2007, 12:23 PM
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Root Rib


Root rib trial fit. Tabs on the front of the rib fit into former #4, for alignment and strength. Notches mate with the formers at the rib center and near the TE. Hole for brass box not yet cut.

Dave


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