SFS 31 Milan

[Noël Rumers]

I believe I first have to explain a bit my wing design before I move on...
Enclosed a few PDF files that I made in the time I designed the SF27.
This was the best way to explain it now too.
Noël

[Noël Rumers]

The wing was now so far ready that the fake spars and the so called gutter was in...
Now the shear webs could be made and put in as well. At the root, where the wing joiner is, the shear webs are 1.5 mm ply. The gutter at this point is also made from 6 mm ply the same distance. The rest of the gutter is made in balsa, simple and good.
The shear webs are printed in Compufoil, so I know how high they have to be. The grain of the balsa has to be upright !!!
I calculated the total amount of wood I needed to make all the webs. The strips of balsa were glued together on a piece of scrap paper where the glue didn't stick onto. All was sanded a bit and the strips were cut by my old ruler and knife.

[Noël Rumers]

With the shear webs cut to height the job comes easy to make them to fit between the ribs. Note that it is not that important that the webs fit 200% between the ribs... I leave some room 1 à 2 mm so I can get them in easily
I use the back of the knife to mark the cutting line. Goes fast, just push the strip from one side mark of a wing rib, to the other side and mark the next length, etc, etc... afterwards just cut the all and keep them in line for the height!
I glue them in fast first one side than the other side. I have two shear webs in, they outline the gutter very well.
At the wing joiner only the front part is glued in!!!

[Noël Rumers]

The next step is the wing joiner part.
here the shear web on the back side must be put into place.
For me it is very important that the top and bottom spars, can't move to each other lengthwise at all. the wing would break if that was possible.
So to make a strong point I fill the gap around the wing joiners always fully with thickened epoxy with micro balls or cotton flocks...
Maybe overkill but that is what I do... I can lift one wing tip and take the fuselage of the ground that way, I am happy.
The next step is to cut glass roving to length, soak them with epoxy and lay them in the gutter. On top a balsa strip is pressing everything down so the roving are squeezed from shear web to shear web front and back and I leave a small gap too, so the roving are squeezed in there too. This way I get a kind of “ I ” or ” U “ shaped real spar that is very strong. The epoxy glues everything together in the end!!!
The balsa strip is grinded down to the shape of the wing ribs afterwards. Ready to build in the rest of the top wooden parts now.

[Noël Rumers]

How I know that I have a strong spar ...
Well I did build this one a few years back...
Flying on another field ...I still can cry one eye out, there was a small tree...I hit it with the LH wing tip...
This was not such a good idea in the end.
What I learned from the bits that I had left, and I had more than I build into the model...
The spar was still fully there!!!
But that wing I kept it, now it is repaired to flying conditions too. Waiting for a new designed fuselage of a very strange bush plane...
The Lawhorn Kee Bird.
See the rebuild...

[Noël Rumers]

... and more...
The model was the Boeing Scout, only 12 build and one back into flying conditions! I was in contact with the owner builder in Alaska for detailed info.
It happened that the same wing of the Boeing Scout was also used to build the very special Lawhorn Kee Bird. The designer/builder was also living in Alaska. I was able to track him down too and have now the original drawings, pictures and much more to build that plane as a model instead of the Boeing Scout! I hope to finish that model too by the end of this year!
Noël

[Noël Rumers]

...I must say, the Boeing Scout was the weirdest thing I ever have flown! Very stable and a very strange set-up...
The New one will beat that experience I believe...

Now back to the Milan.

The airbrakes box was build in together with the wing retainer system.
A special alu hook was made to fit the system.
With these things ready the top sheeting was the next step to do...

[Noël Rumers]

...for the sheeting of the wing, I used 0.6 mm ply on the root side and 0.4 mm on the tip side of the wing.
Holes are cut so not all of the wing was covered with ply.
The wing tip however is sheeted fully with ply top and bottom.
Until now no worry about the twist in the wing. The only thing I did so far was when the epoxy spar went in, let the epoxy harden with the wing flat to the table.
Now the top sheeting will go on the same way with no extra help... this comes later only for the bottom sheeting...

I drilled in the corners a hole so I could cut with my knife easy the rest of the holes where the cover material had to be ironed on.
I know again that I could have saved material, but all the joints grinding them down an gluing all perfect takes a lot of time too.
The joint at about mid wing was grinded down to have a almost perfect top surface.

Know that you have to mark the ribs on both the top and bottom sheeting before closing one side. It save a lot of extra work...

[Noël Rumers]

...to glue the sheeting on I always use contact glue.
Look at the pictures of the Boeing Scout wing that had been beaten... the glue was still very firm on the bits that were not torn off!
So I like this system. You cover all on the top wing in two parts, first the root part and later the tip part with contact glue.
I rub it down with the toothed comb that comes with the glue.
Then I glue the sheeting also the same way.
I use a sheet of baking paper to prevent the pats from sticking together the wrong way.
I first line up the LE and press the sheeting on.
I use a wall paper rubber roller to press the gluing firmly together.
Gradually I pull the baking paper backward and press and roll on.
It as faster done than explained!!!
With that done I cut the edges down to outer the shape of the wing and grind it to be perfect.
Than the tip part is next, all the same way.
Two wings, job done!
Note that the first 3 ribs at the root, are different from the rest. The wing TE sits a little up to the fuselage. The SF25 and others have this too! A change on Milan 2 to Milan 1… I did cut a small strip of balsa wedge to be able to hold the angle while rolling the sheeting on.

[Noël Rumers]

With the top sheeting installed the wing starts looking as a wing...
The best part is now on hand. The installation of all that has to be build in the wing for proper funtioning after it is ready.
So the two servos need a proper place and I always design the movement of the arms etc to make sure that all does what it should do controling the brakes and ailerons.
The brake servos came first...BUT...
there is a very important thing to do first before I would forget about it...
Drilling holes to mark the cutting line of the top aileron shape.
To do this I use a 1 mm drill and drill enough holes so that I can easy draw a line with a ruler to mark the exact shape.
No cutting yet, the aileron should be sheeted first before cutting it from the wing. The wash out on the tip has to be build in properly in the aleron as well!!!
So with that job done faster than ecplaining, the angled blocks are cut to fit the airbrake bottom with the spars around it. The hole was cut in the airbrake box to fit the servo arm and controls.