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Gentle Curves - Lucas his Skywriter

Build blog - MB2017 - Skywriter

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Lucas Hofman05/02/2017 14:36:16
668 forum posts
375 photos

Nope. Take a look and compare the pictures:

img_3653 (small).jpg

making a big hole in the aft side of the cockpit is not clever. Happily I keep all those pieces (Dutch...) so I could easily glue it back. Especially since the front will not be covered with film but glassed/painted a hole there is not desired.

Starting on the wings now. Well, starting to cut ribs. By the way, would it be needed to make the ribs that hold the struts in 2mm light ply? I think, given the size of the model and the flexibility of the struts, that that is over the top. What do you think?

Lucas

Edited By Lucas Hofman on 05/02/2017 14:36:51

john stones 105/02/2017 19:59:30
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11507 forum posts
1516 photos

I went with balsa, may get a ply doubler where the fixing plate is, i don't see it as a weakness though unless you have a bump.

John

Chris Barlow06/02/2017 00:27:33
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1904 forum posts
1308 photos

You could leave the cut out in F5 and just cover over it with film?

I didn't bother with the step in the fuselage sides bit it will help when sheeting the top deck.

BTW I like where you're going with the cabane struts Lucas! yes

Lucas Hofman06/02/2017 08:50:02
668 forum posts
375 photos

Chris, I would if I would have planned to cover the model with film. But the front of the fuselage will be glassed and painted, and then a hole undesireable.

Blanks for all ribs are cut:img_3654 (small).jpg

Thanks for the tip about using pins to fix the balsa under the template, that this make everything more accurate. How do you make (varying) cutouts for spars, so that they line up?

Lucas

McG 696906/02/2017 09:28:06
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3232 forum posts
1225 photos

Hi Lucas,

Very nice & neat progression there.

I don't know if it can be of help, but for my Ballerina ribs, I made some cuts in my template to mark the place of the notches, using the pin trick as well to 'prick' through the Depron.

1763_test_ribtemplate_900.jpg

The cuts were transferred - or not - to the foam where needed depending on the placement of the rib in the wing.

I also used an ali tube to cut some holes in each rib allowing me to align them easily for the finishing and also using the holes later for the servo wiring.

1772_test_ribs_sanding_900.jpg

Regarding F5, I think Chris has a point there. As you will be covering the aft deck anyway why not leave the hole and 'cover' F5 as well as your glassing will stop at the side stringers anyway, also gaining a bit of weight behind your CoG?

Cheers

Chris

Lucas Hofman06/02/2017 09:56:47
668 forum posts
375 photos

This is a really good idea Chris!. I can make multiple vertical cuts for the different types of ribs and then use these to cut trough a "block" of a certain type of ribs. The horizontal cuts go easily with a chisel type of knife. Thanks!

Lucas

ps. I try to make a tube to make holes in balsa but did not manage to make i sharp enough the wood would not crush around the hole. How did you make the tube?

McG 696906/02/2017 10:22:04
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3232 forum posts
1225 photos

Really glad that it was a bit of help, Lucas.

As you wrote, if you group the needed ribs of each kind, it works quite fast. But - knowing me - I made a few 'spares' anyhow... blush

1850_wing_ribcutting_900.jpg

For the holes I cut a small length (60 > 70mm) of ali tube and glued a 'protective' bit of hardwood on top. Cfr bottom left of picture.

The inside edge of the tube got simply sharpened with a Dremel sanding drum. For the Depron, you don't need any 'teeth' filed in but for balsa use it could be helpful to have 3 or 4 teeth filed in. Also maybe a brass tube could be better for wood. In order to save my cutting mat, I also used some sacrificial bits of foam under the rib while cutting through by slightly 'turning' the tube in both directions.

Cheers

Chris

Lucas Hofman07/02/2017 07:42:24
668 forum posts
375 photos

An evening with preparation for building the upper wing:

img_3655 (small).jpg

Making two new "slotter for sanding the bottom of the spar slots to depth (sanding paper is glued to the 1/4''x1/2'' pieces with double sided carpet tape):

img_3656 (small).jpg

Cleaning the building board and taping down the drawing. I printed one copy as a mirror image to have left wing halves:

img_3658 (small).jpg

Tonight pinning down the lower sheeting an glueing the lower spars on the sheeting. And then we will see if I manage to sharpen a tube to make holes in all ribs.

