Realizzazione bordo English

How I rounded the corners of the fuselage (CH7)

First goal was to deduce the radius of curvature (fig 7) from F22 to landing brake so I started cutting off a thin plywood sheet a square at 90° (fig 1). After I put the square on the corner of the fuselage and I sharpened a toungue depressor, and glued it on the plywood square so that the its point touched the corner of lower longeron (fig 2)

In next step I drew on a paper sheet two straight lines at 90° called 0-A1 and 0-A (fig 3) and I did to correspond the sides inside of the square with the two straight lines drawn on the paper sheet fig (3 e 4). I marked a point with the pencil on the paper correspondent at the point of the toungue depressor, I called this point "L" that correspond to corner of

lower longeron (fig 4). From this point "L" I drew a straight line at 45° 0-B and after I marked a second point along this straight line that I called "L1" distant 1/8 in. from "L" (fig 5). Obviously L1 was the point correspond to the planed corner of the fuselage. With a compass I did some attempts moving its needle along

the straight line 0-B and easily I deduced the arc that was tangent to straight lines 0-A1 and 0-A and intersected the point "L1" (fig 6) . In my fuselage's corners the radius was 4.37 in. (11,15 cm) and the diameter was 8.75 in. (22,3 cm).

I drew on the paper the central section of my fuselage in scale 1
to 1 so I could trace one line at 45 deg. and two lines at 22.5 deg. From these 3 lines I could deduce the distance from point 0 to following points A and A1, B and B1, C1 and C2 (fig 7). After I transfered the distance

Foto 1

0- A1 to a simple wood tool that in Italy is called tracker-line at 90 deg. myself-made (fig 8). I drill the hole in the tracker-line so that the center hole and inside corner of the traker-line is the same distance as 0-A1. I inserted a felt pen in the hole so I could trace a precise curvelinea on the fuselage bottom, (foto. 1) then turning upside-down the tracker-line I tracked another lines on the fuselage sides at same distance from point 0.
So I was ready to cut the foam at 45 deg.. I utilized a saw to cut out the most part of foam but then to get a flat surface at 45 deg. with sharp
edge I utilized only and exclusively a adjustable plane (foto. 2) and I did not utilize the sanding block for 3 reasons:

Foto 2

Foto 3

1) because of the different hardness of the foam, the sand-paper abrade more soft foam than the hard foam
2) with sand-paper

Foto 4

I was not able to get a very flat surface in widht direction
3) high precision with the plane to get the very sharp edges
The sharp edges was important because it will guide the next tracker-line at 45 deg. which will trace four lines to get two cut at 22.25 deg (foto 3 and 4). Infact this second tracker-line slide on sharp edges of foam and the sharp edges works as a guide for the tracker-line (foto 2 and 3 and fig 9).
Also these two cut at 22.25 deg. I finished always with the plane.

Foto 5

Foto 6

Finally I wanted to get a complementary shape of the round edge so I dismounted from my car a bottle methane which has the same radius (11,15 cm) of finished round edge (foto 5), so I put a form (foto 6) on the bottle and I filled with gipsum rapid hardening . (my car burn methane, not fuel because the fuel costs more 3 time than in U.S.A.). An American Cozy builder has improved my method substitutind the gipsum with layers of BID.
After only 30 minutes my complementary shape was done (foto.7) so I could glue the sand-paper 60 grit on the concave surface of the gipsum (foto. 8) and to sand on the bottom edge of my fuselage (foto. 9). Obviously this system can be used only from F 22 to about half landing brake area because between these two points the curvature radius is always costant,

Foto 7

Foto 8

instead from half landing brake to forward blkgear I used the system as call for plan, but always tracking the lines so that I cut at 45 deg and 22.5 deg and finishing always with the plane
The results have been: no bumps, no depression and neither imperceptible smaller bump or depression but only an harmonious and perfect round edge

Foto 9