Building Tips and technical articles. > Building techniques
Foam core canopy/hatch treatment for testbed model
fred cesquim:
--- Quote from: Bob Hunt on May 20, 2022, 07:12:12 AM ---Over in the All Amped Up section I have an ongoing thread about a testbed twin that I'm building using the "Lost Sheeting" method of construction (I'm actually going to change the name of that process to the "No BS Wing Construction" standing for "No Balsa Sheeting." But that's a story for another time and another thread. If you want to know more about it now, go to the twin testbed thread over on the electric section).
In the process of building this new twin, which is named Double Take, I tried to cut down on the amount of "good" balsa that would be required. I'm trying to save that good wood for actual contest models. When it came time to make a swoopy canopy for this ship I decided to use the Dow Buoyancy Billet foam that I normally use for my fuselage shell mold bucks. This material is very easy to carve and sand to shape. After carving and sanding it I decided to cover it with a piece of 1/2-ounce glass cloth applied with Z-Poxy. The next step is to hollow out all but about 1/16-inch of foam. I'm pretty sure that with the Z-Poxy and glass barrier, I can then apply a normal finish without dissolving the foam inside. Time will tell. Either way this is a good way to make a testbed model component part like a canopy/hatch. It may even be developed into a way of making full contest model components. The paradigms are a changin'...
Enjoy the photos... Bob Hunt
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awesome method and awesome work! thanks for changing paradigms so many times! c/l needs that!
Dwayne Donnelly:
--- Quote from: Bob Hunt on May 20, 2022, 01:32:29 PM ---Hi Lauri:
Yes, as a matter of fact I was just having a phone discussion about that very thing with a friend. This buoyancy foam is pretty stout stuff, and I think a 1/16-inch wall thickness with a layer of 1/2 ounce glass inside will work very well.
Thanks - Bob
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Hi Bob, I would like to see how you're going to cut/carve it out.
Thanks
Howard Rush:
Sure is better than the way I did the hatch on my new dog.
Bob Hunt:
Time will tell if this is a viable method for making a hatch (or wing tips...) for a "real" stunt model, but it is looking good so far. It would sure cut down on having to raid that dwindling stock of 4-6 pound balsa for hatches and such.
Later - Bob
Bob Hunt:
--- Quote from: Dwayne Donnelly on May 20, 2022, 03:21:26 PM ---Hi Bob, I would like to see how you're going to cut/carve it out.
Thanks
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Hi Dwayne:
Sorry for not answering your question about the hollowing of the foam canopy hatch sooner... I've been painting pretty much around the clock.
Actually I just used a 1-inch dowel wrapped with 60 grit sandpaper to do the bulk of the hollowing. The blue buoyancy foam sand extremely well and fast. When I had the majority of the foam removed I used a variety of spindle sanding drums to do the detail removal of foam to yield nominally a 3/32-inch wall thickness. The result was better than I had hoped; the hatch was very stiff and I did not see the need to glass the inside. The hatch did compress at the sides where it met the fuselage just a bit, so a couple of balsa spreaders were installed to achieve a perfect fit. The final weight of the hatch ready for paint is 15 grams.
The next step is to put in the holdowns, but that will have to wait until I'm finished with the paint trimming of the new Genesis LC (Last Chapter) and my new Turning Point retract twin!
Attached are a few photos that should help.
Later - Bob
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