Cheers, Lucas

Steven Shaw07/02/2017 14:35:44
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366 forum posts
191 photos

Extending the rib location lines on your print makes it easier to line the ribs up on the spars.

Lucas Hofman07/02/2017 14:59:33
668 forum posts
375 photos

They are extended Steven. To forward of the leading edge and aft of the trailing edge (you see them ending in the aileron/filling piece.

Edited By Lucas Hofman on 07/02/2017 14:59:44

Lucas Hofman08/02/2017 07:31:24
668 forum posts
375 photos

Lower sheeting for the upper wing done:

img_3664 (small).jpg

Clean and easy work, and quick results. Spars and ribs will be next.

 

Edited By Lucas Hofman on 08/02/2017 08:40:35

Chris Barlow09/02/2017 02:31:02
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1904 forum posts
1308 photos

Very methodical and tidy Lucas. yes

Whenever I build wings like that I draw on the rib positions on the inboard sheets to help line them up. Positions on the cap strips is easy so I don't mark them!

Lucas Hofman09/02/2017 07:25:49
668 forum posts
375 photos

Thanks Chris.

If you look at the picture below you see the little dashes sticking out under the front and trailing edge sheeting. I remembered (when drawing) that the Ballerina drawings where lacking that so I extended the rib position lines.

img_3663 (small).jpg

john stones 109/02/2017 17:56:37
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11507 forum posts
1516 photos

I forgot the cap strips, nice long board Lucas yes

John

Lucas Hofman09/02/2017 19:50:24
668 forum posts
375 photos

Nearly 2m John. Plasterboard (cheap, flat and accepts nails well on plywood. Placed on a cupboard on wheels, so I can move it around to get the light on the spot where I work. Over the top for this size models, but handy when setting up an F3A plane.

Made holes in all ribs for the upper wing tonight. I do not manage to make a hole puncher that makes nice holes. Always wood braking out at the back. So I resorted to the (for me) proven method of clamping 4-5 ribs together and using a routing bit in a dremel to make a rough hole. Then make it round with a sanding drum. That took about an hour for all ribs, and most have more than one hole.

Finished by glueing the lower spars in place.:

img_3665 (small).jpg

As you can see I use the spars to support the tips. On hte ballerina I had one tip breaking away (before the covering was in place). I do not know yet whether this will work but I can always cut them off.

Lucas

Edited By Lucas Hofman on 09/02/2017 19:52:18

Lucas Hofman10/02/2017 21:21:10
668 forum posts
375 photos

Every day a little further. It starts to look like a wing:

img_3667 (small).jpg

Lucas Hofman12/02/2017 16:23:03
668 forum posts
375 photos

Som may have seen that there were a few ribs missiing in the picture above. These are the second halfs of the rib pairs that hold the brackets for the struts. (note this is not standard Skywriter, this is my construction). I have created "pockets" with some 2mm balsa:img_3669 (small).jpg

The lugs will be from 15x2mm Aluminium strip, the same the struts are made of. But they will not be glued in place before the covering is in place.

Center section with most in:

img_3671 (small).jpg

Spar doublers are tapered to avoid stress concentration points. Sometimes it is difficult to hold bits in place when sanding. I find that a sanding block with a coarser grade than you are sanding with hold them fine:

img_3668 (small).jpg

john stones 112/02/2017 18:00:40
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11507 forum posts
1516 photos

Coming on nicely Lucas, not decided on strut fixing yet, mine might be an ali plate glued in after covering.

John

kc12/02/2017 18:50:15
6497 forum posts
173 photos

Cutting holes in balsa.

The tube cutter should be sharpened on the INSIDE not the outside. It cuts better with a couple of hacksaw cuts across the rim. It is not used as a punch but rotated by hand. Needs a balsa or other backing to the hole to get neat edge.

Lucas Hofman13/02/2017 07:02:08
668 forum posts
375 photos

I will give it another try kc. The tube was sharpened on the inside, but may not enough cuts or pressed to much instead of rotating.

Another hour last night saw the spar webbing coming in place (this is not on the original drawing, but adds a lot to the torsion stiffness of the wing without adding much weight).

img_3672 (small).jpg

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