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Jul 02, 2018, 02:34 PM
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Build Log

Ultra Sport Build/Bash


I'm starting to build an Ultra Sport from plans and will be making some changes to suit my own preferences. I thought I would post this to see if there's enough interest in a full blown build thread. If not, then I won't bother.

I have scaled down a set of RCM Ultra Sport 1000 plans that I bought on Ebay, to 90% which gives a wingspan of about 67 inches. I did this to make the size fit (I hope) a motor that I already have which is a Turnigy SK5065-380. I plan to run this motor on an 8S pack.
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I like to build with foam cores, so the wings, rudder, stab and turtle deck will all be balsa sheeted foam. The wing and stab will be two piece, and the tail surfaces will all be airfoiled. The wing will also be moved upwards to a mid wing location.

The yellow lines on these pictures give a general idea what I'm planning to do.
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Jul 02, 2018, 06:40 PM
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Interesting project.... I'm interested, particularly in the steps in turning the foam cores into completed wings and the mid wing position change.

Michael in Ontario, Canada
Jul 02, 2018, 07:52 PM
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My Ultrasport 1000 bash.

L.
Jul 03, 2018, 07:28 AM
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2michaely, I will cover all of the foam wing process

Cherokee, good looking twin! What engines did you use?
Jul 03, 2018, 07:44 AM
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The first step in the process of cutting the foam cores will be to make the templates. I'm using 1/8 inch plywood cut with my bandsaw and sanded to shape. I like to seal the templates with Minwax clear urethane. This makes a good smooth surface to apply strips of foil furnace tape to the edges.

Center lines are marked on all of the templates and holes drilled for nails to hold the templates to the foam blocks.
Jul 03, 2018, 08:23 AM
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It currently has two well used OS Surpass 70’s in it. I am thinking of changing them for Saito 72’s just because I have them and don’t want to rebuild the Surpasses. I have flown it quite a bit and have had at least two engine failures that I didn’t know had happened til I throttled back up. When I went to power up to taxi back, it only wanted to turn. It’s about 15 years old and I need to do a full overhaul of the fuel system.

L.
Jul 03, 2018, 09:17 AM
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I had a half sheet of 3 1/2"x4'x8' foam left over from a previous project. I cut the outlines for all the parts from it with a regular cutting bow and gravity feed. A center line was drawn around the edges. The templates are then attached to the foam block with nails making sure the center lines all match up.
Jul 04, 2018, 02:23 PM
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I don't have a fancy hot wire cutting setup but it works very well. For tapered wings, this is something I saw on youtube and decided to try it. The wire is tethered to the work surface, the foam block is placed at the correct distance so the wire starts and ends at the perfect angle. The wire is pulled tight by hand and simply pulled through the foam following the templates, top and bottom. Works great!

Here's a couple of pictures of the wire and my heat source which is my Lipo charger. It has foam cutting feature and the amps and voltage can be set as needed. I make a few test cuts on scraps to get the heat set correctly.
Jul 05, 2018, 11:07 AM
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All foam parts are now cut and it's time to cut holes in the wings for the wing tube. I have a 7/8" aluminum tube salvaged from a previous airplane for the wings and a 1/2" carbon fiber tube for the stab.

I made a simple jig for this from scrap wood I had laying around. The fiber glass wing tube sleeve will be used to drill the holes and same thing for the stab. The pictures show how I did this.
Jul 05, 2018, 11:16 AM
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A false rib will be added in the wing to support the end of the tube in the wing. I cut the slot in the wing on my table saw with a thin kerf blade, The false rib is made from 1/8" lite ply and glued in with Gorilla glue.
Jul 05, 2018, 02:41 PM
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I made the false ribs for the stabilizers with 1/16" plywood and cut the slots with a fine tooth jigsaw blade by hand. They were also glued in with Gorilla glue. The foam core surfaces are lightly sanded with an 80 grit drywall block being careful not to remove too much material.
Jul 06, 2018, 06:27 AM
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Very impressive scratch build. I love foam core wings and yours look perfect!
Jul 06, 2018, 11:00 AM
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Thanks Dave; They're a long way from being perfect, but still acceptable by my standards.
Jul 06, 2018, 11:18 AM
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Next up is sheeting the cores. I have enough contest weight 1/16" sheeting on hand to do the stabilizers so I'll start there first. Meanwhile, I'm working on an order to National Balsa for enough wood to finish the project.

First, the edges of the sheeting are trued up with a straight edge and a good sharp exacto knife. The sheets are then taped together with masking tape ( no need to edge glue the sheets together).

I use Gorilla Glue, a plastic spreader and a foam roller. Spread the glue evenly and then use the roller. The roller picks up excess glue an makes a nice uniform application.
Jul 06, 2018, 11:26 AM
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Next, the sheeting, the cores and the shucks are stacked and weighted down for a few hours. A vacuum bag system would be nice to have, but bricks work very well too.

I let these dry for six hours and then trimmed the excess sheeting off the edges.


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