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Old Nov 02, 2003, 06:33 PM
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Cessna 185 with floats in foam project..

I would like to take this opportunity to tell all of my building technique regarding scratchbuilding a foam scale model..
A lot of the material I will present will be review to some of the older gents, but hopefully it may answer some questions that some of our newer modelers may have.. I hope to be helpful and entertaining, and thank you in advance for your attention..

I decided on the Cessna 185 with a 33 inch wingspan and would hope to fly in with a GWS 400C and three blade prop.

Step 1....Making the patterns

I start by making a clear transparancy of the 3 view drawing of the Cessna on my copy machine and then use an overhead projecter to project the image onto a piece of poster board hung on the wall and trace the outline..This enlarged outline is then cut out with scissors, and becomes my pattern.. By backing up or going forward with the projector on tshe floor, I can make the image larger or smaller until the correct size appears..

The next 4 photos will illustrate...
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Old Nov 02, 2003, 06:34 PM
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Photo 2...
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Old Nov 02, 2003, 06:36 PM
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Photo 3...
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Old Nov 02, 2003, 06:37 PM
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Photo 4..
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Old Nov 02, 2003, 06:45 PM
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i had never thought about the over head projector Jerry .. i will have to try to find one .. that will save me a fortune at Kinkos .. watching this one with anticipation
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Old Nov 02, 2003, 06:50 PM
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The next step concentrates on marking and cutting the wing...

Cut a piece of foam ( 2 inch pink shown ) to the top view of the wing section to be cut.. In this case I allow for a 1/4 inch leading edge and a 1/2 inch trailing edge to be glued on in a later step..

Lay the foam on a flat surface and mark the leading and trailing edges on both ends with a short mark... This mark will guarantee that the rib template will be in the proper place when temporarily pinned to the foam for cutting..

Please note that the Cessna wing design provides for 4 degrees of washout on the tapered tip section only... There is no washout in the constant cord root section...The section of the wing that covers the fuselage is flat and dihereral starts at the edge of the fuselage...I will cut the wing in 5 sections to accomodate all these requirements...

The next 5 photos will illustrate these points...

Photo 1
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Old Nov 02, 2003, 06:52 PM
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Phoro 2 ..
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Old Nov 02, 2003, 06:53 PM
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Photo 3..
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Old Nov 02, 2003, 06:56 PM
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Pin the tip rib template to the foam...Raise the trailing edge to make the 4 degree washout...The root template will be not tipped, but will allign with the mark..
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Old Nov 02, 2003, 07:00 PM
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The 5 sections of the wing that make up the Cessna design are shown..They will be joined and dihederal will be incorporated on a later step when the leading and trailing edges are glued on...
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Old Nov 02, 2003, 07:21 PM
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We will return to the wing construction a little later...Right now I want to tackle the fuselage..

The Cessna has a rather slab-sided fuselage and lends itself to a technique that is easy to do and results in a very light structure..

I first cut out a piece of 3 inch blue foam about an inch higher than the highest dimention of the fuselage and about 2 inches longer that the fuselage..I true up the sides nice and square with a table saw for a later step when the fuse is cut out on the band saw..

Using the patterns made from the poster board, I draw with a ballpoint the outline of the side and the top view..Pay careful attention to the wing saddle and the saddle for the horizontal stabilizer at this time to guarantee the the desired angle of incidence is attained.. .. Lay out and mark the firewall by placing the proposed motor in place to guarantee there is plenty of room in the cowling. Mark the firewall location and at the same time make a mark on the top and bottom of the fuselage as reference to it's location. The fuselage sides will be covered later with Depron and will cover the marks on the sides...You will have to then transfer the firewall side marks back on the sides after the Depron is put on and the nose is shaped..

Mark a cut line for the interior of the fuselage for removal of unneeded foam...Leave enough foam on the top and bottom for rounding of the fuselage contour later...( approximately 1/2 inch)
Lay down a piece of 3mm Depron and very carefully trace the outline of the fuselage right and left sides on it...This is useful as when you relieve the interior, the allignment of the top and bottom cannot be guaranteed by it's own strength.. You will use waterbased contact cement to attach the Depron to the sides and there is no room for error...When gluing, use the traced outline on the depron to guarantee allignment...

Then go to the band saw and cut away the unwanted foam in the interior of the fuselage..

The next 4 photos will illustrate...

Photo 1 ..
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Old Nov 02, 2003, 07:25 PM
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Cut the fuselage out on the band saw..Save the cut outs for registering the fuslage in the bandsaw if later cuts are needed..Simply tape the waste back on to make the cut if needed..Note the green tape in one of the photos holding the cutourin place...

Photo 2..
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Old Nov 02, 2003, 07:29 PM
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This is the photo showing replacing the cut out for a bit..This keeps the fuselage level when going through the band saw..
Photo 3..
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Old Nov 02, 2003, 07:40 PM
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Photo shows the fuselage after the relieving process is done...
Now coat the left over fuselage sides ( both right and left) and the contact area on the Depron with WATER BASE CONTACT CEMENT and allow to dry...Do not use the Formica type cement, as it will attack the foam..If in doubt,, test some on a piece of scrap foam...

Make sure you have a right and a left side cut out of the Depron, not 2 rights, or 2 lefts....and that you place glue on the appropriate side..

Photo 4..
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Old Nov 02, 2003, 07:45 PM
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After the contact cement has dried CAREFULLY allign the fueslage side and make contact.. Press in place and repeat for the other side.. Carefully trim away the excess Depron..

There is an area on the nose that the cowl needs to be taperd, so mark it now and cut it awaay on the band saw...
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